Abstract
This paper presents an optimized washing protocol for as-received natural fibers, prior to large-scale composite manufacturing, for the structural strengthening of historic masonry. The aim was to achieve a simple protocol for standard cleaning of fiber surfaces from low molecular weight constituents that may be detrimental towards interfacial strength without damaging the fibers. The proposed procedure employs the application of the solvent sequence: ethanol, acetone, hexane, with optimized incubation times and stirring conditions. Additionally, this procedure may change the surface of the fiber, thereby enhancing the durability of the fiber-matrix interface. The washing protocol resulted in an increase of tensile strength by 56%, 52% and 22% for flax, hemp and sisal fibers, respectively, as compared to the corresponding non-washed fibers, without loss of elongation. The static contact angle measurements confirmed exposure of a higher fraction of the hydrophilic crystalline cellulose, with a higher wettability observed after washing protocols.
Highlights
It is manifestly known by researchers that natural fiber textiles present an appealing and promising solution as green, economical and strong reinforcements for composite materials; this is investigated in different fields of science [1]
Hexane is a non-polar liquid with the ability to reach the fiber lumen, typically forming a contact angle of ~0◦ with the surface of natural fibers
The protocol employed washing with selected solvents, individually and in sequence, for cleaning compounds that may be detrimental to interfacial strength, exposure of the crystalline cellulosic backbone, and enhancement of the mechanical properties of the fibers
Summary
It is manifestly known by researchers that natural fiber textiles present an appealing and promising solution as green, economical and strong reinforcements for composite materials; this is investigated in different fields of science [1]. The deterioration kinetics of these hydrophilic fibers are represented mainly by the mineralization of fibers, owing to the migration of hydration salts (i.e., calcium hydroxide; present in water of mortar pores) to the fiber lumen This leads to aging, a drop in the fibers’ mechanical properties and embrittlement of their composites [7,8]. The excessive presence of such extractive compounds might interfere with chemical protocols designed for further fiber treatments [15] Their partial removal can enhance the fibers’ mechanical properties, adding better dimensional stability in their composites
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