Iranian Polymer Journal
Year:2005 | Volume:14 | Issue:1 (55)|Papers Count:10

The subject of research was to assess the changes of properties of PA/PE packaging used for vacuum packing of lactic acid cheese. The influence of storage time, low temperature and the presence of lactic acid, produced by lactic fermentation bacteria, on the packaging features such as barrier properties towards water vapour and the degree of swelling are investigated. The assessment comprised a period of 14 days of cheese storage at temperature 4±2°C. At the same time, the tests in model conditions were conducted, consisting in storage of the packaging filled with solutions of lactic acid and distilled water at this temperature. The results showed that during period of 14 days of lactic acid cheese storage, an increase and a decrease in the permeability of PA/PE packaging coming from the stored cheese had occured. The results achieved from the study revealed a differentiation in the permeability and the degree of swelling of films coming from the cheese vacuum packing and packaging of bags filled with lactic acid. The study revealed the influence of even a small fluctuation of acidity on the level of changes in water vapour permeability of the film in model conditions. In packages taken from the refrigerated lactic acid cheese a significant dynamics was discovered in the increase in degree of swelling up to 7 days of storage in comparison to the results achieved in model conditions. The study shows that lactic acid is not the only factor determining the dynamics in the changes in permeability of the films during storage of the cheese.

Copolymerization of ethylene with propylene is carried out semi-continuously in toluene at atmospheric pressure and with various propylene/ethylene molar ratios. The polymerization temperature and cocatalyst/catalyst molar ratio were also varied in a wide range. Cp2ZrCl2/MAO System was used as catalyst. The viscosity average molecular weights of copolymers obtained were determined by measuring the intrinsic viscosity [ h] and application of the Mark-Houwink equation. The values of molecular weights were found to be dependent on operating conditions except on polymerization time in the range 5-30 min. increasing the polymerization temperature, propylene/ethylene and cocatalyst/catalyst molar ratios caused a continuous decrease in molecular weight. An important reason for this effect was shown to be accelerated chain transfer reactions.

The main objective of the present work was to study the effect of electron beam radiation on morphology stabilization and properties of polystyrene (PS) and poly vinyl methyl ether (PVME) blends both in single and two phase state, formed during spinodal decomposition process. Morphology development in particular, the domain growth rate of PVME dispersed phase was studied by using optical microscopy. The increasing rate of the interphase thickness resulted from interdiffusion of the samples produced by melt mixing was studied by differential scanning calorimetry (DSC). Radiochemistry and Flory-Rhener analysis were performed to determine the cross-link density of samples. The cross-link density of the interphase was measured using FTIR. A combination of thermal analysis techniques and physical properties measurement were used to study the effect of electron beam radiation dose on morphology stabilization due to interfacial modification and properties of both single and two phase polymer blends. The phase separation rate of PS/PVME miscible blend was found to be a power law type function of separation time with an exponent 0.77. The interphase growth rate was found to be about 3.5 nm min-1. It was demonstrated that the irradiation process can play a significant role in stabilization of PS/PVME blend morphology through immobilization of the interphase resulting from copolymerization and/or cross-linking.

The graft copolymerization of acrylic acid-methyl methacrylate (AA-MMA) onto poly(ethylene terephthalate) fibres has been studied using benzoyl peroxide (Bz2O2) as an initiator. The use of MMA as a comonomer increased the amount of AA introduced to the PET fibre up to 60% while the grafting of AA onto fibres alone gave low graft yields. This synergistic effect was found to be at its highest when an AA-MMA mixture having 30% AA (wt) was used. The grafting increased the diameter and moisture regain of the fibres. The results of dyeability with the disperse dye suggested that the diffusion into the fibre structure was moderately difficult when the graft yield reached 15-16%. The decomposition temperature values obtained from thermogravimetric analysis (TGA) showed that the thermal stability of poly (ethylene terephthalate) fibres decreased as a result of grafting.

The elastic properties of composite materials depend on diverse factors like the configuration of the laminates, constituent materials used, production method adopted, etc.. Hence, it is generally impossible to find these properties in standard tables or databases. The determination of material parameters of the complex materials, such as fibre reinforced composites, present serious difficulties when applying traditional test methods. To overcome these difficulties, an optimized search procedure, viz., genetic algorithm (GA), has been used to provide an additional technique of evaluating material properties from the measured natural frequencies. In general, GA performs directed random search through a given set of criteria. These criteria are required to be expressed in terms of objective function, which is usually referred to as a fitness function. This paper describes the capability, reliability and modelling of GA for indirect (non-destructive) prediction of mechanical properties regarding the model development in the finite element method (FEM) and the analytical formulation (exact solution). A few examples are presented to identify the material properties of homogeneous isotropic, orthotropic, and anisotropic plates with various stacking sequences, boundary conditions and aspect ratio for showing the ability and performance of this technique.

Vinylpyrrolidone-vinyl acetate (VP-VA) hydrophobically associating water-soluble copolymers were synthesized by free radical copolymerization. The effects of hydrophobic content and temperature on the viscosity and refractive index behaviour were investigated in detail. The critical concentration C* of the hydrophobically associating water-soluble copolymers was studied in the static state and in flowing solution by refractometry and viscosimetry, respectively. A dramatic decrease in solution viscosity of P(VP-VA) copolymers is observed with increasing the VA content at all temperatures. Also as the VA content in the copolymer increased, the solution refractive index of the copolymer decreased. The lowering in viscosity and refractive index reflects the contraction of the polymer coil because of intramolecular hydrophobic interactions. Variation of the dynamic and static critical concentration as a function of the temperature for P(VP-VA) copolymer in water has been investigated. The critical concentrations are lower when determined by refractive index measurements in the static state compared to the critical concentrations determined in the dynamic state using viscometer.

Polyaniline and polypyrrole are two conducting polymers that show ion-exchange properties. Due to their easy processibility, they can be used for surface modification of different substances. For instance they can be coated on silica particles. In this work anion-exchange properties of polyaniline-coated silica gel for some sulphonic acid anions such as, p-toluenesulphonic acid (PTSA) and methanesulphonic acid (MSA) were investigated qualitatively and quantitatively. Also the concentration effects of sulphonic acids and flow rates were investigated and kinetic experiments were performed. The column capacities for two acids were calculated and the accuracy of titrations with micropippet were confirmed with UV-Vis spectrophotomertric methods. Also the effect of ion exchange on conductivity of the polymer has been investigated.

One-step and two-step isothermal sheet-casting processes for producing poly(methyl methacrylate) (PMMA) sheets, based primarily on water and water-air systems, were studied and compared. The main objectives were: (1) to assess the optimal production time for each system in producing 3-mm thick PMMA sheets at various process conditions, and (2) to assess and compare the quality of the PMMA sheets obtained in terms of their mechanical integrity. It was found that the mechanical integrity of the PMMA sheets prepared by the two-step (water-air) isothermal process was much better than those prepared by the one-step (water) isothermal process, a direct result of the much higher ultimate percentage of monomer conversion.

Manufacture of polymeric composite magnets using isotropic NdFeB powder and different polymeric matrices; polyethylene glycol (PEG) as thermoplastic, epoxy as thermoset and styrene butadiene rubber (SBR) as elastomeric matrices have been studied in this work. Magnet powder was crushed mechanically and sorted in the particle sizes of 74-100, 2-10, and ≤1 microns. PEG nano-powder was also prepared via solvent/non-solvent method. The effects of particle size of the magnetic powder, polymer content, type of polymeric matrices and processing conditions on the magnetic properties of the product, i.e. residual magnetic induction (Br), coercive field strength (Hc), maximum energy product (BH)max and density were investigated. NdFeB-PEG permanent composite magnet made of magnetic powders with particle size range of 74-100mm and 5 php (the ratio of polymer loading per 100g magnetic powder) of PEG nano-powder was found to have the best magnetic properties. The measured properties of this product were as follows: final density; r=5.444 g/mL; Br=3.82 kG, Hc=8.415 kOe; (BH)max=14.454 MGOe.

Aliphatic dianhydride, Epiclon [3a,4,5,7a-tetrahydro-7-methyl-5-(tetrahydro-2,5-dioxo-3-furanyl)-1,3-isobenzofurandione] or [5-(2,5-dioxotetrahydrofurfuryl)-3-methyl-3-cyclohexyl-1,2-dicarboxylic acid anhydride] 1 was reacted with (s)-(+)-valine 2 in acetic acid and the resulting imide-acid 3 was obtained in high yield. The diacid chloride 4 was obtained from the reaction of 3 with thionyl chloride. The polycondensation reaction of diacid chloride 4 with several aromatic diamines such as 4,4-sulfonyldianiline 5a, 4,4-diaminodiphenylmethane 5b, 4,4-diaminodiphenylether 5c, p-phenylenediamine 5d, m-phenylenediamine 5e, 2,4-diaminotoluene 5f and 4,4-diaminobiphenyl 5g was developed by using a domestic microwave oven in the presence of a small amount of o-cresol. The polymerization reactions were also performed by two another methods: low temperature solution polycondensation and reflux conditions. A series of optically active poly(amide-imide)s with inherent viscosity of 0.13-0.32 dL/g were obtained. All of the above polymers were fully characterized by IR, elemental analysis and specific rotation techniques. Some structural characterizations and physical properties of these optically active poly(amide-imide)s are reported.