فصلنامه بسپارش
سال سوم شماره 4 (پیاپی 9، زمستان 1392)

The effects of processing conditions were studied for ternary polymer blends based on polyamide 6 (PA6)، polycarbonate (PC) and Acrylonitrile-butadiene rubber (NBR). The ternary blends were accumulated at fixed compositions (PA6/ PC/NBR: 80/10 /10 wt%) using counter-rotating twin-screw extruder under three levels of blending sequence، die temperature، and screw speed. The experimental design was fulfilled by using Taguchi experimental analysis and the field emission scanning electron microscopy (FESEM) micrographs were used to investigate the microstructure. The mechanical properties such as tensile properties (Young''s modulus and yield stress) and impact strength were highly influenced by processing conditions and the mean effects of each factor were calculated to investigate their role on mechanical properties of the blends.

Hemicelluloses are the second major compounds in the chemical structure of wooden fibers. The same with cellulose، hemicelluloses are carbohydrates، but unlike cellulose، which is a homopolysaccharide، hemicelluloses are heteropolysaccharides. The use of strength additives in papermaking process is important to ensure that the products are suitable for their specific purpose. Nowadays، strength additives are developed to produce papers with specific strength and surface properties، by minimum quantity of cellulosic fibers. More reasons in using hemicelluloses، as dry strength additives، are due to many free hydrogen and hydroxyl groups available in their chemical structure. When a hemicellulose is adsorbed onto the cellulose fibers، these free hydrogen and hydroxyl groups provide more hydrogen bonding sites. The more hydrogen bonding sites available on the cellulose fibers، the more tightly bonded the paper web is obtained. Hemicelluloses are naturally interwoven in woods'' micromolecular structure، which indicates a strong relationship between them and cellulose. Xyloglucans and galactomannans are examples of hemicelluloses that can be accumulated in seeds of many plants. Guar gum and starch are polysaccharides currently used as wet-end additives in papermaking. In this study، the hemicelluloses: their effects، types and their applications in papermaking are investigated.

Skins related-morphing technology، are studied with relation to their mechanical and thermal properties. Morphing wings are those wings that can undergo self-change in shape and geometry. Although، engineers present different configurations for self-changing wings but there are not much studies on skin materials in this wings. A suitable material in morphing skins has to be elastic and flexible and capable of fast recovery to its initial condition. Also، it should be resistant against different environmental conditions، chemicals and abrasive agents، and sufficient hardness number of its structure to tolerate the aerodynamic loads. According to the above notes، the commercial materials are selected to meet the necessary requirements and include thermoplastic polyurethane، elastomeric copolymer، shape memory polymers and woven materials. First، history of different configurations of morphing wings is described and it is concluded that different configurations and shapes must not include hard materials as morphing wings.

Differential scanning calorimetry (DSC) is one of the thermal decomposition analytical methods which have most diverse applications in the study of polymeric systems. For example، it is used in determination of specific heat capacity and changes in enthalpy of a chemical reaction from the endothermic or exothermic reaction type. Photo-differential scanning calorimeter is a new type of calorimeter that due to its simplicity and high speed provides the ability to study the light initiated polymerization kinetics in a short timeframe. Photo-DSC assesses many variables such as monomer structure and optical triggers at polymerization، formulation composition، temperature and the effect of atmosphere (inert gas or air (oxygen)) and it gives reliable results which is widely employed in recent years.

Today different resins are used in order to crosslink the cellulose fibers in paper products and improve their strength characteristics، especially wet strength. Some neutral، low-molecular-weight molecules (formaldehyde، glyoxal) can impart wet strength if they are retained and dried up in pulp. However، these materials cannot be used at the wet end of a paper machine، since they lack a means of retention. Polyamide-epichlorohydrin (PAE) and glyoxylated acrylamide (GPAM) resins are applied in papers made under alkaline condition. Polyamide-epichlorohydrin (PAE) and glyoxylated acrylamide (GPAM) resins are applied extensively، which are retained by fiber and improve the dry and wet strengths of the papers. Compared to PAE، GPAM presents some advantages such as more efficiency in increasing the wet and dry strengths of paper، retention of fine and drainage of pulp. The curing of GPAM occurs at room temperature and therefore it is able to improve wet strengths of paper before drying. This reduces paper breakage during the open draw transfer of paper and improves paper machine efficiency. Overall، GPAM is a valuable resin which may be applied in papermaking successfully.

Because of importance of crystal structure effect on specification of piezo-electric poly (vinylidene fluoride)، PVDF، and elongational flow effect on enhancement of this crystal structure، a new geometry is simulated in the form of cylindrical shape that includes a channel with convergence end zone. The melting flow in die was analyzed by the Fluent software. The results of this modeling show that there is very effective elongated flow in convergence zone. With the help of this research results a die could be made so to induce high elongation flow on melt. With the introduction of this technology the need for cold drawing of polymer will be eliminated and this simple geometry with a small modification could be used for processing of cylindrical films and hollow tubes.

Rheological، morphological and mechanical studies were performed on various blends of polypropylene (PP) and ethylene-octene copolymer (EOC). The oscillatory flow properties were determined at 220°C on a cone-plate rheometer (dynamic rheometer، SR 200) at an angular frequency range of 0. 01 to 100 rad/s. The rheological studies showed material flow behavior in the molten state. Scanning electron microscopy (SEM) revealed that as the amount of ethylene-octene copolymer increased، the size of elastomeric domains increased; and that dual-phase continuity occurred between 50 and 60 (wt%) of EOC. Studies on mechanical analysis showed that PP/EOC blends displayed higher impact strength than PP. With the addition ethylene-octene copolymer into polypropylene، the mechanical properties of the final blend improved because of lower elastic modulus intended for soft and flexible product and a low glass transition temperature to impart impact strength at low temperatures. This copolymer was compatible with PP in creating brightness and surface luster. The amount of long chain branches had significant effect on mechanical and rheological properties of ethylene-octene copolymer.