Controlled Preparation And Adjusting The Properties Of Lightweight Polymer Composites With Their Versatile Applications

In comparison with general metal or inorganic materials,polymers are lightweight,flexble and feasible of processing.To meet the developing and different requirments of applications,thermoplastic commen polymers?polyolifens and thermoplastic elastomers?have been catering to lightweight composites with controllable structure,adjustable properties and outstanding functions.As there have been highlighted and frontier researches on polymer processing,especially sound insulation and piezoresistivity,the thesis studied lightweight polymer composites,involving thermoplastic polymer and inorganic micro-/nano-particles.In order to achieve excellent sound insulation or piezoresistivity,the dissipation and orientation of micro-/nano-particles are pivotal to controlling the morphology of composites,and supercritical fluid foaming can be essential for optimizing the functions.Furthermore,we studied the injection foaming of commen polypropylene with in-situ fibrillation strucutures,aiming to lightweight and high-performance polymer composites employed in vhiecle industry.1.In this thesis,flexible thermoplastic elastomer?TPE?and inorganic particles were selected to design a high-efficiency acoustic resistance composite material with a multiphase system.The composite consisted on a rubber phase of ethylene-propylene-diene monomer?EPDM?,a continuous phase of polypropylene?PP?,inorganic fillers of lightweight calcium carbonate?Ca CO₃?and hollow glass bead?HGM?.This mulptphase structrure allowed the incident sound wave refracted and scattered on interfaces of island rubber phase,inorganic phase and continuous phase,further extended the soud propagation routine and dissipated in the rubber phase.And the incident sound was reflected on the surface of composites due to high stiffenss.The composites showed excellent sound transmission loss?TL?of 50 d B at low frequncy zone,combining good mechanical properties and processing feasibility.It was expected to be applied to the sound insulation and noise reduction in transportation and daily life.2.Supercaritical carbon dioxide?Sc CO₂?assited extrusion foaming was used to prepare a series of polystyrene?PS?microcellular foam with controllable celluar structure.These foams showed very low density and adjustable sound wave absorption.The microcellular structure was controlled by using lignin,multi-walled carbon nanotube?MWCNTs?and micro-graphite as the hetero-nucleation agent,separately.It is confirmed that the foams with different cell size and cell density showed different absorption frequency of sound wave.Meanwhile,the mechanical properties of composite microfoams were studied in detail.3.In this thesis,by designing a three-dimensional conductive network,combining in-situ synthetic polymer and supercritical carbon dioxide foaming technology,a flexible piezoresistive material with high sensitivity,high specific compressive strength and high cycle stability was prepared.Firstly,cellulose/MWCNTs composite aerogels were synthesized by using a freeze-drying method;secondly,the thermoplastic polyurethane?TPU?was in-situ synthesized in the cavity of composite aerogels;Finally,TPU/cellulose/MWCNTs composite foames was prepared by a Sc CO₂-assited batch foaming processs.The density,cell porosity and conductivity of composite aregels were studied,and the mechanical and thermal properties of three kinds of TPU resins were tested to optimize the compositions.The composite foams were tested by conductivity,compression,cycling compression and piezoresistivity.It is confirmed the composite foam exhibited good mechanical preoperty and repeatable piezoresistivity after 100compression cycles.It was expected to be applied in flexible piezoresistive sensing.4.This paper explored the injection foaming process of in-situ fiber-forming polypropylene composites.Using PP as the continuous phase,polytetrafluoroethylene?PTFE?as the dispersed phase,multi-wall carbon nanotubes?Multi-wall carbon nanotubes?as the conductive filler,PP grafted with maleic anhydride?Polypropylene grafted with maleic anhydride,PP-GM?as the compatibilizer,MWCNTs/Polypropylene grafted with maleic anhydride?PP-G-M?masterbatch was prepared by using a solution blending method;by means of extruder granulation and supercritical nitrogen?Sc N2?injection foaming,a lightweight,conductive composite foamed material was prepared.The composite foams were analyzed by morphology,mechanical property and conductivity.Besides,the composites were measured by the morphology,rheology and so on.The injection foaming conditions were also optimized.It was expected to be applied in the lightweight and high-performance automotive industry.