Flame Retardant Thermal Reversible Crosslinking Polyurethane And Polyurethane Adhesive

The dicyclopentadiene dicarboxylic acid(DCPDCA),a kind of thermal reversible crosslinking agent with Diels-Alder structure,was introduced into polyurethane with chemical cross-linkage for reprocess.Firstly,the isocyanate-ended component was prepared by DCPDCA and polyaryl polymethylene isocyanate(PAPI).It was determined by FT-IR that the proper reaction time is half an hour under 50 degrees.The solvent was dioxane and trimethylamine acted as catalyst.The amounts of both were 300-500%and 3%-4%the weight of DCPDCA.It was suggested by FT-IR,TGA and NMR that the reaction product of DCPDCA and PAPI was formed by direct addition reaction.The hydroxyl-ended polyurethane prepolymer was also synthesized by polyester polyol and polyisocyanate.The FI-IR spectra showed that the isocyanate group disappeared in three hours under 60 degrees.The thermal reversible crosslinking polyurethane material was prepared by mixing of isocyanate-ended component and hydroxyl-end prepolymer.Several method had been applied to testify the thermal reversibility of the materials with DCPDCA,and good result was observed.The retention of tensile strength was up to 82%.Then polyester polyol was partly replaced by flame retardant polyether polyol to impart polyurethane flame retardancy.The properties of material with different amount of flame retardant polyol was studied and it was best when 25%polyester polyol was replaced(by moles of hydroxyl).The limiting oxygen index(LOI)increased to 31.0%from 26.6%and the tensile strength is had no remarkable change compared to the unmodified material.Moreover,the polyurethane adhesive was prepared with both high bonding strength and flame retardancy by PAPI,flame retardant polyether polyol,phenolic resin,aluminum hydroxide(ATH)and chloride rubber(CR).The best amount of ATH was 30phr and 7phr of CR(10Ophr of basic resin).Final recipe of adhesive was 111:100:57.6:81:18.9 by weight of PAPI,flame retardant poly ether polyol,phenolic resin,ATH and CR.The LOI was 38.0%and the bonding strength up to(11.1±0.5)MPa.