Synergistic Tailoring Of The Crystallization And Dielectric Properties For Poly(Lactic Acid) And Its Blends By Ionic Liquid And Graphene

In this paper,the graphene(Gra)modified by ethoxycarbonyl ionic liquid(IL)and IL copolymer were mixed with poly(lactic acid)(PLA)though the solution blending and hot-pressing methods.The effect of modified Gra on PLA crystallization was investigated by crystallization kinetics.Meanwhile,the variation of dielectric behavior of PLA composites was studied by broad dielectric spectroscopy.In addition,the PLA and polycaprolactone(PCL)blends were prepared by solution blending and investigated the effect of IL copolymer on morphological evolution and dielectric polarization of PLA/PCL blends.The paper research includes three parts mainly:(1)For PLA/IL/Gra system,POM result shows that the samples contained IL can accelerate the growth rate of spherulites for PLA,Gra as a good nucleating agent during the isothermal crystallization.DSC result shows that PLA/IL/Gra has the faster crystallization rate than PLA/2Gra at 130℃,which might be attributed to the Gra-imidazolium cation interaction between IL and Gra,increasing the nuclei density of PLA/IL/Gra at high temperature.Dielectric measurements show that PLA/IL/Gra and PLLA/2Gra have the same relaxation strength and time of the αn relaxation that corresponds to the longest normal mode motion at 110-140℃ and 2Gra of PLA/2Gra has the same effect on chain movement as IL/Gra of PLA/IL/Gra.(2)For PLA/P[MPEGMA-IL]/Gra system,TEM and SEM results show that Gra was modified by P[MPEGMA-IL],and P[MPEGMA-IL]can improve the dispersion of Gra in PLA matrix.The crystallization rate of PLA composites were increased with increasing the content of P[MPEGMA-IL]and Gra due to the plasticizing effect of P[MPEGMA-IL]and the nucleating effect of better-dispersed Gra.In the frequency spectra of PLA composites,a relaxation and interfacial polarization resulted in high values of dielectric permittivity.The incorporation of modified Gra into the matrix can accelerate interfacial polarization through cold crystallization process.The effect of modified Gra on charge carrier movement was resulted from the increase of the mobile charge carriers at the interphase and the dielectric strength of interfacial polarization.(3)For PLA/PCL/P[MPEGMA-IL]system,the DSC result shows that P[MPEGMA-IL]has a great influence on the crystallization of PCL phase,P[MPEGMA-IL]has a great influence on the crystallization of PCL phase,this indirectly proves that P[MPEGMA-IL]mainly dispersed in PCL phase.SEM graphs indicate that the "sea-land" phase sturcture of blends transformed into co-continuous phase morphology.The increasing content of P[MPEGMA-IL]result in an increase of dielectric loss of blends,whose values are higher than that of PLA/PCL blend at low frequencies.This property is related to the number of the mobile charge carriers at the interphase and increase the dielectric strength of MWS polarization.Comparison with PLA/PCL/4P[MEGMA-IL],the σac of PLA/PCL/8P[MEGMA-IL]was much higher at lower frequency,which due to increase of ion mobility induced by polymer chain segmental motion at interphase.