Table 4.

Previous studies of CNCs preparation using various raw materials and methods.

Raw Materials	Preparation Methods		Crystallinity Index (in %)	Morphology	Particle Size (in nm)	ζ-Potential (in mV)	References
	Pretreatment	Treatment
Bleached hardwood pulp	Alkaline pretreatment	Acid hydrolysis (46 & 63 wt% H2SO4)	70–80	Rod- or needle-like shape	±600 (46 wt% H2SO4)	-	[45]
					±250 (63 wt% H2SO4)
Cucumber peels	Hot water, acid, and alkaline pretreatments + NaOCl bleaching	Acid hydrolysis (60 wt% H2SO4)	74.1	Irregularly shaped flakes (freeze-drying method) and rod-like shape (drop-casting method)	582.96 (without sonication)	−48.4 ± 1.3	[43]
					110.9 (with sonication)
Seaweed	Acid and alkaline pretreatments + NaOCl & H2O2 bleaching	Acid hydrolysis (51 wt% H2SO4)	98.89 ± 0.24	Rod-like shape	239.43 ± 38.57 (length)	-	[44]
					22.45 ± 6.51 (width)
Cashew tree pruning residue	Acetosolv pretreatment + alkaline-peroxide bleaching	Acid hydrolysis (60 vol% + 25 vol% HCl)	-	Needle-like shape	276 ± 45.7 (length)	−26.1 ± 2.4	[46]
					17.5 ± 4.52 (width)
Grape pomace	Organosolv, acid, alkaline pretreatments + alkaline-peroxide bleaching	Acid hydrolysis (64–65 wt% H2SO4)	74.89	Needle-like shape	323 (length)	-	[47,48]
					7 (width)
Ferula gummosa roots	Alkaline pretreatment	Acid hydrolysis (64 wt% H2SO4)	84.01	Spherical shape		22.11 ± 5	[49]
Cornstalk	Organosolv extraction + acid and alkaline pretreatments	Acid hydrolysis (60 wt% H2SO4)	69.20	Needle-like shape	120.2 ± 61.3 (length)	-	[50]
					6.4 ± 3.1 (width)
Oil palm mesocarp fibers	Alkaline pretreatment + acetate buffer-NaClO2-water bleaching	Acid hydrolysis (65 w% H2SO4)	77.80	Rod-like shape	4.52 (width)	-	[51]
Tea leaf waste fibers	Alkaline pretreatment + acetate buffer-NaClO2-water bleaching	Acid hydrolysis (65 w% H2SO4)	83.1	Rod-like shape	7.97 (width)	-	[52]
Wheat bran	Organosolv, enzymatic, and alkaline pretreatments + NaClO2 bleaching	Acid hydrolysis (64 wt% H2SO4)	66.67 (30 min)	Needle-like shape	644.77 ± 225.20 (30 min)	−36.5 ± 0.8 (30 min)	[53]
			70.32 (60 min)		568.81 ± 229.66 (60 min)	−39.8 ± 1.0 (60 min)
			66.74 (30 min)		486.18 ± 177.36 (30 min)	−39.6 ± 1.2 (30 min)
Passion fruit peels waste	Alkaline pretreatment + alkaline-peroxide bleaching	Acid hydrolysis (52 wt% H2SO4)	77.96	Rod-like shape	103–173.5	−25 to −22	[54]
Bamboo shoots	Alkaline pretreatment + alkaline-peroxide bleaching	Acid hydrolysis (55 wt% H2SO4)	83.65	Rod-like shape	-	-	[55]
Waste cotton from hospital	NaOCl bleaching	Ultrasound-assisted acid hydrolysis (50 wt% H2SO4)	81.23	Spherical shape	221	-	[56]
Dissolving bamboo pulp	-	Microwave-ultrasound-assisted acid hydrolysis (oxalic acid)	78.31	Rod-like shape	285 (length) 17 (width)	−42.9	[57]
Bleached Eucalyptus Kraft pulp	-	Acid hydrolysis (62 wt% H2SO4)	90.3 ± 0.0	Needle-like shape	<10 (width)	-	[58]
		Enzymatic hydrolysis using Cellic CTec 2 (Novozymes)	94.1 ± 2.7	Needle-like shape	6–12 (width)
Sugarcane bagasse	Steam explosion + alkaline pretreatment + alkaline-peroxide bleaching	Enzymatic hydrolysis using Cellic CTec 2 (Novozymes)	96.5 ± 1.1	Needle-like shape	14–22 (width)
Cotton cellulose powder	Alkaline pretreatment + NaClO2 bleaching	High-pressure homogenization	79 ± 1	Needle-like shape	177.5 ± 123.7 (length)	-	[59]
					7.7 ± 3.0 (width)
Microcrystalline cellulose	-	Subcritical water	79.0	Rod-like shape	242 ± 98 (length)	-	[60]
					55 ± 20 (width)
Eucalyptus bleached hardwood Kraft pulp	-	Ionic liquids treatment	-	Spherical shape	123 ± 48 ([bmim][HSO4])	−24 ± 2.5 ([bmim][HSO4])	[61]
					77 ± 25 ([emim][Cl])	−12 ± 6 ([emim][Cl])
Crown flower	Alkaline pretreatment + acetic acid-H2O2 bleaching	Solid acid-catalyzed exfoliation	43.02	Rod-like shape	242.06 ± 80.79 (length)	−15.6 ± 1.4	[42]
					8.80 ± 2.92 (width)