Introduction
Acrylic fibre is a synthetic polymer fiber composed of at least 85% by mass of acrylonitrile units (CH2=CH-CN). Developed to offer a low-cost, durable alternative to natural wool, it is widely used in apparel and home furnishings due to its warm, soft, and lightweight characteristics.
Preparation (Manufacturing Process)
Acrylic fiber production is a complex process starting from petrochemical raw materials. The key stages are polymerization and spinning.
1. Raw Materials:
- The main monomer is Acrylonitrile, derived from fossil fuels (petroleum/coal-based chemicals).
- Comonomers (like methyl acrylate or vinyl acetate) are added to improve dyeability, softness, and processing.
2. Polymerization:
Acrylonitrile and comonomers (e.g., Methyl Acrylate or Vinyl Acetate) are reacted to form the long-chain polymer, polyacrylonitrile (PAN), typically via a free-radical polymerization reaction in a solvent solution such as dimethylformamide (DMF), dimethylacetamide (DMAc), or aqueous sodium thiocyanate.
n CH2=CH-CN + m (CM) → [(CH2-CH-CN)n (-CM-)m]
3. Spinning (Fibre Formation):
Since PAN does not melt easily, it is processed via solution spinning, where the polymer is dissolved in a solvent (forming a viscous solution called 'dope') and extruded through a multi-holed device called a spinneret.
- Wet Spinning: The dope is extruded into a coagulation bath (e.g., water or DMF-water mix) where the polymer solidifies into filaments. This often produces fibers with a round cross-section.
- Dry Spinning: The dope is extruded into a stream of heated gas (air) which evaporates the solvent, and the filaments solidify. This often produces fibers with a dog-bone or kidney-shaped cross-section.
4. Post-Spinning:
The fibers are then washed, dried, stretched (to increase strength), and crimped (to give it bulk and a wool-like texture) before being cut into staple fiber (short lengths) for spinning into yarn.
Properties
Acrylic fibers possess a unique combination of mechanical and chemical properties:
| Property | Description |
|---|---|
| Warmth & Feel | Lightweight, soft, and warm, often imitating the loft and hand-feel of wool. |
| Resilience & Shape Retention | Excellent elasticity and resistance to wrinkling and shrinkage, holding creases well. |
| Strength | Tenacity: 2.0–3.0 g/den (dry); slightly lower when wet. |
| Moisture Regain | Very low (0.2–0.6%), making it quick-drying but with low breathability. |
| Thermal Properties | Softens at 200–230°C; melts at ~320°C; good insulator. |
| Dyeability | Dyed with cationic (basic) dyes; good color fastness. |
| UV & Weather Resistance | Excellent resistance to sunlight, fading, and degradation from weather, ideal for outdoor use. |
| Chemical Resistance | Good resistance to most acids, weak alkalis, and common chemicals. |
| Flammability | Flammable; it melts and drips when exposed to heat (unlike wool), though modacrylic variations offer fire resistance. |
Applications
Due to its low cost and insulating properties, acrylic fiber is widely applied in various sectors:
- Apparel: Sweaters, fleece garments, socks, scarves, hats, gloves, and linings.
- Home Textiles: Blankets, carpets, rugs, upholstery fabrics, and curtains.
- Outdoor Use: Awnings, boat covers, and patio furniture fabrics (due to high UV resistance).
- Industrial/Technical: Precursor for making carbon fiber (known as PAN-based carbon fiber), which is used in aerospace and high-strength composites.
- Aesthetics: Used to create realistic faux fur, wigs, and hair extensions.
Environmental Impact
As a synthetic, petrochemical-based fiber, acrylic has several significant environmental drawbacks across its life cycle:
- Fossil Fuel Dependence: The primary raw material, acrylonitrile, is derived from petroleum, making it a non-renewable resource-intensive product.
- Non-Biodegradable: Like most plastics, acrylic fibers do not naturally decompose. They can persist in landfills for centuries.
- Microplastic Pollution: When acrylic garments are washed, they shed microscopic plastic fibers (microplastics). These microfibers enter wastewater systems and ultimately contaminate rivers and oceans, posing a threat to marine life and human health.
- Toxic Emissions: The manufacturing of acrylonitrile and the solvents used in the spinning process can release volatile organic compounds (VOCs) and hazardous chemicals, requiring strict regulation to prevent harm to workers and local ecosystems.
- High Energy Use: The polymerization and subsequent spinning, stretching, and finishing stages are highly energy-intensive, contributing to a large carbon footprint.
