| As a response to the problem of increasing domestic waste, biodegradable polymers have attracted more and more attention.To date, aliphatic polyesters have been found to be the most attractive biodegradable synthetic polymers and have been applied to textiles because of good biodegradability.However,poor properties and high cost restrict its large-scale application in textiles.On the contrary,in spit of non-biodegradability,aromatic polyesters have been known to possess excellent thermal and mechanical performances.Therefore,introducing aromatic unit into the main chains of aliphatic polyesters seems an interesting strategy to produce new aliphatic-aromatic copolyesters, sharing the favorable biodegradability of aliphatic polyester component and the good physical performance of more rigid aromatic counterpart.In this case,this investigation is expected to yield information on biodegradable fiber processing and resultant fiber properties.Firstly,poly(butylene succinate-co-butylene terephthalate)(PBST) copolyesters with different molecular weight were efficiently synthesized from the starting materials of dimethyl terephthalate(DMT),dimethyl succinate(DMS)and 1,4-butanediol(1,4-BD)in the presence of tetraisopropoxide titanium(TTiPO)as the bulk polycondensation catalyst and macromolecule-instructure-adjusted regent.~1H NMR proved the prepared products of the PBST copolyesters,and the molar ratios of BS to BT comonomers were almost equal to the feeding ratios of DMS to DMT.GPC results showed that the weight average molecular weights (M_w)of the PBST copolyesters were in range of 9.8×10~4,11.1×10~4 and 12.2×10~4.According to capillary viscometer,the intrinsic viscosity increase from 0.72 dl/g to 0.93 dl/g with increasing of molecular weight of PBST copolyesters.Furthermore,melt index was tested for 49.07 g/10min,34.01 g/10min and 23.95 g/10min,respectively.Through DSC,TGA and WAXD investigations,it was found that good thermal properties were entitled to PBST copolyesters,whose melting point at about 180℃, decomposition temperature at about 380℃,and degree of crystallinity at 46%or so and similar crystal structure as that of PBT.By the investigation on isothermal crystallization kinetics,it could be known that the crystallization behaviors of PBST copolyesters accorded with Avrami equation.The Avrami exponent n was more than 3, indicating that homogeneous nucleation and spherulitic growth,which was confirmed by POM experiment.Based on the DLI test,the maximum crystallization rate temperature could be obtained for 90℃.In addition, the equilibrium melting point of PBST copolyesters calculated by Hoffman-Week equation was calculated for 192.5℃.In order to study the spinnability,the rheological behavior of PBST copolyesters with different molecular weight was investigated by capillary rheometer.The results showed that the apparent viscosity of PBST copolyesters decreased with the increase of shear rate and temperature.The shear-thinning results indicated the PBST melts belonged to non-Newtonian pseudoplastic fluid.The flow activation energy of PBST copolyesters decreased with the increasing of shear rate, so the sensitivity to temperature decreased.With the increase of temperature,structural viscosity index of PBST tended to decrease, however,the possibility of thermal decomposition increased.In the same shear rate,the higher molecular weight of PBST copolyesters was,the larger shear stress,apparent viscosity and structural viscosity index were, but the smaller non-Newtonian index became.Moreover,the melt-spinning process of PBST copolyesters was investigated as the key point.Based on the studies,the molecular weight plays a dominant role in spinnability of PBST copolyesters.When the molecular weight exceeded 1.1×10~5,PBST copolyesters appeared the good spinnability.Moreover,there was a wide range of melt-spinning temperature for PBST copolyesters and the optimum was 210-225℃.The mechanical properties of PBST fiber was improved by increasing take-up velocity,the optimum spinning speed was 1000 m/min.From the experiments,the suitable drawn processing temperatures were selected for 80℃and heat-setting for 160℃.In the above parameters, the strength of last drawn PBST fibers can get maximum of 3.5 cN/dtex.In addition,the enzymatic degradation of PBST fibers were carried out in the presence of a lipase originated from Pseudomonas cepacia(Lipase PS(?)),activated sludge and other environment.The change of molecular weight,strength,weight and the surface between the original and degraded fibers were investigated.The results clearly showed that the degradation of PBST fibers were observed under enzymatic environment and the degradable rate was independent of the molecular weight of PBST fibers...
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