| As one of the world’s largest producer and consumer of textiles and garments,China has a total annual fiber consumption of more than 55 million tons with a rapid growth rate of about 10% every year.The waste ratio of the textile and garment industry in the three major production processes of fiber-forming,textile weaving and clothing and shoemaking is about 30%,resulting in a large amount of solid waste.In 2019,the recycling rate of waste textiles in our country was less than 10% with only about 4million tons were recycled.Unutilized waste textiles not only waste resources,but also cause serious environmental problems,leading to great threats to human health and ecosystems.Therefore,the key to improving the utilization rate of solid waste in the textile and garment industry is to develop universal method to realize the high-quality and high-value utilization of waste textiles.The main components of solid waste in the textile and garment industry are various types of fabrics,among which polyester fiber is the largest variety of chemical fiber,accounting for more than 80% of the total chemical fiber.However,there are many problems in the recycling process of waste polyester fabrics,such as large differences in sources,properties and quality,impurities include difficult-to-separate dyes and mixed polymers.As a result,the viscosity of polyester fabrics decreases and fluctuates greatly during the regeneration process,resulting in poor processing performance and difficult to be recycled by melt spinning technology.Thus,our studies were developed based on the National Key Research and Development Program of China named “The key technologies of cascade and high-quality utilization for solid waste from textile and garment industry”(2019YFC1904502).Using waste fiber-derived polyester(rPET-F)as raw material,we aim to develop in-situ reaction viscosity increasing technology to achieve high-value,closed-loop uprecycling from fiber to fiber and obtains high-quality recycled polyester.In addition,the mechanism of viscosity increase caused by chain extension and self-polycondensation was elucidated through the research on the rheological properties of fiber-derived polyester.In this paper,1,4-Butanediol diglycidyl ether(EPOX)with 2 epoxy groups,ADR-4468 with about 9～15 epoxy groups and three synthesized poly(glycidyl methacrylateco-methyl methacrylate-co-styrene)(P(GMA-co-MMA-co-S))with 38～132 epoxy groups per molecule,were used as chain extender of discarded PET fibers(rPET-F).And we comprehensive analysis these five chain extenders with different number of epoxy groups to a deeper understanding of the influence on the molecule weight,molecular architecture and thermal properties of rPET-F.The effects of epoxy functionality and addition amount of chain extenders on the molecular weight,molecular structure,crystalline properties and rheological properties of chain-extended regenerated polyesters were investigated via intrinsic viscosity,DSC,rotational rheology test and other analytical methods.The results showed that the molecular weight and branching degree of the modified rPET-F increased with the addition of chain extender and the epoxy functionality of the chain extender.Among them,ADR-4468 inhibits the crystallization of the modified rPET-F,while PGMS copolymer have little change in the crystallization properties of the modified rPET-F.ADR-4468 and PGMS copolymer showed faster reactive rate of chain extension than EPOX.Structural rheological analysis showed that more functional groups lead to the more branchedchain of the modified rPET-F,and the 1.5wt% PGMS1/rPET-F system showed the highest degree of branching.This study provides an effective strategy for high-value utilization of rPET from waste texiles,suggesting that rPET-F with different qualities can be modified by chain extenders with different number of epoxy groups,and can be used in wide applications,such as film,foam materials,etc.However,the modified rPET-F with branched structures is not suitable for spinning.Secondly,in order to realize the recycling from fiber to fiber,we studied the "micro-alcoholysis-self-polycondensation" technology to conduct in-situ viscosity increase of rPET-F,which could inhibit the generation of branched structures during chain extension.We chose spinning grade PET pellets(vPET)and rPET-F as research objects,and explored the effect of twin-screw extruder process parameters,the type and dosage of alcohol on polyester alcoholysis process,and characterized the thermal properties,molecular structure and rheological properties of recycled polyester product.The experimental results show that the screw temperature has a greater impact on the alcoholysis of polyester than the screw speed,and the amount and type of alcohol have the greatest impact on the alcoholysis.The intrinsic viscosity of vPET pellets by 1%EG alcoholysis decreased from 0.68 d L/g to 0.30 d L/g and the decreasing trend of the intrinsic viscosity of the alcoholysis product would slow down with the continued addition of EG.The alcoholysis rate of DEG on polyester is faster than that of EG,which is difficult to control.Then,the self-polycondensation process effectively improved the intrinsic viscosity and complex viscosity of the recycled polyester.The intrinsic viscosity of vPET-R and rPET-F-R can reach up to 0.78 d L/g and 0.60 d L/g respectively,which are higher than the original ones.The structural rheological analysis showed that the molecular structure of both vPET-R and rPET-F-R are linear chains and could be used for spinning.Subsequently,the blends of bottle flakes(rPET-B)and recycled polyester(rPET-F-R)prepared by the "micro-alcoholysis-self-polycondensation" were studied.The results showed that the complex viscosity of rPET-B/rPET-F-R blend system decreased with the increase of rPET-F-R content,and the crystallinity improved.Among them,the blend sample of 10wt% rPET-F-R and 90wt% rPET-B had rheological properties close to recycled bottle flakes and maintained good viscoelasticity.In Fujian Baichuan Resources Recycling Science & Company,we used a blend of 15wt% rPET-F-R and85wt% rPET-B as raw material to produce recycled colored yarns,which meet national standards in various performance indicators.Finally,waste polyester fiber inevitably contains a small amount of other fiber impurities,such as polypropylene(PP),nylon(PA),etc.,resulting in unstable viscosity of waste polyester.To solve this problem,we studied the compatibility and rheological properties of high-component PET(above 90%)blends with a small amount of PA and PP(below 10%)by means of DSC,SEM,rotational rheological testing and other characterization methods.The results showed that the PET/PP blends had an obvious sea-island phase structure,and the size of the island phase increased with the increase of the amount of PP.The complex viscosity of the blend system decreased with the increase of PP addition,which indicated that reasonable addition of compatibilizer can improve the compatibility and rheological properties of the blends.Adding 4% PP-gMAH to PET/PP(92/8 w/w)blends can achieve the best compatibility and good rheological properties.In the PET/PA blend system,PET with 4wt% and 2wt% PA have good compatibility and maintain a high complex viscosity and melt strength.The above results pointed out the research direction for realizing the high-value utilization of waste blended fabrics. |
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