Iranian polymer journal
Volume:13 Issue: 3, 2004

Effects of filler (carbon black N110, silica and calcium carbonate) on the mechanical properties of natural rubber (NR) / linear low-density polyethylene (LLDPE) blends have been investigated. The blends were prepared by melt blending in a Haake Rheomix at 140°C, 15 min mixing time and a rotor speed of 50 rpm. Fillers were incorporated into the blends for 10-60 vol.%. The mechanical and physical properties of the blends were found dependent on the filler characterization. Swelling index and elongation- at-break showed a decreasing trend with increasing volume percent of filler loading in the blend. The significant changes in other physical properties included the gel content, and bound rubber of the samples indicated a strong interaction between the filler particles and polymer matrix. In conclusion, mean agglomerate particles size and polymer- filler interaction are the factors determining the mechanical and physical properties of NR/LLDPE blends.

Semi-continuous ethylene/propylene copolymerization is carried out at atmospheric pressure in toluene using Cp2ZrCl2/methylaluminoxane catalyst system. The effects of operating conditions including polymerization temperature, monomer feed composition, catalyst/cocatalyst molar ratio and reaction time (as mean residence time of the catalyst system in reactor) on kinetics of the copolymerization is investigated. The catalyst activity seems to increase with a decrease in catalyst concentration but decreasing with either propylene/ethylene molar ratio in feed or with reaction temperature. Chain transfer to propylene is shown to be the main reason for catalyst deactivation. The rate-time profiles are also shown to be of decaying character after passing a maximum indicating that the deactivation of active growing centre occurs as soon as the catalyst components are mixed in the presence of monomer mixture.

We have developed a pH- sensitive terpolymeric hydrogel system based on acrylamide, methacrylamide and acrylic acid by aqueous polymerization. The hydrogels exhibited a fair pH-dependent swelling behaviour with transition from Fickian (n = 0.43) to non-Fickian (n = 0.83) as the pH of the swelling medium varied from 1.0 to 8.0. The gel exhibited a number of swelling-deswelling cycles as the pH of the swelling medium was varied from 7.4 to 1.0. The equilibrium water uptake was found to increase with the amount of acrylic acid in the gels when studied in the media of pH 7.4. However, at pH 1.0, the degree of swelling was observed to decrease with monomer acid content. The activation energy for the swelling process, as calculated from the Arrehenius plot, was found to be 15.52 kJ mol-1. The gel also showed a good swelling response when put in the media of continuous varying pH. The minimum swelling in the acidic pH was explained on the basis of formation of complex structure within the gel network due to H-bonding interactions between -COOH and -CONH2 groups.

Linear aromatic polyester-amides (PEAs) have been synthesized by interfacial polycondensation of aliphatic and aromatic diacid chlorides (terephthaloyl chloride, isophthaloyl chloride, adipoyl chloride, and sebacoyl chloride) with aminophenols (p-aminophenol, m-aminophenol) in a chloroform/water system employing phase transfer catalyst. These polymers were characterized by elemental analysis, FTIR, 1H NMR, solubility studies, intrinsic viscosity and TGA analysis. The polyester-amides so obtained show good thermal stability.

To produce interlining fabric, various kinds of chemicals such as cross-linking, softening, stiffening and water repellent agents have been employed. In this work, a mixture of dimethylol dihydroxy ethylene urea (DMDHEU), polyvinyl acetate (PVAc) and some other resins were examined in special finishing of cotton for producing interlining cotton fabrics properties. Majority of cross-linking agents used today is DMDHEU based with low formaldehyde level. In order to elucidate the role of DMDHEU and PVAc in this specific finishing, some physical properties of fabric such as bending length, crease recovery angle, wettability time and thickness were studied with varying their concentrations. Both bending length, thickness and wettability time of cotton fabrics increased on increasing PVAc and DMDHEU concentrations. But, crease recovery angle decreased on increasing PVAc concentration and on the contrary increasing DMDHEU concentration improved the crease recovery angle.

Brominated flame-retardants are one of the common and efficient groups in producing flame retardant plastics, such as high impact polystyrene. Antimony trioxide is often used as a synergistic agent for halogenated flame-retardants. Aluminium trihydrate (ATH), also is a primitive additive for making flame retardant plastics but no report exists on synergistic effect of this compound in presence of brominated flame-retardant. In this research, the synergistic effect of Sb2O3 and ATH, in presence of tetrabromobisphenol- A as a flame-retardant agent has been compared. Limited oxygen indexes (LOI) of the compounded samples were measured by flammability tests. Also thermal gravimetry analysis (TGA) and scanning electron microscopy (SEM) were applied in order to study the thermal behaviour and morphology of the samples, respectively.

4-(4í-Aminophenyl)-1,2,4-triazolidine-3,5-dione (1) was reacted with 1,8-naphthalic anhydride (2) in a mixture of acetic acid and pyridine (3:2) under refluxing temperature and gave 4-(4í-N-1,8-naphthalimidophenyl)-1,2,4-triazolidine-3,5- dione (NIPTD) (3) in high yield and purity. The compound NIPTD was reacted with excess acetyl chloride in N,Ní-dimethylacetamide (DMAc) solution and gave 1,2- bisacetyl-4-[4í-(1,8-naphthalimidophenyl)]-1,2,4-triazolidine-3,5-dione (4) as a model compound. Solution polycondensation reactions of monomer 3 with succinyl chloride (SucC), suberoyl chloride (SubC) and sebacoyl chloride (SebC) were performed under conventional solution polymerization techniques in the presence of different catalysts and led to the formation of novel aliphatic polyamides. These novel polyamides have inherent viscosities in a range of 0.08-0.19 dLg-1 in con. H2SO4 or N,Ní-dimethylformamide (DMF) at 25°C. Some structural characterization and physical properties of these novel polymers are reported.

Cellulose acetates (CA) with different degrees of substitution (DS) and different distributions of substituents within the anhydroglucose unit (AGU) have been synthesized in conventional (acetic acid/water) and unconventional (toluene or benzene/ acetic acid/water) media and their susceptibility to enzymatic attack has been investigated using a purified cellulase from Trichoderma reesei. The degradation experiments have been carried out in heterogeneous (water suspension) or homogeneous (water solution) conditions, dependening on the DS of the derivatives. The behaviour of CAs to enzymatic attack has been correlated with their structural characteristics which are dependent on the procedure used for their synthesis. CA Samples with DS value above 1.3 have been treated with enzyme in water suspension for 14 days. It has been observed that the decrease of the reduced viscosities of these acetates solutions in adequate solvents after the enzymatic treatment depends on the procedure and conditions employed for their synthesis. Gel permeation chromatograms show some associations of macromolecules for polymers with DS higher than 1.3. These fractions of apparent high degree of polymerization seem to be preferentially degraded by the enzyme. Water soluble cellulose acetates undergo similar degradation, irrespective of the reaction medium used for their synthesis.

Two model thickeners of HEUR polymers were synthesized by step-growth polymerization of poly (ethylene oxide) (PEO) with dicyclohexylmethane diisocyanate (H12MDI). First, the prepolymers were produced with different molecular weights by changing the molar ratios of the initial reactants. Then, S-G HEUR model thickeners were produced via reacting of the prepared isocyanate terminated prepolymers with monofunctional dodecyl alcohol. In this way, two polyurethane based model thickeners were obtained with different molecular weights arising from various hydrophilic lengths. The response of these S-G HEUR thickeners in aqueous solutions to both steady shear and oscillatory shear was determined. Considerable increases in thickening efficiency as decreasing molecular weight of model thickeners were observed. Also dynamic measurements verified the results obtained from the steady shear measurements about the effect of molecular weight on the viscoelastic properties of aqueous S-G HEUR solutions.