Polyester fiber offers high strength, good elasticity, and excellent processability. It can be used alone or blended with natural fibers, requires no ironing after washing, and is widely used in apparel, home furnishings, and industrial applications. However, its lack of polar groups causes low moisture absorption (0.4%), leading to static buildup, pilling, and poor dyeability. Since its invention, efforts have focused on overcoming these drawbacks. So, how can polyester fiber be modified? Here are three main modification approaches.

1. Chemical Modification

Standard polyester (PET) has a regular, linear structure with rigid benzene rings but lacks polar groups, resulting in poor dyeability despite high strength. Adding tertiary or quaternary monomers during polymerization changes the molecular structure, improving dyeability and physical properties.
This method chemically bonds monomers into the PET chain, creating permanent changes. However, it has limited flexibility, high cost, complex processing, and few suitable monomer choices. The most successful variants are:

Cationic Dyeable Polyester (CDP): Uses the monomer sodium dimethyl 5-sulfoisophthalate (SIPM). SIPM increases molecular spacing (improving dye adsorption) and adds sulfonic acid groups (-SO₃⁻) that bind cationic dyes, significantly enhancing dye uptake. CDP chips are widely used for superfine fibers.

Easy Cationic Dyeable Polyester (ECDP/EDDP): Offers easier dyeing than CDP.

While the domestic Chinese market mainly offers bright CDP and ECDP chips, our company supplies specialized grades:

Semi-dull CDP for Korean clients.

Semi-dull ECDP for Turkish and Indian clients.

Our bright ECDP achieves a sodium content of 13% by weight. It can act as a CD masterbatch during the cationic fiber production.

For more information about CDP and ECDP PES chips, please click https://www.polyestermfg.com/cationic-dyeable-polyester-chip/.

2. Physical Modification

This simpler, lower-cost alternative to chemical modification involves melt blending functional additives (e.g., for UV resistance, antistatic properties, conductivity) with PET chips to create masterbatches. These are then mixed with standard PET for spinning.

The main drawback is that additives bind to PET via weaker intermolecular forces (van der Waals, hydrogen bonds). Consequently, the modified properties can degrade over time.

3. Process Modification

Modifying production parameters or fiber cross-section shape during spinning achieves specific properties. Examples include high-shrinkage fibers, profiled fibers, and sea-island fibers.
Sea-Island Fibers comprises two components:
“Island” (e.g., PET, PA6, PA66, PP).
“Sea” (alkali-soluble polyester – COPET).
Our COPET chips offer excellent spinnability, enabling stable composite spinning with clear interfaces.
After fiber formation, the COPET “sea” is dissolved in alkali solution (e.g., NaOH), releasing the bundled “island” components as ultra-fine fibers (single-filament fineness ≤ 0.05 denier).

Sea-island Fiber

Sea-island Fiber

Our company also offers pre-crystallized bright-grade high-shrinkage PES chips. The boiling water shrinkage rate of the high-shrinkage short fibers generated from them can reach 60%- 80%. For more information, please refer to https://www.polyestermfg.com/high-shrinkage-polyester-chip/.