Iranian polymer journal
Volume:18 Issue: 10, 2009

An environmentally acceptable cellulose dissolution procedure was employed to prepare a membrane directly from an unsubstituted cellulose. The effects of coagulants and coagulation conditions on the structure and properties of regenerated cellulose membrane prepared from cellulose in a NaOH complex solution (8 wt% NaOH/6.5 wt% thiourea /8 wt% urea/77.5 wt% H2O) are discussed. A series of cellulose membranes are prepared from cellulose solutions by coagulation with 5 wt% H2SO4, 5 wt% HCl, 5 wt% HAc, CH3CH2OH (abs.), 5 wt% H2SO4/5 wt% Na2SO4, 10 wt% Na2SO4, 10 wt% (NH4)2SO4 and 10 wt% NH4Cl, respectively. Moreover, the membrane coagulated at relatively low temperature possessed better mechanical properties compared to those coagulated at relatively high temperatures. The results indicated that in the coagulation bath of 7 wt% HAc aqueous solution, with coagulation temperature at 10ºC for duration of 5 min, the tensile strength of novel cellulose membrane could reach 134 MPa, which was much higher than the commercial cellophane and those of the membranes prepared from NaOH/urea and NaOH/thiourea aqueous solutions. The CP/MAS 13C NMR, WAXD and FTIR spectra indicate that the regenerated membrane possesses a specific cellulosic crystal type. The novel cellulose membrane showed dense structure and the crystallinity which was higher than that of a viscose fiber, was an indication that it possessed much more stable structure. The coagulation mechanism can be described as a two-phase separation. Cellulose in the gel was precipitated and regenerated with the coagulation process to form a cellulose membrane. This work provides a potential promising way to prepare novel cellulose membrane with excellent physical properties by controlling thecoagulation conditions.

Precipitation polymerization is a non-homogeneous free radical polymerizationmethod in which polymer chains are separated from continuous phase as polymer particles. In this method, all polymerization reactions occur in continuous phase as well as in polymer dispersed phase. We found that the initial concentrations of initiator and monomer are determining factors in polymerization behaviour. Unlike the other free radical polymerization methods, termination by precipitation induces the formation of polymer chains with similar chain length to take over bimolecular termination. Thus, the number- and weight-average degree of polymerization depends slightly on the reaction time. In this work, the yield of reaction was measured using a gravimetric method. The yield of reaction and number- and weight-average degree of polymerization of polymer particles were found to be dependent on the non-solvent type and purification process. When the solubility parameter differences of non-solvent and polymer decrease, the yield of reaction dropps but the Mn and Mw tended to increase. The purification process affected the yield of reaction and molecular weights through the oligomer sedimentation. We concluded that polydispersity index (PDI) of precipitation polymerization is lower than that of the free radical homogeneous and heterogeneous polymerization methods.

Grafting of binary vinyl monomer mixtures such as methylmethacrylate (MMA) +acrylamide (AAm), MMA + acrylonitrile (AN) and MMA + acrylic acid (AA) ontoSaccharum spontaneum-L (Ss) fibre, was carried out in air. The synthesized graft copolymers were characterized with FTIR spectroscopy, scanning electron microscopy (SEM), TGA/DTA/DTG and X-ray diffraction (XRD) techniques. Initial optimization of different reaction parameters was carried out for graft copolymerization of MMA onto fibre backbone. The different optimized parameters were: reaction time, 180 min; temperature, 40ºC; pH 6; solvent, 125 mL; FAS/KPS (0.225/0.112 g/g) 1/0.75 and MMA, 2.94x10-3 mol/L. The optimum graft yield with MMA was found to be 144.4%. Maximum graft yield was found to be 155.6%, 161.4% and 173.5% with MMA + AA, MMA + AN and MMA + AAm, respectively. On thermal analysis, the rate of weight loss per minute was found minimum in case of Ss-g-poly(MMA+AAm) followed by the weight losses for Ss-g-poly(MMA+AN), Ss-g-poly(MMA+AA) and S. spontaneum-L fibres. Thermal stability of Ss-g-poly(MMA+AAm) was found to be more than that of S. spontaneum-L fibre and other graft copolymers. On grafting, the crystalline lattice of the fibre was disturbed due to incorporation of homopolymer chains onto fibres back bone. Graft copolymers were found to possess lower percentage of crystallinity and crystallinity index. It was observed that graft copolymers were more resistant towards 5N HCl and 5N NaOH as compared to original fibres backbone. The graft copolymer of MMA + AN with S. spontaneum-L fibre was found to be more moisture resistant than the other aformentioned graft copolymers.

Nanofibre structures of self-assembling peptides as biological materials have recently been studied for their promising uses in tissue engineering and biomedical research. We report here a self-assembling peptide RADA16 that forms nanofibre scaffold to be used as a three-dimensional (3D) cell culture matrix. The 16-residue peptide forms a β-sheet structure and undergoes molecular self-assembly into nanofibres and eventually into a higher-order scaffold hydrogel. In this study, we indicate that the nanofibres assemble into much stiffer scaffold networks which can mimic the tumor microenvironment in vivo more effectively. Circular dichroism spectroscopy, atomic force microscopy, transmission electron microscopy, and rheology were used to study the structure of the peptide nanofibres and the kinetics of the cell culture scaffold formation. The change of this assembly into stiffer scaffold is important for a 3D cancer cell culture. We have studied cellular behaviour of human lung cancer cell A549 within RADA16 nanofibre scaffold including morphology, growth, drug resistance, and adhesion ability to elucidate its application in cancer cell research. Different cell morphologies in a 3D scaffold and on two-dimensional (2D) plastic may be related to the enhanced drug resistance of A549 cell colonies in a 3D culture which forms a 3D gradient to mimic the in vivo conditions and modifies the cellular behaviour that are missing in 2D monolayer culture. Adhesion assay also shows that the 3D cell colonies have significantly different adhesion abilities to ECM proteins of laminin and collagen IV due to the variations of cell-cell and cell-matrix interactions, compared to the 2D cells. Our data suggest that self-assembling peptide RADA16 nanofibre scaffold could provide new insights into cancer studies.

Mercaptoacetic acid-stabilized CdTe quantum dots (QDs) are prepared directly in aqueous solution. The multi-layer films of acrylate copolymer and CdTe nanoparticles were obtained by the layer-by-layer electrostatic self-assembly. It is shown that positively charged acrylate copolymer can be directly assembled outside the anionic CdTe QDs through an electrostatic force. The optical properties of the CdTe nanoparticles and the film build-up are monitored by employing the absorption and fluorescence spectroscopy. The deposition process is linearly related to the number of bi-layers as monitored by UV-vis absorption spectroscopy. The fluorescence intensity of ultrathin film rises with the DM content (9.69%, 16.29%, and 36.55%) in the acrylate copolymer and the photoluminescence spectra of multi-layers exhibit a red shift, indicating the enhancement of electrostatic forces between the carboxyl groups of thioglycolic acid capped on CdTe quantum dots and quaternization acrylate in cationic copolymer. The electrostatic interaction on the surface of the CdTe was enhanced with the DM content in the copolymer. Characterization of the multi-layer structures has been carried out by X-ray photoelectron spectroscopy. At the same time, the membrane morphology is investigated by atomic force microscopy. Electrostatic forces between anions in CdTe nanocrystals and cations in the copolymer strengthen the stability of the inorganic/organic compound because it played the role of surface passivation in CdTe QDs.

Anthranilic acid-thiourea-formaldehyde terpolymer resin was synthesized by an eco-friendly technique using dimethylformamide as a reaction medium. The resin was characterized by FTIR, 1H NMR, 13C NMR, thermal analysis and viscosity-average molecular weight. The physicochemical parameters have been evaluated for the terpolymer resin. The kinetic parameters such as energy of activation and the order of the reaction have also been evaluated on the basis of the thermogravimetric data using Freeman-Caroll method. The surface morphology of the terpolymer resin was examined by scanning electron microscopy and the transition state between crystalline and amorphous nature was established. The colour of the terpolymer resin was confirmed by optical microscopy. The electrical property of the terpolymer resin showed an appreciable change in its conductivity at various concentrations and temperatures. One of the important applications of these types of polymers is their capability to act as chelating ion-exchangers. The chelation ion-exchange property of the terpolymer showed a powerful adsorption towards specific metal ions like Zn2+, Mn2+, Cu2+, Ba2+, and Mg2+. A batch equilibration method was adopted to study the selectivity of the metal ion uptake involving the measurement of the distribution of the given metal ion between the polymer sample and a solution containing the metal ion over a wide range of concentrations and pHs of different electrolytes.

Nanocomposites based on high-density polyethylene-grafted maleic anhydride (HDPE-g-MA) were prepared by in situ reactive melt mixing using a twin-screw extruder. The effects of different modified clays and maleic anhydride content on intercalation and mechanical properties were studied. The nanocomposites were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy techniques and tensile testing. The results show that clay I.30TC is suitable for preparation of HDPE-g-MA/clay nanocomposites. Grafting HDPE with MA contributed to higher degree of intercalation in clay particles and increases the tensile modulus of nanocomposite. MA content should be maintained at a certain level to improve the extent of intercalation. During the process, grafted maleic anhydride groups on HDPE backbone are converted to acid pendant groups. In order to determine the extent of cross-linking as a function of MA content, the gel content of the samples were measured. A significant improvement in the tensile modulus of the HDPE/clay nanocomposites was observed without changes in tensile strength and elongation-at-break values.