Sustainable Textile and Fashion Value Chains by Unknown

Author:Unknown
Language: eng
Format: epub
ISBN: 9783030220181
Publisher: Springer International Publishing

12.7.2 Polyamide: Existing Examples

Polyamides (PAs) are widely used in many engineering applications due to their very interesting mechanical properties and ease of processing, as they allow the injection of thick components with complex geometries (Naveau et al. 2011). As reported in the literature, PA6 is an important engineering material which exhibits excellent mechanical properties, chemical resistance, wear resistance, dimensional stability, low friction, etc. (Laredo et al. 2003). For these reasons, it is one of the most often used engineering fibres, due to its good mechanical (strength, hardness, toughness, damping) and tribological (sliding, wearing resistance) properties (Kohan 1995). Hence, it has found various applications in industrial and domestic sectors, such as transport, aviation, sealing, and coating.

PA6 fibres are tough, possessing high tensile strength, as well as elasticity and lustre. These are wrinkle proof and highly resistant to abrasion and chemicals such as acids and alkalis. The fibres can absorb up to 2.4% of water, although this lowers tensile strength.

Reusing and recycling PA6 from waste can be achieved in different ways, including: (i) depolymerization of PA6 chains into their monomers or oligomers (Moran 1994; Sifniades et al. 1997), (ii) extraction and separation of polymeric components without significant degradation (Subramanian 1995; Stefandl 1998), and (iii) melt compounding of the waste stream with additives and modifiers (Kotlair and Fountain 1997; Young et al. 1999).

Unfortunately, the same properties that make it so useful in products are also causing large environmental consequences. In fact, nylon does not break down easily and accounts for about 10% of the debris in the ocean. According to the World Society for the Protection of Animals, more than 600,000 tons of fishing gear is dumped into oceans every year, including nylon nets. Fishermen often discard the nets because the alternative is paying someone to dispose of them properly.

Nylon is not just found in fishing nets. It is also in clothing, carpets, and packaging. It was first introduced at the New York World’s Fair in 1939 in the form of women’s tights, but the fibre really took off after Second World War. Before 1945, fibres like cotton and wool dominated the apparel market; however, post-war synthetic fibres like nylon had risen to around 25% of the market share due to applications in military supplies such as parachutes, ropes, tents, and uniforms.

Contamination is another concern. Unlike metals and glass, which are melted at high temperatures, nylon is melted at lower temperatures, meaning some contaminants—non-recyclable materials and microbes or bacteria—can survive. Therefore, all nylon waste must be cleaned thoroughly before the recycling process.

When looking at industrial solutions to recycle effectively this synthetic fibre, one company name stands clearly and at large distance: Aquafil, already leading manufacturer of Nylon, and its ECONYL® product. In 2007, they began developing a machine that can churn through most kinds of nylons, producing new threads ready to be repurposed. The commissioning of ECONYL® back in 2012 marked the activation of a ‘closed cycle’ that recovers products made from polyamide-6, which have reached the end of their life and can

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