Iranian polymer journal
Volume:15 Issue: 9, 2006

Zein (prolamin of corn) has good film forming properties. The pure zein film is very brittle and plasticizers can improve its mechanical and film making properties and represses its permeability to gases. Polyols are natural plasticizers for food biopolymers. In this research, three types of polyols (sorbitol, manitol, and glycerol) were used as plasticizers and the water vapour permeability (WVP), contact angle and microstructure of different zein films were studied. The pure zein film had high WVP and adding glycerol and sorbitol by 0.7 g/g zein lowered WVP but this effect was not observed in films containing manitol. The films containing glycerol had the lowest WVP. The zein films containing glycerol had the highest water contact angle compared with the plasticized films. The pure zein films and the films containing manitol had the higher critical surface tension of wetting (γc) than the films containing glycerol and sorbitol. Adding polyols to zein films increased the surface tension of the zein films. In the unplasticized zein films and those plasticized by manitol, loose structural integrity and a lot of cavities and voids have been detected. The films plasticized by glycerol had smooth glassy surface.

The direct polycondensation of dicarboxylic acids with diols using diphenylammonium triflate (DPAT) as catalyst is described. We investigated the solvent effect on molecular weight in the polyesterification reactions, influence of the reaction period for a fixed catalyst amount. Also, to determine the effect of catalyst the reaction between succinic acid and 1,6-hexanediol using different catalyst amounts for the constant time was examined. Different types of polyesters were synthesized via solution polycondensation using DPAT catalyst. Molecular weights of the synthesized polymers were determined using GPC and an Ubbelohde viscosimeter. It is found that the molecular weights of polyhexamethylene succinate, polyhexamethylene adipate, polydecamethylene adipate, polyhexamethylene sebecate, polybutylene adipate and polyethylene adipate, are 12900 g/mol, 13300 g/mol, 8400 g/mol, 8100 g/mol, 2750 g/mol and 2600 g/mol, respectively. The polyesters were characterized by 1H NMR and FTIR spectroscopy. DPAT gave the highest yields of polyhexamethylene succinate and polydecamethylene adipate (93%). It is found that toluene is the best solvent, an appropriate reaction period is 12 h and the optimum catalyst amount is 0.25 mol% for polyesterification. DPAT is efficient for the synthesis of aliphatic polyesters under mild conditions because of the polycondensation, it was revealed that DPAT seems to catalyze not only the esterification but also etherification is catalyzed as a side reaction.

The objectives of this study are to evaluate the effects of a hydrophilic polymer (Superab A200) on the growth indices of an ornamental plant (Cupressus arizonica) under reduced irrigation regimes in the field and on the soil water retention curve in a laboratory. The RETC computer programme was used for obtaining optimum model parameters. Superab A200 in two levels, 4 and 6 g/kg, were mixed with two soil textures of clay and sandy loam, respectively. The results of the soil water retention model showed that, Superab A200 caused the residual water content (θr) and saturated water content (θs) to increase. Air entry value (hb) was observed to decrease in the clay and increase in the sandy loam. The results of the statistical analysis showed that there is a significant difference between samples containing Superab A200 and without hydrophilic polymer (the control) and the levels of polymer application. Available water content increases 2.3 fold of the control at maximum, with hydrophilic polymers application of 6 g/kg in sandy loam soil. The field trials were conducted as a split plot on the random complete blocks design in which the main plot treatments were two irrigation regimes consisting 33% and 66% evapotranspiration (ETc) and two sub-plot treatments were soils containing 4 and 6 g/kg hydrogel, respectively. The control blocks had no hydrophilic polymer and irrigated with 100% ETc. The results indicated that plant height, shoot diameter and length of green, are the same in treatments containing 4 and 6 g/kg Superab A200 and receiving irrigation water 66% ETc with the control. Thus, application of 4 and 6 g/kg hydrophilic polymer reduced the required water to 1/3 of the control. Application of Superab A200 can result in significant reduction in the required irrigation frequency particularly for light soil texture. This is an important issue in arid and semi-arid regions of the world.

Polyacrylonitrile (PAN) was converted to polyacrylonitrile-monoethanolamine (PAN-MEA), through reaction with 2-aminoethanol (MEA) in a simple and one step method. The obtained polymer was hydrosoluble and hydroxy-functionalized. The polymer-metal complexes were prepared in an aqueous solution in different pHs via two different methods, namely precipitation and dialysis tube. In all cases, increasing the pH values raised metal sorption capacities of PAN-MEA. The maximum metal sorption capacity was obtained for Fe(III) at pH 3 with 100.7 mg and the minimum for Ni(II) at pH 2 with 22.34 mg per one gram PAN-MEA metal complex. The selectivity of polymer for the adsorption of Fe(III) is greater than that of Cu(II) in the mixture of these ions and in the mixture of Zn(II) and Ni(II) the adsorption is greater for Zn(II). FTIR Spectra of polymer-metal complexes showed wavenumber shifts due to metal complex formation. UV-Vis spectroscopy studies showed the presence of metal ions in polymer-metal complexes due to the absorption in the region between 400 nm to 800 nm. Also, thermal gravimetry analysis of polymer-metal complexes confirmed the presence of metal in the final polymer complexes.

Aseries of aqueous anionic polyurethane dispersions with ionic groups in the soft segments were synthesized from a polyether glycol, maleic anhydride modified castor oil, isophorone diisocyanate, and α,α-dimethylol propionic acid according to the prepolymer mixing process. Samples were neutralized by the addition of triethylamine. The reaction mixture was dispersed in water and the polymer chains were extended with ethylene diamine. The effect of NCO/OH molar ratio on the structure and properties of these polyurethanes were characterized by particle size analyzer, DSC, TG/DTG, IR, WAXD and tensile tester, etc. Particle size distribution becomes broader and the average particle diameter increases as NCO/OH molar ratio increases, which is mainly attributed to the decrease in chain flexibility and increase in viscosity of the dispersed particles. IR Study shows that the hydrogen bonding increases with increasing NCO/OH molar ratio. DSC Results identify that the phase mixing increases when some ionic groups were incorporated in soft segments and phase separation increases as NCO/OH molar ratio increases. TG/DTG Results show better thermostability under higher NCO/OH molar ratio that can be attributed to forming thermostable urea groups and more intermolecular hydrogen bonding. Broad scattering halos of WAXD graphs imply that all the samples are amorphous. The tensile strength and hardness of the polyurethane films increase with increasing NCO/OH molar ratio.

Processing of polymer blends is mainly controlled by the behaviour of their components, interfacial area and strength. Therefore, many experimental and theoretical investigations have been devoted to elucidating their basic governing principles. Nonetheless, there are only limited data in the literature about the effect of compatibilizers on the rheological properties of blends. The resistance-to-flow of low density polyethylene/plasticized starch blend and their compatibilized versions with poly(ethylene-r-vinyl acetate), maleated poly(styrene-ethylene-butadiene-styrene) and maleated polyethylene was investigated with a capillary rheometer at different temperatures. Furthermore, the melt elasticity enhancement of the aforementioned alloys was compared with their non-compatibilized polyethylene/thermoplastic starch blend via rheomechanical spectroscopy at 190ºC and 500 Hz as an index of their interfacial strength. The results showed that by lowering the temperature of the melt alloys, the compatibilizer was directed toward interfacial localization and led to concomitant elasticity enhancement in comparison with their virgin blends. In addition, the resistanceto- flow of the blend and their alloys through capillary rheometer were enhanced and distinctively differentiated. This was attributed to the blend positive χ parameter which pushes compatibilizers localization at the interface with different adsorption densities and conformational resistance against flow of the system. In other words, a quasi core/shell structure formation at the dispersed phase/matrix interface was proposed as the origin of resistive capillary flow, leading to a viscoelastic loss enhancement. In analogy with Gent-Schultz equation governing the joint adhesion energy of polymers, the energy loss during capillary flow of a multicomponent blend was correlated for the first time to their interfacial strength. Interestingly, the calculated energy loss for the investigated melt blend and its compatibilized alloys in capillary flow was proportional to the solid state deformation loss during peeling of a corresponding joint interfaces reported by our group.

The reinforcing effect of chopped rice husk (CRH) into polypropylene has been studied. Composites containing different amounts of CRH with 0 to 40 parts per hundred part of polymer (php) were prepared using a co-rotating twin screw extruder and characterized by mechanical properties and also water absorption. In order to increase the interphase adhesion, polypropylene grafted with maleic anhydride was added as a coupling agent to all the composites studied. It was found that the tensile and flexural modulus of the composites containing 40 php of CRH increased approximately by 33% and 100%, respectively. The results also showed that while flexural strength was moderately improved by increasing of CRH into the matrix, elongation-at-break and energy-at-break decreased dramatically. A reasonable adhesion between the main components was also observed by examining the scanning electron micrographs. Water absorption experiments showed that although the diffusion coefficient increased with CRH loading, all the composites followed case I diffusion.