Exequiel S. Rodríguez

Characterization of composites based on natural and glass fibers obtained by vacuum infusion

The mechanical properties of composites based on different natural fibers and glass fibers using unsaturated polyester and modified acrylic as matrix are evaluated. In spite of the several works done in natural fiber composites, there are very few results on acrylic as matrix. Fabrication of the composites is done by means of vacuum infusion. Flexural, tension, and impact test are conducted on the composites. Ignition, thermal degradation, and water absorption are determined. Jute composite with unsaturated polyester resin as matrix showed the best results on flexural and tensile strengths and the lowest in impact energy, because of the strong interphase developed. Flax composites show higher impact energy than the other natural fiber composites, due to the existence of the effective energy dissipation mechanisms, like pull-out and axial splitting of the fibers. Scanning electron micrograph confirmed this fact. None of the samples resisted the five-second exposition to the flame on the ignition test. All of them were completely consumed, and flax composites burned the longest.

Effects of Fibers' Alkali Treatment on the Resin Transfer Molding Processing and Mechanical Properties of Jute—Vinylester Composites

The aim of this paper is to evaluate the effect of the alkali treatment on the mechanical properties of jute fibers and its composites. The effect on the processing conditions was also analyzed. Woven jute preforms were used to prepare the composites using the vacuum infusion technique. The fibers were treated with NaOH (5wt.%) for 24 h at room temperature. Single filament tests showed that the treatment was detrimental for the mechanical properties of the fibers. The injection times increased in the treated jute preforms as a consequence of the increase in the exposed area and the flow resistance. The preform permeability decreased, also, in the tubular structure collapse of the fibers, which could reduce the capillary pressure. Flexural and impact properties of the treated jute composites decreased mainly in the lower mechanical properties of the fibers.

Experimental study of the compaction response of jute fabrics in liquid composite molding processes

The aim of this work is to characterize the compaction behavior of jute woven fabric preforms. The maximum compaction pressure, permanent deformation, and stress relaxation of the preforms were found to be dependent on the final fiber volume fraction and the compaction speed. Higher compaction speeds led to higher compaction pressures, stress relaxation, and permanent deformation. On the other hand, as the fiber content was raised, the maximum compaction pressure and the permanent deformation increased, while the stress relaxation decreased. In addition, it was found that the structure of natural fibers affected the compaction behavior of the preforms. Each fiber is composed of several hollow elementary fibers, which collapsed due to the compressive loading. Furthermore it was found that fluid absorption reduced the compaction pressure in natural fiber preforms due to fiber softening.

Key differences on the compaction response of natural and glass fiber preforms in liquid composite molding

In the present work, the effects of fiber structure and fluid absorption on the compaction behavior of jute woven fabrics and sisal mats were analyzed and compared with the response of glass fiber mats. It was found that the fiber content that can be achieved with a certain compaction pressure is lower in the case of natural fiber preforms. In addition, due to the hollow structure of these natural fibers, jute and sisal preforms suffered larger permanent deformation than glass fiber preforms after the compressive loading cycle. In addition, it was found that fluid absorption reduced the compaction pressure in natural reinforcements due to fiber softening. These phenomena were not observed in glass fiber mats.

Preparation and characterization of polystyrene/starch blends for packaging applications

Polystyrene/thermoplastic starch blends from 90/10 to 50/50 (w/w) were prepared by melt blending. Blends were characterized by scanning electron microscopy (morphology); thermogravimetric analysis (thermal stability and weight content of each component); Fourier transform infrared spectroscopy (identification of functional groups); differential scanning calorimetry (thermal properties); tensile tests (strength, modulus, elongation at break and tenacity) and biodegradation in soil (biodegradability). The biodegradation process was also followed by thermogravimetric analysis calculating the loss of each component after removing the samples from soil at different time intervals. Scanning electron microscopy results showed good starch dispersion in the blend. The Fourier transform infrared spectroscopy analysis suggested that only physical interaction took place between the polystyrene and the thermoplastic starch. The tensile tests revealed a considerable decrease in the mechanical properties of the polystyrene-thermoplastic starch blends as a function of the thermoplastic starch content. The 50/50 blend showed decreases of 48% in the Young’s modulus, 62% in the tensile strength and increases of 62% in the elongation at break, in comparison to neat polystyrene. The biodegradability tests showed that the greater the thermoplastic starch concentration in the blend, the faster the mass loss, which was also confirmed by the thermogravimetric analysis and Fourier transform infrared spectroscopy analysis.

Development of carbon fiber/phenolic resin prepregs modified with nanoclays

This work is focused on the study of the main variables involved in the development of phenolic/carbon prepregs and how these variables are affected by the incorporation of nanoclays. For this, phenolic resin was obtained from phenol and formaldehyde, performing the reaction under basic conditions and with formaldehyde excess. Resin curing kinetics was studied by means of Fourier transform infrared spectroscopy measurements. Organo-modified clay was added to the phenolic resin in order to evaluate their effect on the general performance of the material. Carbon fiber/phenolic resin and carbon fiber/clay modified phenolic resin prepregs were obtained by hand-layup and vacuum bagging. Prepregs were characterized in terms of fiber content, flexural stiffness, and degree of tack. In both the cases, intermediate fiber volume content, nearly 50%, was obtained. The addition of 5 wt% of clay to the phenolic resin did not produce a significant change on the prepregs stiffness but increased the degree of tack, which implies that the incorporation of such particles was useful to enhance the prepregs properties. Composite materials were obtained by compression molding of the prepregs obtained, and were characterized by its fiber content, mechanical behavior with the three-point bending test and its thermal degradation by thermogravimetry. High fiber content composites materials were obtained, nearly 75% by volume. However, modified composites showed lower fiber content, which resulted in a decrease of the flexural modulus and strength. In relation to thermal degradation, the addition of nanoclay did not change the behavior of the materials.

Novel approach for mold filling simulation of the processing of natural fiber reinforced composites by resin transfer molding

Modeling the infiltration of reinforcements during the processing of composite materials by liquid composite molding techniques is an important instrument for the prediction of flow front patterns, filling times and pressure gradients. Darcy’s law is widely used to model most of these processes. However, when polar fluids are used together with natural fibers, fiber swelling may occur and introduce further complexity to the simulation. In this work, a model that includes the aforementioned phenomena is proposed, leading to a more accurate prediction of the flow front position than the classic models that use a constant permeability value.

Mechanical Properties Evaluation of a Recycled Flax Fiber-reinforced Vinyl Ester:

Flax fiber-vinyl ester composites are milled and mixed with virgin matrices to produce recycled composites. The effect of this powder incorporation on the mechanical properties of a thermosetting matrix (vinyl ester) and a thermoplastic matrix (polypropylene) is studied. In the case of thermosetting matrix, flexural and tensile strength decrease with the addition of powder. For filler contents higher than 50 vol%, the strength reaches a constant value. Flexural and Young’s moduli remain constant for different powder contents. In the case of thermoplastic matrix, strength and modulus decrease when powder is replaced by fibers. Both, fibers and powder act as reinforcement as moduli increase. Impact properties are improved with the addition of powder and fibers in comparison with the pure matrix.

Fire performance of composites made from carbon/phenolic prepregs with nanoclays

This article describes the development of fire resistant composite materials based on phenolic resin and carbon fibers. Two types of composites were developed, with neat phenolic resin and with phenolic resin/modified bentonite. Composite materials were processed from prepregs by compression molding and were characterized by density, fiber content, cone calorimeter test, scanning electron microscope, and mechanical properties before and after the exposure to fire. In both cases, high fiber content materials were developed, about 75% by volume. The addition of clay improved some fire properties such as the peak of the heat release rate and the residual mass of the burned samples. Also, the bentonite-modified composite required higher time to develop the maximum of the heat release rate in the material; therefore, the addition of modified nanoclays improved the fire properties of the developed composites. Regarding to mechanical behavior the modified composites presented low modulus and flexural stiffness than the unmodified materials, and presented a higher decreased in the properties after fire, which could be related with the different fiber content in both composites.

PHB coating on jute fibers and its effect on natural fiber composites performance

In this work, a novel treatment on plant fibers is presented and its effect on the mechanical properties and water absorption of vinyl ester matrix composites is analyzed. The treated fibers used in this study consisted in alkaline-treated jute fibers and alkaline-treated jute fibers coated with polyhydroxybutyrate (PHB). Bending tests and IZOD impact tests were performed to evaluate the mechanical performance of the composites. The samples were immersed in water (at room temperature and at 80℃) and the water sorption and flexural modulus were measured in time. Flexural strength and impact energy were measured on dry specimens and the detrimental effect of water on those properties was evaluated by testing the samples after the immersion tests. The composites manufactured with alkali-treated fibers coated with PHB showed the best performance in terms of water absorption and mechanical properties.