Study On Curing Behaviors Of Nitrile-Based Resin Containing Benzoxazine And Properties Of Composites

Biphthalonitrile resin composite is suitable for extreme fields of high performance polymer materials.Its glass transition temperature can be up to 400℃above,has excellent high temperature resistance,flame retardant,thermal stability and durable performance.Phthalonitrile resin containing benzoxazine is a kind of double phthalonitrile resin containing benzoxazine ring structures in monomer,which has both the high-performance characteristics of biphthalonitrile resin and benzoxazine resin.However,for phthalonitrile resin containing bisphenol A type benzoxazine（BA-ph）,it still has the shortcomings of low curing rate and high curing temperature.Therefore,this thesis took BA-ph as the research object,two modifiers through molecular design were synthesized,and the influence of modifiers and curing process on BA-ph curing performance were studied.This were to achieve the goals of improving the curing reaction rate,reducing curing temperature,improving the crosslinking density and curing degree of BA-ph resin.Thus,glass fiber（GF）reinforced resin matrix composites with better thermal and mechanical properties were obtained.The main research contents of this paper are as follows:（1）The effects of curing agent on curing properties of BA-ph resin and its composites were investigated.A low melting point cyano-functionalized aromatic diamine hardener,2,6-bis（4-aminophenoxy）benzonitrile（BAB）,was synthesized.The influence of BAB on BA-ph reaction behavior was studied by orthogonal test and the preparation conditions of the prepolymer were optimized.The results showed that BAB significantly improved the curing rate and crosslinking degree of BA-ph prepolymer.In addition,improving the pretreatment temperature of BA-ph/BAB/GF composites significantly improved the flexural strength of the composites,and good thermal stability and thermodynamic properties were obtained.At the same time,BAB and BA-ph resin showed good compatibility.（2）The effects of chain extender on curing properties of BA-ph/BAB resin and its composites were explored.A monocyano-functionalized diamine-type benzoxazine monomer（MD-cn）was synthesized as chain extender for BA-ph/BAB system.The results showed that MD-cn significantly increased the curing rate of BA-ph/BAB system,decreased the initial reaction temperature,and increased the crosslinking density and curing degree.The cured resin mainly consists of triazine rings,phthalocyanine rings,phenol type and aromatic amine type Mannich bridge structures.Appropriate amount of MD-cn could improve the brittleness of BA-ph/BAB resin matrix and the interface interaction between matrix and fiber after curing,so as to improve the mechanical properties and dimensional stability of BA-ph/BAB/MD-cn/GF composites,while maintaining the original good thermal stability and dynamic thermodynamic properties.（3）The effects of post-curing temperature（pretreatment temperature and hot-pressing temperature）on the properties of BA-ph/BAB/MD-cn resin and its composites were investigated.The results showed that the higher the pretreatment temperature and hot-pressing temperature,the more promoted the curing polymerization of BA-ph/BAB/MD-cn resin,and the better thermal and mechanical properties of BA-ph/BAB/MD-cn/GF composites(Thermal weight loss 5%temperature(T_5%):427.7℃,char yields at 800℃(Y_c,800℃):68.80%,bending strength:511 MPa,thermal expansion rate:0.72%;coefficient of linear thermal expansion（CTE）:36.92 ppm/℃).