Study On The Preparation And The Dispersing-Curing Mechanism Of Siloxane Hybrid Acrylic Polymer Latex Powder

Steric stabilized siloxane hybrid acrylic polymer (SSPA) dispersion were prepared by surfactant-free emulsion polymerization with thiol end group polyvinyl alcohol (PVA-SH) as protective colloid. Online Fourier Transform Infrared Spectroscopy (FTIR) monitoring proved that graft polymer of PVA-SH and MMA was forming mainly at the seed polymerizing stage of the emulsion polymerization. Transmission Electron Microscopy (TEM) morphology of latex showed the steric stabilizer layer was integrated at a surfactant-free condition but fragmentary while adding SDS at the initial stage. Gel Permeation Chromatography (GPC) test showed, number average molecular weight ( Mn ) and polydispersity index (PDI) of the acrylic polymer stabilized by PVA-SH and(or) PVA-S-PMMA can be controlled to 50000-70000 and 1.5-1.7, respectively.Under the alkalescence condition, 11.2wt% vinyl triisopropoxysilane (C-1706) were hybrid into the MMA-BA backbone successfully. In the same time, no more than 4.8wt% of vinyl trimethoxysilane (A-171) can be grafted. The self-condensed reaction of the high stable isopropoxysilane hybrid polymer can be catalyzed by acid.SSPA dispersion stabilized via PVA-SH possesses very high shear stability. It can preserve particle size distribution even after spraying through a 24000rpm (about 62m/s) atomizer.Redispersible polymer powder (RPP) of the SSPA were prepared in a co-current centrifugal spray drying system. The operating parameters of drying were optimized for a model spray feed consisting SSPA dispersion, silica sol, polyvinyl alcohol (Celvol 205), hydroxyethyl cellulose (Natrosol 250LR), NaHCO₃ and water. Relationship between outlet temperature, spray speed to feed rate ratio, inlet-outlet temperature difference of dryer and particle size distribution, water content, bulk density of product were corrected via carried out a series of drying operation and product characterization.We found the water content of RPP product were controlled by outlet temperature and inlet-outlet temperature. On the other hand, the bulk density and particle size distribution were dominated by spray additives in feeds. When high Tg water soluble polymer PVA or HEC and super fine inorganic particle were used as carrier and dispersant, a high performance RPP product can be obtained. The RPPs using HEC(Tg=135℃) as carrier have smaller particle size and much better storage stability than those using PVA (Tg=73-80℃). It proved that carrier with higher Tg would...