Tensile testing of cellulose based natural fibers for structural composite applications

A series of tensile tests were conducted on a Lloyd LRX tensile testing machine for numerous natural fibers deemed potential candidates for development in composite applications. The tensile tests were conducted on the fibers jute, kenaf, flax, abaca, sisal, hemp, and coir for samples exposed to moisture conditions of (1) room temperature and humidity, (2) 65% moisture content, (3) 90% moisture content, and (4) soaked fiber. These seven fibers were then tested for the four conditions and the mechanical properties of tensile strength, tensile strain to failure, and Young's modulus were calculated for the results. These results were then compared and verified with those from the literature, with some of the fibers showing distinctly promising potential. Additionally, a study on the effect of alkalization using 3% NaOH solution was carried out on flax, kenaf, abaca, and sisal to observe impact that this common fiber pre-treatment process has on fiber mechanical properties. The result of the investigation indicated that over treatment of natural fibers using NaOH could have a negative effect on the base fiber properties. It is consequently apparent that a treatment time of less than 10 min is sufficient to remove hemicelluloses and to give the optimum effect

Characterization and physical properties of aluminium foam−polydimethylsiloxane nanocomposite hybrid structures

This article reports on the fabrication and characterisation of hybrid structures prepared by impregnating an open-cell aluminum foam with polydimethylsiloxane (PDMS) or PDMS reinforced with graphene oxide, GO (PDMS nanocomposite). The effect of the PDMS and the GO on the mechanical, thermal, acoustic absorption and fire retardancy properties of the resulting hybrid structures were evaluated and compared to the individual components (PDMS, PDMS nanocomposite, open-cell aluminium foams). Results demonstrate that the use of the PDMS cured at 65 °C, as an void filler of the open-cell aluminium foams, changes mechanical and deformation performance, from a rubbery to brittle behaviour, however attaining a higher level of strength (quasi-static: ∼5 MPa; dynamic: > 15 MPa) in the resulting hybrid structures. This change is due to the low chain mobility of the polymer and effective adhesion with struts of the open-cell aluminium foams. Furthermore, these hybrid structures are extremely sensitive to strain-rate testing, exhibiting a maximum compressive stress increase of more than 300 % and 200 %, respectively. The presence of the GO within the PDMS improves significantly the non-flammability of the hybrid structures and increases the sound absorption coefficient.publishe

Quantifying damping coefficient and attenuation at different frequencies for graphene modified polyurethane by drop ball test

In this study, polyurethane (PU) was modified by direct mixing of carboxyl functionalised graphene (GNP–COOH) referred to as f-GNP, without using any solvent, during in-situ polymerization. In a further attempt, the neat PU was modified with f-GNP and a hydrophobic silica-based solution (SG) during in-situ polymerization. The damping coefficient and attenuation capacity of neat polyurethane (PU), f-GNP based PU nanocomposite (PU + f-GNP), and f-GNP and hydrophobic silica-based solution PU nanocomposite (PU + f-GNP + SG), together with polytetrafluoroethylene (PTFE), high-density polyethylene (HDPE), ultra-high molecular weight polyethylene (UHMWPE), polyethylene terephthalate (PET), polyvinyl chloride (PVC) and NYLON have been obtained by the drop ball tests under controlled and consistent conditions. The results show that among the tested materials, polyurethane modified with carboxyl functionalised graphene and silica-based Sol-Gel (PU + f-GNP + SG) displays the greatest attenuations and PTFE the least.The attenuation of the various materials has been identified with the SVD-QR method. This experimental modal analysis method has been used to analyse the free response signal of the system during the drop ball test and identify the modal parameters such as damping ratio and frequency of the modes of deformation of the system. The drop ball test results show that the damping coefficient of polyurethane modified with 0.5 wt% carboxyl functionalised graphene (PU + f-GNP) increased by 37% at frequency range 200–300 Hz, by 34% at frequency range 500–600 Hz and by 32% at frequency range 700–1000 Hz. The developed nanocomposite materials have great potential for protecting leading edge erosion (LEE) of wind turbine