Regina Nunes - Profile on Academia.edu (original) (raw)

Papers by Regina Nunes

Short fiber reinforced thermoplastic polyurethane elastomer composites

Polymer Composites, Apr 1, 1998

Mechanical properties of thermoplastic polyurethane elastomer (TPE) reinforced with short fibers ... more Mechanical properties of thermoplastic polyurethane elastomer (TPE) reinforced with short fibers were studied. Two types of fibers were used as the discontinuous phase: an aromatic polyamide (Twaron, diameter: 12 μm) and carbon fiber (FCI 140/90‐R33—diameter: 8–10 μm). Because of processing limitations, the maximum length of both fibers, after incorporation in the composites, was reduced to 3 mm. The TPE (continuous phase) was a polyol‐polyester type [Elastollan—glass transition of short fiber segments: −42°C (1)]. Both types of composites had fiber concentration of 10, 20, and 30 phr. Component interaction is discussed, as well as the application of a third power polynomial to establish a relationship between the amount of fiber added and stress at break data. Stress‐strength, tear resistance, shore A and B hardness, abrasion resistance, and compression set tests were performed. Composites reinforced with aromatic polyamides showed higher values in most of the tests, except in the abrasion resistance test, in which a smaller material loss was observed.

Efeito Da Pós-Cura Em Nanocompósitos De Copolímero De Butadieno-Estireno (SBR) Com Fluoromica ME100

Natural rubber (NR) composites using cellulosic fiber reinforcements

Elsevier eBooks, 2014

Abstract: This chapter discusses three kinds of composites with natural rubber (NR) and cellulose... more Abstract: This chapter discusses three kinds of composites with natural rubber (NR) and cellulose. The properties and features of several kinds of short fibers used as fillers of NR are discussed. The chapter also discusses the preparation and importance of nanocomposites with cellulose and presents a review of NR/regenerated cellulose nanocomposites. NR/cellulose composites find technological interest in that they exhibit additional features like biodegradability and renewability, along with the inherent stiffness, low cost and low density.

Applied Clay Science, Sep 1, 2018

Fluoromica is a clay mineral obtained from chemical modification of talc with Na 2 SiF 6 . In thi... more Fluoromica is a clay mineral obtained from chemical modification of talc with Na 2 SiF 6 . In this study, it was used to prepare clay mineral polymer composites (CPN) based on nitrile rubber. The composites were compounded in a roll mill and it was studied the effect of the fluoromica content as well as the shear ratio employed during the preparation. The composites were assessed based on the mechanical properties, dynamic-mechanical performances, rheological properties, and morphological aspects. The results suggested that the formation of chemical crosslinks was affected with the presence of the clay mineral, moreover, little or no reinforcement effect was achieved most likely to the lack of interaction with the matrix.

Polimeros-ciencia E Tecnologia, Sep 21, 2017

Epoxidized natural rubber (ENR) and synthetic non-modified hydrotalcite (HT) compounds were prepa... more 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).

Development and characterization of composites with ground elastomeric vulcanized scraps as filler

Materials Science and Engineering: C, Mar 1, 2009

ABSTRACT Mechanical recycling of vulcanized rubber scraps is a low-cost alternative in the search... more ABSTRACT Mechanical recycling of vulcanized rubber scraps is a low-cost alternative in the search for the recovery of this kind of industrial solid waste. The aim of this study is to incorporate styrene–butadiene rubber (SBR) industrial scraps into a base formulation of SBR used in the fabrication process of extruded profiles. Rheometric, mechanical and morphological characteristics of this base formulation with industrial scrap powder (SBR-r) added as filler were evaluated. Eight composites with different proportions, varying from 10 to 80 phr (parts for hundred of rubber) of SBR-r were prepared and the results were compared with the control sample (base formulation with 0 phr of SBR-r). The results indicated that the incorporation of rubber powder did not significantly affect the cure characteristics of the composites. The mechanical properties such as tensile and tear strength showed that up to 50 phr of SBR-r can be added without adversely affecting these properties. Micrographs corroborated the mechanical results, indicating the homogeneity of the scraps in the elastomeric matrix.

Aging effect on the reflectivity measurements of polychloroprene matrices containing carbon black and carbonyl-iron powder

Polymer Degradation and Stability, 2001

... The reflectivity curves were obtained from measurements of the permeability (μ) and permissiv... more ... The reflectivity curves were obtained from measurements of the permeability (μ) and permissivitty ( ) of the samples. The technique adopted was the transmission/reflection (T/R) method, carried out in a waveguide [11]. ... The measurements were made with an HP 8510 ...

Journal of Applied Polymer Science, Apr 18, 2002

In a previous work, two methods using rheometric parameters to calculate the kinetic constant wer... more In a previous work, two methods using rheometric parameters to calculate the kinetic constant were compared, and the results showed that the higher significative variables could be accurately determinated in opposition to the lower significative ones. Thus, a modification is suggested in this article, by limiting the conversion of the cure reaction to 80% to minimize the effects due to the deceleration curing. This allowed a precise determination of which variables have an effective influence on the cure kinetic constant.

European Polymer Journal, Sep 1, 1994

There is an ever increasing technological interest in the use of blends of dissimilar rubbers to ... more There is an ever increasing technological interest in the use of blends of dissimilar rubbers to improve specific properties of vulcanizates. In this work the system natural rubber (NR) and cellulose II (regenerated cellulose) was mixed with EPDM (ethylene-propylene<liene terpolymer). For reference, pure gum mixtures EPDM/NR were also prepared. The incorporation of cellulose II to NR was based on a technique already developed in this Institute according to which it was possible to observe that the composite consisting of 15 phr of cellulose II in NR (NR-15 phr Cell II) had shown the best mechanical properties. The NR-15 phr Cell II masterbatch was then mixed in different amounts to EPDM in a roll mill and the mechanical properties of the resulting compositions were studied. Two types of EPDM were used and the results were analysed as for the influence of both types of EPDM as well as the relative amounts of EPDM and NR-Cell II system in the blends.

Rubber nanocomposites with nanocellulose

Elsevier eBooks, 2017

Abstract The goal of this chapter is to assess the use of nanocellulose as a reinforcement filler... more Abstract The goal of this chapter is to assess the use of nanocellulose as a reinforcement filler in rubbers. The choice of these nanofillers is based on features such as being of renewable sources and biodegradable allied to high performance and low density. The different kinds of nanocellulose are discussed as well as the procedures to obtain an elastomeric nanocomposite with these nanofillers. The major characterizations are discussed for the best structure analysis and properties of nanocomposites based on different rubbers.

Rheokinetic investigations on the thermal cure of phenol-formaldehyde novolac resins

Materials Science and Engineering: C, Oct 1, 2010

... Revised date: 19 May 2010 Accepted date: 2 July 2010 Please cite this article as: Albertina A... more ... Revised date: 19 May 2010 Accepted date: 2 July 2010 Please cite this article as: Albertina Artmann, Otavio Bianchi, Marcos R. Soares, Regina CR ... bUniversidade Federal do Rio Grande do Sul, Departamento de Qu mica Org nica, Zip code 91501-970 Porto Alegre, RS, Brazil. ...

Journal of Cellular Plastics, Mar 8, 2023

Rongalite is an essentially strong carcinogen, which due to its properties as a bleaching and bri... more Rongalite is an essentially strong carcinogen, which due to its properties as a bleaching and brightening, is illegally added to the food processing. In this study, a sandwich-type enzyme-linked aptamer assay (ELAA) is developed by using a rongalite-specific aptamer G02 modified fluorescein amidite (FAM) as a capture probe and aptamer C01 modified biotin as a signal element. In the presence of rongalite, the aptamer G02-rongalite-aptamer C01 complex is produced, and the absorbance value can be subsequently measured. The sandwich-type ELAA was shown to detect rongalite with high specificity and affinity, with a K D value of 19.91 ±1.321 nM. In addition, the standard curve was established, with the limit of quantification (LOQ) for rongalite at 10 ng mL -1 . By calculating the slope of the standard curve and the standard deviation of the blank values, the method detection limit (MDL) was 0.572 ng mL -1 . Additionally, the accuracy of the sandwich-type ELAA was demonstrated in real food samples. Compared with high-pressure liquid chromatography (HPLC) assay, the sandwich-type ELAA can detect rongalite directly, and it has great advantages in pre-treatment, operation technique and cost. In short, our data suggest that the sandwich-type ELAA may be applicable as a molecular detection technique for rongalite.

Microscopy and Microanalysis, 2003

Thin Solid Films, 2013

A method is proposed in order to reduce significantly the influence of the coating shear stress a... more A method is proposed in order to reduce significantly the influence of the coating shear stress and its cohesion failure on the normal adhesion stress of metallic films on polymers. Most methods used so far were not able to avoid the interference of the cohesion failure when the interface was delaminated in order to measure the adhesion strength. Our method has been proved to work and the results are more accurate than the standard pull-off method. The experiments consisted in delaminating copper films deposited by physical vapor deposition on four different kinds of polymeric substrates: polypropylene, polyamide 6, high impact polystyrene and polyethylene terephthalate. The polymer surfaces have also been modified by means of substrate sanding and flaming processes. Optical and scanning electron microscopies were used to study the morphology of both the removed copper film and the polymer surface after pulling-off. Adhesion work was measured by contact angle to determine the necessary energy to pull-off the metal-polymer interface.

Polymer Testing, 1993

Blends of thermoplastic polyurethane elastomer (TPU) and ABS resin (acrylonitrile-butadiene-styre... more Blends of thermoplastic polyurethane elastomer (TPU) and ABS resin (acrylonitrile-butadiene-styrene) were observed by SEM (scanning electron microscopy) before and after their treatment with methyl ethyl ketone (MEK). Samples were treated with MEK for different periods of time and dried at two temperatures in order to optimize the etching conditions. It was found that 3 h of etching is adequate to reveal the phase morphology of these blends. In contrast, a 4h period has provoked serious artifacts in the samples and no information about phase structure could be obtained. At appropriate conditions, this technique can be used to quantitatively estimate the component dispersion in these blends.

Journal of Applied Polymer Science, 2001

The production of Brazilian shale oil gives rise to 6600 ton/day of a solid waste of retorted sha... more The production of Brazilian shale oil gives rise to 6600 ton/day of a solid waste of retorted shale, and larger amounts of dolomitic waste rock are generated during mining. Two vitreous materials were obtained through the melting of different proportions of these two wastes. By leaching these materials with hydrochloric acid at 90°C, two different kinds of silicas (powder and gel, both amorphous) with specific surface areas reaching up to ϳ 420 m 2 /g were generated. These silicas were further modified through an Ostwald-ripening type of treatment in ammonium hydroxide solution at 80°C. The process eliminated almost completely the deleterious micropores. The obtained silicas were evaluated as reinforcing fillers for SBR-1502. The employment of one of the modified silicas gave rise to a composite with better mechanical properties than those displayed by the one with untreated silica. Scanning electronic microscopic observation disclosed the existence of great morphological differences between these silicas. Apparently, the aging treatment gave rise to the production of better anchoring sites for the elastomer molecules. NMR studies also showed the reduction of the silanol content of the treated silica. The fracture surface of the composite disclosed a good wetting of this silica by the elastomeric matrix.

Journal of Elastomers and Plastics, Jan 2, 2019

Carbon black and high performance silica have been widely employed as binary system filler in tir... more Carbon black and high performance silica have been widely employed as binary system filler in tire tread formulations. This study evaluated the total and partial substitution of silica by metakaolin (MK) on the properties of tread rubber composites. Dynamic mechanical thermal analysis and abrasion tests were conducted as typical assessments of tire tread performance: rolling resistance (fuel consumption), wet traction (safety), and abrasion (durability). Further the energy spent by the equipment during the processing of formulations was also analyzed, as well as rheological and mechanical properties. A significant reduction of rolling resistance was obtained with 75% and 100% of silica substitution by MK, which could lead to lower heat buildup in tire tread applications, without showing negative effects on wet traction, although abrasion showed undesired

DOAJ (DOAJ: Directory of Open Access Journals), 2011

Resumo: Este trabalho tem como objetivo a incorporação da mica à matriz do elastômero termoplásti... more Resumo: Este trabalho tem como objetivo a incorporação da mica à matriz do elastômero termoplástico de poliuretano (TPU) tipo poliéter, para o desenvolvimento de novos materiais nos quais as propriedades inerentes da mica possam ser combinadas às do TPU. Este elastômero termoplástico tem alto custo, ao contrário da mica, que é de baixo custo e abundante no Brasil. Os diferentes compósitos, com teores de mica variando de 0 a 20 phr (por cem partes de resina), foram preparados em misturador interno, acoplado a um reômetro de torque Haake. Estes compósitos foram analisados termicamente por análise termogravimétrica (TGA) e análise dinâmico-mecânica (DMA). Foi observado que a incorporação de mica ao TPU altera as propriedades dinâmico-mecânicas bem como a estabilidade térmica deste polímero em diferentes atmosferas. A adição de mica desloca o início da degradação para temperaturas mais baixas nas duas atmosferas (inerte e oxidante) e a temperatura de transição vítrea tem ligeira diminuição com o aumento do teor de mica. Os resultados decorrem principalmente das interações entre a mica e o segmento rígido do TPU, durante o processamento em misturador interno. Palavras-chaves: Elastômero termoplástico de poliuretano, mica, análise térmica.

A new device to simulate the performance of rubber dams for dental applications

Polymer Testing, Feb 1, 2021

Abstract Rubber dams employed for endodontic treatment are commonly based on natural rubber latex... more Abstract Rubber dams employed for endodontic treatment are commonly based on natural rubber latex compounds and it is essential that they remain unbroken throughout the different procedures. The in-use failure of some types of rubber dams can be related to the time spent under tension in contact with saliva and/or to sodium hypochlorite. Five different types of commercial rubber dams were assessed with respect to physico-mechanical properties (crosslink density, stress at break, tear strength and stress relaxation), morphological aspects (Scanning Electron Microscopy), and elemental analyses (energy-dispersive X-ray spectrometry). Moreover, a special bench apparatus was developed to mimic actual conditions of rubber dams during endodontic procedures. Results showed that the device performance was reliable and comparable to observations during clinical activity corroborated by the stress relaxation test. Samples based on sulfur curing system with predominance of accelerator has better performance under stress relaxation tests than those samples with higher concentration of sulfur.

Effect of different cure systems on natural rubber/nanocellulose nanocomposites in rheological, physical-mechanical, aging, and mechanical properties

Journal of Elastomers and Plastics, Mar 23, 2022

The effect of different crosslink structures was studied in nanocomposites obtained by co-precipi... more The effect of different crosslink structures was studied in nanocomposites obtained by co-precipitation of natural rubber (NR) latex and aqueous solution of cellulose xanthate for obtaining nanocellulose. Cure systems characterized as conventional (CV), semi-efficient (SEV), and efficient (EV) were used in compositions of NR and also in natural rubber/cellulose (NR/CEL) nanocompositions with 15 phr of cellulose. The characterization of the developed compositions was based on rheological, physical-mechanical, aging, and mechanical properties. The obtained results allowed the conclusion that cellulose is a reinforcing filler as it promoted a significant increase in all these properties, that were sensitive to the cure systems used and protects NR from accelerated aging. The experimental results are presented and discussed also by Payne effect, entropy (ΔS), and Gibbs free energy (ΔG) to enable an understanding on cellulose distribution throughout NR influenced by the different cure systems.