| Phenolic resin is widely used in military and aerospace industries because of its good heat resistance,good flame retardancy,electrical insulation and low smoking rate.However,the pure phenolic resin matrix is brittle enough to meet the requirements of high performance composite materials such as ballistic proof,rocket and aircraft.Therefore,in order to obtain high toughness,high strength phenolic resin and to solve the process problems that occur during the experiment,this paper has conducted in-depth research.In this paper,two kinds of modifiers,epoxy resin(0%-100%)and PVB(0%-14%)were selected to toughen and strengthen phenolic resin respectively.The curing mechanism of the modified phenolic resin was characterized by infrared spectroscopy.The curing behavior of the modified phenolic resin was investigated by DSC and gel time.The thermal decomposition process of modified phenolic resin was analyzed by TG.Activation energy and reaction series of curing reaction were obtained according to Kissinger method and Crane method.The effects of two modifiers on the mechanical properties of modified phenolic resin were studied by mechanical tests.Based on the actual experimental process,there are many process problems such as many bubbles in the phenolic resin casting body and easy to break the mold,which makes it impossible to test its mechanical properties.a preparation method of long-size phenolic resin castings in semi-gel state was proposed.The semi-gel-state phenolic resin was prepared by controlling the reaction temperature and reaction time.The complete and defect-free phenolic resin castings were obtained by this method.It was found that there were almost no bubbles in the castings,which could be used to test the mechanical properties of the castings.The mould for long size phenolic resin casting was designed.Epoxy resin and phenolic resin undergo ring opening reaction.The tensile strength of 14%PVB/phenolic resin was 44.459 Mpa,increased by 48.8%,the Imaximum elongation at break was 1.191%,increased by 36.5%,the maximum bending strength was 93.061 Mpa,increased by 135.25%,and the effect of strengthening and toughening was obvious.With the increase of epoxy resin content,the curing peak of the system moves towards high temperature gradually.When the epoxy content was 80%and 100%,the experimental reaction was carried out in two steps.The gelation time increased with the increase of epoxy content.According to gel time and characteristic temperature,the curing system of resin system was finally determined.According to Kissinger equation,when the content of epoxy resin exceeds 40%,the activation energy of the system increases greatly.With the increase of epoxy resin content,the heat resistance of the resin gradually decreases,and finally tends to balance.The PVB and the phenolic resin undergo a graft reaction.The tensile strength of 14%PVB/phenolic resin increased by 48.8%,the bending strength increased by two times,and the strengthening and toughening effect was obvious.After adding PVB,the characteristic temperature,gel time and activation energy of the system increased,but all of them had nothing to do with the amount of PVB added.Through thermogravimetric analysis,with the increase of PVB content,the thermal stability decreases,but the decrease is not significant.14%PVB/phenolic resin can also maintain good heat resistance. |
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