Diffusivity And Solubility of Solvents in Semi-Crystalline and Glassy Polymer

The solubility and diffusivity of solvents in polymers has direct industrial applications. Two of the remaining frontiers in this area of research focus on diffusion and solubility of solvents in polymer below the glass transition temperature and in semi-crystalline polymers. This work has extended the work of Vrentas and Duda1, Michaels and Hausselin2 and Doong and Ho3 in those areas.;This work provides an in depth investigation into the effect the crystalline regions within semi-crystalline polymers have on both solubility and diffusion. Michaels and Hausselin attributed the decrease in solubility with temperature within of semi-crystalline polymers to polymer chains that extend across the amorphous region and tether two crystalline regions together. Doong and Ho extended the theory of Michaels and Hausselin to be used in combination with the UNIFAC group contribution method. Using a similar approach to that of Doong and Ho, this work investigates the amount of tie chains within various forms of polyethylene and has found two correlations that agree with mechanical experiments such as the brittle fracture experiments of Brown et al.4 The first is that the amount of tie chains increase for polyethylene that was polymerized with a comonomer such as 1-butene or 1-hexene when compared to that of a linear high density polyethylene homopolymer. The second correlation indicates that polyethylene that is crystallized significantly below the melt temperature has more tie chains than the same polyethylene crystallized near the melt temperature. This was shown in solubility experiments conducted on granules directly from a gas phase polymerization reactor. A new theory for diffusion in semi-crystalline polyethylene based on Vrentas and Duda's free-volume theory is shown to accurately capture the effect of temperature, solvent concentration, and the amount of crystallinity on diffusion.;The volumetric behavior of polymers abruptly changes below the glass transition temperature. This change in volumetric behavior creates a deviation between experimental diffusion coefficients and the diffusion coefficients predicted by Vrentas and Duda's original freevolume theory. This work uses the model of Vrentas and Vrentas5 for diffusion below the glass transition temperature as a basis for a new modification of Vrentas and Duda's free-volume theory. This is shown to accurately predict diffusion below and above the glass transition temperature of solvents in HPMCAS. To apply this work to the spray drying of HPMCAS, a model was derived to capture the drying of a droplet containing HPMCAS and solvent. Using the diffusion coefficients determined by the modified free-volume theory, the droplet drying model accurately predicts when the droplets shape deviates from being spherical.