Structure Design And Electromagnetic Shielding Application Of Polylactide-based Conductive Composites

Carbon filled conductive polymer composites(CPC)are recognized as one of the most promising electromagnetic interference(EMI)shielding materials.At present,most conductive polymer-based EMI shielding materials are concentrated on petroleum-based composite materials.To solve the problems of electromagnetic interference,severe environment and petroleum energy crisis caused by frequent use of electronic products,the development of bio-based EMI shielding materials is of great significance.Polylactide(PLA)is a kind of thermoplastic polyester material with biodegradable,good mechanical properties and sustainable development.But at the same time,it has the inherent shortcomings of brittleness,poor toughness,and low heat distortion temperature(HDT),especially when conductive nano-fillers are added,there are problems such as poor dispersion,and the mechanical properties become worse,which severely restricts its wide application.In response to the above requirements,this thesis mainly includes the following three parts of research:1.Preparation and characterization of multi-walled carbon nanotubes(MWCNTs-g-PDLA)grafted with poly(D-lactide)(PDLA)and its poly(L-lactide)(PLLA)composites.The grafting rate of MWCNTs-g-PDLA was 4.9%,and the molecular weight of the grafted chain was about 1029 g mol^-1.After grafting,the conductivity of the PLLA/MWCNTs composites increased slightly.Because the interface stereocomplex crystallization improves the dispersion of MWCNTs in PLLA,the lower grafting rate and molecular weight avoid the negative effects on electrical conductivity.2.Improving the mechanical properties and EMI shielding performance of PLLA composites through reactive blending and MWCNTs induced phase morphology optimization.Torque changes and FTIR indicate that the order of feeding MWCNTs and polyethylene glycol diacrylate(PEGDA)was critical.The addition of MWCNTs promoted the size reduction of CPEGDA domain,and MWCNTs were selectively distributed in the continuous phase of PLLA.Rheological tests show that CPEGDA and MWCNTs form a dual percolation network,which is a contribution to achieve the balance between stiffness and toughness.The selective distribution effect of MWCNTs appeared as a low percolation threshold with a conductivity of 0.19 vol%.The test results of the vector network instrument show that absorption was the main mechanism for the attenuation of electromagnetic waves in the ternary composite material.When2.4 vol%MWCNTs were added,the electromagnetic shielding efficiency reached 26.4d B.3.The effect of thermal annealing on PLLA/CPEGDA/MWCNTs ternary composites was studied and PLA composites with high heat resistance and toughness was obtained by adjusting the thermal annealing time.XRD showed that?'crystals were formed under thermal annealing conditions at 80 ^oC,and the crystallinity increased with the extension of thermal annealing time while the crystal form remained unchanged.The increase in crystallinity greatly increased the HDT of the composite material,but resulted in a decrease in tensile toughness.The conductivity test found that the conductivity of the composite material increased slightly after thermal annealing.When the thermal annealing time was 10 min,the composite material can obtain the best HDT(150 ^oC)and tensile toughness(15.1 MJ/m³),which were 3 and 6 times that of neat PLLA,respectively.