Study On Toughening And Flame Retardant Of Solid Epoxy Resin Composites

Epoxy resin（EP）is widely used in various fields of national production because of its good chemical stability,electrical properties,bonding properties and mechanical strength.However,EP has two inherent defects:poor toughness due to its high crosslinking density and very easy to burn as an organic polymer material.Therefore,the toughening and flame retardancy modification of EP has always been a research focus.However,the research on toughening and flame retardancy modification of epoxy resin is almost focused on the liquid EP that with higher epoxide equivalent at present.Compared with liquid EP,solid EP has the advantages of solvent-free volatilization,convenient storage and transportation,and can be used as a single component thermosetting for long-term storage.In this study,a series of toughening and flame retardancy modification studies were carried out based on solid EP,and some positive exploration was made to expand the application range of solid EP.The main research contents are as follows:（1）A medium temperature curing high toughness solid EP composite system was constructed by using2-methylimidazole,dicyandiamide and block copolymer as accelerator,curing agent and toughening phase,respectively.It is found that the toughness of EP composites with 10%EVA-g-MAH is significantly improved compared with neat EP.While maintaining the mechanical strength,the impact strength,tensile toughness and bending toughness are increased by 135%,195%and 145%,respectively.With the addition of 4%EGMA,the tensile toughness and flexural toughness of EP composites increased by 206%and 130%respectively,and the tensile strength and flexural strength also increased by 22%and55%.（2）3-Aminophenoxy phthalonitrile（3-APN）was synthesized by nucleophilic substitution reaction of3-aminophenol and 4-nitrophthalonitrile which can be self-crosslinked at high temperature.Phosphorus containing self-crosslinking flame retardant DPPN was synthesized by nucleophilic substitution of 3-APN and diphenylphosphinyl chloride.The results show that when the amount of DPPN is 10%,the peak heat release rate（PHRR）and total heat release（THR）of EP composites are reduced by 53.8%and 42.1%respectively compared with neat EP.Furthermore,taking 3-APN as the intermediate,it first condenses with 4-formylphenylboric acid to form Schiff base structure（C=N）;Then,self-crosslinking flame retardant DBPN containing phosphorus and boron flame retardant elements was prepared by phosphorus hydrogen addition reaction with 9,10-dihydro-9-oxa-10-phosphophenanthrene-10-oxide（DOPO）.The results show that with the addition of 7%DBPN,the PHRR and THR of EP composites are reduced by34.2%and 29.5%respectively compared with neat EP.（3）The"core sheath"structure of fully bio-based flame retardant P-MCC@CS@PA-Na was prepared by layer by layer self-assembly in aqueous environment using microcrystalline cellulose,chitosan and sodium phytate as raw materials.P-MCC@CS@PA-Na has excellent flame retardant and mechanical strengthening and toughening effects on EP.When the addition of P-MCC@CS@PA-Na was 15%,the PHRR,THR,PSPR and TSP of EP composites decreased by 50.2%,25.7%,38.5%and 38.6%respectively compared with neat EP,and the LOI reached 26.2%,which passed the UL-94 V-1 rate.Benefit from P-MCC@CS@PA-Na has good dispersion,interfacial compatibility in EP matrix and mechanical strength of microcrystalline cellulose.Compared with neat EP,the tensile toughness and flexural toughness of EP/15%P-MCC@CS@PA-Na increased by 141.4%and 73.3%respectively,while the tensile,flexural and impact strength increased by 30.7%,34.2%and 40.3%,respectively.（4）A functional flame retardant PA-DAD was synthesized by rapid acid-base neutralization of biological materials phytic acid（PA）and decanediamine（DAD）.The results show that PA-DAD is an excellent bio-based toughening flame retardant with ionic bond.Adding 25%PA-DAD can make the EP composite pass UL-94 V-0 rate,and the LOI reaches 28.0%.Compared with neat EP,the PHRR,THR,PSPR and TSP of EP composite are reduced by 72.2%,28.3%,57.0%and 49.5%respectively,and the mechanical properties of EP composite can still be maintained to a great extent.The excellent flame retardancy of the composites is mainly due to the synergistic effect between the dense expanded carbon layer formed by the condensed phase and the inert gas（NH₃）and PO·which can quench H·and OH·free radicals produced by the gas phase.In addition,when the coordination ion bond formed between PA-DAD is subjected to stress,it can break as a sacrificial bond and dissipate energy,so as to improve the toughness of the material.When the addition amount of PA-DAD is 6%,the toughness of EP/6%PA-DAD is greatly improved compared with neat EP,the tensile toughness and flexural toughness are increased by 697%and 1028%respectively,and the impact,tensile and flexural strength are increased by201%,42%and 45%respectively.（5）The toughening flame retardant MPA-DAD with higher phosphorus content was prepared from methylphosphonic acid（MPA）and decanediamine（DAD）by one-step neutralization.The addition of MPA-DAD significantly improved the flame retardancy and mechanical properties of EP.The finding showed that EP/8%MPA-DAD reached UL-94 V-0 rate and LOI was 29.0%,its PHRR and THR decreased by 32%and 25%respectively compared with neat EP,and the impact strength,tensile strength,bending strength,tensile toughness and bending toughness of EP/8%MPA-DAD increased by 69%,18%,20%,1030%and 611%respectively compared with neat EP.Furthermore,a nano material with toughening,flame retardancy and wear resistance was prepared by coating two-dimensional mica nanosheets（MNs）with MPA-DAD.The addition of MNs@MPA-DAD not only ensures the flame retardancy and toughness of EP composites,but also greatly improves the wear resistance of composites.The results show that the FIGRA value of EP 8%MNs@MPA-DAD was decreased by 35.4%and 25.0%respectively compared with neat EP and EP/8%MPA-DAD.And the tensile toughness and bending toughness increased by 302%and 268%respectively,and its wear area also decreased by 76.6%compared with neat EP.It shows that the composite of two-dimensional materials can better inhibit the heat release of polymer.At the same time,due to the lubrication transfer of two-dimensional materials,the generation of friction heat is effectively reduced,so as to significantly improve the wear resistance of EP.