This twin-screw extrusion technology can be used to conduct continuously and efficiently the pretreatment of lignocellulosic biomasses prior to fiberboard molding. The homogeneous thermo-mechanical pulps are produced at low cost and using a reduced volume of water. And the versatility of extrusion enables the addition of a natural binder in a single pass.
Using combined temperature moisture content is a key for a successful twin-screw extrusion of lignocellulosic fibers. So you always start with an excess of water, then you decrease the amounts until getting the desired texture. As the process is really sensitive we have to rely on all of the senses.
So the video adds sight and hearing to the paper, smell and touch in the near future. Demonstrating the procedure will Laurent Labonne, an engineer in my laboratory. Laurent will be assisted by Saif Ullah Khan, a PhD student in the lab.
Begin by using half clamps to connect the twin-screw extruder modules in the correct configuration for fiber defibration only. Position the water inlet pipe laterally at the end of module two to connect the piston pump to the machine, and check the screw element type, length, pitch, and staggering angle. Insert the screw elements along the two splined shafts in pairs, taking care that the threads of each inserted screw element are always perfectly aligned with the previously assembled elements.
Once the entire screw profile has been assembled, manually screw the screw points at the ends of the two shafts. Completely close the barrel of the machine and use a torque wrench to tighten the two screw points to the tightening torque recommended by the manufacturer. With the barrel of the machine partially reopened and the shafts retracted into the barrel over a distance of approximately one dimension, turn the screws at a maximum of 25 revolutions per minute to ensure that the entire screw profile is correctly fitted.
When both shafts have been entirely trapped inside the barrel, use half clamps to secure the barrel to the machine and use a level tester to confirm that the barrel is perfectly horizontal. For twin-screw extrusion treatment, enter the set temperatures of each of the modules and start the temperature control of the barrel. When the temperature has stabilized, turn the screws at a maximum of 50 revolutions per minute and gently feed the twin screw extruder with water at a flow rate of five kilograms per hour.
Wait about 30 seconds for water to come out of the end of the barrel before introducing the oleaginous flax shives into module one at a three kilogram per hour flow rate. Wait about one minute for the solid to begin coming out of the extruder before gradually increasing the speed of the screws, water, and shive flow rates in at least three success steps until the desired set points have been reached. Allow the machine to stabilize for 10 to 15 minutes until the electrical current consumed by the engine over time varies no more than 5%from the 125 amp average value.
For the addition of natural binder, once the machine has stabilized begin introducing the plasticized linseed cake at a rate of 0.5 kilograms per hour. Then, increase the flow rate in at least three successive steps up to the desired set point. Once the electrical current consumed by the twin-screw extruder motor is perfectly stable, make sure that the temperature profile measured along the barrel conforms to the set values given by the operator, and start sampling the extruded shives at the outlet.
At the end of production, switch off the two solid dosing units and the piston pump, and empty the machine while gradually reducing the speed of the rotation of the screws to 50 revolutions per minute. When no additional sampling is coming out of the barrel end, use water to clean the inside of the barrel of the twin-screw extruder while the screws are still rotating, until the solid residues disappear completely at the outlet of the barrel. Then, stop the rotation of the screws and switch off the heating control of the machine.
Immediately after the twin-screw extrusion process, dry the extrudates with hot air flow to a humidity between 3%and 4%When the extrudate has dried, position the material in a preheated mold and preheat the material. After three minutes, apply the appropriate amount of pressure to the material and mold the material for 150 seconds at the 200 degrees Celsius already set up. Once the press is open, demold the panel and check its cohesion.
Following the extrusion refining pre-treatment, the chemical composition of the extrusion refined fibers can be determined. In the absence of liquid extract generation during the extrusion refining pretreatment, no significant difference in chemical composition was observed between the raw shives and the extruded ones. In terms of appearance, extrusion refined fibers have a fluffy material form, indicating that the extrusion process, in particular the high shear rate applied, contributes to a modification of the flax shive structure.
This is confirmed by the lower apparent and tapped densities of the extruded shives compared to the values obtained with the raw shives. Morphological analysis of the fibers also confirms this observation as a very significant increase in their aspect ratio, using a fiber morphology analysis device. Boards made from extruded fibers alone, without the addition of plasticized linseed cake as an external binder, are not only all three cohesive, but above all present significantly improved usage properties compared to boards obtained by hot pressing of the raw shives.
Overall, the addition of plasticized linseed cake to the extrusion refined fibers increases the flexural properties of the fiber boards obtained. Indeed, with the addition of 25%of this binder the obtained board has a flexural strength of 10.6 mega pascals, instead of only 3.6. For process intensification, the fiber refining and the binder addition can be conducted in a single pass.
This process will adapt to all types of raw materials.
