Synthesis And Film-forming Performance Of Polymer Latexes

Waterborne coatings exhibit safety and environmental benefit and have been extensive studied and application, present water-based coatings possess some disadvantages including the volatile organic compounds(VOC) contents is still high and mainly from the use of small organic molecules coalescent. Using reactive coalescent could not solve thia question due to high cost and not good film properties. And complexed hard and soft polymer emulsion could reduced the contents of coalescent to lower the film hardness and chemical resistance; Consequently, the assistant-film-forming polymer emulsion was developed to prepare ultra-low VOC contents waterborne wood coatings, and the syntheses and properties of assistant-film-forming polymer emulsion were studied.The polyacrylate emulsion(PA) with small particle size were synthesized and used as a coalescent. Effects of Tg of PA, proportions and dosages of emulsifiers, and amounts of MAA on emulsion polymerization stability and assistant-film-forming performance of PA were studied. The results showed that polyacrylate emulsion with good assistant-film-forming performance could be obtained under the optimized conditions as follows: the mass ratio of the reactive emulsifier/anion and nonionic emulsifier was 2/1 and the content was 2.1%, the Tg was-20℃, the MAA dosage was 4.5%. The total VOC content of waterborne wood coatings formulated by PA was low to 33 g/L, and the film properties could meet the requirements of HG/T 3828-2006 with 13.9% of the water absorption ratio and B class of the pencil hardness.The novel diol chain-extender trimethylol propane monolaurate(TMPLA) was synthesized to prepare novel polyurethane aqueous dispersions(n-PUD),which was used as a coalescent to assist the film forming of high Tg polyacrylate emulsion. Effects of NCO/OH molar ratios, soft/hard segment contents and molar ratios of TMPLA/BDO on assistant-film-forming performance of n-PUD were studied. It was found that TMPLA possess assistant-film-forming ability. The optimized conditions to prepare assistant-film-forming n-PUD as follows: the molar ratio of TMPLA/BDO was 4/2, the NCO/OH molar ratio was 1.3 and the mass ratio of soft/hard segment was 55/45. Ketone-hydrazine crosslinking modification could improve the film performance of the blending systems. When the molar ratio of ADH/DAAM was 0.9, the best film performance of blending emulsion could meet the requirements of HG/T 3828-2006 with 7.1% of the water absorption ratios, 20% of the alcohol absorption ratios and B class of the pencil hardness.In order to improve the assistant-film-forming performance of conventional PUD, various mono-alcohols had been used to prepare blocked polyurethane aqueous dispersions(b-PUD). Effects of blocking agent types, NCO blocked percent, NCO/OH molar ratios and polyol types on assistant-film-forming performance of b-PUD were studied. It was found that dipropylene glycol mono butyl ether(DPn B) could improve the assistant-film-forming ability of b-PUD significantly. The optimized conditions to prepare assistant-film-forming b-PUD as follows: the NCO blocked percent was 80%, the NCO/OH molar ratio was 1.5 and the optimal polyol type was N210. The assistant-film-forming performance of b-PUD prepared under optimized conditions was better than PA and n-PUD mentioned before. The total VOC content of waterborne transparent primer formulated by b-PUD was low to 28 g/L with good sanding property and high transparency.