Abstract

Currently there is a need to develop more sustainable and renewable materials compromised with the environment. From these needs, hemp stalk has great potential because it is mostly a waste material. Moreover, hemp shives are a lightweight material with a high insulating property. This study aims to increase the knowledge in a material made solely from stalk and ECF (elementary chlorine free) bleached eucalyptus kraft pulp and a second 100% recycled material where the kraft pulp is replaced by recycled cardboard fiber, also a vegetable coating is added to protect against moisture. The hemp/fiber ratio influence is studied. Samples are evaluated in terms of mechanical behaviour (compression and shear), thermal and acoustic insulation. To study the thermal insulation, a testing camera is used where the heat transfer through the material is measured in order to study the thermal resistance. A Kundt tube is used in the acoustic insulation study to calculate the absorption of sound waves in a range from 0 to 6500 Hz. The results show that by increasing the percentage of hemp, the mechanical properties increase (compression and shear). Also, the eucalyptus pulp acts as a binder between the shives; nevertheless, if there is not enough, the material is not stable. Therefore, a maximum of 70 wt.% of hemp is recommended. In the case of thermal insulation, better thermal resistance is obtained in the case of 60 wt.% of hemp, while in acoustic insulation a higher percentage of hemp have a high performance, reaching attenuation values greater than 0.8 for frequencies greater than 1000Hz. The carboard sample improves the shear and acoustic insulation performance. The coating improves the thermal resistance but worsens the acoustic insulation.

Abstract

Heat dissipation is an issue that is acquiring great importance to increase the efficiency in the utilization of the energy and extending the lifespan of the equipment. Traditionally, heat dissipation has been carried out using metals, but the increase in the requirements of equipment and devices, composites have gained importance. Graphite based composites have relevance in heat dissipation, particularly when the disperse material is a metal or metal carbide. The reason is the great value of thermal conductivity combined with good mechanical properties and lightness. Research has focused until nowadays on the composite graphite-MoC, although there are other composites with great potential, as that proposed in this manuscript: graphite- Cr3C2. The preparation of the composite graphite-Cr3C2 consisted in mechanical mixing of the staring powders, subsequent obtaining of the green compact of 40 mm in diameter and, finally, sintering at 2000 °C for 20 minutes under an applied pressure of 30 MPa in the Spark Plasma Sintering apparatus. The sintered material exhibited electrical and thermal conductivities in the in-plane direction of 1.08 MS/m and 215 W/m · °C, respectively, and a flexural strength of 113 MPa, which makes this material a suitable candidate for its application in heat dissipation.