Construction Of Nano-reinforced And Heat Conduction Networks In Polymer Matrix Composites And Study Of Their Structure And Properties

Nano-functional network filling technology is an important way to achieve high performance and multifunction of polymer composites and has broad application prospects.The continuous nano-functional network is an independent phase unto itself in the polymer matrix,continuous at both micro and macro scales.The nano-functional network further interacts with the polymer matrix to form an interpenetrating network structure,which will enable the nano-fillers to greatly perform their functions of stress transmission,stress bearing,and information transmission in the polymer matrix.However,there is still a lack of systematic theoretical basis on the reinforcement and functionalization mechanisms of the continuous nano-functional network in polymer.By studying and clarifying these issues,it can effectively guide the improvements of the performance and product quality for polymer composites and better expand their application fields.Based on the surface modification and in-situ coating of nano-fillers,some in-situ constructions of nano-functional networks in polymer matrices were achieved by melt blending or solution blending.The construction principles,reinforcement and thermal conduction mechanisms of nano-functional networks were further clarified.The main research contents of this work are as follows:(1)Based on the secondary dispersion technology of masterbatch melt blending,a graphene micro-crosslinked network was in-situ constructed in thermoplastic polyurethane(TPU)by the strong interaction(hydrogen bond,acid-base ion pair)between TPU and functionalized graphene(FGr).Due to the multiple functions of FGr-micro-crosslinking,isolation and induced crystallization,FGr micro-crosslinking network has an important influence on the rheological properties,crystallization properties,mechanical properties and shape memory properties of composites.Compared with pure TPU,the tensile strength of composite containing 0.5 wt%FGr increased by 139%,and its shape fixing rate and shape recovery rate reached 96.0%and 94.0%respectively.(2)By using the strong interaction between the surfaces of cellulose nanocrystals(CNC),a 3D CNC network with sea urchin-like CNC nanoclusters as nodes and radial CNC nanofibers as connecting structures was in-situ assembled in polyurethane(PU).Through the interpenetrating of PU network and CNC network and their interactions(hydrogen bond,acidbase ion and induced crystallization),the reinforced structure of interpenetrating-network-like structure(IPNL)is further constructed and has significantly improved the mechanical and shape memory properties of composites.Compared with pure PU,the tensile strength and elongation of the composite containing 1.0 wt%CNCs increased by 186%and 15%respectively,and its shape fixing rate and shape recovery rate reached 96.7%and 92.6%respectively.Because the continuity of nano-reinforced network is further improved,the reinforcement effect of 3D CNC network on PU-based composites is better than that of FGr micro-crosslinked network.(3)Polyamide 12 composites were prepared by double doping technology and uniaxial stretching process with graphene and carbon nanotubes.During tensile deformation,with the help of the mutual contact,coating and entanglement of carbon nanotubes and graphene caused by their spatial deformation and relative displacement,a nano-carbon network with carbon nanotubes as the skeleton and the contact point of graphene winding carbon nanotubes as the node was in-situ constructed in the composite.Due to the heterogeneous nucleation of nanocarbon filler and the influence of tensile orientation,the crystallinity of polyamide 12 is increased,the crystalline orientation degree is improved and the grain size is refined,coupled with the formation of whole continuous nano-carbon network,the mechanical strength of the composite is greatly improved.When the content of graphene and carbon nanotubes is 0.3 wt%,the tensile strength of the composite reaches 509.21 MPa,which is 11.73 times that of polyamide 12 and 7.83-folds that of corresponding unoriented composite.(4)A PU composite filled with self-assembled BN nano-plates(BN micro-plates)was prepared by solution mixing method using π-π interaction between surfaces of BN nano-plates.On this basis,the composite was multi-calendered to promoted the stacking,orientation and connection of BN micro-sheets,thus a 3D BNNS network with in-plane oriented layered BN as the skeleton and non-oriented BN micro-sheets as the connection structure was formed.The 3D BNNS network can be used as the heat conduction channel of the composite and significantly improve the heat conduction and heat dissipation performance of the composite.When the content of BNNS is 50 wt%,the in-plane thermal conductivity of the composite is as high as 23.8 W/(m K),and the through-plane thermal conductivity is still higher than that of corresponding uncalendered composite.The infrared thermal imaging test shows that the surface temperature of the composite is about 20 ℃ lower than the heat source temperature.In addition,when the content of BNNS is 30 wt%,the in-plane thermal conductivity of the composite is 7.7 W/(m K)and it has outstanding mechanical flexibility and insulation.After being folded for 1000 times,its mechanical properties and thermal conductivity only slightly decrease,and its volume resistivity is higher tha 1×1012Ω/cm.