Study On Crystallization Kinetics Of Biodegradable Aliphatic Polyester

Nowadays,poly(glycolic acid)(PGA)and poly(butylene succinate)(PBS)are crystalline polymers,but there is a great difference in terms of crystallization rate with each other due to their molecular chain structure and crystallization condition.Therefore,the exploration on crystallization kinetics of PGA and PBS contributes to adjust the procedure of crystallization in industrial processes,which achieves the purpose of improving the property of products.It is of great practical significance and theoretical value to research specific processing and practice application.For PBS produced by various manufacturers,the interaction of components brought by different processing techniques has some effect on the crystallization property of the PBS base,influencing the macro performance of materials.In this dissertation,the thermal crystallization behaviors of laboratory-made PGA and PBS produced by BASF and Showa were investigated by differential scanning calorimetry(DSC).The equilibrium melting points of these polymeric materials were obtained by Hoffman-Weeks Equation.Their crystallization kinetics were analyzed by Avrami Model,and the related kinetic parameters of thermal crystallization were calculated accord to the above equation.The result indicated that the Avrami index of laboratory-made PGA and PBS produced by BASF and Showa was distributed between 3 and 4,which demonstrates that they were spherical crystals with three-dimensional growth.The elevating temperature in a certain range of temperatures had an impact on the process of their crystal growth and changed their crystallization behaviors,obviously,which led to the increase of crystallization rate and was beneficial to the occurrence of crystallization.Meanwhile,the non-isothermal crystallization process of laboratory-made PGA and PBS produced by BASF and Showa was analyzed by Avrami Model modified by Jeziorny Model,Ozawa Model,Mo Model,and the related kinetic parameters were calculated.Eventually,the activation energy of their crystallization process was obtained by Kissinger Equation.The result indicated that the modified Avrami index demonstrated that they were spherical crystals with three-dimensional growth,which corresponded to the above conclusion analyzed by thermal crystallization.The gradual decrease of the cooling rate resulted in an increase of regularity about the arrangement of the crystal nucleus.This phenomenon acted as nucleating agents,causing an acceleration of the growth rate of the crystal nucleus and improve the crystallization of polymers.At the same time,a subtle difference in molecular weight and structure existed in products from various manufacturers,which is the reason of imparity in activation energy measured in the end.Finally,PBS produced by BASF and Showa were treated by Self-nucleating(SN)to determine their ideal self-nucleating temperature.Then,Successive Self-nucleating and Annealing(SSA)was designed according to the above ideal self-nucleating temperature,and thermal fractionation and analysis on results were carried out.The result indicated that PBS produced by BASF and Showa showed excellent thermal fractionation.