Dehydration and drying poly(vinyl)chloride (PVC) porous grains: 2. Thermogravimetric analysis and numerical simulations

• Measures drying rates PVC porous grains by thermogravimetric analysis.
• Shows the constant rate period and the falling rate period in drying beds with a double porosity (interstitial and internal pores).
• Shows in adimensional units the drying rate and drying time of water inside small pores (1 μm).
• Analyzes the role of geometrical parameters and surface properties in the dehydration process.
• Shows the drying patterns of droplets containing of poly(vinyl)alcohols with different hydrophilicity.

This paper analyzes the drying rates of humid porous grains of poly(vinyl)chloride PVC by thermogravimetry. Grains have variable volume fractions of pores, representing between 16 and 33% g water/g PVC, with pore sizes varying between 0.6 and 1 μm. It is shown that the humid cakes exhibit three different drying rate regimes at constant temperature, characterizing evaporation of free water, of interstitial water and of water inside the pores. The constant rate period (CRP) and the falling rate period (FRP) of drying are clearly identified. The drying rates and drying times are presented in adimensional units by comparison with evaporation of pure water. The thermogravimetric analysis identifies a fraction of water which dries very slowly inside the pores. A method of quantifying the strongly bound water is presented. Numerical simulations of water evaporation were performed on a 2D array of channels and illustrate the contribution of geometrical effects (diameter of channels, tortuosity, etc.) in pore drying. Visual observations of the drying of droplets of solutions containing dispersants used in PVC synthesis show interesting patterns. The phase separated solutions of dispersants are analyzed and their role in drying is highlighted.

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