Accelerated crystal growth in cryogenic mechanically milled polymers and polymer blends

摘要

Previous comparative studies on the impact of cryogenic mechanical milling (CMM) of polymers showed significantly changed thermal and mechanical properties and-in the case of some polymer blends (e.g., PMMA/PVDF) an improved miscibility. Those changes were mainly attributed to a reduction of the molecular weight average during the milling process. The crystallization process in macromolecular systems is strongly affected by any small change of the initial chain structure like the chain conformation, the presence of branches and of course a decrease of the molecular weight average. Therefore, the aim of this paper was a comparative study of isothermal crystallization of cryogenic mechanically milled and original (unmilled) polymers and polymer blends. The overall crystal growth rates were determined and the development of the spherulitic morphology was studied in detail by means of hot stage polarized light microscopy. Isothermal crystallization of bulk samples was also investigated using differential scanning calorimetry (DSC). The average spherulite growth rates of the milled homo-polymer as well as the blends were significantly higher than in unmilled samples; even when all experiments started from the molten state. Moreover, the increase in crystal growth was almost independent of the chosen crystallization temperature and thus the degree of undercooling.