Gülten Gürdağ

Graft copolymerization of acrylic acid on cellulose: Reaction kinetics of copolymerization

Acrylic acid (AA) was grafted to cellulose by using ceric ammonium nitrate (CAN) initiator in aqueous nitric acid solution at 30, 50, 70, and 907C during reaction periods of 30 to 180 minutes. About 45% of the AA was polymerized at 907C after 180 minutes. The grafted polymer and homopolymer were isolated by acetone from the reaction mixture, dried, and subjected to Soxhlet extraction with dioxane to separate the homopolymer, poly(acrylic acid), from the graft copolymer. The water absorption capacities and grafting values of grafted cellulose were also determined. The maximum grafting yield was obtained at 307C. It was also observed that polyacrylic acid-grafted cellulose produced at 307C had the highest water retention capacity. The time depen- dence of AA conversion allowed calculation of first-order reaction rate constants. These rate constants were then used to determine apparent activation energies. q 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 929-934, 1997

Cellulose Graft Copolymers: Synthesis, Properties, and Applications

Grafting of vinyl monomers onto cellulose is an important tool for the modification of cellulose. Depending on the monomer grafted onto cellulose, it gains new properties. The grafting can be performed in heterogeneous or homogeneous medium. In the grafting performed in heterogeneous medium, the reaction is carried out in aqueous medium using a suitable initiator. As initiator, the radiation or chemical initiators such as ceric ammonium nitrate (CAN), various persulfates, azobisisobutyronitrile (AIBN), and Fenton reagent (Fe(II)–H2O2) are mostly used. In case of CAN initiator, the grafting should be performed in acidic medium in order to prevent its hydrolysis. In the homogeneous grafting reactions, either a water-soluble cellulose derivative is used in the grafting or cellulose is dissolved in a suitable solvent, and then the grafting is performed. Higher number of grafts per cellulose chain is obtained in homogeneous grafting than those in heterogeneous medium.

Electric field responsive chitosan–poly(N,N-dimethyl acrylamide) semi-IPN gel films and their dielectric, thermal and swelling characterization

The electroresponsive, dielectric and swelling behavior of semi-interpenetrated polymer network (semi-IPN) gel films prepared from chitosan (CS) and N,N-dimethyl acrylamide (DA) were investigated and compared with those CS film. CS?DA semi-IPN films were also characterized by Fourier transform infrared, x-ray diffraction and differential scanning calorimetry measurements. The electrosensitivity of CS?DA films to an electric field was investigated by determining their bending at 8?V in (0.05?M/0.1?M/0.15?M) NaCl solution. Equilibrium swelling values of CS?DA films both in distilled water and buffer solution with pH?=?2.2 decreased with poly-DA (PDA) content of the films. While the maximum decomposition of CS film took place at about 296??C, the presence of PDA in CS?DA semi-IPN films reduced the thermal stability, and their maximum decomposition temperature shifted from 261 to 240??C with the increase in PDA content. In addition, the PDA network led to a decrease in the dielectric constant (??), dielectric loss (??) and conductance (?) of CS?DA semi-IPN films in the frequency range between 12?Hz and 100?kHz. The values of electric modulus and impedance, and Cole?Cole plots confirmed that the conductance values of CS?DA films are lower than that of CS film. The PDA network also led CS?DA films to respond more slowly to electric field. The increase in NaCl concentration in the bending medium increased the response rate of CS?DA films to an electric field. The final bending angle of all CS?DA films was 90?, and it was not dependent on either NaCl concentration or PDA content of the films.