Abstract Cross-link density impacts most mechanical properties of rubber, therefore it is necessary to have a method to measure it. The most widely used method is via equilibrium swelling, however, it is time consuming and uses organic solvents. Dynamic Shear Test (DST) can be used to calculate both chemical and physical cross-links in rubber compounds in shorter times than by swelling equilibrium method, and without the use of solvents. In this work, equilibrium swelling using toluene and acetone was used to validate the dynamic shear tests for different nitrile rubber (NBR) compounds. The DST had a good correlation with the swelling equilibrium method using acetone, with a correlation coefficient of ~0,91, validating the use of DST. Moreover, the use of the Modified Guth-Gold equation (instead of Guth-Gold Equation with Medalia correction) also allowed to deduct the effect of carbon black on the cross-link density from the DST.

Abstract This study evaluates the influence of processing parameters and reactive extrusion on the mechanical and thermal behavior of PLA/PBAT (70/30, wt.%) blends. The effect of reverse mixing elements (RME) and feed rate (FR) of the extruder were studied using a factorial design of experiments. Further, two types of blends were processed by extrusion molding: with (AD) and without (NAD) additives. The FTIR analysis showed that PLA suffered some degree of degradation, being this process more pronounced for NAD blends. A better interaction between the PLA and PBAT phases occurred for reactive extrusion, inducing an improvement in the impact properties and thermal behavior. The cold crystallization temperature of the NAD blends decreased when two RME was used. Both RME and FR parameters affected the elastic modulus of NAD blends, while only FR affected the elastic modulus of AD blends.

Abstract Biodiesel has been considered a suitable substitute for petroleum diesel, but their chemical composition differs greatly. For this reason, biodiesel interacts differently than petroleum diesel with various materials, including rubbers. Therefore, the resistance of some elastomers should be thoroughly evaluated, specifically those which are commonly used in automotive industry. Nitrile rubber (NBR) is widely used to produce vehicular parts that are constantly in contact with fuels. This paper aimed to assess the resistance of carboxylated nitrile rubber (XNBR) with 28% of acrylonitrile content to soybean biodiesel in comparison with non-carboxylated nitrile rubber samples, with high and medium acrylonitrile content (33 and 45%). NBR with medium acrylonitrile content showed little resistance to biodiesel. However, carboxylated nitrile rubber even with low acrylonitrile content had similar performance to NBR with high acrylonitrile content.

Abstract Epoxidized natural rubber (ENR) and synthetic non-modified hydrotalcite (HT) compounds were prepared and evaluated. Natural rubber (NR) was epoxidized with 20.6% of epoxy groups from a chemical modification of the latex. A sulfur-based curing system formulation with accelerators was used. The amounts of HT in the ENR-HT compositions was varied between 0, 2, 3 and 5 phr. All compositions were evaluated as to cure parameters, rheological properties, thermal resistance and crosslink density. The results showed that the mineral filler does not have a significant influence on the cure parameters. Different methods of crosslink density determination were used (swelling at equilibrium and elastic modulus). The results turn out to be equivalent and rise as the amount of filler is increased. The best results were found for the 5 phr hydrotalcite compound (ENR-HT5).

Abstract Silica was extracted from rice husk ash (RHA) by a sequence of reactions to produce nanosilica. Two laboratory routes, co-coagulation and spray drying, were used to incorporate the nanosilica into the rubber matrix. Samples were characterized regarding filler incorporation efficiency, thermal stability, rheological behavior and morphology. Thermogravimetric analysis showed that spray-drying was the most efficient filler incorporation process and also the presence of silica increased the thermal resistance of the rubber compound when compared to the unfilled rubber. The rheological behavior showed that NBR filled with silica presented higher elastic torque (S’), storage modulus (G’) and complex viscosity (η*) than unfilled rubber. The Payne effect was also observed for the composites produced by spray-drying. In addition, the thermal behavior and Payne effect results were supported by the comparison of morphology observed by FEG-SEM analysis.

Abstract In the tire industry carbon black is being replaced by silica as a filler in recent due to the development of “green tires”. Amorphous precipitated silica in combination with a silane coupling agent as a filler in tread compounds can result in fuel savings of 3% to 4% compared to a tire having treads made from compounds with carbon black. This means a 20% reduction of the rolling resistance and consequently lower greenhouse gas emissions. On the other hand, rice is one of the most important food crops generating around 22% in weight of husk during its milling, a material that is mainly used as fuel for energy generation, resulting in ash. Rice husk ash (RHA) contains over 70% of silica in amorphous form. In this paper we evaluated the effect of replacing carbon black with RHA in a basic tread formulation. Compounds mechanical, dynamic properties and morphology were analyzed.

AbstractAs consumers become more demanding, the importance grows of guaranteeing the quality of products. The employment of reliable testing techniques that assure the origin and characteristics of the inputs used by industry is a key factor in this respect. In the rubber processing industry, the most commonly used characterization tests include determination of the total solids and dry rubber content, mechanical stability, odor, color and presence of volatile compounds, among others. For the most part, these tests are sufficient for the latex transformation industry. However, in situations where there is a need to know the behavior of latex in reaction to the mechanical forces of machines (mixers, pumps, etc.), other tests must be used. Rheological tests to determine viscoelastic data by means of plotting flow curves combined with the application of theoretical models can provide important details for characterization of different types of latex. This article presents the protocol employed by the Rheology and Image Laboratory of Rio de Janeiro State University (UERJ) for the rheological study of Brazilian latex. The samples analyzed came from the state of São Paulo.

In this study, composites based on poly(lactic acid) (PLA)/talc were prepared at different compositions by melt mixing in a twin screw extruder. The effect of a nucleating agent, talc, on the crystallization behavior, rheological and morphological properties of PLA was investigated. DSC results showed that the addition of the mineral filler in the range between 1 and 5 wt. % to the PLA matrix increases the degree of crystallinity. This finding shows that talc acted as a nucleating agent for PLA during the processing stage. The composites morphology was also studied using a scanning electron microscope (SEM). The micrographs showed that a good dispersion of talc was achieved in all compositions analyzed. The rheology of PLA/talc composites was evaluated with the dynamic mode and correlated with the aforementioned observed morphology. The results showed that the addition of the mineral filler to the PLA matrix decreased system viscosity, thus highlighting the filler's lubricant effect. As talc content increased, system's viscosity also increased, providing material with higher elastic behavior. Thermal analysis showed that the composition of 3 wt.% of talc added to polymer matrix seems to be interesting with regard to the need of articles possessing good dimension stability.