Laura H. Carvalho

Bio: Laura H. Carvalho is an academic researcher from Federal University of Campina Grande. The author has contributed to research in topics: Organoclay & Materials science. The author has an hindex of 20, co-authored 103 publications receiving 1664 citations. Previous affiliations of Laura H. Carvalho include Federal University of Rio de Janeiro & Federal University of Paraíba.

A review on sisal fiber reinforced polymer composites

Abstract: O uso da madeira como material de construcao continua crescendo mundialmente enquanto a disponibilidade deste recurso natural esta diminuindo. Esta situacao tem conduzido ao desenvolvimento de materiais alternativos. Dentre os varios materiais sinteticos que tem sido explorados, os compositos polimericos reivindicam e buscam uma maior participacao como material de construcao. Nos ultimos anos tem se observado um crescente interesse na utilizacao de fibras naturais como reforco de matrizes polimericas para a producao de materiais de baixo custo. As fibras naturais sao reforcos com grande potencialidade e seu uso tem se dado de forma mais tradicional do que cientifica. Elas tem se prestado a inumeras aplicacoes ao longo do tempo, mas a aplicacao da tecnologia dos materiais visando a sua utilizacao como reforco de matrizes polimericas e relativamente recente. As dificuldades economicos e sociais observadas em muitos dos paises em desenvolvimento, onde as fibras naturais sao abundantes, requerem que cientistas e engenheiros apliquem tecnologias apropriadas para utilizar estas fibras da forma mais eficiente possivel, de tal maneira que se possa produzir materiais compositos polimericos de boa qualidade visando a atender a demanda da populacao por habitacoes e componentes habitacionais. Dentre as varias fibras naturais, a fibra de sisal e de particular interesse uma vez que os compositos que a utilizam como reforco apresentam alta resistencia ao impacto alem de possuirem moderada resistencia a tracao e a flexao. O presente artigo apresenta uma revisao dos trabalhos de pesquisa publicados no campo dos compositos polimericos ecologicos, especialmente no que se refere aos compositos reforcados com fibras de sisal, visando seu uso como material de construcao. Enfase especial e dada a micro-estrutura e propriedades da fibra de sisal, as tecnicas de processamento e as propriedades fisicas e mecânicas dos compositos polimericos reforcados com fibras de sisal.

Application of Infrared Spectroscopy to Analysis of Chitosan/Clay Nanocomposites

Abstract: In recent years, polymer/clay nanocomposites have attracted considerable interest because they combine the structure and physical and chemical properties of inorganic and organic materials. Most work with polymer/clay nanocomposites has concentrated on synthetic polymers, including thermosets such as epoxy polymers, and thermoplastics, such as polyethylene, polypropylene, nylon and poly(ethylene terephthalate) (Pandey & Mishra, 2011). Comparatively little attention has been paid to natural polymer/clay nanocomposites. However, the opportunity to combine at nanometric level clays and natural polymers (biopolymers), such as chitosan, appears as an attractive way to modify some of the properties of this polysaccharide including its mechanical and thermal behavior, solubility and swelling properties, antimicrobial activity, bioadhesion, etc. (Han et al., 2010). Chitosan/clay nanocomposites are economically interesting because they are easy to prepare and involve inexpensive chemical reagents. Chitosan, obtained from chitin, is a relatively inexpensive material because chitin is the second most abundant polymer in nature, next to cellulose (Chang & Juang, 2004). In the same way, clays are abundant and low-cost natural materials. Although chitosan/clay nanocomposites are very attractive, they were not extensively investigated, with relatively small number of scientific publications. In addition, the successful preparation of the nanocomposites still encounters problems, mainly related to the proper dispersion of nano-fillers within the polymer matrix. In this chapter, in addition to discussing the synthesis and characterisation by infrared spectroscopy of chitosan/clay nanocomposites, data of x-ray diffraction and mechanical properties are also considered.

Mechanical properties of phenolic composites reinforced with jute/cotton hybrid fabrics

Abstract: Mechanical properties (tensile, flexural, impact, and dynamic mechanical thermal analysis) of novolac type phenolic composites reinforced with jute/cotton hybrid woven fabrics were investigated as a function of fiber orientation and roving/fabric characteristics. Scanning electron microscopy (SEM) was carried out to investigate the fiber-matrix adhesion. Results showed that the composite properties are strongly influenced by test direction and rovings/fabric characteristics. The anisotropy degree was shown to increase with test angle and to strongly depend on the type/architecture of fabric used, i.e., jute rovings diameter, relative fiber content, etc. It was possible to obtain composites with higher mechanical properties and lower anisotropy degree by producing cross-ply laminates. Best overall mechanical properties were obtained for the composites tested along the jute rovings direction. Composites tested at 45° and 90° with respect to the jute roving direction exhibited a controlled brittle failure combined with a successive fiber pullout, while those tested in the longitudinal direction (0°) exhibited a catastrophic failure mode. Our results indicate that jute promotes a higher reinforcing effect and cotton avoids catastrophic failure. Therefore, this combination of natural fibers is suitable to product composites for lightweight structural applications. POLYM. COMPOS., 26:1–11, 2005. © 2004 Society of Plastics Engineers.

Scaling and root planing, systemic metronidazole and professional plaque removal in the treatment of chronic periodontitis in a Brazilian population. I. clinical results.

Abstract: Objective: The current investigation evaluated the clinical effects of scaling and root planing (SRP) alone or in combination with systemic metronidazole and/or repeated professional removal of supragingival plaque in subjects with chronic periodontitis Methods: Fourty-four adult subjects (mean age: 45±6 years) with periodontitis were randomly assigned to four treatment groups; a control (C, n=10) that received SRP and placebo and three test groups treated as follows: Test 1 (T1) (n=12) received SRP and metronidazole (400 mg tid, M) for 10 days; Test 2 (T2) (n=12) received SRP, weekly professional supragingival plaque removal for three months (professional cleaning (PC)) and placebo; and Test 3 (T3) (n=10) received SRP, M and PC Pocket depth (PD), attachment level (AL), bleeding on probing (BOP) and presence of visible plaque and suppuration were measured at six sites per tooth at baseline and at 90 days post-therapy Significance of differences over time was determined using the Wilcoxon test, and among groups using ancova Results: A reduction in full-mouth mean clinical parameters was observed at 90 days after all therapies Sites with baseline PD 6 mm The major clinical benefit occurred when the combination of SRP, M and PC was used Group T3 showed the least attachment loss in initially shallow pockets This group also exhibited the greatest reduction in the % of sites with BOP and suppuration as well as in mean PD and AL at sites with baseline PD>4 mm Conclusion: The data suggest a significant clinical benefit in combining SRP, systemic metronidazole and weekly professional supragingival plaque removal for the treatment of chronic periodontitis

Chemical Treatments of Natural Fiber for Use in Natural Fiber-Reinforced Composites: A Review

Abstract: Studies on the use of natural fibers as replacement to man-made fiber in fiber-reinforced composites have increased and opened up further industrial possibilities. Natural fibers have the advantages of low density, low cost, and biodegradability. However, the main disadvantages of natural fibers in composites are the poor compatibility between fiber and matrix and the relative high moisture sorption. Therefore, chemical treatments are considered in modifying the fiber surface properties. In this paper, the different chemical modifications on natural fibers for use in natural fiber-reinforced composites are reviewed. Chemical treatments including alkali, silane, acetylation, benzoylation, acrylation, maleated coupling agents, isocyanates, permanganate and others are discussed. The chemical treatment of fiber aimed at improving the adhesion between the fiber surface and the polymer matrix may not only modify the fiber surface but also increase fiber strength. Water absorption of composites is reduced and their mechanical properties are improved.

Pretreatments of Natural Fibers and their Application as Reinforcing Material in Polymer Composites—A Review

Abstract: In recent years, natural fibers reinforced composites have received much attention because of their lightweight, nonabrasive, combustible, nontoxic, low cost and biodegradable properties. Among the various natural fibers; flax, bamboo, sisal, hemp, ramie, jute, and wood fibers are of particular interest. A lot of research work has been performed all over the world on the use of natural fibers as a reinforcing material for the preparation of various types of composites. However, lack of good interfacial adhesion, low melting point, and poor resistance towards moisture make the use of natural fiber reinforced composites less attractive. Pretreatments of the natural fiber can clean the fiber surface, chemically modify the surface, stop the moisture absorption process, and increase the surface roughness. Among the various pretreatment techniques, graft copolymerization and plasma treatment are the best methods for surface modification of natural fibers. Graft copolymers of natural fibers with vinyl monomers provide better adhesion between matrix and fiber. In the present article, the use of pretreated natural fibers in polymer matrix-based composites has been reviewed. Effect of surface modification of natural fibers on the properties of fibers and fiber reinforced polymer composites has also been discussed. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers