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Hemp fibre (HF) is a natural fibre that has gained increased application in interior material for automobile industries (Sanjay et al., 2016). However, good interfacial bonding between fibre/matrix is necessary to enhance the mechanical properties of the composite (Pickering et al., 2007). This study focuses on the effect of fibre length, alkali and silane treatments on the mechanical and physical properties of hemp fibre reinforced polypropylene composites. Compression moulding technique was used to produce the composite, fibre lengths of 50, 100 and 150 mm were selected and combined with polypropylene powder at a fibre/PP ratio of 60/40%, a pressure of 1.67 MPa and temperature between 160-200 °C. The results obtained show that longer fibres enhanced mechanical strength. The tensile test result, for instance, shows a 21% increase in flexural strength at 150 mm compared to the fibre length of 50 mm. The modification resulted in a 46% decrease in strength, especially for 150 mm long fibres. This may have been as a result of fibre damage, inadequate modification, less quality fibre or higher initial moisture content in the modified fibres as observed from FTIR spectroscopy. Further investigation of these factors is required to be able to conclusively determine if they may have affected the mechanical performance (Alao, 2018). [ABSTRACT FROM AUTHOR]

Heat treatment of wood helps to lower the hydrophilicity and polarity of wood fibres used in wood-plastic composites. By means of heat treatment it is possible to reduce the access to wood hydroxyl (OH) group, which causes hydrophilic and polarity of wood fibres. Therefore improving compatibility between the wood and polymer matrix. In this research, the effect of wood flour (WF) heat treatment and chemical modification with 3-aminopropyltriethoxysilane (APTES) were investigated. WPC test samples were prepared using alder (Alnus incana) WF with mesh size of 0.05 mm as a filler material and polypropylene (PP) as the matrix material. WF was chemically modified with NaOH and APTES to increase the adhesion and compatibility of WF to polymer matrix. The composites were manufactured using a twin-screw extruder and the test samples were made by injection molding. The composites mechanical properties were tested using three-point flexural test and Charpy impact test. The composite physical properties were investigated with Fourier transform infrared spectroscopy (FTIR). The effect of silane (APTES) and NaOH modification on thermally treated and untreated WF was examined with contact angle measurement. Comparisons were made between the untreated WF and thermally treated WF. Also the effect of NaOH and silane (APTES) modification on the properties of thermally modified and unmodified WF composite were investigated. Using WF as a filler material increased flexural strength, while impact strength decreased thus making the material more rigid and brittle. The test results revealed that there was no significant difference in the mechanical properties between thermally treated and untreated composites. However, chemical modification improved the mechanical properties of the composites. [ABSTRACT FROM AUTHOR]

The poor compatibility between the highly hydrophilic wood fibres and the hydrophobic polymers is associated with a loss of mechanical properties. Therefore, to improve the interfacial adhesion between the polymer matrix and wood flour (WF), a chemical modification of WF is an appropriate solution. This study analyzes the influence of different chemical modifications of WF on the mechanical properties of wood-plastic composites (WPCs). WPC test samples were prepared from birch (Betula) WF with a mesh size of 0.63 mm as the filler material and polypropylene (PP) as the matrix material. WF was chemically modified by six different methods to increase its adhesion to, and compatibility with, the polymer matrix. The six chemical methods used were: alkaline (NaOH) modification, polyvinyl alcohol (PVA) modification, silane treatment with 3-aminopropyltriethoxysilane (APTES), acetylation with acetic anhydride, cyanoethylation, and wood fibre esterification. The composites were produced using a twin-screw extruder and the test samples were prepared by injection moulding. The composites' mechanical properties (three-point bending test), Charpy impact strength and thermal properties were tested. In addition, SEM micrographs of WPC surfaces were generated. WF as a filler material enhanced the flexural properties, while impact strength decreased, making the material more rigid and brittle. The test results revealed that the chemical modifications of WF improved the mechanical properties and crystallinity of WPC materials, while the melting temperature decreased. However, the influence of the chemical modification on the mechanical and thermal properties of WPC varied by method. [ABSTRACT FROM AUTHOR]

This research investigates an effective alkali (NaOH) treatment and fire-retardant coating to produce biocomposites from frost-retted hemp fiber and PLA. The fiber surface treatment with various NaOH concentrations was investigated throughout a range of soaking times. The results show that the extracted non-cellulosic fiber content increases with treatment duration and NaOH concentration, while the fraction of targeted components removed remains nearly unchanged after soaking for 1, 2, and 4 h with a 5 wt.% NaOH solution. At the composite level, the treatment with 5 wt.% NaOH solution for 1 h emerged as the most efficient, with tensile strength, Young's modulus, flexural strength, and flexural modulus of 89.6 MPa, 9.1 GPa, 121.6 MPa, and 9.6 GPa, respectively, using 30 wt.% fibrous reinforcement. The fire performance of the examined batches of biocomposites improved significantly with the novel fire-retardant (Palonot F1) coating. However, the tensile strength notably decreased, while the flexural properties showed only a slight reduction. In most cases, the biocomposites with the alkali-treated hemp fiber had delayed ignition during the 5 min exposure to the cone heater. The findings in this work contribute to studies that will be required to give design guidelines for sustainable building options.

The effects of surface pretreatment (water and alkali) and modification with silane on moisture sorption, water resistance, and reaction to fire of hemp fiber reinforced polylactic acid (PLA) composites at two fiber loading contents (30 and 50 wt.%) are investigated in this work. Moisture adsorption was evaluated at 30, 50, 75 and 95% relative humidity, and water resistance was determined after a 28-day immersion period. The cone calorimetry technique was used to investigate response to fire. The fiber surface treatment resulted in the removal of cell wall components, which increased fiber individualization and homogeneity as shown in scanning microscopic pictures of the composite cross-section. Although the improved fiber/matrix bonding increased the composite's water resistance, the different fiber treatments generated equal moisture adsorption results for the 30 wt.% reinforced composites. Overall, increasing the fiber amount from 30 to 50 wt.% increased the composite sensitivity to moisture/water, mainly due to the availability of more hydroxyl groups and to the development of a higher pore volume, but fire protection improved due to a reduction in the rate of thermal degradation induced by the reduced PLA content. The new Oswin's model predicted the composite adsorption isotherm well. The 30 wt.% alkali and silane treated hemp fiber composite had the lowest overall adsorption (9%) while the 50 wt.% variant produced the highest ignition temperature (181 ± 18 °C).