Study On Application Of Transesterification In Epoxy/polyester Resins

Thermosets,as an important kind of polymer,are widely used in adhesives,protective coating,electrical insulation,3D printing applications for their excellent heat resistance,dimensional stability and good mechanical properties.Unlike plastic polymers,conventional thermosets can't be melted or dissolved after be cured,some properties such as insufficient toughness,brittleness and difficulty in secondary molding limit their further application and cause problems like energy waste.Recent studies on covalent or non-covalent bonds and their dynamic reversible activities allows thermosets exhibiting some thermoplastic properites: the dynamic reversible reaction can be triggered at a temperature higher than the glass transition temperature,which can be used in solid state plastic deformation and self-repairing design of the materials.By introducing dynamic reversible reaction to the network,defects such as insufficient toughness,secondary molding problems of thermosetting materials could be remedied,as well as durability and flexibility.Self-healing capability can avoid frequent maintenance and replacement of materials,and solid state plasticity can promote multiple deformation of thermosetting materials.In this study,transesterification catalyst 1,5,7-triazabicyclo [4.4.0] dec-5-ene(TBD)has been introduced into bisphenol A epoxy resin to explore the influence of catalyst content on the curing process and simulate the solid plastic behavior of the material at a controlled glass transition temperature.It has been found that the reversible transesterification reaction in the material could be activated under heating and controllable and recoverable shape of the material could be obtained.The shape fixation rate and shape recovery rate of the epoxy resin can be stably maintained above 80% when the elongation is nearly 100%.Epoxy materials with a certain cross-linking density have been prepared to achieve shape transformation ability above the glass transition temperature,which further expands the application field of materials.Furthermore,epoxy composite materials can be recycled based on the dynamic reversible transesterification,which could reverse the embarrassing situation of the one-time use of the epoxy materials,save resources and reduce material waste.Based on the results of the transesterification catalyst in the dynamic reversible transesterification reaction,another transesterification catalyst zinc acetylacetonate(ZAA)has been incorporated to the field of self-healing coatings.Combined with the general trend of solvent-free coatings and self-healing capability,we propose a new method for introducing reversible bond exchange network into powder coating structure.Anchoring with laboratory-made low molecular weight polyethylene wax,the optimal dosage of transesterification catalyst in polyester powder coating is determined to be 0.2wt.%.After heating,the dual effect of the physical migration of wax and the transesterification reaction can repair some cracks on the coatings.The scratches on the surface of coatings are basically invisible after repairing.Multiple performance tests such as aging,scratch resistance,acid salt spray have proved the effect and practicability of the self-repairing powder coating,which can extend the durability of the product.The results of this study also indicate that it is a potential and effective method in future to improve corrosion protection and weather resistance properties by introducing dynamic reversible transesterification into a proper network design for self healing coating.