Iranian Journal of Polymer Science and Technology
Year:2001 | Volume:14 | Issue:2 (ISSUE NO.52)|Papers Count:7

Polyolefine foams such as polyethylene, polypropylene and their copolymers have been extensively used in packaging, automotive, military, marine, cable industries and sports, due to their unique properties namely: light weight, chemical resistance, thermal insulation, inertness, abrasion resistance, buoyancy and low cost. With regards to domestic mass production of polyethylene, replacement of polyurethane with polyethylene foam is very important in some applications from economical point of view. In this research preparation of high density and low density polyethylene foams were studied and the effect of formulation factors such as blowing agent, cross-linker, calcium carbonate, zinc oxide and processing factors such as heat, pressure and reaction time on density and cell size were investigated.

In the present paper, rotational rheometers along with their different measuring geometries are reviewed. The governing equations for calculating material functions in using each geometry are discussed and the advantages, shortcomings, the sources of error and the way to avoid them are well explained. The coaxial cylenders are very sensitive at very low viscosities, whereas, making normal force measurements are not practical The parallel-plate geometry can be easily used but very gross approximations are needed in calculations of rheological material functions. In the case of cone-plate geometry there exists straightforward relation between measured quantities and rheological material functions. The only withdrawal of this geometry is their interactions with solid materials in composite materials. The ability of accentric geometry to produce oscillating mode of loading using simple rotation has attracted many attentions. Some examples of diverse applications of rotational rheometers are also reported.

Improvement of PE properties has been carried out by several methods. In this work dicumylperoxide was used for crosslinking of LDPE and hence improving the polymer properties. For sample preparation, an intensive mixing of polymer, peroxide and antioxidant in an Haake internal mixer at 110-115°C was performed and followed by two-roll mixing. Finally process of crosslinking was conducted at 200°C under 15 MPa pressure. After gel content determination, tensile, DSC, DMTA and density tests were carried out on the samples. Results showed improved alterations in the properties.

Polyester (PET) is one of the hydrophobic fibers. Disperse dyes are the most important dyestuff for dyeing of this fibers. Dyeing can be applied by carrier, HT and the thermofix methods. In this research, hydrolyzed polyester fibers by lipase in different conditions are dyed by disperse and ionic dyes in using various methods. The results of dyeing by disperse dyes show that the enzymatic hydrolysis increases the surface rate of dyeing but being non-effective on final adsorption of dyes. On the contrary dyeing with ionic dyes indicated that no adsorption of these dyes (acid and cationic dyes) takes place on hydrolyzed fibers.

The structure of polyvinyl acetate prepared from solution polymerization of vinylacetate in methanol with benzoyl peroxide initiator is studied. Nuclear magnetic resonance spectroscopies (1H and 13C NMR) are used to study the structure of polyvinyl acetate and the hydrolyzed polyvinyl acetate. On this basis, the principle reactions of the polymerization are also discussed. The experimental design was used to calculate the time-conversion of the polymerization. The percent hydrolysis and number average molecular weights of the copolymers are also calculated and reported. The Bernoullian statistics is used to model the structure and the hydrolysis of the copolymer. This modeling is useful in the structural studies of the copolymer and the effect of temperature, solvent and polymerization time.

Printing by a paste containing caustic soda is one of the methods used for obtaining the so called Seersucke effect. After printing a cotton cloth with a paste containing caustic soda, the fibers in the printed area swell and contract in direction of yarn axis. As a result, the unprinted area is forced to follow the contracted area and, therefore, a kind of waviness appears on this part of the fabric. In this study besides caustic soda, potassium hydroxide has been used and parameters of alkali concentration, treatment duration and also fabric pretreatment have been investigated. This study showed that the Seersucker effect obtained on grey cotton cloth is not considerable. After boiling off and bleaching, considerable Seersucker effect is obtained. The optimum conditions for obtaining considerable effect on the boiled off and bleached cotton fabric are 350 g of caustic soda or potassium hydroxide in one kilogram of printing paste with 25 to 30 min of relaxation after printing.