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

Table 3

Advantages and disadvantages of fibre physical treatments.

Treatment	Advantage	Disadvantage	Remarks	Ref.
Stretching	Better load distribution in composite as a result of a reduction of fibre rigidity and density	High heating rate during stretching can generate shrinkage on the fibre surface	Heat treatment will improve the fibre strength and develop high tensile modulus	[66, 67]
Calendering	Enhancement of surface area available for matrix interaction by yielding bundle separation of long fibres	Fibres exposed to potential damage during the process	Fibres became tightly packed, and the filtration efficiency is increased by regulating density and permeability	[68, 69]
Rolling	Fibres became plasticized and will enhance the performance of the composite when added into the matrix	Longer processing will decrease fibre performance and disallow matrix interface benefits	Surface and structural properties of the lignocelluloses fibre were partially changed	[70, 71]
Solvent extraction	High fibre cellulose content was extracted from plants due to removal of impurities	Discharge from the solvent extraction process is harmful to the ecosystems and produces environmental pollution	New renewable and biodegradable bioderived solvents are of great interest and can contribute to an environmentally sustainable solvent extraction	[72, 73]
Corona treatment	Fibre wettability improved through fibre surface polarity and compatibility between hydrophilic fibres and the hydrophobic matrix	Surface ablation and etching can reduce fibre firmness	Usable as standalone surface treatment or early treatment to activate cellulose for chemical modification such as grafting	[74, 75]
Plasma treatment	Simple process without any pollution to modify the surface of NF without altering the bulk properties of the fibres and increase in the wettability of the fibre-matrix interface	Degradation and changes on the fibre surface occur from an etching mechanism that generates pits on the fibre surface area exploiting the plasma properties	PF have stronger interaction with the matrix and enhanced the mechanical interlocking of the fibre-matrix in composites	[76, 77]
Ionized air treatments	Altering the NF structure by separating the fibre bundles through removal of impurities from fibre surfaces	Mechanical properties and the performance of PF as a reinforcement were affected by longer ionized air treatment	Increases the wettability of fibre, but the interfacial property enhancements are lower compared to chemical treatments	[24, 78]
Thermal treatment	Improved thermal stability, crystallinity, and physical and mechanical properties of the NF	Longer thermal exposure decreases the moisture content and changes the physical and chemical composition of the fibre	The combination of chemical and thermal treatment can increase the initial strength and improve the durability of fibre	[79, 80]
Steam explosion	Environmentally friendly and low cost	Does not have much influence on fibre strength, crystallinity, or thermal stability	The temperature is varied between 120–220°C with a variation in time period from 30 min to 2 h	[81, 82]
Ultraviolet (UV)	Polarity of the fibre surfaces, wettability, and fibre-matrix interfacial along with mechanical properties of biocomposites are increased	Fibre strength decreased	Surface oxidation improved the mechanical properties and adhesion between the fibre-matrix compared to traditional electrochemical treatments	[83, 84]
Electron radiation	Improves the interfacial bonding of NF and matrix due to free radicals, which ensure crosslinking between the fibre-matrix	Degradation of high cellulose content under the effect of irradiation will reduce the maximum thermal decomposition temperature	Development of composite materials with good mechanical properties and morphology but lack of durability	[25, 85]
Fibre beating	An effective treatment to mitigate the fibre degradation in composites related to accelerating ageing conditions	Decrease the average fibre length, curling, and tensile strength	Improvement in terms of durability but lower mechanical strength due to defibrillation	[26, 86]
Dielectric barrier	Increased the incorporation of fibres and polymerization into the matrix	Fibre strength decreases due to primary decomposition and short decolourization of low energy consumption and time	Surface roughness increases and leads to improvement in wettability due to changes in fibre surface microstructure but a reduction in tensile strength	[87, 88]