J. Nazábal

Effects of reprocessing conditions on the properties of unfilled and talc-filled polypropylene

Abstract The effects of repetitive injection molding cycles at different temperatures and shear rates on the structure and mechanical properties of unfilled and talc-filled polypropylene were studied. The main effect of reprocessing in both materials is a decrease in molecular weight of the polymeric matrix, which is more marked and concomitant with breaking of particles at high shear levels. The chemical structure, however, remains unchanged. The observed degradation processes only slightly affect the crystalline behaviour and the small strain properties of the materials studied. However, the break properties are affected, their decrease depends on the filler content and they appear more sensitive to high shear level than to high processing temperatures.

Influence of molding conditions and talc content on the properties of polypropylene composites

Abstract Polypropylene composites with several talc contents were injection molded under different processing conditions. DSC, density and SEM were used to characterize the materials. Melt flow index, DSC and tensile tests were carried out to study the properties of the composites. Both the nucleation effect of talc and most of the thermal properties, except the MFI, did not depend greatly on the talc content or the processing conditions. The adhesion level was poor as often seen in unmodified composites. The variation of the tensile properties with filler content was compared with that predicted by the most characteristic models. Among the processing conditions, both the mold and the melt temperature were found to be the most important parameters in the ranges studied. The former through densification of the amorphous PP phase at high mold temperature, and the latter probably through improved homogenization at high melt temperature.

Solid state features and mechanical properties of PEI/PBT blends

Extrusion-blended and injection-molded PEI/PBT blends were found to be miscible whatever the composition. The processability of the blends clearly improved with the presence of PBT. The melt pressure at the exit was seen to be a parameter as representative of the processability of the blends as the torque of blending. In the blends with 80 and 90% PBT, a positive volume of mixing and the maintenance of the crystallinity of PBT were seen. However, in the rest of the blends, negative volumes of mixing and important decreases in the crystallinity of PBT were found. These solid state features gave rise to a ductility similar to that of the pure PEI and to a synergism of the modulus of elasticity and of the yield stress in the 90/10 and 80/20 blends such that the values were higher than those of either of the pure components.

Compatibilization of PP/Vectra B “in situ” composites by means of an ionomer

Ionomer addition has been investigated as a compatibilizer for the immiscible polypropylene (PP)/Vectra B 950 (VB). Both modified and unmodified blends as a reference, with VB contents up to 30% were obtained by direct injection moulding. The crystallinity of PP/VB was barely influenced by the presence of the ionomer. The compatibilization leads to the presence of thinner fibres that broke during testing. Compatibilization reduced toughness, but at VB contents of 15 wt% or more, both the modulus of elasticity and the tensile strength significantly increased with respect to the uncompatibilized blends. The properties of both compatibilized and uncompatibilized blends, as a whole, were similar in the case of PP modified by either maleic anhydride or ionomer addition. However, favourable experimental conditions such as thinner specimens or higher compatibilizer content were used in the case of maleic anhydride modified PP. This indicates a more important positive effect on compatibilization by means of ionomer addition.

Interfacial tension as a parameter to characterize the miscibility level of polymer blends

The interfacial tensions of fourteen polymer pairs were determined by means of contact angle measurements of the surface of each polymer component, with at least two liquids, and the relation with the different miscibility levels of the corresponding blends evaluated. Although exceptions were found, the values obtained appeared to be related to the miscibility level of the blend, immiscible blends giving high interfacial tension values that decreased as miscibility increased. The relation may be affected by additional parameters and was clearer when the components of the blends compared were similar.

Phase behaviour, morphology and properties of poly(ether imide)/polyarylate blends

Abstract Poly(ether imide) (PEI)/polyarylate (PAr) blends of different compositions were obtained by melt blending followed by compression moulding. 90/10 and 80/20 blends appeared miscible by both differential scanning calorimetry and dynamic mechanical thermal analysis. The other compositions were biphasic; one phase was almost pure PAr and the other PEI with a fairly constant PAr content of roughly 25%. This phase behaviour agreed with both the observed transparency and the fracture surfaces observed by scanning electron microscopy. The mechanical properties of the blends as a function of composition showed values close to linearity or were even enhanced, with an unexpected synergism in ductility. This behaviour and that observed in other polymer blends, suggest that, assuming isotropy and constant crystallinity content, the relation between increased miscibility level and improved ductility is not a general rule.

Poly(butylene terephthalate)/phenoxy blends : synergistic behavior in mechanical properties

Abstract The mechanical properties of miscible poly(butylene terephthalate) (PBT)/poly (hydroxy ether of bisphenol A) (phenoxy) blends obtained by melt mixing have been studied by means of the tensile test. The crystallinity of the blends has been studied by means of DSC and density measurements. A synergistic behavior, principally in the break properties, at high PBT contents in the blends is observed. As can be seen from the torque and density data, this synergistic behavior is related with the high level of miscibility which seems to exist at high PBT contents compared with that of the high phenoxy content region.

Miscibility level and properties of poly(ether imide)/poly(ethylene terephthalate) blends

Blends composed of poly(ether imide) and poly(ethylene terephthalate) were obtained both by kneading followed by compression molding and by direct injection molding. Both procedures gave rise, probably at all compositions, to biphasic structures with similar homogeneity that showed wide single T g peaks by dynamic-mechanical analysis. The modulus of elasticity and the yield stress values appeared, respectively, close to and above those predicted by the additivity rule, probably due to the density increase and slight orientation observed. The ductility values against composition appeared well below the additive values, probahly due to the presence of a dispersed phase together with the notch-sensitive nature of the blends.

Phase behavior and physical properties of injection-molded polyamide 6/phenoxy blends

Polyamide 6 (PA 6)/poly(hydroxyether of bisphenol A) (phenoxy) blends were obtained by direct injection molding over the whole composition range. Differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), and scanning electron microscopy (SEM) showed the almost full immiscibility of the blends and the lack of effect of phenoxy on the crystalline phase of PA 6. The rodlike and fine-dispersed phase of the tensile specimens was strongly deformed during tensile testing, giving characteristic fibrilar structures. The Youngs modulus and yield stress showed small deviations from additivity that appeared related mainly to the blending-induced free-volume change. Despite immiscibility, the ductility behavior was also additive, probably due to the fibrilar morphology. However, the thicker impact specimens gave rise to less oriented larger dispersed phases and to full plane strain conditions that, in opposition to ductility, yielded impact strength values well below linearity.

Biphasic compatible blends from injection‐molded poly(ether ether ketone)/polysulfone

Poly(ether ether ketone)/polysulfone blends were obtained by direct injection molding throughout the composition range. The almost full immiscibility and biphasic nature of these blends was seen by differential scanning calorimetry and dynamic-mechanical thermal analysis and their homogeneously dispersed phase by scanning electron microscopy. The elastic modulus showed an usual behavior slightly below additivity. However, the strain-related break properties such as ductility or impact strength showed a surprising and positive, for an immiscible blend, behavior close to additivity both in as-molded and in annealed blends. Some possibilities, such as fast cooling, the largely aromatic nature, similar solubility parameters, different dilatation or Poisson coefficients, and the inherent chemical structure of the blends are discussed as reasons for the observed behavior.