(699g) Dissolution of Semicrystalline Polyethylene

A phenomenological model is presented that captures the phenomena governing the dissolution of semicrystalline polymers, e.g., solvent diffusion, transformation from crystalline to amorphous domains, specimen swelling, and polymer chain untangling. The model is validated for the case of polyethylene swelling and dissolution in good solvents. A parametric sensitivity analysis is carried out to assess the impact of decrystallization rate constant, disentanglement rate, and solvent diffusivity on the swelling and dissolution of semicrystalline polyethylene films. When decrystallization is important, the dissolution rate increases more with a reduction in the crystallinity compared to the film thickness. However, when the dissolution is controlled by polymer chain disentanglement, a reduction in the thickness could accelerate dissolution. The insights obtained from this study facilitate the design of efficient solvent systems and processing conditions for the dissolution/precipitation-based separation of polyolefins. Dissolution/precipitation is a low-GHG emission methodology for recycling waste plastic that cannot be mechanically recycled. Through this method, individual polymers can be separated from mixtures or blends, purified from additives or fillers, reduced in volume, and obtained in an acceptable form without negatively affecting the properties of the original polymers.