Interleaf Toughening And Mechanisms Of Thermosetting Polyimide Composites

Thermosetting polyimide resin always has good comprehensive properties but tend to comes with poor toughness properties which limits their use in certain structural applications requiring high toughness properties.Therefore,how to improve the impact resistance of thermosetting polyimide on the basis of the original excellent performance,especially the heat resistance,has become an important research direction of the current polyimide resin based composite materials.Starting from the structural design of the toughening material,considering the matching principle of the toughening agent and the bulk resin,four kinds of thermoplastic polyimide tougheners with linear structure were designed and synthesized.This article studied the effects of imidization methods on the polyimide chemical structure and properties.And the suitable synthesis methods of polyimide with different structures were clarified.This research also studied the preparation method of thermoplastic polyimide ultrafine particles and obtains micron-sized ultrafine particles suitable for blending modification.The compatibility between molecular structure and content of the toughening agent and the thermosetting resin was also studied.The influence of the toughening agent on the heat resistance,mechanical properties,reaction characteristics and rheological properties of the modified resin was also studied.The results showed that the glass transition temperature of the modified resin system was between the original Tg of the corresponding thermoplastic resin and the thermosetting resin.The TPI-3 toughening agent was a crystalline polymer.Therefore,the Tg of the modified resin was as high as 406.1?.The thermal decomposition temperature of the modified resin systems were above 550?,which shows good thermal stability;the toughness of the modified resin system is positively correlated with the toughness of the thermoplastic polyimide toughening agent introduced,impact performance of the TPI-2 thermoplastic particles modified resin could reach14.28kJ/m²,compared with HT-1 resin increased 52%;In addition,the study found that with the introduction of thermoplastic toughening particles,the modified resin system viscosity increases,the active end base reaction rate is reduced,and thus the curing temperature of the resin systems moves to the high temperature side.The modified polyimide prepregs were prepared by hot melt method.The toughened polyimide composites were prepared by compression molding.The modified effects were evaluated by the type I and type II interlaminar fracture toughness G_IC and G_IIC.The results showed that the TPI-1,TPI-2 resin had good compatibility with HT-1,and the thermoplastic resin was not enriched in the interlayer.The G_IC,G_IIC decreased slightly and did not show obvious inter-layer toughening effect.Relatively speaking,the G_IC and G_IIC of TPI-3 modified composite system obtained a certain improvement,and within a certain range with the toughening agent content the G_IC value was326.5J/m² when the content was 15%,which was 60%higher than that of HT-1 unharmed resin.The G_IIC value was 738J/m²,an increase of 31.6%.According to the microstructure analysis,TPI-3 resin has the characteristics of semi-crystallization and poor solubility with HT-1 resin,but can form a good bonding interface with it.The thermosetting resin is continuous phase to thermoplastic resin as a non-continuous"cluster"continuous phase structure,under the action of open or shear load which can absorb energy of the crack propagation through plastic deformation,played a certain layer of toughening effect.Adopting the thermoplastic polyimide superfine particles with certain heat resistance and toughness for interlaminar toughening can play a certain toughening effect and has guidance significance for exploring toughening and modification methods of thermosetting polyimide composites.