G. Guerrica-Echevarría

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.

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 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.

Synergistic mechanical behaviour in new polyamide 6/poly(amino-ether) blends

New polyamide 6 (PA)/poly(amino-ether) (Blox) blends were obtained by direct injection moulding covering the full composition range. The blends comprised an almost pure PA phase and a Blox-rich phase in which significant amounts of PA were miscibilized. A very positive mechanical response was obtained, as synergisms were observed both in Youngs modulus/yield stress and in elongation at break. The combined effects of the observed partial miscibility, and the very small dispersed phase size, are stated as the main factors responsible for the mechanical behaviour.

Influence of the preparation method on the mechanical properties of a thermotropic liquid crystalline copolyester

The dependence of the mechanical properties of injection molded tensile specimens of a liquid crystal polymer (Rodrun) on the preparation method of the specimen were studied by means of the change in each of four processing parameters over the maximum range that the machine allowed, whilst holding the other parameters constant. The parameters studied were the injection rate, the melt temperature, the screw rotation rate during plasticization and the injection pressure. The common analysis of the results of this and previous works, allows us to propose parameter ranges at which the mechanical properties are independent of the preparation method.

Water Sorption in Polyamide 6/Poly(Amino-ether) Blends. II. Mechanical Behavior

Polyamide 6 (PA)/poly(amino-ether of bisphenol A) (Blox) blends were placed in water for different times in an attempt to both find out whether the positive effects of Blox on the mechanical properties of PA are maintained in wet conditions, and to study the effects of solvent sorption on the mechanical properties of polymer blends. After one weeks sorption, the positive effects of the presence of Blox on the mechanical properties of PA were much larger than the composition would indicate, as 20% Blox led to a 100% increase in the modulus of elasticity with respect to that of the wet PA. After sorption for six weeks, the positive effects had decreased, attributed to a decrease in the interactions between PA and Blox, which was a consequence of the high miscibilized water content. The sorption/desorption process appeared to be only partially reversible as significant water contents remained in the blends even after very long desorption times and cracking was observed in blends very rich in Blox.

Water Sorption in Polyamide 6/Poly(Amino-ether) Blends. I. Sorption Characteristics and Phase Behavior

New partially miscible polyamide 6 (PA)/poly(amino-ether) (Blox) blends were immersed in water to study the change in both the significant water uptake of PA, and the phase behavior of the blends. Water sorption was partially irreversible and always Fickian, with a much greater decrease in the water uptake and in the diffusion coefficient of the blends than expected. This was attributed to hindering by Blox of water diffusion both at microscopic and molecular levels. Plasticization of Blox was clearly less important than that of PA, as its Tg decreased 26°C in wet conditions while in the case of PA the decrease was 60°C up to sub-zero temperatures. No intermediate condition between fully dry or fully wet was seen either in PA or Blox. The displacement of the tan δ peak of PA to clearly lower temperatures and its greater intensity in wet conditions, suggest that the presence of a PA phase might be detected by water sorption, as the tan δ peak is difficult to detect in dry conditions.

Solvent Sorption and Its Influence on the Mechanical Properties of Talc-Filled Polypropylene

Toluene, carbon tetrachloride, and tetrahydrofuran (THF) sorption and desorption by polypropylene (PP) and 20% and 40% talc-filled PPs were studied, and the effects of the solvent presence on the structure and mechanical properties were measured. The diffusion coefficients were related to the affinity of each solvent for the PP and their molecular volume. Whatever the solvent, the rate of solvent uptake and the equilibrium sorption decreased as the talc content increased as a consequence of the impermeable nature and lack of effect on sorption of the talc particles. All the materials showed highly reversible plasticization by the solvents. The relative decrease in the modulus of elasticity and tensile strength was the same in unfilled and filled PPs. However, important ductility increases, not seen in the unfilled PP, were obtained in the composites as the solvent content increased, probably due to the presence of both cavitation and rubberlike behavior.

Morphology and physical properties of injection-molded, mineral-filled Polyamide 6/poly(hydroxy ether of bisphenol A) blends

Polyamide 6 (PA 6)/poly(hydroxy ether of bisphenol A) (phenoxy) blends filled with up to 30% of both mica and calcium carbonate were obtained by extrusion and subsequent injection molding over the whole composition range. DSC and SEM showed the lack of influence of the fillers on the thermal properties and the morphology of the immiscible thermoplastic blends. The obtained positive effects of fillers on the Youngs modulus and yield stress of the blends were, in many cases, larger than those observed in the pure components. The filler-presence-induced usual decrease in large-strain mechanical properties was smaller in the case of calcium carbonate than in the case of mica-filled blends. The shape of the inorganic particles, their adhesion level to the thermoplastic matrix, and the contact of the particles with the best performing component imposed by the large particle size, play probably the most important role in the physical properties.