Marcia G. Oliveira

The compatibilization of SBR/EVA by mercapto-modified EVA

Abstract Styrene–butadiene copolymer/ethylene–vinyl acetate copolymer (SBR/EVA) blends with different ratios were prepared by using a Haake internal mixer. These blends were compatibilized with mercapto-modified EVA (EVALSH), which promotes bonding between the SBR phase and the EVALSH through a chemical reaction between the mercapto groups of the reactive compatibilizing agent and the double bond of the unsaturated rubber. The presence of EVALSH resulted in an improvement of the tensile strength of the unvulcanized SBR/EVA blends and also a more uniform dispersion of the EVA phase inside the SBR matrix for blends containing higher amount of the rubber phase. The formation of insoluble material in the blends containing EVALSH indicates reactive compatibilization, which was confirmed by Fourier transform infrared analysis and also by dynamic mechanical analysis. In this case, a decrease in damping properties of the SBR phase was observed as a consequence of decreasing chain mobility. EVALSH also caused a decrease in degree of crystallinity of the EVA phase as observed by differential scanning calorimetry analysis.

Influência do Sistema de Vulcanização nas Propriedades da Mistura NBR/EPDM

NBR and EPDM differ in the number of double bonds and also in polarity, thus presenting different cure rates. Their blends frequently result in a maldistribution of crosslinks. In this work, sulfur-based systems varying in accelerator type and sulfur amount were investigated as vulcanizing systems for NBR/EPDM blends. The accelerator type and the sulfur concentration affected the curing characteristics of the blends. Some formulations were able to crosslink the EPDM phase to a larger extent and consequently displayed better mechanical and ageing properties.

Thermal degradation studies of poly(EVAL-g-methyl methacrylate)

The thermal stability of poly[(ethylene-co-vinyl alcohol)-g-methyl methacrylate] (EVAL-g-PMMA) was investigated by thermogravimetric analysis. The graft copolymers were prepared by free-radical polymerization of MMA in the presence of mercapto-modified ethylene-vinyl alcohol copolymers (EVALSH) as transfer agent. The thermal stability of PMMA segments in the graft copolymers is usually higher than that of the corresponding PMMA homopolymers and is related to the amount of free SH groups in the EVALSH backbone after the graft copolymerization.

Caracterização de artefatos elastoméricos obtidos por revulcanização de resíduo industrial de SBR (copolímero de butadieno e estireno)

The recycling of waste rubber has very important significances, such as protection of the environment and conservation of energy. Considering that most of published works concerning this subject are about tire recycling, the objective of this work was to develop and characterize formulations containing a type of industrial waste, from the manufacture of automotive profiles, based on styrene-butadiene rubber (SBR) for possible application in the industry. The compositions were formulated and characterized by thermal (differential scanning calorimetry), rheological (rubber processor analyzer), rheometrical (oscillatory disc rheomether), mechanical (tensile strength and tear resistance), chemical (cross-link density) and morphological properties (scanning electron microscopy). The results obtained for these compositions were compared to a control sample purchased for the industry, with the same formulation of the SBR scraps. Obtained results show that the revulcanization process was effective. Values for tensile strength and tear resistance were 70 and 50%, respectively, compared to values found for the control sample, indicating the possibility of using this residue as artifacts of lower technical requirement.

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.

Nanocompósitos de Poliamida 6 e Argila Organofílica: Estudo da Cristalinidade e Propriedades Mecânicas

Nanocomposites of polyamide 6 and Claytone 40 organoclay were prepared with the melt intercalation technique using an internal mixer chamber coupled with roller type rotors. The addition of increasing amounts of Claytone 40 into the PA6 matrix was evaluated for the degree of dispersion, crystallinity, thermal and mechanical properties. The compositions were characterized with X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and mechanical properties. The diffraction patterns and microscope images suggest the formation of partially exfoliated or intercalated structures, which was associated with an increase in stress values and elastic modulus. The comparison of DSC and XRD results from the mixtures revealed changes in the behavior of crystalline structures, thus indicating that the PA6 crystallinity is correlated with the mechanical properties.

Characterization of Green Coconut Fiber Composites

Abstract Composites of polypropylene and green coconut fiber were prepared in an extruder with temperatures of 140°C in the first zone and 170°C in the other five zones. The screw speed varied from 60 to 140 rpm. Two fiber granulometries were used, X (0,500–0,250 mm) and Y (0,841–0,500 mm). The homogeneity and the effect of the strain history of these composites could be studied by rheological data of molten composites. Flexural modulus was improved by using an adequate fiber granulometry and extruder screw speed. Results showed that the composite with Y fiber, obtained at 140 rpm, was the better one.

Efeito Payne em nanocompósitos de NBR com montmorilonita organofílica

In this work the Payne effect was evaluated as a measure of the filler-filler and filler-polymer interactions in nanocomposites of organomontmorillonite (MMTorg) on acrylonitrile-butadiene-rubber (NBR) by using the Rubber Process Analyzer - RPA 2000. The nanocomposites of NBR and MMTorg were prepared on a Berstorff two-roll mill and the evaluation of the Payne effect was carried out in unvulcanized pure gum and varying the MMTorg content from 5, 10, 15 and 20 phr. The composition with 5 phr of MMTorg showed the best filler-polymer interaction as a consequence of the smaller amount of agglomerates of the filler in the elastomeric matrix.

Evaluación de la adherencia de uniones adhesivas metálicas con adhesivos epoxídicos modificados

In this work the adhesive properties of epoxy resins based on diglycidyl ether of bisphenol A have been evaluated. The epoxy resin was modified with butadiene and acrylic copolymers to obtain toughened adhesives. The aliphatic primary amines triethylenetetramine, N-(2-aminoethyl)piperazine and isophorone diamine were investigated as curing agents. The adhesive properties were investigated using the epoxy resins as independent systems as well as the modified resin. The adhesive properties of modified and unmodified epoxy resins were studied using steel alloy (ASTM A36) as adherent. The adherence has been evaluated using three geometric assays of steel-steel bonded joints. The rheological behavior of the adhesives was investigated under isothermal conditions. The rheological parameters associated with the curing reaction such as reaction rate, pot life and gel time of the pure adhesives were related to the chemical structure of the curing agents. The cloud point and the gel time of the modified adhesives were related to the morphology and the reaction rate, respectively. The morphology was characterized by scanning electronic microscopy. The adherence of the adhesive joints at different mechanical solicitations was related to the generated morphology by the dispersed phase of each modifier and the networks structures of the epoxy adhesives.

PA6/NBR blends: improvement of processability and mechanical properties

Abstract This work deals with the study of the processability of blends based on PA6 and NBR. The aim is to achieve reduced PA 6 melting temperatures in order to avoid degradation of the NBR phase during processing. The effect of different additives in PA has been studied. For this purpose PA6 was blended with nonylphenol, EVA 18, EVA 33 and EVAMA. Among several masterbatches based on PA6; the sample containing 5% of EVAMA presented the best combination of processability and mechanical properties. The influence of additives in the processing behavior, crystallinity of the PA6 phase, mechanical and physicochemical properties are discussed in the present work.