Dispersion Structure Of Silicon Carbide Micron-wires And Graphenes In Poly (Propylene Carbonate) And Their Composites

It has been of vital importance to effectively improve the mechanical and thermal properties of poly(propylene carbonate)(PPC)and simultaneously endow PPC with functionality for expanding its potential applications.Compounding with functional fillers is an effective approach to modify polymer materials.However,the weak interfacial interaction between PPC and fillers leads to a serious agglomeration of the fillers and poor functionality in the composites.In the dissertation,silicon carbide microwires(SiC)and graphene were used as fillers and the PPC-filler dispersion structures were optimized by stretch-induced alignment process and construction segregated structure and hybrid system in PPC.It emphasized the research of the mechanical,thermal properties and thermal conductivity of the PPC-based composites.The main work includes the following aspects:(1)The PPC/SiC composites with the uniformly dispersed and aligned structure(PPC/SiC-a)were prepared by the stretch-induced alignment and thermal laminating process.The relationship between the stretch ratio and the dispersion and orientation of SiC,and their effects on the mechanical,thermal properties and thermal conductivity of PPC/SiC-a composites were discussed.The results showed that SiCs are highly aligned in the PPC matrix at the stretch ratio of 200%,the dispersion of the composites is also effectively improved.At the 15 wt%loading of SiCs,the tensile strength and Young’s modulus of the PPC/SiC-a composites are respectively increased by 112.1%and 456.2%comparing with those of PPC.Since the aligned structure reduces the free volume in composites and restrict the mobility of PPC segments,the PPC/SiC-a composites show slightly higher T_gthan the random PPC/SiC composites(PPC/SiC-r)with same loading.At 5 wt%loading,T_gof the PPC/SiC-a composite increases to 33.7℃,which is 33.2%higher than that of PPC.Meanwhile,the aligned SiCs construct a continuous thermal conductive network along their axis direction,so the thermal conductivity percolation thresholds and interfacial thermal resistance of the PPC/SiC-a composites respectively decrease by 5 wt%and 50%as compared to PPC/SiC-r composites.At 50 wt%loading,the thermal conductivity of the PPC/SiC-a composite increases to 1.22 W/m K,and is 454.5%higher than that of PPC.The stretch-induced alignment process is proven to be efficient and energy saving,which can also be applied in polymer composites with inert 1D or 2D fillers.(2)The PPC/reduced graphene oxide(RGO)composites with the segregated structure(PPC/RGO-s)were prepared by the emulsion method combined with in-situ reduction and hot pressing process,and the dispersion of RGO was effectively improved.The relationship between the dispersion structure and the mechanical and thermal properties as well as the thermal and electrical conductivity of the PPC/RGO-s composites were investigated.It was found that the rigid RGOs form a continuous and regular 3D network in PPC matrix,which effectively improves the mechanical properties of PPC/RGO-s composites.At the content of10 wt%RGOs,the tensile strength and modulus of the PPC/RGO-s composite are respectively increased by 51.6%and 100%as compared to PPC.Since the RGO networks efficiently restrict the mobility of PPC segments,the PPC/RGO-s composites have better thermal resistance than the random PPC/RGO composites(PPC/RGO-r).At the content of 5wt%RGOs,T_g of the PPC/RGO-s composite is respectively 11.6℃and 2.4℃higher than those of PPC and PPC/RGO-r composite.Moreover,the RGO networks reduce the thermal and electrical conductivity percolation thresholds in the PPC/RGO-s composite,and significantly improve the thermal and electrical properties of the composites.At the content of 30 wt%RGOs,the thermal and electrical conductivities of the PPC/RGO-s composites increase to 0.35 W/m K and 33.4 S/m,respectively.Besides,the continuous RGO networks provide the high electromagnetic interference shielding properties and UV light resistance with PPC,which extend the service life of PPC based composites.(3)Through facile hybridization of SiC and graphene oxide(GO),the uniformly dispersed PPC/SiC-GO composites were prepared.The effects of SiC and GO hybrid mass ratio on the dispersion of SiC,the relationship between the dispersion structure of SiC-GO hybrid and the mechanical,thermal properties and thermal conductivity of PPC-based composites were investigated.It was found that the hydrogen bonding exists between the hydroxylated SiC and GO.The SiC-GO hybrids form a scroll-like structure with SiC as axis and GO as coating layer when the mass ratio of SiC to GO is less than 1,and can be stably dispersed in water and uniformly dispersed in PPC matrix.Meanwhile,the SiC-GO hybrid structure has strong interfacial interaction with PPC,which the composites show the excellent performances,such as the thermal,mechanical,barrier,shape memory properties and thermal conductivity.At the loading range of 0.1-3 wt%,the PPC/SiC-GO composites have higher T_g than PPC/SiC composites.Especially,T_g of the PPC/SiC-GO composites with 0.5 wt% loading increases to 34.6℃,and is 36.2%higher than that of PPC.Besides,the reinforcement and toughening of the PPC-based composites are simultaneously realized at0.1 wt%loading of SiC-GO hybrids.