Effect of heat history on thermal properties of diaminodiphenyl methane type benzoxazines
Benzoxazines resins are phenolic-like thermosetting materials with a unique chemical structure and excellent prop-erties,which have enormous development and application potential in different special scenarios.According to the different heat history obtained from each of three heat treatment processes in different setting modes of temperature and time,the 4,4'-diaminodi-phenyl methane type benzoxazines(MDA-BZ)mixed 1 wt%curing agent and curing agent-free references of MDA-BZ were heated in the same batch by a high-temperature oven.The thermal properties of the curing samples were individually compared from the perspective of combination of either different curing type with the same heat history or the same curing type with different heat histo-ries.An approach was achieved to optimize the curing parameters of MDA-BZ matrix for composites.The thermal properties were tested under the same conditions utilizing simultaneous thermal analyzer.The results show that,the heat history characteristics of temperature increase and time extension shift curing exothermic peak to a higher temperature for curing agent-free samples.In addi-tion,thermogravimetric mass loss ratios at 600℃of polybenzoxazine increase,and thermal stabilities of polybenzoxazine worsen.Temperature increase and time extension have different effects on 1 wt%curing agent-mixed samples.Among them,1 wt%curing agent promotes ring-opening reaction in the two stage curing parameters of 185℃(1 h)and 205℃(1 h),increases an initial degra-dation temperature,reduces thermogravimetric mass loss ratio at 600℃,and raises the thermal stability.It is elucidated that 1 wt%curing agent generates different effects on thermal degradation mechanism compared with the curing agent-free samples.When MDA-BZ resin is selected as composite matrix,a preferred curing strategy is obtained by combining 1 wt%curing agent with two stage curing parameters of 185℃(1 h)and 205℃(1 h).
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