Laura H. Carvalho

Effect of wettability and ageing conditions on the physical and mechanical properties of uniaxially oriented jute-roving-reinforced polyester composites

Abstract In order to obtain reliable composite materials in structural applications and to utilise fully the potential of reinforcing fibres, both perfect impregnation and strong interfacial bond formation have to be guaranteed. In the present study the tensile, flexural, and impact behaviour of jute roving reinforced polyester composites were investigated as a function of fibre loading and fibre surface wettability. Two types of unsaturated polyesters viz; (a) Resana having a wetting agent and (b) Elekeiroz without wetting agent, were used to study the influence fibre surface wettability. It was noted that Resana polyester composites showed mechanical properties superior to those of Elekeiroz composites. The impact strength of the Resana polyester composite with 30% fibre content was found to be 80 J/M 2 , which is about 350% higher than that of the polyester matrix. Jute rovings were alkali treated in 10% aqueous NaOH solution for 3 h periods under two different conditions, i.e. (a) immersion at room temperature and (b) reflux at 100°C. It was observed that jute rovings refluxed in alkali for 3 h showed better tensile properties than those treated at room temperature. The mechanical properties of the jute Resana polyester composites were evaluated under three ageing conditions, i.e. (1) immersion in water at 50°C for 48 h (2) under reflux in water for 2 h; and (3) thermal ageing in an air circulating oven at 100°C for periods up to 8 days. Our results indicate that the composites refluxed in water for 2 h showed a slight improvement in their tensile properties compared to those of immersion-aged composites. It was observed that thermal ageing tended to decrease the composite mechanical properties, which was attributed to oxidative degradation of both fibre and matrix.

Application of Infrared Spectroscopy to Analysis of Chitosan/Clay Nanocomposites

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.

Propriedades mecânicas de tração de compósitos poliéster/tecidos híbridos sisal/vidro

Hybridization can alter both mechanical performance and cost of polymer composites, and novel composite materials can be obtained by the combination of both fibrous and mineral reinforcements. In the present work the mechanical performance of unsaturated polyester/hybrid sisal-glass fabrics was determined as a function of fibre content and test direction. Three different hybrid fabrics (30, 40 and 50% w/w glass content) with sisal strings in the warp and glass roving in the weft were hand weaved. Aligned fabric compression moulded composites were obtained at room temperature. The results showed enhanced properties with fibre content for all composites under investigation. Composites reinforced by fabrics with low glass fibre content exhibited lower properties when tested along the glass fibre direction than when tested along the sisal fibre direction and, at high glass fibre content the opposite trend was observed. These behaviours were associated with the low glass fibre content along the test direction and to the high sisal fibre diameter. At low glass fibre content the sisal fibres would act as inclusions or defects, thereby lowering the mechanical performance of the composite; at high glass fibre contents the superior mechanical properties of the glass would surpass the defects caused by sisal fibres.

Propriedades mecânicas e morfologia de uma blenda polimérica de PP/HIPS compatibilizada com SEBS

In this work the effect of a 2-7% w/w styrene-b-ethylene-co-butylene-b-styrene triblock copolymer (SEBS) addition on the properties of a 70:30 polypropylene/high impact polystyrene (PP/HIPS) polymer blend was investigated. Tensile and impact properties, the Vicat temperature and blend morphology were determined as a function of SEBS content. Processing was carried out in a twin-screw intermeshing counter-rotating extruder and the samples were compression moulded. Our results indicate that the SEBS addition, albeit promoting very slight increases on tensile strenght and modulus, led to increases on the elongation at break and impact strenght of the blends, and the Vicat temperature of the blends was higher than that of HIPS. The SEM analysis showed that SEBS addition promotes a significant reduction on particle size, which was taken as an indication that SEBS exerted an emulsifying and stabilizing effect on the morphology of the PP/HIPS blend under investigation. The best overall properties were obtained at 5 wt.% SEBS content.

Influência da adição e da modificação química de uma carga mineral nanoparticulada nas propriedades mecânicas e no envelhecimento térmico de compósitos poliuretano/sisal

This work deals with filler hybridization effects, by the addition of a nanoparticulate mineral filler (bentonite), on the mechanical performance of compression molded Polyurethane/sisal composites with 25 wt % fiber content. Composite tensile and impact properties were evaluated as a function of mineral filler content (0-10 wt %) and chemical modifications. Thermal aging effects onf tensile (s, E, e) properties of selected composites were also ascertained. The mineral filler (Brasgel PA sodium bentonite) was employed in the following forms: a) as received; b) treated with a 0,6N HCl solution; c) chemically modified with dodecyl dimethyl benzyl ammonium chloride (Dodigen) and d) chemically modified with cetyl trimethyl ammonium bromide (Cetremide). Our results show that bentonite addition increases the mechanical properties of PU/sisal composites and that best overall mechanical performances was achieved with addition of the hydrochloric acid trated mineral filler. Thermal aging for short times (up to 4 days) led to small increases in composites elastic modulus na tensile strengths, which was attributed to post-curing of the matrix. Long thermal exposure (32 days) led to decreases in composite tensile properties (s, E, e), which was attributed to oxidative degradation of both: matrix and sisal fibers. The most thermally resistant composite was the hybrid (PU/sisal-bentonite) whose mineral filler was chemically modified with Cetremide. DRX and SEM data indicate the hybrids with organofilized bentonites to be composed of micro and nanocomposite structures.

Cold Plasma Surface Treatment of UHMWPE Membranes to Improve Fouling Characteristics

The influence of cold plasma internal surface treatment on the fouling characteristics of UHMWPE membranes was investigated. Two sets of sintered tubular UHMWPE membranes were manufactured. One set of membranes was prepared with as-received powdered UHMWPE and another set was prepared with the same powder sieved through #200 mesh. The tubular membranes were obtained by sintering the UHMWPE powders at 180°C for 130 min, and were characterized by SEM, contact angle and flow permeation. The flow permeation measurement was conducted in a locally built apparatus and the amount of permeated fluid was determined by gravimetry, as a function of time. Water collected from a local source was used in the tests. Modification of the membrane internal surface was achieved by methane cold plasma treatment, applied during 60 min. The data indicates for both membranes, fouling was reduced after plasma modification and that the effect was more pronounced for the membranes prepared with the sieved UHMWPE powder. This behavior was associated to the increased surface tension (after plasma modification) leading to solid particle repulsion by the membrane surfaces and to a better plasma surface modification on the smaller grain sizes displayed by the membranes prepared with the #200 mesh sieved UHMWPE powder.

Influência da adição de uma carga nanoparticulada no desempenho de compósitos poliuretano/fibra de juta

In this work the mechanical properties of polyurethane/jute fiber composites were evaluated as a function of fiber content and mineral filler addition. A polyurethane (PU) derived from castor oil was used as the matrix and hessian cloth as reinforcement. The effect of the incorporation of small amounts of local clay (bentonite), in its calcium and sodium forms, on the mechanical properties of polyurethane/jute composites was also investigated. The results indicate that the tensile properties of the composites substantially increased with jute fiber addition and that although the mechanical properties of the matrix were affected by the addition of nanoparticulate clay, the improvement was not as expected. This was attributed to poor mixing and dispersion of the filler, which was confirmed by SEM. A synergistic effect was observed for the hybrid clay/jute fiber composites, with considerable improvement in the mechanical performance of the hybrid composites.

Tailoring PBAT/PLA/Babassu films for suitability of agriculture mulch application

ABSTRACT Babassu was studied as a vegetable filler in a blend consisting of polybutyrate adipate terephthalate and polylactic acid aiming at preparation of bio-based and biodegradable films by solvent casting. The morphology, thermal, and mechanical properties were investigated with optical, thermoanalytical, and spectroscopic methods and correlated with the sample setup. Although only laboratory scale for film production has been applied in this work, the results suggest that the composite PBAT/PLA with 10% Babassu may be a suitable material for the application as agricultural mulch films. Such Babassu-based films would be environmentally friendly and cost-effective at the same time.

Moisture Transport Process in Vegetable Fiber Composites: Theory and Analysis for Technological Applications

This chapter provides theoretical and experimental information about water absorption in unsaturated polyester polymer composites reinforced with vegetable fibers. The use of raw materials from renewable sources, such as natural fibers, has shown great promise in a variety of engineering applications. Composites reinforced with natural fibers are sensitive to influences from environmental agents such as water and temperature. The organic nature of vegetable fibers is responsible for the higher moisture sensitivity of the mechanical properties of natural fiber reinforced composites when compared to synthetic fiber reinforced composites. Here, topics related to theory, experiments, mathematical modeling and numerical procedures, and technological applications for different natural fibers are presented and discussed in detail. Results of microscopy, water absorption kinetics, moisture content distribution, and area/volume relationships for unsaturated polyester composites reinforced with caroa and macambira vegetable fibers are shown and analyzed. The knowledge of moisture distribution allows the determination of areas that may show delamination problems (moisture induced degradation) due to the weakness of the fiber-matrix interface and consequently reduction in the composites mechanical properties.

Propriedades mecânicas de blendas de PS/resíduo de borracha: influência da concentração, granulometria e método de moldagem

Polystyrene was toughened by blending with rubber waste obtained from shoe and tire industries. The blends were twin-screw extruded and test specimens were compression and injection moulded. The effects of concentration (0-15% w/w) and particle size (1200 to 180 µm) of the waste rubbers on the blends mechanical properties were evaluated and their fracture surfaces examined. It was shown that tensile strength tends to lower and impact resistance to increase with increasing rubber content of decreasing particle sizes. Morphological analysis confirms these results. Injection moulded specimens showed greater sample uniformity and consequently, better mechanical properties than compression moulded samples.