Iranian Polymer Journal
Year:2005 | Volume:14 | Issue:5 (59)|Papers Count:10

In the presence of H2O2, H2O2 + Fe3, NaOCl, OH + O2 oxidants, 1,3-benzenediol (BD) enters into reaction of oxidative polycondensation and forms the oligomer product, including dihydrooxyphenylene links. The kinetic regularities of BD oxidative polycondensation with oxygen in the alkaline medium have been studied by volumetric and EPR methods. It has been established that the reaction is of a first order both in terms of monomer and alkali. In the reaction course the quintiplet EPR signals have been registered, each line of which is faintly split into a triplet that has been assigned to the dimeric radical. It has been established that BD oligomer oxidation with oxygen in the alkaline medium proceeds without an induction period and has a first order on concentration of dihydrooxyphenylene-linked anions. At the same time, the accumulation of relatively stable macroaroxylic radicals has been observed. The mechanism of 1,3-BD oxidative polycondensation has been suggested, including the stages of single-electron oxidation of BD anion into oxyphenoxyl radicals and recombination of their resonance forms.

The effects of differently functionalized polypropylene (PP) and styrene-ethylene-butene-styrene copolymer (SEBS) on different properties of stretched-extruded films of PP/EVOH blend were examined. The effect of melt stretching after die was also studied. The stretched films of the original and polymer g diethyl maleate (DEM) modified blends showed laminar morphology whereas, their maleic anhydride (MA) functionalized counterparts showed fibrillar morphology. Rheology of the neat polymers along with their straight and compatibilized blends was studied to assess the quality of mixing under the actual conditions of blending in a counter-rotating twin-screw extruder to control and retain laminar morphology. Differential scanning calorimetry (DSC) tests showed a higher rate of interactions in the case polymer g MA modified blends. The SEBS-modified blends showed a lower elasticity at low temperatures. Mechanical properties were improved for almost all modified blends. SEM Micrographs revealed that as a result of melt-stretching a finely dispersed EVOH phase in PP matrix was obtained in the case of polymer-g-MA compatibilizer, whereas a laminar one was obtained in the case of polymer-g-DEM compatibilizer. The lowest permeability to oxygen gas observed for DEM-grafted polymers. The SEBS g DEM modified blends showed a barrier performance 90% better than that of pure matrix (PP) and 60% better than that of the original stretched blend.

In this study, polysulphone (PS) membranes were prepared from quaternary systems containing N,N´-dimethylacetamide (DMAc) as solvent, polyvinylpyrrolidone (PVP) as constant additive and acetic acid, acetone and formamide as variable additives. Phase inversion via immersion precipitation was employed for manufacturing of membranes. The prepared films were immersed in the mixture of pure water and 2-propanol (30/70 vol %) as non-solvent. The morphology and performance of the prepared membranes were investigated by scanning electron microscopy (SEM) and separation experiments using milk as the feed. The porosity of the prepared membrane was slightly increased with addition of acetic acid due to faster exchange rate between solvent and non-solvent. This would result in a minor increase in flux. The presence of acetone and formamide in the casting solution declined the flux due to formation of membranes with denser skin layers. Evaporation and delay demixing are responsible for tighter membrane structures in the case of addition of acetone and formamide, respectively.

The effect of mechanical and physical properties of polymer matrices on stress amplification factors is studied in a composite monolayer. The lamina is subjected to an elliptical damaged zone of radii "a" and "b" while loaded at infinity by a force "P". The matrix takes both axial and shear loads. The ratio of a/b is allowed to vary in a range of 0 < a/b , to simulate almost a crack and a circular hole, for the two values of a 0 and a = b, respectively. Any reduction in stress amplification factor Kr, and peak shear stress in the matrix (Sxy)max, appears to well depend on the value of matrix to fibre volume fraction Vm/Vf, and their mechanical properties, as well as shape and size of the hole. For polypropylene and epoxy matrices, at a/b = 0.5 and r = 5, increasing Vm/Vf from 0.5 to 2.0 decreases (Sxy)max by 62% and 73%, respectively, while Kr is decreased by 17%.

Approximately 22% of waste from the oil palm industry consists of empty fruit bunch (EFB). This type of biomass along with a vast quantity of agricultural residues can be utilized in natural fibre-based composites. Previous studies on palm kernel oil have successfully turned it into a polyurethane polyol in producing natural oil-based polyurethane foam. The incorporation of different EFB fibre size at level of 5.5% of 45-56 µm, 4.5% of 100-160 µm and 2.5% of 200-315 µm in the foam has shown tremendous improvement in the mechanical properties of the composites compared to the control foam. The compressive strength increased by 11.1%, 11.6% and 29.1% for the 45-56 µm, 100-160 m and 200-315 µm fiber size, respectively. The 45-56 µm fibre size at 5.5% fibre loading showed the maximum compression strength and modulus. There is more tearing of cellular structure during expansion of the foams when larger size of fibres and larger amount of fibres are used. These lead to poor strength for the composites. Micrographs of the cellular structure of the EFB-filled polyurethane foam showed that the presence of the fibrous EFB of size 200-315 µm torn the cellular structure, whereas the powder form of EFB filled the struts of the cellular network and enhanced the strength of the cell's wall.

In order to prepare polyurethanes with improved thermal stability as well as proper processability, novel poly(ether-imide-urethane)s (PEIUs) were prepared by polycondensation reaction of a diisocyanate containing oxyethylene units and build-in imide rings with ethylene glycol (EG), diethylene glycol (DEG), triethylene glycol (TEG), respectively. Synthetic procedures for preparation of monomer and polymers were described. The properties of prepared polymers including thermal stability and thermal behaviour were studied by TGA and DSC methods. The investigation of results showed that co-presence of oxyethylene groups and imide structures in the polyurethane backbone can improve thermal stability and maintain processability of final polymers.

A novel redox system, potassium diperiodatocuprate(III) (DPC) sodium alginate(SA), was employed to initiate the graft copolymerization of methyl acrylate (MA) onto SA in alkali medium. The effects of reaction variables, such as the initiator concentration, the ratio of monomer to SA, the SA backbone concentration, as well as temperature and time, were investigated, and the grafting conditions were optimized. Graft copolymers with both high grafting efficiency and high percentage of grafting were obtained, which indicated that DPC-SA redox system is an efficient initiator for this graft copolymerization. The structures and the thermal stability of SA and SA g PMA were characterized by scanning electron microscope (SEM), infrared spectroscopy (IR) and thermogravimetric analysis (TGA). A mechanism is proposed to explain the generation of radicals and the initiation.

Because of the interdependency between molecular structure, rheological properties and material response during processing, the rheological properties of controlled-rheology polypropylene (CR-PP) are investigated. The reactive experiment is carried out in a modular self-wiping co-rotating twin-screw extruder. The initiator was dicumylperoxide (DCP). The concentration range of DCP was 0.02-0.6% by wt. The purpose of this study was to characterize the influence of peroxide degradation on rheological properties of polypropylene homopolymer. The results showed that rheological properties of PP change with peroxide degradation significantly. With increasing of peroxide concentration the complex viscosity ( h*) and torque decrease. Degraded resins had more Newtonian behaviour than original resins. Storage modulus (G’) and loss modulus (G”) decreased with peroxide concentration. Dissipation factor (tan d) and complex compliance (J*) increased with increasing DCP concentration.

Pyromellitic dianhydride (benzene-1,2,4,5-tetracarboxylic dianhydride) (1) was reacted with s-valine (2) in acetic acid and the resulting imide-acid [N,N'-(pyromellitoyl)-bis-s-valine] (4) was obtained in high yield. The compound (4) was converted to the N,N"-(pyromellitoyl)-bis-s-valine diacid chloride (5) by reaction with thionyl chloride. The polycondensation reaction of this diacid chloride with several aromatic diamines such as 1,4-phenylenediamine (6a), 4,4'-diaminodiphenyl methane (6b), 4,4'-diaminodiphenylsulphone (4,4'-sulphonyldianiline) (6c), 4,4'-diaminodiphenylether (6d), 2,4-diaminotoluene (6e), and 1,3-phenylenediamine (6f) was developed by using a domestic microwave oven in the presence of a small amount of a polar organic medium such as o-cresol and trimethylsilyl chloride as an activating agent for diamines. The polymerization reactions were also performed with two other methods: low-temperature and high-temperature solution polycondensation in the presence of trimethylsilyl chloride. The polymerization reactions proceeded fast and produced a series of optically active poly(amide-imide)s with good yield and moderate inherent viscosity of 0.25-0.43 dLg-1. One of the polymers (7b) showed high thermal resistance, the temperature of 5% weight loss for (7b) was 490°C and the residual weight at 600°C was 76%. All of the above polymers were fully characterized by IR, elemental analysis and specific rotation. Some structural characterizations and physical properties of these optically active poly(amide-imide)s are reported.

Isothermal crystallization kinetics, melting, structure and dynamic mechanical properties of a polypropylene (PP) random copolymer were studied. In order to study the effect of cooling rate on melting, two different cooling rates were applied to the samples. While water cooled samples revealed a broad single melting endotherm with  a-crystalline structure, the slow cooled samples showed a shoulder at lower temperature followed by a sharp melting endotherm and a mixture of a and g-crystalline phases. The effect of annealing on log E of the b-relaxation for the PP copolymer showed that the b-transition increased in intensity with increasing annealing temperature. No considerable difference was found in the activation enthalpy of relaxation, ΔH, values for the annealed compared to that of the water cooled samples using the Arrhenius equation. The isothermal crystallization kinetics was also studied for PP and the values of nucleation constant, Kg, and end-surface free energy of the crystal growth, se, were calculated using Lauritzen-Hofffman theory.