Construction And Thermal Properties Of Full Bio-Based Benzoxazine With Low-Temperature Curing Property

With the rapid development of the world,a large amount of non-recyclable resources are consumed,and the environment is continuously deteriorating.Therefore,the search for sustainable,green and environmentally-friendly resources to replace non-recyclable resources such as fossil-based has attracted the attention of many researchers.Bio-based benzoxazine is a new type of resin material synthesized from green environmental protection and sustainable biomass resources as raw materials,which has important research significance.Firstly,two novel bio-based benzoxazines(resorcinol/furfurylamine benzoxazine,PHG-F-BOZ;resorcinol/p-aminobenzoic acid benzoxazine,PHG-P-BOZ)were synthesized from resorcinol,furfurylamine and p-aminobenzoic acid based on biomass raw materials.In terms of curing performance,compared with the fossil-based bisphenol A aniline benzoxazine(BPA-A-BOZ)monomer,the curing temperature of PHG-F-BOZ and PHG-P-BOZ monomers has been significantly reduced,especially PHG-P-BOZ monomer whose curing peak temperature was reduced by about 75?,and it was completely cured at about 170?.Which indicated that both furan rings and carboxyl groups can reduce the curing temperature,Thermogravimetric analyzer(TG)and micro calorimeter(MCC)results show that the initial decomposition temperature(J5%)decreased due to the absence of the tetrasubstituted phenylamine Mannich bridge structure in the cured resin structure,but the introduction of furan rings can increase the crosslinking density of the resin,significantly reduced the decomposition rate under high temperature conditions and increased residual carbon ratio at 800?.In MCC,the total heat release and heat release rate of PPHG-F-BOZ are at the lowest levels,which are represented by total heat release(HRC),peak heat release rate(PHRR),and total heat release rate(THR)of 37 J/g·K,33.3 W/g and 8.3 kJ/g,while PPHG-P-BOZ has a three-fold increase in HRC and PHRR.After mixing PPHG-F-BOZ and PPHG-P-BOZ at a ratio of 9:1,it can achieve low-temperature curing characteristics of complete curing below 200?,while maintaining good thermal stability of the mixed resin.Then according to the in situ infrared analysis,it is known that the curing crosslinking point of the resorcinol benzoxazine is single,only the ortho position of the furan ring or the meta position of the carboxyl group,so the initial decomposition temperature was relatively low.Therefore,combining the furan ring and the carboxyl group has the characteristics of reducing the curing temperature and improving the heat resistance of the resin,this paper has designed three monomers(phloretic acid/furfurylamine benzoxazine,PHA-F-BOZ;p-coumaric acid/furfurylamine benzoxazine,PRA-F-BOZ;ferulic acid/furfurylamine benzoxazine,FEA-F-BOZ)that have only one oxazine ring but have both a furan ring and a carboxyl group.And at the same time,double bonds and methoxy groups were introduced respectively.The curing performance results show that the curing temperatures of the three monomers are lower than that of BPA-A-BOZ,and all are lower than 200?.The curing temperature of PHA-F-BOZ is the lowest,which can complete curing at 178? while PRA-F-BOZ and FEA-F-BOZ accelerate the decomposition of carboxyl groups due to the conjugate effect of double bonds and carboxyl groups,resulting in a higher curing temperature than PHA-F-BOZ,but still maintained lower level.In terms of heat resistance,in the nitrogen atmosphere,due to the decomposition of the carboxyl group of PPRA-F-BOZ,the double bond becomes a chain end group,thereby forming a polyolefin structure and further increasing the crosslinking density of the resin.At 800?,the carbon residue rate reached 56%,and the maximum decomposition rate was only 2.66 wt%/min.However,due to the poor stability of the polyolefin structure under air,PPHA-F-BOZ without double bonds has the highest carbon residue rate and the lowest two-stage maximum decomposition rate in air atmosphere,which are 6.9%and 2.83 wt%/min and 5.85 wt%/min.So in general PPHA-F-BOZ is a resin that has both low temperature curing properties and good heat resistance.The MCC results show that the total heat release(HRC),peak heat release rate(PHRR),and total heat release rate(THE)of PPRA-F-BOZ are the lowest values,which are 25 J/g·K,23.6W/g,and 5.6 kJ,respectively.At the same time,the temperature corresponding to the maximum exothermic rate is as high as 448.0?.Compared with PBPA-A-BOZ,HRC,PHRR and THR of the other two resins are also at lower levels.