Effects Of Shear On Epitaxial Crystallization Of Poly(?-caprolactone) On Reduced Graphene Oxide

Polymer nanocomposites are new materials with excellent properties by adding nano-particles or nano-structured materials into polymer materials by means of melt blending,solution blending or in-situ polymerization.Polymer nanocomposites are composite materials prepared by adding polymer as matrix materials,and are common techniques for preparing high-performance polymers.Polymer materials are affected by the flow field during processing,and the applied external field has a great influence on their structure and performance.In this dissertation,poly??-caprolactone?/graphene composites are mainly used as the research object,which are using in-situ SAXS,in-situ WAXD,rheology measurement and DSC.The effect of shear on its crystalline structure and surface bonding force was studied.Static analysis of the crystallization behavior of 30°C isothermal crystallization of PCL/0.5wt%RGO nanocomposites after shear at shear rates of 3 s^-1 and 75 s^-1 with shear temperatures of65°C,70°C and 75°C.The experimental results show that the shear rate of 3 s^-1 is better than the shear rate of 75 s^-1 for PCL chains to epitaxially crystallize on RGO surface at given shear temperatures.After at the shear rate of 3 s^-1,the shear temperature of 75°C is more suitable for PCL chains than the temperature of 65°C and 70°C.However,after shear at the shear rate of 75 s^-1,the shear temperature of 70°C is more suitable for PCL chains on RGO surface than the temperature of 75°C and 65°C.In-situ analysis of the crystallization behavior before and after shear at shear rates of 3 s^-1 and75 s^-1 with shear temperatures of 65°C,70°C and 75°C.The experimental results show that the crystalline structure of PCL/RGO nanocomposites does not change from 40 s to 120 s after shear.At 160 s,PCL chains complete epitaxial crystallization on the surface of RGO,forming a surface crystal layer.From 200 s to 480 s,the crystalline structure of PCL tends to be complete,and the long period decreases as the crystallization time increases.The thickness of lamella,crystallinity,the orientation degree of the?110?plane increase with the crystallization time.PCL/0.5 wt%RGO nanocomposites after shear at the shear rate of 3 s^-1,the shear temperature of 75°C is more suitable the PCL molecular chains to transform from the random coil to the surface of RGO to form the surface crystal layer.And after at the shear rate is 75 s^-1,the shear temperature of 70°C is more conducive to the degeneration of PCL chains on the surface of the RGO.This is because the return of the stretched chain to the random coil is not conducive to the formation of surface crystalline layer on RGO surface by the PCL chains.In summary,the imposed shear field can make the PCL chains better epitaxially crystallize on the RGO surface,forming surface crystal layer,and then affect the surface binding force.A lower shear rate requires a higher shear temperature,while a higher shear rate does not require a higher shear temperature for the PCL molecular chain to epitaxially crystallize on RGO surface.