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

Papers by Regina Nunes

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.

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

Polimeros-ciencia E Tecnologia, Sep 21, 2017

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.

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

European Polymer Journal, Sep 1, 1994

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.

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

Microscopy and Microanalysis, 2003

Journal of Applied Polymer Science, 2001

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.

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.

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.