Effect Of Polyamide Nucleating Agents On Polymorphic Crystalline Structure,Crystal Morphology And Property Of Biodegradable Poly(1,4-Butylene Adipate)

Poly?1,4-butylene adipate??PBA?,is a typical linear aliphatic polyester.Its two copolymers,poly?butylenesuccinate-co-adipate??PBSA?andpoly?butylene adipate-co-terephthalate??PBAT?are widely used in medical materials,environmental protection and agricultural plastic films.Depending on the melt-crystallization temperature?T_c?,two crystal modifications can be assigned for the PBA.PBA shows polymorphic crystalline structure followed by?crystal,??+??crystal mixture and?crystal.Different crystal modification has different crystal morphology.Both the?and?crystal exhibit the typical Maltese-cross spherulitic morphology,while the??+??crystal blend presents the ring-band spherulitic morphology.It is interesting that the PBA?crystal with the larger crystal lattice size and crystallinity shows the higher biodegradation rate than the?crystal,and the??+??crystal blend presents the lowest biodegradation rate.The results above indicate that there is a close and direct relationship between the crystal morphology and polymorphic crystalline structure?polymorphism?,which further codetermine the biodegradability and thermal stability of the PBA.Hence,control of the crystal morphology and polymorphism is a feasible way to tailor the biodegradability and thermal stability of the PBA.With respect to the efficiency,convenience,simplicity,low cost,and short production cycle,nucleating agents?NAs?have been used in attempts to manipulate polymorphic crystalline structure and the biodegradation of the PBA.Several organic NAs have been reported to be partially or completely dissolved in the polylactide?PLA?melting and further recrystallize,self-assemble during the melt processing.The polyamido NAs are applied to PLA greatly increase the crystallization temperature,accelerate the crystallization rate.The interaction between the amide bond?O=C-N-H?and the hydrogen bond of PLA formed special crystals such as pin type,cone type and string crystal,which enhanced the thermal stability of PLA.Therefore,three kinds of polyamides NAs?EDPO,DMC-DBH and TMC-328?can tailor the thermal stability and biodegradability of PBA by studying the crystal morphology,polymorphic structure and crystallization behavior of PBA.The experimental results are as follows:?1?As three effective nucleating agents,EDPO,DMC-DBH and TMC-328 highly increased the crystallization rate and crystallization temperature,decreased spherulite size and increased the density of the PBA.The NAs not only facilitated the formation of the PBA?crystal,but also accelerated the?-to-?phase transition of the PBA.It maybe attribute to a good crystal lattice matching between the PBA?crystal and the NAs crystal,which induces the epitaxial growth of the PBA?crystal on the NAs surface.It is mainly due to the fact that the greater temperature gap of(T_a-T_c,e)in the presence of the NAs provide more energy to accelerate the?-to-?phase transition of the PBA.The accumulated energy during a particular annealing temperature should be the predominant driving force to realize the phase transition.The?-to-?phase transition of PBA not only changes the size of?and?lattices,but also involves the adjustment or rearrangement of the molecular chains.?2?The addition of EDPO and TMC-328 NAs can greatly improve the thermal stability of PBA.There is a hydrogen bond interaction between the NAs and the PBA.The nonflammable gas generated after the high temperature degradation of the nitrogen-contained NAs,the concentration of other degraded flammable gases mainly from the PBA will be diluted by the above nonflammable gases.Moreover,the accumulated heat in the confined sealed chambers is helpful to generate the char with the higher heat-resistance and lower heat conductivity.These all enhanced thermal stability of the PBA.?3?Polyamide NAs are not conducive to the biodegradability of PBA.This is due to NAs increase the crystallinity of the PBA and hinder the contact of the PBA molecule with the esterase molecule.