Mechanical and moisture absorption characterization of PLA composites reinforced with nano-coated flax fibers

This research is intended to improve the interface between the fibers and the matrix and limit water absorption of bio-based material thereby decreasing degradation of the composites when they are exposed to external environment such as high temperature and humidity. In this study, flax fibers were treated with an organic surface coating containing SiO2 nanoparticles. This coating was a dispersion of silica fume in epoxy. One composite was also made with raw fibers as reference as well as one sample of pure PLA. Flax fibers/PLA composites were manufactured by hot pressing by stacking 4 PLA films and 3 pieces of flax fabric. Morphology and dispersion of the coating on the fibers was observed by scanning electron microscopy (SEM), small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). Accelerated ageing was carried out on the 3 materials by placing them in a 50°C water bath until saturation to investigate the influence of the coating on water diffusion. Mechanical properties of the different composites were investigated by tensile (before and after conditioning) and short beam shear (SBS) testing in order to evaluate the impact of the coating on the interfacial properties of the materials. The results show that the fibers surface was homogenized and that a better adhesion was reached because of the coating. Coating the fibers also allowed the decrease in water uptake by more than 10 % and their protection during conditioning, preserving their mechanical properties

Retarding Effect of Hemp Hurd Lixiviates on the Hydration of Hydraulic and CSA Cements

Wood wool panels are widely used in the construction industry as sustainable cementitious composites, but there is a growing need to replace traditional Portland cement with a binder that has a lower embodied carbon footprint. In addition, the sustainability of these panels may face serious impediments if the required amount of wood for their production needs a harvest rate higher than the rate at which the tree sources reach maturity. One solution is to use the wooden part of fast-growing plants such as hemp. However, the compounds extracted from the mixture of plants and water are the main cause of the delay observed during the hydration process of hydraulic binders in these cementitious composites. The objective of this study is to evaluate the effect of bio-aggregate lixiviates (hemp hurd) on the hydration kinetics of calcium sulfoaluminate (CSA) cement as a low-embodied-carbon alternative to ordinary Portland cement (OPC). The isothermal calorimeter showed that the hemp hurd lixiviate caused a greater delay in GU’s hydration process than CSA’s. At a 5% concentration, the main hydration peak for GU cement emerged after 91 h, whereas for CSA cement, it appeared much earlier, at 2.5 h. XRD and TGA analysis showed that after 12 h of hydration, hydration products such as calcium silicate hydrates (C-S-H) and portlandite (CH) were not able to form on GU cement, indicating low hydration of silicate products. Moreover, at 5% concentration, the carbonation of ettringite was observed in CSA cement. The compressive strength values obtained from the mixes containing hemp hurd lixiviate consistently showed lower values compared to the reference samples prepared with distilled water. Furthermore, the CSA samples demonstrated superior compressive strength when compared to the GU samples. After 28 days of hydration, the compressive strength values for CSA cement were 36.7%, 63.5% and 71% higher than GU cement at a concentration of 0.5%, 2% and 5% hemp hurd lixiviate, respectively