Synthesis And Studies On Properties Of Biodegradable Aliphatic-Aromatic Random Copolyester

The product properties of aliphatic-aromatic copolyester are designed to meet the requirements of a biodegradable plastic:ideally, a combination of processability, utilization properties, and biodegradability. The market for biodegradable materials is growing significantly every year. From the existing market and promising applications, it is estimated that good opportunities exist especially for the successful development of large volumes in materials such as compost bags, fast food/disposables, agricultural films, hyginen films, and paper coatings. Development and research on the aliphatic-aromatic biodegradable polymeric materials are of increasing interst and an important research goal to company and govement on a world scale. Aliphatic homopolyesters and aliphatic-aromatic copolyesters based on1,4-butanediol (1,4-BD), adipic acid (AA) and dimethyl terephthalate (DMT) were synthesized by condensation reaction using catalyst. Average molecular weight, thermal properties, mechanical properties, and biodegradability were respectively investigated. Aliphatic-aromatic copolyesters also were synthesized by condensation in TBOT/TiO2catalyst.Aliphatic homopolyesters and aliphatic-aromatic copolyesters based on1,4-butanediol, adipic acid and dimethyl terephthalate were synthesized by condensation reaction using two-step method in one reaction kettle. We investigated the effect of different glycol/diacid ratios on raction rates and degree of polymerization. On basis of analysis of distillation produced in ester interchange and esterification reaction, the correlation between reaction temperature and side reaction is presented. Rates of ester interchange and esterification reaction are increased by increases stirring rates. Generally, we can find the rates of ester interchange, esterification, and polycondensation reaction and the degree of polymerization are satisfied when glycol/diacid molar ratios are from1.2to1.4, heated temperature of ester interchange reaction is220～230℃and reaction temperature less than205℃, heated temperature of esterification reaction is230～250℃, rates of ester interchange and esterification reaction are more than1200r/min. Under above reaction conditions, we can make copolyesters with high molecular weight while the extent of reaction is high and the rate of reaction is high, and by-products decrease.Nanosized TiO2was prepared from TiCl4by sol-gel method. The structural properties of the particles were characterized by means of XRD and TEM techniques. Aliphatic-aromatic copolyesters based on1,4-butanediol, adipic acid and terephthalic acid were synthesized by polycondensation in presence of TBOT/TiO2catalyst. Number-average molecular weight and melting temperature were respectively measured by gel permeation chromatography (GPC) and differential scanning calorimeter (DSC). Tensile strength at break and Elongation at break were examined to represent the material property of copolyesters. Therefore our results on the catalytic properties of TBOT/TiO2catalyst is:the molecular weight and material properties of the copolyester were enhanced by using TBOT/TiO2catalyst, and weight-average molecular weight of the copolyester exceeds80000with the composite catalyst as the optimum molar ratio of n(TBOT)/n(TiO2) is1.2. We initially have checked the composition and the average sequence length of the copolyesters by1H NMR. Average molecular weight, thermal properties, mechanical properties, rheological characteristic, and biodegradability were respectively investigated by gel permeation chromatography (GPC), differential scanning calorimeter (DSC), thermogravimetry(TG), tensile tester, capillary rheometer, and scanning electron microscopy (SEM). Degree of randomness of the copolymer is close to unity of entire composition range, indicating that random copolyesters were obtained. Besides that, the average block length of aromatic unit and aliphatic unit are less than3. The results also exhibits more BT contents to copolymer leading to an increase, for the average sequence length of aromatic unit, but a decrease for the average sequence length of aliphatic unit. Copolyester contains more aromatic repeating units, showing higher melting temperature, glass transition temperature and mechnical properties. Therefore, aromatic unit enhance the thermal stability of these copolyeseers. The rheological behavior of copolyester is more close non-Newtonian melt material. The apparent viscosity decreases with the apparent shear rate increasing, and temperature will effect more obviously on the apparent viscosity under lower shear rate.The biodegradability and biodegradation behaviors of the copolyesters were investigated by using data of weight loss rate, weight loss per area (WPA) and change of molecular weight from compost experiments. In order to investigate the complex degradation behavior of such copolyesters, the change of the microstructure and composition of the copolymer detail is investiged by1H NMR. And the attack and cleavage action of microorganisms to the copolymers was described. It can be concluded that the aliphatic-aromatic copolyesters, within a range of approx.40%—60%molar fraction of terephthalic acid in the acid components, provide good material properties under maintenance of their biodegradability. And better degradability of aliphatic-aromatic copolyesters depends on the lower aromatic composition and lower molecular weight. A noticeable change in composition and microstructure is observed. We also found an obvious stains and cracks, which provide supportive evidence that these copolyesters are degraded by the attack of microorganisms.