TEMPERATURE-AND DEFORMATION-DEPENDENT STRUCTURAL CHARACTERIZATION OF SEMI- CRYSTALLINE POLYMERS BY X-RAY SCATTERING

ABSTRACT The special mechanical behaviour of semi-crystalline materials is caused by the temperaturedependent interaction between the crystalline and the amorphous phase with their specific mechanical properties. Thereby, the crystalline phase has higher strength and stiffness, it fails mainly under shear stress. The amorphous phase is tough above the glass transition with steadily decreasing strength with increasing temperature. Crazing may appear during. Under the complex load between the crystallites the amorphous phase tends to cavitation if the internal strength is too low with respect to the external load. This general behaviour was investigated and presented in the past by several different groups [1-2]. Recent investigations by synchrotron x-ray scattering enabled a highly time-and strain-resolved as well as temperature dependent investigation of structural changes during deformation. While wide angle diffraction enables a detailed characterization of the crystallites with respect to their orientation and deformation small angle scattering enables information about the size of the different phases and cavitation. Therefore the SAXS patterns were processed to estimate corddistribution-functions according to the procedures developed by Stribeck for samples with fiber symmetry [3]. The behaviour of different semi-crystalline polymers will be presented and compared with the behaviour of pure amorphous materials. A special attention will be turned on the structural events with respect to the stress-strain-curve. Some micrographs confirm the structural units, which were discussed on the basis of the x-ray pattern

301 Fracture Toughness Studies of Polypropylene

In this paper, a comparative study on the fracture toughness of woven glass fibre reinforced polypropylene, chopped glass fibre reinforced polypropylene and nanoclay filled polypropylene composites is presented. Nanoclays (Cloisite 15A) of 1 wt. % to 5 wt. % were filled in polypropylene (PP) matrix and they were subjected to fracture toughness studies. The specimen with 5 wt. % nanoclay showed 1.75 times and 3 times improvement in critical stress intensity factor (KIC) and strain energy release rate (GIC), respectively, over virgin PP. On the other hand, 3 wt. % nanoclay PP composites showed superior crack containment properties. These structural changes of composite specimens were examined using Transmission Electron Microscopy (TEM) and X-ray diffraction (XRD) methods. It showed that exfoliated nanocomposite structures were formed up to 3 wt. % nanoclay, whereas, intercalated nanocomposite structures formed above 3 wt. % nanoclay in the PP matrix. Furthermore, the woven fibre reinforced PP composites demonstrated superior crack resistant properties than that of clay filled nanocomposites and chopped fibre PP composites. However, KIC and GIC values for woven fibre composites were lesser than that of chopped fibre composites. Moreover, KIC and GIC values for both nanoclay filled PP composites and woven fibre composites are comparable even though the clay filled PP demonstrated catastrophic failure. Also, the crack propagation rate of PP-nanoclay composites is comparable to that of chopped fibre composites