Iranian polymer journal
Volume:16 Issue: 9, 2007

Synthesis of polyethylene terephthalate (PET) in laboratory is a challenging task due to high reaction temperature up to 280ºC and high pressure in esterification step and low vacuum in polycondensation step. In this research, synthesis of PET, in a laboratory size unit was studied via direct esterification of terephthalic acid and ethylene glycol. Antimony oxide was added as catalyst for polycondensation. Mathematical model of process is presented based on the mass balance of different species such as acid and hydroxyl end groups, water output, diester groups during both esterification and polycondensation steps. Derived governing equations were integrated numerically using Runge-Kutta method. Reacting mixture mass variation was included in the model. Comparison of experimental and simulation results shows promising and good agreement. Hence, the model could be used as a powerful tool for engineering process. The model was applied to study different aspects of polymerization process.

The physical protection by microencapsulation is a new method to increase the survival of probiotic bacteria. The size of beads containing probiotics has significant effect on organoleptic properties of foods. Reduction of the sphere size to less than 100 μm would be advantageous for texture considerations and allow direct addition of encapsulated probiotics to a large number of foods. In microencapsulation process, Tween 80 can be replaced by lecithin in order to prevent its detrimental effect on the viability of probiotic bacteria. Calcium alginate as an edible polymer was used for the microencapsulation of probiotic bacteria by emulsion technique. A modified microencapsulation method based on emulsion technique was investigated in this study to produce microcapsules with diameters below 100 μm. A completely randomized design (CRD) experiment was applied in triplicates to evaluate the effect of surfactant (0, 0.2, 0.4 and 1% lecithin with 0.2% Tween 80 as control) and calcium chloride solution (100 and 200 mL) on the microencapsulation process yield of microencapsulated Lactobacillus casei. Microsphere characterization was performed by scanning electron microscopy (SEM). The microencapsulation process yield increased with increasing the volume of calcium chloride solution and it decreased with increasing the amount of lecithin. The highest microencapsulation process yield was obtained whe 0.2% Tween 80 was used as surfactant. The shape of beads was spherical and their mean diameter was 17.80±3.55 μm.

Nucleophilic substitution reaction of two moles of benzilic acid with terephthaloyl chloride in the presence of triethylamine hydrochloride yielded terephthalic acid bis-(carboxydiphenyl methyl)ester (TBE) as a new monomer for the preparation of polyesters. This diester-diacid (TBE) was converted to its acid chloride derivative, terephthalic acid bis-(chlorocarbonyldiphenyl methyl)ester (TBECl), using thionyl chloride. Polymerization reactions of TBECl with different aromatic diols including hydroquinone, 1,5-dihydroxy naphthalene, phenolphthalein, 1,4-dihydroxy anthraquinone, 1,8-dihydroxy anthraquinone, and bisphenol A in the presence of triethylamine hydrochloride using high temperature solution polycondensation method resulted in different polyesters. All the polymers were characterized and their physical and thermal properties such as thermal behaviour, thermal stability, solution viscosity, and solubility behaviour were studied. Polymers showed good thermal stability while the presence of bulky groups improved their solubility.

The polymeric ligand (resin) was prepared from 2-hydroxy-4-methoxybenzophenone with 1,2-propylene glycol in presence of polyphosphoric acid as a catalyst at 160ºC for 13 h. The poly[(2-hydroxy-4-methoxybenzophenone) 1,2- propylene glycol] (HMBP-1,2-PG) form 1:2 metal:ligand chelates with La(III), Pr(III), Nd(III), Sm(III), Gd(III), Tb(III) and Dy(III). The polymeric ligand and its polychelates were characterized on the basis of elemental analyses, electronic spectra, magnetic susceptibilities, IR spectroscopy, NMR and thermogravimetric analyses. The molecular weight was determined using number average molecular weight (Mn) by vapour pressure osmometry method. All the polychelates are paramagnetic in nature except La(III) which is diamagnetic. Ion-exchange studies at different electrolyte concentrations, pH and rate have been carried out for lanthanides (III) metal ions.

Polypropylene (PP) as a linear resin has low melt strength. The melt strength of polymer is the main feature for the success of low density extrusion foam. Use of a high melt strength such as branched PP (Br-PP), is required to achieve large volume expansion by preventing cell coalescence and gas loss. In this paper, the effects of long chain branched polypropylene on melt elasticity and volume expansion in the extrusion process of PP ternary blends are investigated. The equilibrium creep compliance (Je0) and damping factor (tan δ) of melts were evaluated as melt elasticity index by oscillation rheometry. To setup the extrusion foaming process, the Haake 25 L/D single-screw extruder was improved by design and manufacturing to a special 38 L/D screw with a long mixing zone. Extrusion temperatures were optimized to reach a stable foaming process. The consistency of process pressure as a measure of foam extrusion system stability was evaluated. The cell population density and expansion ratio were determined for foam samples. The effects of the blowing agent (BA) on the amount of pressure build-up were measured at various branched PP levels in the blend. The experiments showed that, by increasing the branched PP, Je0 increases, and tan δ decreases, which is an evidence of improved melt elasticity. The maximum expansion ratio for the blends was achieved at about 55% of branched PP resins and 20% of B.A. The results also showed that, by increasing the branched PP, the cell population density increases to a maximum of 7.5×106 (cell/cm3) and no significant increase was observed at higher branched PP levels.

Due to rapid increase in consumption rate of EPDM in rubber industry in the last decade, recycling and reusing of this rubber have attractive and extensive studies. lending with the other polymers can be an efficient method for reusing of ecycled EPDM. In this study, ternary blends of polypropylene (PP), high density polyethylene HDPE) and mechano-chemical devulcanized EPDM (D-EPDM) were prepared sing a laboratory twin-screw extruder. Three levels of D-EPDM (20, 40, 60 t%) at constant concentration of HDPE (20 wt%) were used. Sulphur dynamic vulcanization as applied on the samples. Mechanical properties such as: tensile properties, ompression set, hardness, impact resistance and morphology of samples ere studied and compared to samples containing virgin EPDM. Tensile strength and ompression set decreased with increase in both D-EPDM and EPDM content in the ernary blend. Dynamic vulcanization improved the mechanical properties and its ffect on the samples containing D-EPDM was more considerable. The dominant morphology f both ternary blends was the separate dispersion of HDPE and EPDM (or -EPDM) in the PP matrix. The D-EPDM formed droplets dispersed in PP matrix similar o the virgin EPDM.

The modified chlorinated polypropylene (CPP) was prepared upon chlorination of PP, initiated by benzoyl peroxide (BPO), grafted with methyl methacrylate (MMA), butyl acrylate (BA) and methacrylic acid (MAA) as graft monomers by tetrabasic graft copolymerization. The modified CPP was characterized by FTIR. The effects of reaction temperature, reaction time, initiator concentration and monomers concentration on the graft degree were investigated. The optimum reaction condition was determined as follows: reaction temperature 105ºC, reaction time 5 h and the mass ratio of CPP/monomers/BPO = 1:0.3:0.03. The adhesive power of graft copolymer on polypropylene sheets was 100%. The solubility parameter and solvent properties of CPP and modified CPP were systematically studied to characterize their polar change. The solubility results of CPP and modified CPP in various solvents indicated that the polarity of CPP gradually increased with grafting monomers onto its chain, which would cause the moderately hydrogen bonded solvents for polymers improving more with an increase in monomers graft content, whereas that of poorly and strongly hydrogen bonded solvents for polymers show no clear change. This is consistent with the results of their dilution ratio and solubility parameter.