The Co₂ Affinity Modification Of Mesoporous Silica Particles And Its Application In Polymer Scco₂ Foaming

Microcellular foaming polymer is a new material whose cell diameter is less than 10 μm and cell density is between 109 cells/cm3 and 1015 cells/cm3,which can significantly reduce the usage of raw material while does not deteriorate the mechanical properties of the polymer,and increase impact strength and practical life of the material,at tne same time,give the material low dielectricity and low heat conductivity.Usually,SB A-15 mesoporous silica particles with smaller cell diameter and higher cell density,the mechanical performance and heat insulation performance is higher.Adding heterogeneous nucleating agent in foaming process can decrease the cell diameter and increase the cell density,which is the main method for regulating the cell structure.This paper used particles with porous structure in polymer supercritical CO2 foaming to realize low nucleation energy barrier and high efficiency of hegerogeneous nucleation by enrichment of foaming agent and "air-pocket structure"which cousing of high Specific surface area and porous structure.At the same time,the efficiency of hegerogeneous nucleation of mesoporous particles structure included particle morphology,pore structure and surface energy structure in polymer foaming was studied systematicallyAt first,we choosed commercial SBA-15 mesoporous silica particles,used silane couping agent grafted,ionic liquid impregnation and fluorine silane grafted to modify the particle suface and hole to increase their CO2 affinity,and used in polylactic acid supercritical carbon dioxide foam.The results showed that only silane coupling grafted of three methods improved the CO2 adsorption value,the others’ CO2 affinity were decreased due to its occupying of the channel volume.Modifed mesoporous particle blended with PLA can more evenly dispersed in polymer matrix,but fluorde silane modified mesoporous particles dispersion was not ideal.By analysising the cell structure of foaming,we found that the modified particles had well heterogeneous nucleation,reduced cell diameter,improved cell density,although the expansion ration was lower.By comparing the heterogeneous nucleation of several different modified methods,fluoride sliane grafted particles showed lowest nucleation energy barrier and highest nucleation efficiency,which proved that the interface between particles and polymer palyed a key role in the process of heterogeneous nucleation.Through the sduty of the influence of heterogeneous nucleation of PLA and fluoride sliane grafted particle composite foam in different foaming condition includes temperature and pressure,the result showed that mosoporous particles in low foaming temperature and pressure had more significant heterogeneous nucleation.Secondly,we systhesized SBA-15 particle whose length about 800 nm,width about 200 nm by hydrothermal,using in PMMA supercritical carbon dioxide microcellular foaming after modified by silane coupling agent and fluoride sliane.We also found fluoride sliane grafted particles greatly increased the heterogeneous nucleation,at the same time,we tested the mechanical properties of the PMMA composite foaming materials,and found that the tensile modulus had improved compared with the pure PMMA foaming materials,but that was similar,showed that the tensile modulus increased mainly comes from the mosoporous particle not the cell structure change.Further shows that under the same density of matrix,decreasing of cell diameter and increasing of cell density would not significantly improve the mechanical performance of foaming materialsAt last,we systhesized three different morphology SBA-15 particle by changing the reaction condition,modified by fluorinated silane,and using as nucleating agents in PLA scCO2 foaming to investigate the effect by various morphologies on the foaming.As a result,the addition of SBA-15 particles could act as heterogeneous nucleation in the foaming process of PLA,although they all could decrease the cell average diameter,increase the cell density and expansion ratio,the effect was different,and the nucleation effect of ring-shaped SB A-15 was superior than ball-shaped and rod-shaped due to its side channel structure.