Synthesis And Modification Of Waterborne Polyurethane Wood Coatings Based On Polypropylene Carbonate Diol

CO₂ copolymer polyol（PPC）is a novel material to synthesize polyurethane.Compared to traditional polyether and polyester based polyurethane,PPC-based polyurethane has excellent hydrolysis resistance and mechanical strength.Our research team has been engaged in the research of PPC application for decades,and has successfully synthesized PPC-based waterborne polyurethane material with excellent performance.In this paper,a series of waterborne polyurethane were synthesized used PPC,IPDI and DMPA as the main raw materials to prepare wood coating.The effects of hard segments,DMPA content,TMP,type of small molecule chain extender and soft segment structure on the properties of waterborne polyurethane and wood lacquers were studied.Meanwhile,PUD was separately modified by vegetable oil and silane coupling agent SCA-37,and then modified by the combination.The structure of PUD was characterized by FT-IR,and the particle size of emulsions was analyzed by Zeta-potential analyzer.The effects of SCA-37,vegetable oil,curing process and curing agent on the properties of emulsion and wood coating were investigated.Moreover,PUD was modified with nano-silica by in-situ polymerization and physical blending to prepare wood coating.The surface chemical composition was detected by using FT-IR,the morphology of the composite investigated by SEM,and the thermal degradation process of the modified PUD was characterized by TGA.The effects of two modification methods on the properties of PUD and wood coating were investigated.The results were listed as follows:（1）The properties of PUD and wood coating were significantly influenced by the hard segment,DMPA content,TMP and the type of small molecule chain extender.With the increase of hard segment content,the hardness and water resistance of wood coating were improved,and the heat storage stability of emulsion was decreased.With the increase of DMPA content,the appearance of the emulsion improved,the water resistance of the film decreased,and the glossiness increased.The raise of the TMP content resulted in the raise of the hardness,water resistance and ethanol resistance.Small molecule alcohol chain extender with rigid hexagonal ring is superior to the straight chain extender in hardness,water resistance and ethanol resistance.（2）Compared with the traditional polyether polyol-based wood coating,PPC based wood coating exhibited superior hardness,glossiness,fullness,sandability,and broad industrial application prospects.（3）PPC-based waterborne polyurethane wood coating exhibited excellent comprehensive properties except the ethanol resistance.（4）The boiling water and ethanol resistance of the wood coating modified by SCA-37 were significantly improved,however,the hardness was greatly reduced.When the amount of SCA-37 reached 2wt%,the boiling water and ethanol resistance met the requirements of the water-based wood coating.（5）The water-resistance,ethanol-resistance and the glossiness of the wood coating modified by vegetable oil were significantly improved,accompanied by the slight decrease of hardness.The sanding property tented to be inferior.When the vegetable oil content reached 7.4wt%,the boiling water and ethanol resistance met the requirements of waterborne wood coating,the wood coating exhibited superior sanding property and hardness.（6）The ethanol resistance of wood coating modified by the combination of vegetable oil and silane coupling agent was further improved.When the content of SCA-37 was 3wt%and the vegetable oil was 7.4wt%,the coating film was resistant to70vol%ethanol for 8h in immersion test,and was resistant to 50vol%ethanol for more than 500 times in ethanol wiping test.（7）The stability and appearance of VSPUD emulsion was greatly influenced by the curing temperature.When the curing temperature was at 45⁵5℃,the emulsions showed superior appearance and storage stability.（8）The performances of VSPUD wood coating could be further improved by using curing agent.The glossiness and the resistance to ethanol of the wood coating increased with the curing agent amount.When the curing agent was at 4wt%,the resistance to the70vol%ethanol was more than 500 times in ethanol wiping test.（9）Modified with nano-silica by in-situ polymerization,the water resistance and hardness of the film and the wood paint were obviously improved,but the ethanol resistance had no significant variation.The glossiness was slightly decreased.Modified with nano-silica by physical blending process,the water resistance,ethanol resistance,glossiness of the wood coating decreased significantly,while the hardness increased.（10）TGA analysis showed that the heat resistance of the modified film was significantly improved,and the modification by in-situ polymerization was more effective.The results of SEM showed that the film modified by in-situ polymerization had good compatibility between nano-silica and polyurethane,and the film surface was smooth.The film modified by physical blending method showed inferior compatibility between nano-silica and polyurethane,and the surface of the film was rough.