Iranian polymer journal
Volume:16 Issue: 10, 2007

The barrier polypropylene (PP) films were prepared via reactive blending of PP with polyethylene terephthalate (PET) in an intermeshed co-rotating twin-screw extruder. Films were prepared via extrusion through a flat die followed by postextrusion stretching. The effects of compatibilizer, PP-g-MA, content and draw ratio were investigated. SEM micrographs showed that the dispersed phase inclusion size decreases significantly upon the addition of compatibilizer. Morphological studies of the films have shown that laminar morphology was developed in the machine direction rather than in transverse direction. The optimum morphology was observed at 5% compatibilizer concentration. Tensile tests showed that melt stretching has resulted to the inferior properties except modulus. Mechanical properties of blends decreased significantly upon the addition of PET and increased as the compatibilizer content was raised to 10%. Higher contents, however, showed no improvement, as it just improves the physical properties of the blends. Blending results in 200% improvement in the oxygen barrier properties. Permeability of the stretched films and compression moulded films showed 25-35% improvement in the oxygen barrier properties. The maximum barrier property of the extruded films was observed at 5% compatibilizer and draw ratio of 2. Higher contents (up to 15%) resulted in decreased oxygen barrier properties.

Improvement in physical and mechanical properties of butyl rubber by application of a modified montmorillonite (MMT) organo-clay (Cloisite15A) has been the main objective of this research. Butyl rubber is widely used in tyre industry thus, reduction in its consumption by decreasing the products thickness/weight along with improvements in physical-mechanical properties of the composite has economical significance. In this work, melt mixing in an internal mixer was selected as the method of dispersing organo-clay in the rubber matrix. Organo-clay content in the nano-composite was altered as 3, 7, 11, and 15 phr, and intercalation of polymer chains into the clay gallery was deduced from the increase in basal spacing of the silicate layers as was measured by XRD. The highest basal spacing detected for the 3 phr nano-composite was about 4.5 nano-meters. Dispersion and distribution of the organo-clay were observed by SEM. Effects of organo-clay content and structure on mechanical and rheological properties of nano-composites as well as permeability of CO2 gas through their films were evaluated. It was shown that as small amount as 3 phr montmorillonite organo-clay reinforces butyl rubber to a great extent, affects its elastic and viscous behaviour in dynamic conditions, and increases its barrier properties to CO2 gas. The rate of improvement in properties slows down at organo-clay contents higher than 3 phr.

Low density polyethylene (LDPE) properties could be modified by cross-linknig. In this research, crosslinking of LDPE was studied under microwave irradiation. Moreover, carbon and chlorinated paraffin were added to LDPE as UHF-active aids. Carbon, chlorinated paraffin, and peroxide contents, as well as irradiation time were determined as the most important and effective parameters based on some initial experiments. LDPE compound was prepared in an internal mixer. Torque-time curve, during the mixing process was measured an the indication of the suitable compounding with no partial cross-liking. The gel content of cross-linked LDPE (XLPE) was studied as a measure of cross-linking degree. In theoretical section, L9 orthogonal array method (Taguchi design) was applied as the design of experiments (DOE). Results were analyzed using Minitab and Qualitek4 softwares. Various statistical criteria were applied on the results showing the same conclusion on the parameters behaviour. It was found that an experimetal relationship (by regression) may be offered between the gel content and the main parameters. Consequently, optimum cross-linking condition was determined. The result may be used as a quantitative relationship in product design applications.

Phase inversion emulsification technique, as a versatile method for emulsification of high-viscosity materials has received considerable attention in recent years due to its potential for producing particles of precise geometries, sizes, and size distributions. This report involves an investigation on the effect of emulsifier concentration on the inversion behaviour and the morphological aspects of the resulting solid epoxy particles. Emulsion inversion was induced by increasing the amount of initially dispersed deionized water in presence of a non-ionic block copolymer surfactant. The process of inversion was followed by monitoring the changes in the rotational speed of the stirrer. These changes are introduced in this study as a means to probe the viscosity variations of the emulsifying system during the process. It is shown that under a specific emulsifier concentration mainly the rod-shaped and ellipsoidal particles are formed. The fully spherical particles, however, were formed above this specific concentration. Further increase in the emulsifier concentration significantly reduced the size of spherical particles, controlled, and narrowed their random size and wide distributions. Dynamic light scattering analysis and scanning electron microscopy were used to study the particles size and distribution. In addition, the study of rotational speed variations of the stirrer which is directly related to the viscosity changes of the emulsifying system revealed that during the inversion process a correlation could be established between the physical aspects of the inversion behaviour and the viscosity changes.

The copolymers (CPVAc) with various proportions of N-p-chloromalemide (CMI) and vinyl acetate were prepared by free radical polymerization in tetrahydrofuran (THF) using 2,2''-azo-bis-isobutyronitrile (AIBN) as an initiator at 70±2°C. The series of copolymers (CPAVc1-CPAVc9) were characterized by FTIR and 1H NMR spectroscopic methods. Solubility and viscosity parameters were studied for all the nine copolymers. The viscosity data were used to evaluated Huggins (KH), Kraemer (KK), Schulz-Blaschke (KSB), and Martin (KM) constants. Their energy of activation was calculated from thermogravimetric analyses of the copolymers using Broido''s method and copolymer compositions were established by elemental analysis. The copolymer chains were comprised of the first monomer M1(CMI) and the second monomer M2(VAc). Units were distributed in a particular sequence for a definite chain length which was dependent on the feed composition of each monomer. The reactivity ratios of copolymerization were computed by using Finnmen-Ross and Kelen-Tüdös methods and were found to be r1 = 1.177 and r2 = 0.419.

Highly practical conditions were accomplished to prepare new ionically crosslinked polymer network hydrogel beads (Caralgi) composed of polysaccharides carrageenan and sodium alginate. Disodium phosphate and the acetate derivatives of betamethasone were simultaneously loaded while the hydrogel network was being formed. A maximum loading efficiency of 91% was achieved at pH 4.8 and temperature 75ºC. The morphology of the Caralgi hydrogels with and without drug was investigated using SEM analysis. A more regulated morphology was observed when the drug was incorporated into the hydrogel. The in vitro release behaviour of the drugloaded Caralgi samples prepared under various conditions was also studied. The full natural system has exhibited release behaviour with no burst effect. No major difference was found in the loading and release when a highly water-soluble derivative of the drug, i.e., betamethasone disodium phosphate was used.

Home-made single screw extruder was designed and constructed with screw length to diameter ratio 20:1 operating at different screw speeds ranging from 7-28 rpm and at different temperatures. The extruder was used to produce rod composite samples composed of low density polyethylene and short E-glass fibre. The effects of fibre contents and extruder operating variables on the tensile modulus and ductility were investigated. The tensile modulus increased with fibre weight percent up to 10.52 wt% as residual fibre content (20 wt% prepared sample before processing) and had a value of 827 MPa, then slightly decreased to lower values due to bad wettability and poor distribution/dispersion of fibres in the LDPE matrix. The clear decrease in fibre content after processing (residual fibre content) which is about 40- 55% is due to the sticking of fibres in hopper or in the different extruder zones. On the other hand, ductility as percentage elongation-at-break decreased significantly at low fibre concentration then decreased in lower rate at higher fibre contents. Operating variables of the extruder were found to affect the tensile properties of LDPE/glass fibre composites by affecting the interfacial adhesion between the two components. This effect was clear from the analyzed data of the modulus efficiency factor KE.