Study Unit 9: Manufactured non-cellulosic: acrylic Flashcards
History
DuPont developed an acrylic fibre in 1944 and commercial production of this fibre, called Orlon®, started in 1950. Other companies soon followed suit and manufactured acrylic fibres such as Acrilan®, Creslan®, Courtelle®, Dralon® and Crylor®. Most articles bought locally are simply labelled “acrylic”.
Fibre production
Acrylic is a manufactured polymer in which the fibre-forming substance is any long-chain synthetic polymer composed of at least 85% by weight of acrylonitrile units. Acrylic is made by addition polymerisation of acrylonitrile (and not condensation polymerisation as in the case of nylon and polyester).
After polymerisation, the acrylonitrile is dissolved in dimethyl formamide. Both wet and dry spinning methods are now used for acrylic fibres.
A number of acrylic fibres are manufactured as bicomponent filaments.
These form a fibre that is mushroom-shaped in cross-section (See figure 3.1). Each component has different properties. One component may shrink less or curl and give a spiral crimp to the fibre
when dry.
The other may absorb more moisture and therefore dye a deeper colour, giving an interesting variation in colour to the final yarn.
Fibre properties
Acrylic fibres are soft and warm. They are produced primarily as staple fibre and then spun into wool-like knitting yarns or fabrics. Most of the jerseys that we buy today are made from acrylic yarns. Acrylic yarns have many advantages over wool. They are cheaper, do not shrink and are therefore easier to wash. They are also non-allergic so many people are less likely to develop a rash from wearing acrylic than from wearing wool, to name but a few.
Physical structure
As with most other manufactured fibres, the length and diameter of acrylic can be controlled. It is generally used as a staple fibre. A wide range of cross-sections are produced. The fibre surface has mini-striations and indentations. The fibres are usually textured after extrusion. Many types of acrylic are manufactured, including heat stabilised, light stabilised, pigmented, acid dyeable, solution dyed, bicomponent and fibrillated acrylics.
Properties relating to durability
1. Abrasion resistance
Abrasion resistance is moderate and slightly better than for wool. Pills will form on some acrylic fabrics, although this is less of a problem than for polyester fabrics.
- Strength
Acrylic fibres are not very strong; they are slightly weaker than cotton fibres. However, their tenacity (23–29 cN/tex) is adequate for their end use. They are stronger than wool. Acrylic fibres are slightly weaker when wet (2 –27 cN/tex).
- Flexibility
Acrylic is a fairly flexible fibre, but not as flexible as wool.
- Elongation
Acrylic has an elongation at break of 20%, slightly lower than wool’s.
Properties relating to comfort
1. Moisture absorption
Acrylic has low moisture absorption (1.2–2.0% moisture regain). This contributes to problems involved in dyeing and printing, as well as the build up of static electricity. Wicking is better than expected for a non-cellulosic fibre because of the surface contour of the fibres.
- Heat conductivity
Acrylic fibres are poor conductors of heat and therefore warm to wear.
Properties relating to appearance retention
1. Resiliency
Acrylic fibres have good resiliency and resist wrinkling. They can be textured. These crimped staple fibres are spun into thick, soft spongy yarns called high-bulk yarns, which combine warmth with light weight.
- Dimensional stability
With proper pre-treatment and care during washing, acrylic fabrics are dimensionally stable. Excessive heat and steam can cause acrylic fibres to shrink. The crimp developed during manufacture may disappear over time, causing the product to lose shape. An acrylic jersey that has been washed at a temperature of 40 oC or more ends up looking like an oversized garment. Acrylic fibres cannot be heat-set like polyester or nylon because acrylic does not melt, but decomposes and discolours when heated.
- Elasticity
Most acrylic fibres have excellent elastic recovery (92% at 3% stretch). Elasticity is lower in modacrylic fibres.
Properties relating to care
1. Effect of alkalis
Concentrated alkalis cause a loss of strength
- Effect of acids
Concentrated acids cause a loss of strength.
