Browsing by Author "Lin, Wen"

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    Morphology of polymer particles and its impact on the coalescence process
    (2003) Lin, Wen; Bellehumeur, Celine
    Coalescence of polymer particles occurs in industrial processes of rotational molding, powder coating, and rapid prototyping. The extent and rates of binding between particles govern the production cycle and the physical properties of the product. Polymer coalescence is promoted by heating the powder to the glass transition/melting temperatures and the melt viscosity, elasticity and surface tension are reported to be important parameters. It is also suggested that the molecular structure of the polymer and its morphology in the solid state may be important, and this is of current interest. The morphology of polymer particles is to be modified to achieve optimal processability and product quality through controlling the processing conditions and changing the material composition with additives. Commercial grade ethylene copolymers and polypropylene were used in this work. The resins were melted in a mold with and without a nucleating agent (bis 3 ,4 dimethylbenzylidene sorbitol) and solidified to form cylinders under various thermal treatments. Results showed that samples with slower cooling rates exhibited higher crystallinity and increased thermal stability. Coalescence experiments were conducted by heating two juxtaposed discs. There were only small differences with coalescence behaviors for samples subjected only to thermal treatments. However, the addition of the nucleating agent led to the formation of crystalline structures with higher crystallinity, melting and crystallization temperatures, and consequently slows the coalescing rates significantly.