The Diffusion of Bioplastics: What Can We Learn from Poly(Lactic Acid)?

Abstract

Environmental and social impacts caused by petrochemical plastics are generating significant concerns on a global scale. Bioplastics can contribute to the transition to more sustainable materials, but they did not expand at the expected rates in the early 2000s. With recent predictions indicating that the bioplastic capacities will almost triple in the next five years, what are the conditions that may now be combined to justify and enable such an expansion? This paper uses the case of PLA and general insights into other bioplastics (stylized facts) to detail these conditions. The results show that many bioplastics remained unused during the 20th Century, with interest increasing when plastic pollution became flagrant in the 1980s. For PLA, many efforts have been made to solve the technical and market issues, including through intense cooperation among stakeholders. While environmental concerns have propelled bioplastics, the general absence of structured end-of-life alternatives (e.g., recycling and composting infrastructures) hinders their diffusion. Conversely, the expanding regulations related to plastic pollution are now the primary driver of the growth of bioplastics. Therefore, for bioplastics, and especially PLA, the conditions seem to be emerging for them to diffuse at the predicted rates, but structural limitations in the bioplastics value chain still compromise the large-scale substitution of petrochemicals. This trend indicates that establishing end-of-life alternatives for bioplastics could help to remove the bottleneck in their diffusion process.

1. Introduction

Petrochemical plastics are ubiquitous materials in our day-to-day life, combining unrivaled properties with low costs. They display a high strength-to-weight ratio, high moldability, impermeability to liquids, sometimes sound gas barriers, and resistance to physical and chemical degradation. Since their exponential and unprecedented growth in the 1950s, these plastics have been helping to preserve food, make electronics, insulate buildings, increase the fuel efficiency of vehicles, etc. Plastics offer features that cannot be provided by glass, metal, or wood, the dominant materials in the first half of the 20th Century [1,2].

Despite their benefits, the issues related to fossil-based plastics are becoming increasingly flagrant. Plastics have a high production-related carbon footprint, generate large volumes of waste, cause persistent pollution, including microplastics, clog urban infrastructures, and negatively impact tourism and fisheries [1,2]. Additionally, petrochemical plastics production is associated with deforestation and the displacement of indigenous peoples for oil extraction, the contamination of potable water, health problems of communities living near oil refineries, and occupational hazards for plastic waste collectors [3]. According to the OECD (Organisation for Economic Co-operation and Development), in 2019, 353 million tons of plastic waste were generated globally, which is more than double the volume in 2000. Of this, only 9% was recycled, with 49% being landfilled, 19% being incinerated, and 22% being mismanaged [4].

In this context, circular economy actions have been proposed for plastics [5,6]. The circular economy may be conceptualized “…as an economic system that replaces the ‘end-of-life’ concept with reducing, alternatively reusing, recycling and recovering materials in production/distribution and consumption processes” [7]. Hence, preventing and recycling plastic waste, its conversion or disposal, and the large-scale advent of bioplastics are initiatives to curb plastic pollution [1,8,9]. The bioeconomy also has an untapped potential for job creation, increasing wages and education in rural areas, and fostering gender equality [10,11].

Bioplastics can contribute to the transition to more sustainable materials if land use impacts are managed [1,8,12]. These materials are made from renewable feedstocks and/or are biodegradable, which means they can display lower carbon footprints and/or decompose into CO₂ and water (naturally or in composting conditions), lowering waste management burdens [13,14]. Despite some controversies regarding their sustainability, such as impacts on food supplies and land use changes [1] bioplastics are touted as promising alternatives to address plastic pollution [15]. The production of feedstocks such as corn or sugarcane may lead to direct or indirect deforestation. Yet, the current bioplastics pressure for agricultural lands is negligible due to their small production volumes [1].

However, the large-scale diffusion of bioplastics has not occurred at the levels predicted in the early 2000s. For example, NatureWorks announced, in 2000, its intention to have a poly(lactic acid) (PLA) capacity above 450 kta by 2006 [16], but its capacity in 2021 was only around 150 kta [17]. This low market reach is common to other bioplastics. In 2021, bioplastics represented less than one percent of the more than 367 million tons of plastic produced annually [18]. Yet, the bioplastic capacity is expected to increase from nearly 2.22 million tons in 2022 to about 6.30 million tons in 2027 [18]. These figures suggest that bioplastics may start to make more significant contributions to the sustainability goals for plastics in the coming years.

A question at this point is which conditions may now be emerging to justify and enable this significant diffusion of bioplastics in the next five years. Some papers have studied the recent development and prospects of bioplastics, including Kawaguchi et al. [19], Nanda et al. [20], Jem and Tan [21], and Narancic et al. [22], to name a few. Yet, most studies focus on the technical aspects of production, applications, and bioplastic degradability, giving less attention to other dimensions that are equally important for explaining the diffusion of new products. These include the role of corporate application development efforts, product acceptance by consumers, regulatory frameworks, competition with established solutions, and cooperation with suppliers and complementors to commercialize the innovation [23,24,25,26,27]. A remarkable exception is Döhler et al. [28], who implemented a system dynamics approach to identify critical factors in biodegradable bioplastics market growth. However, due to limitations concerning data availability, the authors do not consider social and political effects in the model.

This paper aims to answer the above question through a multidimensional lens, considering the technical, market, and regulatory/policy aspects. For this purpose, this study reviews the history of PLA as a case study of a non-drop-in bioplastic, i.e., a bioplastic that does not have a chemically identical petrochemical counterpart [29]. By describing PLA’s development trajectory and current growth drivers, we devise “stylized facts” [30] likely common to other bioplastics, mainly of the non-drop-in type. Such stylized facts are then used to infer which technical, market, and regulatory challenges need to be tackled to enable the large-scale diffusion of bioplastics.

This paper shows that many efforts have been devoted to overcoming PLA’s technical challenges, and demand has increased through the establishment of plastic pollution regulations worldwide. The combined actions of stakeholders such as resin producers, converters, equipment manufacturers, brand owners, and end users are also crucial to enabling PLA’s large-scale diffusion. Other bioplastics such as PHA and PBS may be at a less mature stage. On the other hand, the sustainability scrutiny of PLA and other bioplastics is a challenge that was not faced by petrochemicals in the past, which partially hinders diffusion. The general absence of end-of-life (EOL) alternatives for bioplastics compromises their adoption at larger scales since they may not degrade in the environment. Therefore, PLA may achieve the envisioned capacities, but a long road lies ahead to guarantee the sensitive displacement of petrochemical plastics.

This paper is structured as follows: After this introduction, we present the methodology used to construct the PLA case study and discuss the role of stylized facts in empirical works. Then, we give an overview of bioplastics and present the basic properties of PLA, followed by a detailed description of its development trajectory. Finally, we address the lessons drawn from PLA and similarities to other bioplastics, highlighting the advances already made and their challenges. We describe the limitations of this work and future avenues for research.

2. Methodology

PLA is a good case study on the diffusion of non-drop-in bioplastics. In 2022, it was the first biodegradable bioplastic in production capacity. By 2027, PLA’s global capacity is expected to increase over five times, surpassing 2.38 million tons, making it the bioplastic with the largest capacity [18]. It is one of the first bioplastics to be widely produced, with large-scale manufacturing starting in 2002 [31]. For this reason, its development trajectory is well documented, allowing extended discussion of its diffusion process.

Two primary sources of information were consulted to describe the technical, market, and regulatory/policy dimensions of PLA’s diffusion: specialized media focused on industry, market news, and academic publications. The backbone of PLA’s trajectory was constructed from a systematic review of Chemical & Engineering News Archives, which provides industry information from 1942 to 2015 [32]. The term “lactic” was used in the search since it is deemed more general than “poly(lactic) acid” is, for example. Relevant news was identified by reading the title and abstract. Next, a review of publications on Plastics Technology (www.ptonline.com) was carried out. Its articles discuss industrial and market aspects of PLA, including the outcomes of industrial conferences and the development of equipment, new additives, regulatory trends, etc. The archives have been available since 1999, and once again, the term “lactic” was used as a keyword [33]. After the basic description of PLA’s trajectory, other open publications were consulted to complement mainly market and regulatory information, such as ICIS, IHS, company websites, etc. Having described PLA’s historical trajectory, academic publications were consulted to deepen the understanding of what was encountered. Highly cited review papers and book chapters were prioritized in this phase since they summarize the development trends. Relevant references were gathered in other topics to illustrate academic research concerning PLA. All the searches were conducted in Google Scholar and Google Books.

Having constructed the PLA case study, comparisons were established with petrochemical plastics and other non-drop-in bioplastics. This procedure aimed to identify “stylized facts” that could help to explain the current state and prospects of bioplastic diffusion. Stylized facts may be defined as “…empirical regularities in search of theoretical, causal explanations. Stylized facts are both positive claims (about what is in the world) and normative claims (about what merits scholarly attention)” [34]. When a phenomenon can be observed in multiple cases, a broader and more generalized understanding of the world can be achieved [30]. In this paper, the phenomenon of PLA diffusion and its prospects is the first detailed case study, while the comparisons with non-drop-in bioplastics highlight similarities and counterpoints. Thus, this paper brings insights into the current conditions that might favor or hinder bioplastic large-scale diffusion. For this part of the work, review papers, book chapters, and reference reports (e.g., from OECD) were used to make comparisons.

3. An Overview of Bioplastics

Bioplastics are made from renewable feedstocks and/or are biodegradable materials [14]. These include non-biodegradable materials that are chemically identical to fossil products (drop-in), including bio-based polyethylene (PE) and polyethylene terephthalate (PET), and plastics that have reached more significant markets more recently, such as polytrimethylene terephthalate (PTT). It is also possible to obtain biodegradable plastics from fossil resources, such as polybutylene adipate terephthalate (PBAT) and polycaprolactone (PCL). However, some authors find it misleading to refer to fossil-based biodegradable plastics as “bioplastics” [6]. Finally, some bioplastics reconcile both features, including poly(lactic acid) (PLA), polybutylene succinate (PBS), polyhydroxyalkanoates (PHA), and starch blends [14].

Table 1. Main bioplastics, feedstocks, and capacities. Source: developed by the authors based on [6,18,35,36,37].

Group	Polymer	Direct Raw Material(s)	Capacity in 2022 (tons)	Capacity in 2027 (Forecast, tons)
Bio-based, non-biodegradable	PA (polyamides)	Dicarboxylic acids + Diamines OR Amino acids OR Cyclic amides	246,420	1,178,100
	PE	Ethylene	328,560	743,400
	PP (polypropylene)	Propylene	86,580	378,000
	PTT	1,3-Propanediol + Terephthalic acid	295,260	296,100
	PET	Ethylene glycol + Terephthalic acid	93,240	113,400
	PEF	Hydroxymethylfurfural + 2,5-Furandicarboxylic acid	0	6300
	Other	-	24,420	25,200
Bio-based, biodegradable	PLA	Lactic acid	459,540	2,387,700
	PHA	Fermentable sugars	86,580	560,700
	Starch blends	Starchy materials	397,380	396,900
	Regenerated cellulose films	Cellulose	79,920	94,500
	PBS	Succinic acid + 1,4-Butanediol	19,980	18,900
Fossil-based, biodegradable	PBAT	1,4-Butanediol + Adipic acid + Terephthalic acid	99,900	100,800

lists the main bioplastics available, their feedstocks, and current and predicted capacities. Green PE has the largest capacity among the bio-based, non-biodegradable bioplastics, but should be surpassed by polyamides by 2027. Green PP is forecasted to display a significant capacity increase of over four times. PLA is now the main bioplastic and should grow to largely dominate the bioplastics market. PHA capacity should increase six-fold, exceeding 560 thousand tons in 2027 [18].

4. The Properties of PLA

Poly(lactic acid) or polylactide is a thermoplastic polyester produced from lactic acid, a naturally occurring organic acid and bulk food additive. Lactic acid is a chiral molecule possessing two optical isomers, L(+) and D(-) [38]. Lactic acid is a naturally occurring acid that was discovered in 1780, with industrial manufacturing established in 1881 in the USA. Since around the 1990s, new lactic acid production plants have been based on microbial fermentation processes of carbohydrates, which mainly generate the L(+) isomer. Depending on the microorganisms employed, fermentative processes can also generate D-lactate and DL-lactate. Mixtures of L(+) and D(-) are obtained via chemical synthesis [39,40].

The proportion of lactate isomers in the polymer chain is a crucial factor affecting PLA’s processing, crystallization, and degradation behavior. Isotactic poly-L-lactic acid (PLLA) is a semicrystalline material with the highest melting point. In contrast, including the D-isomer reduces the material’s melting point and crystallization behavior. When a limit of 12–15% D-isomer content is reached, the polymer becomes amorphous [38]. A neat PLA shows a high Young’s modulus, scratch resistance, and transparency, besides good printability and heat sealability. Conversely, it is brittle with low impact strength, displays low heat resistance, is relatively hydrophilic (a detrimental property for engineering applications), and only degrades at temperatures above 60 °C, i.e., it is not home compostable [41,42].

PLA’s enantiomer content dictates which processing technique best suits the polymer and its end uses. Generally speaking, materials requiring heat-resistant properties can be injection molded using PLA resins of less than 2% D-isomer, which leads to high crystallinity. The same applies to fibers that must show adequate thermal resistance. Conversely, PLA resins of higher D-isomer contents (in the 4 to 8% range) tend to be suitable for thermoforming and two-stage stretch blow molding, since the probability of crystallization during the reheating step is less pronounced [43]. Finally, amorphous PLA copolymers are typically used for medical devices, especially for slow drug release [44].

Different alternatives have improved PLA’s properties and processing behavior, including copolymerization, blending with other polymers, plasticization, and additives. Rubber modification via copolymerization is especially effective at increasing PLA toughness [43,44]. There are some excellent works on PLA modification and processing. For example, Kühnert et al. [42] reviewed the state-of-the-art and new developments concerning PLA processing; Tripathi et al. [45] discussed PLA blends and composites for durable applications; Parameswaranpillai et al. [46] reviewed, specifically, the use of cellulose and nanocellulose in PLA composites; Zhao et al. [47] reviewed strategies to improve the toughness of PLA, aiming at overcoming its inherent brittleness and relatively poor impact strength.

One of the distinguishing features of PLA is its biodegradability. PLA’s degradation occurs chiefly through the scission of ester bonds. Yet, natural factors, including oxidation, photodegradation, thermolysis, hydrolysis, biodegradation, or enzymolysis, can also induce PLA’s biodegradation [48]. However, it does not degrade successfully in the natural environment by the action of microorganisms and at room temperature. Nevertheless, PLA is considered to be a biodegradable plastic since it is compostable (in compliance with ISO standards) [13]. It takes 6–9 weeks to degrade in industrial conditions, and more than 1.5 years in the ocean [6].

PLA’s physical and chemical structure and environmental conditions affect its biodegradation. For example, different behaviors are expected if the polymer is in the human body or the environment. Higher crystallinity and non-biodegradable additives may reduce the PLA’s biodegradation rate. On the other hand, adding hydrophilic fillers (e.g., starch and wood-flour) can improve the degradation rates [13,43,49].

As further detailed in the following sections, PLA has interesting properties, but also, inherent deficiencies. Innovation to improve such properties is becoming crucial to guarantee some level of competitiveness with petrochemical plastics. Conversely, techniques to improve PLA’s properties can affect its biodegradability, making it more challenging to structure adequate EOL alternatives. These aspects are relevant points of its diffusion.

5. PLA: A Timeline of the Main Advances, Players, and Drivers Impacting Its Diffusion

This section presents the history of PLA. It tracks the scenario surrounding its invention, the main technological advances of the last decades, its market and commercial relevance, the leading players involved with the production, its environmental aspects, and main demand drivers.

The events concerning PLA are segmented into three timeframes: from 1932 to the early 1980s, from the late 1980s to 2002, and from 2002 to the present. The first period encompasses its invention and the decades of it being given limited attention as a large-scale plastic, only having niche medical uses. The second one encompasses the renewed interest in PLA (and other bioplastics) due to growing concerns about plastic pollution. This second period ends with the launching of the first large-scale production facility by the Cargill Dow joint venture (JV). Finally, the third period is marked by relative stability on diffusion, but with production capacity set to increase in the next five years.

5.1. Invention and Decades of Limited Diffusion (from 1932 to the Early 1980s)

Théophile-Jules Pelouze first synthesized PLA in 1845 via the condensation of lactic acid. In 1932, Wallace Carothers, a scientist at DuPont, developed a method to polymerize lactide to produce PLA, patented by the company in 1954 [50]. Carothers was responsible for discovering two major plastics in 1930: nylon and neoprene rubber. These were the main focus of DuPont in this period, and thus, PLA received only a little bit of attention [51]. During the 20th Century, petroleum became the primary raw material for modern chemistry, and the chemical industry structured itself around it [52].

The first PLA resins produced by DuPont showed a low molecular weight, and only after some development was it possible to achieve relevant polymer masses [50]. A problem with PLA was its poor hydrolytic properties (i.e., breakage by water), which compromised its intended use in textile fibers. Renewed interest came in the 1970s when these same hydrolytic properties were shown to be beneficial for medical applications [53]. In 1970, PLA products were approved by the US Food and Drug Administration (FDA) for direct contact with biological fluids [54]. Copolymers with glycolic acid (poly(lactic-co-glycolic acid), PLGA) have been used since the 1970s for commercial sutures and drug delivery systems. The slower degradation of PLA hinders its direct use as a suture, but favors ligament and tendon reconstruction and stents for vascular and urological surgery [55].

Aside from the medical field, PLA could not reach significant markets since the high costs for separation, purification, and polymerization of lactide were prohibitive [53,56]. According to a 1993 report, PLA for medical applications was priced at USD 100–1000/lb [57]. Around the same period, PP prices ranged within USD 0.30–0.50/lb [58].

5.2. Renewed Interest Due to Environmental Concerns (from the Late 1980s to around 2002)

5.2.1. Environmental Concerns on Plastics

In 1987, about 55 billion pounds of plastics were produced, with 22 billion being discarded and only 1% of plastics being recovered. The general public perception was that plastics could not be recycled or safely incinerated and should be removed from waste streams [59].

The negative public perception and the resulting regulations to mitigate plastic pollution led producers of resins and plastic artifacts to become involved with the issue. Such involvement was meant to diminish their association with the solid waste crisis and avoid restrictions on their industries. Corporate initial responses included forming internal divisions and cooperative industry associations focusing on plastic EOL, mostly trying to raise recycling awareness to counteract plastic bans. At this point, the plastics industry generally saw new biodegradable plastics with limited applications in agriculture or dealing with litter [59].

Nonetheless, biodegradability started to be re-evaluated. For example, the Biodegradable Plastics Society of Japan was established in 1989 to promote the recognition and business development of biodegradable and bio-based plastics [60].

Politicians also began to respond to plastic pollution. One example was the Plastic Pollution Control Act on 28 October 1988 in the USA. It required plastic ring carrier devices to be degradable [59]. New York’s Suffolk County and that in Berkeley, California, were considering laws to ban PS packaging in fast food restaurants. Many other federal and state laws were enacted in this period to promote the recycling of plastics or degradable materials in the USA [61].

Life cycle assessments (LCA) were also underway. The basic principle of LCA is that all environmental burdens associated with a product (or service) have to be assessed from the raw materials to wastes (from cradle to grave) or even from raw materials to raw materials (from cradle to cradle). This technique was invented in around 1970, but was genuinely developed in the late 1980s [62,63]. In 1997, Neste (Finland) partnered with the Finnish institute VTT Chemical Technology to evaluate PLA for substituting traditional diapers based on petrochemical plastics [64].

5.2.2. The New PLA Producers

The first biodegradable plastics in the 1980s had production and performance problems. These included blends of starch with non-biodegradable petrochemical plastics, which were only partially biodegradable and led to a poor public image of bioplastics. In around 1990, the second generation of bioplastics emerged in the USA, Western Europe, and Japan with greater strength. New bioplastics included starch-based polymers, PLA, and PHA [53,65].

PLA, in particular, drew a lot of attention in the early 1990s.

Table 2. Leading companies involved with PLA production during the 1990s.

Company	Capacity (kta)	Location	Remarks	References
Cargill Dow LLC	4 (to be doubled by late 1998)	Savage, Minnesota, USA	Primary global producer at the time	[31,66,67]
EcoPol (jv between Chronopol and EcoChem)	1	Johnstown, Colorado, USA	EcoChem was a JV between DuPont and ConAgra that ceased operations in 1994	[67,68,69]
Galactic (Brussels Biotech)	Tens of tons	Escanaffles, Belgium	-	[70]
Hycail	-	The Netherlands	-	[69]
Kyowa Hakko	-	USA	Entered a non-exclusive license with Argonne National Laboratory (USA) of its BioLac process	[71]
Mitsui	0.5	Japan	Already a producer of PLA and copolymer for medical applications	[72,73]
Neste OY	-	Finland	No significant production, but had some application development efforts	[69]
Shimadzu	0.1	Japan	Production in collaboration with Mitsubishi Plastics	[73]

summarizes the leading PLA research and production companies during this period.

The agroindustrial company Cargill established itself as the leading player in PLA in this period. Cargill was a lactic acid producer and wished for opportunities to expand the use of corn and associated byproducts. PLA offered a potentially lower environmental footprint than petrochemical plastics did, could be cost-competitive, and could have its properties improved. In 1994, Cargill built a facility to produce PLA in Savage, Minnesota. This plant was claimed to be four times larger than those of other producers were [31,66,74]. In early 1995, Cargill realized it needed a partnership with a company experienced in the plastics industry, forming a joint venture with Dow Chemical in 1997 called Cargill Dow LLC [31]. The companies predicted the early PLA market capacity to be around 450,000 kta [75].

Galactic, a lactic acid producer, is now an important PLA manufacturer. The firm began researching PLA in the 1990s with a pilot plant [70]. Many other companies identified the PLA opportunity, but eventually left the market due to technical and/or market difficulties. For instance, Mitsui ceased developments of PLA as a commodity, but still produces copolymers for medical uses [76].

Current PLA production technologies involve carbohydrates fermentation to lactic acid, the conversion of lactic acid to its cyclic dimer, called lactide, and lactide polymerization to PLA [21,77]. PLA production involves challenges such as the tolerance of microorganisms to the acidic environment when lactic acid is generated [78], the generation of large amounts of gypsum (CaSO₄) if Ca(OH)₂ is used to control the pH and recover lactate [79,80], the multiple downstream steps required to purify lactic acid to a polymer-grade molecule, the conversion and purification of lactide isomers, and polymerization itself [38]. Hartmann [81] provided an excellent overview of PLA production technologies in the late 1990s.

5.2.3. Initial Properties of PLA and Applications

Although promising, the bioplastics markets had been slow to take off, and PLA had a very restricted supply. By 1993, Cargill expected the PLA prices to be USD 4410–6610/ton, which was considerably higher than that of other plastics [57]. Mitsui estimated the PLA global market to reach 4 million metric tons annually in 2010. PLA was seen as a substitute for petrochemical plastics such as PE, PS, PP, and PET [82,83].

The first PLA resins were stiff, strong, and clear, but suffered from several characteristic deficiencies. PLA displayed reduced crystallinity, was brittle, and had low heat resistance [84]. It had low melt strength, a high tendency to stick, and degraded quickly during processing [85]. In the late 1990s, Cargill Dow LLC admitted that much work needed to be conducted on PLA additives, blends, and copolymers [67]. Yet, PLA could be tailor made for different applications by controlling, for example, branching, the D-isomer content, and the molecular weight distribution [86].

Food packaging was one of the leading applications envisioned for PLA. For example, Mitsui [72] and EcoChem [68] targeted this market. Fibers were another promising market. Kanebo in Japan started producing PLA fibers sourced by Shimadzu in 1994 [87]. Kanebo initially targeted agricultural applications for its PLA fibers, but later made them available for apparel [88]. It is interesting to highlight that although applications where biodegradability is a differential (e.g., mulch films or bags) were indicated for PLA resins, the significant growth of the polymer was expected in applications that are not dependent on biodegradability [86].

5.3. Slow Growth and the Achievement of an Apparent Tipping Point (from around 2002 to the Present)

This subsection discusses the factors involving the large-scale industrialization of PLA. It covers the technical, market, competitive, and regulatory evolutions during this period.

5.3.1. New Entries and Exit of Producers

Table 3. Leading companies currently involved with PLA production.

Company	Capacity (kta)	Location	References
B&F PLA (BBCA + Futerro)	30	Bengbu, China	[89]
COFCO	10	Changchun, China	[90]
Futerro (Galactic)	1.5	Escanaffles, Belgium (demonstration)	[91]
Hengtian	10	China	[21]
Hisun	45	China	[21]
Jiangxi KeYuan	1	Jiujiang, China	[92]
LG Chem + ADM	75 (due to 2025)	USA	[93]
NatureWorks (Cargill + PTT Global)	150	Blair, Nevada, USA	[17]
	75 (due to 2024)	Nakhon Sawan, Thailand	[94]
Uhde Inventa-Fischer	0.5	Guben, Germany (pilot)	[95]
Sulzer	<1	Winterthur, Switzerland	[96]
SuPLA	10	Suqian, China	[97]
Synbra (purchased by BEWi Group in 2018)	5	Allschwil, Switzerland	[98]
TianRen	3	China	[21]
Tong-Jie-Liang Biomaterials	10	China	[21]
Total Corbion PLA	75	Rayong, Thailand	[99]
	100 (due to 2024)	Grandpuits, France	[100]

details the existing capacities and locations of PLA plants. Next, Figure 1 depicts the milestones of the current three leading PLA producers, i.e., NatureWorks, Total Corbion PLA, and Galactic. Figure 1 starts from the formation of Cargill Dow LLC in 1997, and also describes some other producers’ initiatives. It provides a schematic view, highlighting the main actions and interactions of industrial players involved with PLA production. Hence, it shows the relevance of collaboration to make the polymer commercially available.

Among the semi-commercial PLA producers in the 1990s, only Cargill and Galactic remained involved with higher scales of production. No further information was found during the research on the other producers, although some new entrants started developing their technologies. These include Futerro and Purac (later Corbion Purac), which became a large PLA producer through the Total Corbion JV.

In the late 1990s, Cargill Dow LLC announced a commercial facility of around 140 kta capacity to become available in late 2001, making the company the largest PLA producer globally [31]. Cargill Dow LLC claimed that there was a significant interest from buyers in its PLA and that all its production capacity would be sold out by its opening. With this promising forecast, the company was expected to build a new plant in Europe soon after the Blair facility was operational, followed by new plants every 18 to 24 months. It intended to have a capacity of above 450 kta by 2006 [16].

In early 2005, however, Dow decided to leave Cargill Dow LLC due to difficulties selling PLA. Dow claimed customers were unwilling to pay price premiums for environmentally friendly polymers [101]. Cargill then renamed the venture NatureWorks and recognized the necessity to reduce efforts in applications that were more difficult to compete with, including injection molding and teabags. Conversely, it focused on packaging and non-woven fabrics from 2005 onwards [102].

In 2007, Cargill announced that another polymers producer was entering NatureWorks, Teijin Limited. However, Teijin decided to leave in 2009 due to portfolio restructuring [103]. A few years later, in 2011, PTT Chemical, a leading producer of PE and petrochemicals, acquired a 50% stake in NatureWorks. The companies announced their intention to build a second PLA facility in Thailand [104], which only began construction in 2021 [94].

Concerning Purac, in around 2006–2007, the firm established more a stable position in the PLA field, recognizing its growth as a driver for its lactic acid market [105]. Its business model consisted of supplying D- and L-lactides to PLA producers. For instance, it partnered with the Swiss engineering firm Sulzer to build a PLA plant for Synbra in the Netherlands [106].

In 2016, Corbion Purac (the company’s new name) and Total Petrochemicals established a JV to produce and market a PLA named Total Corbion PLA. In 2019, they built a 75 kta PLA plant at Corbion’s site in Thailand [107]. In 2020, the company announced its intention to construct a PLA facility in Grandpuits, France, with a capacity of 100 kta, and to begin construction in 2024 [108]. It is interesting to note that by 2013, NatureWorks and Corbion Purac did not see each other as competitors. Given the much larger scales of petrochemical plastics, they saw greater competition with traditional plastics [84].

Regarding Galactic, the company formed a JV called Futerro with Total Petrochemicals in 2007 [109]. Total entered Futerro to start offering bio-based plastics in its portfolio [110]. However, in 2016, Total opted out of the JV, leaving Galactic as the sole owner of Futerro [111].

In December 2018, Futerro, Sulzer, and TechnipFMC formed the PLAnet™ initiative to supply integrated PLA technology: Futerro specializes in lactic acid and lactides production technologies; Sulzer in lactides separation (L and D isomers) and polymerization, and TechnipFMC is an engineering company that integrates the technologies and provides the engineering package [112].

Other players in PLA production include the engineering firm Uhde Inventa-Fischer (UIF) [95]. Recently, in September 2021, LG Chem (South Korea) and Archer Daniels Midland (ADM) (USA) announced plans to construct lactic acid and PLA plants in the USA by 2025 with a PLA capacity of 75 kta. The JV is motivated by increasing the regulations on disposable products worldwide and the consequent bioplastics market growth [93]. It is interesting to note that ADM left a venture in PHA in 2012 due to customers’ slow adoption of the material [113].

There are also some Chinese producers of PLA: in 2019, the total production capacity of PLA in China was around 149,000 tons [114]. In 2021, BBCA announced plans to produce up to 700,000 tons of PLA by 2023 [115].

5.3.2. Main PLA Markets and Capacity Build-up

In 2002, Cargill Dow LLC expected to sell up to 50,000 metric tons of PLA from its Blair facility [74], aiming at high-value niches of PLA’s technical performance and environmental advantages [116]. Rapid success was a characteristic of petrochemical plastics such as PE, PP, and nylon, since they could bring improvements across various applications. However, bioplastics were being launched in a scenario where these materials were already available and well established [117], with the result that the PLA capacity was growing below the initial expectations. In his study of social-ecological economics of eco-innovation promises, Befort [118] used PLA as a case study. He showed a build-up of hype for PLA until around 2003, followed by disappointment due to poor functionalities and high production costs. In 2007, he described an increasing interest in promoting PLA blends.

Figure 2 presents estimates of PLA capacity from 2002 to 2022 and forecasts ranging from 2025 to 2027. The steep growth in 2019 can be mainly credited to the startup of the Total Corbion PLA plant, increases in NatureWorks’ production [119], and new capacities in China (e.g., B&F PLA).

In 2020, PLA and its compounds were mainly consumed in north-east Asia, followed by Western Europe and North America [128]. In 2019, Chinese demand was from 160 to 180 thousand tons, mainly for packaging (65% of the market). Local demand should exceed 475 thousand tons by 2025 [114]. Despite the efforts of NatureWorks and others and the early receptiveness of Japan to PLA, the high costs of bioplastics are the main reason why demand is not increasing in the country [129].

Europe follows Japan as a fast-growing market for PLA. In 2020, the European PLA market capacity was estimated at 103,000 tons. It is forecasted to grow 12% annually from 2021 to 2026, reaching more than 200,000 tons by 2026 [130]. The US market was slower to take off than Japanese and European ones, but many large-scale consumers emerged (e.g., Wild Oats Market and Wal-Mart [131]). Some references point out that the US had the biggest PLA market in 2021, with over 42% of the total [132].

5.3.3. Prices, Properties, and Processability of PLA

The introduction of new plastic materials is linked to four inter-related aspects: availability (quantities and supply stability), prices related to existing solutions, processability, and performance in the applications. Increasing demand leads to more capacity, thus bringing the prices down. For bioplastics, demand can only be established if they have the processability and properties to compete with petrochemicals, i.e., through successful application development efforts [133,134].

The enhancement of production technologies was a factor that drove PLA prices down. Processes patented in the late 1990s with the potential to improve PLA production included gypsum-free processes (e.g., using recyclable ammonia or caustic soda rather than calcium hydroxide) and other techniques to enhance lactic acid recovery (e.g., technology, ultrafiltration, resin-based ion exchange, chromatography, and electrodialysis) [81]. Recent reviews have discussed advances in different aspects of PLA production [135,136,137,138,139,140].

PLA prices stood at around USD 6610/ton in 1995, and reached USD 1870/ton in 2007 [141]. The typical effects of technological maturity and production scale-up are also evident for petrochemicals. For instance, the PS prices decreased from USD 4409–6305/ton in July 1955 to USD 2006–2138/ton in June 2008 (prices adjusted for inflation) [141].

Figure 3 compares historical PLA prices with PS and PP, taking the US as the baseline country. The PLA prices were stable, ranging from around USD 1800 to 2100/ton. PP, for example, saw large price fluctuations from USD 1251 to USD 2116/ton. Recent PLA price increases are associated with a tight supply [142]. Despite the price stability, PLA still tends to be more expensive than commodity petrochemical plastics are.

At this point, it is interesting to discuss the work of Elvers and coworkers [144] concerning a patent analysis of biodegradable polymers between 1999 and 2013. The authors indicate that recent patents involving PLA primarily focus on application development rather than production technologies. Hence, they suggest that the technologies have reached maturity. Although innovations such as new feedstocks for lactic acid production, including methane [145] or biological wastes (e.g., paper, tree, crop, and wood processing residues) [146], have been proposed, technological breakthroughs in the last 10–15 years are not apparent. This seems consistent with the relative stability in PLA prices depicted in Figure 3.

PLA displayed limitations when it was introduced in terms of its properties, especially in heat and impact resistance. PLLA homopolymers were typically capable of withstanding up to 55 °C. PDLA/PLLA stereocomplexes are very efficient nucleating agents, capable of increasing both the crystallization rate and the crystallinity of PLLA [147]. With this procedure, it became possible to increase the heat resistance to 100–120 °C, enabling commercial PLA use in coffee cups and lids, for example, and approximating PLA’s heat resistance to PP and high-impact polystyrene (HIPS) [148,149]. The stereocomplexation of enantiomeric PLA is also associated with superior mechanical properties [150,151].

Fillers, modifiers, and blends have been proposed to enhance PLA’s mechanical properties. Early studies have suggested blends with non-biodegradable petrochemical plastics, including polyethylene (PE), acrylonitrile–butadiene–styrene (ABS) copolymers, and polyurethanes (PU). The use of bio-based and/or biodegradable materials as blends has been increasingly sought after, such as polyamide 11, poly(butylene adipate-co-terephthalate) (PBAT), PBS, starch, and cellulose [47]. Modifications of PLA have been reported by producing companies that can generate polymers with an impact resistance that is similar to that of ABS [148,149].

Other blends have been proposed to improve the sustainability claims of fossil-based materials. For instance, BASF has been marketing a blend of PLA and PBAT under the name ecovio^® since 2006 [152]. Blending PLA with PMMA, PP, ABS, and other petrochemical plastics became common for durable uses, as exemplified by the NatureWorks and Altuglas partnership to co-market PMMA/PLA blends for acrylic parts [153].

Composites with natural fibers are a relevant option for improving PLA’s typical deficiencies. Natural fibers such as hemp, ramie, kenaf, rice straw, jute, and flax have improved strength [154]. For example, Jung et al. [155] showed that PLA reinforced with jute fibers displayed improved heat resistance and impact strength, making them potentially useful for auto parts. In 2021, the chemical company Lanxess launched a PLA composite with flax fibers. The material is 100% recyclable and lighter than glass-fiber-reinforced materials. It is suitable for interior car parts, housing components of electronics, and sports equipment [156]. As another example, the German resin producer FKuR provides a wood-plastic compound based on PLA and softwoods for decorative cosmetics, plant pots, and technical plastic parts [157].

Greatly enhanced mechanical properties can also be achieved by combining PLA and carbon fibers [158]. The startup Carbon Mobile GmbH plans to introduce a very light and thin smartphone, possibly based on PLA/carbon fiber composites, to cite one example [159]. Additives are crucial to making a new polymer suitable for different applications. In the case of PLA, these include toughness-reinforcing fillers, cross-linking agents, chain extenders, plasticizers, antistatic agents, impact modifiers, and fiber compatibilizers/coupling agents (see Sin and Tueen [160] and Fiori [161] for more details on PLA additives). Major companies supply additives for PLA and are not polymer producers. For example, in 2008, Arkema launched its first additives for PLA under the Biostrength brand. Specific products enhanced the melt strength, minimized pre-drying requirements, minimized brittleness, and facilitated other processing operations. Nonetheless, the low volumes of bioplastics and the consequent small market for additives made some companies reticent to dedicate resources to R&D. For instance, Milliken Chemical, a producer of plastic additives, had doubts about where to focus resources. Even if the bioplastics market fulfilled its growth projections, Milliken claimed the corresponding additive market would be small [85,134].

Overall, PLA has more processing nuances than petrochemical plastics do, such as polyethylene terephthalate (PET) or PP, demanding extensive learning. For example, the processing of PLLA at temperatures of 185–190 °C tends to reduce its molecular weight, compromising the polymer’s mechanical properties. The fast cooling after extrusion, blow molding, injection molding, etc., may also complicate the polymer chains’ rearrangement into a crystalline structure [160]. Yet, industrial participants acknowledged similar challenges in processing HDPE, PP, or PET when these resins were introduced decades ago. Fabri-Kal, for example, commented that its first trial run with PLA in 2004 lasted one week and produced zero usable products [162].

Sensitiveness to moisture is one of the significant processing problems of PLA. It tends to absorb ambient moisture very rapidly, which causes the degradation of polymer chains and loss of molecular weight and mechanical properties during melt processing. The polymer is usually dried to less than 100 ppm (0.01%, w/w), but lower levels (e.g., 50 ppm) are recommended for processes with long residence times or temperatures near 240 °C [163]. Drying is also a requirement of PET [66].

Another factor during PLA processing (and for other bioplastics) is tackiness. Fabri-Kal highlights significant equipment differences needed to deal with PLA’s tackiness in opposition to those of PS or PET. Around 2004, the firm contacted an equipment supplier, Universal Dynamics, to modify the equipment Fabri-Kal had been using for PET. Fabri-Kal solved the issue, and Universal Dynamics could supply improved equipment to other firms. Despite the initial challenges, new PLA-dedicated processing lines set by Fabri-Kal started up better than, for example, the PS lines [162].

Therefore, solving the technical challenges of PLA involved (and still involves) actors across the entire plastics value network (resin and additives producers, equipment suppliers, converters, brand owners, and end users). Still, it is interesting to note that this was similar to what happened to petrochemical plastics. See, for example, the work of Bomtempo [164] on PP development for a comparable pattern.

5.3.4. PLA Applications

In around 2002, Cargill Dow LLC sought applications for PLA, mainly in fibers and packaging. For the former one, the JV envisioned PLA blended with other fibers or on its own for apparel, carpets, and bedding [117]. However, by 2007, from 70% to 80% of PLA global consumption was for thermoformed trays and cups. The other markets were coating paper (for coffee cups) and blown and bi-oriented films [66]. There are now more diverse applications, but PLA is still very relevant for packaging, as shown in Figure 4.

At the current stage of development, PLA shows good technical potential to replace HDPE, PP, PET, and PS in some applications [165]. PLA is a ‘‘GRAS’’ (Generally Recognized As Safe) material according to the US FDA for food contact applications [166], has a transparency that is comparable to those of PS, low-density polyethylene (LDPE), and PET, and demonstrates better protection of food against photodegradation than PS, PET, and LDPE do. However, PLA has a yellowish coloration, which can demand colorizing agents [161]. Other applications of PLA include wipes, diapers, landscape fabric, mulch film, phone cases, electronics, and 3D printing, among others [167].

Since PLA has a high water affinity and, consequently, good potential for microbial growth compared to that of petrochemical materials, packaging made from PLA (and other bioplastics) tends to be more suitable for food with a high respiration rate and short storage life, such as vegetables and some bakery products [168]. Nevertheless, it has been applied for dairy products due to beneficial moisture, light, and gas barriers. High crystallinity contributes to low gas permeability. PLA is also resistant to grease, which favors food packaging usage. Multiple modifications are able to improve PLA’s properties specifically for these applications, including modifiers, blending, copolymerization, and physical treatments [169,170].

PLA has been applied to other consumer goods, for example, automotive applications. In this case, improving thermal, moisture, and weathering resistance is crucial. For instance, floor mats made of PLA fibers were created by Toyota by capping its end groups, and a spare tire cover was made using PLA with enhanced impact resistance. Incorporating UV absorbents can also contribute to making PLA suitable for these applications [171].

Textiles are another relevant application of PLA. PLA fibers have similar properties to those of PET fibers. However, PLA displays low melting and glass transmission temperatures, poor heat resistance, poor hydrolytic resistance to strong alkaline, high elongation, and relatively poor storage stability. For instance, since cotton fabrics require strong alkaline conditions for scouring and dyeing, PLA/cotton fabric blends may suffer from degradation. Despite the necessity of technological improvements in PLA fibers, there are many examples of applications, such as industrial fabrics, filters, towels and wipes, and clothing [172,173].

Other properties of PLA make it suitable for different applications. These include biodegradation for agriculture (e.g., mulches, possibly in blends with other biodegradable polymers [174]); heat-resistant PLA for coating disposable paper cups [175]; as biodegradable substrate with flax to substitute printed circuit boards in electronics [176].

As for PLA processing, application development frequently involves different stakeholders, which is crucial for establishing demand. An example is the food trays launched by Iper grocery chain in Italy in the early 2000s. Focusing on providing high-quality fresh foods, the company wished to use more environmentally-friendly packaging by substituting traditional high-impact PS packaging [116]. For this purpose, Iper worked with the European packaging suppliers Autobar and Trespaphan GmbH to develop thermoformed containers and film lidstock, respectively. Both companies were already partners of Cargill Dow LLC and experimented with PLA. After approval by Iper, Autobar began commercial production of the packaging. The success of Iper’s five test locations prompted the firm to expand the PLA packaging to all its 21 stores, representing a consumption rate of 500 tons/year of PLA [177].

5.3.5. Sustainability Aspects of PLA Production and EOL Alternatives

Compliance with the increasingly rigid sustainability goals is a crucial requirement for plastics and bioplastics. Bioplastics must have lower carbon footprints than petrochemical plastics have, be compatible with existing recycling streams, and have some biodegrading capacity in controlled or predictable environments. Conversely, they may negatively impact agricultural systems (e.g., acidification potential and eutrophication), competition for food supplies, and unestablished EOL alternatives [6].

PLA faced scrutiny regarding its environmental footprint and circularity from its very early days. Between 2002 and 2015, NatureWorks launched five publications on its PLA’s eco-profiles in peer reviewed journals, comparing PLA to the petrochemical alternatives [178]. Total Corbion performed similar assessments in 2010 and 2019 [179]. Ghomi et al. [180] summarize other existing LCAs of PLA. The use of biological wastes is a path envisioned to minimize the impact of PLA on agriculture. For instance, researchers at the Argonne National Laboratory and National Renewable Energy Laboratory in the USA have recently published a paper on the LCA of waste stream conversion to PLA. They evaluated wastewater sludge, food waste, and swine manure as feedstocks [181]. Despite the efforts to quantify the impacts of PLA and other bioplastics, recent LCAs have displayed significant variations due to the different assumptions and methodologies. Thus, promoting consistent and systematic frameworks for LCA studies is still an obstacle for properly evaluating bioplastics [6,182].

The feedstocks employed are also the subject of discussions, including on the use of genetically modified (GM) plants. For example, around 2011, Danone was accused of greenwashing for displaying “new, environmentally-friendly tub” on a yogurt tub partially made of PLA. The accusation was due to its non-recyclability and being partly derived from GM corn [183]. In their study of bioplastics adoption in Germany, Brockhaus et al. [184] showed that this was a recurrent theme among the interviewed firms. Greenwashing allegations were perceived as a barrier to changing to using bioplastics, although this was not a reason to discard them from the research agenda [184]. Feedstock sourcing stands as a relevant aspect as well. For instance, in 2019, NatureWorks pledged that by 2020, 100% of its raw material would be certified as sustainably managed and responsible. The such certification encompasses practices to protect biodiversity, implement best practices for agrochemicals usage, promote safe working conditions, and comply with human, labor, and land rights, among other principles [185].

The EOL options are a fundamental concern for this bioplastic. PLA is bio-based and biodegradable, but it only degrades quickly under industrial composting conditions. The biodegradation behavior of PLA is mainly influenced by the polymer’s stereochemistry, crystallinity, molecular weight, and the presence of additives in the resin [160,186]. PLA artifacts buried in soil generally displayed little to no visible degradation after several months of trials [187]. Although some studies confirmed the biodegradability and disintegration of PLA-based materials (e.g., Kawashima et al. [188]), the absence of composting infrastructure is a significant drawback to allowing the deployment of PLA. For example, in around 2007, the UK engaged in no industrial composting, and some resin converters did not recommend PLA to customers [66]. Another problem is that organic waste is sometimes directed to anaerobic digestion facilities to make biogas, but some of these are incapable of processing biodegradable plastics [128].

Part of the issue regarding PLA disposal is communicating to customers how to do it properly. Taufik et al. [189] studied how German consumers dispose of compostable bio-based packaging and found that packaging was often not discarded in line with the instructions on the labels. The authors highlight that terms such as “compostable in industrial composting plants”, “home compostable”, “biodegradable in soil/freshwater/marine water”, and “bio-based” are not easy to understand by regular consumers. Additionally, labeling has not yet advanced to making the communication clear [190]. Although a lot of efforts have been devoted in the last years to creating standards to define and evaluate compostability and biodegradability, a lot of work is still ahead. In a recent review by Bartolo et al. [5], the authors highlight that standards do not effectively address environmental conditions that are less controlled or uncontrolled. Ultimately, this may lead to the underestimation of the ecological impacts of bioplastics.

When it comes to recycling, PLA faces other challenges. For example, the visual separation of PLA bottles from PET bottles is deemed to be very difficult due to their similarity, although separation efficiencies through near-infrared (NIR) spectroscopy of between 86 and 99.6% are reported [191]. This is an issue considering that the acceptable level of PLA contamination in PET streams to avoid deterioration of properties would be 0.1 wt.%. For other polymers, the allowed contamination levels are around 3 wt.% for PP, 2 wt.% for high-density polyethylene (HDPE), and 10 wt.% for polystyrene (PS) [192]. For this reason, the US trade association National Association for PET Container Resources (NAPCOR) demonstrated concerns about PLA contamination in PET recycling. Besides compromising properties, back in 2009, NAPCOR questioned establishing a feasible PLA recycling business model since the volumes processed were relatively small [193]. Additionally, degradation processes are common to plastics during their life cycle, leading to changes in the recycled polymers’ thermal, viscoelastic, and mechanical performance [194]. Implementing upgrading strategies can at least partly maintain the quality of PLA. Such methods include thermal annealing, chemical modifications with stabilizers, antioxidants, and chain extenders, and blending/compositing with other constituents [195]. Finally, recycling plastics and bioplastics is generally complicated by the presence of additives, a common feature of almost every plastic artifact [196].

Chemical recycling is another alternative to PLA’s EOL. Hydrolysis and alcoholysis are the main methods available for this purpose. The hydrolysis of PLA can recover lactic acid, which can then be repolymerized to PLA. Alcoholysis by methanol or ethanol, for example, yields alkyl lactates that serve as solvents [197]. Hydrolysis of the alkyl ester can also result in lactic acid. In an active patent of Futerro—the developer of the LOOPLA^® chemical recycling process—the catalytic hydrolysis of PLA is carried out in an alcohol. The ester can be optionally hydrolyzed to lactic acid [198]. Futerro’s LOOPLA^® was developed in around 2009. It is specific to PLA, i.e., if other plastics are present, they do not breakdown and contaminate the process. However, the process can lead to L- and D-lactic acid mixtures that yield low-crystallinity PLA, and its energy consumption is generally too high compared to that of typical mechanical recycling [199]. In 2021, Total Corbion unveiled what it claims to be the world’s first commercially available PLA made from chemically recycled polymer [200].

The enzyme-enabled depolymerization of PLA is another alternative being researched [201]. For instance, the French company Carbios has launched an additive that can be incorporated into PLA during its manufacturing to make PLA 100% compostable under industrial and domestic composting or methanization conditions [202]. However, the industrial scalability of enzymatic depolymerization is still questionable [203].

5.3.6. Demand Drivers

According to analyses by IHS Markit in 2018, Europe became a leading demand center for PLA and biodegradable plastics, primarily due to new legislation promoting plastic materials’ circularity. Enhanced properties and processability, growing consumer awareness, and activism regarding environmental issues have contributed to developing the market. Nevertheless, the growth has been slow or has stagnated in locations that lack mandates [204]. For instance, in 2021, China passed a law banning non-biodegradable shopping bags, straws, and utensils, which will spur the use of bioplastics in these hard-to-recycle applications [142].

IHS also highlights that mandatory composting programs can increase demand, possibly expanding the already relevant compostable trash bags and food service ware applications [204]. The shift of interest from compostability to renewable content has been a trend since the last half of the 2000s. In other words, bioplastics have been considered for use in blends with petrochemical materials [134,205].

A recent article by Cherel-Bonnemaison et al. [206] pointed to a rapid increase in sustainable packaging regulations worldwide, despite the challenges of deploying them. The issues include the highly heterogeneous regulatory maturity across countries, the absence of uniform terminologies, the variability and low maturity of regulations, and the many regulatory levels (federal, state, or even city levels) present. The OECD has recently provided a roadmap of policies to improve the sustainability of plastics, highlighting the need for more consistency worldwide in this matter [1].

Although multinational companies could have difficulties reliably planning considering this heterogeneous regulatory scenario [207], corporate sustainability initiatives are driving the demand. For example, major brand owners have switched to biodegradable drinking straws, compostable hot cups, and biodegradable tea bags [128] and are making public commitments to diminish their plastic environmental impacts [208]. These initiatives are part of a global movement that favors Environmental, Social, and Corporate Governance (ESG) investments. In the US, the investors’ interest in sustainable investing reached 85% in 2019, with climate changing and plastic reduction topping their lists [209].

6. Stylized Facts of the Diffusion of Bioplastics

From the PLA case study, it is possible to devise some commonalities with other bioplastics, which are, herein, described as stylized facts. Since technological developments can be very specific to each bioplastic, this section tries to identify the general trends. It brings together examples that correlate the drivers and bottlenecks of PLA with those of other bioplastics.

6.1. Stylized Fact 1: The Prevalence of Petrochemical Plastics Restricted the Increase in the Capabilities of Bioplastics

The case of PLA shows that there was only a little bit of interest in bioplastics for a long time. Although the first polymer materials were bio-based ones (e.g., cellulose derivatives and rubber), the wide availability of petroleum made bioplastics uninteresting [41]. For instance, PHA—biodegradable polymers produced by the fermentation of renewable resources—was characterized in 1925, but was only re-evaluated for industrial uses in the 1980s [210]. PBS is another example. It was also investigated by Carothers at DuPont in the 1930s, with limited market reach until recent years when its raw materials (succinic acid and 1,4-butanediol) became available from renewable feedstocks [211]. PHA capacity is projected to expand rapidly in the coming years, while that of PBS will stagnate [127].

This trend implies that only a little bit of development effort has been devoted to bioplastics for decades [212]. This includes measures to optimize the production processes for larger industrial scales, interest in developing processing techniques, additives, sorting/composting infrastructures, etc. Therefore, knowledge and infrastructures were augmented around petrochemical plastics, establishing lock-in effects [213].

6.2. Stylized Fact 2: Plastics Generally Present Property Issues When They Are Introduced

With rare exceptions, high polymers are very unstable: they are inherently prone to oxidize, ozonize, hydrolyze, re-crystallize, depolymerase, discolor, embrittle, become insoluble, or suffer various combinations of these and other issues [214]. As discussed in Section 5.2.3, PLA exemplifies these limitations. PHAs are materials with similar limitations, including brittleness and very low resistance to thermal degradation, which has been demanding the development of additives and blends [215]. The same is true for petrochemicals. Early PP artifacts were unstable when they were exposed to heat, light, and air [216]. Only in the early 1970s (around 15 years after its discovery) was this issue solved by the additives manufacturer Ciba Geigy [164].

Application development in the case of new plastics is intimately related to identifying their intrinsic weaknesses and finding means to mitigate them, which typically include chemical modifications of the polymers and/or compounding them with additives [214]. This trend implies that adapting plastic artifacts to different uses requires a non-negligible development time. Considering that large-scale PLA production began in 2002 and other bioplastics have not reached comparable volumes, continued efforts will be required to tune their properties.

6.3. Stylized Fact 3: Plastic Pollution Was a Key Trigger of Bioplastics Diffusion

Bioplastics emerged in response to plastic pollution issues becoming increasingly flagrant worldwide and the negative public perception of plastics. Corporate, institutional, and regulatory movements emerged in this period, motivating developments in bioplastics. Biodegradable bioplastics were desired in this period to minimize waste generation and reduce the pressure on landfills. This trend propelled not only PLA, but starch blends, PHA, and other bioplastics [212]. The more significant development of LCA techniques in the late 1980s indicates how quantifying the environmental impacts of products and services became critical to society. On the other hand, the intended growth of PLA was not solely associated with its biodegradability [86], meaning that bioplastics still have to combine other properties required for their applications.

6.4. Stylized Fact 4: Bioplastics Experienced Lower-than-Expected Market Growth, Which Compromised Corporate Commitment

As described in Section 5.3.3., the introduction of new plastic materials is linked to four inter-related aspects: availability, prices related to existing solutions, processability, and performance during use [133,134]. For the new bio-based polymers, the last few decades highlighted a chicken and the egg issue: large brands often cannot use bioplastics because they have limited supplies (including a reduced number of producers), yet supplies will not be established until a demand is present. Additionally, bioplastics tend to be more costly than fossil-based alternatives are [217,218]. Although bioplastics can offer new features, such as superior barrier properties in breathable packaging, they still lag behind the properties of fossil-based plastics in highly demanding applications (e.g., under-the-hood automotive parts). Petrochemicals had many decades to evolve, which helps to explain this trend [219,220]. Thus, the higher prices of bioplastics are not usually justifiable by having better properties.

Optimizing technologies is still an obstacle to reducing the production costs of some bioplastics. In their patent analysis from 1999 to 2013, Elvers et al. [144] suggested that both PLA and PBAT reached technological maturity, shifting the focus to application development. On the other hand, patents concerning PHA and PBS technologies were still in a growth phase. In its 2019 “Roadmap for the Chemical Industry in Europe towards a Bioeconomy”, the European Union recognized the production cost as a barrier to bio-based plastic uptake. The roadmap suggested implementing R&D/demonstration-scale projects to optimize production technologies and the development of a specific Strategic Research Innovation Agenda for bioplastics [35].

Since bioplastics usually display higher prices than fossil-based plastics do, a controversial topic relates to the consumers’ willingness to pay premiums for environmentally friendly products. Some indicate that consumers are not inclined to pay price premiums [101,184,221], while others claim the contrary [222,223]. Nevertheless, there are many factors that may possibly affect purchasing behavior, including education level [224], gender [225], and region (e.g., differences between northern and southern countries [226]). Moreover, many studies analyze the willingness to pay rather than actual purchasing behavior [227]. Therefore, consumers’ acceptance of more costly bioplastics is questionable.

Petrochemical plastics did not face this uncertainty level, despite their high prices, when they were introduced. Back then, plastics offered evident improvements compared to those of incumbent materials such as glass, wood, and metal. For this reason, companies saw the infant plastics industry as a major opportunity, and the capacity quickly increased [228,229]. For instance, PP was discovered in 1957, and as early as 1966, there were already 15 producers in the USA alone [230]. In another example, Karl Ziegler invented HDPE in 1952, and by 1955, they had already issued 16 licenses for its new polymerization catalyst [231].

The undefined scenario of bioplastics is reflected in the entries and exits of producers. As discussed in Section 5.3.1., Dow and Teijin exited from NatureWorks, and early researchers such as Ecopol and Shimadzu did not pursue the PLA opportunity. In PHA, ADM entered a JV with Metabolix and started producing the bioplastic in 2010 [232]. However, in 2012, ADM decided to leave the JV due to uncertainties concerning the projected capital and production costs, market adoption rate, and, consequently, uncertain projected financial returns [233]. Metabolix later sold its technology to CJ CheilJedang, which inaugurated a PHA facility in 2022 [234]. Drops in petroleum prices compromised the deployment of 100% bio-based PBS. Succinic acid production, one of the monomers for PBS, was primarily sought after in the 2000s and 2010s, with four industrial projects becoming available. However, the availability of shale oil and gas made petrochemicals cheaper, leading to the exit of most succinic acid producers [235].

Finally, accumulating capabilities to produce a new material at a large scale is paramount to secure a stable supply. For instance, the PHA producer Danimer Scientific recognized its limited experience, producing at larger scales. Despite having pilot-scale experience, it pointed to possible difficulties in making PHA cost effectively at a commercial level or with the quality required by customers [175].

Overall, different circumstances led to a global bioplastics market capacity that was below the expectation set in the early 2000s. In this sense, technological discontinuities and difficulties in scaling up production were present in some cases, which tended to delay the improvements required to make bioplastics more cost competitive.

6.5. Stylized Fact 5: Co-Operation Is Key to Promoting Bioplastics

Solving technical issues across the emergent bioplastics value chains is fundamental to deploying these materials successfully, and the PLA case study shows that on many levels. At the production level, agroindustrial/food ingredients and petrochemical companies often joined capabilities to produce PLA, as in the cases of Cargill and Dow (later Teijin and next PTT Global), Corbion and Total, and ADM and LG Chemical. It is interesting to highlight that in the absence of a partner with a foot in the plastic business, Purac’s previous business model concentrated on the polymer intermediate, i.e., lactides. As recognized by Cargill, experience in plastics was necessary for the formation of Cargill Dow LLC [31]. In application development, Iper’s work with Autobar and Trespaphan highlights how brand owners can spur innovation in bioplastics. Finally, the joint work of Universal Dynamics and Fabri-Kal to modify the processing equipment exemplifies efforts to adapt infrastructures to new plastics.

Another fascinating example is the collaborative project Competence Network for the Processing of Bioplastics promoted by the German Federal Ministry of Food and Agriculture (BMEL). With it having financial support since 2013, the project aims to bring together researchers in bioplastics processing and industrial practitioners, especially medium-sized companies willing to use bioplastics. It resulted in extensive guidelines and open databases collating their properties, processing parameters, and application examples, besides certifications, prices, and sales partners [236,237]. Other entities also play a role in promoting bioplastics. This is the case of a recent partnership between the PHA producer CJ Biomaterials, the South Korea Ministry of Science, and ICT, and the Korea Innovation Foundation, to promote the eco-friendly materials industry [238].

Hence, the combined action of resin producers, converters, additive suppliers, equipment manufacturers, brand owners, government agencies, researchers, etc., is paramount to solving the technical limitations of bioplastics, promoting market development, and creating institutional settings that favor bioplastics. Although it is limited in quantity, the evidence herein gathered suggests that actions have been taken in this direction.

6.6. Stylized Fact 6: Sustainability Scrutiny Simultaneously Propels and Hinders Bioplastics

The interest in PLA intensified in the last few decades due to its bio-based content and biodegradability potential. As discussed in Section 5.3.6, regulations regarding plastic pollution worldwide are the key drivers for the growth of biodegradable plastics. They became more important than improving the polymer’s properties and processability, growing consumer awareness, and activism regarding environmental issues did [204]. Additionally, ESG investments and corporate commitment to plastics sustainability have increased [208,209]. Thus, environmental concerns are crucial to sustaining the bioplastic market growth.

On the other hand, bio-based content and/or biodegradability potential are insufficient to guarantee that bioplastics are better than petrochemical plastics are. For PLA, this translated into the need for LCA studies, the socially responsible sourcing of feedstocks, and sustainable EOL alternatives. These topics have been extensively addressed in the literature for other bioplastics (see, for example, [239,240,241,242,243,244]).

According to a 2022 OECD report, innovation in biodegradable plastics has slowed down since 2013 in comparison to that which occurred during the period between 1995 and 2013, as measured by patenting activity. The OECD points out that the uncertainties surrounding their biodegradation in the environment, possible adverse effects on recycling, and poor communication with consumers regarding disposal may be reasons for this behavior. Additionally, technology developers are concerned about the indirect environmental impacts related to agricultural feedstock production [1]. These factors are reflected in some country-level diffusion of bioplastics. For instance, the absence of composting infrastructure is considered to be tone factor that has hindered biodegradable bioplastics growth in Japan [245]. In France, stakeholders are divided on the potential of bioplastics due to recyclability and biodegradability concerns [246]. Even so, he demand increased after restrictions on using non-biodegradable plastic shopping bags (as in Italy) [204].

Bioplastics are also associated with concerns related to poor labor conditions in developing countries, water shortages, and health problems in local communities due to the use of pesticides [247]. However, the Social Life Cycle Assessment (SLCA) methodologies that could help to evaluate these impacts are not mature yet [248]. A recent review by Spierling and coworkers [249] points to the existence of a few SLCA studies focused on bioplastics. Certifications considering multiple aspects of sustainable development are an alternative to address this limitation (as carried, for example, by NatureWorks).

Hence, while bioplastics can bring about positive ESG effects, they must comply with multiple sustainability dimensions. In this sense, they are not recognized as a solid solution to plastics pollution, which limits their market growth.

7. The Lessons from PLA and Insights into Diffusion of Bioplastics

The recent market data indicate that the bioplastic capacity should jump from nearly 2.22 million tons in 2022 to 6.30 million tons in 2027, 56.5% of which refers to biodegradable plastics [18]. This paper aimed to identify which conditions would justify and enable this steep growth in such a short period. From the PLA case studies and the stylized facts drawn, it is possible to see a convergence of factors contributing to this scenario.

Table 4. Stylized facts from the PLA case study and their implications. Source: developed by the authors.

Stylized Fact	Main Trends Identified	Implications
1. The Prevalence of Petrochemical Plastics Restricted the Bioplastic Capabilities	Some bioplastics were invented during the 20th century. The plastic industry primarily structured itself around fossil-based materials (lock-in effects).	Little capability building on bioplastics at relevant scales.
2. Plastics Generally Present Property Issues When They Were Introduced	New plastic materials generally display technical limitations in terms of their properties when invented.	A non-negligible development time is required to improve properties through additives, blends, and compounding. A learning period occurs for stakeholders involved with the polymer advances.
3. Plastic Pollution Was a Key Trigger of Bioplastics Diffusion	Plastic pollution has stood out as a global concern.	(Re-)Assessment of bioplastics as solutions to plastic pollution. Large-scale industrial production envisioned.
4. Bioplastics Experienced Lower-than-expected Market Growth, which Compromised Corporate Commitment	“The chicken and the egg” scenario of supply vs. demand. Bioplastics are usually more costly and may not match the properties of fossil-based plastics. It is unclear if consumers would pay more for bioplastics based on sustainability claims.	A limited number of large-scale bioplastics producers (adverse effect on learning curves). For some bioplastics, production technologies still need to evolve (e.g., PHA and PBS).
5. Co-operation is Key to Promoting Bioplastics	Presence of coordinated actions of resin producers, converters, additive and equipment suppliers, brand owners, government, funding agencies, universities, etc., to advance bioplastics.	Examples of successful technical and market developments. An increase in capabilities and knowledge-sharing initiatives.
6. Sustainability Scrutiny Simultaneously Propel and Hinders Bioplastics	Plastic regulations are rapidly increasing and are the leading promoters of bioplastics market growth. Different dimensions of sustainability are being considered to assess the circularity of plastic materials. Low maturity of EOL alternatives for bioplastics. Low maturity of SLCA methodologies to evaluate social impacts of bioplastics.	Bioplastics demand growth (e.g., in France and Italy). Bioplastics are not undisputed solutions to plastic pollution. Recycling, reuse, and design for circularity may keep petrochemicals interesting. Certifications are being created to guarantee the environmental and social responsibility of bioplastics.

below summarizes the main lessons learned.

Although many bioplastics were discovered during the 20th Century, they remained niche markets due to the prevalence of fossil-based plastics. With the increasing concerns about plastic pollution in the 1980s, solutions that offered better environmental profiles were demanded, promoting the diffusion of bioplastics.

The bioplastics growth foreseen in the early 2000s was not observed. Bioplastics tend to be more costly than traditional plastics do, and they do not necessarily match their properties [219,220]. This uncertainty reduces the number of producing firms, which limits the market’s confidence in supply stability [217,218]. Moreover, learning effects that optimize costs are reduced due to the limited production capacity available [28,250]. While some bioplastics such as PHA and PBS still have low production rates, PLA and PBAT seem to have a good maturity level [144]. For PLA, sharp price decreases were noticed from 1995 to 2007 [141], reaching relative stability in 2007 (see Figure 3).

PLA and other bioplastics have shown a myriad of examples in which cooperation among stakeholders occurs. This is a trend also experienced by petrochemicals that have contributed to problem solving for these traditional plastics [164]. However, it is worth noting that low market volumes may reduce corporate commitments to the bioplastics businesses, as Milliken suggested in 2008 [134].

It is clear that plastic pollution regulations are the main drivers for bioplastic growth. However, different approaches are available to improve the circularity and sustainability of plastic materials. The OECD identifies four critical levers to reduce the environmental impacts of plastics: (1) establish recycled plastics markets, (2) technological innovation for more circular plastics value chains, (3) improve international cooperation, and (4) more coherent and ambitious domestic policies (e.g., invest in collection and disposal infrastructure, ban items such as plastic bags, and restrain demand and designing for circularity) [1]. The OECD’s roadmap clarifies that a total rupture with petrochemical plastics is not considered. Instead, its recommendations imply that there are paths to make fossil-based materials more circular and more sustainable. A similar conclusion can be drawn from the report of The Pew Charitable Trusts and SYSTEMIQ, an evidence-based roadmap written by a global panel of experts to end ocean plastic pollution [251].

For this reason, the renewable content and/or biodegradability of bioplastics are probably not sufficient to drive the large-scale transition away from petrochemical plastics. Bioplastics must comply with different sustainability dimensions, considering the entire life cycle of the materials.

8. Conclusions

In summary, while the expected bioplastics growth of the early 2000s was not confirmed, the most recent decades have seen relevant improvements in technological and market terms, especially for PLA. These are critical enablers for the steep growth forecasted for the next five years. On the other hand, the growing demands are mainly explained by worldwide regulations targeting plastic pollution. They create a scenario where plastics are reassessed through a sustainability lens, which creates space for bioplastics. However, there are essential obstacles to the more significant substitution of petrochemical plastics. The general absence of consistent EOL alternatives makes bioplastics a questionable solution to plastic pollution, even more so considering that additives and blends can affect the degradation behavior (for better or worse). Hence, the diffusion of bioplastics at the forecasted rates seems possible, but caution is advised due to the structural changes necessary to guarantee their sustainability.

Some exciting avenues for future work can be suggested. One limitation of this paper is the main focus on a single bioplastic (PLA). Although more general stylized facts were discussed, they lack depth on the constraints of other biodegradable bioplastics. Therefore, it would be interesting to compare this case study with starch blends, PHA, PBS, and even the fossil-based PBAT. Additionally, we have not addressed drop-in bioplastics such as “green” PE, PET, or PP. Since these polymers are chemically identical to their fossil-based counterparts, their challenges differ from those of novel bio-based polymers. Their innovation dynamics may concentrate upstream in resin production and business models [252], entailing new facets to their diffusion drivers. On the other hand, some bioplastics such as polyethylene furanoate (PEF) could combine characteristics from non-drop-in and drop-in bioplastics [253].

Another limitation of this paper consists of its empirical methodology. As discussed in the Methodology Section, we rely on the detailed empirical description of PLA and stylized facts to assess the diffusion capacity of bioplastics. In other words, our methodology allowed us to identify the broad outlines of this phenomenon. A possible venue for work is to use more rigorous methods to assess this diffusion process, such as agent-based modeling and system dynamics approaches. A remarkable example of the latter methodology applied to the bioeconomy context is the work of Bennett [254].