Abstract
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).
Highlights
The EU Green deal policy aims to achieve a carbon neutral economy by 2050, which requires redesigning different industrial sectors, their processes and their products
This study focused on inspecting the contribution of surface pretreatment and modification on the moisture adsorption, water absorption and reaction to fire of hemp fiber reinforced polylactic acid (PLA) (HPLA) composites
The 4% weight reduction measured on the water pretreated hemp fibers is the result of the removal of water-soluble, fiber cell wall contents, as it was qualitatively characterized by Fourier transform infrared (FTIR) in a previous work [10] and observed by Bourmoud et al [22]
Summary
The EU Green deal policy aims to achieve a carbon neutral economy by 2050, which requires redesigning different industrial sectors, their processes and their products. There is a growing challenge toward the use of healthy, sustainable, non-hazardous, biodegradable and renewable resources while maintaining reliability in product performances [1]. Studies [5,6,7,8] have shown that hemp fiber can be a suitable natural reinforcing material for composite application due to its vast availability, price stability and good mechanical properties. PLA is produced from annual bioresources, mainly through the fermentation of corn, and display a cost-effective production compared to other polymers developed from renewable resources such as soya oil-based epoxy, lignin and starch [9]. Hemp PLA composites have shown promising results [10] and can be regarded as appropriate materials for a vast range of applications and minimize the environmental threats associated with petroleum-based products
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