Synthetic polymers

Story about synthetic polymers

Synthetic fibres transformed the textile industry by making it possible to produce yarns with properties that natural fibres alone could not offer. Their story begins with polymers: long chains of repeating molecular units that form the basis of materials such as polyester, nylon and acrylic.

Although natural fibres like wool and cotton are made of polymers too, synthetic polymers are manufactured through chemical processes, usually using raw materials derived from petroleum or natural gas. By controlling their molecular structure, scientists can develop fibres with specific characteristics, including strength, elasticity, softness, durability and resistance to moisture.

The development of synthetic fibres accelerated during the twentieth century. Nylon was introduced commercially in the late 1930s, followed by the rapid expansion of polyester and acrylic fibres during the 1940s and 1950s. These materials offered an alternative to natural fibres, often at a lower cost and with more consistent properties.

In knitting, synthetic yarns opened up new possibilities. They can provide excellent abrasion resistance, dimensional stability, vibrant colours and easy-care properties. Depending on their composition and construction, they can also be engineered for stretch, lightweight fabrics or technical applications.

However, synthetic fibres also present challenges. Most conventional varieties are derived from fossil resources, are not readily biodegradable and can release microplastic fibres during washing and use. Their environmental impact depends on factors such as production methods, garment lifespan, recycling and disposal.

Today, research is exploring recycled polymers, bio-based raw materials and improved fibre-recycling technologies. Synthetic yarns remain an important part of modern knitting, balancing performance, cost and versatility with the growing need for more responsible material choices.

Polyester: The Versatile Workhorse of Knitting Yarns

Polyester is one of the most widely used synthetic fibres in the textile industry. Its popularity comes from a combination of strength, durability, dimensional stability and relatively low production cost.

Most textile polyester is made from polyethylene terephthalate (PET), the same type of polymer used in many plastic bottles. The polymer is melted, extruded through tiny openings called spinnerets and cooled to form continuous filaments. These filaments can be used directly or cut into shorter staple fibres, which are then spun into yarn.

For knitting, polyester offers several useful characteristics. It resists abrasion, dries relatively quickly and generally retains its shape well. It also absorbs little moisture, which can help knitted garments dry faster, although it may reduce comfort in some situations by limiting moisture absorption into the fibre itself.

Polyester yarns can be produced in many forms, from fine, smooth filaments to textured or bulky yarns. Their properties can be modified through spinning, texturing, blending and heat-setting. Polyester is commonly used in sportswear, fleece, upholstery, socks and everyday knitwear. It is also blended with cotton, wool or other fibres to combine their respective advantages.

One important consideration is heat. Polyester is thermoplastic, meaning it softens when heated and can be permanently shaped under suitable conditions. This property makes heat-setting useful in textile manufacturing, but excessive heat can damage fibres or alter the fabric's dimensions.

Conventional polyester is usually derived from fossil fuels, and its low moisture absorption and resistance to biodegradation can create environmental challenges. Recycled polyester, often made from PET bottles or textile waste, can reduce reliance on virgin raw materials, although textile-to-textile recycling remains technically challenging.

For knitters, polyester is a versatile choice when durability, quick drying and shape retention are priorities. The final result, however, depends not only on the fibre itself but also on yarn construction, twist, thickness, stitch structure and finishing.

Nylon: Strength, Elasticity and Performance in Knitting

Nylon was the first fully synthetic fibre to achieve widespread commercial success. Developed by researchers at DuPont in the 1930s, it was introduced commercially in 1939 and became famous for its use in stockings. It soon found applications far beyond hosiery, including parachutes, ropes, industrial textiles and knitted sportswear.

Nylon belongs to a family of polymers called polyamides. The most common textile types include nylon 6 and nylon 6,6, which differ in their chemical structures and manufacturing processes. These differences influence properties such as melting temperature, strength and processing behaviour.

In knitting, nylon is valued for its excellent tensile strength, abrasion resistance and flexibility. It can withstand repeated friction, making it especially useful in socks, sportswear, swimwear, activewear and technical knitted fabrics. Its resilience also helps fabrics tolerate repeated deformation.

Nylon fibres can be manufactured as continuous filaments or as staple fibres. Fine filaments can produce smooth, lightweight yarns, while textured filaments create bulk and a softer hand. Nylon is also frequently blended with wool to improve the durability of socks, or combined with elastane to produce stretch fabrics.

Despite its advantages, nylon has some limitations. It absorbs more moisture than polyester, although it is still generally considered a relatively low-moisture-absorption fibre. It can also be sensitive to heat, and its properties vary according to the nylon type and yarn construction. In knitted fabrics, these factors influence drying time, dimensional stability and finishing requirements.

Like conventional polyester, most nylon is produced from fossil-based raw materials. Its manufacture can be energy-intensive, and discarded nylon is not readily biodegradable. Recycled nylon, including materials recovered from industrial waste and discarded fishing nets, offers one route towards reducing demand for virgin resources.

For machine knitting, nylon can be particularly useful where a yarn needs to withstand friction, repeated movement or demanding wear conditions. It is worth remembering that nylon itself is not inherently elastic in the same way as elastane: its flexibility and recovery depend on the fibre, yarn structure and knitted construction.

Acrylic: A Wool-Like Alternative for Knitting

Acrylic fibres were developed as an alternative to wool, offering warmth, softness and a relatively low-cost option for producing knitted textiles. Commercial acrylic fibres became available in the mid-twentieth century and quickly gained popularity in knitwear, blankets and home textiles.

Textile acrylic is produced from polymers based primarily on acrylonitrile. Under widely used textile classifications, a fibre is generally called acrylic when it contains at least 85% acrylonitrile units; related fibres with lower proportions are often classified as modacrylics. The polymer is dissolved in a suitable solvent and spun into fibres, which are then processed into staple fibres or other yarn forms.

One of acrylic's main advantages is its ability to imitate some of the qualities of wool. Acrylic yarns can feel soft, provide good thermal insulation and be manufactured in a wide range of colours. They are often lightweight, resist moth damage and are relatively easy to care for. These qualities make them popular for sweaters, scarves, hats, blankets and decorative knitted products.

Acrylic is usually supplied as staple fibre yarn rather than as a smooth continuous filament. The fibres can be crimped or processed to create bulk, loft and a wool-like handle. Different spinning techniques and yarn constructions produce anything from smooth, compact yarns to fluffy, brushed varieties.

However, acrylic does not behave exactly like wool. It generally absorbs less moisture, may develop static electricity and can pill with wear. It is also thermoplastic, so excessive heat during ironing, steaming or washing can cause deformation or damage. Careful temperature control is particularly important during knitting-related finishing processes.

From an environmental perspective, conventional acrylic is typically derived from fossil resources and is not readily biodegradable. Acrylic garments can release microplastic fibres during washing, and recycling is challenging because many garments contain blends, dyes and finishing treatments.

For knitters, acrylic is a practical option when affordability, colour variety, warmth and ease of care are important. It can be especially suitable for decorative pieces and everyday knitwear, although its behaviour under heat and its tendency to pill should be considered when selecting a yarn for a specific project.

At a glance: Comparing the three fibres

For machine knitting on a Kniterate, fibre composition is only one part of yarn selection. Yarn count, ply, twist and surface finish all influence how smoothly the yarn feeds through the feeders and how reliably the machine forms stitches. Kniterate generally works best with yarns in the Nm 6–8 range, although suitability depends on the yarn construction and the fabric being produced. For example, a plied yarn can behave differently from a single yarn of the same count, while hairy or uneven yarns may affect stitch formation. When choosing a synthetic yarn, consider not only its thickness but also its elasticity, friction and ability to withstand the mechanical action of knitting. Testing a small swatch before starting a larger project is the best way to check stitch formation, fabric quality and overall machine performance.