Iranian Polymer Journal
Year:2006 | Volume:15 | Issue:10 (76)|Papers Count:8

Loss of a high molecular weight hindered amine light stabilizer (HALS) from irradiated low density polyethylene-ethylene vinyl acetate blends (LDPE/EVA) in hot water has been investigated. The effects of Chimassorb 944 and two trifunctional monomers, triallyoxy-1, 3, 5-triazine and 2-ethyl-2-(hydroxymethyl)-1, 3-propandiol trimethacrylate on LDPE/EVA properties after irradiation and on migration of stabilizer from the polymer base during thermal aging in hot water have been studied. The samples in both pure form and mixed with additives were exposed to electron beam radiation at doses between 50 and 150 kGy, at room temperature, in air. In order to study the thermal aging property, irradiated samples were placed in hot water bath at 95ºC for 1000h and in an oven at 140ºC for several hours. Irradiated samples showed noticeable changes in mechanical properties. Long term heat stability of polymer blend was improved significantly by using of polyfunctional monomers. From the results of the thermal aging procedures, the HALS showed a convenient influence on the increasing of the polymer blend thermal stability at 95ºC. However in the accelerated condition, the value of oxidation induction time (OlT) decreased as a result of depletion of HALS from the polymer base during the immersion in hot water.

One of the zein film forming methods is thermomoulding by hot press. Pure zein film is very brittle and plasticizers can improve its mechanical and film making properties. In this research, polyols (glycerol, sorbitol, and manitol) at three levels (0.5, 0.7 and 1 g/g of zein resin) were used separately as a plasticizer and for determining their plasticization effectiveness the rheological and thermal properties of zein resin samples were studied. Sorbitol and glycerol had good plasticizing effects and could decrease viscoelastic modulus of zein resin considerably, but manitol was not as effective as them. Resins containing manitol remained rigid and had unfavorable chalky appearance. The effects of plasticizers on thermal properties of resin were investigated by DSC at -100 to 150°C. No crystallization and melting peaks related to zein resin and plasticizers were observed. Thermograms showed that polyolic plasticizers and zein resin remained a homogeneous material throughout the cooling and heating cycles. As well as, at glass transition temperature, there is not any significant difference among zein resins containing various plasticizers. The Tg of different resins were at 60 -70°C. This was probably due to similar molecular weight of the selected polyols. In addition, after initial decreasing of Tg of resin, subsequent increase of plasticizer levels did not cause considerable reduction in it.

To make the naturalized synthetic fibres, grafting of soybean protein isolate (SPI) onto poly acrylic fibres (PAC) was investigated after chlorination of the hydrolyzed PAC fibres. The effects of preparation conditions, including chlorination temperature, chlorination time, grafting temperature, grafting time, and amount of sodium hydroxide (NaOH) on the grafting efficiency were studied. The grafted products were evaluated by fourier transform infrared spectroscopy (FTIR) and X-ray diffraction techniques. The FTIR studies confirmed that the SPI had been grafted onto the PAC fibres. The X-ray diffraction revealed that the crystalline structure of the grafting modified fibres did not change as compared with that of the ungrafted fibres. Microscopic observations were carried out to investigate the surface characteristics of the ungrafted and grafted fibres. The scanning electron microscopy (SEM) analysis showed that the external surface of the grafted fibre was coated with SPI. The grafted PAC fibres exhibited good moisture absorption and water retention behavior. Mechanical properties of the grafted fibres could meet the requirement for wearing fibres.

Water mediated reactions offer useful and more environmentally friendly alternatives to their harmful organic solvent versions and have received increasing interest in recent years. Furthermore, water has unique physical and chemical properties, and by its utilization it would be possible to realize reactivity or selectivity that cannot be attained in organic solvents. Polyacrylamide supported phenolate is synthesized, characterized, and introduced as a new basic heterogeneous catalyst for aza- and thio-Michael addition reactions of both aliphatic and aromatic amines and thiols to α, ß-unsaturated electrophiles in aqueous media at room temperature. Di-thio-Michael addition of dithiol was performed successfully. Results showed that thio-Michael addition is faster than aza-Michael addition due to higher nucleophilicity of thiolate anion in comparison with neutral amino functionality. Mild reaction condition, low catalyst/substrate ratio, high efficiently, and reusability make this new basic heterogeneous catalyst as one of few reported polymer supported catalysts for aza-and thio-Michael reactions in green aqueous media.

Chromatographic column separations of metal ions from their binary mixtures [Zinc (II)-Lead (II), Cadmium (II)-Lead (II), and Cadmium (II)-Zinc (II)] were achieved in tartaric acid media at optimized (Kd) values with a synthesized chelating ion exchange resin (AFR) derived from anthranilic acid-formaldehyde-resorcinol. The physico-chemical properties of this resin were also studied. The studies of total ion exchange capacity, effect of pH, and concentration for different metal ions were carried out. AFR resin was characterized by FTIR and elemental analysis techniques. The kinetic parameters (Ea) have been evaluated from the thermogravimetric data and the morphology of the resin was examined by SEM technique.

Chitosan is the most important derivative of chitin, the second most abundant biopolymer just after cellulose, which has received great attention because of its unique characteristics. Without doubt, its biomedical usages have gained more importance among the vast variety of chitosan applications owing to its good biocompatibility and biodegradability. In recent years, particular interest has been devoted to chitosan hydrogels as a promising alternative in competition with conventional sutures or bioadhesives. In the current work, we have investigated the effectiveness of chitosan hydrogel to stop bleeding and air leakaging of lung fistula. Polycationic chitosan was obtained with solubilization of chitosan powder in aqueous acidic media. Different parameters such as acid type and concentration, and degree of deacetylation (DD%) of chitosan, were altered to modify hydrogel properties including viscosity, pH, cohesive strength, and tissue bioadhesiveness. In vivo experiments have been conducted on sheep models which provide a convenient way to evaluate the efficacy of prepared samples. The lung was punctured in distinctive geometries and hydrogel then injected on. Bioadhesive strength as well as irritant effects were discussed. Samples with higher degree of deacetylation, includig Chs-16 (DD%=99, MW=230,000) and Chs-19 (DD% = 98, MW=300,000) that were dissolved in lactic media showed best sealing effect. Further studies are now conducted to optimize the sealing properties of chitosan based hydrogels.

The atom transfer radical polymerization of methyl acrylate (MA) with poly vinylacetate telomer (PVAc-CCl3) as a macroinitiator and CuCl/N,N,N',N',N''- pentamethyldiethylenetriamine (PMDETA) as a catalyst was successfully carried out in the bulk. The reaction temperature had a direct effect on the conversion and apparent propagation rate constant (Kpapp) of MA polymerization reaction. In this study the apparent enthalpy of activation and enthalpy of equilibrium are 83.68 and 65.98 kJ/mol, respectively. for this polymerization reaction. In a similar polymerization system, PVAc-CCl3 macroinitiators were used with several molecular weights, it was found that the rate of polymerization was independent of molecular weight of the macroinitiator, but the percentage of telomer used had a direct effect on the Kpapp of this polymerization. In all reactions studied the first order kinetics showed a linear dependence, indicating a constant number of propagating species during the polymerization. Kelen-Tüdös and Fineman-Ross linear methods were used to determine monomers chemical reactivity of methyl acrylate and methyl methacrylate in atom transfer radical polymerization. The synthesized block copolymers showed a relatively narrow molecular weight distribution (1.1<PDI<1.3) specific of the controlled polymerization reactions of ATRP. A broadening trend of PDI in block copolymers was observed with polymerization temperature. This work shows that it is possible to synthesis the novel block terpolymers of PVA c-b-poly (MA-co-MMA) with further narrowing in PDI which is shows that there is a chemical selectivity within the mechanism of ATRP.

Recently, it has been shown that the addition of a small quantity of nanoclay can greatly enhance the efficiency of low profile additives (LPAs) on volume shrinkage control of low profiled unsaturated polyester (UP)/styrene/LPA systems. In this study, however it was found that the organically-modified nanoclay (Cloisite 15A) can also affect the volume shrinkage control of non-low profiled UP/styrene systems. The effect of nanoclay on volume shrinkage of UP resin was investigated by an inhouse constructed shrinkage measurement apparatus. Experimental results revealed that the nanoclay somewhat decreases the volume change of UP/styrene system. The polymerization kinetics of the nanoclay filled UP systems was studied in a quasi-adiabatic reactor. The quasi-adiabatic exothermic measurements showed that, at higher nanoclay content, the reaction rate increased and the induction time decreased. The reduced viscosity measured by a rheometric dynamic analyzer. The gel time calculated by both quasi-adiabatic reactor and rheometric dynamic analyzer data. Results have showed that adding nanoclay into the UP/styrene mixture makes the onset of the viscosity rise happen much earlier which leads to a higher reaction rate, faster viscosity rise, and earlier gelation. It is clearly observed that measuring the gel time at different level of Cloisite 15A is similar to using rheometry and exothermic experiments.