Physical and Chemical Modifications of Plant Fibres for Reinforcement in Cementitious Composites

Table 4

Advantages and disadvantages of fibre chemical treatments.

Treatment	Advantage	Disadvantage	Remarks	Ref.
Alkaline	Rough fibre surfaces provide better mechanical interlocking and stronger interfacial strength between the fibre-matrix	More than 6% increment of alkaline concentration and longer than 24-hour soaking periods damage the fibres and reduce tensile strength	The types and concentration of the alkaline solution, time of treatment, and the temperature used for modification affected the efficiency	[128, 129]
Silanes	Increases toughness and reduces water adsorption of the fibres resulting in hydrophobic composites	Treated fibre tensile strength decreased due to cellulose microfibrils receiving less support against tensile loading	Silane treatments could be more effective when combined with physical treatment	[130, 131]
Acylation	Increases crystallinity and reduces water adsorption	Increasing the degree of acetylation decreases the mechanical properties due to degradation of cellulose and cracking of fibres	Acylation may not be as effective as alkaline treatments for improving the interfacial interaction between fibres and matrices	[132, 133]
Graft copolymeriza- tion	Increases fibre-matrix adhesion, reduces water adsorption, thermal stability, and enhances the mechanical properties of the composites	High initiator concentration, temperature, and fibre loading influence the grafting effect	Maleic anhydride (MA) is the most prominent functional group due to cost, performance, and commercial availability	[134, 135]
Reductive bleaching	Fibres are highly hydrophobic and bright	Not as efficient as oxidative bleaching	Bleaching effects have a positive reaction with a 1–2% dosage of reductive bleaching agents and higher than 60°C temperature	[136, 137]
Oxidative bleaching	No separate pretreatment is needed due to the combined effect of bleaching and cleaning with fibre quality intact	Expensive treatment requires high temperatures, and fibre-coloured compounds are destroyed and cannot reform due to the permanent bleaching process	Combination treatment with coupling agents is needed to modify the wet-out and interfacial bonding	[138, 139]
Enzyme	Effectively used to produce homogenous fibre surfaces with improved thermal properties by removal of the hygroscopic pectin and hemicellulose content	Differences in enzyme quality including contamination of enzymes during preparations with others of varying specificity will require careful and detailed analysis	Variation types of fibre and enzymes have different reactivity to the targeted components because of geometrical shapes	[140, 141]
Peroxide	Increases crystallinity, thermal stability, and mechanical performance	Possibility of forming mechanical and chemical bonding at the fibre surface is mainly dependent on the surface morphology and chemical composition of the fibres	It may facilitate both mechanical interlocking and the bonding reaction due to the exposure of the hydroxyl groups to the chemical	[142, 143]
Permanganate	Rough fibre surfaces provide better mechanical interlocking and stronger interfacial strength between the fibre-matrix	The use of hazardous chemicals causes environmental pollution	4% is the maximum dosage of the compound to yield tensile strength	[144, 145]