Ana Maria Furtado de Sousa

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.

Epoxidized natural rubber and hydrotalcite compounds: rheological and thermal characterization

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).

Nitrile rubber and carboxylated nitrile rubber resistance to soybean biodiesel

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.

Mixing process influence on thermal and rheological properties of NBR/SiO2 from rice husk ash

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.

Natural rubber latex: determination and interpretation of flow curves

As 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 Sao Paulo.

An investigation of crystallization and rheological behaviors of PLA/HDPE/Nano-CaCO3 composites by experimental design

Nowadays, the development of products from renewable raw material has been an important subject of interest for a great number of researchers. Poly(lactic acid) is versatile polymer, synthesized from renewable resources, biodegradable and biocompatible and that has been considered as stronger candidate to replace fossil-based polymers in many application. However, the PLA still has some shortcomings to be solved, such as low thermal resistance, rate crystallization, impact resistance and gas barrier properties. Thus, adding nanofiller can be an interesting method to extend and to improve the PLA properties. The aim of this work is to evaluate the rheological and thermal properties of composites based on PLA/nano-CaCO3/HDPE by using a design of experiments (DOE)-2n Factorial, with three center points. Three factors were studied: HDPE/nano-CaCO3 masterbatch content, temperature and mixer speed. All PLA/Nano-CaCO3/HDPE experiments were characterized by differential scanning calorimetry (DSC), torque rheometr...

Preparation and characterization of composites based on poly(lactic acid) and CaCO3 nanofiller

In recent years, extensive studies have been conducted on the study of the poly(lactic acid) (PLA) properties, because of its being a typical biobased and biodegradable polymer, with good mechanical properties. However, its toughness and gas barrier properties are not satisfactory and can be improved by the addition of nanofillers, such as calcium carbonate (n-CaCO3). The present work PLA composites with nano-sized precipitated calcium carbonate (n-NPCC) were prepared by melt extrusion. Thermal, mechanical and flow properties of the composites were evaluated by using a factorial design.The results showed that the addition of the nanofiller in the PLA matrix didn’t improve thethermal and mechanical properties of the matrix significantly. This behavior is probably due to the presence of the stearic acid that is coating on the n-NPCC particles, resulting in a weak polymer-particle interaction. Beyond this, it was also observed a decrease in MFI of the composites when nanofiller was added and at a higher scre...