Iranian Journal of Polymer Science and Technology
Year:2008 | Volume:20 | Issue:5 (ISSUE NO. 89)|Papers Count:9

The effects of temperature, time and the strategy of prepolymerization were studied on the morphology of polypropylene particles. Propylene polymerization was carried out in slurry phase using 4th generation of Ziegler-Natta Catalyst, cyclohexylmethyl dimethoxysilane as external electron donor, and triethyl aluminum as co-catalyst. Prepolymerizations were carried out based on two strategies: isothermal and non-isothermal conditions. Particle imaging using SEM, bulk density, and particle size distribution was used to analyse the particle morphology. It was found that the variation of initial condition together with the change in the mechanism of particle fracture has a dominant effect on particle morphology. Each combination between the temperature and reaction time causes to have a special effect on the product particle morphology. It has become clear that in isothermal prepolymerization, spherical particles with identical properties were produced. In low temperature experiments particles with porous surface were observed. At increasing temperature, however, the pores disappeared. Non-isothermal prepolymerization produced different morphological types. In all experiments coreshell structures were observed that seemed to be related to the structure of catalysts.

The effects of trichloroacetic acid/methylene chloride (TCAc/MC) on the mechanical properties and solvent texturing of polyester yarns are studied. The treatments are carried out in unstrained and strained states at different concentrations of TCAc for various treatment times. Breaking load and elongation-at-break of treated yarns have been recorded. Treatments of polyester yarns with TCAc/MC in unstrained state have increased the elongation-at-break without significant changes in breaking load, whereas, treatments of the yarns in strained state improved breaking load without significant changes in elongation-at-break. Solvent texturing of polyester yarns using TCAc/MC has been performed by twisting-solvent setting-untwisting process. The effects of setting times and TCAc concentration on the permanent and reversible shrinkage of textured yarns have been examined. It was shown that the shrinkage and texturing properties of solvent treated yarns increased with increasing concentration of TCAc and setting time. The results are discussed on the basis of the fine structure of polyester yarns.

In the past decade, electrospinning as a facile and effective means in producing nanofibers with diameters ranging from microns down to a few nanometers has been developed and considered important. In this work, electrospinning of an interesting natural biopolymer, sodium alginate, has been investigated. The results showed that water solution of sodium alginate cannot be electrospun into nanofibers. Moreover, using different organic solvents and surfactants did not help the spinnability of the polymer solution. To improve the solubility of the polymer in organic solvents, we used ammonium alginate or alginic acid instead of sodium alginate, but the results were not satisfactory. However, we were able to electrospin the sodium alginate from aqueous solution by blending it with a synthetic polymer, poly (ethylene oxide) (PEO). The type of interactions between sodium alginate and PEO was examined by FTIR. The morphology and diameter of the electrospun fibers were observed and determined by using an optical microscope and a scanning electron microscope (SEM). The measurement of solution properties such as viscosity showed a strong dependence of spinnability and fiber morphology on solution viscosity and thus on alginate-to-PEO blend ratios.

Thin films of polymer doped with nonlinear optical organic dye, Disperse Red 1, at thickness of 1 to 2 micrometers, were prepared and studied. In order to induce an axial and orientational alignment of dye molecules within polymer matrix, a contact electric field poling was used. By this process the inherent inversion symmetry in the polymer matrix was eliminated to achieve the desired macroscopic second order nonlinear optical response. With a method based on spectroscopy, poling process and parameters related to orientation were studied. Different parameters such as temperature and residual solvent effects and also temporal and spatial dependencies were investigated and analyzed.

Bioedegradable nanoparticles are intensively investigated for their potential applications in drug delivery systems. Being a biocompatible and biodegradable polymer, chitosan holds great promise for use in this area. This investigation was concerned with determination and optimization of the effective parameters involved in the production of chitosan nanoparticles using ionic gelation method. Studied variables were concentration and pH of the chitosan solution, the ratio of chitosan to sodium tripolyphosphate therein and the molecular weight of chitosan. For this purpose, Taguchi statistical method was used for design of experiments in three levels. The size of chitosan nanoparticle was determined using laser light scattering. The experimental results showed that concentration of chitosan solution was the most important parameter and chitosan molecular weight the least effective parameter. The optimum conditions for preparation of nanoparticles were found to be 1 mg/mL chitosan solution with pH=5, chitosan to sodium tripolyphosphate ratio of 3 and chitosan molecular weight of 200,000 daltons. The average nanoparticle size at optimum conditions was found to be about 150 nm.

This work has setup to determine the effects of a solvent on the structure and properties of polypropylene fibres with different physical structures. Samples of continuous filament yarns with different physical structures (partially oriented (POY) and drawn yarns) are treated with decahydronaphthalene (decalin) at 28, 55, 75 and 95oC. At 95oC, the samples are dissolved completely in decalin and after cooling to room temperature (28oC), only 94% of the polypropylene precipitated. The results of the treating yarn samples with decalin at 28, 55 and 75oC, show a small reduction in the weight of the samples. Breaking strength and elongation remained unchanged and stress-strain curve of the POY samples in the yield region did not change. Fourier transform infrared spectra of the samples are compared with those of the published literature and the changes in the spectrum as the results of the treatment with decalin are verified. X-ray diffraction studies show the changes in the structure of POY samples. Differential scanning calorimeter shows no changes in the melting point of the samples, but confirms the results of X-ray diffraction regarding the changes in the structure of POY samples. For the drawn samples X-Ray diffraction diagrams did not show considerable changes. Measurement of birefringence of the samples shows considerable changes in the molecular orientation of the samples due to solvent treatment. The changes in the structure of the samples treated at low temperature with decalin are explained with reference to the pertinent structural models of polypropylene fibers.

This research was performed to study the effect of Murray red gum tree age (4, 6, 8 years) on the chemical components, viscosity and the cellulose degree of polymerization. The Eucalyptus trees were cut at the ages of 4, 6, and 8 from hand planted forests. The contents of cellulose, hemicellulose, lignin, extractives and ash for each age were then determined. The results show that with increasing age the contents of cellulose, hemicellulose and lignin increased but the extractives and ash contents decreased. After measuring the viscosity of cellulose solution, the degree of polymerization (DP) was also determined by using the standard equation. The viscosity numbers for 4, 6 and 8 year old trees were 290, 503 and 566 mL/g, respectively, and the DP were 272, 568 and 652, respectively. Finally after analyzing and comparing the results, the age of 8 was found to have best properties for viscose industry. But in order to reduce the forestry and production costs, 6 year old tree instead of 8 could be cut because of the close results in DP and cellulose content.

Blown bitumen (110/10) was mixed with heavy vacuum slops (H.V.S), 60/70 penetration grade bitumen and recycled isotactic polypropylene (iPP) at different levels. The resulting resins were used to impregnate non-woven poly (ethylene terephthalate) fibers to form composites. The modulus and penetration grade of the resulting bituminous resins were determined. It was found that these bituminous resins drastically affect the modulus of the composites formed by low-Young’s modulus fibers such as polyesters. Consequently, interactions between resin and fibers and the correlation length of asphalthenes (in absence of iPP) and interdiffused coalescence and segregated network of asphalthenes (in presence of iPP) result in a non-linear behavior of composite’s modulus. The behavior of the composites with or without iPP is controlled by resin toughness and resin interactions with the fiber through the viscosity. Comparison of the experimental composite modulus data with the theoretical modulus data revealed that the Takayanangi’s model best predicts the behavior of these composites. The adjustment factors of this model were reported and proposed as an indication of fiber-resin interaction. It was also found that the modulus of fibers is affected by toughness, viscosity and the iPP content of the bituminous resin.