Conductive Application And Graphitization Modification Of Thermal Expansion Microcapsules Research

Thermally expandable microcapsules(TEMs),as a physical foaming agent for preparing polymer foam materials,have a closed shell and air source core material,which can produce an expansion effect.Foaming materials are widely used in automotive interiors and packaging,but they are prone to electrostatic hazards during use.Research and preparation of foam materials with antistatic properties can avoid such situations.In antistatic composite materials,the dispersion of conductive fillers directly affects the conductive properties of the materials.In this paper,zero-dimensional conductive agent carbon black(CB)?one-dimensional conductive agent multi-walled carbon nanotubes(MWCNTs)?and conductive thermal expansion microcapsules were used to prepare foam materials with antistatic properties.Using the thermal expansion microcapsule's property that the shell can expand in the polymer melt,it induced the displacement of the conductive additives on the surface and the melt,and then changed the dispersion state of the conductive agent,so as to study the relationship between dispersion state of the conductive additive and the conductive performance of the composite material.Porous carbon microspheres have a wide range of applications in the fields of catalyst support and adsorption materials.In this paper,thermal expansion microcapsules were used as the precursor for preparing porous carbon microspheres.By controlling the gasification process of the internal gas source and matching the shell carbonization process,a porous carbon sphere rich in N was prepared,which has important theoretical and practical significance for expanding the application fields of thermally expandable microcapsules.The main research contents of this paper were as follows:(1)The EVA/CB antistatic composite foam material was prepared by melt blending-molding method with ethylene-vinyl acetate copolymer(EVA)as matrix,carbon black(CB)as conductive filler,and thermally expandable microcapsules(TEMs)as foaming agent.By adjusting the content of TEMs,the relationship between the expansion ratio of the EVA/CB antistatic composite foam material and the electrical conductivity of the composite foam material was studied.The results showed that the apparent density of EVA/CB antistatic composite foam material decreased by 0.6 g·cm^-3 with the increase of the content of thermally expanded microspheres,and its foaming ratio increased by3 times;The resistivity of EVA/CB antistatic composite foam material presented a trend of first decreasing and then increasing.When the foaming ratio was 1.69times,the resistivity of the foam composite showed the lowest value,which was3.26×10⁷?·cm;When the foaming ratio was 3 times,the resistivity of the foam composite material presented the highest value,which was 7.02×10⁸?·cm.The main reason were the volume occupied by the cells and the conductive network structure of CB in the antistatic composite foam material.(2)A conductive material with a core-shell structure of PPy/thermally expanded microcapsules was prepared by in-situ polymerization,with thermally expandable microcapsules(TEMs)as a template,pyrrole(Py)as a functional monomer,and sodium persulfate(Na₂S₂O₈)as an oxidant.EVA/CTAB-MWCNT antistatic composite foam material was prepared by melt blending-molding method with ethylene-vinyl acetate copolymer(EVA)as the matrix,modified multi-walled carbon nanotubes(CTAB-MWCNTs)as conductivefillers,andpolypyrrole/thermallyexpandable microcapsules(PPy/TEMs)conductive composites as foaming agent.The relationship between the expansion ratio of EVA/CTAB-MWCNT antistatic composite foam material and the electrical conductivity under different contents of polypyrrole/thermal expansion microcapsules was studied,and the mechanism of the volume expansion ratio of thermal expansion microcapsules on the electrical conductivity of the composites was clarified.The results showed that the stable bubble temperature range of PPy/TEMs conductive composites basically did not change with the increase of PPy content.Compared with TEMs,the expansion ratio of PPy/TEMs 1:3 was reduced by 0.2 times and the expansion ratio was reduced by 9%.Besides,the concentrated thermal decomposition temperature was increased by 13.7?,and the thermal stability was significantly improved.With the increase of the content of PPy/TEMs conductive microspheres from 0 vol%to 8.05 vol%,the foaming ratio of EVA/CTAB-MWCNTs antistatic composite foam material increased from 1 time to 2.69 times.The electrical conductivity of the antistatic composite foam material showed a trend of first increasing and then decreasing.When the expansion ratio was 1.79 times,the effect of the conductive network formed by CTAB-MWCNTs was stronger than that caused by the cell volume occupancy to reduce the concentration of CTAB-MWCNTs,and the electrical conductivity of the antistatic composite foam material rised to the maximum value of 7.24×10^-5S·cm^-1.Its conductivity had increased by nearly 7 orders of magnitude,when compared with the EVA/CTAB-MWCNTs antistatic composite material containing the same content of CTAB-MWCNTs.(3)Heat-expandable polyacrylonitrile microcapsules(PAN)were prepared by the suspension polymerization method with acrylonitrile(AN)as the monomer,azobisisobutyronitrile(AIBN)as the initiator,and isooctane as the blowing agent.Then,PAN-based carbon microspheres were prepared by pyrolysis and controlling the pre-oxidation temperature,graphitization temperature and other factors with polyacrylonitrile-based thermal expansion microcapsules as the precursor.The formation process and the influence of foaming agent on the pore structure of PAN-based carbon microspheres were studied.The mechanism of the influence of foaming agent on the pore structure of PAN-based carbon microspheres was explained.The main results were as follows:PAN-based thermal expansion microcapsules had a smooth surface?high sphericity?uniform dispersion and an average particle size of 6.4?m.After pre-oxidation and graphitization,the particle size was reduced by about1.6?m,and the original spherical shape was maintained.The carbon content of PAN-based microspheres was 76.02 wt%,nitrogen content was 19.1 wt%and oxygen content was 4.88 wt%.Compared with PAN-based microspheres,the carbon content of PAN-based microspheres after pre-oxidation was reduced by6.4 wt%,the nitrogen content decreased by 1.68 wt%,the oxygen content increased by 8.08 wt%.After graphitized,the carbon content of the PAN-based microspheres increased to 93.18 wt%,increased by 17.16 wt%,and the oxygen content decreased by 2.21 wt%,the nitrogen content was reduced to 4.15wt%,with a decrease of 14.95 wt%.These were because during the pre-oxidation process,PAN macromolecules form a ring structure with carbonyl and hydroxyl groups and undergo a cyclization reaction,which promoted carbon content,decreased nitrogen content and increased the oxygen content.During the graphitization of PAN-based microspheres,PAN-based microspheres undergone a cyclization reaction while releasing small gas molecules such as NO₂ and CO₂,which promoted a decrease in nitrogen and oxygen content and an increase in carbon content.The pores of PAN-based carbon microspheres were microporous.With the increase of foaming agent content,the specific surface area of PAN-based carbon microspheres increased by 747.8 m²g^-1,the pore volume increased by 0.4011 cm³g^-1,and the average pore diameter remained basically unchanged.This was because during the graphitization process,the foaming agent in the PAN-based microspheres was heated and moved violently,breaking through the shell layer to form more pores,which promoted the increase of the specific surface area and pore volume of the PAN-based carbon microspheres.