Preparation And Properties Of Collagen Extracted From Leather Waste Based Adhesives

With the rapid development of plywood industry,the demand for adhesive is increasing.At present,the adhesives sold on the market are mainly"triple-formaldehyde"(urea-formaldehyderesin,phenolicresinand melamine-formaldehyderesin),andtherawmaterialsforthe"triple-formaldehyde"mainly come from non-renewable resources,and aldehyde resin and its products will also release free formaldehyde and other harmful substances that endanger human health.Millions of leather solid wastes are produced in the processing of leather.However,the traditional disposal methods will not only engender wasting of resouces,but also heavily pollute the environment.Actually,those wastes are rich in abundant collagens.Thus,the industrial gelatin and collagen hydrolyzate extracted from the leather wastes were used to prepara adhesives by crosslinking modification,which not only prepared environmentally friendly collagen-based adhesives,and also achieved resource utilization and reduced the environment pollution.Firstly,industrial gelatin(INGE),sodium hydroxide(NaOH),sodium dodecyl sulfate(SDS)and commercial epoxy resin(EP)were used to prepare collagen-based adhesive.Taking adhesive strength as index,the synthesis conditions were optimized by single factor experiment and orthogonal experiment.The changes of solid content and water resistance of the adhesive were studied.The structure and performance of the adhesive was characterized by FTIR,TG,XRD and SEM.The hot pressing conditions of the adhesive applied to the wood board are optimized by single factor experiment method.The results showed that the optimal conditions for the preparation of INGE/SDS/Ep adhesive were as follows:the reaction temperature was 50?,the reaction system pH was 8,the reaction time was 2 h and the amount of epoxy resin was 8 g.Under this condition,the adhesive strength was 2.53 MPa.Results showed that a cross-linking network structure was formed by the reaction of epoxy resin with amino and hydroxyl groups in gelatin molecules,so that the crystallinity of the adhesive decreased and its water resistance was improved by240%.In addition,the solid content of adhesive increased to 33.42 wt%,the wet shear strength increased to 1.19 MPa(?0.7 MPa),and the water contact angle increased to 85.8o.The TG result also showed that the thermostability of adhesive was improved.The SEM photographs showed that the surface of INGE/SDS/Ep adhesive film was smoother than INGE adhesive film.The optimal conditions of hot-pressing were as follows:the temperature was 100?,the time was 5min and the amount of adhesive was 300 g/m~2.Secondly,a collagen based adhesive was prepared by using polyurethane prepolymer as the cross-linking agent,and collagen derived from tanned leather wastes as the raw material.Five different wood adhesives were obtained through controlling the molar rate of the amino group and the isocyanate group.The properties and structure were measured by solid content,water resistance and modern instrument characterization.The hot pressing conditions of the adhesive applied to the wood board are optimized by single factor experiment method.The results indicated that the water resistance was the best when the molar rate was 1:1(namely PU-COL-1adhesive)and the wet shear strength could reach to1.08MPa(?0.7 MPa),which met the requirement of GB/T9846.3-2004.The solid content(38.16%)and the stability of PU-COL-1adhesive were also the optimal.The relative molecular mass of PU-COL series adhesive was obviously increased,the crystallinity was obviously reduced and the thermal stability is improved significantly after modification.The optimal conditions of hot-pressing were as follows:the temperature was 120?,the time was 5min and the amount of adhesive was 300 g/m~2.Finally,the performance of the two adhesives obtained from this study and commercial adhesive were comparaed.The application performance of self-made adhesives and commercial adhesive were compared respectively by solid content testing,water resistance testing,XRD testing and TGA analysis.The results showed that the solid content of self-made INGE/SDS/Ep(33.42%)and PU-COL-1(38.16%)was significantly higher than commercial adhesive(21.67%).The water resistances of the self-made adhesives are better than the commercial adhesive.The results of XRD showed that the two self-made adhesives had low crystallization performance and the crystallinity was far lower than that of commercially available adhesives,which indicated that the self-made adhesives had better performance at low temperature.TG analysis results show that two self-made adhesives have good thermal stability.