H. W. Kammer

Mechanical properties and morphology of isotactic polypropylene/ethylene-propylene copolymer blends

Abstract Mechanical tensile and dynamic mechanical tests have been performed at different temperatures on specimens of polypropylene (iPP)/ethylene-propylene copolymer (EPR) blends, obtained under various crystallization conditions. The initial morphology was observed by optical transmission and scanning electron microscopy. Furthermore the influence of the rubber composition on the neck formation was analysed and the tensile mechanical properties of the fibres evaluated as well. Up to 10% of EPR in the blend, the morphology of iPP was only slightly changed. At higher EPR content, a decrease in spherulite size was observed. The curves of modulus Eversus drawing temperature Td exhibited a change in the drawing mechanism at a temperature Ti. This transition temperature increased on enhancing the crystallization temperature Tc and is almost independent of the EPR content. The change in the flowing mechanism was also visible by direct inspection of the specimen fibres which were opaque for Td Ti. These features were indicative of a dependence of the drawing mechanisms on the initial morphology and on the testing temperature. The fibre modulus depended strongly on the drawing temperature Td but not on the crystallization temperature Tc. This suggested that an almost complete cancellation of the initial morphology occurred after fibre formation. The effect of the rubber addition was a decrease of the Youngs modulus of the fibres in all the blends. A tentative interpretation of the above illustrated features has been provided.

Phase behaviour of poly(ϵ-caprolactone)/(polystyrene-ran-acrylonitrile) blends exhibiting both liquid-liquid unmixing and crystallization

Abstract Miscibility and morphology in blends of poly(ϵ-caprolactone) (PCL) and poly(styrene-ran-acrylonitrile) (SAN) were examined by light scattering and optical microscopy. The blends display miscibility in the amorphous state in a limited range of copolymer composition. Morphologies, formed as a combined effect of liquid-liquid phase separation and crystallization of PCL, are discussed. Crystallization leads to spherulite structure in the blends. Upon crystallization, PCL segregates from the amorphous state resulting in the observation of ring patterns in miscible blends. Its periodicity decreases with increasing fraction of SAN in the blend. Ring-banded spherulites have not been observed in neat PCL or in immiscible blends. These effects are discussed in terms of twisted crystallization.

SHEAR-INDUCED PHASE CHANGES IN POLYMER BLENDS

Abstract The phase behaviour of polymer blends exposed to shear is analysed in terms of a mean-field theory. One result of the theory is that shear-induced phase changes depend on the stored elastic excess energy. For a negative stored excess energy the miscibility region of the system is enlarged. The shift of the binodal for blends for poly(methyl methacrylate) and poly(styrene-co-acrylonitrile) undergoing shearing flow is determined by light-scattering experiments. It has been found for these blends that shear flow elevates phase-separation temperatures.

Study on polymer blends of poly(styrene-co-acrylonitrile) and poly(styrene-co-maleic anhydride)

Abstract Polymer blends of poly(styrene- co -acrylonitrile) and poly(styrene- co -maleic anhydride) have been investigated by differential scanning calorimetry and light scattering measurements. Depending on the copolymer compositions it is possible to obtain miscible and immiscible blends and blends with lower critical solution temperature behaviour. In this way a miscibility channel can be designed. Fourier transform infrared spectroscopy suggests that the miscibility is caused chiefly by intramolecular interactions, and intermolecular interactions can be partially neglected.

Upper and lower critical solution temperature behaviour in polymer blends and its thermodynamic interpretation

Abstract The simultaneous occurrence of upper (UCST) as well as lower critical solution temperatures (LCST) in polymer blends can be explained in terms of a refined version of the Prigogine-Flory-Patterson theory. A generalized interaction parameter is introduced which is ruled by three contributions: (i) the segmental interaction, (ii) the free-volume effect, and (iii) the size effect represented by a parameter ϱ. The gap between LCST and UCST depends highly on the parameter ϱ. With increasing size effect, the UCST and LCST approach and, finally, merge into an hourglass-shaped binodal.

Phase separation in blends of aromatic polyoxadiazole and polyamide-6

Abstract The phase-separation phenomena in blends of poly(p-phenylene-1,3,4-oxadiazole) (p-PODZ) and polyamide-6 (PA-6) were studied and compared with results obtained for blends of poly(p-phenylene terephthalamide) and polyamide-6. It can be shown that p-PODZ exhibits no lyotropic liquid-crystalline phase in concentrated sulphuric acid solutions up to concentrations of 24%. The ternary solutions of p-PODZ/PA-6/sulphuric acid phase-separate into two isotropic phases. p- PODZ PA -6 blend films could be coagulated from the ternary solutions under conditions that prevent large-scale phase separation. Transparent films of p- PODZ PA -6 blends can be obtained from the ternary solutions if the p-PODZ content is higher than 30% of total polymer below and slightly above the critical concentration. The thermal properties of such ‘forced’ blends of p-PODZ and PA-6 were investigated. Interconnected two-phase structures, which are characteristic of spinodal decomposition, were found after thermally induced phase separation of the blends.

Examination of the deformation of isotactic polypropylene and isotactic polypropylene/ethylene-propylene rubber blends by wide-angle X-ray scattering

Wide-angle X-ray investigations have been carried out on isotactic polypropylene (iPP) and on isotactic polypropylene/ethylene-propylene rubber (iPP/EPR) blend fibres. The initial material has been crystallized and drawn at various temperatures using an Instron machine. The index of anisotropy Ia and the degree of orientation have been calculated from the X-ray photographs. It can be shown that drawing at Td = 150°C creates a bimodal crystal texture if the iPP/EPR blends contain 20wt% EPR or more. The EPR prevents complete orientation of the iPP matrix crystals. This can be shown by the decreases in the index of anisotropy and degree of orientation with increasing EPR content. A bimodal crystal texture was also observed for iPP and the iPP/EPR 8020 blend drawn at Td = 120°C immediately after neck formation. This bimodal texture disappeared during further drawing, in contrast to fibres drawn at 150°C. An oriented ‘smectic’ phase of iPP was observed for samples drawn at Td = 20°C, whilst iPP and the blend fibres consist of oriented monoclinic α-phase crystals in all other cases. The study shows that two main deformation processes occur: deformation of the initial spherulites to a fibre structure and then plastic deformation of the oriented fibre structure.

Phase dissolution in polymer blends Estimation of diffusion coefficients and the associated activation energy

SummaryIsothermal phase dissolution of regularly phase-separated structures at deep quench depths below the lower critical solution temperature was studied by light scattering technique for the blend of poly(styrene-co-acrylonitrile) and poly(methylmethacrylate). The phase dissolution studied in this work was that in the diffusion-controlled regime. During the process of phase dissolution the light scattering intensity decays exponentially with time at a rate depending on an effective diffusion coefficient for the center-of-mass motion of the chain molecules in the melt. The diffusion coefficient and the associated activation energy were estimated to be in the order of 10−14 cm2/s and 50 kJ/mol, respectively.

Polymer blends of poly(p-phenylene 1,3,4-oxadiazole) and poly(p-phenylene terephthalamide): morphology and mechanical behaviour

Abstract Film specimens and blend fibres of poly( p -phenylene1,3,4-oxadiazole) ( p -PODZ) and poly( p -phenylene terephthalamide) (PPTA) have been prepared. Morphologies were studied by optical and electron microscopy. Transparent films could be coagulated from ternary solutions under conditions that prevent large-scale phase separation while morphologies change in blend fibres with composition. A fibril matrix morphology is formed at low PPTA contents. Co-continuous morphologies result when the PPTA fraction increases and, finally, p -PODZ is spherically dispersed in PPTA. The mechanical behaviour has been examined using stress-strain and drawing experiments. The modulus of elasticity increases strongly when small amounts of PPTA are added to p -PODZ. The results are discussed in terms of the Halpin-Tsai model.

Phase separation in a thermotropic copolyester via spinodal decomposition

SummaryNovel experimental evidence is presented for the phase heterogeneity of a thermotropic copolyester containing 50 % of p-hydroxybenzdic acid (HB). Characteristic phase morphologies accompanying spinodal decomposition in polymer blends can be detected. Fractionation and a NMR-analysis demonstrate that the copolyester contains two constituents which differ in their HB-contents.