Preparation And Application Of Benzoxazine-phthalonitrile Foam

Polymer based rigid foam exhibits excellent thermal insulation and mechanical properties,and has broad application prospects in aerospace,national defense and other manufacturing industries.Benzoxazine-containing nitrile-based resin（BZPN）is a kind of thermosetting polymer containing bifunctional groups.Its unique molecular structure gives it good processing properties on the one hand,and excellent physical and chemical properties of its curing material on the other hand.BZPN has the advantages of short curing time,low curing temperature,no release of small molecules,high temperature resistance,high strength,high modulus,corrosion resistance and self-flame retardant properties,so it is expected to be an excellent matrix for the preparation of high performance rigid foam.Based on this,BZPN has great potential advantages as the matrix of high temperature and flame retardant rigid porous foam.In this paper,the preparation and application of bi-functional benzoxazine-containing cyclonitrile resin（BZPN）as polymer matrix,azodibonamide（AC）as foaming agent,Tween-80 as foam stabilizer were studied.Firstly,by adding different contents of foaming agent（AC）to BZPN for chemical foaming,hard porous polymer foam was obtained.The effects of AC content on foaming efficiency,morphology,mechanics,heat insulation and so on were studied.The results showed that the bifunctional BZPN could bubble spontaneously,but the foaming efficiency was limited and the surface of the foam was uneven.After adding AC,its compression strength and cell uniformity are more excellent,so the use of AC is helpful to improve foaming efficiency,as well as the role of uniform cell and closed cell structure.In addition,AC can be used as curing agent in the whole system.The compressive properties of BZPN foams are largely determined by cell structure rather than density.BZPN foam has excellent thermal stability,with T_5%,T_maxand C_r above 370°C,400°C and 60%,respectively.Secondly,the effects of foaming process parameters on the structure,mechanical and thermal properties of BZPN foam were studied.The results showed that the optimum foaming temperature of BZPN foamprecursor was lower than 180℃.The structure and mechanical properties of BZPN foam are much better than those prepared in Chapter 2.In the compression test,BZPN foam has a hierarchical fracture mechanism,and its compressive strength can reach more than 6 MPa.In the combustion test above 380℃,BZPN foam does not appear obvious smokiness,softening and droplet phenomenon,and maintains a good macro structure.Finally,the effect of calcination temperature on hard porous BZPN foam,decomposition mechanism and products of BZPN foam at high temperature were studied.The results show that the decomposition of hard porous BZPN foam at high temperature can be divided into three stages.In the first stage（200-400℃）,some unreacted cyanogroup breaks off from the main chain,and weak bond breaks（such as C-N and C-C bond）between isindoles and phthalocyanine rings,resulting in a small amount of NH₃,HCNO,CH₄,etc.The second stage（400-800℃）:heterocycle compound ring opening and benzene ring decomposition,the generated phenoxy radical will reduce the stability of benzene ring,destroy the resin skeleton,and release gas（CO,CO₂,etc.）,at the same time,benzene ring fracture release CH₄.The third stage（800-1000℃）:the fracture of heterocyclic and adenine structures leads to the generation of many aromatic fragments until an extended array of aromatic graphite is formed.