| Polyethylene terephthalate(PET)is widely used in the chemical fiber and packaging bottle industry because of its excellent mechanical properties,chemical stability and processing properties,so it also produces a large amount of waste every year,and bottle recycled PET as a recycling product of these wastes,compared with virgin PET has environmental advantages.Melt spinning with recycled PET is a high-value-added embodiment of the reuse of waste resources.As a textile,under the background of diversified demand,the development technology of using recycled PET as the spinning raw material to further integrate differentiated and functionalized fibers has become a development trend,so as to further realize the combination of green and functional fibers.In this paper,the representative of matting masterbatch as inorganic powder masterbatch and polyphosphate flame retardant masterbatch as the representative organic masterbatch were used to modify the recycled PET and native of the bottle flakes by melt blending,respectively,and focused on tracking and analyzing the adaptability of different types of masterbatches in these two spinning grade polyesters.Firstly,the chemical structure of recycled PET was characterized,and the results showed that its chemical structure contained 3.85 mol% isophthalic acid structural units.The intrinsic viscosity of recycled PET chips reached 0.735 d L/g,which was higher than that of virgin PET chips.The thermal degradation characteristics of these two polyesters during thermal processing were studied by intrinsic viscosity test and end carboxyl test,and the intrinsic viscosity drop and end carboxyl group change of melt at different temperatures were analyzed.The results show that the intrinsic viscosity of PET gradually decreases with the increase of processing temperature,while the terminal carboxyl group begins to increase significantly above 290 °C.On this basis,the two representative masterbatches were introduced into the recycled PET according to the no addition ratio,and the results showed that the amount of matting masterbatch,that is,the amount of titanium dioxide added,increased from1.5 wt% to 2.5 wt%,and the whiteness of the blended modified recycled PET was small.For flame retardant masterbatches,when the amount of phosphorus added reaches 5000 ppm,the limiting oxygen index of the blended modified bottle flake recycled PET reaches a flame retardant level of more than 27%.The non-isothermal crystallization properties of the blended products with a ratio of 1.5 wt%titanium dioxide and 5000 ppm phosphorus were selected to matte masterbatch and flame retardant masterbatch,and the rheological properties were studied to guide the determination of the basic parameters of the spinning process.The results of non-isothermal crystallization test showed that the recycled PET of bottle flakes showed a faster crystallization rate than that of virgin PET,which was inconsistent with the trend of crystallization performance caused by the change of chemical structure,considering that the presence of trace impurities exerted the effect of nucleating agent.Recycled PET has a high intrinsic viscosity and shows a high shear viscosity in the melt,and increasing the spinning temperature is conducive to the spinning of recycled PET in the bottle.The addition of matting masterbatch caused the regenerated PET to exhibit a nonNewton index similar to that of virgin PET,indicating that when the recycled PET was blended with the powder-type masterbatch,the rheological properties of the melt were significantly affected by the masterbatch.The addition of organic flame retardant masterbatch improved the spinnability of PET,but the fluidity of recycled PET was not as good as that of virgin PET,indicating that the melt was greatly affected by its own structure and compatibility between PET and organic masterbatch when blended.In the process of spinning and hot drafting to prepare PET fiber,orientation-induced crystallization effectively improved the crystallization rate and crystallinity of virgin PET,and the crystallinity of recycled PET fiber was basically the same as that of virgin PET.The longer molecular chain of recycled PET and the bond angle of isobenzene monomer lead to greater free volume of amorphous region,which is conducive to the curling of molecular chains,resulting in higher boiling water shrinkage rate of recycled PET fibers in bottle flakes.For the same reason,the color rate of recycled PET fiber in bottle flakes is higher than that of virgin PET fiber.Due to the thermal processing of recycled PET in the front recycling,certain side reactions such as thermal oxygen degradation occur,and the hue of the raw materials is yellow,resulting in the hue of recycled PET and its blend fibers being yellowish compared with the original PET and its blend fibers,making the recycled PET more suitable for fabrics that need to dye dark colors. |
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