Polyester and Acrylic

In industrial chemistry, synthetic fibres are engineered polymers designed with high molecular weight, linear chain orientation, and strong intermolecular forces. Polyester and Acrylic represent two major classes of synthetic fibers derived from petroleum precursors. Both are produced via distinct addition or condensation polymerization pathways, replacing natural fibres like cotton, silk, and wool.

• Polyester is a category of polymers that contain the ester functional group in their main chain. It is typically synthesized via condensation (step-growth) polymerization.
• Acrylic refers to polymers composed of at least 85% acrylonitrile monomers. It is synthesized via addition (chain-growth) polymerization.

Polyester (Terylene / Dacron)

Polyester is the most widely used synthetic fibre globally. The most prevalent commercial variant of polyester is Polyethylene Terephthalate (PET), known as Terylene in the United Kingdom and India, and Dacron in the United States.

Chemical Synthesis and Polymerization

PET is manufactured through the condensation copolymerization of two bi-functional monomers: ethylene glycol (ethane-1,2-diol) and terephthalic acid (benzene-1,4-dicarboxylic acid) heated at 420–470 Kelvin in the presence of a zinc acetate-antimony trioxide catalyst.

The reaction proceeds by eliminating water molecules, binding the repeating aliphatic and aromatic structural units through highly stable ester linkages (-CO-O-).

Key Physical and Chemical Properties

• Wrinkle and Deformation Resistance: The presence of rigid aromatic benzene rings within the polymer backbone restricts structural twisting and chain slippage. This gives the fibre high resiliency, allowing it to recover its shape and resist wrinkling.
• Hydrophobic Nature: Polyester chains lack free polar hydroxyl or amino groups capable of forming hydrogen bonds with water. This makes the fabric hydrophobic, ensuring low moisture absorption and quick-drying properties.
• Chemical and Biological Inertness: It exhibits high resistance to mineral acids, oxidizing agents, moths, mildew, and microbial degradation.

Major Industrial Applications

• Apparel and Blended Textiles: Extensively blended with natural fibres to combine properties. Common blends include Polycot (Polyester + Cotton) and Polywool (Polyester + Wool), which provide the comfort of natural fibers alongside the wrinkle-free durability of synthetics.
• Packaging and Containers: Amorphous and low-crystallinity grades are molded into PET bottles, food jars, and transparent sheets.
• Industrial and Safety Equipment: Used to manufacture heavy-duty conveyor belts, safety helmets, sailcloth for boats, and high-strength industrial ropes.

Acrylic (Orlon / Acrilan)

Acrylic fibres serve as a synthetic substitute for natural wool due to their lightweight, warm texture and structural crimp.

Chemical Synthesis and Polymerization

Acrylic is produced via the addition (chain-growth) polymerization of acrylonitrile (CH₂ = CH-CN) monomers in the presence of a peroxide initiator.

This reaction converts the unsaturated carbon-carbon double bonds of the acrylonitrile monomers into a saturated hydrocarbon chain featuring bulky, electronegative nitrile (-C≡ N) pendant groups. Commercially, it is often synthesized as a copolymer by adding small percentages of vinyl acetate or methyl acrylate to improve its dyeability and flexibility.

Key Physical and Chemical Properties

• Thermal Insulation: The bulky nitrile side groups prevent tight, dense packing of the polymer chains, creating microscopic air pockets within the irregular yarn structure. These pockets trap air, giving acrylic low thermal conductivity and excellent heat-retention properties that mimic natural wool.
• Weather and UV Resistance: Acrylic features excellent resistance to degradation from sunlight, ultraviolet (UV) radiation, and atmospheric weathering.
• Lighter Density: It has a lower density (1.18 g/cm³) compared to natural wool (1.32 g/cm³), making it highly lightweight while providing similar warmth.

Major Industrial Applications

• Winter Wear and Knitwear: Production of sweaters, shawls, cardigans, athletic socks, tracksuits, and thermal underwear.
• Home Furnishings: Used to manufacture faux fur coatings, blankets, carpets, upholstery fabrics, and heavy draperies.
• Outdoor Fabrics: Due to its high UV resistance, it is used for outdoor boat covers, commercial awnings, car convertible tops, and outdoor upholstery.

Comparative Analytical Framework

Technical Parameter	Polyester (Terylene / PET)	Acrylic (Polyacrylonitrile)
Polymerization Mechanism	Condensation (Step-growth)	Addition (Chain-growth)
Monomer Structural Units	Ethylene Glycol and Terephthalic Acid	Acrylonitrile (CH2 = CH-CN)
Defining Chemical Group	Ester Linkage (-CO-O-)	Nitrile Group (-C≡ N)
Primary Natural Counterpart	Mimics Cotton / Silk properties	Mimics Wool properties
Moisture Regain	Extremely low (≈ 0.4%); strictly hydrophobic	Low to moderate (≈ 1.5-2.0%)
UV and Sunlight Stability	Moderate resistance	Exceptional resistance; highly stable outdoors
Combustion/Burning Profile	Melts and burns with a dark smoke, forming a hard, round chemical bead	Melts and burns rapidly with a yellow smoky flame, leaving an irregular brittle black residue

UPSC Prelims Applied Science Core Concepts

The Chemistry of Blended Fabrics

Pure cotton absorbs water readily but wrinkles easily, while pure polyester resists wrinkling but seals in sweat due to its hydrophobic nature. When blended into Polycot, the hydrophilic cotton fibers absorb body moisture through surface capillary action, while the rigid, ester-linked polyester chains provide a structural framework that prevents the cotton fibers from collapsing and wrinkling. This balances comfort and durability.

Alkaline Hydrolysis (Polyester Degradation)

Although polyester is highly resistant to acids, it is vulnerable to high concentrations of strong alkalis (such as sodium hydroxide) at elevated temperatures. The hydroxide ions (OH^-) attack the carbonyl carbon within the ester linkages (-CO-O-), breaking the ester bonds via a process called saponification. This chemical vulnerability is used industrially in “weight reduction” processes to make coarse polyester fabrics feel as soft and smooth as natural silk.

The Microplastic Microfiber Crisis

Both polyester and acrylic textiles present a significant environmental challenge through microfiber shedding. During domestic laundering, mechanical agitation and detergent action break off microscopic synthetic fragments (microfibers less than 5 millimeters in length) from the fabric yarns. Because these polymers are non-biodegradable petrochemicals, the microfibers escape municipal wastewater filtration plants, enter marine ecosystems, absorb persistent organic pollutants (POPs), and bioaccumulate up the marine food chain.

Last Modified: May 27, 2026