Preparation And Characterization Of Polyvinyl Alcohol Based Adhesives And Blocked Isocyanates

With the development of economy,and the rising demand of society as well as the public environmental protection awareness,the pursuit for green environment protection are growing stronger.In the construction of a resource-conserving and environment-friendly society,the demand of green environmental protection adhesives becomes more and more urgent.The utilization potentiality of environmentally friendly adhesive represented by polyvinyl alcohol(PVA)adhesive and isocyanates are increasing.In this paper,environment-friendly water-based adhesives were prqPared from PVA,vinyl acetate and butyl acrylate by polymerization reaction and the performance was optimized.The green wood adhesive was also prepared using glutaraldehyde as crosslinking agent,polyvinyl alcohol and lignin as raw materials and the performance was analyzed.Respectively,the sealing isocyanates were prepared using ethyl acetate and ethanol as solvents and the effects of the isocyanates upon the properties of the emulsion and phenolic resin adhesive were investigated.The main research contents and results were summarized as follows:(1)The emulsion adhesive was prepared by emulsion polymerization.It was found that different content of redox initiator(H2O2-TA)had great influence on the properties of polymer emulsion.With the increase of initiator dosage,the bonding strength of plywood prepared by the as-prepared emulsion adhesive increased from 2.34 to 2.97 MPa.The results of the analysis indicated that a polymerization reaction occurred between two monomers(VAc and BA)and that the polymerization was gradually completed as the initiator dosage increased.A film with the highest thermal stability was fabricated when the amount of initiator was 1.0%,and the structure of the core-shell became distinct.(2)Polymers were fabricated from polyvinyl alcohol and lignin through crosslinking reaction using glutaraldehyde as crosslinking agent.The cross-linked reaction between PVA and lignin was proved by analyses.With the increasing amount of crosslinking agent,the reaction became more and more intense,and tended to be more complete.When the amount of oxidant potassium persulfate was 2.5%,the oxidation temperature was 60℃,PVA:lignin=4:1,the crosslinking temperature was 70℃,and the amount of crosslinking agent reached 5%,the adhesive property of adhesive was optimal.It was observed that the peak intensity at 20-.19.80 decreased significantly in the XRD analysis,which suggested that a strong crosslinking reaction occurred.(3)The blocked isocyanates were prepared from caprolactam using ethyl acetate and ethanol as solvent,respectively.The effects of isocyanates on the properties of white latex and phenolic resin mechanical adhesives were investigated.The results showed that the closed isocyanate with ethyl acetate as solvent could enhance the performance of white latex and phenolic resin.When the content of the closed isocyanate was 15%,the optimal result was achieved,but with the further increasing of the content,the invalid bonding components increased and the enhancement effect decreased.Closed polyurethane adhesive using ethanol as solvent with white latex and phenolic resin were also tested,the isocyanate adhesive enhanced effect at low concentration(5%),but along with the increase of the content of effective components,the enhancement effect was deteriorated.