Abstract:The objective of this work was to evaluate some of the important physical and mechanical properties of particleboard panels manufactured from three different cultivars of date palm (Phoenix dactylifera) fronds, namely Saqui, Barhi and Sukkari. Experimental panels were manufactured from hot water extracted and non-extracted, and fine and coarse particles of the raw material under two target panel densities of 650 and 750 kg/m 3 . Bending properties and internal bond strength, along with dimensional stability in the form of thickness swelling, water absorption, and linear expansion of the samples was tested. Based on the findings of this work, panels manufactured from high density level and Saqie cultivar, as well as fine particles, had better performance for their mechanical properties. The effect of hot water-treatment had less robust mechanical and physical properties. It appears that date palm fronds are underutilized resources that have the potential to be used in the manufacture of value-added panel products.
The objective of this work was to evaluate some of the important physical and mechanical properties of experimental oriented strandboard panels manufactured from four different cultivars of date palm (Phoenix dactylifera) fronds. Currently date fronds are considered as waste and under-utilized. Open burning and landfill are common practices for such resources. Therefore experimental panels were manufactured from strands washed with water to determine the effect of such treatment on panel properties. Bending characteristics, internal bond strength, thickness swelling, water absorption, and linear expansion along and across the grain orientations of the samples were tested. Based on the findings in this work, the internal bond strength values of the samples were found to be satisfactory. However, the samples manufactured from water-soaked strands had lower mechanical and physical properties as compared to those made from unwashed material. Water treatment also adversely influenced dimensional stability, namely thickness swelling, water absorption, and linear expansion of the samples. It appears that untreated date palm fronds as underutilized resource show promise sustainable raw material for the manufacture of oriented strandboard panels, but further research is required to maximize their potential.
Plants are able to extract metal(loid) contaminants from the soil or water through their roots and translocate them to harvestable aerial shoots. Of late, this plant potential has been used as a phytotechnology, termed as phytoextraction, for cleaning contaminated sites, and this process has successfully removed elements like As, Cd, Cu, Ni, and Pb, among others. Exploring plants with high metal-accumulation capacity, as well as engineering new hyperaccumulators, is a need of the hour. It is assumed that hyperaccumulators have a >1 shoot:root metal-accumulation ratio, which they achieve by way of (i) overexpression of transport systems for improved sequestration, (ii) tissue-specific protein expression, and (iii) high concentration of metal chelators. Unlike nonhyperaccumulators, the hyperaccumulating species normally bind metal ions to weak oxygen ligands and use strong ligands only for transient binding during transport to storage sites. Adequate understanding of genetics, biochemistry, and molecular biology of metal accumulation is a prelude to developing transgenics with improved phytoremediation capacity. Current research in plant breeding, genomics, and proteomics suggest promising leads to the creation of “remediation” cultivars. Several transporter genes associated with metal uptake, transport, and accumulation have been identified. Efforts are underway to enhance the phytoextraction capacity of relevant species, not only by using chelating agents but also by attempting hybridization, protoplast fusion, as well as genetic engineering through novel gene transfer, overexpression of genes, and (or) reverse gene insertion, to enhance (i) transpiration rate; (ii) uptake, translocation, and metabolism of metals; (iii) activity of enzymes related to rate-limiting steps; and (iv) transformation of accumulated metal to volatile forms, and (or) silencing gene(s) that encode proteases. Genome evolution in hyperaccumulators needs to be understood through a systematic study of ecological and molecular genomics. Sequencing of a complete genome of hyperaccumulators can help in identifying the promising functional noncoding regions in the genome, thus making the experimental analysis more accurate. In addition to the constitutive overexpression of a single gene, simultaneous expression of several genes in specific cellular components has to be focused. Other areas that require expert attention include identification of metal-transporter proteins and the introduction of genes encoding the metal transporters, overexpression of metallothioneins and phytochelatin synthase, and overproduction of nicotianamine and histidine in plants. A comprehensive study of transgenic gene frequency, covering several plant generations growing on polluted as well as nonpolluted soils, may assess the possibility of gene escape into the environment and its transfer to the microorganisms present in the surroundings. This review attempts not only to collect and collate information available on mechanisms of metal accumulation and detoxification in plants and on the factors affecting the tolerance and phytoextraction capacity of plants but also the strategies that have been or can be devised for raising novel plant genotypes with elevated capacity of metal accumulation and toxicity tolerance.
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