Search results for " crystallization kinetics"

Solidification of syndiotactic polystyrene by a continuous cooling transformation approach

2007

Syndiotactic polystyrene (sPS) was solidified from the melt under drastic conditions according to a continuous cooling transformation methodology developed by the authors, which covered a cooling rate range spanning from approximately 0.03 to 3000 °C/s. The samples produced, structurally homogeneous across both their thickness and surface, were analyzed by macroscopic methods, such as density, wide-angle X-ray diffraction (WAXD), and microhardness (MH) measurements. The density was strictly related to the phase content, as confirmed by WAXD deconvolution. The peculiar behavior encountered (the density first decreasing and then increasing with the cooling rate) was attributed to the singular…

Solidification of Polypropylene Under Processing Conditions – Relevance of Cooling Rate, Pressure and Molecular Parameters

2012

1989

Heat of crystallization significantly slows down polymer cooling and thus pressure drop increase during mould filling with thermoplastic crystalline polymers. If a correction of thermal diffusivity can account for such a cooling slow down at least as far as the effect on pressure drop is concerned, the use of nonisothermal crystallization kinetics may be avoided in the simulation of mould filling. A procedure to identify such a correction is outlined in this work. Pressure drop values during cavity filling calculated by using a corrected thermal diffusivity in the model proposed by Lord and Williams favourably compare with literature data taken with polypropylene and polyethylene resins. Be…

Improved experimental characterization of crystallization kinetics

2005

Polymer solidification occurring in many processes, like for instance injection molding, compression molding and extrusion, is a complex phenomenon, strongly influenced by the thermo-mechanical history experienced by the material during processing. From this point of view, characterization of polymer crystallization in the range of processing con- ditions, i.e. including high cooling rate, is of great technological and academic interest. Quiescent, non-isothermal crys- tallization kinetics of two polypropylene resins were investigated using a new method, based on fast cooling of thin samples with air/water sprays and optical detection of the crystallization phenomenon. The range of cooling …