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Study on the Relationship between Mechanical Properties and Spherulite Structures of Isotactic Polypropylene

Author: YaoXueMin
Tutor: JiangShiChun
School: Tianjin University
Course: Materials Science
Keywords: Isotactic polypropylene Variable temperature tensile Spherulites relationship with the mechanical properties
CLC: TQ325.14
Type: Master's thesis
Year: 2010
Downloads: 159
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Abstract

The mechanical properties of polymeric materials is closely related to its structure, and mechanical properties of the polymer structure to understand the relationship between the material properties has been a research hotspot. Characterization of polymer deformation behavior is an important basis for its mechanical properties, deformation behavior in addition to the structure of the material itself, but also with temperature and strain rate and change. Currently, the deformation characteristics of the polymer is still in the phenomenological description of phase deformation mechanism is controversial, its essence still lack sufficient knowledge and understanding. In this paper, isotactic polypropylene (i-PP) for the study, by in situ synchrotron radiation small-angle X-ray scattering (SR-SAXS) for the i-PP system at different temperatures isothermal crystallization process Mesoscopic structure and its changes were observation, that the scattering curve SAXS scattering peak obvious, and with the extension of crystallization time i-PP scattering intensity increases, indicating that the isothermal crystallization process there is an ordered crystal structure. At various isothermal crystallization temperatures of the sample, with the extension of a long period of time and the thickness of the amorphous layer tends to decrease, and the lamellar thickness basically unchanged, at higher temperatures this trend is more obvious; with the crystallization temperature rise high long-period and lamellar thickness were increased. Temperatures for the different isothermal crystallization i-PP, stretched using a polarizing microscope equipped with a hot plate at different temperatures observed when stretched morphology changes, higher temperatures found in the isothermal crystallization temperature of the sample in the experiment stretching both showed no yield brittle fracture, fracture occurs between the spherulites; isothermal crystallization temperature of the sample at the test temperature stretching showed a typical ductile deformation behavior; moderate isothermal crystallization temperature of the sample in the lower stretching temperature is no yielding occurs brittle fracture, fracture occurs between the spherulites, stretching at a high temperature is yielding occurs, at the ductile fracture strain softening, fracture also occurs in between spherulites. Determination of spherulite size changes in the drawing process, the results show that during stretching the size of spherulites basically unchanged. Using a polarizing microscope equipped with a hot stage observed temperature stretching, stretching rate and sample thickness on the mechanical properties of i-PP, the results show that the tensile test, the tensile rate and reduce the temperature rise effects are similar. Increase or decrease the stretching temperature tensile rate, i-PP Young's modulus, yield stress and breaking stress were decreased, while the elongation at break was increased. i-PP and the tensile yield stress of the logarithmic rate, namely (?) ~ ln_V. This can be activated crystal plasticity theory and Eyring theory to explain. The study also found that the thickness of the i-PP and 1mm thickness of 0.1mm i-PP difference compared to the Young's modulus is not obvious, it is considered a different thickness of the sample to bring the difference in mechanical properties of samples of the same thickness and the tensile tensile properties compared to the acceptable error range.

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CLC: > Industrial Technology > Chemical Industry > Synthetic resins and plastics industry > Polymer resin and plastic > Polyolefin plastic > Polypropylene
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