Effect of the structure at the micrometer and nanometer scales on the light transmission of isotactic polypropylene

Abstract

The spherulitic superstructure, crystallinity, and structure and morphology of crystals of isotactic polypropylene were controlled by the conditions of melt crystallization and related to the transmittance of visible light. Spherulitic samples, which contained monoclinic lamellae, were prepared by slow cooling of the quiescent melt at rates lower than 10 K/s and by isothermal melt crystallization at temperatures between 373 and 413 K. Nonspherulitic specimens, which contained nonlamellar mesomorphic domains, in contrast, were obtained by rapid cooling of the melt with rates faster than 100 K/s. The crystallinity and the size of crystals were furthermore fine-tuned by subsequent annealing at elevated temperatures. Analysis of such films of different structure by ultraviolet-visible spectroscopy revealed that the light transmission was independent of (1) the fraction, (2) the internal structure, and (3) the size of the crystals. In contrast, the light transmission increased with decreasing size of spherulites and finally exceeded 90% in films of 100 lm thickness when spherulites were completely absent. The crystallinity and the structure and size of the crystals of the films of isotactic polypropylene could be adjusted within wide limits without affecting the light transmission.

Formation and Reorganization of the Mesophase of Isotactic Polypropylene

“…Spherulitic samples of identical crystallinity, in contrast, are rather opaque and the light transmission is about only 50%. The reasons for the different optical behavior of spherulitic and non-spherulitic samples have been described in detail in a separate study [34].…”

Morphology of cold-crystallized polyamide 6

“…The mesophase domains can then be reorganized to crystals by heating, with the shape and non-spherulitic superstructure preserved. As such, it is possible to obtain semicrystalline iPP of qualitatively different crystal morphology and superstructure, which, naturally, exhibit different property profiles [28][29][30]. Similar study of the effect of variation of the pathway of solidification of the melt of PA 6 on the morphology of the ordered phase and its superstructure is not available and therefore object of this work.…”

Study on adhesion strength, thermal creep resistance, and light transmittance of ethylene‐polypropylene copolymer grafted with silane for photovoltaic application

“…It is seen that EPR15/EPR9(5/5) blend shows bigger spherulites than those of EPR9. It has been reported that the transparency of a semi‐crystalline polymer is mainly influenced by the size of the spherulite . The bigger spherulites result in strong light scattering and poor transparency .…”