Iranian Polymer Journal
Year:2004 | Volume:13 | Issue:2|Papers Count:9

Zinc salts of ethyl, isopropyl and butyl xanthates were prepared in the laboratory. The effect of these xanthates with zinc diethyldithiocarbamate (ZDC) on the vulcanization of HAF filled NR compound has been studied at different temperatures. The rubber compounds with the three xanthate accelerators and ZDC were cured at various temperatures from 60°C–150°C. The sheets were moulded and properties such as tensile strength, tear strength, cross-link density, elongation-at-break, compression set, heat build up, abrasion resistance, flex resistance etc. were evaluated. The properties showed that zinc xanthate/ZDC accelerator combination has positive synergistic effect on the mechanical properties of NR compounds. The curing of HAF filled NR compound containing zinc xanthate/ZDC is slightly slower than the curing of the corresponding gum compounds. It is seen that, by gradually increasing the amount of the accelerator, the cure time of black filled NR compound can be made equal to that of the gum compound.

Seven new optically active poly(amide-imide)s (3a-g) were synthesized by microwave assisted polycondensation of N,N´-(Pyromellitoyl)-bis-L-alanine diacid chloride (1) with seven different derivatives of tetrahydropyrimidinone and tetrahydro-2-thioxopyrimidine compounds (2a-g) by using a domestic microwave oven. The polycondensation reactions were carried out in the presence of a small amount of a polar organic medium that acts as a primary microwave absorber. Suitable organic media was o-cresol. The polycondensation proceeded rapidly, compared with the conventional melt polycondensation and solution polycondensation and was almost completed within 10 minute giving a series of poly(amide-imide)s (3a-g) with inherent viscosities about 0.22-0.42 dL/g. The resulting poly(amide-imide)s were obtained in high yield and were optically active and thermally stable. All of the above compounds were fully characterized by means of FT-IR spectroscopy, elemental analyses, inherent viscosity (ηinh), solubilities test and specific rotation. Thermal properties of the poly(amide-imide)s were investigated using thermal gravimetric analysis (TGA).

Effect of the blends of different polyethylenes (LDPE=low-density polyethylene, LLDPE=linear low density polyethylene and HDPE=high density polyethylene) and rubbers (PBR= polybutadine rubber, SBR=styrene butadiene random copolymer, NR=natural rubber and SEBS=styrene-ethylene-butylene-styrene block copolymer) on bitumen properties was investigated. PBR-PE blends form a physical network in bitumen medium, whereas their SBR, NR and SEBS counterparts do not. The properties of the resulting bituminous blends are comparable with those of SEBS blends. LLDPE shows a higher rate of effectiveness on bitumen properties as compared with other polyethylenes. SBR blends show a better elastic recovery and film forming properties. Addition of heavy vacuum slops (HVS) oil into the ternary blends of rubber-PE-Bitumen results in rubber inclusions volumes. The rubber swelling increases as HVS oil concentration increases. HVS oil concentration could be adjusted depending on the designed performance grade (PG). SBR-PE blends found to be the most effective blends on bitumen properties.

In this research, producing a particulate conductive composite is being investigated. The composites are made of ethylene-vinyl acetate (EVA) and polyvinyl choloride (PVC) as matrix and graphite as filler. There are two different procedures applied: dissolving the polymer matrix in a suitable solvent and then add the filler to the solution, which does not work out for PVC because phase separation takes place between the melt mixing of the matrix and filler. The solvents used were toluene for EVA and THF for PVC. The composites were prepared in different volume fractions. After having the composites prepared they were compression moulded into the shape of dumbbells when two extreme sides were covered with a conductive coating. Electrical resistance of the samples before and during applying the strain was measured. Then, gauge factor (strain sensitivity factor) for each sample was calculated and finally the sample with higher gauge factor was chosen. .

The structure-property relationships in segmented-chain liquid crystalline polyesters based upon diphenols and aliphatic dibasic acid chloride was studied by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). Two mesogenic monomers were synthesized by direct esterification of hydroquinone with p-hydroxybenzoic acid in a convenient method. The well-characterized mesogenic monomers incorporated into segmented liquid crystalline polyesters with short linear chain and COOH-end groups. The structure of the monomers and the polymers was studied by FTIR,1 H NMR, MS. The temperature of transition between the phases and, as a consequence, the range of mesomorphism is highly dependent upon the molecular weight of the polyesters and the length of the mesogenic monomers.

In this study chitin was extracted from Persian Gulf shrimp's shell and deacetylation was carried out with 5 wt% NaOH at 90°C in a nitrogen atmosphere.Chitosan was prepared with high degree of deacetylation. The effect of deacetylation conditions in the multistage alkali treatments in comparison with continuous alkali treatment was studied. Chitosan’s nitrogen content and the extent of degree of deacetylation were measured using FTIR spectroscopy and elemental analysis (CHNO analysis) respectively. Significant differences observed between multistage and single stage alkali treatments on the nitrogen content and degree of deacetylation of the resultant chitosan. In the multistage treatments deacetylation of chitin reached to 90.9% that is effective to improve biomedical application of the resultant chitosan. The morphological effect of the chitin macromolecules chains and the alkali agent concentration as a driving force for promotion of deacetylation reaction were studied. Our results showed that the ability of NaOH diffusion into chitin macromolecules was highly decreased in the continuous treatment while in the multistage treatments the degree of deacetylation was enhanced due to more diffusion of the alkali agent into chitin macromolecules and many acetamide sites on these chains were subjected to alkali treatments.

There are many different methods for production of peroxide cross-linked polyethylene in the form of pipe, cable, sheet, etc. In this study shear head as a new approach method was applied for continuous cross-linking of low density polyethylene. The shear head was designed and constructed and coupled with a modular single screw extruder.The screws of shear head were Maddock, Egan and Troester with 0.4mm gap. The highest increment in temperature of compound was around 30°C in shear head for Maddock screw. Cross-linking was confirmed by gel fraction and mechanical properties tests. The highest gel fraction was related to 2 wt% of dicumyl peroxide (DCP) and Maddock screw. With increasing of DCP tensile strength and elongation at-break increased. The highest increment in tensile strength belonged to samples with above 70% gel fraction (2 wt% DCP and Maddock screw). Due to stretching and chain orientation of polymer compound in shear head (by high speed rotation of screw in short die land) these properties increased continuously to high gel fraction (90 %). If this method were coupled with other commercialized methods, the efficiency of cross-linking reaction of low density polyethylene and the quality of product would be better. In such case the energy consumption would also be lowered and the length of the production lines would be considerable shortened than the current methods.

Two-step investigation was made to determine antioxidant properties of fullerenes C60/C70 and C70 in polystyrene. The antioxidative activity of fullerenes C60/C70 has been studied by model reaction of the initiated oxidation of styrene and then in accelerated tests of C60/C70 and C70 mixtures with polystyrene. It was established that the initiation and oxidation rates of the model reaction is substantially reduced in the presence of C60/C70. The rate constant for the addition of styryl radicals to C60/C70 was determined as K(333 K) = (9.0 ± 1.5).107 M-1 s-1. By differential scanning calorimetry (DSC) and thermogravimetry (TGA) it was demonstrated that fullerenes show a stabilizing effect comparable with the influence of the sterically-hindered phenol Irganox 1010 and amine Agerite White. The suggestion was made that the retarding effect of fullerenes is connected with its interaction with macroradicals R. leading to formation of less active compounds.

Inorganic polymeric materials comprise a very unique area of polymer science. These macromolecule which contain inorganic elements as part of their main chain structure or as pendent group, attract considerable attantion as speciality materials with unique properties and novel applications. Two main classes of these compounds, inorganic and organometallic polymers, which represent a growing field of research has found broad diverse applications. As, organic and inorganic components with countless combinations, which are found in these classes of polymers, they offer a wide range of interesting properties and novel applications. In this paper, the main properties of inorganic and organometallic polymers are discussed on the basis of their structural features, and some examples of the novel applications of these materials are presented.