Mechanism And Application Of In-situ Fibrillar Reinforced Microcellular Foams

Recent developments in the field of automobile lightweight,aerospace military industry and healthcare have attracted an increasing interest in polymeric functional composites and much effort has been directed towards regulating the morphological distribution of reinforced phase.As the typical polymer processing technique,microcellular foaming could tune the morphological distribution of reinforced phase by the introduction of micronscale porous structure meet the demands of functional applications.However,it is often difficult to reach the full potential of blend polymer and functional filler,which restricts the effect of cellular structure on the morphological distribution of reinforced phase.In-situ microfibrils,formed by already well-dispersed domains during processing,are proposed to improve melt strength,heterogeneous nucleation and foaming behavior of thermoplastic polymer.To date,most studies associated with in-situ fibrillation have only focused on the regulation of cell structure and mechanical properties,which can not fulfill the demands of functional composites.This work is aimed at in-situ fibrillar reinforced functional microcellular foams with the polymer matrix of polypropylene(PP),in-situ fibrillation phase of polytetrafluoroethylene(PTFE),and reinforced phase selected based on the functional demands.The in-situ microfibrils were used to regulate the morphological distribution of reinforced phase,morphology and performance of multicomponent composites.The forming mechanism of in-situ fibrillar reinforced microcellular foams and the effect of in-situ fibrils on the reinforced phase with different structures and components were investigated,which is conducive to establish the relationship between structure and performance of functional composites,and thus lay the groundwork for the industrialization of polymeric microporous materials.The detailed contents are as follows:(1)The fibrillar network in matrix were developed by already welldispersed polymer phase based on in-situ fibrillation.The critical content of microfibrils in in-situ PTFE fibrils reinforced composites was determined according to the frequency independence of loss tangent.Moreover,the content and distribution of elements fluorine under different PTFE content were analyzed by elemental energy spectrum,and in-situ microfibrils with different morphological distribution characteristics were found in the SEM observation of the etched samples.(2)The introduction of in-situ microfibrils was utilized to improve the morphology distribution of thermoplastic polyester elastomer(TPEE)for insitu fibrillar reinforced composites.It was found that in-situ microfibrillar network could reduce the agglomeration problem caused by the collision of polymer particles under the force field,thereby reducing the size of TPEE and improving its distribution characteristics.Comparing the single TPEE reinforced composites and in-situ fibrillar PTFE reinforced binary composites,it was further proved that the improvement of the mechanical properties and surface quality of in-situ fibrillar reinforced multi-component composites was mainly due to the improved morphological distribution of blend polymer.(3)According to the morphology regulation of blend polymer,the influence mechanism of the in-situ fibrillar network on the dispersion characteristics of inorganic fillers were studied.It was found that in-situ fibrillar network can improve the dispersion of inorganic fillers with different contents throughout the matrix,and alleviate the spontaneous aggregation behavior of fillers to reduce the interfacial energy during processing.The inorganic fillers with improved dispersion and the in-situ fibrillar network synergistically promoted crystallization and viscoelastic response switching,cell structure of microcellular foams,and the enhancement effect of impact strength.(4)Based on the heat transfer principle of porous materials,the two materials before and after the improvement of filler dispersion characteristics were applied to the preparation of high-expansion microcellular foams.It was found that thermal insulation performance and compressive strength of the insitu fibrillar reinforced composites were higher than those of the single talc filling reinforced composites under the high-pressure microcellular injection molding,but there was a certain drop in compression performance for highexpansion microcellular foams with same components.(5)To meet the demands of conductive polymer composites for electromagnetic shielding application,in-situ fibrillar network was used to improve distribution characteristics of conductive fillers.The results demonstrated the promoting effect of the in-situ fibrillar network on the distribution of carbon-based conductive fillers,which is benefited from the fact that the high aspect ratio microfibrils reduced the collision attraction of carbonbased fillers and induced their distribution along the surface of in-situ microfibrils.The carbon-based fillers with improved distribution characteristics and in-situ fibrillar network synergistically promoted the crystallization and cellular structure.At the same time,the finer cellular structure not only reduced the content of carbon-based fillers,but also improved the electromagnetic shielding efficiency of the composites.Therefore,in-situ fibrillar reinforced microcellular fomas with electromagnetic shielding efficiency exceeding 20 d B and a tensile elongation at break of 194.40 % were obtained.