Table 3.

Chemical Treatment Properties of NFRPC.

Chemical Treatment	Name of the Fiber	Chemical Reagents Used	Method	Structure Improvement	Application	References
Alkaline	Hemp	NaOH	Treated fiber with NaOH at 20 °C for 48 h and washed using distilled water and acetic acid to neutralize the excess of NaOH.	Better fiber-matrix adhesion led to an increase in interfacial energy and thus enhancing the thermal and mechanical properties of the composites	Polymer reinforcements	[69,94]
	Jute,					[69,94]
	Sisal					[69,94]
	Kapok					[69,94]
	Kenaf	NaOH	Treated kenaf fiber with 6% of NaOH solution for 24 h. Then, kenaf fibers were rinsed and immersed into a solution that contained distilled water and 1% acetic acid to neutralize the remaining NaOH. After washing, the kenaf short fibers were dried in an oven for 24 h.	Better physical, morphological, and mechanical properties because of the compatibility of kenaf with polypropylene composites	Automotive	[69,95]
	Napier grass	NaOH	Napier grass fibers were treated with 2% and 5% of NaOH at room temperature for 30 min. The fibers were washed with tap water and distilled water many times and dried at 100 °C.	enhanced tensile properties	Reinforcement for composites	[69,96]
	Carica papaya	NaOH	Carica papaya fibers were treated with 5% NaOH for 60 at 25 °C. Then, the fibers were washed many times using HCI solution and deionized water. Then, the fibers were dried at 100 °C in an oven for moisture removal.	Better performance in mechanical properties, thermal stability, and good interfacial bonding between cellulosic fiber and the matrix.	Light weight industrial	[69,97]
Saline	Sugar palm	Saline	Sugar palm fibers were immersed with 2% saline for 3 h. Then, the fibers were immersed in a mixture of methanol–water (90/10 w/w) for 3 h hydrolysis under agitation. The fibers were thoroughly rinsed with distilled water and then oven-dried at 60 °C for 72 h.	Improve properties of sugar palm fiber and enhance fiber-matrix bonding sugar palm fiber–thermoplastic polyurethane composites.	Industrial application	[69,98]
Acetylation	Dombeya buettnerri	Acetyl anhydride	The fibers were soaked with 2% up to 6% of acetyl anhydride for 3 h at room temperature. Then, the fibers were washed with tap water and repeatedly rinsed with distilled water until all excess acid had been removed. Then, the fibers were dried for 2 h at 105 °C.	Enhanced surface morphology and mechanical properties.	Engineering materials applications	[69,99]
	Combretum racemosum
	Banana (Musa parasidica)
Alkaline hydrogen peroxide	Citrus fibers	Hydrogen peroxide	The citrus fibers were immersed in hydrogen peroxide for 4 h at 60 °C. Then, the fibers were adjusted to pH 6 with acid hydrochloric (1.0 M) at 25 °C. The mixture was centrifuged at 6000× g for 15 min; the residue was then collected and washed in pure ethanol and dried via oven at 60 °C for 7 h.	High water holding and swelling capacities could be used as emulsifiers in juice and jam. It also has better thermal stability and viscosity properties.	Application in food industry	[100]
Benzoylation	Sisal fiber,	Benzoyl chloride		Increase strength of composite and thermal stability, decrease water absorption	Industrial application	[101]
	Sugar palm		Soaked with a mixture solution of 1% NaOH and 5 mL of C7H5ClO with respective soaking times. Then, fibers were washed and soaked in absolute ethanol for 1 h, washed again until pH became neutral, and dried overnight at 50 °C.	Improvement in tensile strength	Furniture and components inside vehicle	[102]
Acrylation and Acrylonitrile Grafting	Flax-fiber	Acrylic acid solution	Flax fibers were immersed in NaOH solution for 0.5 h and then soaked in acrylic acid solution at 50 °C for 1 h, washed with distilled water, and dried.	Improving the physical and mechanical properties	Plastic, automobile, and packaging industries	[103]
Maleated Coupling Gents	Jute fiber	Maleic anhydride- polypropylene (MAPP)	The fibers were immersed in MAPP solution in toluene at 100 °C.	Increase in mechanical strength	Industrial applications with offer cost-effective and value-added composite material	[104]
Permanganate Treatment	Sisal fiber	Potassium permanganate KmnO4	Sisal fibers were soaked carefully in a solution of KmnO4/acetone with a concentration of 0.02% for 3 min. After that, the fibers were taken out, washed many times with distilled water, and dried	Improve fiber strength and fiber-matrix adhesion	Industrial application	[101]
Peroxide Treatment	Sisal fibers	Benzoyl peroxide from acetone solution	Fibers were coated with benzoyl peroxide from acetone solution after alkali pre-treatment. A saturated solution of the peroxide in acetone was used. Fibers were then dried.	Enhance in tensile properties	Substitute the wood	[105]
Isocyanate Treatment	Pineapple leaf fiber	toluene solution containing poly(methylene)-poly(phenyl)isocyanate	Fibers were dipped in toluene solution containing PMPPIC (5 wt% of fiber) for half an hour at 50 °C. The fibers were then decanted and dried in an air oven at 70 °C for 2 h. Later these were mixed with polyethylene using toluene as the solvent containing PMPPIC (6 wt% of fiber) at a temperature of 120 °C.	Enhance mechanical properties	Structural and non-structural application	[106]
Ionic Liquid	Chitin fiber	1-ethyl-3-methylimidazolium acetate	Chitin derived from shrimp shell biomass that has been thermally pretreated, pressed, and ground. Chitin was isolated using a microwave-assisted dissolution of [C2mim][OAc], followed by water coagulation, washing, and oven drying.	Improve the mechanical strength of chitin fibers	High-performance chitinous sorbents for applications such as metal recovery from seawater	[107]
Thermal decomposition kinetic	Wood, bamboo, agricultural residue, and bast fibers	Phosphonium ionic liquids	All raw materials were washed with water to remove impurities before being dried in an oven at 75 degrees Celsius for 12 h. The dried materials were then ground and screened using a Wiley mill. For testing, samples with particle sizes ranging from 20 to 28 meshes were collected. Various degradation models, including the Kissinger, Friedman, Flynn–Wall–Ozawa, and modified Coats–Redfern methods to determine the apparent activation energy of these fibers.	Improve the thermal stability of the fibers	Renewable biomass energy/natural fuels and forest fire propagation control, practical engineering applications.	[108]