|
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] |
|