Preparation And Properties Of Nano-SiO 2 Fiber, Diatomite/PMMA Composites

Polymethyl methacrylate（PMMA）was widely applied in various industries such as building,display window,medical denture,advertising license plates,and lampshades and so on.However,its field of application was restricted because it has some aspects with low mechanical properties and low thermal stability.Therefore,it is the focus of research to improve the mechanical properties and thermal stability of PMMA.Also it is the main task in this paper.Diatomite is a siliceous porous material with SiO₂ as the main component.The diatomite is abundant in our country.The application of diatomite in the polymer is of great significance for the rational exploitation and utilization of diatomite resources.Fiber-like SiO₂ materials have high mechanical properties and are excellent reinforcement materials.The nanoscale SiO₂ fiber has an excellent performance,which plays an important role in improving the mechanical properties of the polymer.In this experiment,diatomite and nanoscale SiO₂ fiber were used as fillers to study.The contents of several aspects were studied in this paper:（1）The nanoscale SiO₂ fiber was modified withγ-aminopropyltriethoxy silane coupling agent（KH-550）on the surface by wet process.Subsequently,the modified nanoscale SiO₂fiber and methyl methacrylate（MMA）were used to prepare polymer composites by in-situ polymerization.Also the effect of modification nanoscale SiO₂ fiber surface was explored.The effects of mechanical properties and thermal stability properties of nanoscale SiO₂ fiber dosage on the composites were studied.In the surface modification experiment of nanoscale SiO₂ fiber by KH-550,it was found that the tensile strength of composite can be increased within a certain concentration range of coupling agent,and the strength was the highest when the volume fraction of KH-550 and deionized water was 1:5.When the content of nano SiO₂fiber in composite was 0.30wt%,the tensile strength and impact strength of nano SiO₂ fiber/PMMA composites reach the maximum value,61.83MPa and 25.79kJ/m² respectively,which increased by 13%and 48%than that pure PMMA.The value of bending strength is 95.71MPa and increased by 2.3%than pure PMMA.Its hardness value reached 115.5 and increased by3.3%.With the increase of the mass content of nano SiO₂ fiber in composite,the glass melting temperature of the composite was increases.When the content of fiber was 0.80wt%,the glass state temperature value reaches 115.2℃,which was higher 12.2℃than pure PMMA.With the increase of the mass fraction of the nano SiO₂ fiber,the TG curve of the composite also moves to the high temperature zone.When the material weight loss rate was 25%,the corresponding temperature increases gradually,and the decomposition temperature increases gradually.It was possible to draw a conclusion that the thermal stability was improved.（2）The diatomite purified with physical method was modified byγ-methacryl propyl trimethoxy silane with wet process.The diatomite/PMMA composite was prepared by in-situ polymerization.Investigate the influence of diatomite modified effect and influence of diatomite content on composite material properties.From the discovery of surface modification experiments by KH-570 on the physical purification of diatomite diatomite it can be found that the surface modification effect of diatomite was poor,because the hole of diatomite purified with physical purification contains more impurities.Other more in the process of filtration carried out in the process of surface modification,a large amount of KH-570 was filtered out,resulting in the surface of diatomite low coverage rate.Furthermore,there was a larger gap between the diatomite and the PMMA matrix,which causes the continuity of the material to be destroyed,and the mechanical properties of the composites are reduced.However,with the increase of the content of the diatomite,the glass transition temperature of the composite increases significantly.When the addition of modified diatomite was 0.80wt%,the glass melting temperature of the composite material reaches 112℃which increased by 9℃than that of pure PMMA.From the TG curve of the composite,it can be found that the thermal decomposition temperature of the composite is improved and the thermal stability is improved.（3）The diatomite was treated by acid pickling to remove the impurities from the diatomite and to clean the pore of the diatomite.The surface modification of diatomite was carried out by KH-570 with wet process,and the influence of the content of modified diatomite on the mechanical properties and thermal stability of the composite was studied.The surface of the diatomite was modified,and the results showed that the modified effect of the acid washing diatomite was good by the characterization of FTIR,TG and wetting angle.When the addition of diatomite is 0-0.80wt%,the tensile properties and hardness of the composites tend to increase.At 0.80wt%,the value of tensile strength and hardness reached62.5MPa and 117.8,which was 14.3%and 5.46%higher than that of pure PMMA,respectively.When the content is 0.40wt%,the nick impact and bending strength of the composites are 21.8kJ/m² and 107.67MPa respectively,which was 25.3%and 15%higher than that of pure PMMA.With the increase of the mass content of the diatomite,the glass transition temperature of the composite increases significantly.When the content of diatomite was 0.60wt%,the glass melting temperature of the composite can be raised to 116.7℃and higher 13.7℃than pure PMMA.From the TG curve of the composite,it can be found that the thermal decomposition temperature of the composite increases and the thermal stability was improved.By comparing the modification effect of acid washed diatomite and physical purification diatomite,it was easily found that the porous structure of diatomite purified by the acid has strong adsorption and good surface modification effect.Moreover,there are more physical entanglement and chemical band between the modified diatomite with polymer matrix.These physical entanglements and chemical forces can transfer the load stress and absorb the energy of the external force to increase the strength and toughness of the composite.The interaction force between the diatomite and the polymer can also impede the moving of the molecules chains.The diatomite can also reduce the heat transfer rate in the polymer.For those reason the thermal stability of the composite was improved.After the surface modification of the inorganic filler,the bonding force between the inorganic filler and the polymer matrix can be enhanced.When the binding force was large enough,the inorganic filler can increase the strength and increase the toughness of composite.The physical entanglement formed between the inorganic filler and the polymer also plays an important role in the increase of the mechanical strength of the polymer.