Rosario E. S. Bretas

Rheological, mechanical, thermal, and morphological properties of polypropylene/ethylene‐octene copolymer blends

Rheological and morphological studies were performed on polymer blends of ethylene-octene copolymer [polyethylene elastomer (PEE)] and polypropylene (PP). The viscosities of PEE, PP, and PEE/PP blends were analyzed using an Instron capillary rheometer and a Rheometrics Dynamic Stress Rheometer, SR 200. A non-Newtonian flow behavior was observed in all samples in the shear rate range from 27 to 2700 s−1, whereas at shear rates in the range from 0.01 to 0.04 s−1, a Newtonian flow behavior was verified. The scanning electron micrographs showed that dual-phase continuity may occur between 50 and 60 (wt %) of PEE. This result is consistent with the Sperlings model. The mechanical analysis showed that PEE/PP, with 5 wt % of PEE, presented an increase on the mechanical properties and as the PEE content increased, a negative deviation in relation to an empirical equation was observed. Thermal analysis showed that there were no change in the crystallization behavior of the matrix when different elastomer contents were added. Dynamic mechanical thermal analysis showed that samples with low PEE contents presented only one peak, indicating a certain degree of miscibility between the components of these blends.

Evaluation of rheological and mechanical behavior of blends based on polypropylene and metallocene elastomers

Abstract Rheological and mechanical studies were performed on polymer blends of different grades of ethylene–octene copolymers (EOCs) and polypropylene (PP). The oscillatory flow properties of EOC, PP and EOCs/PP blends were analyzed using a Rheometrics Dynamic Stress Rheometer, SR 200. The results showed that the systems with elastomers of different grades presented diversified rheological and mechanical behavior. This behavior is probably related to the differences in molecular weight and the long chain branch content present in the copolymers.

Rheological and thermal properties of binary blends of polypropylene and poly(ethylene-co-1-octene)

Dynamic viscoelastic properties of binary blends consisting of an isotactic polypropylene (i-PP) and ethylene-1-octene copolymer (PEE) were investigated to reveal the relation between miscibility in the molten state and the morphology in the solid state. In this study, PEE with 24 wt % of 1-octene was employed. The PEE/PP blend with high PEE contents showed two separate glass-relaxation processes associated with those of the pure components. These findings indicate that the blend presents a two-phase morphology in the solid state as well as in the molten state. The PEE/PP blend with low PEE content showed a single glass-relaxation process, indicating that PEE molecules were probably incorporated in the amorphous region of i-PP in the solid state. The DMTA analysis showed that the blends with low PEE contents presented only one dispersion peak, indicating a certain degree of miscibility between the components of these blends. These results are in accordance with the results of the rheological analysis.

Rheological and morphological properties of blends based on ethylene-octene copolymer and polypropylene

Rheological studies have been performed on polymer blends based on ethylene-octene copolymer and polypropylene. The flow behaviour of polyethylene elastomer (PEE), polypropylene (PP) and PEE/PP blends were analysed using an Instron capillary rheometer and a Rheometrics dynamic stress rheometer, SR 200. A non-Newtonian flow behaviour was observed in all the samples at high shear rates, and a Newtonian flow behaviour at shear rates in the range of low values. The scanning electron micrographs showed that the size of the elastomer domains increases as the PEE content increases. The SEM analysis also showed that dual-phase continuity may occur between 50 and 60 (wt.%) of PEE. The morphology of the extrudates examined by optical microscopy revealed that a more severe distortion of the extrudate was only observed at high PEE content and high shear rate.

Dynamic and transient rheological properties of glass filled polymer melts

The dynamic and transient rheological properties of a low density polyethylene melt and a plasticized polyvinylchloride melt filled with glass beads were measured at 200 °C and 180 °C respectively in a modified Weissenberg Rheogoniometer R-17. Its main modification consisted of the use of a piezoelectric transducer instead of the conventional torsion bar, and of the interfacing of a microcomputer Apple II plus to the Rheogoniometer for data acquisition and analysis. The glass beads were pretreated with silane and titanate coupling agents to observe the effect of the chemical modification of the polymer filler interface on these properties. It was observed that both the dynamic viscosity and the storage modulus increased with the weight fraction, but this last parameter did appreciably affect the stress growth and stress relaxation curves of the polymeric matrices at low shear rates. The effect of coupling agents on these properties was varied.

Thermoplastic/carbon fibre composites: Correlation between interphase morphology and dynamic mechanical properties

Abstract Three thermoplastic matrixes (ultrahigh molecular weight polyethylene, medium molecular weight polypropylene and high molecular weight polypropylene) were used to produce three thermally treated carbon fibre composites. Their dynamic mechanical properties were measured: they were correlated with the morphologies of the composites in order to determine the influence of interphase trans -crystallinity and bulk crystallinity on mechanical performance. It was observed that, besides these structural parameters, the thermoplastic molecular weight also governs the final mechanical behaviour.

In Vitro and in Vivo Studies of Novel Poly(D,L-lactic acid), Superhydrophilic Carbon Nanotubes, and Nanohydroxyapatite Scaffolds for Bone Regeneration.

Poly(D,L-lactide acid, PDLLA) has been researched for scaffolds in bone regeneration. However, its hydrophobocity and smooth surface impedes its interaction with biological fluid and cell adhesion. To alter the surface characteristics, different surface modification techniques have been developed to facilitate biological application. The present study compared two different routes to produce PDLLA/superhydrophilic vertically aligned carbon nanotubes:nanohydroxyapatite (PDLLA/VACNT-O:nHAp) scaffolds. For this, we used electrodeposition and immersion in simulated body fluid (SBF). Characterization by goniometry, scanning electron microscopy, X-ray diffraction, and infrared spectroscopy confirmed the polymer modifications, the in vitro bioactivity, and biomineralization. Differential scanning calorimetry and thermal gravimetric analyses showed that the inclusion of VACNT-O:nHA probably acts as a nucleating agent increasing the crystallization rate in the neat PDLLA without structural alteration. Our results showed the formation of a dense nHAp layer on all scaffolds after 14 days of immersion in SBF solution; the most intense carbonated nHAp peaks observed in the PDLLA/VACNT-O:nHAp samples suggest higher calcium precipitation compared to the PDLLA control. Both cell viability and alkaline phosphatase assays showed favorable results, because no cytotoxic effects were present and all produced scaffolds were able to induce detectable mineralization. Bone defects were used to evaluate the bone regeneration; the confocal Raman and histological results confirmed high potential for bone applications. In vivo study showed that the PDLLA/VACNT-O:nHAp scaffolds mimicked the immature bone and induced bone remodeling. These findings indicate surface improvement and the applicability of this new nanobiomaterial for bone regenerative medicine.

Effect of molecular weight and long chain branching of metallocene elastomers on the properties of high density polyethylene blends

Abstract In this work, rheological properties and morphological characteristics of blends based on high density polyethylene (HDPE) and two different grades of poly(ethylene-co-octene) metallocene elastomers (EOC) were studied. These elastomers were commercial samples differing in molecular weight, and rheology index (DRI). Blends were processed in a single screw extruder (L/D=32), at 230 °C and 50 rpm, using mass fraction weight percent of EOC in the range from 5–80%. The rheological properties were evaluated in dynamic experiments at 190 °C and frequency range from 10 -1 s -1 –10 -2 s -1 . The blends exhibited pseudoplasticity and complex rheological behavior. That complex behavior was intensified by increasing molecular weight and long chain branching proportion (DRI) of EOC elastomers. The morphological characterization was carried out by using scanning electron microscopy (SEM). The blends exhibited dispersed morphologies with EOC domains distributed homogeneously and with particle size inferior to 2 μm.

Quiescent crystallization kinetics and morphology of isotactic polypropylene resins for injection molding. I. Isothermal crystallization

The quiescent isothermal crystallization kinetics of polypropylene was studied as a function of molecular weight (Mw), amount of ethene, and amount of maleic anhydride and acrylic acid grafting. Differential scanning calorimetry and polarized light optical microscopy were used to follow this kinetics. It was observed that the linear growth rate, G, decreased with the increase of Mw, but increased with the amount of ethene. In the grafted polymers, as the amount of grafting increased, G decreased. The fold surface free energy, σe, was found to increase with the increase in Mw. The heterophasic and grafted polymers had σe values higher than the homopolymers. All samples showed spherulitic morphology, except the acrylic acid-grafted polypropylene that showed axialitic morphology.

Poly(p-phenylene sulfide)/liquid crystalline polymer blends. II. Crystallization kinetics

The crystallization kinetics of blends made of poly(p-phenylene sulfide) (PPS), with a liquid crystalline polymer (LCP) was studied. The blends were found to be immiscible by dynamic mechanical thermal analysis (DMTA). Results of non-isothermal and isothermal crystallization experiments made by differential scanning calorimetry (DSC) showed that both components had their crystallization temperatures increased ; also the LCP melting temperature was found to increase in the blends. It was concluded that the addition of LCP to the PPS increased the PPS overall crystallization rate due to heterogeneous nucleation. The fold interfacial free energy, σ e , of the PPS in the blends was observed not to vary with composition.