Study On Chain Extension Of Pet Bottle Flakes Through Polycondensation And Reactive Extrusion

Chain extension of PET bottle flakes was studied through solid-state polycondensation (SSP) method and reactive extrusion method respectively, intrinsic viscosity (IV) variation of PET product was researched by using different residence time, reaction temperature, crystallization time in SSP or using different moisture content, melt temperature, kind of chain extenders, chain extender dosage, screw speed, vacuum, etc. in reactive extrusion, and the best method and conditions for IV increasing was found out.For SSP, average IV of PET paticle was0.540dL/g, when residence time was21h, reaction temperature was220℃and crystallization time was1h at180℃, IV of PET product achieved maximum0.614dL/g.For reactive extrusion, average IV of PET bottle flake was0.786dL/g by random sampling, and IV was not affected by bottle flake’s colour; chain extension effect of PET product was studied with polycondensation reactive extruder, results showed the best melt temperature range was (256±2)℃, the best moisture content of PET bottle flake was under0.2%.PET bottle flakes were extruded using different kinds of chain extenders with polycondensation reactive extruder, the best chain extension effect for each chain extender was as follow:IV of product was0.745dL/g when Diisocyanatotoluene (TDI) dosage was0.35%; IV of product was0.749dL/g when Antimony trioxide (Sb2O3) dosage was0.35%; IV of product was0.770dL/g when Phthalic anhydride dosage was0.2%; IV of product was0.763dL/g when Naphthalenetetra carboxylic dianhydride (NTDA) dosage was0.25%; IV of product was0.821dL/g when Pyromellitic dianhydrde (PMDA) dosage was0.3%; PMDA had the best chain extension effect after comparison, and its best melt temperature range was256-258℃.Using the mixture of PMDA and Phthalic anhydride as PET chain extender, the maximum IV of product was0.96dL/g when PMDA and Phthalic anhydride dosages were0.3%and0.2%respectively, while CV of product was30.9mol/g, but the extrudate was uneven thickness because there was some gel in it. When PMDA and Phthalic anhydride dosages were0.3%and0.25%respectively, PET product also achieved a high IV,0.92dL/g, and CV was41.2mol/g, extrudate was uniform thickness and traction was sTab... The main parameters of extruder were studied under this chain extender dosage, results showed the best melt temperature range was (256±2)℃, the corresponding temperatures in each screw tube were240,255,250,250,230℃(nose section), screw speed was at50—70r/min range, vacuum was-0.1MPa.