International Journal of Polymer Science / 2018 / Article / Tab 1

Review Article

Recent Strategies in Preparation of Cellulose Nanocrystals and Cellulose Nanofibrils Derived from Raw Cellulose Materials

Table 1

Introduction of various preparation methods of CNCs including major chemical reagents, typical conditions, yield, thermal stability, and some other advantages/disadvantages.

MethodMajor chemical reagentsTypical conditions (%) (°C)Other advantages/disadvantages

Mineral acid hydrolysis H2SO4, HCl, H3PO4, HBr64 wt.% H2SO4, at 45°C for 30 min [30].15.7253.2It is difficult to treat waste acid. H2SO4 has a serious corrosion problem to equipment. The CNCs have excellent suspension stability. [3575]
6 M HCl, 110°C, 3 h [58].80347.2It is difficult to treat waste acid. HCl has a serious corrosion problem to equipment. The CNCs have bad suspension stability.

Solid acid hydrolysisCation exchange resin (NKC-9), Phosphotungstic acid75 wt.% Phosphotungstic acid, at 90°C for 30 h [77].60350Phosphotungstic acid could be recovered through extraction with ethyl ether and is low corrosion to equipment.[7679]

Organic acid hydrolysisFormic acid, oxalic acid, Maleic acid, -toluenesulfonic acid0.015 M FeCl3, 88 wt.% HCO2H, at 95°C for 6 h [63].75355Formic acid could be recovered by reduced pressure distillation and is low corrosion to equipment. [63, 80, 91101]
Melt oxalate dihydrate, at 110°C for 2 h, then, sonicated for 18 min [91, 93].80.6360Oxalate dihydrate could be recovered by crystallization and is low corrosion to equipment.

Enzymatic hydrolysisCellulase20 u/mL complex enzymes (cellulase : xylanase = 9 : 1), at 50°C for 5 h [104].13.6--This method is environment-friendly, but the cost is very high. [81, 102105]

Oxidation degradation(NH4)2SO5, NaIO4, NaClO21 mol/L (NH4)2SO5, at 80°C for 16 h [110].35330.9Carboxylation CNCs could be produced. A large number of oxidants were consumed in the process.[106117]

Ionic liquid[BMIM]HSO4, [BMIM]Cl, [EMIM][OAc], TBAA/DMAc[BMIM]HSO4, at 70–90°C for 1 h [119].--260Ionic liquid could be reused. It has advantage to preparing functional CNCs. However, ionic liquid is very expensive at present.[82, 118125]

Transition metal catalysisCr(III), Fe(III), Al(III), Ni(II), Co(II), Mn(II)Solid-liquid ratio was 1 : 30 and 0.8 M Cr(NO3)3 was adopted at 80°C for 1.5 h [126].83.6344Transition metal could be used to enhance the hydrolysis reactivity and reduce the amount of acid.[68, 126129]

Subcritical water--H2O, 120°C and 20.3 MPa for 60 min [130].21.9345The method is environment-friendly. The cost of preparing CNCs was estimated to be 0.02 $/kg. The CNCs have bad suspension stability.[83, 130]

DESCholine chloride/Oxalic acidCholine chloride/Oxalic acid dihydrate = 1 : 1 (Molar ratios), at 100°C for 6 h, then Mechanical disintegration with microfluidizer [131].78300DES is recoverable, biodegradable, and environmentally friendly. However, the reaction degree is low, so it needs follow-up mechanical treatment to get the CNCs products.[131]

AVAPSulfur dioxide/EthanolSO2/EtOH/H2O, 130–165°C [84].24--AVAP method could produce hydrophobicity and morphology adjustable CNCs. The method is low cost and has been used for industrial production of CNCs.[84, 132]

: the reference of typical conditions; : the details come from the reference of corresponding typical condition; : the max decomposition temperature, the details come from the reference of corresponding typical condition; : the reference of corresponding method of preparing CNCs.

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