Study On Structure And Properties Of Fly Ash Modified Polybenzoxazine Resin

Benzoxazine resin is a new type of phenolic resin,which has the advantages of no release of small molecules and near zero shrinkage during curing,low product porosity,excellent thermal properties of cured products,good flame retardant properties,excellent mechanical properties,and high modulus.Benzoxazine resins have been widely used in electronic packaging materials,aerospace industry,composite materials,high temperature electrical insulation materials,coatings and other fields.However,like other thermosetting resins,benzoxazine also faces the disadvantages of high brittleness of the cured product,high curing temperature and long curing time.These shortcomings greatly limit its promotion and application as a high-performance structural material in high-tech fields such as aerospace.Therefore,it is of great significance to find a way to toughen benzoxazine while shortening the curing time for the industrialization of benzoxazine.The main research contents and conclusions of this paper are as follows:1.First,the fly ash(FA)was modified with surfactants,and then different proportion of modified fly ash(KH570-SA-F)was used as BA-a filler to prepare KH570-SA-F/BA-a modified resin system by microwave curing(MW)and thermal curing(CV).The modification effect of fly ash was studied by Zeta particle size and FTIR test.The results showed that the dispersion and stability of fly ash modified by surfactants are good in resin.The curing behavior of KH570-SA-F/BA-a blend system was studied by DSC and FTIR.The results showed that the curing time for the sample to obtain the best curing degree was reduced from 8 h for CV curing to 15 min for MW curing.The thermal properties of the KH570-SA-F/BA-a blend system were studied by DMA and TGA tests.The results showed that the T_g of the 3%KH570-SA-F/BA-a blend resin system,the CV curing blend resin system is 228.4?,which is 24.6?higher than that of pure BA-a,while the T_g of the MW curing blend resin system is 223.4?,the T_g of the CV cured sample is slightly higher than that of the MW cured sample for the same process variables.The addition of KH570-SA-F significantly improved the heat resistance of BA-a.When the addition amount of KH570-SA-F was 5%,the carbon residue rate of the blend system increased from 39.1%to 46.9%at 800?.The mechanical properties of the KH570-SA-F/BA-a blend system were tested.The results showed that the blend system had the best mechanical properties when the amount of KH570-SA-F was 3%.The impact strength of the MW sample is 18.71±1.20 k J·m^-2,which is 137%higher than that of pure BA-a,and the impact strength of the CV sample is 18.36±0.27 k J·m^-2,which is 133%higher than that of pure BA-a,the impact strength of MW blends has a certain degree of improvement compared with CV curing;the flexural strength of MW samples is 135.9±6.6 MPa,which is 28.1%higher than that of pure BA-a,and the flexural strength of CV samples is 137.7±7.6 MPa,which is 30.4%higher than pure BA-a.The impact section of KH570-SA-F/BA-a blend system is rough and has obvious fibrous cracks.The viscosity of KH570-SA-F/BA-a blend system was studied by rheological test.The results showed that the processing window of 3%KH570-SA-F/BA-a blend system is 101?,and the minimum viscosity is only 0.17 Pa·s,provides a sufficient temperature range for the preparation of BA-a matrix composites,and has good processing performance.The introduction of KH570-SA-F and MW not only improves the toughness of BA-a but also shortens its curing time.2.Firstly,benzoxazine(BA-a)and epoxy resin(EP)were used as research objects to prepare BA-a/EP blend system,then different proportions of modified fly ash(KH550-F)were used as filler in BA-a/EP blend system,and KH550-F/BA-a/EP modified resin system was prepared by MW curing and CV curing.And use it as resin matrix to prepare carbon fiber composites.The curing behavior of BA-a/EP blend resin system was studied by DSC and FTIR test.The results showed that with the increase of EP content,the onset temperature(T_onset)and peak temperature(T_peak)of the curing reaction gradually increased,the addition of KH550-F has little effect on the ring-opening curing of KH550-F/BA-a/EP.MW curing of KH550-F/BA-a/EP samples only takes 15 minutes.The thermal properties of the KH550-F/BA-a/EP blend system were studied by DMA and TGA tests.The results show that the curing method has little effect on the storage modulus(E')of the blend system.With the increase of the content,the E'of the blend system increases gradually.However,the addition of KH550-F reduced the carbon residue rate of the system slightly.When the addition amount was 5%,the carbon residue rate of the blend system decreased from 29.9%to 28.3%at 800?.The mechanical properties of KH550-F/BA-a/EP resin system were tested.The results show that the addition of EP can effectively improve the toughness of BA-a.The results show that the addition of EP can effectively improve the toughness of BA-a.When the EP content is 30%,the impact strength reaches 16.96±1.2 k J·m^-2,which is 93%higher than that of pure BA-a.When the addition amount of KH550-F is 3%,the blend system has the best mechanical properties.The impact strength of the CV sample is 19.38±0.56 k J·m^-2,which is 14.3%higher than that of the BA-a/EP blend system,and the impact strength of the MW sample is 18.36±1.36 k J·m^-2.The rheological test results show that the addition of EP reduces the viscosity of the system,the processing window becomes larger,and the processing performance of BA-a is improved.The addition of KH550-F has little effect on the viscosity of the BA-a/EP system,and the temperature range of the processing window of the system is about 130?,which provides enough for the processing and molding of KH550-F/BA-a/EP resin-based carbon fiber composites.temperature range.The flexural properties of KH550-F/BA-a/EP resin-based carbon fiber composites were studied.The results showed that the addition of EP could improve the flexural properties of carbon fiber composites.The flexural strength of pure BA-a carbon fiber composites was 507.8 MPa.When the EP content is 30%,the bending strength of the carbon fiber composite can reach 713.4 MPa,an increase of 40.4%;the addition of KH550-F will further improve the bending performance of the carbon fiber composite.When the content of KH550-F is 5%,the flexural strength of the composite reaches 930.5 MPa.