Efficient flocculation of an anionic dye from aqueous solutions using a cellulose-based flocculant

In this current work, a series of cellulose-based flocculants, carboxymethyl cellulose-graft-poly[(2-methacryloyloxyethyl) trimethyl ammonium chloride] (CMC-g-PDMC) with different grafting ratios were successfully synthesized. CMC-g-PDMC bears high flocculation performance in removal of an anionic dye, Acid Green 25 (AG25), at various pH conditions, which is due to improvement of both positive charge and molecular weight after modification. Moreover, the dye removal efficiency is mostly improved with the increase of grafting ratio. Among the four tested salt additives, CMC-g-PDMC exhibits good salt resistance except for sodium chloride in the measured salt concentration range. Furthermore, the image analysis in combination with fractal theory has been employed to investigate the flocs properties including floc size and fractal structure for studying the flocculation mechanism in detail. It is confirmed that charge neutralization and bridging flocculation effects both play important roles in removal of AG25 from water.     

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.     

“One pot” homogeneous synthesis of thermoplastic cellulose acetate-graft-poly(l-lactide) copolymers from unmodified cellulose

Using native cellulose as the starting material, cellulose acetate-graft-ploy (l-lactide) (CA-g-PLA) copolymers were successfully synthesized by “one-pot” process in an ionic liquid 1-allyl-3-methylimidazolium chloride (AmimCl). In this process, cellulose was first reacted with acetic anhydride, yielding cellulose acetate (CA), and then ring opening graft copolymerization of l-lactide was carried out from the residual hydroxyl groups of CA in the same solution using 4-dimethylaminopridine (DMAP) as the catalyst. Both acetyl and ploy (l-lactide) contents in CA-g-PLA copolymers could be well controlled by changing reaction conditions. The structures and thermal properties of CA-g-PLA copolymers were characterized. The glass transition temperature T_g of copolymers decreased with increasing PLA content. Compared to the pure PLA and cellulose-graft-PLA copolymers, the CA-g-PLA copolymers possessed better thermo mechanical properties in a temperature range of 60–130 °C. When the molar substitution of PLA (MS_PLA) was above 1.71, the CA-g-PLA copolymers exhibited thermoplastic behavior and could be processed by conventional thermal processing methods, such as injection molding and melt spinning.     

Modification of cellulose by graft polymerization for use in drug delivery systems

Cellulose-based biodegradable polymers—as microspheres or hydrogels—are suitable for drug delivery systems. In this work, cellulose microfibers were converted to cellulose esters for subsequent graft copolymerization either by free radical or atom transfer radical polymerization (ATRP). For the former, carboxymethyl cellulose (CMC) was prepared and then modified through grafting of poly(hydroxyethyl acrylate) or polyacrylamide. ATRP was achieved by chloroacetylation of cellulose followed by graft copolymerization of hydroxyethyl acrylate or acrylamide monomers. The degree of substitution for CMC and chloroacetylated cellulose (CAC) was determined by the method described in US Pharmacopeia NF24 and by titration method, respectively. CMC, CAC, and the grafted copolymers were characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, thermal gravimetric analysis, X-ray diffraction, and atomic force microscopy; the latter technique clearly shows the chain growth of the synthetic polymers on the backbone surface. Furthermore, cephalexin antibiotic was loaded on the copolymers, and the resultant in vitro drug release studied in three different media (buffer solutions with pH equal to 3, 6.1, and 8).     

Synthesis and Characterization of Water-Soluble Graft Copolymers from 2, 3-Dihydroxypropylcellulose and Acrylamide

Water-soluble 2,3-dihydroxypropylcellulose-polyacrylamide graft copolymers (DHPC-g-PAM) were prepared by Ce⁴⁺ ion-initiated graft copolymerization of acrylamide (AM) onto 2,3-dihydroxypropylcellulose (DHPC) dissolved in dilute nitric acid at room temperature under argon. The ratios of the concentration of Ce⁴⁺ ion to the concentration of DHPC were shown to affect the number and the length of the polyacrylamide grafts. The average number of grafts per chain was determined by acid-catalyzed degradation of the cellulose backbone and was found to be consistent with the presence or absence of free DHPC in the polymerization product prior to hydrolysis. The average number of grafts per DHPC molecule was found to be 2.7 or less depending on the reaction conditions.     

Comparative study of the behavior of carboxymethyl cellulose-g-poly(N-isopropylacrylamide) copolymers and their equivalent physical blends

A comparative study of the behavior of carboxymethyl cellulose and poly(N-isopropylacrylamide) (PNIPAM) as graft copolymers and physical blends, in solution and in solid state was accomplished by viscometry, turbidimetry, IR spectroscopy, X-ray diffraction, thermogravimetry, and enzymatic degradation. Both in diluted and concentrated solutions, the graft copolymers exhibited a thermothickening effect, while the corresponding mixtures of the two components exhibited an Arrhenius behavior. Solid phase investigations showed morphological differences between graft copolymers and their equivalent physical blends. The enzymatic degradation behavior is essentially similar both for copolymers and blends (enzymatic degradation activity has similar values) although a slight increased enzymatic activity was noticed for the graft copolymers in comparison with the blends.     

Flocculation of dilute titanium dioxide suspensions by graft cationic polyelectrolytes

The flocculation of a dilute titanium dioxide (TiO₂) suspension using homopolymers and graft copolymers of acrylamide (AM) and diallyldimethylammonium chloride (DADMAC) was investigated. The graft copolymers produced by γ-irradiating the mixtures of polyacrylamide (PAM) and polyDADMAC gave better flocculating performance than homopolymers, reflecting the higher fractions of large particles and bigger floc size. A kinetic delay in the onset of flocculation was observed after adding the copolymers in the dose range 5–30 [mg polymer]/ [g TiO₂]. Increasing dosage resulted in a longer delay period. No significant flocculation was observed when the dose was above 50 [mg polymer]/[g TiO₂]. This delay was interpreted in terms of the re-conformation of polymer chains driven by charge neutralization, between the positively charged polymer branches and the negative particle surface. Depending on the dosage used, the flocculation behavior of the graft copolymer has been suggested to be equilibrium and non-equilibrium flocculation. It was also observed that re-conformation is not affected by the ion strength of the media, but a strong shear force significantly reduces the chain reconformation time. Received: 9 April 1998 Accepted in revised form: 28 August 1998     

Grafting polyelectrolytes onto polyacrylamide for flocculation 2. Model suspension flocculation and sludge dewatering

Low-molecular-weight high-charge-density cationic poly(diallyldimethylammonium chloride) (polyDADMAC) was grafted onto high-molecular-weight nonionic polyacrylamide (PAM) via a free radical mechanism using a gamma radiation technique. The graft copolymers having various charge densities were evaluated as flocculants for titanium dioxide (TiO₂) model suspensions, and as conditioners for a pulp and paper mill sludge. Their flocculation performance was optimized with respect to polymer composition, gamma irradiation time and polymer dosage. Measurements included turbidity, particle size distribution and drainage rates. The graft copolymers showed a significant improvement over the homopolymers and dual polymer systems in their flocculation and sludge dewatering performance. Received: 6 April 1998 Accepted in revised form: 28 August 1998     

Synthesis of cationic guar gum-graft-polyacrylamide at low temperature and its flocculating properties

Acrylamide grafted cationic guar gum (CGG-g-PAM), induced by ceric ammonium sulfate, was synthesized using aqueous polymerization technique at 10 °C and the flocculation property was studied with high-turbidity tobacco wastewater (NTU > 4500). Thus five grades of graft copolymers were obtained through alteration of initiator and monomer concentrations in order to understand the effect of molecular weight on flocculation. The grafted copolymer was characterized by FTIR and SEM. Study of DTG demonstrated that CGG-g-PAM had better heat-resistant performance than guar gum, cationic guar gum (CGG) and polyacrylamide. The dosage of polyaluminium chloride (PAC) and CGG-g-PAM, pH value and molecular weight were considered to be the factors that can influence flocculation efficiency. The result showed best flocculation efficiency occurs at pH 5 when the dosage of CGG-g-PAM and PAC are 3.6 ppm and 120 ppm, respectively. The percentage of turbidity and COD removal are 98% and 24% correspondingly, and its flocculating efficiency prevails over that of CGG and cationic polyacrylamide (CPAM).     

Synthesis,self‐assembly,and thermosensitive properties of ethyl cellulose‐g‐P(PEGMA) amphiphilic copolymers

Ethyl cellulose graft poly(poly(ethylene glycol) methyl ether methacrylate) (EC‐g‐P(PEGMA)) amphiphilic copolymers were synthesized via atom transfer radical polymerization (ATRP) and characterized by FTIR, ¹H NMR, and gel permeation chromatography. Reaction kinetics analysis indicated that the graft copolymerization is living and controllable. The self‐assembly and thermosensitive property of the obtained EC‐g‐P(PEGMA) amphiphilic copolymers in water were investigated by dynamic light scattering, transmission electron microscopy, and transmittance. It was found that the EC‐g‐P(PEGMA) amphiphilic copolymers can self‐assemble into spherical micelles in water. The size of the micelles increases with the increase of the side chain length. The spherical micelles show thermosensitive properties with a lower critical solution temperature around 65 °C, which almost independent on the graft density and the length of the side chains. The obtained EC‐g‐P(PEGMA) graft copolymers have both the unique properties of poly(ethylene glycol) and cellulose, which may have the potential applications in biomedicine and biotechnology. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 46: 6907–6915, 2008     

Surface Functionalization of Sisal Fibers Using Peroxide Treatment Followed by Grafting of Poly(ethyl acrylate) and Copolymers

Grafting of poly(ethyl acrylate) and its copolymers was carried out on peroxide-treated sisal fibers. Effect of reaction conditions on graft parameters like rate of graft copolymerization and % grafting were studied. The kinetics of graft copolymerization of ethyl acrylate onto peroxide-treated sisal fibers was studied, and the rate expression for the graft copolymerization was found to be R_g = k[EA]^1.74[FAS]^0.51. Grafting of poly(EA) and copolymers onto peroxide-treated sisal fibers was confirmed by FT-IR spectroscopy, scanning electron microscopy (SEM), and X-ray diffraction studies. Thermal stability and percentage crystallinity of sisal fibers were enhanced with peroxide treatment and graft copolymerization.     

Poly(N-isopropylacrylamide) thermoresponsive cross-linked conjugates containing polymeric soybean oil and/or polypropylene glycol

Synthesis, characterization and solution properties of a new series of the PNIPAM-soybean oil and/or polypropylene glycol, PPG, conjugates (conjugates also referred to as co-networks) have been described. For this purpose free radical polymerization of NIPAM monomer was initiated by macroinitiators based on PSB and/or PPG in order to obtain PSB-g-PNIPAM, PPG-g-PNIPAM and PSB-g-PPG-g-PNIPAM cross-linked graft copolymers. The autooxidation of soybean oil under air at room temperature rendered waxy soluble polymeric soybean oil peroxide associated with cross-linked parts. The soluble polymeric oil macro-peroxide isolated from the cross-linked part was used to initiate the free radical polymerization of NIPAM to give PSB-g-PNIPAM cross-linked copolymer. To obtain PPG-macromonomeric initiator, PPG-MIM, PPG-bis amino propyl ether with Mn 400 (or 2000) Dalton was reacted with 4,4′-azo bis cyanopentanoyl chloride and methacryloyl chloride, respectively. PPG-MIM also initiated the free radical polymerization of NIPAM at 80 °C to yield PPG-g-PNIPAM cross-linked thermoresponsive product. In order to obtain PSB-g-PPG-g-PNIPAM cross-linked triblock copolymer, NIPAM was polymerized by using the mixture of two macroinitiators, PSB and PPG-MIM. PSB contents in the graft copolymers were calculated via elemental analysis of nitrogen in graft copolymers. Thermal analysis, SEM, FTIR and ¹H NMR techniques were used in the characterization of the products. The effect of polymeric soybean oil, PSB, and/or PPG on the thermal response rate of poly(N-isopropylacrylamide, PNIPAM, cross-linked-graft copolymers swollen in water has been investigated by means of swelling-deswelling and drug release behaviors against to temperature change. Lower critical solution temperatures (LCST) of the cross-linked PNIPAM conjugates (conjugates also referred to as co-networks) were determined from the curves of swelling degrees versus solution temperatures. The response temperature of the hydrophobically modified PNIPAM conjugates was reduced to 27 °C, 23 °C and 27 °C for PSB-g-PNIPAM, PPG-g-PNIPAM and PSB-g-PPG-g-PNIPAM, respectively. We have found that the graft copolymers were not pH-responsive. In addition, higher pH ranges cause the hydrolysis of the PSB ester linkages, quickly and makes the cross-linked graft copolymers soluble.The fastest shrinking of the gels was observed by loosing water between 65% and 98% at 50 °C.Methyl orange (MO), was used as a model drug, loaded into cross-linked graft copolymers to examine and compare the effects of controlled release at lower and higher temperatures of lower critical solution temperature (LCST).     

Enhanced electrochemical performance of straw-based porous carbon fibers for supercapacitor

The efficient utilization of natural biomass as renewable raw materials is of importance. We herein prepared porous carbon fibers (PCFs) by activation of the extracted cellulose microfibers from the agriculture byproduct of corn straw. Different from the porous carbons (PCs) by directly activating straw, the obtained PCFs had typical one-dimensional morphology with high surface area (2013 m² g^?1) and large pore volume (1.27 cm³ g^?1). The influence of the ZnCl₂/cellulose mass ratio on the electrochemical performance was studied, and the optimized PCF(1:1) possessed a much higher specific capacitance than the PC(1:1) sample, which was attributed to the improved specific surface area as well as the fiber-like morphology where it had short ion diffusion route and small interfacial resistance in comparison to PCs. PCFs have a high specific capacitance of 230 F g^?1 at 0.5 A g^?1, and 183 F g^?1 was retained at 20 A g^?1 (79.6%), revealing an excellent rate capability. The assembled symmetrical supercapacitor exhibited a wide potential window of 1.8 V, small electrochemical impedance, and superior cycle performance. Moreover, a high energy density of 16.0 Wh kg^?1 was obtained at a power density of 450.4 W kg^?1, which was preserved of 6.9 Wh kg^?1 at a high power density of 14,194.3 W kg^?1.     

Graft copolymerisation of acrylamide onto cashew gum

The synthesis of cashew gum-g-polyacrylamide was carried out at 60 °C by a radical polymerisation using potassium persulphate as the redox initiator under N₂ atmosphere. A series of graft copolymers, varying in acrylamide concentration and keeping the concentration of the initiator and polysaccharide constant, was prepared. These graft copolymers were characterised by elemental analysis, infrared and ¹³C NMR spectroscopy, rheological studies, differential scanning calorimetry and thermogravimetric analysis. Comparisons amongst grafting parameters of the reaction of various natural polysaccharides with polyacrylamide (PAM) were carried out. High percentages of acrylamide conversion (%C) and grafting efficiency (%E) were obtained for cashew gum (CG), even with a low acrylamide/gum ratio. All copolymers had intrinsic viscosity and thus the hydrodynamic volume much higher than the CG value and closer to the PAM. The CG-g-PAM solution had an absolute viscosity at 2.5% concentration (wt./vol.) up to 33 and 3.3 times the CG and PAM values, respectively. Grafting of PAM chains onto the polysaccharide enhances its thermal stability.     

Oligomers Derived from 2-Oxazolines

This paper describes the synthesis and properties of oligomer chains derived from 2-oxazolines. First, poly(styrene-g-N-acetyl-ethylenimine) was prepared, and its hydrolysis gave poly(styrene-g-ethylenimine) which showed good chelating properties. Secondly, ABA type triblock copolymers were prepared in which an N-acylethylenimine chain is used as A block and ethylene oxide chain is employed as B block. These triblock copolymers showed good compatibility with Nylon 6, which were shown to posecess effective anti-electrostatic properties for Nylon 6. Thirdly, AB type block copolymers from 2-oxazolines have been prepared by using living polymerization technique. These block copolymers are soluble in water and showed good surfactant nature as reflected by surface tension (γ), when A block is consisted from N-acetyl- or N-propionylethylenimine chain (hydro-philic) and B block is made of N-tridecanoyl or N-aroylethylenimine chain (lipophilic). Finally, graft copolymers of cellulose diacetate having N-acetylethylenimine chain were prepared. It has been found by using a rheovibron that these graft copolymers are compatible with poly(vinyl chloride).     

Effect of catalyst systems and reaction conditions on the synthesis of cellulose‐g‐PDMAam copolymers by controlled radical polymerization

Various copper‐based catalyst systems and reaction conditions were studied in the graft copolymerization of N,N‐dimethylacrylamide (DMAam) with a cellulose‐based macroinitiator by controlled radical polymerization. The cellulose macroinitiator with degree of substitution DS = 0.44 was synthesized from dissolving softwood pulp in a LiCl/DMAc solution. The graft copolymerizations of DMAam, using the cellulose macroinitiator and various copper‐based catalyst systems, were then carried out in DMSO solutions. The copolymerization kinetics was followed by ¹H NMR. Water‐soluble cellulose‐g‐PDMAam copolymers were comprehensively characterized by ATR‐FTIR and ¹H NMR spectroscopies and SEC analyses. DLS and steady‐shear viscosity measurements revealed that when the DP_graft of the cellulose‐g‐PDMAam copolymer is high enough, the copolymer forms a more compact structure in water. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis and Characterization of Sulfonated Polyphosphazene-graft-Polystyrene Copolymersfor Proton Exchange Membranes简

A novel series of polyphosphazene-grafl-polystyrene （PP-g-PS） copolymers were successfully prepared by atom transfer radical polymerization （ATRP） of styrene monomers and brominated poly（bis（4-methylphenoxy）phosphazene） macroinitiator. The graft density and the graft length could be regulated by changing the bromination degree of the macroinitiator and the ATRP reaction time, respectively. The PP-g-PS copolymers readily underwent a regioselective sulfonation reaction, which occurred preferentially at the polystyrene sites, producing the sulfonated PP-g-PS copolymers with a range of ion exchange capacities. The resulting sulfonated PP-g-PS membranes prepared by solution casting showed high water uptake, low water swelling and considerable proton conductivity. They also exhibited good oxidative stability and high resistance to methanol crossover. Morphological studies of the membranes by transmission electron microscopy showed clear nanophase-separated structures resulted from hydrophobic polyphosphazene backbone and hydrophilic polystyrene sulfonic acid segments, indicating the formation of proton transferring tunnels. Therefore, these sulfonated copolymers may be candidate materials for proton exchange membranes in direct methanol fuel cell （DMFC） applications.     

Recent developments in cellulose grafting chemistry utilizing Barton ester intermediates and nitroxide mediation

Esters or carbonates of N‐hydroxypyridine‐2‐thione (Barton esters) were appended to either carboxymethyl or hydroxypropyl cellulose. Irradiation of the cellulose bound Barton esters in monomer initiated free radical graft copolymerization with minimal concomitant homopolymerization. Grafting of styrene to carboxymethyl cellulose was accompanied by backbone cleavage. The hydroxypropyl spacer group minimized backbone degradation; styrene, acylamide and N‐isopropyl acrylamide could be grafted to hydroxypropyl cellulose in tetrahydrofuran solution. Treatment of Barton carbonate modified hydroxypropyl cellulose with styrene in the presence of TEMPO afforded corresponding TEMPO adducts, which can be used to promote the controlled radical graft polymerization of styrene. Grafts were analyzed independently after hydrolysis of the cellulose backbone.     

Ceric-initiated polymerization onto polyacrylonitrile with carbohydrate end groups. Graft versus block copolymer formation

Starch-g-polyacrylonitrile (starch-g-PAN) copolymers were prepared by ceric ammonium nitrate initiation, and the major portion of the starch in these graft copolymers was then removed by acid hydrolysis to yield PAN with oligosaccharide end groups. Although these PAN-oligosaccharide samples reacted with methyl methacrylate in the presence of ceric ammonium nitrate, the resulting products were largely graft copolymers rather than the expected PAN-poly(methyl methacrylate) (PMMA) block copolymers. The following evidence is presented for a PAN-g-PMMA structure: (i) PAN without oligosaccharide end groups also produced a copolymer with methyl methacrylate under our reaction conditions. (ii) Starch-g-PAN (51 or 37% add-on) was a less reactive substrate toward ceric-initiated polymerization than PAN with oligosaccharide end groups. (iii) Low-add-on (18%) starch-g-PAN reacted with methyl methacrylate to give a final graft copolymer in which a large percentage of PMMA was grafted to the PAN component rather than to starch.     

Homogeneous alkalization of cellulose in <Emphasis Type="Italic">N</Emphasis>-methylmorpholine-<Emphasis Type="Italic">N</Emphasis>-oxide/water solution

Alkali cellulose is an important intermediate in the production of cellulose derivatives. N-methylmorpholine-N-oxide (NMMO)/H₂O was used as a homogeneous reaction medium for the cellulose alkalization process to intensify the alkalization degree and improve the substitution uniformity. The morphology, specific surface area and crystalline structure of pristine cellulose, the as-synthesized alkali cellulose and dissolved-regenerated cellulose were characterized by SEM, BET, XRD and FT-IR, respectively. The results showed that the homogeneous reaction medium not only offered a low mass transfer resistance, but also facilitated a disruption of the hydrogen bond in cellulose, thus resulting in the transformation of the cellulose structure from complicated stacking chains to simple glucose chains. The interior hydroxyl groups in the cellulose became accessible to the alkaline reagent NaOH to enhance the alkalization process for the increase in bonding alkali content and the improvement in substitution uniformity. The bonding alkali content was calculated by the difference between total added alkali and free alkali and was achieved as 0.61 g/g cellulose at the optimized operation conditions: reaction temperature of 95 °C, reaction time of 90 min, NMMO dosage of 90.00 g, cellulose 1.0 g and NaOH concentration of 1.40 wt%. Meanwhile, in the conventional alkalization process, the bonding alkali content was just 0.41 g/g cellulose. The alkali cellulose prepared in NMMO/H₂O medium has a large specific surface area of 125 m² g^?1 and an extremely low crystallinity degree. The NMMO/H₂O system represents a potential homogeneous solvent for the cellulose alkalization process.