**1. Introduction**

In different kinds of activities, coatings are used to protect structures, goods and packaging from the aggressiveness of the environment mostly by providing special characteristics to the associated material. High-performance coatings is a generic term used to define coatings that provide great mechanical resistance along with other interesting features. These coatings must have particular properties in addition to mechanical resistance to ensure good protection against corrosion or to avoid the occurrence of cracks and fissures among other anomalies [1,2] without loss of performance throughout their life cycle. In particular, polymer resins are widely used as coatings in many industries from aerospace and automobile to pharmaceutical and food industries [3–5]. Resins normally used as high-performance coatings are actually polymer matrix composites reinforced by mineral aggregates, natural or synthetic fibers, as well as other fillers that provide great mechanical resistance along with high durability and waterproof conditions, together with any property of specific interest [6–8].

A particular case related to the civil construction common in Brazil is the highperformance coated floor (HPCF). Traditional floors are made of concrete plates with or without mortar and ceramic tiles. The joints in these floors pose problems such as biohazard contamination. This can be bothersome in places such as hospitals, and pharmaceutical

**Citation:** Carvalho, J.P.R.G.d.; Simonassi, N.T.; Lopes, F.P.D.; Monteiro, S.N.; Vieira, C.M.F. Novel Sustainable Castor Oil-Based Polyurethane Biocomposites Reinforced with Piassava Fiber Powder Waste for High-Performance Coating Floor. *Sustainability* **2022**, *14*, 5082. https://doi.org/10.3390/ su14095082

Academic Editor: Mariateresa Lettieri

Received: 8 March 2022 Accepted: 7 April 2022 Published: 23 April 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

and food processing buildings. In contrast, polymer-based HPCFs are easy to apply and do not need a previously prepared surface when compared to traditional ceramic tiles. Moreover, HPCFs do not have joints as the polymer is primarily applied in the form of liquid resin over the entire floor. In fact, not only do HPCFs improve the floor's durability, provide oil or waterproof characteristics, and maintain its cleanliness, but they also enhance sports performance because of their good adherence properties when applied on stadium floors [9].

Although it is common to find marketing information for HPCFs, to our knowledge, studies on this subject are scarce and no relevant work has been reported in the literature for their use in civil construction. Therefore, the main objective of this work was to evaluate the potential viability of using the piassava fiber waste in such an application. Although some nanocomposites have shown promising results for HPCFs [9], the reinforcements used are usually from synthetic, non-renewable origins. The use of biocomposites reinforced by natural and renewable piassava fibers for this application would be directly beneficial for the environment. The Brazilian standard NBR 14050 [10] regulates the use of HPCFs made with epoxy resins and provides the requirements for their application, as shown in Table 1. In this table, the "critical" requirements are properties that can be found in other kinds of polymers and their composites.

**Table 1.** Summarized requirements of the NBR 14050 [10] standard for a material to be used as HPCFs.


Epoxy resins are the most common choice not only for HPCFs but also for paints, car components and aerospace parts because of their well-known properties and reliable characteristics [11–13]. However, the production of epoxy-based HPCFs generates the evaporation of large amounts of volatile organic compounds [14]. Moreover, the use of non-renewable source materials poses a long-term problem. Both the academic and the industrial communities have been striving to develop new sustainable materials [15–18].

An alternative to the use of petroleum-derived resins such as epoxy is material from natural sources. One example is polyurethane (PU) synthesized from oilseed plants. The synthesis of PU occurs in stages of polyaddition and from hydroxyl compounds and isocyanates. Hydroxyl monomers can be obtained from vegetable oils [19]. This is the case for castor oil-based polyurethane (COPU). The oil is extracted from the fruit of the "castor oil plant" (*Ricinus communis* L.) a relatively tall shrub from tropical regions that has been successfully used to obtain the COPU polymer [19,20].

Studies have shown some interesting properties of COPU. Santan et al. [21] created an adhesive based on COPU and evaluated both the microstructural relationships and mechanical properties of the new material. Zeng et al. [22] modified the asphalt used for paving roads with COPU and noticed improvements in performance and a reduction in the deformations of these coatings. In fact, COPU is a bi-component polymer composed of prepolymer and polyol, both of them easily found commercially, and characterized by not emanating toxic substances [23,24].

In parallel, several researchers in past decades have suggested natural lignocellulosic fibers (NLFs) [25–32] as composite reinforcement material, mostly owing to its attractive features such as good mechanical properties, low density cost-effective production and sustainable motivation. The environmental appeal of these materials can be further enhanced by adding industrial, residential or agricultural wastes as reinforcement of these composites [32–36]. Usually, natural lignocellulosic fiber (NLF) waste is burned during its

end-of-life cycle, and not only does the use of waste as a composite reinforcement or filler in natural source-derived resins directly reduce the cost associated with its disposal, but it also presents itself as a good alternative to materials with carbon neutral emissions.

One specific NLF commonly used in Brazil as a raw material in the manufacture of brooms for households is the piassava fiber. In the manufacturing process, the fibers are cut to a standard length, and those shorter are discarded and become disposable waste. These piassava fiber wastes have limited commercial use and are normally burned [37]. As an alternative, this fibrous waste can be further processed and ground to powder to be incorporated into polymer composites.

The use of piassava fiber powder, here referred as piassava powder for short, has shown some promising results. Borges et al. [38] initially ground the piassava fibers in a knife mill and sieved them at 50 mesh to incorporate as composite filler in a copolypropylene matrix. They achieved satisfactory results of 35.5 MPa for the flexural strength, while those incorporated into a homopropylene matrix showed an even greater resistance of 47.7 MPa. These results revealed the possibility of using piassava powder as a reinforcement in polymer composites to be applied as an HPCF. Furthermore, a preliminary study [39] disclosed the great potential of the piassava fibers to be used as HPCFs. Indeed, the compressive strength obtained was around 50 MPa, and 0.8% of water absorption was found in 20 vol% of piassava powder-reinforced COPU.

Therefore, the present work aimed to continue the investigation into the use of piassava powder waste obtained as a processed material from a Brazilian broom factory, reinforcing a COPU biocomposite to be applied as an HPCF. In this study a comprehensive investigation was conducted not only to meet the NBR 14050 [10] standard recommendations, but also to perform a more extensive characterization of this HPCF material since, so far, there are no results to compare it to in the literature.
