| Environmentally friendly acrylate latexes have an extensively application in coating,adhesives, et al. Particularly, the latexes with a core-shell structure are receiving an increasingattention due to their excellent performance. Up to now, a range of latexes particles withdifferent morphologies have been developed and become commercially available. In this paper,we have prepared a larger number of novel latexes with core-shell structure bycopolymerization of methyl methacrylate (MMA), butyl methacrylate (n-BMA) and otherfunctional monomers. Followed by spray drying, the dry polymer particles was obtained. Inaddition, rheological and mechanical properties of the dry polymers were investigated andexpected to explore a new application area.Effects of emulsifier, initiator and other factors on latex performance were firstlyinvestigated by particle size analyzer, transmission electron microscopy (TEM), scanningelectron microscope (SEM), and differential scanning calorimetry (DSC), et, al. It was foundthat the more amounts of emulsifier, the smaller particles generated at the seeded emulsionpolymerization stage. However, the less use of emulsifier led to the non-stability of the system.The best emulsifier amount used for the formation of core latexs in our research was0.5%based on the monomers. It was found that the particle size gradually decreased from480nm to300nm and the distribution turned broad as the increase of the amount of emulsifier.Additionally, amount of initiator also affected the gel fraction and particle size. Particle size ofcore-shell latex was found to increase with the reaction time. Observed by laser particle sizeanalyzer and SEM, the polymerication was confirmed to run at the surface of particale and thesize increased with polymerization time, These particles all demonstrated the uniformsphereical structure with narrow particle size distriubtion. The appearance of two glasstransition temperature (Tg) in DSC curve evidenced the core-shell structure.Different particle sizes, core-shell ratio and degree of crosslinking of acrylate core-shellmicrospheres were prepared by semi-continuous seed emulsion polymerization and characterized by particle size analyzer, SEM and other techniques. It was found final particlesizes basically agreed with the theoretical results by caculation. EGDMA and HEMA wereused to modify these core-shell particle respectively. The introduction of HEMA would lead tosecond generation of particles, which has rectified by SEM images. In general, HEMA was agood modify compound for the core-shell emulsion, which can enhance the thermal resistanceof the polymer.The rotational rheometer was adopted to investigate the rheological properties and Sol-gelprocess of acrylate polymers mixed with plasticizer1,2-benzenedicarboxylic acid, diisononylester (DINP) respectively. Prior to the measurement, the storage stability test for the mixture ofspray drying products of pure core and pure shell in DINP was carried out and showned thepoor stability. However, the good storage stability of core-shell latex product in DINP exhibitedverified the existence of core-shell structure. Subsequently, the mixture fluid was proved to bea false plastic fluid whose viscosity decreased with the increase of shear rate before the geltransition. Additionally, particele size, temperature, content of plasticizer, et al, have aninflunece on the viscosity of the sol-gel of core-shell dry polymer. The dynamic test indicatedthat sol-gel phenomenon occured in the heating process. If the core/shell ratio increased, thegel temperature would decrease too. However, gel curing temperature increased with theincreasing use of DINP. In addition, we found that HEMA had no influence on the geltemperature. SEM images confirmed that the acrylate polymer and the plasticizer DINP couldbe melted to form homogeneous phase at high temperature. |
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