Study Of The Effect Of Nucleation Modification On The Crystallization Properties Of Poly-3-hydroxybutyrate

Poly-3-hydroxybutyrate(PHB)is a biodegradable polymer material synthesized by microorganisms.It has excellent biocompatibility and biodegradable properties,and is currently mainly used in the medical field,and is considered to be a promising biodegradable polymer material.However,the poor toughness,low strength,high cost and poor processing performance of PHB lead to a certain degree of limitation in its application in daily life.the disadvantages of PHB mechanical properties mainly come from its low nucleation density and large spherical crystal size,so it needs to be modified by nucleation.Therefore,it is necessary to characterize the crystalline morphology and crystallization kinetics of PHB when different nucleating agents are added,as well as to explore the effects on the crystalline morphology,mechanical properties and heat resistance of PHB when nucleating agents and plasticizers are used simultaneously.In this thesis,PHB/nucleating agent and PHB/nucleating agent/plasticizer modification systems were produced by solution film formation and melt blending methods,and the effects of changing the aggregation structure of PHB on the crystalline morphology,non-isothermal crystallization kinetics,isothermal crystallization kinetics and mechanical properties of PHB were investigated.First,the PHB/TMC composite system was prepared by the solution film formation method,and the effects of TMC-300 nucleating agent and TMC-306 nucleating agent on the crystallization properties of PHB were investigated.The experimental results showed that both nucleating agents could significantly reduce the nucleation time of PHB crystallization,increase the nucleation density of PHB,reduce the size of spherical crystals,increase the crystallization temperature of melt crystallization,and improve the crystallinity.However,when the addition amount of both nucleating agents exceeded 1%,the promotion effect of nucleating agents on PHB crystallization no longer increased with the increase of the amount of nucleating agents.At the same time,there are some differences between the two nucleating agents on the promotion effect of PHB crystallization,and overall the promotion effect of TMC-300 nucleating agent on PHB crystallization is better than that of TMC-306 nucleating agent.In addition,the ring band of PHB spherical crystals disappeared after adding TMC-300 nucleating agent;the phenomenon of melt recrystallization existed at the second temperature rise,and the melting temperature was reduced;the optimal temperature for PHB spherical crystal growth was not changed by the two nucleating agents,but TMC-300 nucleating agent would reduce the growth rate of PHB spherical crystals when the crystallization temperature was lower than the optimal temperature for spherical crystal growth.The tests showed that there might be some hydrogen bonding between the functional groups on the two nucleating agents and the functional groups on the PHB molecular chain,but the two nucleating agents did not change the crystalline shape of PHB.Secondly,the PHB/BN composite system was prepared by the solution film formation method.The effect of BN on the morphology of PHB spherical crystals was observed by polarized light microscopy(POM)for the first time,and the observation results showed that the addition of 0.01% BN did not affect the growth rate of PHB spherical crystals,and the PHB spherical crystals also remained as ring-banded spherical crystals.However,0.01% BN can effectively promote the nucleation process of PHB crystallization,reduce the nucleation time,increase the nucleation density,and reduce the size of spherical crystals.In addition,the addition of BN caused the melt recrystallization of PHB at different heating rates with a certain regularity as the cooling rate increased.BN could improve the crystallinity of PHB up to about 26%.The test shows that BN does not change the crystallinity of PHB.Finally,the PHB/TMC/plasticizer composite system was prepared by melt blending method.It was observed by POM that the ring band of PHB spherical crystals disappeared after the addition of ESO.In addition,although the addition of ESO could increase the crystallization temperature of PHB to some extent,its addition would not only decrease the crystallinity of PHB,but also reduce the promotion effect of BN on the crystallization of PHB.Vicat softening temperature(VST)tests and mechanical property tests showed that annealing as well as BN addition could improve the VST,tensile strength,and elongation at break of PHB.However,after the addition of ESO,the VST and tensile strength of PHB decreased,and the higher the addition of ESO,the more the VST and tensile strength of PHB decreased.Meanwhile,the addition of ESO increased the number of micropores in PHB,and the number of micropores increased with the increase of ESO addition,and the addition of annealing and BN could reduce the number of micropores to some extent.the addition of BN and ESO did not significantly change the thermal degradation properties of PHB,and did not cause the change of PHB crystalline shape.