Iranian Polymer Journal
Year:2004 | Volume:13 | Issue:4|Papers Count:10

A number of ethylene/propylene/diene elastomers (known as EPDM) were prepared in the presence of homogeneous VOCl3-Al2Et3Cl3 and indenyl, rac-Etlnd2ZrCl2-methylaluminoxane catalyst systems to compare their activity towards EPDM terpolymerization and their effects on the molecular weight distribution and the microstructure of the final products. 5-Ethyliden-2-norbornene (known as EBN) was used as the termonomer. Terpolymers prepared with the vanadium-based catalyst were of the higher molecular weight and more random in structure than those obtained with the zirconium catalyst. The latter catalyst system produced comparatively narrower molecular weight distribution. The loss in catalyst activity in presence of the non-conjugated diene was much higher than the anticipated amounts from kinetic parameters.

This study is concerned with the comparison of the properties and behaviour of two false-twist textured polyamide 6 yarns with filaments of circular and triangular cross-section. It was found that the ratio of the tension after and before the pin spindle (T2 /T1) and in other words friction between the yarns and pin spindle depends on the degree of packing and ups and downs on the yarn surface. For disc yarns, this does not seem to be the case and tension ratio is almost not affected by the ups and downs on the surface of the yarn contacting the friction surface. It was also found that the crimp contraction or stretchability of yarns with triangular filament cross-section was lower than the circular ones. This difference is considerably higher for disc type textured yarns. The lower crimp contraction of the triangular filament yarn can be related to its higher form factor than circular one leading to higher torsional and flexural rigidity.

In this paper, strength-generation mechanism of yarn interaction within woven fabrics is discussed and it is shown that the yarn pull-out test is an effective method to examine some of the mechanical properties of fabrics. The nature of internal frictional force is mainly related to yarn interaction at warp and weft crossing points. Since enzymatic hydrolysis removes most of surface fibres and pills and protruding fibres are mainly removed due to mechanical action during bio-polishing process, it is demonstrated that the finishing treatments especially bio-polishing cause the yarn interactions to be localized mainly on the weft and warp crossing points. Also, it was observed that the correlation between static and dynamic pull-out forces, intensity-generating mechanism of yarn interaction within the fabric, and the fabric mechanical properties (fabric shear hystersis and bending hystersis) are improved by bio-polishing.

CEHEP and HEP sequences were used for bleaching of rice straw organosolv pulps and the effects of these sequences were investigated on optical (brightness and opacity) and mechanical (tear index, burst index and breaking length) properties of produced paper sheets. Despite of the significant reduction in mechanical properties, brightness was increased so that it was suitable for writing and printing paper. CEHEP sequence had more increment on brightness and more decrement on mechanical properties than the HEP sequence. The catalytic soda organosolv pulping was used for the pulp production (delignification) from rice straw via batch process at high temperatures and high pressures. The catalytic pulping of rice straw was performed in ethanol-water mixtures (50 and 65% w/w) at various cooking times (150 and 180 min). The ratio of cooking liquor to dry mass of rice straw was 10:1 and the catalyst (soda) was 1(%) dry mass of rice straw.

Water soluble polymers are widely used in various industrial areas. Surface activity is also important for some applications in industry. In this study, a surface-active substance was synthesized by interaction of polyacrylic acid (PAA) with propylene oxide (PO). Polyacrylic acid was synthesized by radical polymerization of acrylic acid (AA) in toluene and under atmosphere of nitrogen. Oxypropylation reaction of PAA was carried out repeatedly for various initial reactant concentration and temperature values in order to investigate the kinetics of the oxypropylation reaction. The probable mechanism of “cooperative” character of oxypropylation reaction of PAA carboxylic groups was proposed on the basis of the obtained experimental data. The obtained compound from the reaction was characterized by a number of physico-chemical methods.

Both photo-and thermal initiated free-radical cross-linking copolymerization of methylmethacrylate and ethylene glycol dimethacrylate (EGDM) have been investigated in toluene at a monomer concentration of 3.5 molar and at 60°C and 27°C for azo and benzoin groups, respectively. The bifunctional initiator used was 4,4'-azo-bis-(4-cyanopentanoyl)-bisbenzoin (ACPB). Conversion of monomer and pendant vinyl groups and the size of the pregel polymers were measured as a function of the reaction time up to the onset of macrogelation. Approximately 97% of the pendant vinyl groups were found to be consumed by cyclization reactions. The fraction of units in cycles is independent of the EGDM concentration. As a result of the cyclization reactions , the accessibility of the radical centres and pendant vinyl groups for other polymer molecules is strongly reduced. Consequently, both termination and cross-linking reactions are controlled by the segmental diffusion of the polymer radicals. Calculations indicate a 1-2 orders of magnitude decrease in the average reactivity of pendant vinyls for intermolecular reactions compared to the monomeric vinyls. This drastic decrease in pendant reactivity is mainly responsible for the delay in the gel point. Contrary to gelation theories, the size distribution curves of the pregel polymers change from monomodal to bimodal distributions as polymerization proceeds. This finding confirms the coagulation-type gelation mechanism of compact primary particles and indicates the polydispersity shape of the pregel polymers. Virtually we observed the same kinetic behaviour in the MMA-EGDM polymer gel systems by bifunctional initiator, as the same way we had found before with photo and thermal initiators.

N-p-Anisylmaleimide (NPAMI) was copolymerized with methylmethacrylate (MMA) to derive copolymaleimide-acrylate poly(NPAMI-MMA). The effects of different free radical initiators: azobisisobutyronitrile (AIBN), benzoyl peroxide and hydrogen peroxide; and of various solvents: p-dioxane (DOX), tetrahydrofuran (THF), cyclohexanone (CHN), dimethylformamide (DMF) and ethyl acetate (EA) have been investigated to find the most suitable initiator-solvent system. Further, employing the equimolar ratio of NPAMI, MMA and acrylic acid (AA) or methacrylic acid (MAA) and using AIBN/DOX system two terpolymers poly(NPAMI-MMA-MAA) and poly(NPAMI-MMA-AA) were synthesized. Density measurement, solubility test, elemental analysis, IR, 1H NMR and 13C-NMR spectroscopic methods were used to characterize these polymer samples. The thermal behaviour was studied by TGA and DSC techniques.

New aromatic poly(amide-imide-urea)s with enhanced thermal stability and high inherent viscosities were synthesized from a new bis(4-trimellitimidophenyl) urea (I) and aromatic diamines. The bis(4-trimellitimidophenyl) urea (I) was readily obtained by the condensation reaction of bis(4-aminophenyl) urea with trimellitic anhydride. Polymers were prepared by direct polycondensation reaction using triphenyl phosphite in N-methyl-2-pyrrolidone (NMP)/pyridine solution containing dissolved CaCl2. The obtained poly(amide-imide-urea)s showed high thermostability. Their decomposition temperatures at 10% weight loss in nitrogen atmosphere were above 515 C and the anaerobic char yield at 800?C ranged from 45 to 65%. Almost all the poly(amide-imide-urea)s showed high glass transition temperature above 205 C by differential scanning calorimetry (DSC) measurements. These polymers were readily soluble in various organic solvents and could be cast into transparent, tough, and flexible films.

The phenomena of wall slip and elastic swell (extrudate swell or die swell) of a tyre tread compound during its flow through a capillary die and the effect of process conditions on them were investigated using a torque driven capillary rheometer. For this purpose, the capillary dies were made up from smooth stainless steel (DKP316) with constant length and various radii. The behaviour of shear stress and shear rate for compound flowing through capillary die were determined with the assumption of Bagley and Rabinowitsch corrections and calculating the slip coefficient (β). The wall shear stress dependency of the wall slip coefficient, β, was also calculated at various temperatures (80, 100, 120°C). The results showed that β increased linearly with wall shear stress and decreased with temperature. So using β at different conditions, the corrected rheological parameters in various temperatures and capillary die radii were calculated and the flow curves were then plotted. It was also shown that the elastic swell (B) depended on L/D of capillaries and increased by decreasing die diameter because of the increase in the extensional deformation at the die entrance. The elastic swell decreased with the increase of temperature.

Thermotropic copolyesters containing an isophthalate unit and mesogenic 4,4'-bis(w-hydroxyalkyloxy) biphenyls with different numbers of methylene units have been synthesized by melt polymerization. The effect of monomer structure and copolymer composition on liquid crystallinity has been studied on the prepared copolymers from isophthaloyl chloride, terephthaloyl chloride, and mesogenic 4,4'-bis(w-hydroxyalkyloxy) biphenyl (n=4,6) and it is compared with that of the analogous homopolymers. Our finding shows that high contents of terephthalic acid depend on spacer type have deleterious effects on liquid crystallinity. All of the obtained compounds were characterized by conventional spectroscopic methods.