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What are the methods for identifying polylactic acid fibers
source：www.kingcharmgroup.com | Release time：2026-10-131、 Combustion method (on-site rapid initial screening)
Phenomenon: Melting and shrinking near the flame, melting and burning when exposed to fire, the flame tends to be blue, and there are droplets of molten material; With a faint sweetness; After cooling, the residue is a light yellow hard rubber block.
Comparison and differentiation: Polyester has a weak burning odor, and the residue is mostly black hard blocks.
Limitations: Belonging to auxiliary means, it is only used for preliminary judgment and cannot be used as a sole basis for judgment.
2、 Microscopic observation method
Longitudinal: The fiber surface is relatively smooth, with some visible small spots and grooves.
Cross section: basically circular, with micropores and cracks present in some sample sections; Polyester cross-section is generally dense and pore free.
Limitations: The morphology of modified PLA will change, making it difficult to identify blended samples and only assisting in screening.
3、 Melting point method
The melting point of polylactic acid fiber is about 165-178 ℃, much lower than the melting point of polyester at around 255 ℃. Observing the melting temperature under a hot stage microscope can quickly distinguish between PLA and PET.
Attention: The melting point of PLA after heat setting and heat treatment may fluctuate slightly.
4、 Chemical dissolution method
At room temperature, dichloromethane and tetrahydrofuran: polylactic acid fibers are soluble; Polyester does not dissolve at room temperature and is a commonly used distinguishing reagent.
Alkaline solution: The strength of PLA fibers rapidly decreases under weak alkaline conditions; Polyester's strength is almost unaffected in the same weak alkaline environment.
Attention: Chemical reagents are corrosive and require proper protection. For blended samples, observe the remaining dissolved components.
5、 Infrared spectroscopy method
Using ATR attenuated total reflection infrared to collect fiber spectra and identify characteristic peaks: 1758 cm ⁻¹ strong ester absorption peak, matched with 1266 cm ⁻¹ and 908/920 cm ⁻¹ characteristic peaks, matched with standard spectra, can accurately determine and distinguish between PLA and PET. This method is commonly used as a basis for determining the composition of imported and exported textiles.
6、 DSC differential scanning (auxiliary confirmation)
By determining the position of the melting endothermic peak and crystallization characteristics, the melting temperature and crystallization enthalpy can be used to distinguish polylactic acid from other polyester fibers, which is suitable for reviewing controversial samples.
7、 Degradation assisted verification
Polylactic acid will gradually hydrolyze and degrade in high-temperature and high humidity composting environments; Polyester is stable and non degradable in similar environments. The disadvantage is that the cycle is very long, only suitable for qualitative reference, and cannot be used as a basis for testing reports.
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