Romina del Rey

Effect of Sodium Hydroxide Treatments on the Tensile Strength and the Interphase Quality of Hemp Core Fiber-Reinforced Polypropylene Composites

The formulation of greener composite materials by substituting glass fibers with natural fibers is a current field of research. If such natural fiber reinforcements come from industrial side streams, as hemp core fibers (HCFs) come from the extraction of hemp strands for the textile industry, an additional advantage can be identified. Nonetheless, such by-product fibers show some drawbacks, such as high lignin contents, which can make it difficult to obtain a good interphase between the fibers and the matrix and to obtain a good fiber individualization. A digestion treatment at different NaOH contents is proposed to eliminate soluble lignin and extractives from the surface of the fibers. At the same time, the use of a coupling agent solves incompatibilities between the fibers and the matrix. The composites were tensile tested and the impact of the proposed treatments is evaluated and discussed. Later, the Kelly-Tyson modified equation and a modified rule of mixtures—the micro-mechanic models—is used to study the impact of such treatments on the quality of the interphase between the polymer and the reinforcement. Both treatments showed a high impact on the tensile strength and the quality of the interphase, obtaining competitive composite materials reinforced with HCFs derived from a by-product.

Characterization of Sheep Wool as a Sustainable Material for Acoustic Applications

In recent years, natural materials are becoming a valid alternative to traditional sound absorbers due to reduced production costs and environmental protection. This paper reports the acoustical characterization of sheep wool. Measurements on normal incidence and diffuse-incidence sound absorption coefficients of different samples are reported. The airflow resistance has also been measured. The results prove that sheep wool has a comparable sound absorption performance to that of mineral wool or recycled polyurethane foam. An empirical model is used to calculate the sound absorption of sheep wool samples. A reasonable agreement on the acoustic absorption of all sheep wool samples is obtained.

Road traffic noise barriers based on recycled materials.

One of the main corrective measures taken to reduce environmental noise produced by roads is using sound barriers. However, the construction of miles of noise barriers implies a high cost. One solution to reduce the costs is using recycled materials in the noise barriers, for example, plastic wastes, which has great environmental benefits. According to EN 1793‐1 to 3:1998, the main acoustic characteristics of noise barriers are the sound absorption and the airborne sound insulation. On the other hand, the technical document CEN/TS 1793‐5:2003 gives guidelines for determining the in situ sound reflection index, which is an important parameter because the reflections from the barrier may increase the background noise in the surrounding area. This method has not been validated for noise barriers having a relatively low airborne sound insulation. In this study, sound reflection index using the impulse method is obtained in the laboratory for a wide frequency range. Environmental designs of road traffic noise ...

An inverse method to characterize fibrous sound absorbing materials.

Characterization of sound absorbing materials is needed to predict its behavior. The most commonly used models to do so consider the flow resistivity, porosity, and average fiber diameter as parameters to determine the acoustic impedance and sound absorbing coefficient. Besides direct experimental techniques, numerical approaches appear to be an alternative to estimate the material’s parameters. In this work an inverse numerical method to obtain the porosity, the fiber density, and the fiber average diameter of a fibrous material is described. Using normal incidence measurements of the sound absorption coefficient and then using the model proposed by Voronina, subsequent application of basic optimization techniques allows one to characterize a sound absorbing material. The numerical results agree fairly well with the experimental data.

Effects of the soil on the noise attenuation of environmental berm barriers

Berm mounds are a commonly used technique to reduce the environmental noise levels produced by highways. A berm is a natural noise barrier constructed of soil, stone, rock, or rubble, often landscaped, running along a highway to protect adjacent communities from noise pollution. An earth mound may be constructed using surplus materials at project site, provided there is sufficient land area available for its construction. Therefore, berms are natural environmental barriers, having relative low costs and they are subjectively well perceived by residents. However, exact noise attenuation provided by berms has not been enough explored in the technical literature, as opposed to common barriers made of vertical rigid walls. Although, some highway noise prediction models assign a noise reduction bonus of 3 dB(A) to sound barriers made of earth mounds, experimental assessments have yielded mixed results. Few theoretical reports have studied this particular problem. In this work, numerical analysis using the clas...

Some important considerations about the use of new materials in sound barriers.

Several alternatives to mitigate road traffic noise impact have been reported, although constructing a noise barrier is probably the most important mitigation measure when the construction of a highway is planned. A noise barrier impedes the transmission of traffic noise, resulting in low noise levels at the receiving point. Earth‐mounds, fences, or walls are common ways to implement a noise barrier. Due to environmental concern and economic costs of sound barriers, the use of new materials in building sound barriers has received a large amount of attention in recent years. However, a sound barrier is a solid structure that has to meet several standards in order to assure its proper use. In this work, the use of new materials in sound barriers is discussed from a practical point of view. Engineering concerns about visual impact, effects on ecosystems, safety for drivers, effects on residents, and public acceptance are discussed. Although the use of new low‐cost and environmentally friendly materials is be...

New absorbing materials obtained from recycled plastic bottles.

In controlling environmental noise, a lot of effort is put in place to optimize noise barriers. However, in doing so, the noise barriers are usually made of materials that are difficult to recycle. Currently, several studies are aimed to use textile‐based materials, such as polyester wool instead of mineral wool, in manufacturing noise barriers. However, the pure polyester chip is made of synthesized polymers obtained from petroleum, whose price has risen during the last years. In this work, alternative polyester wool obtained through processing the polyethylene terephthalate (PET) from recycled plastic bottles is presented. For comparison, the sound absorption material characteristic parameters are obtained for pure polyester fiber and the new polyester wool made from recycled plastic bottles. In addition, an empirical model to predict the acoustic behavior of recycled PET is proposed. Thus, the model can be used both to design and to optimize noise barriers.

Aplicación del Método de los Elementos Finitos para la Simulación de las Transmisiones por Flanco en Uniones con Suelos Flotantes

This paper presents the use of the finite elements method to study the flanking transmission through the use of the vibration reduction index, for the case of constructive solutions that use floating floors. On one side, the insertion of elastic interlayer in new building solutions is now a very common practice. On the other side, the test procedures for the acoustic study of this kind of sets (concrete floor with elastic interlayer) are very laborious and the existing empirical equations do not match reality in many cases. For this reason, the study of the problem using finite elements would allows giving numerical solution to a wide range of different constructive solutions and numerical prediction for the acoustical isolation could be improved.Este trabajo ha sido financiado por el Ministerio de Educacion y Ciencia de Espana (BIA2007-68098-C02-01 y BIA2007-68098-C02-02).