Modulated Crystallization Behavior,Polymorphism And Biodegradability Of Poly(Butylene Adipate): Effect Of Nucleating Agent

Poly?butylene adipate??PBA? is a kind of classical and linear aliphatic polyester with biodegradability and products made from its copolyester have been widely applied in protection of environment, agriculture, and so on. Depending on melt-crystallization temperature, PBA shows polymorphic crystalline structure?aggregation structure?. In the order of enhanced melt-crystallization temperature of PBA, ?-modification?T_c < 29??,mixture of ? and ? modification???+??, 29? ? T_c? 32?? and ?-modification?T_c> 32??.Classical Maltese-cross?ringless? spherulites can be found in ?- and ?-crystal, but??+??presents spherultes with ring band. Although ?-modification shows smaller crystal lattice size,lower melting temperature and thermal stability, it exhibits lower biodegradation rate than?-one. It is noteworthy that? ?+?? with ring band spherulites, possesses the lowest biodegradation rate. Therefore, biodegradation of PBA is not only related to aggregation structure but also associated with spherulite morphology. Due to low cost, high efficience,short processing cycle, in my work, three nucleating agents?NAs? with biocompatibility, such as zinc phenylphosphonate?PPZn??orotic acid?OA? and cyanuric acid?CA?, were used to manipulate aggregation structure and spherulite morphology and further to tailor biodegradation of PBA. Experimeantal results are presented as follows.?1? Increased crystallization temperature and crystallization rate, decreased spherulite size, and enhanced spherulite density of PBA were found in the presence of NAs. It suggests that NAs exhibited high nucleating effect because they provided nucleation sites on which nucleation of PBA could occur at higher temperature and free energy used for nucleation decrased in the presence of NAs.NAs is favorable for formation of ?-modification of PBA and accelerated ??? phase transition. Perfect crystal lattice matching between NA and PBA?-modification and/or enhanced mobility of molecular chain of PBA in the interface between PBA and NA are probably attributed to favorable formation of PBA ?-modification. Upon addition of NA, critical temperature of generation of PBA ?-modification(T_c,e) reduced significantly, so the larger temperature difference between annealing temperaute?T_a? and T_c,e in the presence of NA, that is, greater value in(T_a-T_c,e) facilitates phase transition from ? to ?phase.?2? Upon incorporation of PPZn, biodegradation rate decreased because PPZn hinder attack of enzyme molecule on surface of PBA molecule. Effects of other NAs on biodegradation of PBA are in progress.