Viviane A. Escócio

Rheology and Processability of Natural Rubber Composites with Mica

This work is concerned with the influence of mica in natural rubber compounds on properties such as Mooney viscosity, processability and rheological behavior. The amount of this filler was varied from 0 to 40 phr and the stabilized and totalized torques, specific and mechanical energies were determined in a HAAKE torque rheometer. The elastic torque (S′) and complex dynamic viscosity (η*) were measured on a rubber processing analyzer (RPA). The results show that mica influences processability and rheological properties, by acting as a processing agent in natural rubber composites.

Influência da mica nas propriedades mecânicas e dinâmico-mecânicas de composições de borracha natural

In this work the influence of mica on the mechanical and dynamic mechanical properties of vulcanized natural rubber compositions was studied. The crosslinking density of the compositions was also determined. The data were compared to those of the unfilled composition. The results indicate an increase in modulus, hardness, crosslinking density and compression set as well as a decrease in resilience and abrasion resistance for the natural rubber compositions with increasing mica contents. The best performance for tear strength and stress at break was achieved with 30 phr of mica. The dynamic mechanical behavior of the compositions (DMTA) is in agreement with their mechanical properties.

Rheological, mechanical and morphological behavior of polylactide/nano-sized calcium carbonate composites

Semicrystalline polylactide (PLA) is a promising material to replace petroleum-based plastics since it can be synthesized from renewable resources. PLA exhibits high tensile strength and modulus, but very low strain-at-break and toughness. In this study, the effects of the nano-sized calcium carbonate (nCaCO3) on the rheological, mechanical and morphological properties of polylactide are evaluated. The PLA/nCaCO3 composites with different filler compositions, as well as neat PLA (used as reference) were prepared by melt mixing in a twin-screw extruder. The results show that the presence of 7.0 wt% of nCaCO3 in the composite not only produced an ultimate strain improvement, but also better overall toughness balance in comparison to the other compositions. MEV micrographs showed the presence of microvoids with composition containing 7.0 wt% nCaCO3, which explains the mentioned mechanical behavior. This composition also showed more viscous behavior in relation to neat PLA and 5.0 wt% nCaCO3 composite. Composite with 3 wt% of nanofiller presented the highest viscous behavior in relation to neat PLA and other composites. Both mechanical data and Cole–Cole plots indicated the overall absence of higher filler aggregates in the composites analyzed, corroborating the MEV micrographs.

Efeito do envelhecimento nas propriedades mecânicas e dinâmico-mecânicas de composições de borracha natural com mica

The effects from ageing of materials is important in terms of cost and quality, particularly if the products are to be used under severe weather conditions. In this work, the effect of accelerated ageing in vulcanizable compositions of natural rubber and mica was studied. The amount of the mineral filler employed varied from 0 to 40 phr. The mechanical and dynamic-mechanical properties of different compositions were evaluated as well as crosslink density, before and after ageing, and the results were compared to those obtained for the unfilled composition. It was found that, either before or after ageing, the amount of mica must not exceed 30 phr. It was also concluded that mica is responsible for the protection of natural rubber composites from ageing under the selected conditions. The dynamic mechanical properties obtained from DMTA analysis corroborate the mechanical properties evaluated.

Rheological Behavior of Renewable Polyethylene (HDPE) Composites and Sponge Gourd (Luffa cylindrica) Residue

The present study reports the results of rheological behavior of renewable composites, based on a matrix of high density polyethylene (HDPE), made from ethanol distilled from sugarcane, and lignocellulose filler from waste generated in the processing of sponge gourds for bathing use. The composites were prepared with 10, 20, 30, and 40%wt of filler in a twin-screw extruder. The materials were analyzed in a parallel plate rheometer and a melt-flow indexer. The composite morphology was determined by scanning electron microscopy. The composite viscosity increased with filler content, suggesting possible formation of filler agglomerates. This result was confirmed by Cole-Cole diagrams.

Caracterização térmica e dinâmico-mecânica de compósitos TPU/mica preparados em reômetro de torque

This work is aimed at incorporating mica to the matrix of a polyether type thermoplastic polyurethane elastomer (TPU), for the development of new materials in which the inherent properties of mica could be combined to those of TPU. This thermoplastic elastomer has high cost, unlike mica, which is inexpensive and abundant in Brazil. The different composites, with the mica contents varying from 0-20 phr (per hundred resin) were prepared in an internal mixer, coupled to a Haake torque rheometer. These composites had their thermal properties analyzed by thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). The incorporation of mica caused changes in the thermal stability of TPU in different atmospheres and in its dynamic mechanical properties. The addition of mica shifted the onset of degradation to lower temperatures in the two atmospheres (inert and oxidizing), while the glass transition temperature decreased slightly with increasing mica content. The results stem mainly from the interactions between mica and TPU hard segments during processing in the internal mixer.

Study of mechanical and morphological properties of bio-based polyethylene (HDPE) and sponge-gourds (Luffa-cylindrica) agroresidue composites

Brazil has a remarkable position in the use of renewable energy. The potential of natural resources in Brazil has motivated the use of these renewable resources to make technologies more sustainable. From the large variety of commercially available High Density Polyethylene (HDPE) from different sources, two were chosen for investigation: one produced from sugarcane ethanol, and the other one, a conventional polyethylene, produced from fossil resources. In the preparation of the composites, sponge-gourds also called Luffa cylindrica were selectec. The main application of this product is as bath sponge, whose production generates scraps that are generally burnt. In this work, the composites were prepared by blending the sponge scrap at different proportions (10, 20, 30 and 40% wt/wt) with high density polyethylene (HDPE) from renewable source by extrusion. The melt flow index analysis of the composites was determined and specimens were obtained by injection molding for the assessment of mechanical properti...