Research On Preparation And Electromagnetic Shielding Performance Of Conductive Polylactic Acid Based Composite

In recent years,polylactic acid(PLA)has become a popular material due to its biodegradable properties,and PLA itself has good processability and mechanical strength.At present,the increasingly developing trend of PLA has become more and more importantly,which can not only retain the excellent characteristics of PLA itself,but also significantly improve its shortcomings.Multi-walled carbon nanotubes(MWCNTs)and graphene(GNPs)Modification of PLA to produce conductive polymer components has also become a research focus.In this paper,PLA was used as the matrix and cellulose nanocrystals(CNC)as the second phase.The PLA was first modified by CNC.On this basis,the conductive particles MWCNTs and GNPs were prepared by Pickering emulsion method to prepare two kinds of two kinds of MWCNTs/CNC/PLA and GNPs/CNC/PLA conductive composite materials,in order to reduce the percolation threshold of composite materials and obtain high electromagnetic shielding performance for the PLA-based composites.The research contents are as follows:(1)For the PLA modified with the CNC,the effects of CNC on the mechanical properties and crystallization properties of PLA were studied,and the optimal solution of CNC content was also found to lay a good foundation for subsequent experiments;(2)For the MWCNTs/CNC/PLA composite conductive particles was first prepared via Pickering emulsion method,and then the conductive particles and PLA was melt-mixed to observe whether the expected CNCentangled MWCNTs was formed by POM.And the morphology of the CNC-hybrid MWCNTs was further studied.Effects of the coating structure of PLA after melt-mixing on the crystallization,thermal,electrical and electromagnetic shielding properties of MWCNTs/CNC/PLA conductive composites were studied;(3)GNPs/CNC/PLA conductive masterbatches were prepared by Pickering emulsion method,and then GNPs/CNC/PLA conductive masterbatch and PLA was prepared by melt blending method.the effects of this hybrid GNPs/CNC/PLA masterbatches on the crystallization,thermal,electrical and electromagnetic shielding properties of GNPs/CNC/PLA conductive composites was studied in depth.The results show that adding an appropriate amount of CNC to PLA can improve the crystallization properties of PLA.When 5.0 wt% CNC was added to PLA,the thermal stability was the best;when 3.0wt% CNC was added to PLA,the tensile strength of the composite improved.The tensile strength was as much as 21.18 % higher than that of pure PLA,and the elastic modulus of 7.0 wt% CNC/PLA composite was 26.42 % higher than that of pure PLA.The MWCNTs/CNC/PLA composite conductive particles were prepared by the Pickering emulsion method.It was found that with the help of the Pickering emulsion method,the CNC hybridization of MWCNTs with different contents was successfully realized,and the PLA was coated.The typical percolation threshold formula was calculated.It can be concluded that the percolation value of the MWCNTs/CNC/PLA conductive composite was 0.5 wt%;when the content of MWCNTs added to PLA was1.0 wt%,the electromagnetic shielding efficiency of the MWCNTs/CNC/PLA conductive composite reached the commercial electromagnetic shielding efficiency.After comprehensive analysis of its mechanical properties,it is found that the tensile strength of MWCNTs/CNC/PLA composites was the best when the addition of MWCNTs was 1.5 wt%,which is 26.08% higher than that of pure PLA;When the addition amount of MWCNTs was 2.0 wt%,the elastic modulus of the MWCNTs/CNC/PLA composite was 32.28 % higher than that of pure PLA;when the addition amount of MWCNTs was 0.7 wt%,thermal stability was the the optimal.The optimal crystallinity of CNC/PLA composites is 18.01 % higher than the peak value of pure PLA when the addition of MWCNTs was 2.0 wt%.The GNPs/CNC/PLA conductive composites were prepared by the Pickering emulsion method,and the percolation value of the GNPs/CNC/PLA conductive composites was calculated by the typical percolation threshold formula to be 1.5 wt%;when the GNPs content was 4.0 wt%,The electromagnetic shielding effectiveness of the GNPs/CNC/PLA conductive composite reached the commercial electromagnetic shielding standard.The optimum tensile strength of GNPs/CNC/PLA composite is 6.23%higher than that of pure PLA when the GNPs content is 1.0wt %,The optimal value of elastic modulus appeared when the GNPs dosage reached 4.0wt %,which was 32.96%higher than that of pure PLA.When the addition amount of GNPs reached 1.5 wt%,the thermal stability of the GNPs/CNC/PLA conductive composite was the best;the crystallinity of the GNPs/CNC/PLA conductive composite reached the optimal value when the addition amount of GNPs was 2.0 wt%,it was 14.17% higher than pure PLA.