Study On Heat-resistance And Adhesion Properties Of Acrylate Anaerobic Adhesives Modified By Silicon(Boron) Hybrids

Acrylate anaerobic adhesives are widely used for threadlocking,pipesealing,retaining,etc.The higher heat-resistance and torque-controllable performance of anaerobic adhesive are demanded in the field of aerospace engine industry.Organic silicone was used to improve the heat-resistance and control torque of acrylate anaerobic adhesives,due to its high bond energy of siloxane and the controllable degree of cross-linking.However,the compatible stability and the modified effect of the composite materials were not satisfactory,due to the different polarity between organic silicone and acrylate.The phenylborosiloxane oligomer(PBS)and SiO2 hybrid HEMA oligomer were designed and synthesized for modifiers of anaerobic adhesives,respectively.The synergistic effect of multi-component modification could be obtained by controlling the hybrid component and the hybrid process.As the result,the heat-resistance,mechanical property and compatible stability of the modified anaerobic adhesive were improved.PBS oligomers were directly synthesized by co-condensation of boric acid(BA)with phenyl triethoxysilane(PTEOS).The thermal properties of PBS were tested by thermogravimetric analysis(TGA),differential thermal analysis(DTA).It was shown that the pyrolysis process of PBS was divided into four stages,which include dehydration condensation of B-OH groups(?200?),cross-linking(200??450?),thermal decomposition(450??700?)and ceramic conversion(?700?).The evolution mechanism of the chemical structure and properties of PBS during the heat treatment were investigated by in situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS)and nuclear magnetic resonance(29Si-NMR).The results revealed that B-O-B linkage was mainly formed in the dehydration condensation stage of B-OH groups.In the cross-linking stage,B-OH and Si-OH in the system reacted slowly and the cross-linking network formed gradually,with the increasing of temperature.The Si-O-B bonds were present in the SiO2-B2O3 cross-linking network modified by organic groups,and the heat-resistance and hydrolysis stability were improved.The anaerobic adhesives based on ethoxylated bisphenol A dimethacrylate(EBDMA)were modified by PBS.The wettability of liquid anaerobic adhesive on steel specimens was improved and the curing reaction was promoted by adding PBS,which improve the adhseion of anaerobic adhesive.The breakaway torque strength could be increased by 86%,when 50 wt%PBS resin(B/Si=1)was used as modifier for anaerobic adhesive.The bonding mechanism of hybrid anaerobic adhesive at high temperature was investigated by differential scanning calorimetry(DSC),scanning electron microscopy and energy dispersive spectroscopy(SEM-EDS),etc.The results revealed that the component compatibility of silicone and acrylate was improved and the thermal degradation process of acrylate was inhibited as the increasing of boron content in PBS.PBS containing boron can transform into cross-linking hybrid at 400?,which has the high cohesion,stickability and thermal protective performance.The PBS-modified anaerobic adhesive showed a significant enhancement in the bonding strength at 400? for better wettability and adhesion to specimens.Hydroxyethyl methacrylate(HEMA)/SiO2 hybrid oligomers were prepared by in-situ hydrolysis-condensation reaction which using grafting method and blending method,respectively.The particle size of SiO2 and dispersion state could be changed by different hybrid method.The particle size of SiO2 in grafting hybrid HEMA was about 100 nm and could be evenly dispersed in the oligomer,when the molar ratio of TEOS to HEMA was between 6.2%?18.8%.By contrast,SiO2 particles were agglomerated in blending hybrid HEMA.Both grafting method and blending method could improve the thermal stability of HEMA,which indicated that the interpenetrating network between inorganic component and organic polymer was formed.The synergistic effect on heat resistance could be observed.The Td5 of grafting hybrid HEMA could obtain maximum value when the addition amount of TEOS to HEMA reach to 12.5 mol%,which was 23? higher than unmodified HEMA.Silicone oil modified hybrid anaerobic adhesives were prepared by using SiO2 hybrid HEMA as monomer and silicone oil with terminal hydroxypropyl group as torque modifier.The mechanism of the heat-resistant modification and the controllable torque were demonstrated by UV-Vis absorption spectrum(UV-Vis)and SEM-EDS.The results shown that the coalescence of silicone droplets was restrained and the compatible stability of monomer and silicone oil was improved by hybrid modification.The torque strength of anaerobic adhesive was controlled by the low surface energy and coefficients of friction of silicone oil,and the heat-resistance of HEMA was improved by hybrids.The synergistic effect on heat-resistance and torque-controllable performance could be obtained by silicone modification and SiO2 hybrids.