The Study On Preordering Of Polymer Crystallization With In-situ Synchrotron Techniques

Polymer material is widely used in basic necessities of life, aerospace, national defense and military, etc, because of its physicochemical property and low cost. However most polymers are used in low-end market, the property of polymers should be improved urgently. The strength and stiffness of semi-crystalline polymer are mostly dependent on the structure of crystal, so learning the polymer crystallization mechanism is of great importance in regulating the strength and stiffness of polymer products. Based of the reach results in the last centenary, the general laws of polymer crystallization were captured, however, there is lack of universal polymer crystallization theory. Some issues are in suspense, for example, the existence and structure of precursor are still under debate. The mystery of physical picture of polymer crystallization is still uncovered. The present work focus preorder as well as the physical picture in multi-scales of polymer crystallization. Serious experiment are designed and carried out. Main experiment and results are summarize as following:(1) Home-made fiber pulling device was designed and constructed to impose thermal and extensional field on polypropylene at a wide temperature range. Synchrotron radiation scanning X-ray microdiffraction is highly sensitive detecting technique with high temporal and spatial resolution, which is used to detect shear induced preorder. The result shows that shear can induce crystalline precursor at temperature below melting temperature of polypropylene, the crystallinity and number of crystalline precursors decreases with rising shear temperature. The precursor is stable and doesn’t grow continuously growth at shear temperature. The detection sensitivity of crystallinity of Synchrotron radiation scanning X-ray microdiffraction is 0.1%. No crystalline precursor was shown at shear temperature higher than melting temperature of polypropylene, nevertheless, non-crystalline precursor are induced. The experiment provided convincing evidence on the existence of precursor, the structure of precursor is dependent on shear temperature.(2) Aimed to answer whether there is a sharp boundary between crystal and melt, partially melting and re-crystallization of isotactic polybutylene-1 is carried out as it has unique phase behavior. Fourier transformation infrared micro-spectroscopic imaging and wide/small angle x-ray were used for in-situ measurement. The result shows that memorized ordered melt (MOM) formed when form I crystal was partially melted, MOM may recover back to form Ⅰ when temperature is lowered, it’s different from random melt which tends to crystallized into form Ⅱ crystal. According to the characteristics of MOM, it may locate between preserved crystal and random melt and may be a diffuse interface layer.the physical picture is likely to non-classical crystallization.(3) Crystallization of crosslinked polypropylene is in-situ studied with Fourier transformation infrared and Synchrotron radiation wide/small angle x-ray. The three measurements can provide ordering information in multi-scales which are chain segments, density, and crystal information. The results show that the mechanism at different temperature region is different, coupling of conformation and density can induce liquid-liquid phase separation at temperature below melting point of polypropylene; while temperature is higher than melting point of polypropylene, conformation ordering segment packed into crystal without induce liquid-liquid phase separation.Main innovations involved in the present research work:(1) With highly sensitive detection of Synchrotron radiation scanning X-ray microdiffraction and its high temporal and spatial resolution, the existence and structure of shear-induced preorder is studied.(2) Partially melting and recrystallization of isotactic polybutene-1 was studied with its unique phase behavior. The question whether the boundary of melt and crystal is shap is answered. The crystallization of ordered melt between random melt and preserved crystal is in-situ studied.(3) Fourier transformation infrared and Synchrotron radiation wide/small angle x-ray was used to follow the crystallization process of croslinked isotavtic polypropylene in order to reveal the physical picture of polymer crystallization.