Study On Synthesis And Properties Of Modified Bismaleimide Resin And Its Carbon-fabric Laminate Composites

Bismaleimide(BMI)resins exhibit quite higher heat resistance,electromagnetic wave transparent and mechanical properties than most other thermoset resins,which are broadly used as matrix resins for advanced composite material.Therefore BMI is the most promising high temperature thermosetting resin currently.However,some drawbacks of BMI resins,including high melting point,poor processability,and low fracture toughness,limited its application to a certain extent in many fields.What’s more,the high crosslink density of the cured BMI resins lead to the intrinsic brittleness,affecting their comprehensive performance as structural material.Reducing crosslink density is one effective technique to improve the toughness of BMI.Among the investigated approaches,the copolymerization with allyl compounds has become the most reliable method for decreasing brittleness and improving the processing characteristics of BMI resins.In this paper,Eugenol(EU)is reacted with BMI,and the EU-BMI resin system was synthesized as comparison.Then hydroxymethyl and 4,4’-diphenylmethane diisocyanate(MDI)were respectively copolymerized with EU-BMI to modify EU-BMI resin system,with a view to improve toughness of BMI resins under the premise of maintaining the excellent thermal properties.The specific research content is as following:(1)In order to increase the crosslink density of EU-BMI and improve its heat resistance.MEU was firstly prepared by introdution of hydroxymethyl groups on EU molecule,then MEU-BMI was synthesized by copolymerized with BMI.Rheological and DSC investigations showed that the thermal processing window of MEU-BMI resin was from 74 to 160℃.TGA showed that MEU-BMI resin had better thermal stability than EU-BMI.The DMA test showed that the MEU-BMI resin has a glass transition temperature of 297℃and a low storage modulus,indicating good toughness.Carbon fiber plain fabric reinforced MEU-BMI laminate composites exhibited high glass transition temperature,bending strength(231.9 MPa)and bending modulus(13.18 GPa)at 150℃.The results implied that MEU-BMI is an ideal candidate of high temperature bismaleimide resins for advanced composites.(2)MDI is expected to be a suitable modifier to improve the toughness and resin processability of EU-BMI resin.The thermal curing mechanism and heat resistance of the resin were studied using EU-BMI resin as Comparison.MDI-EG-BMI resin exhibits good thermal stability for its 5%weight loss temperatures around 322.76℃ and its residue of 39.65%at 900℃,which are much higher than EU-BMI resin.In addition,the glass transition temperature of MDI-EU-BMI resin is 327℃.The carbon fiber-reinforced MDI-EU-BMI composites were also fabricated which exhibits obvious bending resistance at 150℃.The mechanical properties of the composites matrixed by MDI-EU-BMI resin are better than EU-BMI resin.This paper designs and synthesizes two modified BMI resin systems with excellent comprehensive properties such as heat resistance,toughness and mechanical properties were.