Modification of Cellulose
With increasing concerns about synthetic polymers for the environment, the application of natural polymers, especially cellulose due to abundance, biodegradability, nontoxicity, and high functionality, is increasing. For inducing the desired properties of cellulose, it’s necessary to manipulate the cellulose structure. Therefore, the modification of cellulose becomes important. The modification of cellulose is introducing organic and inorganic compounds on the polymer. A significant variation in the cellulose properties can be observed with the binding of polymers. Also, mineralization of cellulose has attracted a great deal of attention in recent years. This chapter investigated all of these modifications on cellulose.
KeywordsCellulose Modification Cellulose composites Cellulose nanocomposites Mineralization of cellulose
1 Modification of Cellulose with Organic and Inorganic Materials
Cellulose is a carbohydrate polymer constructed from the repeating of ß-d-glucopyranose units. The polymer is in nature in different forms and has always been a part of nature and human life, such as wood, paper, or cotton fabrics. Cellulose has a high degree of functionality because of the presence of many hydroxyl groups in this molecule. This most abundant natural biopolymer has characteristic properties such as hydrophilicity, chirality, biodegradability, and high functionality. It has applications in composite materials, textiles, drug delivery systems, and personal care products. In recent years, much attention has been paid to cellulose and its derivatives due to their biological, chemical, as well as mechanical properties. Cellulose and its derivatives can be used as supports due to their renewable, biodegradable, and nontoxic properties. One of the drawbacks of this compound is related to its polar and hydrophilic nature. Surface modification has been used for fixing this problem. The surface structure of cellulose contains highly active and attractive hydroxyl groups toward various chemical modifications with the polymers and inorganic or hybrid organic/inorganic compounds.
1.1 Cellulose Esters
Esterifications with inorganic and organic acids are interesting reactions of cellulose with broad applications in the industry. Cellulose acetate, cellulose nitrate, and cellulose xanthogenate are known as the important esters of cellulose. The cellulose esters were investigated in two main categories including organic and inorganic esters of cellulose.
1.1.1 Organic Esters of Cellulose
The reaction of cellulose with carboxylic acids gives cellulose organic esters with removal of a H2O molecule. Cellulose acetate is the most important ester of cellulose with industrial applications such as in the sunglasses, linings, blouses, dresses, wedding and party attire, home furnishings, draperies, upholstery, and slip covers.
22.214.171.124 Cellulose Acetate
The first organic ester of cellulose was synthesized from the reaction of cotton cellulose with acetic anhydride in a sealed tube at 180 °C by Schutzenberger (1865 and 1869) [1, 2]. Franchimont (1879) performed the reaction with H2SO4 and HClO4 catalysts as the industrial approach for the production of cellulose acetate . Commercial cellulose acetates have high strength and high melting point and exhibit a high UV stability and film transparency, combined with low inflammability. Acetic anhydride is predominantly implied as the esterification reagent of cellulose, mostly as a liquid, in special cases, also in the vapor phase. High degree of acetylation was reported for bacterial cellulose in 1-N-butyl-3-methylimidazolium chloride as an ionic liquid . Acetyl chloride represents a still more reactive agent of esterification. Acetylation of cellulose can be performed in dimethylformamide (DMF)/pyridine using an alkali or alkaline earth salt of acetic acid in the presence of p-toluenesulfonyl chloride . Synthesis of cellulose acetate was also performed by the transesterification with ethylene diacetate via dissolving of cellulose in the p-formaldehyde/dimethyl sulfoxide (DMSO) at high temperatures . Acid-catalyzed esterification reactions can promote the reaction yield by shifting the equilibrium reaction to the products. This phenomenon is attributed to the assisting of acids to the formation of acetyl cation CH3CO+ as the reactive intermediate. The esterification reaction with acetyl chloride showed high yields with tertiary amines such as triethylamine (TEA) or pyridine due to forming of acylium complex. 4-Dimethylaminopyridine (DMAP) is an efficient catalyst for the esterification reaction, especially in a homogeneous system with a nonpolar reaction medium . For the acetylation of fibers, the preactivated cellulose is reacted with a large excess of acetic anhydride (Ac2O) in the presence of acetic acid (HAc), usually with HClO4 as the catalyst.
Also, Ac2O vapor can be employed for the fiber acetylation, by adding some propionic or butyric anhydride to the vapor phase, obtaining the appropriately mixed ester, i.e., cellulose acetopropionate or acetobutyrate. Among the numerous nonderivatized solvent systems for cellulose, two systems including the solution in N,N-dimethylacetamide (DMA)/LiCl and a melt solution in N-ethylpyridinium chloride have been successfully employed for the acetylation of this polymer , indicating a preferential substitution at the C-6 position. Ac2O/pyridine in the paraformaldehyde/DMSO solvent is the effective system for the acetylation of all the hydroxy end groups of the methylol side chains. The system afforded a high degree of substitution (DS) of the acetyl groups by transesterification of ethylene diacetate in the presence of natrium acetate at 90 °C . Acetylation of cellulose in the chloral/DMF/pyridine system leads to the complete substitution of the hydroxyl groups by the acetal groups with a DS of 2.5 by Ac2O or acetyl chloride . Production of cellulose acetate from tosylcellulose (DS = 0.9–2.3) has been reported by the reaction with 3 mol of Ac2O per mol of hydroxy groups in the presence of sodium acetate in pyridine at 60 °C . This reaction can be performed with trimethylsilyl (TMS) cellulose (DS = 2) with an excess of Ac2O . Acetylation of the free hydroxyl groups was performed in a benzyl ether of cellulose with DS = 2; in benzene using Ac2O catalyzed with TEA , an addition of 4-dimethylaminopyridine to the system promoted the DS of acetyl groups from 0.1 to 0.35. The reaction was also reported for nanocellulose .
126.96.36.199 Cellulose Formate
Formylation of cellulose for the first time was performed with DS values of about 2.5 using 98–100% formic acid at room temperature after a reaction time of about 2 weeks . The rate of reaction was increased with the addition of H2SO4, HCl, or ZnCl2. Phosphoric acid also can catalyze the reaction in water with a DS of about 0.6 . A special approach was described by Vigo et al. for the synthesis of cellulose formate via reacting of cellulose with thionyl chloride in DMF .
188.8.131.52 Other Cellulose Alkylates
Cellulose esters of higher aliphatic acids were synthesized along the same methods as described for cellulose acetate such as employing the acid anhydride in the presence of the suitable catalyst or the acid chloride with a tertiary base. The propionylation of cellulose can be performed with the corresponding anhydride and an acid catalyst. For obtaining high DS, a cellulose suspension in dioxane/pyridine can be employed with propionic acid chloride for propionylation. The heterogeneous propionylation of cellulose was investigated with Farvardin and Howard using propionic acid, propionic anhydride, and a metal chloride as the catalyst in an aprotic solvent . Acylation of cellulose with an aliphatic chain length of between three and eight carbon atoms can be carried out using a 2% cellulose solution in DMA/LiCl with 9% LiCl, and a mixture of the appropriate acid with its anhydride in the presence of N,N′-dimethylcyclohexylcarbodiimide (DCC) or pyrrolidinopyridine as the catalyst . The propionylation of partially substituted methyl and ethyl celluloses to give stable ether esters has been performed by Guo and Gray .
The esterification with higher aliphatic acids is challenging and must be taken in the dry solvent. For such esterification, a preactivation of the polymer with an aliphatic amine is a good strategy for increasing DS. Esterification of microcrystalline cellulose with pelargonic acid chloride, up to a DS of 3, has been reported by Battista et al. . A mixture of p-toluenesulfonyl chloride and the sodium carboxylate in a medium of DMF and pyridine was found to be effective in the preparation of higher cellulose esters . Homogeneous transesterification of cellulose trinitrite by lauroyl chloride in a N2O4/DMF solution of cellulose was reported by Shimizu et al. .
Palmitoyl ester of cellulose was prepared by the reaction of cellulose with the appropriate acid chloride without the presence of a solvent at a sufficiently high temperature . In this “vacuum acid chloride technique,” the HCl formed is eliminated from the system continuously by vacuum. The effects of fatty acid chain lengths and solvent on the esterification of cellulose with fatty acids are described . The esterification of bacterial (and vegetable) cellulose fibers with a wide variety of anhydrides (acetic, butyric, hexanoic, and alkenyl succinic anhydrides) and hexanoyl chloride suspended in an ionic liquid, tetradecyltrihexylphosphonium bis(trifluoromethylsulfonyl)imide, [TDTHP][NTf2], can be performed . The esterification of cellulose can be performed in the gas phase. In a report, the reaction of palmitoyl chloride vapors with aerogels of cellulose nanocrystals gave palmitate ester of the polymer . Heterogeneous esterification of softwood cellulose nanofibers (CNF) using pyridine/tosyl chloride gives cellulose oleate .
184.108.40.206 Cellulose Aromatic Esters
Phthalic anhydride is generally employed for the esterification of cellulose in the presence of a basic catalyst for the phthaloylation of cellulose. The esterification of cellulose with the anhydrides of phthalic acid, nitrophthalic acid, and trimellitic acid in the presence of TEA and DMAP in DMSO was reported . Cellulose acetophthalates are important commercial products, which are generally obtained by the reaction of cellulose acetate in the DS range between 1.7 and 2.5 with phthalic anhydride in the presence of a basic catalyst such as pyridine or TEA, in a dipolar aprotic or rather a nonpolar medium (DMSO, DMF, dioxane, acetone, benzene). Also, tetrahydro- and hexahydrophthalic acid anhydride have been introduced as esterifying agents in the presence of a catalyst such as TEA, pyridine, picoline, lutidine, DMAP, and 1,4-diazabicyclo-2,2,2-octane (DABCO).
220.127.116.11 Cellulose Esters with Amino Acids
The esterification reaction susceptibility of cellulose makes it possible to bind the polymer with the most of the carboxylic acids. The modifications of cellulose were reported with various hydrophilic (Gly, Ser), aliphatic (Ala, Val, Leu, Ile), and aromatic amino acids (Phe, Tyr, Trp). The carboxylic acid group of amino acids can be reacted with cellulose hydroxyl groups by the esterification reaction while this group is a neighbor of an amine group. It is shown that the aromatic amino acids, particularly Trp, enhanced cell spreading . Modification of cellulose whiskers was reported with l-leucine amino acid via esterification reaction .
18.104.22.168 Cellulose Esters with Sulfonic Acid
Esters of cellulose can be formed also with sulfonic or phosphonic acid groups. Two important sulfonic acids are methylsulfonic acid, so-called mesylcellulose, and the esters of cellulose with p-toluenesulfonic acid, so-called tosylcellulose. The reaction of cellulose with a large excess of p-toluenesulfonyl chloride in pyridine at room temperature up to 80 °C led to the formation of tosylcellulose . In a homogeneous system, tosyl chloride was employed in the presence of TEA as the base, for the tosylation of cellulose with a degree of polymerization (DP) between 280 and 5100, arriving at tosylcelluloses of DS values between 0.4 and 2.3 during 24 h at 8 °C .
22.214.171.124 Phenyl Carbamate of Cellulose
The reaction of cellulose with an excess amount of phenyl isocyanate in a dipolar aprotic medium in the presence of pyridine at 70–100 °C yields a cellulose tricarbanilate. The reaction system changes gradually from a heterogeneous one to a homogeneous one, and only negligible chain degradation has occurred in this process . A homogeneous route to the preparation of cellulose tricarbanilate was reported by dissolving the sample in DMA/LiCl and its reaction with an adequate amount of phenyl isocyanate in the presence of pyridine as the catalyst . Some derivatives of cellulose carbamate such as 3,5-dimethylphenyl carbamate residue in the C-2/C-3 positions and a 3,5-dichlorophenyl carbamate residue in the C-6 position were synthesized by Kaida and Okamoto .
126.96.36.199 Other Organic Esters of Cellulose
Cellulose, extracted from sugarcane bagasse, was successfully succinylated using DMAP as a catalyst in ionic liquid of 1-butyl-3-methylimidazolium . The esterification of cellulose can be assisted to the immobilization of ligands capable of complexation with metal cations on the polymer. The esterification reaction of cellulose with citric acid gives cellulose citrate as a ligand for removal of copper pollutions .
1.1.2 Inorganic Esters of Cellulose
Some of the cellulose esters with inorganic compounds containing S, N, P, and B are introduced. The chemistry of these compounds is challenging due to the impossibility of isolation the products.
188.8.131.52 Cellulose Sulfuric Acid
The reaction of SO3 or XSO3H with the hydroxyl group of cellulose can lead to the formation of cellulose sulfuric acid (CSA). CSA can be converted to a neutral sodium salt soluble in water above a DS of 0.2–0.3. The synthesis of medium to high DS cellulose sulfates was performed with the SO3/DMSO or the SO3/DMF complex . Most frequently H2SO4, SO3, and ClHSO3 were applied as the sulfonating agents of cellulose, which in some cases alcohols, amines, or inert media such as chlorinated hydrocarbons used for improving the yield.
After the first report about the reaction between cellulose and sulfuric acid, the reaction was improved in the presence of some reagents such as SO3 and ClSO3H, also SO2Cl2, FSO3H, ClSO2–OC2H5, CH3–CO–SO4H, and NO–SO4H. Among these reagents, SO3 and ClSO3H showed high activities. Sulfation of cellulose with SO3/DMF in several solvent media was investigated in the presence of TEA, indicating a positive effect of the presence of TEA.
184.108.40.206 Cellulose Inorganic Ester Containing Nitrogen
220.127.116.11.1 Cellulose Nitrate
Cellulose nitrate had been prepared already in 1847 by reaction of the polymer with HNO3 in the presence of H2SO4/H2O . This route is still of interest for the industrial production of cellulose nitrate. Nitration of cellulose was reported under different conditions . The nitration systems of this report include HNO3/H2SO4/H2O, HNO3/inorganic nitrate, HNO3 vapor, HNO3 vapor + NOx, HNO3/H3PO4/P2O5, N2O5, N2O5/CCl4, HNO3/CH2Cl2, HNO3/CH3–NO2, HNO3/CH3COOH/Ac2O, and HNO3/propionic acid/butyric acid. High nitrogen contents, >14%, can be obtained without significant chain degradation by the systems HNO3/CH2Cl2 at 0 to −30 °C, HNO3/H3PO4/P2O5, and HNO3/acetic acid/acetic anhydride. Also, nitronium salts like [NO2]+[BF4]− and KNO3 in 98% H2SO4 can make a little nitration of cellulose . Formation of cellulose nitrate was also claimed to occur on heating a solution of cellulose in N2O4/DMF . Cellulose mixture with 0.5 M [NO2]+[BF4]− in sulfolan, as well as with KNO3 in 98% H2SO4, gives cellulose nitrate .
18.104.22.168.2 Cellulose Nitrite
The O-6 position is preferred for the modification to nitrite formation. Some of the important reagents for the esterification of cellulose with nitrite are N2O4, NOCl, NOSO4H, NOBF4, and NOSbCl6 .
22.214.171.124 Cellulose Inorganic Esters Containing P
The covalent binding of phosphorus to the cellulose gives one of cellulose phosphate Cell-O-P(O)(OH)2, cellulose phosphite Cell-O-P(OH)2, and cellulose phosphonic acid groups Cell-P(O)(OH)2.
126.96.36.199.1 Cellulose Phosphate
Pentavalent phosphorus compounds such as H3ΡΟ4, Ρ2O5, and POCl3 are the most frequently used reagents for phosphorylation of cellulose. Compared to the corresponding compounds of hexavalent sulfur, these phosphorylating agents which usually give anionic cellulose phosphates show a lower reactivity in the esterification and lead to much less chain degradation during this process. Concentrated orthophosphoric acid has been widely used as an effective phosphating agent, and various procedures have been reported for the synthesis of cellulose phosphates with phosphorus contents of about 10% . Water-soluble cellulose phosphates of rather high DP can be obtained with water-free H3ΡΟ4, in which P2O5 was employed for increasing phosphorylation yield . A system including Η3ΡΟ4/P2O5/DMSO, and also with ternary systems of Η3ΡΟ4/P2O5/aliphatic alcohols with 4 to 8 C atoms, produced water-soluble cellulose phosphates . The reaction of cellulose with a melt solution of Η3ΡΟ4 and urea gives a soluble, but strongly degraded, cellulose monophosphate monoammonium salt . Phosphorus oxychloride (POCl3), as an effective phosphating agent for cellulose, in the reaction with a cellulose suspension in DMF or pyridine gives cellulose phosphate with some by-product such as chlorinated cellulose. Phosphorylation of cellulose hydrogels was reported with a mixture of phosphorus pentoxide, triethyl phosphate, and phosphoric acid .
188.8.131.52.2 Cellulose Phosphite
Cellulose phosphite can be prepared by the reaction of cellulose with a trivalent phosphorus such as PCl3  or by transesterification with dimethyl phosphite, arriving at hydrolysis-susceptible phosphite esters of cellulose . Cellulose phosphites have also been synthesized, employing mixed anhydrides of hydrophosphoric and acetic acid and arriving at phosphorus contents of up to 8% .
184.108.40.206.3 Cellulose Phosphonic Acid
Preparation of cellulose phosphonates, the phosphorus directly bound to a C atom of the cellulose, is either an esterification with methyl or phenylphosphonic anhydride  or a two-step reaction consisting of the chlorination of cellulose with SOCl2 to give chlorodesoxycellulose with a high Cl content (up to 16%) and the subsequent reaction of this compound with triethylphosphite to the cellulose phosphonate via an Arbuzov rearrangement. 3-(Hydroxyphenylphosphinyl)-propanoic acid (3-HPP) esters of cellulose were synthesized in DMA/LiCl homogeneously by the method of in situ activation with p-toluenesulfonyl chloride .
220.127.116.11 Cellulose Borates
Boron-containing cellulose derivatives are interesting due to unique properties such as flame retardancy or heat stability. The synthesis of cellulose borates was reported by two approaches including (i) the direct esterification of cellulosic hydroxy groups with orthoboric or metaboric acid and (ii) a transesterification of cellulose with boronic acid esters of lower aliphatic alcohols (boron alkoxides). A direct borylation of cellulosic hydroxy groups can be performed with ortho- or metaboric acid in a melt of urea at 150–200 °C . The preparation of a mixed borate/phosphate cellulose has been described by subsequent reaction of the cellulose borate with H3PO3/urea and with Η4Ρ2O7 or HPO3/urea in the temperature range 100–200 °C .
Preparation of desoxycelluloses via tosyl- or mesylcellulose
Tosyl- or mesylcellulose
Reagents and conditions
NaF in H2O
Tosyl chloride and pyridine at high temperature
LiCl in acetylacetone (2 h at 130 °C)
NaBr in H2O
NaBr in acetylacetone (2 h at 130 °C)
tosylcellulose and mesylcellulose
NaI in acetylacetone (2 h at 130 °C)
H2S in pyridine (8 h at 40 °C, then 70 h at room temperature)
Na2S2O3 in DMSO
KCN in DMF or methanol (100–150 °C)
NaSCN in acetonylacetone (11 h at 110 °C)
NaN3 in DMSO (110–130 °C)
Tosylcellulose is also applied as the starting material for the preparation of aminodesoxycellulose by reacting with NH3, aliphatic amines, or hydrazine .
1.3 Cellulose Ethers
The reaction of hydroxy groups of cellulose with an alkyl chloride in the presence of strong alkali metal hydroxides, according to the Williamson ether synthesis
The ring-opening reaction of an alkylene oxide with the hydroxy groups of cellulose, which is catalyzed by alkali metal hydroxides
Also various silyl ethers have been synthesized by the reaction of cellulose especially with trialkylchlorosilanes.
1.3.1 Aliphatic Ethers of Cellulose
Most important aliphatic ethers of cellulose are methylcellulose, CMC, and hydroxyethyl cellulose (HEC).
18.104.22.168 Alkyl Ethers of Cellulose
As the most important compound from alkyl ether category, methylcellulose is commercially produced by a Williamson reaction of alkali cellulose with gaseous or liquid CH3Cl. The etherification of cellulose in the presence of alkali hydroxide is accompanied by the hydrolysis of methyl chloride with the water. Methylation of cellulose by the Williamson reaction is generally carried out at elevated temperature with cellulose in the solid state. Some of the systems employed in laboratory methylation of cellulose include DMSO/NaOH/CH3I , DMSO/LiH/CH3I , DMF, THF/NaH/CH3I , CH2Cl2/2,6-di-i-butylpyridine (CH3)3O+[BF4]− , and (CH3)3PO4/2,6-di-t-butylpyridine/CF3SO3CH3 (methyl triflate) . Instead of methyl chloride, also methyl iodide, dimethyl sulfate, diazomethane, or special agents such as trimethyloxonium tetrafluoroborate, or methyl triflate can be used. NaH or LiH, metallic Na dispersed in an ammonia, and di-t-butylpyridine are bases applicable in this reaction. Methylcellulose has also been synthesized in aqueous solutions of tetraalkylammonium hydroxides . Some of the methylation systems of cellulose are CH3I/NaH in THF and CH3I/powdered NaOH in DMSO .
Ethylation of cellulose has been performed by reacting alkali cellulose with ethyl chloride, arriving at a substitution pattern with about equal partial DS at C-2 and C-6 and again a low degree of etherification at C-3 . Propylation of cellulose required either a previous partial methylation for “widening” the cellulose structure or employing a tetraalkylammonium hydroxide of high swelling power in aqueous solution as the base and reaction medium .
The preparation of long-chain cellulose alkyl ethers was reported in nonaqueous system by reaction of cellulose acetate with the appropriate alkyl bromide in the presence of NaOH in DMSO . Blasutto (1995) reported the preparation of long-chain alkyl ethers from the reaction of cellulose with appropriate alkyl bromide in isopropanol or in DMSO in the presence of NaOH or NaH . Recently, etherification of cellulose with chloroacetic acid has attracted attentions, since cellulose acetic acid as the product has the ability of more modification. Modification of cellulose acetic acid with D-penicillamine gave a good cellulose-based ligand for grafting of Co(II) . Cellulose acetic acid was also modified with ethylenediamine for preparation of a Pd ligand .
22.214.171.124 Hydroxyalkyl Ethers of Cellulose
The acid-catalyzed cleavage of the epoxy ring for alkylation of cellulose leads to the homopolymerization of epoxy instead of the intended etherification. Hydroxyalkylation of cellulose using basic catalyst is generally performed with the weight ratio of NaOH/cellulose varying within the wide limits of between 0.3:1 and 1:1 and that of H2O/cellulose between 1.2:1 and 3.5:1. In this route, an excess of a fairly inert diluent like i-propanol, t-butanol, or acetone is employed in hydroxyethylation .
126.96.36.199 Etherification with Epichlorohydrin
For this reaction catalytic amounts of NaOH required for epoxy ring cleavage and the stoichiometric amount of 1 mol/mol of epichlorohydrin are necessary for the epoxide formation . Etherification with epichlorohydrin has also been performed with cellulose dissolved in DMA/LiCl and powdered NaOH or with LiOH as the base .
188.8.131.52 Hydroxymethyl Cellulose
The synthesis of a methylol cellulose octadecylcarbamate was reported by the reaction of cellulose with octadecyl isocyanate in the presence of stannic octoate at 50 °C in DMF/LiCl as the solvent .
184.108.40.206 Cyanoethyl Cellulose
Cyanoethylation of cellulose proceeds via a Michael addition of partially anionized cellulose hydroxyl group to an activated C=C bond of acrylonitrile. Bikales reported a procedure for the preparation of a fibrous cyanoethyl cellulose with DS = 2.75 (12.6% N) from regenerated cellulose with acrylonitrile and aqueous NaOH at 50 °C . Wide studies were performed on the cyanoethylation of cellulose. Cyanoethylation of cellulose has been reported as an equilibrium reaction with the cellulose either by simultaneous (one-step process) or by subsequent (two-step process) addition of the components aqueous NaOH and acrylonitrile at a temperature between 30 °C and 50 °C, within some hours. The reaction rate of cyanoethylation can be improved significantly by a preactivation of the cellulose sample by 18% NaOH or by pretreatment with liquid NH3 and could also be enhanced by the addition of DMSO to the system for increasing the solubility of acrylonitrile . N-Methylmorpholine also can play a base role for the cyanoethylation of cellulose . The nitrile group of cyanoethyl cellulose can be reduced to an aminopropyl substituent with diborane . An amidoxime can be prepared from the reaction of hydroxylamine with carbamoylethyl cellulose in a neutral aqueous system at 70 °C .
Sheets of bacterial cellulose were chemically modified with glycidyltrimethylammonium chloride in the presence of sodium hydroxide to introduce a positively charged amine to cellulose . DABCO-cellulose nanofibers can be prepared via the activation of cellulose with tosyl group and subsequent reaction of cellulose tosylate with DABCO . Immobilizing of amine groups on cellulose can be improved metal complex with the modified cellulose. Modification of cellulose can be performed with glycidyl methacrylate (GMA) and diethylenetriamine to deposition of amine groups on cellulose for the preparation of Cu(II) and Hg(II) absorbent . Keshipour et al. modified cellulose with ethylenediamine to improve cellulose activity in Pd or Co complexation for the synthesis of efficient catalyst for coupling , cycloaddition , and oxidation reactions [99, 100].
220.127.116.11 Sulfoalkyl and Thioalkyl Ethers of Cellulose
The order of reactivity of the agents for this reaction is propane sulfone < chloroalkyl sulfonate < vinyl sulfonate. Other reagents for the sulfoalkylation are Cl–CH2SO3Na, HSO3–O–CH2–CH2SO3H, and CH2=CH–SO2–CH=CH2.
Thioalkyl cellulose synthesis can be performed via thiol-ene click reaction in two steps including the reaction of cellulose with allyl chloride to give allyl cellulose and then the reaction of allyl cellulose with a sulfide . The thiol-ene reaction also was reported with vinyltrimethoxysilane and 3-mercaptopropyltrimethoxysilane .
18.104.22.168 Arylalkyl Ethers of Cellulose
Benzyl cellulose as the most important ether of this type was first synthesized by Leuchs in 1917. The chemical library of arylmethyl ethers was developed by the introduction of substitute that contained different types of alkyl residues , halogen substituents , and functional groups like methoxy, nitro, and amino groups mainly in para position of the benzyl units or in some cases aryl groups other than phenyl . The synthesis pathway consists in the reaction of cellulose with the corresponding arylmethyl halogenides in presence of a base . The reaction proceeds in water using sodium hydroxide .
Triphenylmethyl (“trityl”) cellulose as the most important ether of a class of organosoluble aryl cellulose ethers was formed by the reaction of phenylmethyl halides with cellulose in the presence of an organic base . Some similar compounds such as benzhydryl (diphenylmethyl)cellulose, benzyl(phenylmethyl)cellulose, and phenylcellulose were generally prepared via this route. Heterogeneous tritylation of decrystallized cellulose was reported using pyridine by treatment with 15% aqueous ammonia and yields colorless products with DS values from 0.81 to 1.21 .
1.3.2 Aryl Ethers of Cellulose
The introduction of an aromatic group via an ether bond leads to cellulose aryl ethers, especially to phenyl and substituted phenylcelluloses. The reaction can be performed via the etherification of cellulose with activated aryl halogenides or the displacement reaction of cellulose tosylate with corresponding phenolates. Various phenyl derivatives were employed for this reaction such as phenyl containing nitro, carboxylic acid, amine, bromide, chloride, etc. .
1.3.3 Silyl Ethers of Cellulose
The reaction of cellulose with TMS-Cl in the presence of pyridine has been reported for the first time by Schuyten et al. . Silylation of cellulose with TMS-Cl and pyridine gave TMS cellulose with DS values of 2.4 to 3.0. The reaction was investigated in some solvents such as xylene, toluene, and petroleum ether, in which short reaction times in toluene and mild reaction conditions in petroleum ether were obtained. In addition, NH3 instead of pyridine improved the reaction conditions . Klebe and Finkbeiner have synthesized cyanopropyldimethyl-, phenyldimethyl-, and diphenylmethylsilylcelluloses. Hexamethyldisilazane is a convenient reagent for the trimethylsilylation of cellulose . The reaction proceeded in polar solvents in the presence of catalyzers such as NH4Cl or TMS-Cl/pyridine. Cellulose activated with ammonia at 80 °C has been reacted with the thexyldimethylsilylamine, prepared from the reaction of thexyldimethylchlorosilane (TDMSCl) and N-methylpyrrolidone (NMP) to give corresponding silylated cellulose. The chemical modification of cellulose with silanes contains another functional group which assisted the loading of the desired functionality on cellulose. For example, the modification of cellulose paper with 3-aminopropyltrimethoxysilane leads to the deposition of an amine group on cellulose .
1.4 Heterocycles Grafted on Cellulose
A similar strategy using introducing of azide group to cellulose and subsequent reaction of azido cellulose with an alkyne was described . The synthesis of triazide heterocycle on cellulose can be performed by introducing an alkyne group on cellulose and cyclization of the alkyne with an alkyl azide . Chemical modification of cellulose with triazine derivative, 2,4,6-tri-[(2-hydroxy-3-trimethyl-ammonium) propyl]-1,3,5-triazine chloride (Tri-HTAC), was also reported. Tri-HTAC under reaction with NaOH produces a terminal epoxide, in which ring opening occurred under nucleophilic attack of cellulose . Binding of a macrocyclic compound was also investigated, which phthalocyanine-Co(II)  and N-doped graphene quantum dots  were chemically attached to cellulose surface.
2 Polymers Grafted on Cellulose
The modification of cellulose can be performed with absorbent polymers. Modification of microfibrillated cellulose (MFC) by hydroxycarbonate apatite (HAP) or epoxy gives nanostructured adsorbents for the removal of hydrogen sulfide (H2S) from the aqueous solutions .
2.1 Atom Transfer Radical Polymerization (ATRP) of Cellulose
Polymer-grafted cellulosic materials prepared via ATRP method
St, MMA, MAm, AcM
DMF, 130 °C
DMSO, 80 °C
DMF, 75 °C
DMF, 60 °C
DMF, butanone, DMF/H2O
Dioxane, butanone/toluene 40–110 °C
DMSO/MeOH, 40 °C
BMIMCl, 90 °C
DMF. 130, 70 °C
DMAc, 50–70 °C
DMF/H2O, 80 °C
DMF, toluene 90 °C
MeOH/H2O, 25 °C
DMF, H2O, r.t.
H2O, 45 °C
MeOH/H2O, 25 °C
DMVSA, DMMSA, MPC
2-Propanol, 40 °C
Ethyl acetate, r.t.
MeOH, 40 °C
2-Propanol, 40 °C
MeOH/H2O, 30 °C
In bulk, 110 °C
MeOH, 55 °C
Anisole, 100 °C
TEA, DMF, 100 °C
Ethyl acetate, r.t.
DMF/dioxane, 130 °C
H2O, 20, 40, 70 °C
Ethyl acetate, H2O, r.t.
Anisole, in bulk, 90, 100 °C
DMF, 45 °C
H2O, 30 °C
MMA, St, GMA
Anisole, 30, 100, 0 °C
NIPAAm, 4VP, GMA
30, 50 °C
2-Propanol, toluene, r.t.
Toluene, 100 °C
Ethyl acetate, r.t.
Toluene, 30 °C
Acetone, 60 °C
THF, 30 °C
Acetone/H2O, 30 °C
Xylene, 110 °C
Ethyl acetate, r.t.
The ATRP can be performed in both heterogeneous and homogeneous reactions, and the homopolymerization is effectively avoided since the anchored haloacyl groups are the only initiating sites in the system.
2.2 Reversible Addition-Fragmentation Chain Transfer (RAFT) of Cellulose
Polymer-grafted cellulosic materials prepared via RAFT polymerization method
Chain transfer agents
ACPA or γ-ray
H2O/EtOH, 70 °C
Toluene, 60 °C
EtOH, toluene, dioxin/H2O, r.t.
Toluene, 60 °C
St, MMA, MA, DMA
In bulk, 60 °C
ECPDB (free CTA)
MMA,MA, St, p-chlorostyrene
THF, 60 °C
Supercritical CO2, 70 °C
EECX VAc, St, VBC
In bulk, 90 °C
CPADB (free CTA)
Buffer, 70 °C
Dioxane, 70 °C
MeOH, 70 °C
MP, 60 °C
DMF, 68 °C
DMSO, 70 °C
Dioxane, DMAc, 60 °C
Amino acid acrylate, (A-(L)Ala-OH, A-(L)Pro-OH, A-(L)Glu-OH)
DMAc/THF, 80 °C
BMIMCl 60 °C
DMF, 70 °C
2.3 Nitroxide-Mediated Radical Polymerization (NMP) of Cellulose
NMP is based on the use of a stable nitroxide radical, such as (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO), which is the more commonly used nitroxides. In NMP approach, the propagating species (Pn°) can propagate by reacting with a monomer (M), or it can terminate with other radicals . NMP is usually undertaken at high temperatures.
Nitroxide-mediated grafting of cellulose under homogeneous conditions was first reported by Daly et al. . In their approach, carbonates of N-hydroxypyridine-2-thione have first immobilized onto hydroxypropyl cellulose (HPC) backbones and subsequently irradiated the cellulose derivatives in the presence of an excess of TEMPO and styrene (St) to form St-TEMPO adducts promoting the preparation of HPC-g-PS graft copolymers. Nitroxide-mediated polymerization was reported for the synthesis of cellulose-grafted polystyrene (PSt) and poly(methyl methacrylate) (PMMA) as the branches. For this purpose, cellulose was acetylated by 2-bromoisobutyryl bromide, and then the bromine group was converted to 4-oxy-2,2,6,6-tetramethylpiperidin-1-oxyl group by a substitution nucleophilic reaction. The produced intermediate was subsequently used in controlled graft and block copolymerizations of St and MMA monomers to yield cellulose-grafted (g)-PSt and cellulose-g-(PMMA-b-PSt) . Poly(lactic acid)/cellulose nanofiber (PLA/CNF) composites were prepared by TEMPO-mediated oxidation of CNF. MCNF was synthesized by the controlled amidation of CNF with cis-9-octadecenylamine (OA) that resulted in PLA/MCNF composites with improved mechanical properties and tunable elongation compared to PLA/CNF . The CNC surface was also functionalized with the nitroxide SG1 (4-(diethoxyphosphinyl)-2,2,5,5-tetramethyl-3-azahexane-N-oxyl), yielding a CNC-macroalkoxyamine. Poly(methyl acrylate) and poly(methyl methacrylate) chains were then grafted from the CNC-macroalkoxyamine surface to give polymer-modified CNC .
2.4 Single-Electron Transfer Living Radical Polymerization (SET-LRP) of Cellulose
Polymer-grafted cellulosic materials prepared via SET-LRP method
AAm or DMAAm
DMSO, 80 °C
DMF, 75 °C
MMA, BuA, t-BuA
1,4-Dioxane, DMSO, 30, 60 °C
DMSO, 80 °C
DMF, 75 °C
THF/MeOH, 50 °C
2.5 Other Modification Methods of Cellulose with Polymers
Polymer-grafted cellulosic materials obtained from unusual mechanisms
Isophorone diisocyanate (IPDI)
(i) Modification of CNC with IPDI and (ii) polymerization with polyether alcohol
N-Hydroxysuccinimide methacrylate (NHSMA), 2-isopropenyl-2-oxazoline (IPO), methyl methacrylate, styrene
Ps, PMMA, PIPOx, and PNHSMA-grafted CNC
UV-induced photopolymerization in the absence of any initiator
Poly(propylene imine) (PPI)-grafted CNC
Michael addition of acrylonitrile onto amine-functionalized CNC
Cellulose-grafted acrylamide copolymer
Without any radical initiator using microwave radiation in 1-butyl-3-methylimidazolium chloride ionic liquid
Isatoic anhydride (IA), 2-methyl-2-oxazoline (MOZ)
(i) Amination of cellulose with IA and (ii) modification of cellulose-IA with polyMOZ
Ethylenediamine (EDA), polyethylenimine (PEI), bisphenol A epoxy resin
(i) Modification of CNFs with EDA, (ii) reaction of PEI with CNFs-EDA, and (iii) reaction of epoxy resin with product (ii)
3-Methacryloxypropyltrimethoxysilane (MEMO), poly(lactic acid) (PLA)
(i) Modification of CNFs with MEMO and (ii) binding of PLA to CNFs-MEMO
(i) Modification of CNs with LA and (ii) polymerization of LA
Maleic anhydride-grafted polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (MA-SEBS)
Reaction of CNFs with MA-SEBS via ring opening of maleic anhydride
Polyurethane acrylate (PUA) prepolymers
Reaction of cellulose film with PUA prepolymer with UV curing
Isobutyl vinyl ether (IBVE)
Ball milling of MCC and IBVE in vacuum
3 Cellulose Modification by Different Nanoparticles and Other Minerals
Metal nanoparticles have attracted more attention due to their various applications such as water purification, catalysis of chemical reactions, and hydrogen storage. Nanoparticles such as different metals, magnetic nanoparticle (iron oxides, cobalt-iron oxide, nickel, etc.), silica, and metal oxide tend to agglomerate to form stable and larger-size particles due to their high active surface area. In recent years, in order to prevent the agglomeration and to stabilize the nanoparticle structures, immobilization of metal nanoparticles on different kinds of substrates such as dendrimers, synthetic polymers, natural polymers, surfactants, and carbon nanotube-grafted polymers has received considerable interest. These synthesized nanocomposites have important applications in optics, electronic devices, catalysis, sensors, medical applications, etc. .
3.2 Modification of Cellulose Surface with Different Nanoparticles
Surface modification of cellulose with different nanoparticles led to producing of the modified nanocomposite with a wide range of applications. Here we will introduce and investigate the properties of these modified nanocomposites.
3.2.1 Palladium Nanoparticle
Palladium is one of the most efficient transition metals in catalysis field . Recently, much attention has been paid to the palladium-based materials. Palladium nanoparticles have been investigated in a wide range of catalytic applications such as hydrogenations, oxidations, carbon-carbon bond formation, and electrochemical reactions in fuel cells . However, these materials have different applications. For example, due to the tendency of palladium for adsorbing hydrogen, palladium nanoparticles are applied in hydrogen storage and sensing applications . Due to the aggregation and precipitation of palladium metal in homogeneous palladium catalysts, they lose their catalytic activity. However, tedious workup procedures, loss of catalyst, and contamination of residual metals in the final product are the major drawbacks of these methods. Using heterogeneous palladium catalysts is the best choice to resolve these problems. Thus, it is possible by immobilizing palladium on suitable supports, which can be easily separated from the product without losing catalytic activity. Notably, chemical modification of the cellulose can be occurred by immobilization of transition metal onto the cellulose surface. In order to immobilize more metal on the cellulose surface, various polymers and linkers modify the cellulose surface.
22.214.171.124 Catalytic Activity
Transition metal catalysis can be catalyzed by 1,3-dipolar cycloaddition reaction, oxidation, direct arylation, and cross-coupling reactions. Palladium-catalyzed Suzuki, Sonogashira, and Heck couplings are all very important and powerful strategies for the formation of carbon-carbon bonds. There are many examples in this area; some of them will be presented below.
Also, this catalyst was used as an electrocatalyst for oxidation of hydrazine. In this work, cellulose was functionalized with ethylenediamine and then used as a support for the preparation of PdNPs immobilized on ethylenediamine cellulose (PdNPs-EDAC) which consisted of uniformly distributed palladium nanoparticles with the main average size of 4.7–6.9 nm. Finally, electrocatalytic activity of a PdNPs-EDAC has been investigated for the oxidation of hydrazine as an important model compound .
In 2017, a novel ferrocene tethered N-heterocyclic carbene-Pd complex anchored on cellulose has been synthesized in several steps by Salunkhe and coworkers. Then it is used as an efficient heterogeneous catalyst for synthesis of biaryls in Suzuki-Miyaura cross-coupling reaction. Some of the notable features of this procedure are good catalytic efficiency, high yields of products, easy separation, large-scale synthesis, and facile recyclability .
3.2.2 Silver Nanoparticle
Much attention has been paid to silver nanoparticles (AgNPs) due to their unique properties at the nanoscale size. These nanoparticles have several applications in optical, catalytic, magnetic, electrical, and antimicrobial devices. Immobilization of Ag onto polymer and biopolymer surfaces led to improve the properties and applicability of such polymers and biopolymers. As a result, bionanocomposites will be obtained . Some of these applications will be presented as below.
126.96.36.199 Electrical Activity
Liu et al. in 2017 have developed an in situ polymerization of aniline monomer onto the porous-structured cellulose scaffolds, and then electrodeposition of Ag nanoparticles carried out on the obtained conductive composites. In this study, Ag nanoparticles were deposited homogeneously on the matrix of polyaniline (PANI)/cellulose gels which will increase the conductivity of composites. The conductivity of Ag containing PANI/cellulose nanocomposite gels was increased to 0.94 S C m−1, which was higher than that of pure PANI/cellulose composites (3.45 × 10−2 S C m−1). Thus, this synthesized conductive composite could be used as an electrode for the supercapacitors .
Sun and coworkers have presented a self-reporting aerogel toward stress-sensitive electricity (SSE) via combined routes of silver mirror reaction and ultrasonication. Sphere-like Ag nanoparticles (AgNPs) with a mean diameter of 74 nm were tightly immobilized in the cellulose nanofiber. The resulted Ag/CNF as a self-reporting material for SSE not only possessed quick response and sensitivity but also easily recovered after 100th compressive cycles without plastic deformation or degradation in compressive strength. Consequently, Ag/CNF could play a viable role in self-reporting materials as a quick electric stress-responsive sensor .
188.8.131.52 Antibacterial Activity
A porous hydrophobic Ag/Ag2O@cellulose hybrid membrane was prepared by Zhang et al. in 2015. Cellulose is much more flexible, lighter, biodegradable, and ventilated in comparison with most of the existing water-strider-mimicking boats which are built from metals. In addition, the synthesized membrane has shown a water contact angle of 140°. Also, this hybrid membrane exhibited oil/water separation capacity, and it has strong antibacterial activity against Escherichia coli .
Huang and coworkers have synthesized an antibacterial cellulose/titania/chitosan hybrid material. Firstly, these hybrid materials were prepared by continuously depositing titania gel layer and chitosan layer on the cellulose microfibril bundles of filter paper. After that, silver ions adsorbed with the titania/chitosan composite film, followed by in situ reductions of the immobilized silver ions under UV irradiation. The finalized antibacterial cellulose/titania/chitosan/AgNP hybrid materials were obtained having the fibrous structure of the initial cellulose substance. These hybrid composites showed splendid antibacterial activities due to the intrinsic biocidal effect of titania composition, positively charged chitosan component, and high loading content of AgNPs with small size. Therefore, these AgNP-containing cellulose materials have antibacterial applications such as antibacterial wound dressing, antibacterial packaging, antibacterial adhesion, air/water purification, and so on .
Vosmansk and coworkers have presented the three-step modification of the standard cellulose wound dressing. This method is cost-effective and environmentally benign and does not require the large and complicated device. The best outcome has been shown in the three-step modification of wound dressing including argon plasma treatment, chitosan impregnation, and AgCl precipitation. It also has antibacterial activity against E. coli and S. epidermidis. The surface of cellulose wound dressing was hydrophilic with the highest amounts of chitosan and AgCl in it. Chitosan was used here due to the antibacterial and healing promoting activity. The amount of adsorbed chitosan has positively affected on the amount of the AgCl in the surface, and as a result, AgCl and chitosan were responsible for the antibacterial effect of the wound dressing. It was found that the combination of chitosan and AgCl precipitation showed better antibacterial effect than each of them alone .
184.108.40.206 Catalytic Activity
Hussain et al. in 2014 have represented various methods to immobilize gold and silver nanoparticles on the surface of cellulose fibers. It this work, formation and immobilization of gold and silver nanoparticles occurred through boiling of the cellulose fibers in an alkaline solution of gold and silver salts. The synthesized thiol-modified cellulose fibers loaded with gold and silver nanoparticles were investigated for the catalytic reduction of 4-nitrophenol into 4-aminophenol .
3.2.3 Iron Nanoparticle
Among all transition metals, iron is the most important one and the fourth most plentiful element in the Earth’s crust. Iron nanoparticles can be prepared via several methods. Much attention has been paid to this nanoparticle due to their important applications such as treatment to many types of contamination; magnetic data storage and resonance imaging (MRI); medical and laboratory applications, using memory tape due to their magnetic properties; and catalyst applications.
220.127.116.11 Catalytic Activity
In 2014 Lu et al. reported a facile synthetic method for in situ immobilization of Au nanoparticles (NPs) on magnetic γ-Fe2O3@carboxylated cellulose nanospheres. Firstly, the γ-Fe2O3@cellulose NPs were synthesized via an ionic liquid-assisted coprecipitation process. After that, oxidation of cellulose occurred in the presence of TEMPO to produce carboxyl groups on the surface of magnetic nanoparticles (MNPs). Finally, by reducing of Au3+ by cellulose, AuNPs were dispersed onto the surface of magnetic γ-Fe2O3@carboxylated cellulose. The synthesized magnetic biopolymer-metal nanohybrids are used as a magnetic catalyst in the reduction reaction of 4-nitrophenol to 4-aminophenol .
Cellulose-magnetite nanocomposites were synthesized via the adsorption of magnetite onto the surfaces of functionalized nanocellulose, using different organic and inorganic acids such as acetic anhydride, succinic acid anhydride, chlorosulfonic acid, and POCl3 by El-Nahas and coworkers in 2017. The properties of these functionalized nanocellulose derivatives and cellulose-magnetite nanocomposites were evaluated, and then the catalytic activity of the functionalized nanocellulose and cellulose-magnetite nanocomposites was investigated for the esterification of oleic acid with methanol for the production of methyl oleate (biodiesel). In this study, the sulfonated cellulose-magnetite nanocomposite (MSNC) showed the highest catalytic activity toward the esterification reaction (96%) due to the high dispersion of the Lewis acid sites which resulted from the impregnation of magnetite (0.98 wt%) in addition to the already presented Brönsted acid sites on the surface of the nanocellulose .
18.104.22.168 Antibacterial Activity
Glucose-reinforced Fe3O4@cellulose-mediated amino acid was developed by Rezayan et al., and this is the first report of applying magnetic cellulose nanocomposite as a support for bacteria capturing. In this study, two kinds of amino acid were applied as a linker to immobilize glucose on the surface of magnetic cellulose. It was found that using amino acids as a linker for glucose anchoring led to increase capturing efficiency for gram-positive bacteria as a sample pathogen. Also, this synthesized system was evaluated as a green biocompatible nanostructure for water treatment .
22.214.171.124 Wastewater Treatment
Liu and coworkers have reported ferric hydroxide-coated cellulose nanofibers (Fe(OH)3@CNFs) and applied for the removal of phosphate from wastewater. This modified nanofiber has maximum sorption capacity of 142.86 mg/g which has higher adsorption capacity than many adsorbents reported in the literature. It was found that an increased solution ionic strength would increase the adsorption capacity. Furthermore, the effect of PH conditions was investigated for determining a favorable adsorption performance of these nanofibers. The maximum adsorption capacity of Fe(OH)3@CNFs was achieved at pH of 4.5. This study showed that ferric hydroxide-modified CNFs had a unique ability to remove phosphate from aqueous medium .
3.2.4 Zinc Oxide Nanoparticle
Due to nutritional properties, effective antimicrobial properties at low concentrations, high stability against high temperatures, nontoxicity, and good UV absorbance properties, zinc oxide has attracted much attention in food and pharmacy fields. Thus, the addition of ZnO NPs to the film packaging and its probable diffusion of the food products are not harmful to human health because these nanoparticles are used as nutrient agent . Recently, the effective antimicrobial properties of ZnO NPs in active films have been reported for starch films against Staphylococcus aureus , polylactic acid-ZnO NP nanocomposite films against Escherichia coli and Staphylococcus aureus , chitosan-neem oil-based film against E. coli , and sodium alginate-gum acacia hydrogels versus Pseudomonas aeruginosa and Bacillus cereus . Due to the high surface area of metal nanoparticles, they have superior antimicrobial properties .
126.96.36.199 Antimicrobial Activity
Ghanbarzadeh and coworkers have represented an active nanocomposite based on carboxymethyl cellulose-chitosan-oleic acid (CMC-CH-OL) incorporated with different concentrations (0.5–2 wt%) of zinc oxide nanoparticles (ZnO NPs) toward casting method. Then effects of ZnO NPs on the morphological, mechanical, thermal, physical, and antifungal properties of the films were investigated. Antifungal properties of these active nanocomposite films by disc diffusion test confirmed considerable antifungal rule against Aspergillus niger, especially in 2 wt% of CMC–CH–OL–ZnO which illustrated more than 40% fungal growth inhibition .
Rujiravanit and coworkers have reported that bacterial cellulose (BC) is a remarkable natural polymeric template to support the ZnO synthesized via solution plasma process (SPP). In addition, in SPP method, there was no need for a reducing agent. The ZnO/BC composites obtained via SPP had strong antibacterial activity against E. coli and S. aureus. Meantime, by increasing the ZnO content in the ZnO/BC composites, the antibacterial activity of the ZnO/BC composites will be increased. Notably, these composites might be applied in wastewater treatment but also in biomedical applications .
3.2.5 Cobalt Nanoparticle
Cobalt nanoparticles are a gray or black powder with spherical morphology. These nanoparticles have attracted much attention due to their magnetic properties. Due to these properties, they have been shown in imaging, sensors, catalyst, and many other areas.
188.8.131.52 Catalytic Activity
Ethylenediamine-functionalized nanocellulose complexed with cobalt(II) was reported by Shaabani and coworker in 2014 as a highly efficient heterogeneous catalyst for the room temperature aerobic oxidation of various types of primary and secondary benzylic alcohols into their corresponding aldehydes and ketones, respectively. Noteworthy, this catalyst was recovered and reused for five times with no significant loss of efficiency .
Magnetic D-penicillamine-functionalized cellulose as a new heterogeneous support for cobalt(II) was presented by Keshipour and coworker and applied in the green oxidation of ethylbenzene to acetophenone. The catalyst was obtained in three steps: first of all functionalization of cellulose with D-penicillamine occurred, after that deposition of Fe3O4 nanoparticles on cellulose-D-penicillamine, and finally, anchoring of Co(II) to the magnetic cellulose-D-penicillamine. The catalytic activity of composite was investigated for the oxidation of ethylbenzene to acetophenone in ethanol under reflux conditions using H2O as a green oxidant. Also, the recovered catalyst could be used several times without significant loss of activity .
3.2.6 Titanium Dioxide Nanoparticle
Titanium dioxide (TiO2) has attracted considerable attention as a semiconductor for photocatalysis activity because of its high stability, low cost, and safety toward both humans and the environment. TiO2 nanoparticles have been used for resolving the drawbacks of traditional epoxy fillers such as rubber beads and glass and can be overcome by increasing the stiffness, strength, and toughness .
184.108.40.206 Gas Separation
Surface modification of TiO2 nanoparticles with biodegradable nanocellulose and synthesis of novel polyimide/cellulose/TiO2 membrane has been developed by Ahmadizadegan in 2017. In this paper, novel polyimide/cellulose/TiO2 bionanocomposites (PI/BNCs) were synthesized by a simple and inexpensive ultrasonic irradiation method. In this study, PI was synthesized toward direct polycondensation reaction of novel monomer dianhydride with 4-(2-(4-aminophenyl)-1,1,1,3,3,3-hexafluoropropan-2-yl)benzenemine. The gas separation properties of PI membrane with three cellulose/TiO2 concentrations (5, 10, and 15 wt%) are investigated for gas permeation. The titania weight percentage of the PI/BNC membranes was evaluated for the permeability of this membrane, and the results showed that increasing TiO2 concentration increased the permeabilities of CO2, H2, CH4, and N2 .
220.127.116.11 Drug Delivery
Kessler and coworkers have investigated the potential drug delivery systems for dermal applications of cellulose nanofiber-titania nanocomposites. In this work, a new type of cellulose nanofiber-titania nanocomposites grafted with three different types of model drugs such as diclofenac sodium, D-penicillamine, and phosphomycin was successfully synthesized. One of the most important advantages of this work is the use of titania as a binding linker between cellulose nanofibers and a drug molecule, which provides a slow and controlled release. The drug release was investigated in the presence of three drug molecules. It was shown that the quickest release was observed for the more soluble painkiller, slower one for the anti-inflammatory agent, and the longest release took place for the strongly chemisorbed antibiotic agent .
3.2.7 Silica (SiO2) Nanoparticle
Silica particles have wide applications in industries related to the production of pigments, pharmaceuticals, ceramics, and catalysts . Furthermore, silica-based adsorbent materials have industrial applications for the removal of heavy metals and lanthanides [259, 260]. Also, in the recent years, much attention has been paid to improve the adsorptive properties a variety of functional groups grafted on the surface of mesoporous silica.
18.104.22.168 Removal of Lanthanides from Aqueous Medium
Iftekhar and coworkers have successfully synthesized cellulose-based silica (CLx/SiO2) nanocomposite and investigated for the removal of Eu(III), La(III), and Sc(III). In this paper, two different cellulose-based silica (CLx/SiO2) nanocomposites were synthesized and characterized by several techniques. XRD and FTIR analyses have confirmed the presence of mixed phases of cellulose and SiO2. In this study, CLN/SiO2 nanocomposite could be explored as an appropriate adsorbent for Eu(III), La(III), and Sc(III) and can be exploited for the preconcentration of REEs from the diluted aqueous medium .
Nasir et al. have synthesized SiO2-cellulose acetate nanofiber via electrospinning process and investigated the characteristic of nanofiber composites such as nanostructure, morphology, and surface property. SiO2 in nanofiber is a key factor for controlling the spreading time of water droplet on the surface of nanofiber. It was found that the spreading time of water droplet on the surface of cellulose acetate nanofiber is much faster than SiO2-cellulose acetate nanofiber surface. SiO2-cellulose acetate might be used as lithium ion battery separator and water purificator .
3.2.8 Gold Nanoparticle
Gold nanoparticles (AuNPs) have been utilized for the several applications such as optoelectronics , sensing , biomedicine , bioimaging , and gene delivery . In addition, the catalytic activity of AuNPs is investigated for various chemical reactions such as the CO oxidation, C–C coupling reaction, aerobic oxidation of alcohols, and reduction reaction via transfer hydrogenation [268, 269, 270]. However, due to the large active surface areas, AuNPs are unstable and tend to irreversibly aggregate in solution. Therefore, catalytic activity will be reduced. The most effective way to resolve this drawback is immobilization of AuNPs on polymeric supports or inorganic material.
22.214.171.124 Catalytic Activity
TEMPO-oxidized bacterial cellulose nanofiber-supported gold nanoparticles have been reported by Chen and coworkers in 2016. In this work, the nanohybrid was successfully prepared by deposition of gold nanoparticles (AuNPs) onto the surface of TEMPO-oxidized bacterial cellulose nanofibers (TOBCNs). The prepared AuNP/TOBCN nanohybrids were characterized by UV-vis spectral analysis, XRD, TEM, and HRTEM, and their catalytic activity for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) was estimated by UV-vis spectrometry .
Huang and coworkers have shown the deposition of gold nanoparticles on titania gel film pre-coated cellulose nanofibers of filter paper. In this work, the catalytic activities of finalized bulk cellulose-based membranes were investigated for the reduction of 4-nitrophenol to 4-aminophenol through a facile filtration process .
3.2.9 Metal-Organic Frameworks
Metal-organic frameworks (MOFs) have been widely utilized for gas adsorption and separation , catalysis , sensors , drug delivery , humidity measurement , and nonlinear optics  due to their high porosity, high surface areas, versatile synthesis conditions, and unique properties . These crystalline porous materials consist of metal ions or clusters and metal-ligand coordination bonds.
126.96.36.199 Gas Adsorption Activity
Shunxi Song and coworkers have prepared cellulose paper@MOF-5 composites with gas adsorption capacity. The synthesized cellulose paper@MOF composites were characterized by XRD, ATR-FTIR, SEM, and nitrogen adsorption analysis. In this study, cellulose paper@MOF-5 composite materials were prepared via in situ deposition of MOF-5 onto precipitated calcium carbonate (PCC)-filled cellulose paper. Hydrogen bonding between cellulose fibers decreased due to the presence of PCC fillers in the cellulose paper. Therefore, hydroxyl groups on the cellulose surface will be available for reacting with the organic ligand, i.e., 1,4-benzenedicarboxylic acid (BDC) in the MOF-5 formation process. The synthesized cellulose paper@MOF-5 composite materials had zeolite-like frameworks with high specific surface areas. Gas adsorption activity of this composite was investigated, and it was found that prepared paper@MOF-5 composites showed a high nitrogen gas adsorption capacity and could have great potential to adsorb or store gaseous products such as H2, CO2, CH4, etc. .
3.2.10 Copper Nanoparticle
Copper is one of the most widely used materials in the world. The applications of copper (Cu) and Cu-based nanoparticles have attracted a great deal of interest in recent years, especially in the field of catalysis.
Cellulose was found as a susceptible material for various modification reactions. Loading of various organic materials such as esters, ethers, silanes, halogens, amines, carbomates, polymers, and heterocycles on cellulose was reported. High activity of hydroxyl groups of cellulose makes the polymer as an active compound in the modification reactions. Also, cellulose can be modified with inorganic materials for the preparation of special compound with unique properties. While the cellulose reactions were investigated widely, the publications about cellulose modification are increasing that shows the high importance of cellulose-based materials in modern chemistry.
The authors acknowledge Urmia University and Iran University of Science and Technology for providing research facilities and platform.
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