The Preparation And Characteristic Of Water-free Powdery Coating In Supercritical Carbon Dioxide

The dry coating process of paper provides an effective way to eliminate some of the limitations encountered with other techniques in wet-coated and the water-free powdery coating provides possibilities to reduce the usage of water and save energy compared to the traditional paper coating method. Supercritical carbon dioxide which is environmental friendly has generated much interest in the polymer industry as a potential solvent for polymerization reactions. Water-free powdery coating particles mingled polymethyl methacrylate (PMMA) and calcium carbonate inorganic pigment were obtained under water-free conditions and AIBN as the initiator in supercritical carbon dioxide (sc-CO2). Addition of butyl acrylate (BA) as co-monomers resulted a low Tg of the polymer. In order to improve the compatibility between the pigment particle and polymer, the pigment particle was modified.In this study, the methods to control effectively the molecular weight and molecular weight distribution, the glass-transition temperature and the thermostability were studied in detail. The structure of the synthesized polymer was investigated by FT-IR. Molecular weight and the molecular weight distribution were determined by gel permeation chromatography (GPC)-eighteen angles laser light scattering method. The glass-transition temperature (Tg) was determined by differential scanning calorimetry (DSC). The thermostability of the synthesized polymer was measured by thermogravimetry (TG). The mixed particles were characterized by scanning electron microscopy (SEM).The experimental results indicated that the molecular weight and the molecular weight distribution of the PMMA can be controlled within a suitable range when the reaction pressure was 10 MPa, reaction temperature 75℃, reaction time 8 hour, and the monomer concentration was 0.10 g/mL, initiator concentration 0.10 x 10-2 g/mL, stabilizer concentration 0.06 x 10-2 g/mL. From SEM observation, it was found that the pigment granules were able to evenly disperse and embedded in the PMMA and didn't show conglomeration. The glass-transition temperature of the polymer can be controlled by adjusting the co-monomer MMA/BA ratio. Addition of the inorganic pigments can improve the polymer's heat resistance. The modified pigment can increase the thermal properties of mixed particles and control the molecular weight and molecular weight distribution of the polymer.