Evaluation of castor acrylated monomer in acrylic latexes for one-component, low VOC, low odor, ambient cure, architectural coatings
The current drive towards producing low VOC architectural coatings is the development of one-component, ambient curable latexes. This drive is stimulated by governmental regulations to reduce solvent usage in architectural coatings, and customer desire to reduce the odor generated by evaporating solvent. C[barbelow]astor A[barbelow]crylated M[barbelow]onomer (CAM) is a novel monomer derived from a renewable resource that marries two coatings technologies--high molecular weight latexes with oil-modified polyesters--to produce a one-component, ambient curable latex. The synthesis of CAM acrylic polymers can be adequately achieved with standard polymerization conditions with temperatures ranging from 25°C to 80°C, standard atmospheric pressure, redox or thermal initiators, moderate agitation, and common feeding techniques. Homopolymer T g s were determined for BA, MMA, and CAM, and those values are -47 ± 10°C, 132 t 11°C, and -62 ± 13°C, respectively. High polymerization temperatures and long monomer feed times promote chain transfer and the formation of gel. Gel content increases the polymer storage modulus and reduces chain mobility, and both significantly hinder particle coalescence. Polymerization temperatures of 45°C are therefore suggested to provide optimum performance of CAM acrylic latexes. CAM polymer performance has been examined with relevance to both in-house and commercial latex controls, and CAM crosslinking has been proven using 1 H NMR, polymer solubility, DMA, and DSC. The activation energy for CAM crosslinking with 0.2 phr cobalt was determined to be 23,603 ± 770 J/mol. Tg increase differed with cure temperature, and the Tg and tan delta were found to increase 2, 6, and 12°C with 5, 10, and 15 phm CAM, respectively, at ambient temperature. CAM coating T g s were found to increase proportionally in magnitude with latex film Tg . CAM curing was found to improve block resistance and dirt pickup resistance such that higher CAM-containing latex coatings rivaled the commercial control which had a 12°C higher Tg . CAM curing was also found to improve pull-off adhesion and stain resistance, particularly against mustard and grape juice. Total removal of coalescing aids in flat and semi-gloss coatings is possible using 10 and 15 phm CAM acrylic latexes, respectively. A cost increase of 5 and 7 ¢/lb is realized with each coating, respectively, though this cost is insignificant when compared to the environmental benefits gained by solvent reduction. Lower CAM concentrations are possible, though the cost is only reduced 2 ¢/Ib when 5 phm CAM is used in lieu of 10 phm, and when 10 phm CAM is used in lieu of 15 phm. The addition of catalyst for rapid property development is a major concern and it is advised that catalyst concentrations be optimized to increase cure rates, reduce VOCs, and lower coating cost. Thus, CAM polymers provide ambient crosslinking and solvent reduction in architectural coatings while utilizing a renewable resource. These properties offer environmental benefits with minimal cost increase and low odor, while maintaining architectural coating properties.