Iranian Polymer Journal
Year:2005 | Volume:14 | Issue:6 (60)|Papers Count:10

Effects of electron beam irradiation on the mechanical properties and morphological structure of natural rubber (NR)/ linear-low density polyethylene (LLDPE) blend was investigated. The NR/LLDPE blends were prepared by melt blending in a Haake internal mixer at 14oC, rotor speed of 50 rpm, and in 15 min. Liquid natural rubber (LNR) was incorporated into the blend as a compatibilizer. Samples in the form of 1 mm sheets were exposed to 50-300 kGy of electron beam irradiation and analysed for swelling index and gel content, tensile strength, and surface morphology. The result indicated that gel content and mechanical properties of the samples increased with radiation dosage. The honey-comb structure of the surface morphology in low dosage samples slowly transformed into a continuous matrix on increasing radiation dose. The variation of mechanical and physical properties was due to increase in cross-linking density in the rubber and plastic phases and rubber-plastic interaction on irradiation.

Gelatin is a natural protein derived from the organic constituent of bone (collagen type I). Therefore its combination with the natural mineral constituent of bone (HA) is supposed to provide closer properties to the natural bone. In this study, porous scaffolds based on gelatin-hydroxyapatite composite were fabricated by solvent casting method. To increase the biocompatibility of the composite, its fabrication was carried out without any organic solvent. For the following fabricated porous scaffolds with 6 different compositions (0, 10, 20, 30, 40 and 50 wt% of HA in gelatin, respectively), pore size, morphology and bending modulus were characterized and determined. Cell seeding procedure was carried out using mouse fibroblasts to evaluate the scaffolds biocompatibility. The porosities of these scaffolds were obtained without using any porogen. The scaffolds exhibited pore size range from 50 to 200 micrometers with a good interconnectivity. The obtained bending moduli (above 35 GPa) were higher than those of any other biodegradable scaffold such as SR-PGA and PLLA/HA that were reported earlier in the literature. The experiments showed that not only the amount of porosity but also the interconnectivity of pores decreases with HA content. It was also demonstrated that the addition of HA would increase the bending modulus. Cell seeding experiments showed appropriate cell attachments for all the samples.

Velocity profiles are helpful for the confident design of mixing tanks in the transition region. In this work, mean and fluctuating tangential and radial velocity components were measured using a two-component laser doppler anemometry (LDA) for a typical Rushton turbine impeller. The working fluids were different concentrations of polyacrylamide (PAA) solutions with rheological properties typical of those found in polymer processes. It is shown that the correlations for mean and fluctuating velocities of Newtonian and inelastic non-Newtonian fluids do not apply to the case of polymeric viscoelastic liquids. New correlations are given in the lower part of the transition region, i. e., 35 < Re < 1800 for mean tangential and radial velocity components and also corresponding fluctuation values along the discharge plane of the impeller. It is also shown that for a given concentration of PAA solution, the dimensionless mean (radial and tangential) velocity distributions are nearly independent of impeller speed.

The progress of damage in quasi-isotropic carbon/epoxy laminates under tensile loading has been investigated microscopically. One significant mode of failure in laminated composites is delamination initiating at free edges. The interlaminar stress in the boundary ply along the free edges of a laminated composite is the main factor to cause delamination. The laminate stacking sequence affects the interlaminar stress distribution and consequently may change the mode of failure. It is of design importance to determine a suitable criterion based on stress analysis to obtain the best stacking sequence. In the present work, tensile properties of six samples with different stacking sequences have been examined. Results showed that stress analysis at distance very close to the free edges is a suitable criterion to predict the initiation of delamination and the stacking sequence of [90/45/0/-45]s has the highest strength among the other samples. Furthermore finite element analysis showed that the adjacent  ±45 plies cause premature delamination during tensile loading.

The new polyamides and polyurethanes have prepared by reaction of N-tetrachlorophthalimido succinic acid or its diol derivatives with different diisocyanates. The synthetic procedures for preparation of monomers, model compounds and polymers have been described and their chemical structures are characterized by FTIR and 1H NMR spectroscopic techniques. The physical properties of polymers including inherent viscosity, solubility properties, thermal behaviour, thermal stability and flame resistance have studied as well. The result showed that, the incorporation of the pendent N-tetrachlorophthalimide group into polyamides and polyurethanes backbone increases the thermal stability as well as flame resistance compared to the unmodified analogues compound.

Microstructural properties of olefin copolymers (i.e., copolymer composition, sequence distribution, molecular weight and its dispersity) are key factors which affect their behaviour as viscosity modifiers in engine oil. In this article, the variation procedure and control methods of these specifications are described for the synthesis of olefin copolymers using soluble Ziegler-Natta catalyst in a semibatch reactor. Solution copolymerization of ethylene/propylene was performed using VOCl3-Al2Et3Cl3 systems. Finally the synthesized viscosity modifier was characterized by IR, GPC, 13C NMR, DSC, and XRD techniques and elemental analysis method. Molecular weight was controlled by continuous feed of hydrogen during the reaction and its narrow dispersity was maintained by catalyst specifications and initial saturation of solvent by monomers. Although catalyst activity varies with time, 13C NMR and IR results demonstrated steady copolymer composition. This is achieved by using a catalyst system with mostly single active site in batch while monomers feed continuously. Also, it is found that randomness in the microstructure of the copolymer is induced at a specific monomer ratio.

In this study, behaviours of ethylene/norbornene copolymerization using zirconocene catalysts; rac-Et[Ind]2ZrCl2 (cat. A) and Cp2ZrCl2 (cat. B) were investigated. Based on activity profiles at various norbornene concentrations, it can be observed that although cat. A is more active than cat. B, it is less stable, indicating more rapid deactivation rates with time. It was found that a deactivation rate was more pronounced with high concentrations of norbornene for both catalytic systems. Asymmetric activity profiles were observed for both catalytic systems indicating higher deactivation rates compared to the activation rates. The copolymer produced by cat. A exhibited lower melting temperature (Tm), but higher incorporation of norbornene. However, both catalysts produced copolymers with random distribution.

The effect of glycidyl methacrylate (GMA) on mechanical properties, morphology, and thermal degradation of recycled poly(vinylchloride)/acrylonitrile-butadiene rubber (PVCr/NBR) blends was studied. The blends were prepared at 150oC and rotor speed of 50 rpm in an internal mixer. The glycidyl methacrylate was added at 4 php of plastic. The PVCr/NBR (without GMA) blends were also prepared as comparison. It was found that the addition of GMA significantly improved properties of PVCr/NBR blends. At a similar blend composition, the PVCr/NBR + GMA blends show higher stresses at peak and at 100% elongation (M100) but lower elongation-at-break than PVCr/NBR blends. The scanning electron microscopy (SEM) study of tensile fracture surfaces of the blends indicates that the presence of glycidyl methacrylate increased the interfacial interaction between recycled PVC and NBR phases thus improved compatibility between PVCr and NBR phases. However, thermal gravimetry analysis (TGA) of the blends show that the presence of GMA has reduced the thermal stability of PVCr/NBR blends.

Soon at the beginning of the last century after it was discovered that carbon black is an active filler in rubbers, it became one of the most important components in manufacturing of rubber products. In this work, the effect of carbon black's type and loading and the structure of rubbers on rate constant and activation energy of the vulcanization were studied by the rheometer. The rubbers for this purpose are ethylene propylene diene monomer (EPDM), with natural rubber (NR), and butadiene rubber (BR). The overall rate of vulcanization is calculated from the kinetic expression of first order vulcanization. The results have showed that carbon black reduces activation energy in all rubbers and increases overall rate of vulcanization. In this case N330 reduces the activation energy and increases the overall rate of vulcanization rather than N660. On the other hand, this research showed that vulcanization rate of EPDM/BR is less than EPDM/ NR. This is as the same trend as the number of allylic hydrogens in the repeat unit of these rubber chains.

Emulsion polymerization in gas-liquid systems differs from conventional emulsion polymerization. In ethylene-vinylacetate emulsion polymerization different conditions of pressure, temperature, and agitation rate affect mass transfer of ethylene monomer in the reaction sites. In this study effect of scale-up from 1.8 to 7.5 liter and several parameters such as agitation rate, initiator concentration, and pressure on copolymer composition and vinylacetate conversion was investigated. It is found that agitation rate have a direct effect on mass transfer and participation of monomers especially ethylene monomer in the reaction sites(loci). Vinylacetate conversion and ethylene content in vinylacetate-ethylene copolymers vary with initiator concentration, so that by increasing the initiator concentration, polymerization rate of vinyl acetate monomer increases and ethylene content in the copolymer decreases simultaneously. Decreasing vinyl acetate content of the reaction recipe increases the participation of ethylene in copolymerization. Increase of pressure has a direct influence on this copolymerization system through increasing solubilization of ethylene monomer which in turn increases ethylene content in the copolymers. Effect of introducing ethylene in to the polymerization reaction was investigated by using glass transition temperature measurements and dilute solution viscometry of the synthesized copolymers.