Construction Of The Mutli-interfaces In UHMWPE Composites And Study On Their Electromagnetic Shielding Performance And Mechanism

The development of electromagnetic shielding composites（ESCs）is an important means of solving the electromagnetic pollution problems.Multi-interfacial structure conductive polymer composites（CPCs）have attracted extensive attention because of their flexible structure design and adjustable electrical conductivity.However,CPCs usually have low electrical conductivity,low thermal conductivity,and poor mechanical properties,which seriously hinder their application and development in the field of electromagnetic shielding.Therefore,Regulating the dispersion and distribution of conductive fillers,improving the interaction between conductive fillers and polymer matrix,and constructing a perfect conductive network become the key to the research and development of polymer-based electromagnetic shielding composites（PESCs）.In this study,ultra-high molecular weight polyethylene（UHMWPE）was used as the matrix material,polypropylene（PP）and ground tyre rubber powder（GTR）were used as auxiliary phases,and conductive carbon black（CCB）,branched carbon nanotubes（CNS）and hollow glass microsphere（HGM）were utilized as functional fillers.Based on the volume-exclusion effect,crystal volume repulsion effect and in-situ induced orientation effect,the distribution and dispersion of functional fillers were regulated.High specific surface conductive carbon black（h-CCB）,solid-phase shear milling equipment（S³M）and polydopamine（PDA）surface modification were used to improve the interfacial interaction between conductive fillers and UHMWPE matrix.The segregated structure,oriented segregated structure and micro-scale interfaces were constructed in the UHMWPE matrix to enhance the electromagnetic interference shielding effectiveness（EMI SE）and mechanical properties of the composite,and the UHMWPE composite with the functions of electrically conductive,thermal conductive and electromagnetic shielding was prepared.The influence of microstructure on the EMI SE,electrical conductivity,interfacial bonding mechanism,thermal conductivity and mechanical properties of composites were investigated.The percolation behavior of EMI SE,and the electromagnetic shielding mechanism of composites were discussed.The relationship between the electrical conductivity（σ）and EMI SE of composites was also established.The main research contents and conclusions are as follows:Firstly,high-specific-surface-area conductive carbon black（h-CCB）and low-specific--surface-area conductive carbon black（l-CCB）are used as conductive fillers to prepare UHMWPE/h-CCB and UHMWPE/l-CCB composites by mechanical blending and molding technology,and the effects on their EMI SE and mechanical properties were studied.The results showed that the construction of h-CCB dense segregated conductive network has a significant contribution to the electrical conductivity（σ）,electromagnetic parameters and EMI SE of the composites.The EMI SE value of 10 wt%h-CCB composite is 22.3 d B,and the microwave attenuation rate is 99%.The EMI SE value of the composite containing 10 wt%l-CCB is only 5.6 d B.In addition,the tensile strength and elongation at break of 15 wt%h-CCB composite are 32.1 MPa and 185%,respectively,which were much higher than those containing 15 wt%l-CCB.Meanwhile,the tensile specimen morphology,crystallization properties and thermal stability of the composites showed that there is a strong mechanical interlocking effect between h-CCB and UHMWPE matrix.Secondly,the conductive carbon black（CCB）particles were blended with UHMWPE/PP（UP 95 wt/5 wt）,and the UHMWPE/PP/CCB（UPC）composite was prepared by molding method.The distribution of CCB was controlled by the volume repulsive effect of the UP phase in the composites,and the organic-inorganic hybrid conductive interfacial structure was constructed.The results of infiltration coefficient prediction,SEM and Raman mapping analysis indicated that CCB particles are mainly distributed in the PP phase of composites,and the organic-inorganic hybrid structure of CCB-PP is formed at the interface of the UHMWPE microregion.When CCB content is 13wt%,the EMI SE of the composite is 27.29 d B,and the microwave attenuation capability is 99.4%.The formation of continuous PP-CCB hybrid segregated conductive pathways and high electrically conductive interfacial structure can effectively improve the EMI SE of the composite.At the same time,UPC composites have good tensile properties,wear-resistance,and thermal stability,which is mainly attributed to the strong interfacial interaction between CCB and matrix.Thirdly,the UHMWPE/GTR blend is used as the matrix to regulate the distribution of CCB through the phase transition mechanism of sea island-two continuous phase structure in the blend.The UHMWPE/GTR/CCB（UGC）composites with double-percolation and segregated structure was constructed by solid-phase shear milling（S³M）and mechanical blending and molding processes,the percolation behavior of EMI SE of UGC composite system was described by Sigmoidal/Growth models,and the shielding mechanism of the composite was discussed.The results showed that when CCB content is 16.67wt%,the EMI SE of U₃₀G₇₀C₂₀,U₅₀G₅₀C₂₀ and U₇₀G₃₀C₂₀ composite materials are 37.5d B,41.7d B and 43.8d B,respectively.The attenuation rate of microwave radiation is above 99.99%,and the shielding mechanism is mainly electrical loss.The basic functional relationship betweenσand EMI SE of the prepared composites is consistent with Sigmoidal/Growth models,and the percolation threshold range is 10-15 phr,indicating that Sigmoidal/Growth models can successfully predict the percolation threshold of the EMI SE of UGC composites.This can provide technical guidance for transforming GTR into flexible electromagnetic shielding composites.Fourthly,UHMWPE/CNS（UC）composite with micro-zone oriented segregated structure was constructed by mechanical blending and molding technology,and the influence of micro-zone segregated structure on EMI SE,thermal conductivity and mechanical properties of the composite was studied.The results showed that the EMI SE,thermal conductive performance and mechanical properties of UC composites were significantly improved by the construction of microzonal oriented segregated structure in-situ.When the content of CNS is 10 wt%,the EMI SE value of UC composite is 64.5 d B and the thermal conductivity is 0.7217 W/m·K,which is 1.5 times that of pure UHMWPE.Meanwhile,the tensile strength of the composite remains at 37.6 MPa.This is because the structure of the CNS conductive layer in the microzonal orientation structure in-situ is similar to"cell walls"and has an"electromagnetic cage"effect,which enhances the multiple reflection and absorption loss of electromagnetic waves.These obtained results demonstrate a simple and effective method for the design and preparation of high-performance dual-functional composites.Lastly,the lightweight ESCs with low conductive fillers loadings were constructed by introducing hollow glass microsphere（HGM）or polydopamine-modified hollow glass microsphere（PDA@HGM）particles based on the concept of"microscopic interfaces"and"interface polarization multi-loss compound mechanism".The results showed that when the amount of HGM or PDA@HGM is 5wt%and the content of CNS is 5wt%,the EMI SE of UC/HGM and UC/PDA@HGM composites is 44.7 d B and 49.8 d B,respectively,and the attenuation capability of microwave radiation is 99.999%.Due to the formation of microscopic interfacial structure of the"point-plane"synergistic effect,HGM and PDA@HGM can be used as interface polarization centers and scattering centers to enhance the absorption loss caused by multiple reflections/scattering of electromagnetic waves.Moreover,the mechanical properties and EMI SE of UC/PDA@HGM composites are higher than those of UC/HGM composites,realizing excellent EMI SE and good mechanical properties of composites in a low content conductive continuous phase.