Iranian Journal of Polymer Science and Technology
Year:2002 | Volume:15 | Issue:4 (Issue No.60)|Papers Count:6

In manufacturing of composite materials, surface quality of the prepared part is of great importance. Pultrusion is one of the main methods for continuous manufacture of composite profiles with a constant cross section. In this research, factors affecting the surface quality of a pultruded profile have been investigated. Results show that for a rod made of unsaturated polyester resin and E-glass roving, increasing material packing in the die, employing release agents compatible with resin and also type and level of curing agent have determining roles on surface quality of the product. Also, pulling speed and heating profile of the die are important factors and must be selected according to resin formulation used.

Lignocellulosic fibers (e.g., wood) are used to improve bending strength and brittle fracture of plasterboards. They would produce a composite which is so called gypsum board. Two types of fibers; wood fibers from a fiberboard plant and bagasse fibers were used in five different percentage levels (10, 15, 20, 25, 30) by weight with respect to plaster to manufacture sample gypsumboards. The construction type plaster with high value of β-hemihydrate was utillized. Targeted process was a semi-dry one. The ratio of water to plaster was kept as low as 0.4. Mixing consisted of two phases; (1) dry mixing of plaster and fibers resulted in homogenous mixture, (2) then water was added with continuation of mixing process. Then the mixture was moulded and pressed until hydration of plaster initiated and sample boards were dried to 1 to 2 percent moisture content prior to tests. Static bending, internal bond and compression parallel to surface tests were conducted to measure these properties of the boards. Testes were carried out with adapting ASTM D1037-82 specification. Physical properties (water absorption and thickness swelling after 2 and 24 h soaking) were also measured. Boards made with natural wood fibers were inferior in terms of measured mechanical properties, as compared with boards made out of bagasse and plaster. Between two types-of fiber in physical properties no significant difference was observed. Among different percentage levels of fibers of two types of fibers, no significant differences were observed but in 20 percent wood fibers and 15 percent bagasse fibers the highest mechanical properties and more desirable physical properties were observed.

Considering the application of phenolic resins in ablative heat shields, studying the thermal degradation kinetics and effective parameters on their degradation mechanism is very important. In this work, thermal degradation of two grades of phenolic resins was investigated. The effects of resin type, experimental environment and heating rate on degradation mechanism have been investigated by thermal gravimetry analysis (TGA). The experimental results indicate that the modification of phenolic resin structure increases its char performance in ablation process. Presence of oxygen in environment increases thermal oxidation and causing oxidation of char residue of thermal degradation of resin. The results of multi-heating rate experiments show that the calculated maximum thermal decomposition temperatures at the heating rate of 3000°C/min will occur at 469°C. Kinetics parameters of thermal degradation reaction of resin (A, E and n) are determined by Ozawa model and they are in the order 1.5, 72kJ/mol and 2.1 x 106/min, respectively. Results of theoretical thermal degradation model, which was determined by these parameters, show the good agreement with the experimental results.

Pretreatment operations like boiling off and bleaching affect the results of dyeing and printing of cotton fabrics. In boiling off and bleaching of cotton fabrics, controlling the conditions of operation is important, because the fibers are threatened by the destructive action of oxidizing agents. Boiling off and bleaching may be carried out sequentially or simultaneously. The simultaneous system which is gradually replacing the sequential system can be batch wise, semi-continuous or continuous. Sodium hydroxide and hydrogen peroxide constitute the most common chemicals as boiling off and bleaching agents, respectively. In this paper, the results obtained from the tensile tests carried out on the 100% grey cotton fabrics, simultaneously boiled off and bleached discontinuously, with different concentrations of sodium hydroxides and hydrogen peroxide are analyzed. The results show that the maximum reduction in strength due to the conditions employed in this study is about 16%.

Fire retardation effects of Mg (OH)2 on PE was studied utilizing DTA, TGA and DSC methods. Reductions on reaction peak area and mass loss rate with the addition of Mg (OH)2 were observed as indication of retardation effects of Mg (OH)2 on PE. Cone calorimeter tests were performed on samples to verify the thermoanalytical results. It was concluded that when Mg (OH)2 is present it effectively modified the degradation behavior of PE and the thermal analyses are useful and rapid methods to study the retardation effects.

Nowadays, microwave heat treatment is widely used in many textile processings such as drying, dyeing, etc. In this research the effective microwave treatments on the fine structure of POY and FOY polyester filaments have been investigated. Fine structure of polyester filaments after microwave heat treatments was studied by measurements of diameters, finness, degree of orientation, tenacity, extension, surface characteristics by SEM and X-ray diffraction analysis; also chemical degradation of treated samples in methylamine were studied. The results of this research showed the physical structure of FOY and POY polyester filaments were not noticably affected by the microwave heat treatments, though the physical structure of the POY samples were to a great extent affected by boiling water which is a prerequisite for microwave treatment.