PDT (bio-based PET) fiber
PET fiber (polyester) is an important part of synthetic fiber. In 2017, the total amount of chemical fiber in China exceeded 50 million tons, of which polyester production accounted for about 80% of the total. Polyester is widely used in the field of clothing, decoration, civilian fabrics and industrial fabrics. The raw materials of most PET fibers are extracted from petroleum. The global demand for polyester and its raw materials is in contradiction with the limited non-renewable petroleum resources, which limits the development of the polyester industry, and the waste associated with the huge output has caused a serious burden on the environment. Therefore, the development of bio-based materials that can replace petroleum-based polyesters has become a research hotspot.
PDT (polyethylene terephthalate) fiber is a kind of bio-based PET fiber, which is spun from polyethylene terephthalate.
1. Raw material
The raw materials of PET are terephthalic acid (PTA) and ethylene glycol (EG), and major enterprises have developed processes for preparing these raw materials by biological methods.
(1) Bio-based terephthalic acid
Bio-based p-xylene = formic acid can be produced from bio-based p-xylene (PX) or the mixed aromatic hydrocarbon BTX of benzene, toluene and p-xylene. At present, many companies have developed the preparation process of bio-based PX or BTX for the production of Bio-based terephthalic acid (Table 3). Bio-based PTA can also be prepared from biomass through multiple conversions.
bio-based glycol
The preparation methods of bio-based ethylene glycol mainly include the following: ① Biomass hydrolysis and fermentation to prepare EG through sorbitol. In 2005, my country's Changchun Dacheng Group Company took the lead in realizing the process of preparing EG by this method (Figure), and built a 20,000 t/a bio-based EG pilot plant. In 2007, it built a 200,000 t/a industrial demonstration plant. The bio-based diol produced by this method is a multi-component mixed alcohol, which contains multi-component diols such as propylene glycol, butanediol and pentanediol with a mass fraction of about 2%, and is used to prepare PDT polyester . ②Biomass synthesis gas to EG: Biomass is first gasified to produce synthesis gas, and then directly (or indirectly) synthesizes EG. ③ Synthesis of EG by bio-alcohol chemical method: firstly, ethanol is produced by biomass fermentation process, then ethanol is dehydrated to ethylene, then oxidized to produce ethylene oxide, and finally hydrated to generate EG. There are other methods such as bio-based glyoxal to ethylene glycol, cellulose catalytic conversion to ethylene glycol, etc. The production companies and processes of bio-based ethylene glycol are shown in the table:
Synthesis
Bio-based PET is generally polymerized from bio-based PTA or bio-based EG. When the bio-based EG is a multi-component diol, the resulting polyester is PDT. PDT is obtained by polymerizing bio-based ethylene glycol with terephthalic acid or dimethyl terephthalate. The synthesis process is mainly the PTA method, including several stages of esterification, precondensation and final polymerization. Due to the existence of multi-component-alcohols, both the polymerization process and the vacuum degree of PDT need to be improved compared with petroleum-based polyesters. After the polyester is synthesized, the PDT fiber is produced through a silk process, and the spinning device can be completed by using PET equipment. At present, PDT fiber has been industrialized in 10,000-ton equipment.
Performance and Application
PDT fiber has stretch and resilience, it can quickly rebound to the original shape after stretching, and it can improve its comfortable fit when used in clothing. Compared with PET, PDT fiber has higher elongation and has a softer hand.
PET fiber also has a lower glass transition temperature, can be dyed under normal pressure, and has higher washing fastness and ironing fastness. At the same time, PDT fibers have better antistatic properties than PTT and PET fibers. PDT fiber can also be blended with natural fibers such as wool to produce better fabrics. One of the raw materials of PDT fiber can be transformed from biomass resources, which reduces CO2 emissions. It is a low-carbon, environmentally friendly and green new fiber material, which can be used in clothing, decorative materials, industries and other fields.
