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In this work, the effect of annealing on microstructure and tensile properties of polypropylene (PP) cast film was investigated by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (XRD), small-angle X-ray scattering (SAXS), SEM, etc. The SAXS data showed that the elevating annealing temperature led to the increase of thickness of lamellae phase and amorphous phase. The orientation of lamellae along MD direction after annealing was proved with the SAXS data. Moreover, these annealed samples had an extra low-temperature melting peak in the DSC curves and it moved to a higher temperature obviously with increasing the annealing temperature. More importantly, the relationship between the yield strength and the lamellar thickness was built through testing the tensile properties and calculating the Thomson-Gibbs equation, respectively. It revealed that the yield strength first increased rapidly and grew slowly when the lamellar thickness increased to a certain extent. A detailed physical model was also proposed to depict the change of microstructure during annealing. [ABSTRACT FROM AUTHOR]

The investigation about the uniaxial stretching behavior of fully crystallized poly(L-lactide)s (PLLA) containing long chain branching (LCB) is carried out by two dimensional wide angle X-ray scattering (2D-WAXS) and differential scanning calorimetry (DSC). The controlled sample is the linear PLLA containing nucleating agents which owns the similar degree of crystallinity and crystalline morphologies as that of PLLA LCB. The results show that much more chain entanglements in the amorphous area of PLLA LCB make the LCB sample be able to bear much larger stress and then reach larger elongation when it breaks. Although the original lamellae are more difficult to be damaged in PLLA LCB due to the more chain entanglements compared with linear PLLA, the final crystal orientation is much better for it. The higher melting point indicates that the extended chain crystals in this stretched LCB sample are more perfect, especially at high drawing temperature. The original topological structure of chains is supposed to be the governing factor which determines the different evolution of crystalline structures under strain. [ABSTRACT FROM AUTHOR]

The degrading behaviors of three kinds of melt polyolefin elastomers (POEs) at presence of dicumyl peroxides (DCPs) in transient shear flow were evaluated at elevated temperature by parallel plate rheometer. The critical shear rates for degradations of all POEs were different from one to another. The rheological and gel permeation chromatograph (GPC) results showed that the degradation was more and more distinct and the duration to achieve one similar level of molecular weight decreased as the shear rate increased. For quantitative information on chain structure, linear viscoelasticity combined with branch-on-branch (BOB) dynamic model was used to predict probable compositions and chain topologies of the modified products, which were reasonably explained by the suggested mechanism of radical reactions and could confirm that there was a kind of selectivity of shear rate on POE chains for degradation. Higher shear rate can enlarge the differences in mobility of the two scission parts and can further increase the possibility of effective degradation on the original chains. [ABSTRACT FROM AUTHOR]