Ultrasonication‐assisted alkali treatment of hemp fibers to improve the fiber/matrix interface of hemp/epoxy composites: The influence of sodium dodecyl sulfate surfactant.

Alkali pretreatment of fibers is an efficient technique to enhance fiber/matrix bonding in natural fiber composites. This study investigates if the addition of sodium dodecyl sulfate (SDS) surfactant increases the efficacy of alkali treatment of hemp fibers. SDS concentrations ranging between 2 and 10% wt/wt were used with a constant (10% wt/wt) NaOH concentration. Fiber surfaces were observed with scanning electron microscopy (SEM). Fiber surfaces were cleaner when SDS was used compared with alkali treatment with no SDS added indicating the elimination of substances such as lignin, waxes, hemicelluloses, and pectin. Fourier‐transform infrared spectroscopy and TGA studies also confirmed the removal of these substituents. Mechanical performance of the composites was evaluated via static and dynamic tests. The tensile strength and modulus improved 24.9% and 13.6% respectively with the addition of 10 wt% SDS. The flexural strength and modulus also showed an improvement of 22.4% and 26.3% respectively when 10 wt% SDS was added to alkali solution. Dynamic mechanical tests showed that the storage and loss modulus of the composites increase with SDS/alkali treatment. Results indicated that the use of SDS in alkali treatment notably improves the composite performance which is attributable to more efficient elimination of noncellulosic constituents from fiber structure. Highlights: Sodium dodecyl sulfate (SDS) improves the efficacy of NaOH treatment of hemp.Removal of noncellulosic substances from fibers was facilitated by SDS.Ultrasound/SDS assisted alkalization of fibers improved composite properties. [ABSTRACT FROM AUTHOR]