Investigation Of Preparation And Performance Of Ablation Resistant Phenolic Resin Composites

Phenol-formaldehyde?PF?resin is an excellent thermosetting resin with good mechanical properties and heat resistance,and it has been used as matrix for thermal insulation,flame-retardant,and ablative materials.However,the application of PR is often impeded by some of their inherent qualities,such as brittleness,large volumetric shrinkage during processing,and low char yield at elevated temperatures.Therefore,the rapid growth of PF applications has promoted extensive research to improve its heat resistance and mechanical properties,especially high-temperature ablation and charring yield.The main research method of this paper is to find elements or groups with anti-ablation effects such as boron,silicon,phosphazene,maleimide and et al,then the compounds with these elements or groups are designed to be combined differently.The synergistic effect of the components is carried out,or the molecular structure design is carried out to integrate the groups with ablation resistance into the phenolic resin molecular structure to obtain the phenolic resin with high performance and improve the overall ablation performance of the phenolic resin matrix composites.In this paper,the effects of the introduction of elements such as boron,silicon,phosphazene and maleimide on the thermal properties,ablation properties and flame retardancy of phenolic resin matrix composites were investigated.The residue was analyzed by phase and structure,and its ablation mechanism was studied.The main research contents are as follows:1.The silicate coupling agent KH550 was used to modify the surface of high silica and nano Al₂O₃.The results show that the interface between the high silica fibers and the resin after KH550 modification is significantly enhanced,and the silicon content on the surface increases,which increases its thermal and mechanical properties.The nano-Al₂O₃ is modified to reduce the agglomeration effect.SEM results show that KH550 treatment is beneficial to improve the interface properties of fiber and filler.A novel ceramizable organic composite was prepared by compression molding using silicone-modified phenolic resin?PR?as the matrix,nano-aluminum oxide powder as the filler,glass powder with low melting point as the forming additive,and vitreous silica fiber as the reinforced material.The ablative characteristics were explored in terms of linear/mass ablation rate and microscopic pattern of ablation via the oxyacetylene torch tests.Thermal stability of the investigated composites was estimated by means of thermogravimetric analysis.The final charring yields after pyrolysis increased from 63%to 69%and 74%,respectively.The silicone-modified PR acted as cross-linking adhesive at low-temperature region and tended to convert to bonding layer at high-temperature region.The formation and growth of the ceramic phase after thermal treatment enhanced the thermal stability and ablation performance of the composites at high-temperature region.The morphology and phase composition of the residual chars were studied by scanning electron microscopy,energy dispersive spectroscopy,and X-ray diffraction,respectively.The test results revealed that the modified composite possessed excellent thermal stability and ablation property.2.A thermal-resistant cardanol-containing boron–phenolic resin?CBPR?was prepared by copolymerizing salicyl alcohol,cardanol,and boric acid.The structure of CBPR was characterized by Fourier transform infrared spectroscopy.Thermal stability of the investigated composites was estimated using thermogravimetric analysis?TGA?.The results of TGA indicated that the modified resin exhibited excellent thermal stability.Specifically,the B-0.2 thermoset had a char yield of 69%when the boron content was only 1.27 wt.%.The carbon residue at 800?was lower than that of B-0.2?containing cardanol?system,indicating that the addition of cardanol could affect the decomposition process of phenolic resin matrix.The curing kinetics of CBPR was studied using non-isothermal DSC,and the main curing reactions were discussed.The results show that the DSC diagram of CBPR shows a single exothermic peak,which is similar to the primary reaction.The activation energy is low and the reaction is easy to proceed,but the curing temperature is relatively high.The gel temperature,curing temperature and post-treatment temperature were 90?,189?and 259?,respectively.Further,CBPRs,nano-aluminum oxide powders,glass powders with low melting point,and vitreous silica fibers were used as resin matrix,filler,forming additive,and reinforced material,respectively,to produce a novel ceramizable phenolic molding composite.The ablative characteristics of the co-cured blends were explored in terms of linear/mass ablation rate and microscopic pattern of ablation via the oxyacetylene torch tests.After thermal treatment,the formation and growth of the ceramic phase enhanced the thermal stability and ablation performance of the composites at high-temperature region.The morphology and phase composition of the residual chars were studied by scanning electron microscopy and energy dispersive spectroscopy,respectively.The linear and mass ablation rates for the modified composites decreased obviously in comparison with those of the unmodified composites,indicating that the modified composites possessed enhanced thermal stability and ablation property.3.This work reports a novel boron-and-silicon-containing phenolic resin?PF?with excellent thermal stability and formed by copolymerizing phenol,formaldehyde,boric acid?BA?and phenyltriethoxysilane?PTES?.The structure of the modified PF was characterized by Fourier transform infrared spectroscopy?FT-IR?.Thermal stability of the investigated hybrids was estimated by means of thermo gravimetric analysis?TGA?.Compared with the unmodified resin,the temperature at the maximum decomposing rate of BSPF increased by 84?and its charring yield was enhanced by 15.0 percent.The cured products of the modified PFs were further investigated by X-ray diffraction and Raman spectroscopy.The incorporation of boron and silicon into the carbon lattice results in an increase of graphite structure and a decrease of disordered structure upon the modification processes.Further,the modified PFs,nano-Al2O3 powders,glass powders and vitreous silica fibers were used to produce a novel ceramizable phenolic molding composite.The combustion performance of composite was tested by cone calorimeter.The results showed that the combustion performance of modified composite was better than that of the unmodified composite.The ablative characteristics of the composites were explored via the oxyacetylene torch tests.The morphology and phase composition of the ablated composites were studied by scanning electron microscopy?SEM?and energy dispersive spectroscopy?EDS?.The linear/mass ablation rates for the modified composites decreased obviously in comparison with those of the unmodified composites,indicating that the modified composites possessed enhanced ablation property.4.Using HCCP and HPM as raw materials,HMCP was prepared by nucleophilic substitution reaction,which contained maleimide and phosphonitrile ring,and introduced into phenolic resin by curing reaction to obtain phosphorus-containing phenolic resin system.The successful synthesis of HMCP was confirmed by FT-IR,NMR and elemental analysis.The results show that the thermal decomposition temperature of HMCP is 413?and the residual carbon ratio at 800?is 57%.The addition of HMCP improves the glass transition temperature of phenolic resin and reduces the thermal stability of phenolic resin,and promotes the carbonization of the phenolic resin at high temperature.V-PF/HMCP composites were prepared by using PF/HMCP as the matrix,nano-Al₂O₃ powder,low melting glass powder as filler and high silica glass fiber as the enhanced phase.The results show that HMCP can significantly improve the flame retardancy of phenolic resin matrix composites.Py-GC/MS results show that HMCP decomposition releases free radicals with gas quenching effect.The results of SEM-EDX analysis showed that HMCP could promote the formation of high carbon residue and expanded crosslinked carbon layer,and reduce the efficiency of thermal oxygen exchange.HMCP has a gas phase and cohesive phase biphasic flame retardant effect on phenolic resin.The ablation properties of V-PF,V-PF/HMCP-1.5 were tested by oxygen acetylene ablation test.The SEM study of the surface of the material after ablation shows that the porosity of the ablated surface is some high,indicating that the ablation effect of V-PF/HMCP in high speed and high temperature air flow is general.The ablation rate of V-PF/HMCP-1.5 composites decreased by 5%and the ablation rate decreased by 15%compared with that of V-PF.