Study On The Process Of CO₂ Foaming Polyvinyl Chloride

Polyvinyl chloride（PVC）foaming materials prepared by using carbon dioxide（CO₂）produced by sodium bicarbonate（NaHCO₃）or supercritical CO₂ as a blowing agent is green technology.The influence of the composition of PVC on its rheological properties was investigated,and the orthogonal experimental results determined the optimum composition of 100 parts of PVC（SG-5）resin,6.5 parts of composite lead salt stabilizer and 1 part of lubricant calcium stearate,15 parts of chlorinated polyethylene（CPE135A）,5 parts of acrylate copolymer（ACR-401）and 3 parts of plasticizer dioctyl phthalate（DOP）,whose loss tangent tanδof the melt is close to 1,so that it viscoelastic property is suitable for foaming.Then,NaHCO₃ was modified by molten coating method using stearic acid,zinc stearate,glycerol monostearate and PE wax as modifier respectively,it was found that the mass ratio of m（NaHCO₃）:m（stearic acid）of 1:0.5 is better,the initial decomposition temperature of modified NaHCO₃ is around 181℃,and decomposition range reduces 18.8℃.PVC extrusion foaming process was carried out using stearic acid-modified NaHCO₃ as chemical blowing agent.When the foaming temperature is 190℃and the foaming agent is added in an amount of 10 parts,the PVC foam with average cell diameter of 47.5?m,cell density of 8.8×10⁵ cells/cm³ and expansion ratio of 1.24 can be obtained.Thirdly,PVC microcellular materials were prepared by step temperature rising method using supercritical CO₂ as foaming agent.The solubility of CO₂ in PVC was determined by mass weighting method in the range of 40⁵0°C and 10²0 MPa CO₂ pressure,which is 0.044⁰.072 g CO₂/g PVC,and diffusion coefficient is 0.64¹.18×10^-11m²/s,Under the condition of 15 MPa saturation CO₂ pressure at 40℃and 50℃,foaming temperature of 180²20℃,microcellular PVCs with average cell diameter of 1.2⁸.9?m,cell density of 0.2⁵.1×10¹⁰ cells/cm³ and expansion ratio of 1.09¹.32 have been prepared.Finally,PVC microcellular materials was prepared by rapid depressurization method using supercritical CO₂ as a foaming agent.The equilibrium saturation time of CO₂ in PVC at 120℃and 10 MPa CO₂ pressure is about 120 min,and the solubility of CO₂ in PVC is 0.0058 g CO₂/g PVC.It was found that with the foaming temperature increasing,the cell size increases gradually,and the cell density increases first and then decreases;with CO₂ pressure increasing,the cell size increases first and then decreases,and the cell density gradually increases;With the release rate of pressure increasing,the cell size decreases and the cell density increases.When PVC was foamed at 170℃and CO₂ pressure range of 8 to 20 MPa,the cell diameter is 5.1²9.4μm,cell density is 1.1×10⁸²2.2×10⁸ cell/cm³,and the expansion ratio is 1.07².71.These results can give reference for PVC foams with good cell morphology prepared by using CO₂ as blowing agent.