Properties and performance of kenaf fiber-sawdust polymeric sandwich bio-composites

The increasing demand for environmentally friendly and sustainable structures have led the engineers and scientists to develop new bio-based composites. Natural fibers in composites present many advantages which include high strength and stiffness to low weight ratios, biodegradability, renewability, economic viability and so on. Currently, the use of mechanical fastening joints exists in the production of sandwich composite structures, but literature indicates that it has unavoidable drawbacks such as the structure failing prematurely with a load far below the maximum strength of component parts. As a result, an adhesively bonded joint is a better method of joining.This research investigates the properties and performance of a novel sandwich composites incorporating kenaf fiber-polyester matrix as skin material and sawdust-polyester matrix as core material, respectively. To this end, the kenaf fiber-polyester skin was fabricated in a unidirectional orientation with fiber volume fraction of 40 % from preliminary study, while the sawdust-polyester core was produced in a random arrangement with fiber volume fraction of 20%, also from preliminary study and this was produced by varying the thickness of the core. Both the Kenaf Fiber Reinforced Polyester (KFRP) skins and the Sawdust Reinforced Polyester (SDRP) core were tested interm of tension, flexure, compression, and shear. These tests were carried out to determine their constituent material properties. Consequently, three types of bio-composites sandwich were manufactured based on geometry, and was subjected to flexural load through three-point bending test to establish the flexural properties. Numerical investigation was carried out using ABAQUS FEA code to validate experimental results. Besides, it has been observed from literature that the use of natural fiber composites have been restricted to non-structural and semi-structural applications due to not having sufficient test data on fracture toughness at adhesive joint. Therefore, the adhesive bond behaviour of the KFRP adherend and the SDRP adherend sandwich composites was carried out through the Double Lap Shear (DLS) joint test to ascertain the bond shear strength and stresses at the joints. The DLS joints were fabricated with different bond lengths and bond widths using polyester adhesive as joint material and subjected to direct axial compression load. Numerical simulation was implemented to validate experimental results. The results of the KFRP tensile properties shows that stiffness and strength were found to be highest in the longitudinal direction and least in the transverse direction with percentage difference of 152.50 % for the modulus of elasticity and 175.24 % for tensile strength, respectively. Also observed is that there exist a considerably variability in the SDRP tensile, compressive and flexural strengths, nevertheless, their stiffnesses are comparably closed to each other. The results of the core shear stress and facing bending stress of the bio-composites sandwich revealed an increment of 13.90 % was recorded as the core thickness increased from 10 mm to 20 mm for core shear stress, while the facing bending stress saw an increment of 13.93 % as the core thickness increased from 10 mm to 20 mm. Excellent agreement was reached between the numerical simulations and the experiments in predicting the flexural properties. Furthermore, it was found that the lap length and bond width increases the load carrying capacity of the joints but decreases the bond shear strength. The numerical analysis results were in good accord with the experimental results, and the use of KFRP and SDRP in bonded assemblies have demonstrated promised with good potentials for use in structural applications

Major trends in the land surface phenology (LSP) of Africa, controlling for land cover change

Monitoring land surface phenology (LSP) trends is important in understanding how both climatic and non-climatic factors influence vegetation growth and dynamics. Controlling for land-cover changes in these analyses has been undertaken only rarely, especially in poorly studied regions like Africa. Using regression models and controlling for land-cover changes, this study estimated LSP trends for Africa from the enhanced vegetation index (EVI) derived from 500 m surface reflectance Moderate-Resolution Imaging Spectroradiometer (MOD09A1), for the period from 2001 to 2015. Overall end of season showed slightly more pixels with significant trends (12.9% of pixels) than start of season (11.56% of pixels) and length of season (LOS) (5.72% of pixels), leading generally to more ‘longer season’ LOS trends. Importantly, LSP trends that were not affected by land-cover changes were distinguished from those that were influenced by land-cover changes such as to map LSP changes that have occurred within stable land-cover classes and which might, therefore, be reasonably associated with climate changes through time. As expected, greater slope magnitudes were observed more frequently for pixels with land-cover changes compared to those without, indicating the importance of controlling for land cover. Consequently, we suggest that future analyses of LSP trends should control for land-cover changes such as to isolate LSP trends that are solely climate-driven and/or those influenced by other anthropogenic activities or a combination of both

Mechanical properties of kenaf fibrous pulverized fuel ash concrete

The main objective of the experimental work is to identify the mechanical properties of Kenaf Fiber incorporate with Ordinary Portland Cement (OPC) and Pulverised Fuel Ash (PFA) in the mix proportions of concrete. Kenaf Fibrous Concrete (KFC) and Kenaf Fibrous Pulverised Fuel Ash Concrete (KFPC) will be measured on physical and mechanical properties in order to investigate the suitability of this natural fiber as a composite material. A comparison of properties between these two composites will determine the density, workability, compressive, tensile, and flexural strength of the concrete. Eight different mixes with varying percentage of Kenaf fiber were prepared with 30N/mm2 strength at 28days ,56 days and 90 days. Short fiber with 25mm and 50mm length were randomly distribute in composite to enhance the tensile and durability. PFA was obtained by the process of burning in the Power Station Coal Ash at Tanjung Bin, Johor. The unburning powder from the process is called as a PFA generally suitable for cement replacement in the concrete mix. The pozzolanic reaction will improve the adhesion of cement gel, hence increased the properties of concrete in a long-term strength development. The result shows that the inclusion of Kenaf fiber improve tensile strength of composite, furthermore the 25% PFA mix increase the durability of concrete

A systematic review of vegetation phenology in Africa

The study of vegetation phenology is important because it is a sensitive indicator of climate changes and it regulates carbon, energy and water fluxes between the land and atmosphere. Africa, which has 17% of the global forest cover, contributes significantly to the global carbon budget and has been identified as potentially highly vulnerable to climate change impacts. In spite of this, very little is known about vegetation phenology across Africa and the factors regulating vegetation growth and dynamics. Hence, this review aimed to provide a synthesis of studies of related Africa's vegetation phenology and classify them based on the methods and techniques used in order to identify major research gaps. Significant increases in the number of phenological studies in the last decade were observed, with over 70% of studies adopting a satellite-based remote sensing approach to monitor vegetation phenology. Whereas ground based studies that provides detailed characterisation of vegetation phenological development, occurred rarely in the continent. Similarly, less than 14% of satellite-based remote sensing studies evaluated vegetation phenology at the continental scale using coarse spatial resolution datasets. Even more evident was the lack of research focusing on the impacts of climate change on vegetation phenology. Consequently, given the importance and the uniqueness of both methods of phenological assessment, there is need for more ground-based studies to enable greater understanding of phenology at the species level. Likewise, finer spatial resolution satellite sensor data for regional phenological assessment is required, with a greater focus on the relationship between climate change and vegetation phenological changes. This would contribute greatly to debates over climate change impacts and, most importantly, climate change mitigation strategies

Mechanical properties of kenaf fibrous pulverized fuel ash concrete

The main objective of the experimental work is to identify the mechanical properties of Kenaf Fiber incorporate with Ordinary Portland Cement (OPC) and Pulverised Fuel Ash (PFA) in the mix proportions of concrete. Kenaf Fibrous Concrete (KFC) and Kenaf Fibrous Pulverised Fuel Ash Concrete (KFPC) will be measured on physical and mechanical properties in order to investigate the suitability of this natural fiber as a composite material. A comparison of properties between these two composites will determine the density, workability, compressive, tensile, and flexural strength of the concrete. Eight different mixes with varying percentage of Kenaf fiber were prepared with 30N/mm2 strength at 28days ,56 days and 90 days. Short fiber with 25mm and 50mm length were randomly distribute in composite to enhance the tensile and durability. PFA was obtained by the process of burning in the Power Station Coal Ash at Tanjung Bin, Johor. The unburning powder from the process is called as a PFA generally suitable for cement replacement in the concrete mix. The pozzolanic reaction will improve the adhesion of cement gel, hence increased the properties of concrete in a long-term strength development. The result shows that the inclusion of Kenaf fiber improve tensile strength of composite, furthermore the 25% PFA mix increase the durability of concrete