Preparation Of PP-based Segregated Structured Conductive Composites And Its Properties By Pressurization Method

Conductive polymer materials(CPCs),which combine the excellent properties of polymer materials,and conductive fillers,are widely used in electromagnetic shielding,sensors,flexible electronic materials,and antistatic materials,and thus have received focused attention from scholars.Conductive polymer composites(s-CPCs)with an isolated structure can achieve high electrical conductivity and electromagnetic shielding performance at low filler loading due to the selective distribution of conductive fillers inside the conductive network.In order to make s-CPCs exhibit comprehensive performance at low permeation values,it is often necessary to change the matrix of s-CPCs or select high-performance conductive fillers,and new preparation methods are being proposed and optimized.There is still room for improvement in heat pressing as a commonly used method for preparing s-CPCs.This work focuses on the following two points:(1)the mechanical properties of s-CPCs materials prepared by conventional hot pressing are generally poor,especially the toughness needs to be improved,which greatly limits the application of s-CPCs materials;(2)the influence of hot pressing process(including:temperature,pressurization rate,pressurization pressure)on the structure and properties of s-CPCs products needs to be further clarified,so as to further improve the hot pressing molding process.We investigated the effects of hot pressing process parameters on the structure and properties of iPP-based s-CPCs using a controlled variable speed pressurization device,and prepared iPP/MWCNTs conductive polymer products with excellent mechanical properties.In order to enhance the electromagnetic shielding performance of iPP/MWCNTs,we further introduced the two-dimensional conductive filler GNP and investigated the effect of the synergistic effect of onedimensional filler MWCNTs and two-dimensional filler GNP on the structure and properties of s-CPCs,and the main research results are as follows:1.Preparation of isolated structure iPP/MWCNTs composites and properties of products by pressurization method(1)The effects of pressurization temperature and pressurization pressure on the structure and properties of composite products.Constant pressure,as the temperature increases,the viscosity of the iPP matrix decreases,the MWCNTs are more likely to diffuse in the matrix,the formation of the conductive network appears in a wide range of agglomeration phenomenon,and the conductivity of the composite material decreases;when the temperature is constant,as the pressure increases,the formation of the conductive network is more compact,but too high a pressure will make part of the MWCNTs diffuse into the interior of the iPP matrix,resulting in the destruction of the conductive network,so that The conductive properties are reduced.In comparison,the best conductive properties of iPP/MWCNTs composites were obtained at a pressurization temperature of 180°C and a pressurization pressure of 100 MPa,and the overpermeability value of the samples was 0.73 wt%,which was much lower than that of the same samples prepared by conventional hot pressing.(2)The effect of pressurization rate on the structure and properties of the product.When the pressurization rate was 5 MPa/s,the agglomeration of MWCNTs appeared in the products,and as the pressurization rate increased,the agglomeration diminished and the formation of conductive network became more and more perfect,while the conductivity of the products was enhanced and the EMI shielding performance was improved.The EMI SE of the 2.5 wt% iPP/MWCNTs composites was 27.3 d B when the pressurization rate was increased to 20 MPa/s and elongation at break was up to273%.(3)WAXD analysis shows that the crystal structures of iPP are different at different pressurization rates,and the iPP of conventional hot press molded products are usually α-crystals,which have high strength but poor toughness.In this experiment,when the pressurization rate was 5 MPa/s,γ crystals with iPP started to appear in the sample,and the sample was mixed with α and γ crystals at this time.With the increase of the pressurization rate,the complete γ-iPP structure was formed at 20 MPa/s,and the crystallinity was 35.8%.γ-iPP has good mechanical properties.Therefore,the mechanical properties of the isolated structure iPP/MWCNTs composites were greatly improved.The above experiments show that changing the pressurization rate can modulate the crystal structure of iPP-based conductive composites and thus improve the comprehensive properties of the products.2.Preparation and properties of isolated structured iPP/GNP/MWCNTs composites(1)Based on the previous part of the work,the processing parameters for the preparation of ideal iPP-based s-CPCs were obtained by optimizing the hot press molding process,and the two-dimensional filler GNP with better electrical conductivity was selected to successfully prepare iPP/GNP composites with isolated structure by the pressurization method,and the overpermeability value was 0.13 wt%.(2)MWCNTs were introduced into the iPP/GNP composite system,and the effects of different mixing ratios of MWCNTs/GNP on the structure and properties of the composites were investigated.As the mixing ratio of MWCNTs and GNP increased,the addition of MWCNTs strengthened the connection with GNP and reduced the gap between GNP and iPP matrix,and the conductivity,electromagnetic shielding properties,and mechanical properties of the composites were improved.The EMI SE of iPP/GNP/MWCNTs was as high as 43.9 d B and the elongation at break was 233%at a mixing ratio of 4/10 with a total filler content of 2.5 wt%.Moreover,the composite system intrinsic filler GNP/MWCNTs and pressure both promote the formation of γ-iPP by WAXD and DSC,and iPP-based s-CPCs with high electromagnetic shielding properties and excellent mechanical properties are prepared.