Unit 2 Lecture 12 Topic 2 Flashcards
Elastomeric Fibres:
A material which at room temperature can be stretched repeatedly to at least twice its original length, and upon immediate release of the stretch, will return with force to approximate original length. Rubber and spandex are elastomeric.
Spandex:
A long chain synthetic polymer composed of at least 85% by mass of a segmented polyurethane. Also known as elastane, spandex was the first manufactured elastomeric fibre introduced in 1958 as Lycra®. It is more durable than natural rubber, spandex or elastane are the generic names, whereas, Lycra® is a trademark.
What is the structure of Spandex?
Spandex is a block co-polymer with rigid aromatic segments connected by urethane linkages to polyester or polyether. The polyurethane segments are highly crystalline and rigid, meanwhile the polyester or polyether segments are amorphous and randomly coiled.
How do the coils within the structure of spandex work?
When stretched coils straighten there is high elongation. When released coils return to their original position, this is elastic recovery. Rigid urethane segments form highly-hydrogen bonded crystalline areas which prevents polymers from sliding past each other and permanently deforming when stretched.
How is spandex used with other fibres?
Filament spandex yarn may be woven or knitted into fabrics with other yarns (eg, top of sock or waistband). Filament yarn of another fibre type could be wound around a spandex core (eg, swimwear). The core is spun with staple fibres.
How strong is spandex?
Spandex has low strength compared to non-elastic fibres (but stronger than rubber).
What is the elongation and elastic recovery like in spandex?
Spandex has excellent elongation and elastic recovery which makes up for its low strength. Spandex can elongate 400-700% without breaking. Soft segments straighten when stretched and return to relaxed position once released, hard urethane segments keep polymers from slipping.
What is the durability of spandex?
Chemical resistance is good in general. Spandex will not degrade due to contact with body oils, perspiration, and body lotions as rubber does. Spandex can degrade and yellow with chlorine in high concentrations. Polyether based spandex is better than polyester based for these conditions.
What is the modulus and water attraction of spandex like?
Spandex has a very low modulus so it can bend and stretch easily. It is made of hydrophobic fibres so its alternative fibres are important in influencing moisture absorption.
What is the resiliency and dimensional stability of spandex like?
Spandex has excellent resiliency and dimensional stability so it can be made into form fitting garments and maintains shape during use and care.
What can be an issue with the appearance of spandex?
Fibres can pull away from the seams and protrude above fabric surface. This is less related to the fibre but more a problem with the fabric. This effect of “grinning” can be controlled by dyeing spandex the same colour as the end product.
