Highest Grafting Percentage Research Articles

Scanning electron microscopy study of chemically modified coir fibers

Chemical-surface modification of coir fibers was done by dewaxing, using an alkali treatment (5% and 10% NaOH), vinyl grafting with methyl methacrylate (MMA) and cyanoethylation. The chemically modified fibers were characterized by Fourier transform infrared (FTIR) spectroscopy. In addition, the surface features of untreated, dewaxed, alkali-treated, grafted, and cyanoethylated coir fibers were studied using scanning electron microscopy (SEM). Progressive changes in surface morphology were observed. SEM observations showed the removal of tyloses from the surface of coir as a result of alkali treatment (5%), resulting in a rough fiber surface with regularly spaced pits. At a lower percentage of grafting (PMMA), the surfaces became more or less uniform, while the surfaces of the coir fibers with a higher percentage of grafting were increasingly covered with grafted materials, resulting in canal-like cavities between the overgrowths of the grafted materials on the unit cells. Cyanoethylated coir-fiber surfaces showed an insufficient deposit of cyanoethyl groups. SEM analysis of the samples was corroborated by measurements of a mechanical property (maximum stress at break). © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1169–1177, 2001

Photograft copolymerization of methyl methacrylate on silk fiber using titanium(III) chloride-potassium persulphate redox initiator in a limited aqueous system. I

Graft copolymerization of methyl methacrylate (MMA) onto mulberry silk fibers has been investigated in a limited aqueous system employing titanium(III) chloride-K 2 S 2 O 8 as the redox initiator under a photoactive condition with visible light. Polymerization in the presence of light at 32 ± 1°C has been found to be more pronounced than in the dark under identical conditions. The percentage of grafting, the percentage of total conversion, and the percentage of grafting efficiency have been studied by varying the reaction time, concentration of monomer, initiator concentration, solvent composition, and pH of the medium. A high percentage of grafting (∼ 93%), high grafting efficiency (∼ 97%), and the percentage of total conversion (∼ 25%) have been obtained with little homopolymer formation. Characterization of the grafted fibers has been investigated by Fourier transform infrared spectroscopy and scanning electron microscopy. Finally, the reaction mechanism has been discussed by considering hydrogen bonding.

Effect of ultrasonic irradiation on ceric-salt-initiated grafting of methyl methacrylate onto regenerated cellulose film

Effect of ultrasonic irradiation on ceric salt (Ce4+)-initiated grafting of methyl methacrylate (MMA) on regenerated cellulose film (thickness = 20 μm) was investigated under an air atmosphere in water solvent at 60°C. The grafting system with the ultrasonic irradiation was characterized by higher percentage of grafting and graft efficiency than the system without the irradiation. Reaction of cellulose with Ce4+ was also accelerated by the ultrasonic irradiation. No accelerating effect of grafting due to the ultrasonic irradiation was observed for the system under reduced pressure of 5 torr. The effect of the ultrasonic irradiation on the average molecular weight of MMA-grafted chains was also studied. Moreover, the surface layer of the resulting grafted films was examined by attenuated total reflection–infrared (ATR–IR) measurement and scanning electron microscopy (SEM) observation. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 251–258, 1999

Graft copolymerization of methyl methacrylate onto curdlan

Graft copolymerization of methyl methacrylate onto curdlan was first investigated. In the graft copolymerization initiated by ammonium persulfate (APS) in DMSO under a homogeneous condition, the resulting graft copolymers had low molecular weights and low grafting percentages. However, the initiation by APS in water gave graft copolymers having relatively higher molecular weight ( ) and higher grafting percentage (548%) than those copolymers obtained by the homogeneous condition. When the graft copolymerization was carried out by cerium (IV) ammonium nitrate-HNO3 initiation, the graft copolymer had the highest grafting percentage of 1620% without degradation of the curdlan backbone. The resulting graft copolymers were soluble in DMSO. The graft copolymers obtained by the cerium salt had narrow molecular weight distributions () compared with those by the APS catalyst in DMSO or water. The graft copolymers decomposed with sulfuric acid to isolate PMMAs, which molecular weights were larger than that of the corresponding homo-PMMAs. The structure of the grafted copolymers was characterized by IR, 13C NMR, DSC, and SEM. It was found that the graft copolymers exhibited the glass transition temperature (Tg), though curdlan had no Tg. As the grafting percentage increased, the Tg increased to reach 270°C, which was higher than the decomposition temperature of curdlan. The surface image of the grafted copolymers observed by SEM, showed smoothless compared with that of curdlan. It was also revealed that the graft copolymers having the grafting percentage of 1620% swelled in common organic solvents up to 4.5 times of the weight of the dry graft copolymer to form gels. © 1996 John Wiley & Sons, Inc.

Preparation of photoinitiator-bound celluloses and their reactivity

Photoinitiator-bound celluloses (Cell-AQ and Cell-BP) were prepared by reaction of epoxy-activated cellulose with, respectively, 1-aminoanthraquinone (AQNH 2) and 4-aminobenzophenone (BPNH 2) in N, N-dimethylformamide at 70°C. About 60% of the initial epoxy groups (1·90–2·10 mmol/(g cellulose)) was found to participate in the reaction under alkaline conditions. The photoinitiator-bound celluloses exhibited an activity towards photoinduced formation of hydrogen peroxide in aqueous solutions of d-glucose, and isopropyl alcohol. The amount of hydrogen peroxide formed was higher for the Cell-BP than the Cell-AQ. Moreover, the photoinitiator-bound celluloses showed an ability to initiate photografting of methyl methacrylate at 60°C in a water medium, indicating a higher percentage of grafting and a lower percentage of homopolymer compared to photoinitiator-sensitized celluloses, which were prepared by immersing a cellulose sample in acetone solutions of AQNH 2 and BPNH 2 and drying under vacuum to remove the solvent. It was found that the photoinitiator residues introduced into the cellulose substrate are capable of abstracting hydrogen atoms from the substrate.

Studies on impact modification of polystyrene (PS) by ethylene–propylene–diene (EPDM) rubber and its graft copolymers. I. PS/EPDM and PS/EPDM‐g‐styrene blends

AbstractEthylene–propylene–diene (EPDM) rubber is an excellent rubber for outdoor use. High impact polystyrene (PS) containing EPDM rubber may show improved weathering resistance. PS is incompatible with EPDM; hence bulk polymerization technique is adopted for the synthesis of graft products which show limited compatibility with PS. Two initiators were chosen at two different working temperatures to produce high grafting efficiency and grafting percentage. In the present system, it is shown that the graft copolymer and polystyrene compositions show higher improved impact strength behavior than that of the products based upon simple dispersion of EPDM in polystyrene.

Glutaraldehyde Crosslinked Gelatin with Polyacrylamide Grafts

Abstract Persulfate-initiated grafting of crosslinked gelatin with acrylamide in aqueous medium is investigated. the high percentages of grafting are explained as a direct consequence of the heterophase nature of grafting. Optimum reaction conditions for a high percentage of grafting together with low homopoymer yields are discussed.

Cationic Polymerization ofN-Vinylcarbazole andN-Vinyl-2-Pyrrolidone Initiated by Carboxyl Groups on Carbon Fibers

Abstract The effects of solvent and temperature on the grafting of poly(N-vinylcarbazole) (NVC) onto carbon fiber by cationic polymerization initiated by carboxyl groups on the surface were investigated in order to obtain poly-NVC-grafted carbon fiber with a higher percentage of grafting It was found that the rate of the polymerization of NVC increased, depending on the dielectric constant of the solvent, in the following order: toluene < 1,2-dichloroethane < nitrobenzene. However, the percentage of grafting of poly-NVC onto the carbon fiber obtained from polymerization in nitrobenzene was smaller than that in toluene. This may be due to differences in the chain transfer of the growing polymer cation to NVC and these solvents. Furthermore, poly-NVC-grafted carbon fiber with a higher percentage of grafting was formed at a lower polymerization temperature, i.e., 60°C. In addition, it became apparent that carbon fiber is capable of initiating the cationic polymerization of N-vinyl-2-pyrrolidone (NVPD), and p...

A Comparative Study of Chemical‐Initiated and Radiation‐Induced Graft Copolymerization of Methyl Methacrylate onto Bamboo by Infrared Spectroscopic Technique

AbstractGraft copolymerization of methyl methacrylate onto bamboo was evidenced by means of infrared spectroscopic technique. A comparative study of chemical initiated and radiation‐induced grafting methods was made. The chemical‐initiated copolymerization treatment with water as the swelling agent can yield high grafting percentage, whereeas the radiation‐induced copolymerization treatment gives very low grafting percentage.

Polytetrafluoroethylene–N‐Vinylpyrrolidone graft copolymers: Affinity with plasma proteins

N-vinylpyrrolidone was grafted onto films, grains, and tubes of polytetrafluoroethylene (PTFE) using a radiation procedure. By controlling the experimental conditions, it was possible to obtain an analogous grafting percentage on films and grains. Kinetic grafting onto a tube might be used under certain conditions to preserve both size and water tightness. Poly(vinylpyrrolidone) (PVP)-grafted material became hydrophilic and slightly swollen according to the grafting percentage obtained. A scanning electron microscope (SEM) analysis of polymer surfaces showed preferential polymerization sites at a low radiation dose. A regular, velvet-like surface was obtained for a high grafting percentage induced at a low radiation intensity. Biological properties of PTFE were compared before and after PVP grafting. PTFE appeared to be a nonreactive polymer with respect to the blood-clotting proteins. No significant change was observed using different granulometric sizes of PTFE grains, and its noteworthy inertness was preserved after PVP grafting. Interactions between polymer surfaces and human plasma proteins were analyzed using 125I-isolated proteins. Fibrinogen and immunoglobulins have a high affinity for PTFE; on the other hand, albumin was weakly adsorbed on the polymer surface. Marked changes in protein adsorption were observed after PVP grafting. Hydrophilic group grafting induced an increase of albumin adsorption and a decrease of fibrinogen adsorption. Prothrombin affinity was not significatly affected by modified PTFE. Studies of serum protein adsorption using solid-phase radioimmunoassays were developed with monospecific and polyvalent antisera. After incubation of the whole serum protein and polymer, immunoglobulins were found to exhibit the major part of bound protein radioactivity on the polymer surface. No evidence of increasing adsorption of immunoglobulins from rabbit serum after immunization by PTFE or PTFE/PVP was observed. The immunoglobulin adsorption was submitted to a competitive effect with the other serum proteins. It was possible to postulate the competitive action of albumin, particularly after biological property changes induced by chemical grafting.

Ionic graft copolymerization. II. Graft copolymerization of β‐propiolactone onto acrylonitrile–sodium acrylate copolymer

AbstractPolyacrylonitrile–β‐propiolactone (βPL) graft copolymer was synthesized by means of ionic polymerization, in which polymerization of βPL was initiated by polyacrylonitrile containing a small amount of some reactive groups such as COOK, COONa, COOLi, and COOH. Lower electronegativity of the countercation favored higher total conversion and higher grafting percentage. The grafting percentage increased with the reaction time and concentration of reactive groups in the trunk polymer, but grafting efficiency varied very little under these conditions. In the bulk polymerization at 60°C., grafting efficiency was about 60%, but in the solution polymerization in toluene or dioxane, grafting efficiency was higher than in bulk or nitrobenzene.