To study tire tread compound extrudability is a very demanding process. Complicated flow geometry, and a broad range of operating parameters make predictions of process ability a difficult task. In this work the viscoelastic parameters, which affect the rheology of tire tread compound such as relaxation time, lk, and viscosity index, lk in generalized Maxwell model using two-parallel plates rheometer are determined. Then to simulate the flow of rubber compound through a capillary die a Fastflo software which works on mixed finite element (MFE) method is used. After calculation of the generalized viscoelastic Maxwell model parameters, the Fastflo software was used to simulate the flow of compound through a capillary die and laboratory extruder die. Comparisons between the simulation prediction and actual data show a good agreement between capillary die and laboratory extruder die. Numerical simulation in the Fastflo software was based on penalty method algorithm in FEM (finite element method).

Conversion of the organic wastes and losses into compost is an appropriate technique to stabilize organic materials. One of the limitative factors in transportation and storing of composts is their low specific mass which usually leads to increased costs in their handling and processing. To overcome this, several such methods as pelleting have been proposed especially for the efficient handling of voluminous materials. Throughout the present study, the effects of pellet particle size (two levels: 1 and 2 mm), pellet’s moisture content (at three levels: 25, 35, and 45%, wet basis), and kneading length (three levels: 1, 2, and 3 m) have been investigated on some mechanical properties of obtained pellets namely fracture energy, fracture force, as well as toughness. Obtained pellets were produced using a kneading extruder apparatus. Experimental results showed that the effect of length of kneading on all studied mechanical properties was significant (p<0.01). Maximum values were recorded for 3 m kneading lengths. The highest fracture force (556.32N) was determined for pellets with 35% moisture content and 3 m kneading length. Furthermore, a maximum level of toughness (1.03 MJ.m3) was recorded for compost pellets with 1 mm particle size and 3 m kneading length.

The devocalization process of EPDM compound was carried out using a twinscrew extruder. The effects of barrel temperature, screw speed and diphenyl disulphide as a devulcanization agent (DVA) on the devulcanization were investigated. Percent devulcanization, sol fraction, Mooney viscosity and curing behaviour of devulcanized samples were studied. The devulcanized samples could not cure without addition of the curing agents. After the addition of curing agents into the devulcanizates, the general behaviour of rheometry test for rubber compounds was observed. Percent devocalization was dependent on DVA content and screw speed, especially at low and middle level of barrel temperature. Barrel temperature was the most effective parameter on the amount of sol fraction and Mooney viscosity. The devulcanizates were recured with a semi-efficient curing system. Tensile strength, elongation-atbreak, compression set, hardness and cross-link density of revulcanizates were evaluated. It was found that the mechanical properties were slightly inferior compared to virgin compound.

Twin-screw extruder has been attractive with many efficient benefits as one of developing pulping technology from non-wood feedstocks in recent decades. Extrusion pulping is a chemi-mechanical pulping method in which fibers are processed by means of compression and shear forces. In this research, application of this technology was introduced in pulp and paper industries and the extrusion pulping of rice stalk was investigated. Extrusion pulping of rice stalk was conducted following a central composite design using a two-level factorial plan involving three process variables (pretreatment NaOH concentration: 0.4, 0.8 and 1.2%, extrusion temperature: 40, 60 and 80 oC, extruder rotational speed: 55, 70 and 85 rpm). Responses of pulp properties to the process variables were analyzed using statistical software (MINITAB 15). As the results show, a more content of initial ash of rice stalk was remained in the obtained pulp. Also, because of high freeness of obtained pulps, it is necessary to retransfer the obtained pulp from extruder or refine it for fluting paper and linerboard production. Moreover, analysis of the results reveales that this process can be used to obtain a pulp with low kappa number under a relatively long pretreatment time, high NaOH concentration, high extrusion temperature and moderate extruder rotational speed.

Extruders are by far the most important machines in polymer processing. Of these processes the reaction extrusion has recently attracted new interests. Reaction extrusion of thermosets has presented new difficulties in process uniformity and production continuity. To achieve a required degree of stability a special design of self-wiping screws for a co-rotating twin screw extruder has to be made. In this work such a screw has been designed and manufactured, and its performance has been checked for a reaction extrusion of melamine formaldehyde. The results of the stability of the process and the quality of the products are reported.

The forward or backward stagger angles of the kneading disks have great effects on configures of the special center region along axial length in a novel tri-screw extruder. In this paper, the flow and mixing of a non- Newtonian polyethylene in kneading disks of a tri-screw extruder were simulated using three-dimensional finite element modeling based on mesh superposition technique. Three types of kneading disks, neutral stagger, staggered 30° forward and staggered 30° reverse were considered for the tri-screw extruder. The effects of stagger angles of kneading disks on the flow pattern in the tri-screw extruder were investigated. Moreover, at different stagger angles, the dispersive and distributive mixing efficiencies in the kneading disks of the tri-screw extruder and the twin-screw extruder were calculated and compared by means of mean shear rate, stretching rates, maximal stress magnitudes, mixing index, residence time distribution (RTD) and logarithm of area stretch. It is found that increasing the stagger angles decreases the axial velocities of polymer melt in the center region for the tri-screw extruder. The staggered 30° reverse is relatively reasonable for the tri-screw extruder and neutral stagger for the twin-screw extruder for the mixing efficiency. In comparison, the kneading disks in the tri-screw extruder have higher distributive and dispersive mixing efficiencies than those in the twin-screw extruder with the same stagger angles.