Investigation of the Carbon Footprint of the Textile Industry: PES- and PP-Based Products with Monte Carlo Uncertainty Analysis

Abstract

The Carbon Border Adjustment Mechanism was developed to ensure that industrial sectors operating outside the EU follow the same environmental standards and targets while competing with the EU’s carbon market. This mechanism aims to calculate the carbon footprint of goods and services imported into the EU and make carbon adjustments accordingly. The transition phase, starting in 2023, represents the period when the Carbon Border Adjustment Mechanism will be implemented. The completion of the transition phase is targeted for 2025. By this date, the effective implementation of this mechanism is aimed at demonstrating that countries outside of the EU comply with emissions regulations using Carbon at Border certificates. The textile industry’s products have a significant environmental impact throughout their life cycle, from the production of raw materials to the disposal of the finished product. Textile production, especially synthetic yarns, requires large amounts of energy, contributing to greenhouse gas emissions and climate change. In this study, a “cradle-to-customer plus waste” life cycle assessment (LCA) is conducted to evaluate the environmental impacts of two products in the textile sector. The Monte Carlo analysis method can be used to handle uncertainties in LCA calculations. It is a method for modeling uncertainties and statistically evaluating results. In this study, this method is preferred at the stage of determining uncertainties. The processes from chips to yarns are investigated for two synthetic yarns: polyester (PES) and polypropylene (PP). The carbon emissions of PP and PES used in textiles are calculated for the first time in this study using detailed modeling with LCAs and a real application. The main production operations are considered: (i) transport of raw materials and packaging material, (ii) energy consumption during the production process, (iii) transport of products, and (iv) end-of-life steps. When the actual data obtained from a company are analyzed, the carbon footprints (CFs) of the PES and PP are calculated to be 13.40 t CO₂-eq (t PES)-1 and 6.42 t CO₂-eq (t PP)-1, respectively. These data can be used as reference points for future studies and comparisons. According to the results obtained, when the energy consumption and raw material stages in the production of the PES and PP products are compared, it is seen that the CF of PP yarn is lower, and it is more environmentally friendly. These findings can be utilized to enhance government policies aimed at reducing greenhouse gas emissions and managing synthetic yarn production in Türkiye. Since PP and PES raw materials are predominantly used in synthetic yarns, this study’s objective is to quantify the carbon emissions associated with the utilization of these raw materials and provide guidance to companies engaged in their production.

1. Introduction

One of the key components of the Millennium Development Goals (MDGs), which were established at the outset of the concept of sustainability and as the third millennium approached, was ensuring environmental sustainability. However, there has been no research in this field since the Paris Agreement’s sustainable development principles were adopted [1]. The European Green Deal was unveiled and passed into law in 2019, after the Paris Agreement was signed in December 2015, and efforts up until then had been unsuccessful.

A key component of the Paris Agreement is the global adoption of a new economic paradigm that originated in Europe. The first of this model’s three key elements is achieving net-zero emissions via emissions reductions followed by clean, dependable energy that people can purchase and, finally, sustainable transportation. The date of implementation for “Fit for 55” was 14 July 2021. “Fit for 55” refers to the EU’s objective to reduce net greenhouse gas emissions by at least 55% by 2030. This program, which was originally put into effect by the European Green Deal, stipulates that emissions must be cut by 55% by the year 2030. Many researchers consider this ratio to be insufficient and that a reduction of 1.5 degrees should be the primary goal. However, emissions must be reduced by 65 percent to achieve a drop of 1.5 degrees. Carbon pricing systems have become more prominent for this reason. A penalty mechanism has been established for those who have high emissions thanks to carbon trading [2]. Governments, communities, and nonprofit organizations all over the world now face a problem: global warming and the greenhouse effect. The Carbon Border Adjustment Mechanism (CBAM), which the European Union plans to implement, requires a reduction in the carbon and environmental footprints of products to be exported. For this reason, the carbon footprint (CF) of products has become an important issue for companies and their customers [3]. Information on the emissions of greenhouse gases that occur during the life cycles of products helps to determine their CF, that is, the impact of the products on climate change. Since the textile industry has a large share of the worldwide production sector, it draws attention to the problem of global warming. By examining the value of the export industry of our country, it can be concluded that the textile sector occupies an important position.

According to the İstanbul Apparel Exporters’ Association (İHKİB), the ready-to-wear and apparel industry was the third largest exporter in 2021 [4]. The fact that this sector contributes such a large share to exports makes the textile sector and the raw materials used in this field even more important. Fibers, which have been used as raw materials in the textile industry for a long time, are used in many different areas, such as ready-made clothing, home textiles, carpet production, and upholstery fabric production. With the rapid developments in the industrial field since the end of the 1970s, many alternatives, such as technical textiles, have emerged for the use of textile fibers in addition to traditional applications and areas of usage. These diverse and wide new areas of usage include many technical applications in the construction, automotive, defense, sports, medicine, electronics, maritime, and other similar sectors. The prominent features of technical textile materials are their functions at the time of use, as well as the raw materials (polymer material, fiber type, etc.) that provide these functions and the production techniques of these raw materials.

Polypropylene belongs to the polyolefin group and is partially crystalline and nonpolar. The molecular formula of polypropylene with the [-CH2-CH(CH3)-]n designation is (C3H6)n. The methyl group decreases the chemical resistance but increases the mechanical properties and thermal resistance. The properties of polypropylene depend on the molecular weight and molecular weight distribution, crystallinity, comonomer type, and ratio (if used), and isotacticity. In isotactic polypropylene, the methyl groups are oriented to one side of the carbon backbone. This arrangement creates a greater degree of crystallinity and results in a harder material that is more resistant to creep than both atactic polypropylene and polyethylene [5]. Polypropylene is a thermoplastic polymer with applications such as fiber and plastic. This material does not react with water and most chemicals. Polypropylene is considered a hard material. It softens when heated and can be reshaped into different shapes. The main application of this material is as a packaging material.

Polyester is a category of polymers containing ester functional groups in each repeat unit of their main chain. Polyester can contain naturally occurring chemicals as well as synthetics such as polybutyrate. The chemical formula of a polyester, where each polyester is a hydrocarbon, is shown as (R-OCO-R)n. Polyesters are formed from the reaction between dicarboxylic acids and diols. The most common polyester, polyethylene terephthalate or PES, consists of terephthalic acid and ethane-1,2-diol. It consists of polythymethylene terephthalate, terephthalic acid, and propane-1,3-diol. The two reactants of a polyester form an ester bond with the loss of one water molecule. A complete polymer is formed when a chain of these bonds is formed with the loss of a water molecule at each ester linkage. It states that polyesters with benzene rings have high melting points and rigid structures that give them greater strength [6]. Polyesters are chemically composed of at least 85% by weight of an ester, a dihydric alcohol, and a terephthalic acid. In other words, the reaction between the carboxylic acids and alcohols that make up the esters leads to the formation of a polyester. Polyesters are very useful polymers due to their important properties such as high strength, high durability, hydrophobic structure, and fast drying. Polyester materials are useful as fibers, films, packaging materials, etc. The molecular structure of the Polypropylene and Polyester raw materials is shown in Figure 1.

Both polyester and polypropylene are polymers. Polyester is formed by condensation polymerization between a dicarboxylic acid and a diol. Polypropylene is formed via the additional polymerization of propylene monomers. The main difference between polyester and polypropylene is that polyesters can absorb some water, whereas polypropylene does not absorb any water.

In the textile industry, a wide variety of raw materials, including polypropylene and polyester pellets, are processed using a variety of techniques to create the desired output for the consumer. Raw materials, labor, and energy are used in the process. By considering the recent past, it is seen that human beings have progressed rapidly in the technological field. Parallel to this development, limited natural resources such as water, air, soil, and underground mines started to be polluted/depleted rapidly. As a result of this unconscious use, global warming and the greenhouse gas effect, which are some of the most important problems of today, are increasing. The rapid depletion of world resources and the prediction that they cannot be left to future generations in sufficient quantities have revealed the concept of sustainability. Sustainability requires a life cycle approach. The product lifecycle is one of the most important concepts of sustainable product design. Life Cycle Assessment (LCA) [7] is the approach used to identify, report, and manage environmental impacts at different stages of the life cycle, starting from the acquisition of raw materials used in the production of a product or service, including all relevant production, shipping, and consumer use. The Monte-Carlo method is used to overcome the uncertainties. The Monte Carlo analysis method is a numerical calculation technique that utilizes random numbers to solve various problems. When combined with LCA, it enables the consideration of uncertainty in environmental impact assessments, leading to more accurate and robust decision-making. LCA steps are shown in Figure 2.

The LCA methodology, which consists of four stages, fundamentally covers the following steps:

• To make an inventory of the energy, water, and other raw materials and natural resources used in the process of obtaining a product or service and the environmental emissions that arise with it,
• To determine the environmental impacts that may occur in connection with these inputs and outputs,
• To evaluate the environmental impacts by considering the inputs and outputs. In this step, the Monte Carlo analysis method is used to analyze the uncertainties associated with the LCA,
• To evaluate the results systematically and comparatively and to present them to the decision-makers.

The Monte Carlo analysis method, also known as a statistical simulation method, is a precise numerical computation technique based on probability and statistics theory. It is used to solve various computational problems using random or pseudo-random numbers. The Monte Carlo method is a widely used statistical technique for uncertainty analysis in various fields, including Life Cycle Assessment (LCA). It is particularly useful when dealing with complex systems or processes where uncertainty arises from multiple sources and cannot be easily expressed with simple analytical formulas. In LCA, the Monte Carlo method is employed to assess the impact of uncertainty on the results of environmental assessments.

As the current climate action plans of the countries are analyzed, it is seen that the joint decisions taken are in the direction of eliminating unnecessary emissions, reducing existing emissions, and balancing inevitable emissions. By calculating the CF of the products, missed emissions can be reduced, and mandatory emissions can be balanced. Studies on CF amounts have gained momentum in recent years in line with incentives for environmental impacts and the Carbon Border Adjustment Mechanism (CBAM), which is targeted to be implemented soon. Many studies on the life cycle analyses of the products and the improvements that can be made as a result of these analyses are also carried out in the textile industry. Cotton is an important raw material in the textile industry. Cotton clothes have an important place in human life as they contain natural fibers in their structure. For this reason, there are many LCA studies in the literature on raw materials used in the field of textiles, especially cotton. In 2017, cotton fibers obtained from clothing scraps and cotton fibers produced using organic methods were discussed, and life cycle analysis was carried out for these two products. As a result of the calculations, they observed that organic cotton cultivation is more advantageous compared to traditional cotton cultivation. However, the necessity of the dyeing process in the production phase of organic cotton puts this product at a disadvantage in terms of usability and sustainability. On the contrary, the situation is different with recycled cotton. The necessity of cotton planting and the fact that it is a method that will prevent the emergence of environmental effects, with the recycling technology based on the correct color selection of the fiber, makes this product advantageous. In addition, they stated that the waste cotton is recycled and offers a second life to the product, which reduces its environmental impact and cost [8]. In another study conducted in the field of cotton in the textile industry, life cycle analyses were modeled in a scenario created based on the current consumption of cotton, polyester, and wool raw materials in Australia. The life cycle analysis was carried out by developing a supply chain model, starting from the acquisition of the raw material until the product’s life cycle is completed and turned into waste [9]. In 2018, Zhang et al. discussed the most polluting production stages of polyester-cotton production in their study. Using a three-step process, they created an improved design to minimize environmental impact. The LCA method has been used to determine the environmental impact of all processes, from cotton planting to obtaining the final product, polyester-cotton, and to the destruction process. In addition, the benefits of the design developed within the scope of the study, resource consumption, ecological impact, and evaluation of environmental benefits were determined using multiple performance analysis methods [10]. In 2021, the environmental effects of cotton fibers and these products, which show how much ecological products can reduce the effects on the environment, compared to cotton produced with traditional methods, have been reviewed by researching the life cycle analysis method. In line with this study, the amount of fertilizer, pesticide, and water used in cotton production was discussed. When the consumption amounts of these resources are evaluated, it is concluded that the environmental burden of cotton production is significantly higher. At the conclusion of the study, it was emphasized that in the production phase, there is significant overuse of water, energy, and chemicals. To mitigate the negative impact on the environment, the use of alternative chemicals should be encouraged [11]. Powar et al., 2021 [12] investigated the ozone-based color removal process of reactive dyed cotton textiles. Within the scope of the study, data flow along with all inputs and outputs throughout the process were determined, and a life cycle analysis was made for the product. The study was undertaken to determine the main factor of the effects of ozone stripping on the environment and make improvement studies for this process. In a recent study by Korol et al., different production methods based on various polymerization reactions were analyzed for PP [13]. As a result, the total CF of the polypropylene production system is specified as 3.43 kg CO₂ eq/kg PP, and the total water footprint is specified as 0.059 m³ /kg PP. In 2014, van der Velden et al. conducted a detailed LCA study for cotton, PES, nylon, acryl, and elastane products in the textile industry. The data required for this study were obtained from various companies and the Dutch government, as well as from the literature. In the study, detailed information about the products is shown in tables. At the end of the study, it was stated that acryl and PES had the least environmental impact [14]. In addition to these studies, there are also product-oriented LCA studies in the textile sector. Manda et al. conducted a life cycle analysis of a product with antibacterial properties in 2015 [15]. Within the scope of this project called SurFunCell, it has been observed that the environmental damage caused by the antibacterial t-shirt during the production phase is 20% less than the traditional nonantibacterial t-shirts. In addition, it has been stated that the factors that most affect the environment during the production of the t-shirt are natural soil conversion, use of fossil resources, acidification, and clean water eutrophication. In a study conducted in China [16], the CF of fabrics produced from a polyester blend was calculated as 13.5 kg CO₂ eq/kg-fabric. In the same study, it is stated that these values will increase by 70.8% when the yarn dyeing process is taken into account. Then, this value will be 23.1 kg-CO₂ eq/kg-fabric. This result shows that the ability of polyester materials to be dyed afterward (multiple times if desired) is an advantage for the manufacturer, but it is a negative feature in terms of environmental effects. Kirchain et al. conducted a comprehensive study on sustainable clothing materials in 2015 [17]. In this study, the carbon emission amount of a polyester t-shirt was calculated as 3.8 to 7.1 CO₂eq/kg, depending on whether it is knitted or woven. In the study conducted in 2021, the CF of clothing and home textiles sold in France was measured [18]. In this study, manufacturers calculated the CF of 17 garment and home textile products. Based on textile imports, their calculated CF for a French person reaches 442 kg CO₂eq/year, according to the study. To reduce this CF by six times (74 kg CO₂eq/person/year for textiles), different situations were evaluated, and this value was reduced to 43 kg CO₂eq/year. Muthu et al., in their study in 2012, drew attention to the “end of life” stage in the life cycle analysis of products in the textile field [19]. In the study in the USA, the energy and carbon emissions of wool and nylon carpets were calculated. Energy and carbon emission amounts are found as 20.42 MJ and 6.35 kg CO₂-eq for silk carpet and 25.42 MJ and 4.80 kg for nylon carpet [20].

Many studies have been carried out in this field in our country as well as in the world. Yıldız and Arslan emphasized that life cycle analysis is a method developed in 2017 to determine the effects of products and services on the environment and to reduce these effects. In addition, in their study, they defined life cycle analysis as an analysis method used to determine the environmental effects of all stages in the process, starting from the raw materials of the products to their use and disposal [21]. Aydın and Çiner discussed the changing textile trends with fashion in their work in 2016. They concluded that these rapidly changing trends also accelerate the consumption process and increase environmental damage. In this direction, they determined that the life cycle analysis is an important method used in revealing the environmental effects of the products. In their study on a product basis, they discussed the time elapsed from the production stage of the 100% cotton-dyed bed sheet used in home textiles to the use of the consumer and the waste. In the life cycle analysis for 100% cotton-dyed sheets, they found that the most important environmental impact occurred during the use phase. In the production phase, they stated that the most important environmental impact is in the dyeing process [22]. In 2018, Toksöz conducted studies on fabric production performance and environmental impacts within the framework of sustainability. The study was made with four different denim fabrics woven with raw materials containing different cotton types based on the HIGG index. In the production of fabrics, only the main raw material was changed, and all the remaining parameters were kept the same, and the life cycle of these four different products was analyzed. These fabrics produced within the scope of the study were subjected to the same tests. As a result of the study, it has been seen that it is possible to reduce the cost significantly by changing only the main input raw material. With this advantage, it is concluded that the products will be in a better position in the market share [23]. In 2022, energy studies were carried out in a towel production facility operating in the textile sector in Bursa, and studies were carried out on the efficient use of energy and reducing the amount of emission [24]. Another study was carried out in a textile factory operating in the Marmara region, where various calculations were made [25]. The company uses natural gas, electricity, and diesel fuel as energy sources. Additionally, energy is consumed in different forms in the production and transportation of raw materials supplied from abroad. Furthermore, ancillary activities such as the transportation of employees also contribute to energy consumption. Taking into account all contributing factors, the overall CF in the study is stated as 52.8 kg-CO₂eq/kg-fabric. In another study, Coşkun et al. [26] calculated the CF amounts resulting from annual production activities in the apparel, fabric dyeing, printing, and yarn dyeing departments of a textile factory for CF determination. The authors took the emission factor values of the electricity consumption required during the calculation from another study [27]. In another study performed in Türkiye in 2017, the greenhouse gas emission amount of a cotton shirt weighing 175 g was calculated as 8.46 kg CO₂-eq/kg [28].

In this study, the environmental impacts of the two most exported products of Ulusoy Textile Company, one of the leading companies in the textile sector in Türkiye’s Çukurova region, are examined. The “cradle to customer plus waste” stages of Polyester and Polypropylene yarns are analyzed with the LCA methodology. When the literature is examined, it is seen that there is no comprehensive LCA analysis of PP and PES yarns. The main purpose of the study is as follows:

• Calculating the CF of products produced by the same company using different raw materials and,
• Comparing the emission amounts of these two different products produced.

When a detailed literature review is carried out, many studies conducted in the textile sector draw attention. When the studies carried out until today are analyzed, there is no carbon calculation study for PP and PES products. PP and PES materials are chosen to be studied because these two materials are the most widely used value-added products in the production of value-added yarn in the textile sector. The necessary calculations are performed by using the data of Ulusoy Textile Company regarding the supply of raw materials for 2020, the steps of the production process, the transportation of the products, and the end-of-life stages of the products. These two selected substances are two of the most important raw material components not only for this company but also for textile exports that address 80% of the region. In this study, the life cycle is calculated from raw material to waste. Such a detailed study of PP and PES products is conducted for the first time in this study.

The textile sector is one of the sectors with high export rates in Türkiye, and this sector is prioritized in many national calls in the country. Academic calls are also open in this field. Many academic studies have started to be carried out in this direction in the sector [29]. In this study, these products will be studied for the first time and will be guiding the sector. The data used in the study were not taken directly from the company used in the study; on the contrary, the data were collected from the lines together with the researchers in the paper. In addition, the transport data used in the study were added to the scope of the study by contacting the relevant parties.

A number of recently published articles have studied the field of textiles (product-based studies according to 14067 standards), and the products and methods used in the analysis phase are summarized in

Table 1. Carbon emission studies have been carried out in the field of textiles in recent literature.

Product	Area	Method	Value
Recover cotton [8]	textile industry	LCA	the environmental savings are 13.98 kg CO2eq for GWP, 0.32 kg SO2eq for AP, 0.033 kg PO43-eq for EP, and 5594 kg water for the WU impact category
textile supply chain [9]	textile industry	LCA	with the reduction in washing machine energy and washing frequency, the impact of CO2-e emission can be reduced by around 10 and 33%, etc.
Ozone Decolorization of Reactive Dyed Cotton Textiles [12]	textile industry	LCA	according to climate change impact category 0.13248698 kg CO2 eq
Polypropylene-Based Composites Filled with Cotton, Jute and Kenaf Fibers [13]	textile industry	environmental footprint assessment	incorporating 30 wt% of cotton, jute, and kenaf fibers into a polypropylene matrix results in carbon footprint reductions of 3%, 18%, and 18%. (Ecological and Water Footprints results are given.)
textiles made of cotton, polyester, nylon, acryl, or elastane [14]	textile industry	LCA	textiles made from acryl and PET have the least impact on the environment, followed by elastane, nylon, and cotton products.
antibacterial T-shirt [15]	textile industry	LCA	t-shirts constructed with 50% antibacterial fibers in situ (50AB in situ) produced 15–20% less CO2 emissions than commercial antibacterial T-shirts.
Several typical Chinese textile fabrics [16]	textile industry	CFP assessment method	CFP of the pure wool fabric: 14.07 kgCO2e/kg, CFP of the gray fabric: 1.81 kg CO2e/kg.
sold clothes and household linen [18]	Textile	LCA	clothes: 22.87 million tons of CO2eq household linen: 6.75 million tons of CO2eq
Wool and nylon carpets [20]	Textile	LCA	wool carpet: 6.35 kg CO2-e nylon carpet: 4.80 kg CO2-e
Painted and unpainted sheets [22]	Textile	LCA	unpainted sheets: 1.27 kg CO2 eq painted sheets: 4.35 kg CO2 eq
fabric production [25]	Textile	Tier 1 and 3 method	52.8 kg-CO2e/kg-fabric
a cotton t-shirt [28]	Textile	LCA	8.46 kg CO2-eq
Denim Fabric [29]	Textile	LCA	According to the Global Warming Impact Category (2019); LCA results based on “Total Production Capacity”: 7.50 kg CO2 eq LCA results based on “Selected Product”: 4.43 kg CO2 eq LCA results based on “wet process”: 5.28 kg CO2 eq

. When these studies in the field of textiles are analyzed, it is seen that the “cradle to customer plus waste” life cycle assessment (LCA) of PP and PES products is not performed or even compared.

The remainder of the paper is organized as follows: information about LCA and fancy yarn products is shown in the Section 2. Additionally, general information about the company and production processes is presented. In the CF accounting section, the distribution of carbon emission amounts of PP and PES is shown in detail. The most appropriate uncertainty analysis method, Monte Carlo, is selected and applied after a detailed literature review. The concluding remarks and key findings of this examination are revealed in the Section 3 and Section 4.

2. Materials and Methods

Ulusoy Textile Company was established in 1986 in Türkiye’s cotton region Çukurova. Fancy yarn production produces 1000 tons of fancy yarn in the national and international markets with its product variety, quality, dynamic, and structural appeal to a wide range of fields (NACE Code: 13.10.12). Having a strong logistics network, the company exports to 5 different continents and more than 30 countries. The yarns produced comply with ISO 9001 Quality Management System and internationally recognized Oekotex standards. In addition, the company produces its products within the scope of the GRS certificate, using recycled materials with an environmentally friendly approach.

In the company, a new product is obtained as a result of the use of raw materials, machinery equipment related to the production of the product, as well as labor, energy, and water. The raw materials of the products produced in the company are taken in the form of pellets. The raw material received is melted from the extruders and turned into filament yarn, and at the end of this stage, the filament yarn is subjected to texturing and takes its final shape. To strengthen the yarn and bring it to the thickness desired by the customer, folding and twisting are made. Depending on the technical specifications of the product requested by the customer, dyeing can be performed while the raw material is melted from the extrusions, or yarns can be dyed in the form of bob-bins, hanks, gradients at the stage after the product takes its final product form. At every stage of product production, quality control measures are implemented to ensure approval for quality. After the production phase is completed, the product is delivered to the customer. The production processes of PP and PES yarns in the company are shown in Figure 3.

In this process, yarns are prioritized and stored in silos. Then, blends are created from the dosing line based on the product type and according to the relevant order. Subsequently, the production of the requested products is carried out. In the final step, the finished goods produced according to the customer’s order are packaged and shipped. In general flow, a chart of the company production process is shown in Figure 4.

Ulusoy Textile Company has four main markets: home textiles, hand knitting, carpet, and knitwear. Among these markets, home textiles have a large share. The most preferred raw materials in this market are PES and PP. These are the most imported products on a company basis.

2.1. Life Cycle Assessment

Life Cycle Assessment, a major tool in environmental management, is used to evaluate pertinent environmental elements and their possible effects on a product’s or service’s life cycle [30]. LCA procedures are based on the ISO standard 14040, which has four sections: defining the objective and scope, inventory analysis, impact assessment, and result interpretation [31]. To calculate and analyze the CF based on the actual manufacturing process of the product, this study used the LCA tool.

The CF is acknowledged as the recognized indication of greenhouse gas emissions that occur during production and are thought to be the primary cause of global warming in accordance with the Kyoto Protocol and life cycle assessment standards. It quantifies total greenhouse gas emissions in terms of CO₂ equivalent (ISO 2006a). According to their concentration in the atmosphere, the CO₂ in these gases draws attention. Therefore, the greenhouse gas emissions of these gases are shown as CO₂ equivalent [32]. The most important step during LCA calculations is the creation of an inventory table. The inventory table, which forms the basis for the analysis, emerges as a result of the inventory analysis and the collection and arrangement of all data. A systematic approach to inventory analysis is proposed in ISO 14044 (ISO 2006b) [33]. Impact assessment is the stage in which calculations are performed utilizing the information in the resulting inventory table to produce numerical results for the chosen impact categories. The evaluation of the entire LCA process and the results obtained, as well as recommendations for lessening environmental impacts, take place during the interpretation phase [34]. CF is widely used to measure the impact of manufacturing sectors on climate change. The LCA method enables the quantification of total GHG emissions by covering the production processes of the product from the raw material stage to the final product [35].

This paper is completed in four stages in general.

• Step 1—Determine the purpose of the study

At this stage, it aims to use the LCA method to calculate the CF of Polyester Yarn and Polypropylene Yarn. This study aims to estimate the potential environmental impacts of their production on an industrial scale. Greenhouse gas emissions from the supply of energy, fuel, and raw materials to the transportation of their products are included in the CF calculation.

Since the “cradle-to-customer plus waste” life cycle assessment is aimed in the study, the stages from the procurement of the raw material used in the production phase from the supplier company to the delivery of the products to the customer are within the limits of the system. Figure 5 shows the production stages of the polypropylene product. The raw material supplied in chips is shipped in ecru or colored form according to the color requested by the customer. Primarily, in both cases, the yarn is made into filaments. The filament turned into yarn is packaged and stored in the ecru form. According to the workflow/operation plan, the filament yarn taken from the warehouse is subjected to the air text stage. After this stage, the final yarn goes to the packaging unit and is ready for shipment. Colored filament yarn can be sold directly to the customer in this state, or it can be sold to the customer after being subjected to the air text process according to the customer’s demand.

The production processes examined while performing the Life cycle analysis of the polyester product are shown in Figure 6. Raw materials taken in the form of polyester chips are turned into ecru and dyed filaments according to the customer’s request in the continuous filament circle. The yarns that become ecru filaments are first packed and transferred to the warehouse. According to the operation plan, ecru filaments taken from the warehouse are dyed in the form of spaced dyeing and shipped to the customer, or they are subjected to friction processes and dyed as coils after folding and twisting processes and shipped to the customer. Yarns can be turned into filaments as ecru or colored filaments can be produced by the coloring process during filament production or can be shipped to the customer after being processed on folding and twisting machines; it can also be sent to the customer by fixing it.

• Step 2—Determine the functional unit (declared unit)

The study aims to calculate the CF for 1 t (1000 kg) of the products mentioned in the study.

• Step 3—Determining the system boundaries

Figure 5 and Figure 6 show the Life Cycle steps of the selected products. When the various phases of making PP and PES products are compared, it can be seen that the PES product requires two additional steps to produce than the PP product since the crystallizer and dryer stages are included in the process. Blue and orange boxes show processes that are included and excluded during the calculation, respectively. Some processes are limited and unreliable since data on the waiting times of raw materials and intermediate products until the next process, some by-products used during production (Raw materials that make up less than 1% of the product weight can be neglected), and intermediate transports between plants are limited and excluded. The life cycle steps of the products examined in this study are as follows:

• Raw material supply. Raw materials are transported by road and sea. The transportation details of this stage are shown in

  Table 2. The distance in the transport process of products.

  	Polyester Yarn	Polypropylene Yarn
  Sector	Distance (Ton Kilometers)	Distance (Ton Kilometers)
  Raw material supply
  Truck (16–32 t)	239,080.4	245,471.9
  Cargo ship (overseas)	2,930,470.9	2,085,516.8
  Product delivery
  Airplane	53,146	106,616
  Cargo ship (overseas)	1,132,656	1,399,509
  Truck (16–32 t)	3,838,941	1,167,905
  Van (<3.5 t)	-	219
  Total	8,194,294.30	5,005,237.70

  .
• Production process. According to the production cycle of the mentioned factory, the production stages of both products are completed.
• Packaging. Packaging is made using recyclable/nonrecyclable materials for the distribution of the produced products. In

  Table 3. The sum of ton-kilometers in packaging material supply of products.

  	Polyester Yarn	Polypropylene Yarn
  Sector	Sum of Ton Kilometers (per Land)	Sum of Ton Kilometers (per Land)
  Truck (16–32 t)	183	341
  Truck (7.5–16 t)	297,911	266,985
  Van (<3.5 t)	41,257	11,481
  Ton kilometers land total	339,351	278,806

  , the transportation details related to the supply of the materials used at this stage are shown.
• Transportation of final products. It is ensured that the final products are transported to Europe by cargo ships and to companies in Türkiye by using the road. The transportation details of this stage are shown in Table 2.
• Final stage. Disposal of products and packaging.
• Emissions arising from the service life and usage phase of the final products after delivery to the companies are ignored since they are uncontrollable.

• Step 4—Data collection

At this stage, the production, consumption, sales, and purchase information of Polyester Yarn and Polypropylene Yarn products produced by Ulusoy Textile Company for 2020 are used. The data is obtained as follows: raw material information from invoices and the LEO textile program; dyestuff information (dye + chemical) from the LEO textile program; consumables (stretch pallet, cardboard box); production quantity and shipping information from invoices and systematic program information. Since there are no meters in all areas related to energy consumption, this information is mostly calculated based on the installed power of the machines. Primary data is used primarily in the study.

The following annual data are collected from the company (reference year 2020):

• Amount of raw materials bought,
• Details about shipment during the raw material supply,
• Consumption of electricity and natural gas in the production process,
• Amount of Polyester Yarn and Polypropylene Yarn processed by the company,
• Amount of packing material bought,
• Details about shipment during the raw material supply,
• Details of the shipment of products to the buyer,
• Generation of solid wastes and wastewater.

2.2. Carbon Footprint Accounting

A common technique for determining direct and indirect carbon emissions throughout a product’s life cycle is CF analysis. This approach is crucial for accurately assessing the products’ greenhouse gas emission levels [36,37]. Two significant life cycle assessment-based methodologies are used in the emission calculation phase: “bottom-up” process analysis (PA) and “top-down” economic input-output analysis (EIO) [38]. This study used the LCA tool to compute and analyze the CF based on the actual manufacturing process of the product. The primary goal of this study is to conduct the cradle-to-customer plus waste LCA of manufacturing PES and PP yarns to evaluate the environmental impacts. It includes cradle-to-gate processes of the production chain of PP and PES yarns, from raw material extraction to gate-to-customer plus waste processes. The scope of the study comprised the manufacturing of synthetic yarns from petroleum products, propylene, and polyester as raw materials.

In this study, the production line of the selected products in the factory is examined in terms of sustainability, and LCA is made for the selected system boundaries. For this, a detailed process flow chart is created by determining the system boundaries first. Then, the carbon footprint calculation is made with the data obtained as a result of various measurements carried out on the production line and shared by the company. The CF and life cycle analysis of the process from the procurement of the raw materials used for the production of the yarns to the delivery of the produced yarns to the customer, making the next disposal stage, and greenhouse gas emissions were examined. In the production phase of the yarns, Grey electricity is used for Power consumption in the manufacturing process, while natural gas is used for Heat consumption in the manufacturing process. Diesel fuel is used as fuel during the procurement of raw materials, products, and materials used in the packaging stage. This study focuses on the analysis of two distinct types of yarn. The analysis reveals that variations in greenhouse gas emissions arise from the diverse range of raw materials used in these yarns, as well as the discrepancies in the production stages of each type.

The energy consumption amounts of the transportation process in the supply of raw materials and packaging materials of Polyester Yarn and Polypropylene Yarn are shown in Table 2 and Table 3, respectively. Further, energy consumption in the manufacturing process is shown in

Table 4. Energy consumption in the manufacturing process.

	Polyester Yarn		Polypropylene Yarn
Power Consumption
Energy source	Amount	Unit	Amount	Unit
Grey electricity	7,045,044.00	kWh	2,336,767.45	kWh
Heat Consumption
Energy source	Amount	Unit	Amount	Unit
Natural gas	62,542	m3	-	-

.

In the next step, greenhouse gas emissions related to the product are classified as shown in

Table 5. Distribution of carbon emission amounts of PES and PP yarns.

Emissions	Polyester Yarn	Polypropylene Yarn
Material acquisition and pre-processing	8.2	4.37
Raw materials	5.50	2.22
Packaging	2.51	2.07
Inbound logistics	0.19	0.09
Production	4.44	1.19
Electricity	4.30	1.19
Heating	0.14	-
Distribution and storage	0.11	0.21
Outbound logistics	0.11	0.21
Nonattribute	0.47	0.47
General emissions	0.47	0.47
End-of-life	0.18	0.18
End-of-life	0.18	0.18
Total (tCO2-eq) (tons)	13.40	6.42

. The emission amount of Dyed Polyester Yarn product from cradle-to-customer plus waste is calculated as 13.40 t CO₂-eq. In this calculation, the process from the supply of raw materials to the delivery of the product to the customer, even until the end of its useful life, is included. The percentage distribution of the CF resulting from the processes throughout the life cycle of the product is shown in Figure 7 and Table 5.

The emission amount of the Dyed Polypropylene Yarn product during its life cycle is 6.42 tons. The emission distribution over the life of the product is shown in Figure 8 and Table 5.

Examining the PES product’s production process reveals that, unlike the PP product, it has undergone two distinct stages. Due to the increased energy use, there are more carbon emissions as a result. Additionally, the PES product’s increased carbon emissions are a result of the higher fuel consumption during the supply of its raw components. To reduce greenhouse gas emissions at the product level, the company can make improvements in the transportation of raw materials and auxiliary materials. The diversity in the production stages of products directly affects greenhouse gas emissions. It can also benefit from renewable energy sources to reduce the amount of emissions in the production process. Recycling and reuse of textile products will ensure that the damage to nature is minimized during the life cycle of the product.

Polypropylene (PP) is a thermoplastic obtained by polymerizing the monomer propylene. It has a semi-crystalline structure with high molecular weight. It passes through the Extrusion, Measuring, Spinning, and Quenching stages. Due to its semi-crystalline structure, it is frequently used in the textile sector with this natural feature. While calculating the LCA of PP, we included the emission value at this stage in the calculation. As a result of the calculation of the information we received from the company, the pure carbon emission during the production phase of the raw material required for the production of 1 m² PP yarn was calculated as 2.5 kg.

In polyester (PES) chip production, PET plastic pellets are first melted, and long yarns are formed by passing through small holes called spinnerets. In the next stage, melt spinning, the spinnerets are cooled and turned into resin chips and transformed into the raw material we use. While calculating the LCA of PES, we included the emission value at this stage in the calculation. Again, in the calculation we made in line with the information we received from the company, the pure carbon emission during the production phase of the raw material required for the production of 1 m² polyester yarn was calculated as 6.4 kg.

2.3. Monte-Carlo Analysis

The Monte Carlo method is particularly valuable in dealing with uncertainty by randomly sampling the values of uncertain variables using probabilistic analysis. It is then combined with predetermined impact assessment methods to yield statistically significant results for environmental impact assessments. This approach more accurately reflects the influence of uncertain factors. Given the peculiarities of the Monte Carlo and Life Cycle Assessment (LCA) methods, these can be combined to form a powerful approach called Monte Carlo LCA.

There are many benefits of the Monte Carlo method in uncertainty analysis in LCA. Monte Carlo simulations consider the full range of uncertainty in input parameters, providing a more comprehensive view of potential outcomes. The method yields quantitative results, including probabilities of different outcomes, which can be crucial for decision-making and risk assessment. It can be applied to LCA models of varying complexity and can accommodate different types of probability distributions for input parameters. Monte Carlo simulations make it clear how uncertainty in input data propagates using the LCA model to affect the results. It allows for sensitivity analysis, where you can identify which input parameters have the most significant influence on the results. It is a valuable tool for addressing and quantifying uncertainty in LCA studies, ultimately improving the reliability assessments of the study.

The practical problem-solving process of the Monte Carlo method usually consists of two basic stages. First, it is important to generate random variables with certain probability distributions. This step is critical in capturing the uncertainties associated with the issue. Second, the numerical properties of the model are estimated using statistical methods, and numerical solutions are obtained for real-world problems [39]. The Monte Carlo Analysis method has been widely regarded as an efficient strategy for dealing with LCA (Life Cycle Assessment) uncertainties and has been used in many case studies, such as the LCA of an automotive front panel, the LCA of crop production, and the LCA of wave energy converter [40,41,42].

By integrating the Monte Carlo method into LCA, it is possible to effectively address the uncertainties found in LCA-based environmental impact assessments. This integration provides a more scientific and reasonable basis for decision-making processes. Monte Carlo uncertainty analysis generally consists of the following steps: determining the probability distributions of the input data, expressing the outputs as mathematical expressions (usually as a function) relative to the inputs, handling uncertainties using a large number of random samples, and establishing the confidence interval by determining the mean and standard deviation of the outputs. The equations for these steps are as follows:

$$\mu =\mu \left(p_1,p_2,\dots ,p_n\right)$$

(1)

$${\mu }_1=\mu \left(p_{1i},p_{2i}\dots ,p_{ni}\right)$$

(2)

$${\mu }^{\prime }=\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$M$}\right.{\sum }_{i=1}^M{\mu }_i$$

(3)

$${\sigma }^2=\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$\left(M-1\right)$}\right.{\sum }_{i=1}^M{\left({\mu }_1-{\mu }^{\prime }\right)}^2$$

(4)

where $\mu$ and $p$ are the arbitrary output parameter and input parameter, respectively. ${\mu }^{\prime }$ is the mean of the output parameter, and $\sigma$ is the standard deviation of the output parameter, which can be determined after the M sampling step. In this study, more than 1000 shipments were processed in the calculation step of uncertainty values. During the analysis of uncertainty values, the life cycle processes of the products were examined in three steps: first-point stage, mid-point stage, and end-point stage. As a result, the relevant iterations were analyzed to obtain the uncertainty values for PP and PES products. The uncertainty values for PP and PES are shown in

Table 6. First-point stage LCA results with uncertainty analysis via Monte Carlo analysis method.

	PP			PES
Processes	Mean	LCA	Rate (%)	Mean	LCA	Rate (%)
Material acquisition and pre-processing	8.20	8.01	2.34	4.37	4.23	3.23
Raw materials	5.50	5.41	1.71	2.22	2.16	2.81
Packaging	2.51	2.45	2.23	2.07	2.02	2.46
Inbound logistics	0.19	0.19	1.46	0.09	8.73	3.04
Production	4.44	4.36	1.85	1.19	1.15	3.36

,

Table 7. Mid-point stage LCA results with uncertainty analysis via Monte Carlo analysis method.

	PP			PES
Processes	Mean	LCA	Rate (%)	Mean	LCA	Rate (%)
Electricity	4.30	4.20	2.41	1.19	1.16	2.55
Heating	0.14	1.14	1.92	-	-	-
Distribution and storage	0.11	0.11	1.74	0.21	0.20	2.49

and

Table 8. End-point stage LCA results with uncertainty analysis via Monte Carlo analysis method.

	PP			PES
Processes	Mean	LCA	Rate (%)	Mean	LCA	Rate (%)
Outbound logistics	0.11	0.11	1.94	0.21	0.20	2.84
Nonattribute	0.47	0.46	1.72	0.47	0.45	3.29
General emissions	0.47	0,46	1.58	0.47	0.46	2.72
End-of-life	0.18	0.18	1.52	0.18	0.17	3.18

.

The uncertainty calculation is important as it determines the confidence level of the calculated greenhouse gas inventory. If the uncertainty is below 5%, the confidence level is “reasonable”, and if it is above 5%, the confidence level is “limited”. According to the uncertainty analysis calculations, the uncertainty value for both products is within a reasonable interval. When Table 6, Table 7 and Table 8 are examined, it is seen that the confidence interval for the PP product is more satisfactory.

3. Results and Discussion

The objective of this study is to compare the carbon emissions throughout the entire life cycles of the two primary products exported by Ulusoy Textile Company from the cradle to the grave. The system’s boundary is determined using a “cradle-to-customer plus waste” approach. During the calculation of the greenhouse gas emission amounts of the products, they are examined from different perspectives. These are the raw material procurement stages, the procurement stages of the materials used in the packaging stage, the production processes, the delivery of the product to the customer, and the service life of the product. In this study, two synthetic yarn types obtained from Polyester and Polypropylene materials are examined. Polyester is a nonbiodegradable material. The chemicals used during the production of this substance are harmful to the environment. Recycled polyester uses PES as a raw material, thus partially reducing the dependence on petroleum as a raw material. Polypropylene is a recyclable material, and there is no direct evidence of carcinogenicity from in vitro studies with plastics made from polypropylene.

Polypropylene and polyester yarn have many advantages compared to their usage areas and their structures. These advantages of polypropylene can be listed as being the lightest fiber, buoyancy in water, strong, flexible structure, resistance to rust, sunlight, odor, mold, sweat, decay and static probes, and high insulation. Polyester, besides having a thermoplastic feature, has high strength, nonshrink ability, quick drying, and resistance to wrinkles, abrasion, and shrinkage. Both raw materials have a place in the textile sector with their important advantages. However, among synthetic and plastic materials on the market, polypropylene is the most advantageous among synthetic polymers such as polyester and nylon in terms of recycling. This advantage is that the mechanical properties of the yarn are not affected by changes in relative humidity, thanks to the hydrophobic properties of polypropylene. Furthermore, polypropylene yarn is processed in two different machines in the production scheme, while polyester yarn is processed in four different machines. While less energy and resources are used in the production of polypropylene yarn, both more energy and more resources are used in the production of polyester yarn. Energy consumption in the transport process, packaging material supply, and manufacturing process are shown in Table 2, Table 3 and Table 4, respectively. As can be seen in the three tables, the energy consumption of the PES product is higher in these processes. In addition, when the values of the energy consumed in the manufacturing process in Table 4 are examined, it is seen that there is three times more energy consumption for the production of the PES. Considering the CO₂ emission amounts obtained using the life cycle analysis methodology, the analysis results for PP and PES products were calculated as 13.40 t CO₂-eq (t PES)-1 and 6.42 t CO₂-eq (t PP)-1, respectively, as seen in Table 5. In Figure 7 and Figure 8, the proportional distribution of the required emission amounts over the lifetime of the yarn products is shown. With these figures, the numerical results shown are visualized, and the obtained results are understood. The existing body of literature lacks carbon footprint calculations specifically for polyester and polypropylene materials used in various applications, such as textiles or packaging. In this study, it is conducted that a groundbreaking analysis that applies the Monte Carlo method to assess the uncertainties associated with carbon footprint calculations for polyester and polypropylene. Unlike previous studies that may have relied on static or less accurate data, it has been used that real-time and up-to-date information to enhance the accuracy of our assessment. The outcomes of our uncertainty analysis, executed using the Monte Carlo method, hold significant importance. Obtaining data from the Monte Carlo method helps us gauge the confidence level we can place in the accuracy of our calculated greenhouse gas inventory. In essence, they allow us to understand how certain or uncertain our carbon footprint estimates are. If the uncertainty results are less than 5% as a percentage, it is considered that the confidence level is “reasonable”. However, if the uncertainty exceeds 5%, it is regarded that the confidence level is “limited”. Based on our meticulous uncertainty analysis calculations in this study, it is found that the uncertainty values for both polyester and polypropylene fall within the “reasonable” range, meaning that we can reasonably rely on the accuracy of our calculated carbon footprints for these materials. Upon closer examination of Table 6, Table 7 and Table 8 in our research, it becomes evident that the confidence interval for the polypropylene product is notably more satisfactory when compared to the confidence interval for other materials or factors. This indicates a higher level of confidence in the accuracy of our polypropylene carbon footprint calculations. The uncertainty values of the PP product are better than those of the PES product. According to these results, it is seen that polypropylene yarn is a more environmentally friendly product. For this reason, polypropylene should be preferred instead of polyester in fancy yarn production and other suitable sectors.

The insights gained from this study highlight that by enhancing the way products are designed and minimizing the use of specific materials in the design phase, we can effectively lower emissions. Moreover, regional raw material and packaging supply is one of the important steps to be taken in this direction. In addition, the results obtained in this study will guide the companies that produce the relevant products to make arrangements on the type/amount of energy in the production stages. The findings of the study can be used in the development of better government policies on reducing greenhouse gas emissions and in making some regulations on the management of synthetic yarn production in Türkiye. Finally, the results of this study point to new directions for future research.

4. Conclusions

Here, the steps of the “cradle to customer plus waste” process of two different yarn products, PES and PP, have been examined with the LCA methodology. This study aims to use life cycle analysis to determine the environmental effects of all stages in the process, from raw materials to the use and disposal of products. Additionally, determining the more environmentally friendly product in line with these results is to create awareness in line with these results.

According to the analysis results, it is seen that the CF of polyester (PES) and polypropylene (PP) is calculated as 13.40 t CO₂-eq (t PES)-1 and 6.42 t CO₂-eq (t PP)-1, respectively. According to the findings, when the energy consumption and raw material stages of the production stages of PES and PP products are compared, it is concluded that the CF of PP yarn is lower and thus more environmentally friendly. In addition to the numerical results obtained, considering that PP yarn is the most advantageous among synthetic polymers in terms of recycling and the mechanical properties of PP yarn are not affected by relative humidity, it is recommended to prefer this product over other synthetic yarns. Further, by examining the results obtained from the study, arrangements regarding the type/amount of energy consumed in the processes can be carried out. These results can be used to improve the Turkish government’s policies to reduce greenhouse gas emissions and control synthetic yarn production.