Modification of hemp shiv properties using water-repellent sol–gel coatings

Abstract

For the first time, the hydrophilicity of hemp shiv was modified without the compromise of its hygroscopic properties. This research focused on the use of sol-gel method in preparation of coatings on the natural plant material, hemp shiv, that has growing potential in the construction industry as a thermal insulator. The sol-gel coatings were produced by cohydrolysis and polycondensation of tetraethyl orthosilicate (TEOS) using an acidic catalyst. Methyltriethoxysilane (MTES) was added as the hydrophobic precursor to provide water resistance to the bio-based material. Scanning electron microscopy (SEM) and focused ion beam (FIB) have been used to determine the morphological changes on the surface as well as within the hemp shiv. It was found that the sol-gel coatings caused a reduction in water uptake but did not strongly influence the moisture sorption behaviour of hemp shiv. Fourier transformed infrared (FTIR) spectroscopy shows that the coating layer on hemp shiv acts a shield, thereby lowering peak intensity in the wavelength range 1200-1800 cm −1 . The sol-gel coating affected pore size distribution and cumulative pore volume of the shiv resulting in tailored porosity. The overall porosity of shiv decreased with a refinement in diameter of the larger pores. Thermal analysis was performed using TGA and stability of coated and uncoated hemp shiv have been evaluated. Hemp shiv modified with sol-gel coating can potentially develop sustainable heat insulating composites with better hygrothermal properties. A novel method for modification of hemp shiv using sol-gel technology. Graphical Abstract• Coating layer acts as a breathable membrane allowing the hemp shiv to retain its hygric characteristics.• Hemp shiv coated with sol-gel monolayer reduces its water absorption capacity by 200%.• The effects of sol-gel coating on surface morphology, thermal stability and porosity of the shiv increase with increase in coating thickness.

Regionalised Life Cycle Assessment of Bio-Based Materials in Construction; the Case of Hemp Shiv Treated with Sol-Gel Coatings

“…Regarding the contribution of material inputs, TEOS is the environmental hotspot for all impact categories. TEOS as a silica source in the sol-gel material production process is hydrolysed and condensed to make a silicon dioxide network [32]. Looking inside the TEOS production process shows that silicon tetrachloride has the highest impact.…”

“…Hexadecyltrimethoxysilane (HDTMS, 85%), as the hydrophobic agent, was added to the above mixture. The produced sol was stirred for around 2 h and then aged for 48 h in a closed container at room temperature [11,32]. At this stage the sol-gel coating is ready to be applied.…”

Resilient hemp shiv aggregates with engineered hygroscopic properties for the building industry

“…The MCR of uncoated shiv remains the same as its MC which is 19.68% which means that the moisture adsorption capacity of the coated shiv is not significantly different than the uncoated shiv. The fact that the coating increases the mass of the shiv, equations (1) and (2) show that for uncoated hemp shiv MC = MCR but for coated shiv MC < MCR [24,28].…”

“…The readings were taken at frequent intervals for 24 hours, in which the sample was taken out of water using a tweezer, shaken off to remove any visible surface water and then weighed within 30s. Mass readings were recorded to the nearest 0.1 mg and an average of three readings from different samples was reported as the final measurement [24,25].…”

“…For the analysis of the adsorption-desorption isotherm in response to varying humidity levels, a dynamic vapour sorption equipment DVS Advantage, SMS, UK was used. The test protocol was adopted from previous studies [24,26]. The samples weighed around 15 mg and experiment temperature was maintained at 23 °C.…”