Studies On The Preparation Of Biodegradable Poly(Butylenes Succinate-co-butylene Terephthalate)(PBST) Fibers And Its Properties

In recent years, biodegradable polymers have received more and more attention due to the global concern about the increasing synthetic nonbiodegradable waste pollution. Among them, aliphatic/aromatic copolymer is an important category for the balance of its biodegradability and physical properties. Poly (butylene succinate-co-butylene terephthalate) (PBST) just belongs to this kind of copolymers. In addition, there are increasing demands of biodegradable fibers in both agricultural and medical fields, however, all the researches on PBST focused on film samples until now. In the above cases, this investigation is expected to yield information on biodegradable fiber processing and resultant fiber properties.Firstly, the aliphatic/aromatic poly(butylene succinate-co-butylene terephthalate) (PBST) copolyesters with different molecular weight were efficiently synthesized from the starting materials of dimethyl succinate, dimethyl terephthalate and 1,4-butanediol in the presence of tetraisopropoxide titanium as the bulk polycondensation catalyst. ~1H NMR results proved the molar fraction of BT comonomers of the prepared products were almost 70%. GPC results showed that the weight average molecular weights (M_w) of the PBST copoyesters were in the range of 9×10~4～1.4×l0~5. In addtion the intrinsic viscosity was in the range of 0.7～1.1dL/g,melt index was in the range of 23～50g/10min and the density was in the range of 1.28～1.29g/cm~3, which were respectively determined by Ubbelohde, Melt indexer and Density-Gradient Technique. According to DSC, TGA and WAXD investigations, it was found that good thermal properties were entitled to PBST copolyesters, whose melting peak temperatures at about 180°C and decomposion temperatures at about 380°C, and the crystal structure of PBST similar as that of PBT. In order to study the spinnability, the rheological behavior of different molecular weights PBST copolyesters was investigated by capillary rheometer. The results showed that the apparent viscosity of PBST 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 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 was, the larger shear stress, apparent viscosity and structural viscosity index were, but the smaller non-Newtonian index became.Furthermore the melt-spinning process of PBST copolymer was investigated as the key point. Based on the studies, the molecular weight plays a dominant role in spinnability of PBST. When the molecular weight exceeded 1.1×10~5, the 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°C. The mechanical properties of PBST fiber was improved by increasing take-up velocity, the optimum spinning speed was 1000m/min. From the experiments, the suitable drawn processing temperatures were selected for 80°C and heat-setting for 160°C. In the above parameters, the strength of last drawn PBST fibers can get maximum of 3.5cN/dtex.In addition the enzymatic degradation of PBST fiber was carried out in the presence of a lipase originated from Pseudomonas cepacia (Lipase PS(?)), activated sludge and other environment. The difference of molecular weight, strength, weight and the surface between the orignal and degraded fibers were studyed. The results showed that clearly degradation of PBST fiber was observed under enzymatic environment and the degradable rate was independent of the molecular weight of PBST fiber.