Hydrophobic modification of cellulose nanocrystal via covalently grafting of castor oil

Hydrophobic cellulose nanocrystals (CNs) have been prepared by grafting isocyanate-terminated castor oil, a kind of natural vegetable oil, onto their surface. The existence of castor oil component in the modified cellulose nanocrystals was verified by Fourier transform infrared spectroscopy, solid-state ¹³C NMR spectra and X-ray photoelectron spectroscopy. At the same time, X-ray diffraction and transmission electron micrographs further proved that the crystalline structure and large aspect ratio of cellulose nanocrystals were essentially preserved after chemical grafting. Furthermore, the surface of modified cellulose nanocrystals appeared to be hydrophobic as indicated by contact angle measurements. The value of the polar component of surface energy decreased from 21.5 mJ/m² to almost zero via grafting castor oil. These novel hydrophobic castor oil-grafted cellulose nanocrystals appear as valuable alternatives to formulate bionanocomposites with non-polar polymers for optimized performances.     

Physical and Chemical Characterization of Cellulose Based Textiles Modified by Periodate Oxidation

Conversion of dihydroxyl groups to dialdehyde by periodate oxidation is a useful method widely used in derivatization of cellulose to activate the polymer to further reactions as grafting polymerization. To investigate the cellulose behavior at different level of oxidation and to better understand the influence of the crystallinity on the effects induced by oxidative reactions on different cellulose materials, linen and cotton textiles have been oxidized with periodate solutions in different conditions. Oxidized cellulose samples have been characterized by several techniques: solid-state ¹³C NMR, Wide Angle X-Ray diffraction, and SEM. Moreover the mechanical properties of the untreated and oxidized yarns have been evaluated by means of tensile tests, the oxidation degree has been measured by means of the hydroxylamine hydrochloride method.     

Microwave Assisted Graft Copolymerization of N-Isopropyl Acrylamide and Methyl Acrylate on Cellulose: Solid State NMR Analysis and CaCO3 Crystallization

Summary: Graft copolymerization of N-isopropyl acrylamide and methyl acrylate on α-cellulose was carried out under microwave irradiation at specific cut off temperatures with cerium (IV) ammonium nitrate and potassium persulfate (KPS) as the initiating system. The role of KPS was to oxidize Ce (III) to Ce (IV) which is the active species in radical formation. The reactions at a temperature cut off of 60 °C were confirmed by ¹³C nuclear magnetic resonance cross-polarization with magic- angle spinning (¹³C NMR CP/MAS) and Fourier-transform infrared spectroscopy (FTIR). The extent of grafting was calculated from weight gain and ¹³C resonances. The grafted cellulose was thermally more stable than the parent cellulose. An attempt to do grafting at a higher cut off temperature of 80 °C was made, however, no grafting was observed from ¹³C NMR CP/MAS but TGA results showed that a cellulose having more thermal stability resulted which was attributed to cross linking. Crystallization of CaCO₃ was carried out using the grafted materials as templates showed better nucleation and different crystal structure was observed.     

Graft copolymerization ofN‐vinyl‐pyrrolidone and acrylamide on cellulose derivatives: synthesis,characterization and study of their biological effect

Graft copolymers of carboxymethyl cellulose and hydroxyethyl cellulose with N‐vinyl‐2‐pyrrolidone and acrylamide have been synthesized by grafting copolymer of N‐vinyl‐2‐pyrrolidone and acrylamide onto a mixture of carboxymethyl cellulose and hydroxyethyl cellulose by a solution polymerization technique using a redox initiation system. The graft copolymers were characterized by ¹³C‐NMR spectroscopy and scanning electron microscopy. These graft copolymers have been tested for their biodegradability and biological activity. None of the graft copolymer solutions shows any microbial degradation up to 10 days. The reported results are evidence of the possibility of anti‐fungi effect. Copyright © 2002 John Wiley & Sons, Ltd.     

CERIC ION INITIATED GRAFTING ON CELLULOSE FROM BINARY MIXTURE OF ACRYLONITRILE AND METHYLACRYLATE

The Ce(IV)-ion induced grafting on cellulose from the binary mixture of acrylonitrile-methylacrylate has been investigated in heterogeneous and acidic conditions at 25 ± 0. 1°C. Various grafting parameters were evaluated as a function of molarity, feed composition, reaction time, and concentration of ceric ion at constant concentration of nitric acid in the feed. The higher fraction of acrylonitrile in the grafted chains than the feed has indicated the synergistic effect of methylacrylate taken in the feed along with acrylonitrile. IR and elemental analysis for nitrogen contents in the synthesized copolymers were used to determine the composition of the grafted copolymers. The reactivity ratios of acrylonitrile and methylacrylate have been determined by the Mayo and Lewis method and are found to be 1.45 and 0.9, respectively. The grafting parameters have shown increasing trends on varying feed composition (f_AN) from 0.25 to 0.80 and varying monomer concentration from 0. 6 to 5 4 mol dm^?3. The number of grafted moles of synthetic polymer (N_g) on cellulose were found to be dependent on molarity, feed composition, and ceric ion concentration. The experimental results have clearly indicated that maximum fraction of the feed was consumed in the formation of grafted copolymer chains in comparison to the homocopolymers and homopolymers. Estimation of ceric ion disappearance as a function of reaction time has clearly suggested that grafting on cellulose is initiated by the reactive sites generated through hydrogen ion abstraction by single electron transfer process.     

The undesirable acetylation of cellulose by the acetate ion of 1-ethyl-3-methylimidazolium acetate

Abstract  

The ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([C2mim]OAc) is considered to be an inert solvent of cellulose and lignocellulosic biomass. Acetylation (1.7% mol, or DS 0.017) of cellulose after dissolution in technical grade [C2mim]OAc (150 °C for 20 min), is demonstrated by compositional analysis, FTIR analysis and ¹³C NMR spectroscopy (in [C2mim]OAc with ¹³C enriched acetate). This acetylation, in the absence of added acylating agents, has not been reported before and may limit [C2mim]OAc utility in industrial scale biomass processing, even at this low extent. For example, cellulose acetylation may contribute to IL loss in processes where the IL is recovered and reused and inhibit enzyme saccharification of cellulose in lignocellulosic biofuel production processes based on saccharification and fermentation.     

Cellulose organic solutions: A nuclear magnetic resonance investigation

Four solvents of cellulose have been studied by using ¹³C-NMR spectroscopy. All these solvents, N-methyl morpholine-N-oxide, methylamine, hydrazine, and paraformaldehyde (PF), contained dimethyl sulfoxide (DMSO) as a cosolvent. Oligomers of cellulose of DP = 10 soluble in hot DMSO have been used as model compounds. ¹³C chemical shifts and line shapes show that three of the mentioned solvents are “true solvents” of cellulose. On the other hand, dissolution of cellulose in DMSO-PF system occurs by the formation of a statistical derivative of cellulose. Enriched ¹³C bacterial cellulose on C-1 and C-6 positions have been used to identify the ¹³C positions mainly in DMSO-N-methyl morpholine-N-oxide system. This solvent has been found to be degradative for the macromolecule when the solution is kept at 100°C over a long period. Viscosity measurements show a reduction of the molecular weight in these conditions. Polarimetry indicates that no glucose is present in solution and hence there is a statistical break of the chain. Enriched cellulose solution in DMSO–N-methyl morpholine-N-oxide has been also used for relaxation time (T₁) determination both of the solvent and of the enriched carbons of the polymer. Nuclear Overhauser enhancement (NOE) was found to be 1.8 for C-1 and 2.1 for C-6 showing that relaxation phenomenon is not purely dipolar. T₁ values of 97 and 65 msec are found for C-1 and C-6 of cellulose, in good agreement with the values known for polysaccharides. Determination of T₁ for the different carbon atoms of the solvent DMSO-N-methyl morpholine-N-oxide with and without cellulose shows a large reduction of T₁ for N-methyl morpholine-N-oxide molecule. This denotes a slower molecular motion of this molecule and a preferential interaction with the cellulose macromolecule.     

Cellulose surface grafting with polycaprolactone by heterogeneous click-chemistry

This work deals with a new approach of grafting cellulose surface fibres by polycaprolactone macromolecular chains in heterogeneous conditions via click-chemistry. Thus, cellulose esters were prepared by reacting Avicel with undecynoic acid, in order to prepare cellulose substrate bearing multiple CC-terminated hairs. The prepared modified Avicel substrates were characterised by FTIR, XPS spectroscopy, elemental analyses and showed that the grafting have indeed occurred. The degree of substitution of the prepared cellulose esters was around 0.1. In parallel, polycaprolactone-diol (PCL) was converted to azido-derivative and the ensuing products characterised by FTIR and ¹³C-NMR spectroscopy. Both methods confirmed the success of such modification. Finally, cellulose esters were reacted with azido-PCL grafts in heterogeneous conditions through “click chemistry”. The thus prepared modified cellulose substrates were characterized by FTIR and XPS spectroscopy as well as elemental analyses. The three techniques confirmed the occurrence of the grafting. A weight gain of 20% was achieved.     

Grafting of model primary amine compounds to cellulose nanowhiskers through periodate oxidation

This study demonstrates regioselective oxidation of cellulose nanowhiskers using 2.80–10.02 mmols of sodium periodate per 5 g of whiskers followed by grafting with methyl and butyl amines through a Schiff base reaction to obtain their amine derivatives in 80–90 % yield. We found a corresponding increase in carbonyl content (0.06–0.14 mmols/g) of the dialdehyde cellulose nanowhiskers with the increase in oxidant as measured by titrimetric analysis and this was further evidenced by FT-IR spectroscopy. Grafting of amine compounds to the oxidized cellulose nanowhiskers resulted in their amine derivatives, which are found to be partially soluble in DMSO. Therefore, the reduction reaction between amines and carbonyl groups was confirmed through ¹³C NMR spectra, which was also supported by copper titration, XPS, and FT-IR spectroscopy. Morphological integrity and crystallinity of the nanowhiskers was maintained after the chemical modification as studied by AFM and solid-state ¹³C NMR, respectively.     

Antibacterial modification of cellulose fibers by grafting β-cyclodextrin and inclusion with ciprofloxacin

Antibacterial-modified cellulose fiber was prepared by covalently bonding β-cyclodextrin (β-CD) with cellulose fiber via citric acid (CA) as crosslinking agent, followed by the inclusion of ciprofloxacin hydrochloride (CipHCl) as antibiotic. Effects of reaction time, temperature, concentration of β-cyclodextrin citrate (CA-β-CD) and pH on the grafting reaction were investigated, and the grafting ratio of β-CD onto cellulose fibers was 9.7 % at optimal conditions; the loading and releasing behaviors of CipHCl into/from β-CD grafted cellulose fibers were also revealed, the load amount of CipHCl into grafted cellulose fibers increased remarkably, and the release of CipHCl from the grafted cellulose fibers was prolonged. The microstructure, phase and thermal stability of modified cellulose fibers were characterized by FT-IR, ¹³C CPMAS NMR, X-ray diffraction and TGA. Considerably longer bacterial activity against E. coli and S. aureus was observed for grafted fibers loading CipHCl compared to virgin ones. Optical and mechanical properties of the paper sheets decreased generally with more antibacterial-modified fibers added.     

1H, 13C and 7Li nuclear magnetic resonance study of the lithium chloride–N,N-dimethylacetamide system

The complex solvent obtained by dissolving 5-10% of lithium chloride in N,N-dimethylacetamide (DMA) presents a good method for dissolving highly insoluble polymers, such as cellulose. ¹H, ¹³C and ⁷Li NMR spectroscopy have been used, together with viscosity and conductivity measurements, for the study of this complex solvent. The ¹H and ¹³C chemical shift variations of DMA, on increasing the lithium chloride concentration, are found to be in opposite directions. The T₁ relaxation times show a large decrease in the mobility of DMA in the presence of lithium chloride. Methyl-β-D -glucopyranoside has been used as a model for cellulose in order to investigate the mechanism of solution of this polymer. It was found that each hydroxy group of the solute interacts with one lithium chloride molecule in solution.     

Regenerated cellulose film with enhanced tensile strength prepared with ionic liquid 1-ethyl-3-methylimidazolium acetate (EMIMAc)

In this study, environmentally friendly regenerated cellulose films with enhanced tensile strength were successfully prepared by incorporation of plasticizer agents using 1-ethyl-3-methylimidazolium acetate as solvent. The results of morphology from scanning electron microscopy and atomic force microscopy showed that cellulose films possessed homogeneously, and exhibited smooth structure. ¹³C CP/MAS NMR spectra showed that the regenerated cellulose films were transferred from cellulose I to cellulose II. Moreover, the incorporation of plasticizer agents, especially in the presence of glycerol, significantly improved the tensile strength of cellulose film (143 MPa) as compared to the controlled sample. The notable properties of the regenerated cellulose films are promising for applications in transparent packaging.     

Concentration enrichment of urea at cellulose surfaces: results from molecular dynamics simulations and NMR spectroscopy

A combined solid-state NMR and Molecular Dynamics simulation study of cellulose in urea aqueous solution and in pure water was conducted. It was found that the local concentration of urea is significantly enhanced at the cellulose/solution interface. There, urea molecules interact directly with the cellulose through both hydrogen bonds and favorable dispersion interactions, which seem to be the driving force behind the aggregation. The CP/MAS ¹³C spectra was affected by the presence of urea at high concentrations, most notably the signal at 83.4 ppm, which has previously been assigned to C4 atoms in cellulose chains located at surfaces parallel to the (110) crystallographic plane of the cellulose Iβ crystal. Also dynamic properties of the cellulose surfaces, probed by spin-lattice relaxation time ¹³CT ₁ measurements of C4 atoms, are affected by the addition of urea. Molecular Dynamics simulations reproduce the trends of the T ₁ measurements and lends new support to the assignment of signals from individual surfaces. That urea in solution is interacting directly with cellulose may have implications on our understanding of the mechanisms behind cellulose dissolution in alkali/urea aqueous solutions.     

Preparation and characterization of hybrid cationic hydroxyethyl cellulose/sodium alginate polyelectrolyte antimicrobial films

This study aimed to develop polyelectrolyte‐structured antimicrobial food packaging materials that do not contain any antimicrobial agents. Cationic hydroxyethyl cellulose was synthesized and characterized by Fourier‐transform infrared, ¹H NMR, and ¹³C NMR spectroscopy. Its nitrogen content was determined by Kjeldahl method. Polyelectrolyte‐structured antimicrobial food packaging materials were prepared using hydroxyethyl cellulose, cationic hydroxyethyl cellulose, and sodium alginate. Antimicrobial activity of materials was defined by inhibition zone method (disc diffusion method). Thermal stability of samples was evaluated by thermal gravimetric analysis and differential scanning calorimetry. Surface morphology of samples was investigated by SEM. The obtained results prove that produced food packaging materials have good thermal and antimicrobial properties, and they can be used as food packaging material in many industries.     

New associative EHEC‐g‐PAam copolymers: Their syntheses,characterization, and rheological behavior

The syntheses and rheological behavior of ethyl hydroxyethyl cellulose (EHEC)‐based graft‐copolymers were studied. Copolymers were prepared by grafting EHEC with acrylamide (Aam) via reversible addition fragmentation chain transfer (RAFT) polymerization. Hydroxyl groups of EHEC were esterified with a carboxylic acid functional chain transfer agent (CTA) to prepare EHEC‐macroCTAs with different degrees of substitution. EHEC‐macroCTAs were characterized by ATR‐FTIR, ¹³C NMR, and SEC, and elemental analysis was used to quantify the degree of CTA substitution. EHEC‐macroCTAs with different degrees of substitution were copolymerized with acrylamide by “grafting from” technique. Formation of new cellulose‐based copolymers was comprehensively confirmed by ¹H NMR, ATR‐FTIR, and SEC measurements. Further, the associations of EHEC‐g‐PAam copolymers in water were studied at various concentrations and temperatures by means of UV–vis spectroscopy, fluorescence spectroscopy, and rheological measurements. The results indicate that copolymers have both intra and intermolecular association in water depending on the amount of grafts. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1869–1879, 2009     

Graft Copolymerization on to Cellulose Using Binary Mixture of Monomers

The graft copolymerization of acrylonitrile (AN) and ethyl acrylate (EA) comonomers onto cellulose has been carried out using ceric ammonium nitrate (CAN) as an initiator in the presence of nitric acid at 35±0.1°C. The addition of ethyl acrylate as comonomer has shown a significant effect on overall and individual graft copolymerization of acrylonitrile on cellulose. The graft yield (%G_Y) and other grafting parameters viz. true grafting (%G_T), graft conversion (%C_G), cellulose number (Ng) and frequency of grafting (G_F) were evaluated on varying the concentration of comonomers from 6.0–30.0×10^?1 mol dm^?3 and ceric (IV) ions concentration from 2.5–25×10^?3 mol dm^?3 at constant feed composition (f_AN 0.6) and constant concentration of nitric acid (7.5×10^?2 mol dm^?3) in the reaction mixture. The graft yield (%G_Y) and other grafting parameters were optimal at 15×10^?1 mol dm^?3 concentration of comonomers and at 10×10^?3 mol dm^?3 concentration of ceric ammonium nitrate. The graft yield (%G_Y) and composition of grafted chains (F_AN) was optimal at a feed composition (f_AN) of 0.6. The energy of activation (Ea) for graft copolymerization has been found to be 16 kJ mol^?1. The molecular weight (Mw) and molecular weight distribution (Mw/Mn) of grafted chains was determined by GPC and found to be optimum at 15×10^?1 mol dm^?3 concentration of comonomer in the reaction mixture. The composition of grafted chains (F_AN) determined by IR method was used to calculate the reactivity ratios of monomers, which has been found to be 0.62 (r₁) and 1.52 (r₂), respectively for acrylonitrile (AN) and ethyl acrylate (EA) monomers used for graft copolymerization. The energy of activation for decomposition of cellulose and grafted cellulose was determining by using different models based on constant and different rate (β) of heating. Considering experimental observations, the reaction steps for graft copolymerization were proposed.     

Graft copolymerization of 4-vinylpyridine onto cellulose using Co (III) acetylacetonate comlex in aqueous medium

The graft copolymerization of 4-vinylpyridine (4-VP) onto cellulose has been carried out in heterogeneous conditions with cobaltacetylacetonate complex (Co (acac)₃) under nitrogen atmosphere at 35±0.1°C in aqueous media. The grafting parameters such as graft yield, grafting efficiency, total conversion, frequency of grafting and rate of grafting have been evaluated as a function of concentration of 4-vinylpyridine, cobaltacetylacetonate and reaction temperature of graft copolymerization. Variation in concentration of monomer and initiator leads to a consistent increase in grafting parameters and then show a decreasing trend. The efficient grafting of monomer in presence of cobaltacetylacetonate complex is due to the coordination of the -electrons of the 4-vinylpyridine with the metal chelate which facilitate the homolytic decomposition of metal-oxygen bond to form radicals at relatively low temperature. The rate of graft copolymerization is directly proportional to the concentration of monomer and the square root of the concentration of the cobaltacetylacetonate complex. The activation energy (Ea) for graft copolymeriztion has been calculated using a Arrhenius plot and is 31.0kJ mol^–1 within the temperature range of 20–40°C. The grafting of 4-vinylpyridine has also been studied in presence of various additives and their effects have been suitably explained. On the basis of the experimental observations, reaction steps are proposed and rate expression has been derived.     

New Possibilities of the Acetosulfation of Cellulose

Regioselectively substituted cellulose sulfates in C2/3-, C2/6-, or C6-position of the anhydroglucose unit are accessible by certain synthesis routes. Thereby, products with different properties and various application areas are resulted. Important characteristics of cellulose sulfates regarding their applications are solubility (e.g. in water), rheological behavior, different interaction with low or high molecular cations, thermo reversible gel formation, enzymatic degradability, anticoagulant and antiviral activity. In C6-position substituted cellulose sulfates can be synthesized in principle by acetosulfation. The acetosulfation is a quasi-homogeneous synthesis proceeding under gradually dissolution of the cellulose by using different reactivity of the primary and secondary OH-groups as soon as converting cellulose acetate sulfates. After precipitation of the polymer the acetyl groups are cleaved in alkaline solution. The focus of our study was firstly the investigation of the acetosulfation in different polar aprotic solvents by various sulfating and acetylating agents. In general it should be investigated if C6 substituted cellulose sulfates can be obtained by acetosulfation with different solvents and agents. The products were characterized by ¹³C-NMR and Raman spectroscopy.     

Graft Copolymerization of 4-Vinylpyridine Onto Modified Cellulosic Fibers. the Ceric Ion Concentration Effect

The graft copolymerization of 4-vinylpyridine was carried out on mercerized cellulose and partially carboxymethylated cellulose (PCMC) using eerie ammonium nitrate (CAN) as the initiator. the grafting parameters (grafting efficiency (GE), graft yield (G), and total conversion (C¹)) were studied as a function of CAN concentration. It was shown that by increasing the CAN concentration, G and C, reached a maximum. the graft yields for PCMC were significantly higher than those for mercerized cellulose. the largest GE values appeared for PCMC and mercerized cellulose at low and high CAN concentrations, respectively. the Ce(IV) consumption during grafting increased with rising concentration of CAN, and it was greater in the case of PCMC than of mercerized cellulose. After acid hydrolysis of the polysaccharide backbone, the average molecular weight of grafts was determined viscometrically. Molecular weight decreased with initiator concentration. Graft frequency (GF), on the other hand, increased with CAN concentration. GF for PCMC was higher than that for mercerized cellulose. Ce(IV) consumption increased with CAN concentration and it was lower for mercerized cellulose than that consumed during grafting on PCMC. After that, the effect of CAN concentration on the graft copolymerization onto PCMC was examined while the total nitrate ion concentration was maintained constant at 1.59 M by addition of sodium nitrate. Maximum G, C¹ and Ce(IV) consumption were higher than in the previous case.     

Synthese et etude de celluloses echangeuses d'ions. Leur emploi dans l'epuration des eaux residuaires de l'industrie textile—1: Synthese d'une cellulose greffee par des chaines poly (acide acrylique) et d'une cellulose renfermant des fonctions ammonium quaternaire

For use as ion exchangers and particularly as purification agents for textile industrial effluents, cellulose grafted with polyacrylic acid and cellulose substituted by quaternary ammonium functions have been prepared. For both syntheses, the influences of experimental parameters have been studied in detail and the optimum conditions for large-scale preparation have been determined. Large amounts of modified cellulose have been obtained and tested in industry (cf. part III). The grafting by acrylic acid has been carried out by the ceric-ion method; the quaternary ammonium cellulose has been obtained by condensation of cellulose with epoxy propyl triethyl ammonium chloride. Synthesis of this salt in the presence of cellulose has been achieved so that the quaternary ammonium cellulose can be obtained from cellulose and epichlorhydrin in one step.