Publicação
The influence of particle size on mechanical and thermal properties of 100% recycled EVA composites
| Resumo: | The footwear industry is one of the most relevant sectors of the global industry. More than 23 billion pairs of shoes are produced annually, which represents a footwear consumption of 2.7 kg per person annually in Europe. Many materials used in the manufacture of shoes, such as EVA (ethylene vinyl acetate), plastics, leather, and rubber, are non-biodegradable and can take between 40 and 1000 years to decompose These materials release toxic substances, greatly contributing to environmental pollution and public health risks. Therefore, exploring solutions to prevent landfilling and promoting footwear waste recycling is essential to encourage sustainability and the transition from a linear to a circular economy in this sector. Despite being composed of over 40 distinct components, shoes can be divided into 3 main parts (small items, upper and lower parts). EVA, a suitable material for producing soles and insoles (lower parts) accounts for approximately 14% of a typical shoe. Its lightweight, flexible, and shock-absorbing properties make EVA an essential material in the footwear sector, nonetheless, its extensive use poses recycling issues. Current approaches to improve the mechanical recycling potential of footwear waste include its fragmentation below 6 mm, through processes such as crushing or granulation, which enhance the separation and recovery of mono-materials. This approach not only minimizes particle interconnection but also enables effective separation of EVA from other components, thus improving its potential for recycling into value-added products. This study investigates the influence of particle size on the properties of 100% recycled EVA composites. The EVA waste used in this work is post-industrial, originating from sole cuttings and defective soles. After collection, this EVA waste was ground into four different particle sizes (0.5, 1, 2, and 4 mm) to produce composites through compression molding. To ensure comparison, all composites were made under equal experimental conditions (temperature, pressure, and time) without any binder or matrix. In this study, the samples were analyzed using scanning electron microscopy and energy-dispersive spectroscopy (SEM/EDS) to understand the effects on composite pore size, and the thermal and mechanical properties were investigated to understand the effects of particle size on tensile strength, elongation, air permeability, thermal conductivity, and thermal resistance. The results indicate that decreasing EVA particle size enhances thermal conductivity, tensile strength, and elongation. Thus the composites composed of smaller particles are more suitable for applications requiring high mechanical performance. Conversely, composites produced with larger particles show an enhancement in air permeability and thermal resistance, contributing to improved thermal insulation characteristics. In conclusion, this study demonstrates that particle size affects the properties of recycled EVA composites. Therefore, during the production of 100% recycled EVA composites, the particle size must be determined based on the field of application of the composites. |
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| Autores principais: | Guimarães, Renato Filipe Costa Rodrigues |
| Outros Autores: | Alves, Diana Isabel Sousa; Fangueiro, Raúl; Ferreira, Diana P. |
| Assunto: | Particle Size Recycled EVA Composites Footwear Waste Circular Economy Recycling |
| Ano: | 2025 |
| País: | Portugal |
| Tipo de documento: | outro |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade do Minho |
| Idioma: | inglês |
| Origem: | RepositóriUM - Universidade do Minho |
| Resumo: | The footwear industry is one of the most relevant sectors of the global industry. More than 23 billion pairs of shoes are produced annually, which represents a footwear consumption of 2.7 kg per person annually in Europe. Many materials used in the manufacture of shoes, such as EVA (ethylene vinyl acetate), plastics, leather, and rubber, are non-biodegradable and can take between 40 and 1000 years to decompose These materials release toxic substances, greatly contributing to environmental pollution and public health risks. Therefore, exploring solutions to prevent landfilling and promoting footwear waste recycling is essential to encourage sustainability and the transition from a linear to a circular economy in this sector. Despite being composed of over 40 distinct components, shoes can be divided into 3 main parts (small items, upper and lower parts). EVA, a suitable material for producing soles and insoles (lower parts) accounts for approximately 14% of a typical shoe. Its lightweight, flexible, and shock-absorbing properties make EVA an essential material in the footwear sector, nonetheless, its extensive use poses recycling issues. Current approaches to improve the mechanical recycling potential of footwear waste include its fragmentation below 6 mm, through processes such as crushing or granulation, which enhance the separation and recovery of mono-materials. This approach not only minimizes particle interconnection but also enables effective separation of EVA from other components, thus improving its potential for recycling into value-added products. This study investigates the influence of particle size on the properties of 100% recycled EVA composites. The EVA waste used in this work is post-industrial, originating from sole cuttings and defective soles. After collection, this EVA waste was ground into four different particle sizes (0.5, 1, 2, and 4 mm) to produce composites through compression molding. To ensure comparison, all composites were made under equal experimental conditions (temperature, pressure, and time) without any binder or matrix. In this study, the samples were analyzed using scanning electron microscopy and energy-dispersive spectroscopy (SEM/EDS) to understand the effects on composite pore size, and the thermal and mechanical properties were investigated to understand the effects of particle size on tensile strength, elongation, air permeability, thermal conductivity, and thermal resistance. The results indicate that decreasing EVA particle size enhances thermal conductivity, tensile strength, and elongation. Thus the composites composed of smaller particles are more suitable for applications requiring high mechanical performance. Conversely, composites produced with larger particles show an enhancement in air permeability and thermal resistance, contributing to improved thermal insulation characteristics. In conclusion, this study demonstrates that particle size affects the properties of recycled EVA composites. Therefore, during the production of 100% recycled EVA composites, the particle size must be determined based on the field of application of the composites. |
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