Miroslav Raab

Toughness profile in injection-molded polypropylene: The effect of the β-modification

Fracture toughness characterized by the J-integral method has been evaluated along injection-molded bars of isotactic polypropylene. A significant increase in toughness with decreasing distance from the specimen gate has been observed with maximum steepness of the dependence in the central part of the specimen length. Parallel analysis of wide-angle X-ray diffraction patterns has shown a similar dependence of the crystalline β-phase concentration. It is suggested that polypropylene with β-crystallites has better structural continuity in the amorphous phase and, consequently, higher inherent ductility and superior macroscopic toughness than the related material containing only α-crystallites. Consequences of β-phase gradients for practical toughness testing are also discussed.

The effect of specific nucleation on molecular and supermolecular orientation in isotactic polypropylene

The molecular and supermolecular orientation, morphology and structural changes observed during cold drawing of injection moulded isotactic polypropylene modified by specific a, and β nucleating agents were studied by polarised photoacoustic FTIR spectroscopy, wide-angle X-ray diffraction and differential scanning calorimetry. Significantly lower molecular orientation was found in the core of the β-nucleated injection moulded specimens as compared to unmodified and α-nucleated materials. This has been ascribed to the fast growth of the β-crystallites which inevitably dislocates the flow-induced orientation within the crystalline regions and in their vicinity. Moreover, it was found that the presence of the developed (3-crystallites distinctly diminishes the efficiency of the orientational solid-state drawing assessed on both levels of the hierarchical structure (molecular and crystalline). This structural observation is directly connected with macroscopic softening effect of the β-phase: lowering the yield stress and flattening the neck shoulder. Thus, the interrelation between the microstructural and macroscopic effects of the β-phase could be described as a feedback process.

Structural transformation of polyethylene phase in oriented polyethylene/polypropylene blends: a hierarchical structure approach

Injection-moulded specimens of polyethylene/polypropylene blends were drawn at room temperature and subsequently annealed at 140°C, i.e. above the melting temperature of polyethylene, but below the melting temperature of isotactic polypropylene. Structural transformations of the polyethylene phase were assessed at several levels of hierarchical structure by polarised FTIR spectroscopy with photoacoustic detection, DSC, WAXS and SAXS analyses, and dynamic mechanical analysis. The results indicate reorientation of polyethylene chains, corresponding rearrangement of crystalline lamellae and healing of interfibrillar flaws upon annealing.

Structure of polypropylene/ polyethylene blends assessed by polarised PA-FTIR spectroscopy, polarised FT Raman spectroscopy and confocal Raman microscopy

Physical structure and morphology of differently prepared and treated bulk specimens of isotactic polypropylene, linear polyethylene and their blend was studied by polarised FT Raman spectroscopy, polarised FTIR spectroscopy with photoacoustic detection, and by confocal Raman microscopy. The specimens differed in preparation technique, mechanical and thermal history. The orientation and reorientation of molecular chains of individual blend components, their crystallinity and the size and structure of the microdomains both in the skin and in the core of the specimens were correlated with the preparation conditions, mechanical treatment and thermal history. The possibilities and limitations of each method were discussed.

Comparison of two modern infrared spectroscopic methods for the determination of orientation in drawn bulk polymers

The potentialities of the infrared photoacoustic method and the ATR Golden Gate method for the measurements of oriented bulk polymer systems are compared. Both methods are suitable for the estimation of orientation, if low and medium intensity bands are used. The ATR Golden Gate method is faster, while the photoacoustic method gives more straightforward results and eliminates any possible effect on the sample.

Fracture Properties of Polypropylene Reinforced with Short Glass Fibres: The Influence of Temperature, Notch Length and Geometry

Commercial grades of isotactic polypropylene TATREN TI 924 and SLOVALEN PH 61GF 30 were used for preparation of specimens with 0%, 10%, 20% and 30% of short glass fibres reinforcement ratio.