| Waterborne polyurethane (WPU) is synthesized from polyether or polyester polyol and isocyanate. Polyether polyols based WPU has excellent low temperature flexibility and water-resistant properties, but inferior mechanic strength. Polyester polyols based WPU shows superior mechanic strength and excellent adhesion, however hydrolyzable properties. A new type of poly(propylene carbonate) polyols (PPC)derived from carbon dioxide and propylene oxide was synthesized successfully in our laboratory. Preliminary study results showed that the comprehensive properties of PPC based WPU were superior than that of polyester polyols based WPU and polyether polyols based WPU. Due to the existence of the hydrophilic groups in WPU, the film showed poor water resistance and hardness. Therefore, it is necessary to modify it to expand its applications. Polyacrylate has the advantage of hydrophobicity, high hardness and low raw materials cost. Incorporating acrylic resin into polyurethane has complementary advantages, resulting in the improvement of comprehensive performance of WPU.Waterborne polyurethane-acrylate (WPUA) composite emulsion and HEMA grafted core-shell WPUA were synthesized by incorporating acrylic resin into polyurethane via in situ polymerization in this paper. The properties and influence factors of emulsion were studied. Meanwhile, WPU was prepared by compounding HDI with IPDI. The flexibility and production cost of WPU were expected to obtain by the introducing of HDI. The main research results of this paper are listed as follows:(1) The obtained products film was characterized by FTIR. The spectrum of FTIR showed that the absorption peak of-NCO groups disappeared accompanied with appearing of-NH group stretching vibration absorption and the characteristic peak of urethane groups (-NHCO-). Acrylate monomer double bond peaks also disappeared replaced by the appearance of the polyacrylate characteristic absorption peaks, which indicating the reaction of isocyanate and PPC form WPU, and the complete reaction of acrylate monomer to obtain acrylic-polyurethane hybrid emulsions emulsion.(2) The emulsion particle size analysis indicated that introducing of PA into the PU resulted in large particle size attributed to the swelling of PA in PU. According to the above results, certain amount of coupling agent HEMA was introduced to form chemical bonding between PU and PA in modification of polyurethane with acrylate. The improvement of compatibility and blending degree between two resins reduced the particle size of composite emulsion, and improved the appearance and stability of emulsion.(3) The tensile strength of the films decreased with introducing PA into PU. The mechanical intensity of the film increased with introducing of certain amount of coupling agent HEMA by improving the intermolecular forces compared with those prepared by in situ polymerization.(4) The adhesion and pencil hardness of the films improved by introducing PA into PU. The adhesion was enhanced from grade2 to grade 0, while pencil hardness increased from H to 3H. Coupling agent HEMA increased the intermolecular interactions and the connection of molecular chain, which enhanced the resisting pressure from the external. As a result, the film pencil hardness and adhesion was improved, in particular, the pencil hardness reached to 4H.(5) The water resistance of the films analysis showed that water absorption ratio of modified with PA film decreased from 6.9% to 3.8% compared with the unmodified PU film. Based on the above results, water absorption ratio further reduced to 2.8% with addition of certain amount of HEMA, which confirming that acrylate was effective in improving polyurethane water resistance. The surface hydrophobicity tests showed that hydrophilicity of its surface was improved after modification with PA, in contrast to the improvement on hydrophobicity of overall film, resulting in the WPU emulsion easier to carry out second painting.(6) The DSC and TGA results proved the good compatibility between PA and PU and enhancement of glass transition temperature of the films with introducing of PA. Moreover, the enhancement of heat resistance of the film was also confirmed by TGA analysis. On this basis, addition of a certain amount of HEMA further improved the glass temperature and heat resistance of the films.(7) The XRD analysis of the films suggested no significant effect of PA on the crystallinity of the film. Although HEMA generated chemical bond between PU and PA, XRD spectrum was dominated by amorphous dispersion peak, which demonstrated that polymer was in an amorphous form.(8)The results showed that the best performanced film from WPUA hybrid emulsion was obtained when the PU quality score was 70%wt, the quality ratio of MMA and B A at 1:1, and concentration of HEMA at 10%wt.(9) In the synthesis of WPU derived from HDI and IPDI, WPU emulsion and cast film performance were affected by the factors of proportion of HDI/IPDI, R value, the amount of DMPA and EDA. After analyzing the data synthetically, when the mole ratio of HDI and IPDI was 0.5, R was 1.6 and mass fraction of DMPA and EDA was 5% and 1.2% respectively, the emulsion and film were superior. |
PDF Full Text Request