09 · Technology
Manufacturing & Technology
From PET basics to next-generation R&D — the technical foundation behind every claim.
What polyester is
In Earth Protex™ documentation, "polyester" refers exclusively to PET (Polyethylene Terephthalate) — a thermoplastic polyester derived from petroleum via petrochemical refining. PET is built from two monomers:
- MEG — mono-ethylene glycol (an alcohol; commercially fossil-based, bio-based emerging).
- TPA — terephthalic acid (commercially fossil-based and bio-based; CO₂-derived emerging).
MEG and TPA react by condensation to form ethylene-terephthalate units, linked via ester bonds (CO–O) into long PET chains. The aromatic ring in TPA gives PET its stiffness and resistance to biodegradation.
Key polymer terminology
- Polymerisation — building long chains of repeating monomer units.
- Intrinsic Viscosity (IV) — proxy for molecular weight / chain length; higher IV = stronger, more durable fibres.
- Crystallinity — degree of ordered molecular structure; affects strength, transparency and melting point.
- Amorphous region — disordered chain segments; essential for flexibility and dyeability.
- Polymer orientation — alignment of chains along the fibre axis during drawing; raises tenacity, modulus and thermal stability.
- Internal stress — residual tension trapped after spinning / drawing; if unevenly relieved, causes weak points and inconsistency.
PET characteristics
- Melting point ≈ 260 °C for virgin PET.
- Hydrophobic — limited water absorption, moisture resistant.
- High thermal stability — versatile in manufacturing.
- Virgin PET chain length: 18,000–23,000 units; recycled PET narrows due to chain scission, with more chains below 18,000 units unless IV is restored.
Applications of polyester
Textile
- Clothing & apparel — casual, formal, performance.
- Home textiles — bedding, curtains, upholstery.
- Workwear — durable, wear-resistant.
Industrial
- Automotive — seat belts, upholstery, carpets, insulation.
- Packaging — bottles (injection-moulded), films.
- Other — ropes, hoses, conveyor belts.
Fibre specifications to know
- Denier — fibre thickness (g per 9,000 m); lower = finer.
- Cross-section — round, trilobal or hollow; tunes specific properties.
- Staple length — short for spinning, long for wool blends / non-wovens (staple only).
- Orientation — for filaments; chain alignment from drawing tunes strength, stretch and stability.
- Masterbatch — adds colour or function (UV, FR, antimicrobial) directly during fibre manufacture.