Synthesis of superabsorbent from carbohydrate waste

A mixture of acrylamide (AM) and acrylic acid (AA) monomers were grafted on germinated gelatinized wheat starch using potassium persulfate (KPS) as an initiator to yield superabsorbent. The effects of different parameters such as time, temperature, monomer feed (AM:AA), starch: monomers ratio and initiator concentration on graft add-on were studied, and the optimized values were found to be 2 h, 60 °C, 1:1 (w/w), 1:1(w/w) & 1% (with respect to starch powder), respectively. The product so formed was saponified with 0.1N NaOH, dried and finely powdered sample was characterized using FT-IR, TGA. Product showed maximum absorbency of 150 g/g.     

Synthesis, characterization and thermal sensitivity of chitosan-based graft copolymers

Novel chitosan-based graft copolymers (CECTS-g-PDMA) were synthesized through homogeneous graft copolymerization of (N,N-dimethylamino)ethyl methacrylate (DMA) onto N-carboxyethylchitosan (CECTS) in aqueous solution by using ammonium persulfate (APS) as the initiator. The effect of polymerization variables, including initiator concentration, monomer concentration, reaction time and temperature, on grafting percentage was studied. XRD, FTIR, DSC and TGA were used to characterize the graft copolymers. Surface-tension measurements, turbidity measurements and temperature-variable (1)H NMR analysis were combined to investigate the thermal sensitivity of CECTS-g-PDMAs in aqueous solution.     

Free radical grafting kinetics of acrylamide onto a blend of starch/chitosan/alginate

Grafting of monomer onto polymer backbone is one of the effective and accessible methods for the chemical modification of polysaccharides. Grafting of acrylamide (AAm) onto polysaccharides blend (PsB) composed of starch, chitosan and alginate has been carried out using potassium persulfate (KPS) as an initiator. The kinetics of the grafting polymerization also has been studied. The grafting parameters have been evaluated by changing the initial concentrations of AAm from 8 to 16 g, PsB from 6 to 14 g and KPS from 0.2 to 1 g. Evidence of grafting has been obtained from FTIR, XRD and TGA. The kinetics of the grafting polymerization also has been studied. The grafting rate equation of the produced hydrogel (PsB-g-AAm) hydrogel has been expressed by: Rg = k[AAm] [PsB]^0.5 [KPS]^0.5. The grafting rate is a first order dependence to [AAm] initial concentration and square root to [PsB] and [KPS] initial concentrations in the used concentrations range.     

Synthesis and characterization of hydroxypropyl methylcellulose and ethyl acrylate graft copolymers

The synthesis of hydroxypropyl methylcellulose-g-poly (ethyl acrylate) was carried out by potassium persulfate induced graft copolymerization in homogeneous aqueous medium. By varying the reaction conditions, graft copolymers with different percentage of grafting were prepared. These graft copolymers were characterized by fourier transform infrared spectra (FTIR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), thermogravimetric analyses (TGA), X-ray diffraction analysis (XRD), and dynamic light scattering (DLS) methods. The molecular weight of grafted and ungrafted polymer chains determined by gel permeation chromatography (GPC) increased with increasing monomer and matrix concentration but decreased with increasing initiator concentration and reaction temperature. The mechanical properties of graft copolymers were measured as function of the percentage of grafting. In addition, the equilibrium humidity adsorption behavior and the disintegration time of the grafted copolymer films were also studied.     

Syntheses and characterisation of graft copolymers of maize starch and methacrylonitrile

Grafting of methacrylonitrile (MAN) onto dried maize starch using ceric ammonium nitrate (CAN) as an initiator has been studied gravimetrically under nitrogen atmosphere in aqueous medium. The percentage grafting is favoured by increasing monomer concentration and reaction time but is affected by higher concentration of initiator and high temperature. No grafting was observed beyond 45°C. The optimum conditions established for grafting were: [CAN]=0.002 mol/l which was added in molar nitric acid; [MAN]=0.755 mol/l; reaction time, 180 min; and temperature, 35°C. The graft copolymers were analyzed by infrared spectroscopy and acid hydrolysis. The grafting of methacrylonitrile onto starch does not alter the thermal stability of starch. The crystalline region of starch was also involved in grafting. Scanning electron microscopy showed a thick polymer coating of grafted PMAN on the starch surface.     

Preparation of poly(methyl methacrylate)–grafted Hyparrhenia hirta for methyl red removal from colored solutions

Poly(methyl methacrylate)–grafted Hyparrhenia hirta (PMMA-g-Hh) biopolymer was prepared through radical polymerization using potassium persulfate (KPS) and applied in adsorption of methyl red from colored solutions. Solvent amount, initiator concentration, monomer concentration, temperature, and reaction time were the reaction parameters investigated for grafting. The biopolymer was characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and x-ray diffraction spectroscopy (XRD). The adsorption process was investigated with respect to pH, contact time, initial concentration, adsorbent dosage, and temperature. The optimum adsorption parameters were pH 6, contact time 90 min, adsorbent dosage 0.6 g, and initial concentration 50 mg/L. The Langmuir adsorption model best fitted the adsorption process, with maximum adsorption capacities of 19.95, 6.89, and 4.02 mg/g at adsorbent dosages of 0.2, 0.6, and 1.0 g, respectively. The pseudo-second-order model described the kinetics data better. The adsorption process was physical, spontaneous, and endothermic. The adsorbent was still active after 10 adsorption-desorption cycles, showing its suitability for use in colored solutions treatment.     

Modification of Okra mucilage with acrylamide: Synthesis, characterization and swelling behavior

In the present communication, the synthesis and characterization of Okra mucilage, a food grade and water-soluble polysaccharide, based-materials are described. Okra mucilage has been modified by grafting acrylamide (AAm) for developing the new green polymeric materials of specialty applications. Grafting has been done under N₂ atmosphere using redox initiator and hydrogels were prepared by using N,N-methylenebisacrylamide (NN-MBAAm) as crosslinker. The effect of monomer concentration, initiator concentration, reaction time and temperature in terms of grafting efficiency (%GE), percent grafting (PG) and percent gel (%G) has been investigated. The grafted polymers and hydrogels were characterized by SEM, XRD and FTIR techniques to study various structural aspects. The swelling behavior of the crosslinked polymeric material has also been studied as a function of time, temperature and pH. The application area of these polymers is varied from biomaterials to the wastewater treatment.     

Characterization and evaluation of methyl methacrylate-acetylated Saccharum spontaneum L. graft copolymers prepared under microwave

Hybridization of the natural polymers with synthetic polymers is of great interest because of its application to biomedical and biodegradable materials. Synthesis of graft copolymers of methyl methacrylate (MMA) onto acetylated Saccharum spontaneum L. fiber using ferrous ammonium sulphate–potassium per sulphate (FAS–KPS) redox initiator under the influence of microwave radiation (MWR) was carried-out. Different reaction parameters such as time, initiator molar ratio, monomer concentration, microwave power, pH and solvent were optimized to get maximum graft yield (72.2%). On grafting, percentage crystallinity decreases rapidly with reduction in its stiffness and hardness. The graft copolymers thus formed were characterized by FTIR, SEM, XRD, TGA, DTA and DTG techniques. Moreover, graft copolymers have been found to be more moisture resistant and also showed higher chemical and thermal resistance.     

Universal behaviour of gel formation from acrylamide-carrageenan mixture around the gel point: a fluorescence study

The steady state fluorescence (SSF) technique was used to study the sol-gel transition, for the solution free radical crosslinking copolymerization of acrylamide (AAm) with various carrageenan content. N, N'- methylenebis (acrylamide) (BIS) and ammonium persulfate (APS) are used as crosslinker and an initiator, respectively. Pyranine (8-hydroxypyrene-1, 3,6-trisulfonic acid, trisodium salt, HPTS) was added as a floroprobe for monitoring the polymerization. Pyranine molecules start to bind to acrylamide polymer chains upon the initiation of the polymerization; thus, the spectra of the bonded pyranines shift to the shorter wavelengths. Fluorescence spectra from the bonded pyranines allows one to monitor the sol-gel transition, without disturbing the system mechanically, and to test the universality of the sol-gel transition as a function of some kinetic parameters like polymer concentration. Observations around the critical point show that the gel fraction exponent beta obeyed the percolation result for low carrageenan concentrations (< 2.0%) however classical results were produced at higher carrageenan concentration (> 2.0%).     

Preparation of cassava starch grafted with polystyrene by suspension polymerization

Cassava starch grafted with polystyrene (PS-g-starch) copolymer was synthesized via free-radical polymerization of styrene by using suspension polymerization technique. Potassium persulfate (PPS) was used as an initiator and water was used as a medium. The graft copolymer was characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, thermal gravimetric analysis, X-ray diffraction and scanning electron microscopy. The sub-micron spherical beads of PS were observed on the surface of starch granules. SEM micrographs showed porous patches of PS adhering on the starch granules after Soxhlet extraction. FTIR spectra also indicated the presence of PS-g-starch copolymer. XRD analysis exhibited insignificant changes in crystalline structure and degree of crystallinity. The effects of starch:styrene weight ratio, amount of PPS, reaction time and reaction temperature on the percentage of grafting – G (%), were investigated. G (%) increased with increasing starch content. Other variables showed their own individual optimal values. The optimum condition yielding 31.47% of G (%) was derived when the component ratio was 1:3 and reaction temperature and time were 50 °C and 2 h, respectively. Graft copolymerization did not change granular shape and crystallinity of starch. This study demonstrated the capability of polymerization of styrene monomer on the granular starch without emulsifier and the synthesis of graft copolymer without gelatinization of starch.     

Removal of methylene blue dye from aqueous solution by adsorption onto sodium humate/polyacrylamide/clay hybrid hydrogels

A type of novel hybrid hydrogels from sodium humate (SH), polyacrylamide (PAM), and hydrophilic laponite clay were prepared using potassium persulfate (KPS) as the initiator and N,N'-methylenebisacrylamide (MBA) as the cross-linker. The morphology of the hydrogels was characterized by field emission scanning electron microscope (FESEM). The adsorption-desorption kinetics of methylene blue (MB) were also investigated. It was shown that SH/PAM/clay hydrogels exhibited excellent performance in MB adsorption. The maximum absorption concentration of MB was 800 mg/l/g of hydrogel. The adsorption concentration of hydrogels increased with increasing SH or clay content. Less MB were desorbed with increasing SH content, while the clay content had no significant influence on the amount of MB desorbed. This effect was attributed to the formation of a ionic complex between the imine groups of MB and the ionized carboxylic groups of SH. MB diffusion process was dominant in MB desorption.     

Study of polyacrylamide grafted starch based algal flocculation towards applications in algal biomass harvesting

Microalgae may be the source of high amount of lipid and protein. It has the property for carbon dioxide sequestration, recycling and also can remove pollutants from wastewater. Using traditional methods, collection of algal biomass is either cost effective, time consuming or may be toxic due to use of chemical salts. The aim of this study is to harvest freshwater microalgae (Chlorella sp. CB4) biomass by using polymer. Polyacrylamide grafted starch (St-g-PAM) has been synthesized by microwave assisted method involving a synergism of microwave radiation and ceric ammonium nitrate (CAN) to initiate the grafting reaction. The synthesis was optimized in terms of CAN and monomer (acrylamide) concentration. The algal flocculation efficacy of all the grades of this graft copolymer was studied through standard 'Jar test' procedure. Effects of percentage grafting, pH and zeta potential on percentage recovery of algal biomass were thoroughly investigated.     

Enzyme immobilization on ultrafine cellulose fibers via poly(acrylic acid) electrolyte grafts

Ultrafine cellulose fiber (diameter 200-400 nm) surfaces were grafted with polyacrylic acid (PAA) via either ceric ion initiated polymerization or methacrylation of cellulose with methacrylate chloride (MACl) and subsequent free-radical polymerization of acrylic acid. PAA grafts by ceric ion initiated polymerization increased with increasing reaction time (2-24 h), monomer (0.3-2.4 M), and initiator (1-10 mM) concentrations, and spanned a broad range from 5.5-850%. PAA grafts on the methacrylated cellulose fibers also increased with increasing molar ratios of MACl to cellulosic hydroxyl groups (MACl/OH, 2-6.4) and monomer acrylic acid (AA) to initiator potassium persulfate (KPS) ratios ([AA]/[KPS], 1.5-6), and were in a much narrower range between 12.8% and 29.4%. The adsorption of lipase (at 1 mg/ml lipase and pH 7) and the activity of adsorbed lipase (pH 8.5, 30 degrees C), in both cases decreased with increasing PAA grafts. The highest adsorption and activity of the lipase on the ceric ion initiated grafted fibers were 1.28 g/g PAA and 4.3 U/mg lipase, respectively, at the lowest grafting level of 5.5% PAA, whereas they were 0.33 g/g PAA and 7.1 U/mg lipase, respectively, at 12.8% PAA grafts on the methacrylated and grafted fibers. The properties of the grafted fibers and the absorption behavior and activity of lipase suggest that the PAA grafts are gel-like by ceric-initiated reaction and brush-like by methacrylation and polymerization. The adsorbed lipase on the ceric ion-initiated grafted surface possessed greatly improved organic solvent stability over the crude lipase. The adsorbed lipases exhibited 0.5 and 0.3 of the initial activity in the second and third assay cycles, respectively.     

Production of starch foams by twin-screw extrusion: effect of maleated poly(butylene adipate-co-terephthalate) as a compatibilizer

Free-radical-initiated grafting of maleic anhydride (MA) onto poly(butylene adipate-co-terephthalate) (PBAT), a biodegradable aliphatic-aromatic copolyester, was performed by reactive extrusion. 2,5-Dimethyl-2,5-di(tert-butylperoxy)hexane was used as the free-radical initiator. The peroxide concentration was varied between 0.0 and 0.5 wt % at 3.0 wt % MA concentration; the MA concentration was varied between 1.0 and 5.0 wt % at 0.5 wt % peroxide concentration. The reaction temperature was maintained at 185 degrees C for all experiments. Under these conditions, between 0.194% and 0.691% MA was grafted onto the polyester backbone. Size-exclusion chromatography, melt flow index, intrinsic viscosity measurements, thermal gravimetric analysis, and differential scanning calorimetry were used to characterize the maleated copolyester. Increasing the initiator concentration at a constant MA concentration of 3% resulted in an increase in the grafting of MA while decreasing the molecular weight of the resulting polymer. Increasing the feed MA concentration also increased the grafting percentage. The maleation of the polyester proved to be very efficient in promoting strong interfacial adhesion with high amylose cornstarch in starch foams as prepared by melt blending. Thus, the use of maleated copolyester as a compatibilizer between starch and PBAT allowed the reduction of the density of resulting starch foams to approximately 21 kg/m3 and improved the resilience from 84% to as high as 95%. Also, the resulting starch foams exhibited improved hydrophobic properties in terms of lower weight gain and higher dimensional stability on moisture sorption.     

Graft copolymerization of methyl acrylate onto pullulan using ceric ammonium nitrate as initiator

Water absorption resins of pullulan graft methyl acrylate (PU-g-MA) using ceric ammonium nitrate (CAN) as an initiator has been investigated under nitrogen atmosphere in aqueous medium. The percentage grafting (%PG) is favoured by increasing reaction time but is affected by higher concentration of initiator and monomer, and high temperature. Experiments showed that the optimal conditions for grafting were: [CAN] = 0.004 mol/l which was added in 1 mol/l nitric acid; [MA] = 0.0465 mol/l; reaction time; 180 min and temperature, 40 °C. The graft copolymer was analyzed by infrared spectroscopy. The water absorption capacity of the resins decreased significantly with the increase in %PG.     

Effects of amylose/amylopectin ratio on starch-based superabsorbent polymers

Biodegradable superabsorbent polymers (SAPs) were prepared by grafting acrylamide onto starches then crosslinking with N,N′-methylene-bisacrylamide. This work focused on the effects of the amylose/amylopectin ratio of starches from the same source (corn) on the grafting reactions and performance of the resultant starch-based SAPs. To characterise each SAP, the acrylamide groups grafted onto the starch were detected by FTIR; grafting ratio and grafting efficiency were evaluated by a gravimetric method; and graft position and the length of the grafted segment were investigated by NMR. The relationships between the microstructures of the starches, and the graft reactions and performance of the SAPs were studied based on the amylose content in the starches. It was found that under the same reaction conditions, the grafting ratio and efficiency increased with increasing amylose content, which corresponds with water absorption ratio. NMR results indicated that the acrylamide group mainly grafted onto C6, and that the length of the grafted segment decreased with increasing amylopectin content in general, and in particular for waxy starch. The high molecular weight and branched structure of amylopectin reduced the mobility of the polymer chains and increased viscosity, which could explain the graft reactions and performance of the starch-based SAPs.     

Modification of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) film by chemical graft copolymerization

The graft copolymerization of 2-hydroxyethylmethacrylate (HEMA) onto poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBHV) films has been investigated. The graft copolymerization was conducted in aqueous media using benzoyl peroxide (BPO) as chemical initiator. PHBHV films were prepared by solvent casting. Different parameters affecting the graft yield were studied such as monomer concentration, initiator concentration, and reaction time. The extent of grafting has been modulated by the preparation conditions, in particular the concentration of HEMA. However, it is interesting to note that the initiator concentration had only a slight influence on the graft yield. Characterization of the grafted PHBHV films assumed that the graft copolymerization not only occurred on the film surface but also took place into the film bulk. Differential scanning calorimetry showed that crystallinity dramatically decreased with increasing graft yield, indicating that graft copolymerization hindered the crystallization process. Wettability has been obviously improved by grafting a hydrophilic monomer such as HEMA for high graft yield (>130%).     

Immobilization of porcine pancreatic lipase on glycidyl methacrylate grafted poly vinyl alcohol

Graft copolymerization of glycidyl methacrylate (GMA) on to polyvinyl alcohol (PVA) using benzophenone (BP) as initiator was carried out. Grafted PVA was used as carrier for pancreatic lipase immobilization. The effects of GMA and BP concentrations as well as grafting reaction times on grafting yields and activities of the immobilized lipase were determined. The influence of enzyme concentrations was also studied. The optimal conditions for the grafting reaction were: 1 h at 15 mM BP and 2.3 M GMA, the optimum enzyme concentration for immobilization was 1 mg/ml. After optimization of the immobilization process a physical and chemical characterization of the immobilized enzyme was performed. Furthermore, the thermal, pH, storage and operational stability of the immobilized enzyme in comparison to the free form was tested.     

A chitosan-based flocculant prepared with gamma-irradiation-induced grafting

A natural polymer, chitosan, was modified to prepare an efficient flocculant using grafting method initiated by gamma ray in acid-water solution. A vinyl monomer, acrylamide, was used as the grafted monomer. The graft copolymer obtained was characterized using Fourier transform infrared spectroscopy, X-ray diffraction and thermogravimetric analysis. Effects of acetic acid concentration, total irradiation dose, dose rate and monomer concentration on the grafting percentage were investigated. Flocculation experiment results demonstrated that the graft copolymer produced was significantly superior to chitosan and polyacrylamide (PAM).     

Kinetic chain lengths in highly cross-linked networks formed by the photoinitiated polymerization of divinyl monomers: a gel permeation chromatography investigation

Highly cross-linked networks formed by the photoinitiated polymerization of multifunctional monomers are finding application in the field of biomaterials because of their chemical versatility, reaction control, and ability to polymerize under physiological conditions. Typically, degradation is introduced into these networks via the cross-links and leads to the release of nondegradable but water-soluble kinetic chains formed during the chain polymerization process. In this study, gel permeation chromatography (GPC) was used to characterize kinetic chain length distributions in highly cross-linked systems that are being developed for orthopedic applications. By polymerizing divinyl monomers to various conversions and subsequently degrading them, we investigated the aspects of network structural evolution related to kinetic chain formation. In general, the average kinetic chain length increased with conversion until the onset of autodeceleration, when the kinetic chains decreased in length as the propagation reaction became diffusion-controlled. The distribution of kinetic chains also changed when different initiation conditions (i.e., initiator concentration and incident light intensity) were used, and a decrease in the kinetic chain lengths was observed at higher initiation rates. Finally, kinetic chain lengths were examined as a function of depth in thick samples polymerized with different light intensities and with a photobleaching initiator. Light attenuation through the sample led to different initiation rates as a function of depth and, consequently, spatial heterogeneity in the network structure as measured by the distributions of kinetic chains.