Research On PVAc Emulsion With Low-volatile Organic Chemicals

In this paper, modified PVAc emulsion with low-volatile organic chemicals was prepared by optimizing initiation system and the process parameters of various factors in semi-continuous seed emulsion polymerization method:(1)Ammonium persulfate(APS), water-soluble 2,2’-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride(AIBI), oil-soluble azobisisobutyronitrile(AIBN), and both composite azo initiator were applied to initiate the PVAc copolymer emulsion respectively. Comparison of the effects of the PVAc copolymer emulsion by different initiators on conversion rate, residual monomer, molecular weight and its distribution, latex particle size distribution and morphology, Tg and charge stability, and the nucleation mechanism was also analyzed. The results show that the PVAc copolymer emulsion initiated by water-soluble/oil-soluble composite azo initiator has low polymerization temperature (65℃), higher conversion rate(99.13%), lower content of residue monomer (230.47 ppm), better charge stability and initiating efficiency than emulsions by other initiation systems. The PVAc copolymer emulsions prepared by different kinds of initiators have higher Tg than the theoretical value, emulsion initiated by composite azo initiator has the lowest Tg for the highest conversion rate of monomer. The emulsion existed with various nucleation ways, including homogeneous nucleation, micellar nucleation, monomer droplet nucleation and so on, which had combined the advantages of water-soluble and oil-soluble initiators, with less bonding between latex particles and a wide molecular weight distribution, good effects of the performance.( 2 ) Polyacrylamide (PAM) and polyvinyl pyrrolidone (PVP) were applied respectively as protective colloid to obtain different PVAc emulsions instead of polyvinyl alcohol (PVA), the mechanical stability, stability of frozen, electrolyte stability were worse than the PVA emulsion, and PVA emulsion had maximum viscosity. The different effect factors on the gelating phenomenon of PVAc emulsion were discussed by optimizing the formula and the process, selecting the polymerization temperature was 65℃, mass fraction of composite azo initiator was 0.5%, mass fraction of complex emulsifier was 2% to 3% (SDS/OP-10=1:2), mass fraction of PVA protective colloid was 6%, the intensity of Agitation was 160～220 r/min, reaction time was more than 3 h, the prepared emulsion had fine apperance, moderate viscosity, excellent performance and stability.(3)Taking the cost of production and different functional monomers on the modified emulsion properties and stability into account, selecting basic mass fraction of butyl acrylate (BA) was 25%, and mass fraction of acrylic (AA) was 1.5%, mass fraction of N-hydroxymethyl acrylamide (NMA) was 1.0%, mass fraction of methyl-β-hydroxyethyl methacrylate (HEMA) was 1.0% respectively as the cross-linked functional monomers obtained different modified PVAc emulsions, which had better stability of frozen, water resistance, heat-resistant stability than homopolymer PVAc emulsion. The performance of NMA modified emulsion was the best, HEMA modified emulsion was better than AA modified emulsion. Taking contact angle and surface energy testing of the Modified PVAc copolymer emulsions with different kinds of functional monomers, the maximum contact angle date of NMA modified emulsion by water was 61.33°, and the surface free energy was as low as 31.3676 mJ/m2, exhibited excellent hydrophobicity.