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Introduction<\/h3>\n\n\n\n
The ever-increasing amount of waste produced globally, largely driven by urbanization and changing consumer lifestyles, poses a significant environmental challenge. A substantial portion of this waste consists of plastic, which is predominantly disposed of in landfills or released into the marine environment, resulting in widespread environmental pollution and the persistence of small plastic particles in ecosystems. Over the past two decades, global plastic waste recycling has shown notable growth, driven primarily by organisation for economic co-operation and development-countries (OECD) in the European Union, as well as by India and China. By 2019, these regions had achieved recycling rates of 12\u201313%1<\/a><\/sup>. In contrast, non-OECD Asian countries and Latin America have experienced slower progress. The United States and the Middle East & North Africa region have made minimal advancements, with the US reaching only a 4.5% recycling rate by 2019, according to OECD data1<\/a><\/sup>. <\/p>\n\n\n\n Promoting the recycling of polypropylene (PP) and other polymeric materials is crucial to mitigate the impact on the environment and reduce the depletion of natural resources. Given the significant volume of plastic waste generated annually, it is critical to differentiate between the two primary sources: post-industrial and post-consumer plastic waste. Post-industrial plastic waste primarily originates from industrial processes, such as production scrap or off-cuts from manufacturing, and is typically of higher and more consistent quality. In contrast, post-consumer plastic waste is derived from discarded consumer products, such as packaging materials, electronic devices, and household items. Due to its varied composition, exposure to environmental conditions, and the presence of contaminants like food residues or mixed polymer types, post-consumer waste presents greater challenges for recycling into high-quality materials. Nonetheless, post-consumer plastic waste represents the largest proportion of plastic waste globally2<\/a><\/sup>, making its effective utilization crucial for achieving sustainability goals3<\/a><\/sup>and advancing a circular economy. <\/p>\n\n\n\n Extensive research and literature have been dedicated to the three primary plastic recycling technologies: mechanical recycling4<\/a>,5<\/a>,6<\/a><\/sup>, chemical recycling7<\/a>,8<\/a>,9<\/a><\/sup> and energy recycling10<\/a>,11<\/a>,12<\/a><\/sup>. Recycling and reusing plastic waste are more sustainable approaches than landfilling or incineration, but they are hindered by the presence of various contaminants, especially in the packaging industry. Pre-treatment techniques like purification by washing13<\/a><\/sup>, dehalogenation14<\/a><\/sup> or plastic waste separation technologies15<\/a>,16<\/a><\/sup> are emerging as viable solutions to improve the quality of recycled plastics. Some innovative recycling applications include using plastic waste in the construction industry for materials such as paving blocks17<\/a><\/sup>, ceramics18<\/a><\/sup>, and as feedstock for various industrial processes. To address the growing volume of plastic waste, it is essential to consider not only the industrial applications but also the diverse sources of post-consumer plastic waste generated by households and everyday consumer activities. Post-consumer plastic waste encompasses a broad spectrum of products, ranging from single-use packaging to durable household items, which require tailored recycling solutions to manage effectively. Due to the inherently short lifespan of many plastic products, considerable quantities of such waste are generated every year. The average lifespan of plastic products is approximately ten years, though this varies greatly by the application. <\/p>\n\n\n\n While plastic applications used in the industrial machinery and construction sectors can remain in use for decades, those used for packaging are typically in use for less than one year19<\/a><\/sup>. Plastic packaging applications are often used just once before they are disposed of, which is one of the reasons why plastic packaging is the main source of plastic waste worldwide. Despite the considerable volume of post-consumer food packaging waste, effective recycling strategies for these materials remain largely undeveloped20<\/a><\/sup>. <\/p>\n\n\n\n Currently, there is no established approach within the textile industry to repurpose post-consumer food packaging into textile products. However, recent initiatives indicate the potential for progress. For instance, some studies have shown that composite materials, incorporating post-consumer polypropylene and cotton, can be processed into staple fibers21<\/a><\/sup>. By refining the melt spinning process, companies like IGF Asota<\/em>22<\/a><\/sup> have been able to produce melt spun PP yarns with a post-industrial PP content, demonstrating the feasibility of integrating recycled polymers into high-quality fibers. Studies have explored various reinforcement methods and compatibilization strategies to address the inherent limitations of recycled polymers. For example, incorporating short hemp fibers (SHFs) into rPP has demonstrated enhanced stiffness and improved fiber-matrix interaction when compatibilizing agents like maleic anhydride grafted polypropylene (PP-g-MA) are used23<\/a><\/sup>. <\/p>\n\n\n\n Furthermore, recent work on rPP fibers for concrete reinforcement demonstrated that optimized processing conditions can yield rPP fibers with sufficient strength and durability for structural applications, providing an environmentally friendly alternative to virgin polypropylene\u200b24<\/a>,25<\/a><\/sup>. Other studies have focused on integrating natural fibers such as bamboo into rPP matrices, which revealed that chemical treatment of bamboo fibers can significantly improve the composite\u2019s compatibility and mechanical performance26<\/a><\/sup>. Recent studies have explored the potential of recycled polypropylene in various manufacturing processes. For instance, Fused Deposition Modelling (FDM) has been used to process rPP\/aluminum powder composites, demonstrating improved mechanical properties and sustainability27<\/a><\/sup>. <\/p>\n\n\n\n The utilisation of post-consumer plastics in high-performance applications is constrained by their heterogeneous composition, contamination, and degradation, thus rendering post-industrial waste the preferred alternative. Previous studies have demonstrated that the addition of fibres or compatibilisers can enhance rPP composites; however, research on directly melt-spinning post-consumer rPP into high-performance yarns remains limited. The present study endeavors to develop optimized processing techniques to enhance the quality and mechanical performance of post-consumer recycled rPP for textile applications. By systematically analyzing the influence of key melt-spinning parameters – such as draw-down speed, draw ratio, and drawing temperature – on the mechanical properties of rPP multifilament yarns, the research provides a comprehensive framework for improving yarn quality. The optimization of these critical parameters is expected to ensure the competitiveness of rPP yarns with virgin polymer-based alternatives and facilitate their adoption in high-value textile sectors. This approach is expected to support the broader industrial use of rPP and contribute to the development of a more sustainable and circular economy.<\/p>\n\n\n\n For this study, two distinct types (Systalen\u00ae<\/sup> 32.9002 and Systalen\u00ae<\/sup> 32.0999) of recycled polypropylene (rPP) were sourced from post-consumer packaging waste, provided by Der Gr\u00fcne Punkt Holding GmbH & Co. KG, K\u00f6ln\/Germany. These rPP materials were derived from the \u201cGelber Sack\u201d collection system in Germany, which is designed for the sorting and recycling of plastic waste from households. The selected rPP types have been processed using a specialized treatment method that integrates advanced technologies to enhance the quality of the recycled material. This process involves precise color sorting of plastic flakes to improve aesthetic consistency, optimized washing procedures to ensure the removal of impurities, and an advanced odor elimination system to reduce any residual odors commonly associated with recycled plastics. These enhanced methods aim to improve the performance and applicability of rPP for high-quality applications, making them suitable for further investigation in polymer processing and melt spinning.<\/p>\n\n\n\n Thermal analyses were performed using thermogravimetric analysis (TGA, Q500, TA Instruments, New Castle, DE, USA) and differential scanning calorimetry (DSC, Q2000, TA Instruments, New Castle, DE, USA). The thermal decomposition of the materials prior to melt spinning was evaluated in the temperature range of 30 \u00b0C to 800 \u00b0C under an air atmosphere, with a heating rate of 40 K\/min. In addition, the heat flow of all materials was measured from 30 \u00b0C to 400 \u00b0C under a nitrogen atmosphere, employing a modulated heating rate of 5 K\/min. The use of the second heating cycle in DSC ensured that the material was fully relaxed, eliminating any prior thermal history, such as residual stress or crystallization behavior from previous processing. The rheological properties were assessed with an extrusion plastometer (MFLOW, ZwickRoell, Ulm, Germany) in accordance with ISO-1133. Mechanical properties of the multifilaments were determined by tensile testing on a Zwick2.5 testing machine (ZwickRoell, Ulm, Germany), using a gauge length of 125 mm and a testing speed of 125 mm\/min. The rPP multifilament yarns were spun on a modular melt spinning system from Dienes Apparatebau GmbH, M\u00fchlheim am Main, Germany. This system consists of a ZSE-MAXX18 twin-screw extruder (Leistritz Extrusionstechnik, Nuremberg, Germany), two melt pumps (Maag Germany GmbH, Grossostheim, Deutschland) with a pump capacity of 2.642 cm\u00b3 and a spinning package (40 filaments, L\/D\u2009=\u20093, d\u2009=\u20090.3 mm) manufactured by Sossna GmbH, Dorsten, Germany. The yarn runs over 5 godet draw duos (DD) and is wound with a Sahm 3200 (Georg Sahm GmbH & Co. KG, Eschwege, Germany) winder.<\/p>\n\n\n\nExperimental section<\/h3>\n\n\n\n
Materials<\/h3>\n\n\n\n
Measuring, test and machine equipment<\/h3>\n\n\n\n
Process parameters<\/h3>\n\n\n\n