催化剂对聚乙烯醇缩甲醛改性PVAc乳液性能的影响

以聚乙烯醇缩甲醛（PVF）为保护胶体，采用半连续种子乳液聚合方法，合成了固含量为18％左右的聚醋酸乙烯酯（PVAc）乳液，研究了缩醛反应的催化剂种类（硫酸H2SO4、盐酸HCl）、pH值对乳液中游离甲醛含量、缩醛度、黏度及对胶接强度的影响。采用傅里叶变换红外光谱（FTIR）、接触角测量等对乳液的结构和性能进行了表征。研究结果表明，不同的催化体系对乳液性能的影响不同。随着pH4值的降低，乳液中游离甲醛含量降低，PVF的缩醛度升高，乳液黏度和胶接强度均呈先升高后降低的趋势。催化荆种类和pH值对乳液接触角无显著影响。用H，SO。作为缩醛反应的催化剂，反应的pH值为34时，合成乳液的综合性能最佳。

Effect of catalyst on properties of polyvinyl formal modified PVAc emulsion

PVAc emulsion with solid content of about 18% was synthesized by semi-continuous emulsion polymerization. Polyvinyl formal （PVF） was used as the protective colloid. The effects of catalyst type （H2SO4, hydrochloric acid） and pH value on free formaldehyde content, degree of acetalization, viscosity and bonding strength of emulsion were studied. The emulsions were also characterized with Fourier transform infrared spectroscopy （FT-IR） and contact angle measurement. The results indicated that different catalyst leaded to different impacts on the properties of emulsion. With decreasing of pH value, the free formaldehyde content of emulsion decreased, the degree of acetalation increased, the viscosity and bonding strength of emulsion increased first and then decreased. In the conditions of experiment, catalyst type and pH value had little effects on the contact angle of emulsion. When HgSO4 was used as the catalyst, pH value was 3.4, the propei＇ties of emulsion were the best.