The authors would like to express their sincere gratitude to R&#233;gion Occitanie (France) that funded this research through ERDF (GEOFIBNET project, grant number MP0013559).

1. Prepare the raw materials
<ol>
	<li>Use oleaginous flax shives, which are the result of a preliminary stage of mechanical extraction of the bast fibers from straw in an &#34;all fiber&#34; extraction device51. Use a vibrating sieve to remove short textile fibers that they may still contain. 
	NOTE: As the removal of these short textile fibers may be difficult, do not hesitate to repeat this sieving operation as many times as necessary. Here, the objective is to improve the flow of the oleaginous flax shives in the hopper of the weight feeder, and, therefore, facilitate their dosing before their introduction into the twin-screw extruder.</li>
	<li>Use a plasticized linseed cake, obtained by destructuring/plasticizing of the proteins according to the methodology described by Rouilly et al.18. 
	NOTE: By doing so, the proteins show better thermoplastic and adhesive aptitudes.</li>
	<li>Grind the agro-granulates of plasticized linseed cake using a hammer mill fitted with a 1 mm grid, and then sieve the grinded material obtained to retain only the particles smaller than 500 &#181;m.</li>
</ol>
2. Check the proper functioning of the constant weight feeders and the piston pump
<ol>
	<li>For the flow rates at which the operator works during production, chosen to avoid the clogging of the machine (15 kg/h for oleaginous flax shives (OFS), and from 1.50 kg/h to 3.75 kg/h for plasticized linseed cake), check the correspondence between the set value entered to the two constant weight feeders and the solid flow rates really distributed by these dosing devices. 
	NOTE: The actual solid flow rate is determined experimentally by weighing the mass of the solid distributed by the constant weight feeder for a known period of time (5 min). If there is a significant deviation between the set value and the actual measured flow rate, this may indicate a malfunction of the weigh feeder. To prevent this, the entire dosing unit should be thoroughly cleaned, with particular emphasis on the area where the weighing device is located. In fact, the cause of this type of malfunction is very often a poor cleaning of the device, as traces of previously used solids can be found in the smallest corners of the dosing unit. If the problem persists, it will then be necessary to check the correct gauging of the balance itself and, if necessary, recalibrate it.</li>
	<li>Calibrate the piston pump to establish a relationship between the electrical power of the motor and the actual water flow rate distributed by the pump. 
	NOTE: For each tested electrical power, the actual water flow rate is determined experimentally by weighing the mass of the water distributed by the piston pump for a known period of time (5 min). Five different electrical powers are tested to draw the calibration curve. The highest electrical power tested is chosen so that it delivers a higher water flow rate than that chosen during production.</li>
	<li>Once the calibration of the pump has been carried out, check for the water flow rate at which the operator works during production (15 kg/h to avoid the clogging of the machine while preserving the length of the extrusion-refined fibers) the correspondence between the set value given to the piston pump for the engine power and the water flow rate actually distributed.</li>
</ol>
3. Prepare the twin-screw extruder
<ol>
	<li>Correctly arrange the twin-screw extruder modules (AB1-GG-8D, FER, and ABF types) by connecting them one after the other (by means of two half clamps) in the correct order according to the machine configuration to be used:
	<ol>
		<li>Set up the configuration for which only the fiber defibration takes place (Figure 1A).</li>
		<li>Alternatively, set up the configuration which is completed with the addition of the natural binder (Figure 1B). 
		NOTE: For both configurations, the first module is used for the introduction of oleaginous flax shives. This is a type AB1-GG-8D module, which has an 8D length, D corresponding to the screw diameter (i.e., 53 mm). The large upper opening of this module is primarily intended to facilitate the introduction of the shives. Modules 2 to 8 are temperature controlled. They are closed modules (type FER), except module 5 in the case of configuration (step 3.1.2), which is of ABF type (i.e., module equipped with a side opening to ensure the connection of the side feeder used to force the introduction of the plasticized linseed cake inside the main barrel). The side feeder consists of two co-rotating and co-penetrating Archimedean screws of constant pitch and conjugated profile.</li>
	</ol>
	</li>
	<li>Position the water inlet pipe laterally at the end of module 2 to connect the piston pump to the machine.</li>
	<li>Set aside the screw elements (Figure 2) that will be needed to set up the screw profile, either the one used for configuration (step 3.1.1) or the one used for configuration (step 3.1.2) (Figure 3). 
	NOTE: Make sure that these are the correct screw elements by carefully checking their type (T2F, C2F, C1F, CF1C, BB, or INO0), length, pitch (for the conveying and reverse screw elements), and their staggering angle (for the BB mixing blocks).</li>
	<li>Set up the screw profile (Figure 3) by inserting the screw elements along the two splined shafts, from the first pair to the last one. 
	NOTE: The screw profiles used for the two configurations tested, are different and both result from prior optimization25,26,27.</li>
	<li>When assembling the screw profile, make sure that the threads of the screw elements just inserted on the splined shafts are always perfectly aligned with the previously assembled elements.</li>
	<li>Once the entire screw profile is assembled, screw by hand the screw points at the end of the two shafts, completely close the barrel of the machine and then tighten the two screw points to the tightening torque recommended by the manufacturer (30 daN m for the twin-screw extruder used in this study) using a torque wrench.</li>
	<li>With the barrel of the machine partially reopened, i.e., with the shafts retracted into the barrel over a distance of approximately 1D, turn the screws at low speed (25 rpm max) to ensure that the entire screw profile is correctly fitted. 
	NOTE: In the case of incorrect installation of the screw elements (e.g., the misalignment for one of them), accelerated wear of the screw elements will be inevitably observed. When testing the rotation of both shafts with the barrel of the machine almost fully open, this results in the shafts touching each other at the point of the incorrectly positioned screw element.</li>
	<li>Completely close the barrel of the machine so that both shafts are entirely trapped inside the barrel.</li>
	<li>Once the barrel is closed, clamp it to the machine with half clamps, and make sure with the help of a level tester that the barrel is perfectly horizontal. 
	NOTE: If the barrel of the twin-screw extruder is not perfectly horizontal, this may lead to premature wear by abrasion of the screw elements and/or the inner walls of the barrel.</li>
	<li>Position the peripherals (the weight feeders for the two solids to be introduced, and the piston pump for the water to be injected) at the required places along the barrel: above module 1 for the feeder used for the oleaginous flax shives, above the hopper of the side feeder (itself connected laterally to module 5) for the one used for the plasticized linseed cake (case of configuration (step 3.1.2) only), and at the end of module 2 for the water injection.</li>
</ol>
4. Carry out the twin-screw extrusion treatment according to configuration (step 3.1.1) or configuration (step 3.1.2)
<ol>
	<li>From the supervision of the machine, enter the set temperatures of each of the modules and start the temperature control of the barrel: for configuration (step 3.1.1), 25 &#176;C for the feeding module (module 1) and 110 &#176;C for the following ones; for configuration (step 3.1.2), 25 &#176;C for module 1, 110 &#176;C for the refining zone (modules 2 to 4), and 80 &#176;C for the premixing one (modules 5 to 8). 
	NOTE: The temperature control of the barrel is carried out separately from one module to another by (i) heating with two resistive half clamps fixed around each module, and (ii) cooling by circulating cold water inside the module. A 25 &#176;C is privileged for the feeding module. For an efficient refining of the fibers, a 110 &#176;C temperature is preferred. An 80 &#176;C temperature is sufficient for the premixing operation. Since the refining and premixing zones are both located along several modules, all modules in the same zone are assigned the same set temperature.</li>
	<li>Wait for the stability of the measured temperatures and make sure that these temperatures are equal to the set points. 
	NOTE: The measured temperatures are given on the control panel of the machine. In order to ensure a second control of these temperatures, it is also possible to measure them with an infrared thermometer at the level of each module along the barrel.</li>
	<li>Slowly turn the screws (i.e., 50 rpm max). 
	NOTE: Premature abrasive wear of the screw elements and the inner walls of the barrel can occur if the screws turn too quickly while the machine is empty.</li>
	<li>Gently feed the twin-screw extruder with water (5 kg/h flow rate).</li>
	<li>Wait for around 30 s until water comes out at the end of the barrel.</li>
	<li>Then, start to introduce the oleaginous flax shives in module 1 at a 3 kg/h flow rate, and wait (for around 1 min) for the solid to start coming out of the extruder.</li>
	<li>Gradually increase (at least in three successive steps) the speed of the screws, then the water flow rate and finally the shives flow rate until the desired set points are reached: 150 rpm, 15 kg/h and 15 kg/h, respectively (Table 1). 
	NOTE: These set points were determined in previous studies and result from the optimization of the process25,26,27.</li>
	<li>Wait for the machine stabilization by following the evolution of the electrical current consumed by the engine over time (variation of the electrical current no more than 5% from the 125 A average value). 
	NOTE: The stabilization time is usually in the range of 10 to 15 min.</li>
	<li>For configuration (step 3.1.2) only, start introducing the plasticized linseed cake at 0.50 kg/h once the machine has stabilized in amperage after the shives and water addition to the desired set values. Then, increase the flow rate of the plasticized linseed cake in at least three successive steps up to the desired set point (from 1.50 kg/h to 3.75 kg/h, which corresponds to values between 10% and 25% by mass in relation to the shives) (Table 1).</li>
	<li>Once the electrical current consumed by the twin-screw extruder motor is perfectly stable, make sure that the temperature profile measured along the barrel is conform to the set values given by the operator, and then start sampling the extruded shives for configuration (step 3.1.1) or the premix for configuration (step 3.1.2) at the outlet. 
	NOTE: In order to not clog the unit, the current drawn by the motor must always remain below its limit value (i.e., 400 A for the pilot scale twin-screw extruder used in this study). It should, therefore, be checked that this limit value is not reached during the entire flow ramp-up phase as well as during sampling. During production, if the cooling system of the machine is not able to maintain the temperature of at least one module at its set value, this may be the consequence of an inappropriate screw profile (i.e., too restrictive screw elements at this location),which causes a local self-heating of the treated material. It is then necessary to make sure, e.g., by means of a thermogravimetric analysis (TGA) of the solid being processed, that this temperature does not cause any fiber degradation.</li>
	<li>During the entire sampling process, make sure that the machine feed is trouble-free by regularly checking the effective entry of solids and water into the barrel of the machine. 
	NOTE: A stable amperage of the current drawn by the motor of the twin-screw extruder during the entire sampling time is a confirmation of a stable feeding of the machine.</li>
	<li>At the end of production, switch off the two solid dosing units and the piston pump.</li>
	<li>Empty the machine while gradually reducing the speed of rotation of the screws to 50 rpm.</li>
	<li>When nothing comes out of the barrel end, clean the inside of the barrel of the twin-screw extruder with plenty of water, introduced in large excess from module 1, while the screws are still rotating at 50 rpm. Add water 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.</li>
</ol>
5. Dry and condition the resulting extrudates (i.e., extrusion-refined shives or premix)
<ol>
	<li>When the extrudates are not to be molded into fiberboards immediately after the twin-screw extrusion process, dry them with a hot air stream to a humidity between 8% and 12% before their conditioning. For this purpose, use a simple ventilated oven or, in the case of large quantities of extrudate to be dried, a continuous belt dryer. 
	NOTE: With such humidity, the extrudates can be conditioned without the risk of fungus or mold growth over time. Packaging should be carried out in perfectly sealed plastic bags, which should be stored in a dry place.</li>
	<li>Dry the extrudates with hot air flow to a humidity between 3% and 4% when fiberboard molding takes place immediately after the twin-screw extrusion process. 
	&#8203;NOTE: Previous studies showed that a moisture content of 3% to 4% of the solid to be hot pressed is ideal to limit degassing phenomena at the end of molding. When it occurs and it is not controlled, degassing can generate defects (e.g., blisters or cracks) inside the fiberboard,and these defects have a negative impact on its mechanical resistance26,27,31,32. When hot pressing is carried out after the extrudates have been stored in airtight plastic bags at a moisture content of 8% to 12%, they should be dried further, i.e., up to 3%-4%, before molding.</li>
</ol>
6. Mold the fiberboards by hot pressing
NOTE: The operating conditions for hot pressing have been chosen on the basis of previous studies26,27,31,32.
<ol>
	<li>Pre-heat the mold. Then, position the solid material to be hot pressed inside the mold. Lastly, pre-heat this solid material for 3 min before applying the pressure. 
	NOTE: For all the fiberboards produced, the proportion of shives in the mix to be molded represents a mass of 100 g when the mold used is square in shape and with 15 cm sides.</li>
	<li>Apply a pressure of 30 MPa with the raw shives, and 10 MPa, 20 MPa, or 30 MPa with the extruded ones (Table 2).</li>
	<li>Set the mold temperature to 200 &#176;C. 
	NOTE: Because the temperature greatly influences the quality (especially the bending properties) of the boards obtained9,26,27,28,31,32, it is important to check the mold temperature with an infrared thermometer on both its male and female parts.</li>
	<li>Set the molding time to 150 s.</li>
	<li>Manufacture different fiberboards with different contents of plasticized linseed cake (from 0% to 25%) using the extrusion-refined fibers obtained through twin-screw extrusion via configuration (step 3.1.1) or one of the three premixes obtained via configuration (step 3.1.2) (Table 1 and Table 2).</li>
	<li>As references, also manufacture two additional fiberboards based on the raw OFS, one without the addition of exogenous binder (board number 11) and the other with the addition of 25% (w/w) of plasticized linseed cake (board number 12) (Table 2). 
	&#8203;NOTE: For these two boards, the molding conditions are the same, i.e., 200 &#176;C for the mold temperature, 150 s for the molding time, and 30 MPa for the applied pressure.</li>
</ol>
7. Condition and characterize the fiberboards
<ol>
	<li>Once the fiberboards have been produced, place them in a climatic chamber at 60% relative humidity and 25 &#176;C until a constant weight is achieved. 
	NOTE: The fiberboards will then be conditioned and stabilized in terms of humidity.</li>
	<li>Once equilibrated, cut the fiberboards into test specimens. 
	NOTE: The most suitable tool for cutting fiberboards is a vertical band saw.</li>
	<li>From the test specimens, proceed with the characterization of the fiberboards using standardized tests for bending properties (ISO 16978:2003 standard), Shore D surface hardness (ISO 868:2003 standard), internal bond strength (ISO 16260:2016 standard), and water sensitivity after immersion in water for 24 h (ISO 16983:2003 standard).</li>
	<li>Compare the properties measured for the fiberboards with the recommendations of the French standard dedicated to the specifications for particleboards (NF EN 312) in order to determine their possible uses.</li>
</ol>

The authors have nothing to disclose.

The protocol outlined here describes how to process the extrusion-refining of lignocellulosic fibers before using them as mechanical reinforcement in renewable boards. Here, the twin-screw extruder used is a pilot scale machine. With screws of 53 mm in diameter (D), it is equipped with eight modules, each 4D in length, except for module 1 that has an 8D length, corresponding to a 36D total length (i.e., 1,908 mm) for the barrel. Its length is long enough to apply to the processed material the succession of several elemen...

Extrusion is a process during which a flowing material is forced through a hot die. Extrusion, therefore, permits the forming of preheated products under pressure. The first industrial single-screw extruder appeared in 1873. It was used for the manufacture of metallic continuous cables. From 1930 onwards, single-screw extrusion was adapted to the food industry to produce sausages and past. Conversely, the first twin-screw extruder has first been used for developments in the food industry. It did not appear in the field of synthetic polymers until the 1940s. For this purpose, new machines were designed, and their operation was also modeled1. A system with co-penetrating and co-rotating screws was developed, allowing mixing and extrusion to be carried out simultaneously. Since then, the extrusion technology has developed continuously via the design of new types of screws. Today, the food industry makes extensive use of twin-screw extrusion although it is more expensive than single-screw extrusion as twin-screw extrusion permits access to more elaborated material processing and final products. It is particularly used for extrusion-cooking of starchy products but also the texturing of proteins and the manufacture of pet food and fish feed.
More recently, twin-screw extrusion has seen its field of application extended to the thermo-mechano-chemical fractionation of plant matter2,3. This new concept has led to the development of real reactors capable of transforming or fractionating plant matters in a single step, up to the separate production of an extract and a raffinate by liquid/solid separation2,3,4. Work carried out at the Laboratory of Agro-industrial Chemistry (LCA) has highlighted the multiple possibilities of the twin-screw technology for the fractionation and valorization of agroresources2,3. Some of the examples are: 1) The mechanical pressing and/or &#34;green&#34; solvent extraction of vegetable oil5,6,7,8,9,10. 2) The extraction of hemicelluloses11,12, pectins13, proteins14,15, and polyphenolic extracts16. 3) The enzymatic degradation of plant cell walls for producing second-generation bioethanol17. 4) The production of biocomposite materials with protein18 or polysaccharide19 matrices. 5) The production of thermoplastic materials by mixing cereals, and bio-based polyesters20,21. 6) The production of biocomposites by compounding a thermoplastic polymer, bio-based or not, and plant fillers22,23. 7) The defibration of lignocellulosic materials for producing paper pulp13,24, and fiberboards25,26,27,28,29,30,31,32.
The twin-screw extruder is often considered as a continuous thermo-mechano-chemical (TMC) reactor. Indeed, it combines in a single step chemical, thermal, and, also, mechanical actions. The chemical one results in the possibility to inject liquid reagents in various points along the barrel. The thermal one is possible due to the thermal regulation of the barrel. Lastly, the mechanical one depends on the choice of the screw elements along the screw profile.
For the defibration of lignocellulosic materials to produce fiberboards, the most recent works have used rice straw25,28, coriander straw26,29, oleaginous flax shives27 as well as sunflower30,32 and amaranth31 barks. The current interest of lignocellulosic biomasses for such an application (i.e., mechanical reinforcement) is explained by the regular depletion of forest resources used for producing wood-based materials. Crop residues are inexpensive and may be widely available. In addition, current wood particles are mixed with petrochemical resins which can be toxic. Often accounting for more than 30% of the total cost of current commercial materials33, some resins contribute to formaldehyde emissions and reduce indoor air quality34. Research interest has shifted to the use of natural binders.
Lignocellulosic biomass is mainly composed of cellulose and hemicelluloses, forming a heterogeneous complex. Hemicelluloses are impregnated with layers of lignins that form a three-dimensional network around these complexes. The use of lignocellulosic biomass for the manufacture of fiberboards generally requires a defibration pre-treatment. For this, it is necessary to break down the lignins that protect cellulose and hemicelluloses. Mechanical, thermal, and chemical35 or even enzymatic36,37,38 pre-treatments must be applied. These steps also increase self-adhesion of fibers, which can promote the production of binderless boards27 even if an exogenous binder is most often added.
The primary purpose of pre-treatments is to improve the particle size profile of micrometric fibers. A simple grinding offers the possibility to reduce the fiber size27,39,40. Inexpensive, it contributes to increase the fiber specific surface. The components of the inner cell wall become more accessible and the mechanical properties of the obtained panels are improved. The efficiency of defibration is significantly increased when a thermo-mechanical pulp is produced, e.g., by digestion plus defibration41, from different pulping processes42 or by steam explosion43,44,45,46,47. More recently, LCA has developed an original pre-treatment of lignocellulosic fibers using twin-screw extrusion25,26,27,28,29,30,31,32. After TMC defibration, the extruder also enables the homogeneous dispersion of a natural binder inside fibers. The resulting premix is ready to be hot pressed into fiberboards.
During the defibration of rice straw, twin-screw extrusion was compared to a digestion plus defibration process25. The extrusion method revealed a significantly reduced cost, i.e., nine times lower than the pulping one. Furthermore, the amount of added water is reduced (1.0 max liquid/solid ratio instead of 4.0 min with the pulping method), and a clear increase in the average aspect ratio of refined fibers (21.2-22.6 instead of 16.3-17.9) is observed as well. These fibers present highly improved mechanical strengthening capability. This was demonstrated for rice straw-based fiberboards, in which pure non deteriorated lignin (e.g., Biolignin) was used as a binder (up to 50 MPa for bending strength and 24% for thickness swelling after 24 h immersion in water)28.
The interest of TMC defibration in twin-screw extruder has also been confirmed with coriander straw26. The aspect ratio of refined fibers varies from 22.9-26.5 instead of only 4.5 for simply ground fibers. 100% coriander-based fiberboards were obtained by adding to the extrusion-refined straws a cake from the seed as protein binder (40% in mass). Their flexural strength (up to 29 MPa) and especially their resistance to water (up to 24% thickness swelling) were significantly improved compared to panels made from simply crushed straw. Moreover, these panels do not emit formaldehyde and, as a consequence, they are more environmentally and human-health friendly than medium-density fiberboard (MDF) and chipboard29 classically found in the market.
Similarly, panels entirely based on amaranth31 and sunflower32, combining extrusion-refined fibers from bark as reinforcement and seed cake as a protein binder, were successfully produced. They showed flexural strengths of 35 MPa and 36 MPa, respectively. However, their water resistance was found to be lower: 71% and 87%, respectively, for thickness swelling. Self-bonded panels based on extrusion-refined shives from oleaginous flax straw can also be obtained27. In this case, it is the ligneous fraction, released during the twin-screw TMC defibration, that contributes to the self-bonding. However, hardboards obtained show a lower mechanical strength (only 12 MPa flexural strength), and very high thickness swelling (127%).
All the extruded fiber-based panels presented above can find industrial applications and are, therefore, sustainable alternatives to current commercial wood-based materials. According to the International Organization for Standardization (ISO) requirements48,49,50, their specific applications will depend on their mechanical and water sensitivity characteristics.
In this paper, the procedure to extrude and refine lignocellulosic fibers before using them as mechanical reinforcement in renewable boards is described in detail. As a reminder, this process reduces the amount of water to be added in comparison to traditional pulping methodologies, and it is also less energy consuming25. The same twin-screw machine can also be used for adding a natural binder to fibers.
More specifically, a detailed outline for conducting the twin-screw extrusion-refining of shives from oleaginous flax (Linum usitatissimum L.) straw is presented. The straw used in this study was commercially obtained. It was from the Everest variety, and the plants were cultivated in the South West part of France in 2018. In the same extruder pass, a plasticized linseed cake (used as exogenous binder) can also be added in the middle of the barrel, and then mixed intimately to the refined shives along the second half of the screw profile. A homogeneous mixture having the form of a fluffy material is collected at the machine outlet. The one-step TMC operation is conducted using a pilot scale machine. Our goal is to provide a detailed procedure for the operators to conduct properly the extrusion-refining of shives, and then the cake addition. Following this operation, the obtained premix is ready for subsequent manufacture of 100% oleaginous flax-based hardboards using hot pressing.

<table><tbody><tr><td>Analogue durometer</td><td>Bareiss</td><td>HP Shore</td><td>Device used for determining the Shore D surface hardness of fiberboards</td></tr><tr><td>Ash furnace</td><td>Nabetherm</td><td>Controller B 180</td><td>Furnace used for the mineral content determinations</td></tr><tr><td>Belt dryer</td><td>Clextral</td><td>Evolum 600</td><td>Belt dryer used for the continuous drying of extrudates at the exit of the twin-screw extruder</td></tr><tr><td>Cold extraction unit</td><td>FOSS</td><td>FT 121 Fibertec</td><td>Cold extractor used for determining the fiber content inside solid materials</td></tr><tr><td>Densitometer</td><td>MA.TEC</td><td>Densi-Tap IG/4</td><td>Device used for determining apparent and tapped densities of extrudates once dried</td></tr><tr><td>Double-helix mixer</td><td>Electra</td><td>MH 400</td><td>Mixer used for preparing the solid mixture made of the raw shives and the plasticized linseed cake for producing board number 12</td></tr><tr><td>Fiber morphology analyzer</td><td>Techpap</td><td>MorFi Compact</td><td>Analyzer used for determining the morphological characteristics of extrusion-refined shives</td></tr><tr><td>Gravimetric belt feeder</td><td>Coperion K-Tron</td><td>SWB-300-N</td><td>Feeder used for the quantification of the oleaginous flax shives</td></tr><tr><td>Gravimetric screw feeder</td><td>Coperion K-Tron</td><td>K-ML-KT20</td><td>Feeder used for the quantification of the plasticized linseed cake</td></tr><tr><td>Hammer mill</td><td>Electra</td><td>BC P</td><td>Crusher used for the grinding of granules made of plasticized linseed cake</td></tr><tr><td>Heated hydraulic press</td><td>Pinette Emidecau Industries</td><td>PEI 400-t</td><td>Hydraulic press used for molding the fiberboards through hot pressing</td></tr><tr><td>Hot extraction unit</td><td>FOSS</td><td>FT 122 Fibertec</td><td>Hot extractor used for determining the water-soluble and fiber contents inside solid materials</td></tr><tr><td>Image analysis software</td><td>National Institutes of Health</td><td>ImageJ</td><td>Software used for determining the morphological characteristics of raw shives</td></tr><tr><td>Oleaginous flax straw</td><td>Ovalie Innovation</td><td>N/A</td><td>Raw material supplied for the experimental work</td></tr><tr><td>Piston pump</td><td>Clextral DKM</td><td>Super MD-PP-63</td><td>Pump used for the water quantification and injection</td></tr><tr><td>Scanner</td><td>Toshiba</td><td>e-Studio 257</td><td>Scanner used for taking an image of raw shives in gray level</td></tr><tr><td>Side feeder</td><td>Clextral</td><td>E36</td><td>Feeder used to force the introduction of the plasticized linseed cake inside the barrel (at the level of module 5) for configuration (b)</td></tr><tr><td>Thermogravimetric analyzer</td><td>Shimadzu</td><td>TGA-50</td><td>Analyzer used for conducting the thermogravimetric analysis of the solids being processed</td></tr><tr><td>Twin-screw extruder</td><td>Clextral</td><td>Evolum HT 53</td><td>Co-rotating and co-penetrating pilot scale twin-screw extruder having a 36D total length (D is the screw diameter, i.e., 53 mm)</td></tr><tr><td>Universal oven</td><td>Memmert</td><td>UN30</td><td>Oven used for the moisture content determinations</td></tr><tr><td>Universal testing machine</td><td>Instron</td><td>33R4204</td><td>Testing machine used for determining the bending properties of fiberboards</td></tr><tr><td>Ventilated oven</td><td>France Etuves</td><td>XL2520</td><td>Oven used for the discontinuous drying of extrudates at the exit of the twin-screw extruder</td></tr><tr><td>Vibrating sieve shaker</td><td>RITEC</td><td>RITEC 600</td><td>Sieve shaker used for the sieving of the plasticized linseed cake</td></tr><tr><td>Vibrating sieve shaker</td><td>RITEC</td><td>RITEC 1800</td><td>Sieve shaker used for removing short bast fibers entrapped inside the oleaginous flax shives</td></tr></tbody></table>

twin-screw extrusion process to produce renewable fiberboards

A versatile twin-screw extrusion process to provide an efficient thermo-mechano-chemical pre-treatment on lignocellulosic biomass before using it as source of mechanical reinforcement in fully bio-based fiberboards was developed. Various lignocellulosic crop by-products have already been successfully pre-treated through this process, e.g., cereal straws (especially rice), coriander straw, shives from oleaginous flax straw, and bark of both amaranth and sunflower stems.
The extrusion process results in a marked increase in the average fiber aspect ratio, leading to improved mechanical properties of fiberboards. The twin-screw extruder can also be fitted with a filtration module at the end of the barrel. The continuous extraction of various chemicals (e.g., free sugars, hemicelluloses, volatiles from essential oil fractions, etc.) from the lignocellulosic substrate, and the fiber refining can, therefore, be performed simultaneously.
The extruder can also be used for its mixing ability: a natural binder (e.g., Organosolv lignins, protein-based oilcakes, starch, etc.) can be added to the refined fibers at the end of the screw profile. The obtained premix is ready to be molded through hot pressing, with the natural binder contributing to fiberboard cohesion. Such a combined process in a single extruder pass improves the production time, production cost, and may lead to reduction in plant production size. Because all the operations are performed in a single step, fiber morphology is better preserved, thanks to a reduced residence time of the material inside the extruder, resulting in enhanced material performances. Such one-step extrusion operation may be at the origin of a valuable industrial process intensification.
Compared to commercial wood-based materials, these fully bio-based fiberboards do not emit any formaldehyde, and they could find various applications, e.g., intermediate containers, furniture, domestic flooring, shelving, general construction, etc.

During the fiber refining of oleaginous flax shives using configuration (step 3.1.1), water was deliberately added at a liquid/solid ratio equal to 1.0. According to previous works25,26,27, such a liquid/solid ratio better preserves the length of the refined fibers at the twin-screw extruder outlet than lower ratios, which simultaneously contributes to an increase in their average aspect ratio. Furthermore, the amount of water a...

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Twin-Screw Extrusion Process to Produce Renewable Fiberboards

A versatile twin-screw extrusion process to provide an efficient thermo-mechano-chemical pretreatment on lignocellulosic biomass was developed, which leads to an increased average fiber aspect ratio. A natural binder can also be added continuously after fiber refining, leading to bio-based fiberboards with improved mechanical properties after hot pressing of the obtained extruded material.

A versatile twin-screw extrusion process to provide an efficient thermo-mechano-chemical pre-treatment on lignocellulosic biomass before using it as ...

twin-screw-extrusion-process-to-produce-renewable-fiberboards

Research

JoVE Journal

Engineering

6.3K Views.  Université de Toulouse, INRAE, INPT. Deze twin-screw extrusietechnologie kan worden gebruikt om continu en efficiënt de voorbehandeling van lignocellulosische biomassa's voorafgaand aan vezelplaatvorming uit te voeren. De homogene thermomechanische pulp wordt geproduceerd tegen lage kosten en met een verminderd volume water. En de veelzijdigheid van extrusie maakt de toevoeging van een natuurlijk bindmiddel in één keer mogelijk.Het gebruik van het vochtgehalte op gecombineerde temperatuur is een sleutel voor een succes...

Video: Twin-Screw Extrusion Process to Produce Renewable Fiberboards

Process of Making Three-dimensional Microstructures using Vaporization of a Sacrificial Component

Vascular structures in natural systems are able to provide high mass transport through high surface areas and optimized structure. Few synthetic material fabrication techniques are able to mimic the complexity of these structures while maintaining scalability. The Vaporization of a Sacrificial Component (VaSC) process is able to do so. This process uses sacrificial fibers as a template to form hollow, cylindrical microchannels embedded within a matrix. Tin (II) oxalate (SnOx) is embedded within poly(lactic) acid (PLA) fibers which facilitates the use of this process. The SnOx catalyzes the depolymerization of the PLA fibers at lower temperatures. The lactic acid monomers are gaseous at these temperatures and can be removed from the embedded matrix at temperatures that do not damage the matrix. Here we show a method for aligning these fibers using micromachined plates and a tensioning device to create complex patterns of three-dimensionally arrayed microchannels. The process allows the exploration of virtually any arrangement of fiber topologies and structures.

The Vaporization of a Sacrificial Component (VaSC) process is used to fabricate microvascular structures. This procedure uses sacrificial poly(lactic) acid fibers to form hollow microchannels with precise 3D geometric positioning provided by laser micromachined guide plates.

Vascular structures in natural systems are able to provide high mass transport through high surface areas and optimized structure. Few synthetic material ...

Experimental Implementation of a New Composite Fabrication Method: Exposing Bare Fibers on the Composite Surface by the Soft Layer Method

The bipolar plate is a key component in proton exchange membrane fuel cells (PEMFCs) and vanadium redox flow batteries (VRFBs). It is a multi-functional component that should have high electrical conductivity, high mechanical properties, and high productivity.
In this regard, a carbon fiber/epoxy resin composite can be an ideal material to replace the conventional graphite bipolar plate, which often leads to the catastrophic failure of the entire system because of its inherent brittleness. Though the carbon/epoxy composite has high mechanical properties and is easy to manufacture, the electrical conductivity in the through-thickness direction is poor because of the resin-rich layer that forms on its surface. Therefore, an expanded graphite coating was adopted to solve the electrical conductivity issue. However, the expanded graphite coating not only increases the manufacturing costs but also has poor mechanical properties.
In this study, a method to expose fibers on the composite surface is demonstrated. There are currently many methods that can expose fibers by surface treatment after the fabrication of the composite. This new method, however, does not require surface treatment because the fibers are exposed during the manufacture of the composite. By exposing bare carbon fibers on the surface, the electrical conductivity and mechanical strength of the composite are increased drastically.

A protocol to expose bare fibers on the composite surface by eliminating resin rich area is presented. The fibers are exposed during fabrication of the composites, not by the post surface treatment. The exposed carbon composites exhibit high electrical conductivity in the through-thickness direction and high mechanical property.

The bipolar plate is a key component in proton exchange membrane fuel cells (PEMFCs) and vanadium redox flow batteries (VRFBs). It is a multi-functional ...

Manufacturing Of Robust Natural Fiber Preforms Utilizing Bacterial Cellulose as Binder

A novel method of manufacturing rigid and robust natural fiber preforms is presented here. This method is based on a papermaking process, whereby loose and short sisal fibers are dispersed into a water suspension containing bacterial cellulose. The fiber and nanocellulose suspension is then filtered (using vacuum or gravity) and the wet filter cake pressed to squeeze out any excess water, followed by a drying step. This will result in the hornification of the bacterial cellulose network, holding the loose natural fibers together.
Our method is specially suited for the manufacturing of rigid and robust preforms of hydrophilic fibers. The porous and hydrophilic nature of such fibers results in significant water uptake, drawing in the bacterial cellulose dispersed in the suspension. The bacterial cellulose will then be filtered against the surface of these fibers, forming a bacterial cellulose coating. When the loose fiber-bacterial cellulose suspension is filtered and dried, the adjacent bacterial cellulose forms a network and hornified to hold the otherwise loose fibers together.
The introduction of bacterial cellulose into the preform resulted in a significant increase of the mechanical properties of the fiber preforms. This can be attributed to the high stiffness and strength of the bacterial cellulose network. With this preform, renewable high performance hierarchical composites can also be manufactured by using conventional composite production methods, such as resin film infusion (RFI) or resin transfer molding (RTM). Here, we also describe the manufacturing of renewable hierarchical composites using double bag vacuum assisted resin infusion.

We present a novel method of manufacturing rigid and robust short natural fiber preforms using a papermaking process. Bacterial cellulose acts simultaneously as the binder for the loose fibers and provides rigidity to the fiber preforms. These preforms can be infused with a resin to produce truly green hierarchical composites.

A novel method of manufacturing rigid and robust natural fiber preforms is presented here. This method is based on a papermaking process, whereby loose ...

Bioengineering

The Effect of Construction and Demolition Waste Plastic Fractions on Wood-Polymer Composite Properties

Construction and demolition waste (CDW), including valuable materials such as plastics, have a remarkable influence on the waste sector. In order for plastic materials to be re-utilized, they must be identified and separated according to their polymer composition. In this study, the identification of these materials was performed using near-infrared spectroscopy (NIR), which identified material based on their physical-chemical properties. Advantages of the NIR method are a low environmental impact and rapid measurement (within a few seconds) in the spectral range of 1600-2400 nm without special sample preparation. Limitations include its inability to analyze dark materials. The identified polymers were utilized as a component for wood-polymer composite (WPC) that consists of a polymer matrix, low cost fillers, and additives. The components were first compounded with an agglomeration apparatus, followed by production by extrusion. In the agglomeration process, the aim was to compound all materials to produce uniformly distributed and granulated materials as pellets. During the agglomeration process, the polymer (matrix) was melted and fillers and other additives were then mixed into the melted polymer, being ready for the extrusion process. In the extrusion method, heat and shear forces were applied to a material within the barrel of a conical counter-rotating twin-screw type extruder, which reduces the risk of burning the materials and lower shear mixing. The heated and sheared mixture was then conveyed through a die to give the product the desired shape. The above-described protocol proved the potential for re-utilization of CDW materials. Functional properties must be verified according to the standardized tests, such as flexural, tensile, and impact strength tests for the material.

Secondary material streams have been shown to include potential raw materials for production. Presented here is a protocol in which CDW-plastic waste as a raw material is identified, followed by various processing steps (agglomeration, extrusion). As a result, a composite material was produced, and mechanical properties were analyzed.

Construction and demolition waste (CDW), including valuable materials such as plastics, have a remarkable influence on the waste sector. In order for ...

Environment

Fused Filament Fabrication (FFF) of Metal-Ceramic Components

Technical ceramics are widely used for industrial and research applications, as well as for consumer goods. Today, the demand for complex geometries with diverse customization options and favorable production methods is increasing continuously. With fused filament fabrication (FFF), it is possible to produce large and complex components quickly with high material efficiency. In FFF, a continuous thermoplastic filament is melted in a heated nozzle and deposited below. The computer-controlled print head is moved in order to build up the desired shape layer by layer. Investigations regarding printing of metals or ceramics are increasing more and more in research and industry. This study focuses on additive manufacturing (AM) with a multi-material approach to combine a metal (stainless steel) with a technical ceramic (zirconia: ZrO2). Combining these materials offers a broad variety of applications due to their different electrical and mechanical properties. The paper shows the main issues in preparation of the material and feedstock, device development, and printing of these composites.

Fused Filament Fabrication FFF of Metal-Ceramic Components

This study shows multi-material additive manufacturing (AM) using fused filament fabrication (FFF) of stainless steel and zirconia.

Technical ceramics are widely used for industrial and research applications, as well as for consumer goods. Today, the demand for complex geometries with ...

Stereolithographic 3D Printing with Renewable Acrylates

The accessibility of cost-competitive renewable materials and their application in additive manufacturing is essential for an efficient biobased economy. We demonstrate the rapid prototyping of sustainable resins using a stereolithographic 3D printer. Resin formulation takes place by straightforward mixing of biobased acrylate monomers and oligomers with a photoinitiatior and optical absorber. Resin viscosity is controlled by the monomer to oligomer ratio and is determined as a function of shear rate by a rheometer with parallel plate geometry. A stereolithographic apparatus charged with the biobased resins is employed to produce complex shaped prototypes with high accuracy. The products require a post-treatment, including alcohol rinsing and UV irradiation, to ensure complete curing. The high feature resolution and excellent surface finishing of the prototypes is revealed by scanning electron microscopy.

A protocol for additive manufacturing with renewable photopolymer resins on a stereolithography apparatus is presented.

The accessibility of cost-competitive renewable materials and their application in additive manufacturing is essential for an efficient biobased economy. ...

Chemistry

Fabrication and Design of Wood-Based High-Performance Composites

Delignified densified wood is a new promising and sustainable material that possesses the potential to replace synthetic materials, such as glass fiber reinforced composites, due to its excellent mechanical properties. Delignified wood, however, is rather fragile in a wet state, which makes handling and shaping challenging. Here we present two fabrication processes, closed-mold densification and vacuum densification, to produce high-performance cellulose composites based on delignified wood, including an assessment of their advantages and limitations. Further, we suggest strategies for how the composites can be re-used or decomposed at the end-of-life cycle. Closed-mold densification has the advantage that no elaborate lab equipment is needed. Simple screw clamps or a press can be used for densification. We recommend this method for small parts with simple geometries and large radii of curvature. Vacuum densification in an open-mold process is suitable for larger objects and complex geometries, including small radii of curvature. Compared to the closed-mold process, the open-mold vacuum approach only needs the manufacture of a single mold cavity.

Delignified densified wood represents a new promising lightweight, high-performance and bio-based material with great potential to partially substitute natural fiber reinforced- or glass fiber reinforced composites in the future. We here present two versatile fabrication routes and demonstrate the possibility to create complex composite parts.

Delignified densified wood is a new promising and sustainable material that possesses the potential to replace synthetic materials, such as glass fiber ...

Fast Pyrolysis of Biomass Residues in a Twin-screw Mixing Reactor

Fast pyrolysis is being increasingly applied in commercial plants worldwide. They run exclusively on woody biomass, which has favorable properties for conversion with fast pyrolysis. In order to increase the synergies of food production and the energetic and/or material use of biomass, it is desirable to utilize residues from agricultural production, e.g., straw. The presented method is suitable for converting such a material on an industrial scale. The main features are presented and an example of mass balances from the conversion of several biomass residues is given. After conversion, fractionated condensation is applied in order to retrieve two condensates &#8212; an organic-rich and an aqueous-rich one. This design prevents the production of fast pyrolysis bio-oil that exhibits phase separation. A two phase bio-oil is to be expected because of the typically high ash content of straw biomass, which promotes the production of water of reaction during conversion.
Both fractionated condensation and the use of biomass with high ash content demand a careful approach for establishing balances. Not all kind of balances are both meaningful and comparable to other results from the literature. Different balancing methods are presented, and the information that can be derived from them is discussed.

A procedure for thermochemical conversion of biomass residues is presented that aims at maximizing the yield of liquid products (fast pyrolysis). It is based on a technology proven on an industrial scale and especially suitable for treating a straw type of biomass.

Fast pyrolysis is being increasingly applied in commercial plants worldwide. They run exclusively on woody biomass, which has favorable properties for ...

Film Extrusion of Crambe abyssinica/Wheat Gluten Blends

Crambe abyssinica is a plant with potential for use in industrial (non-food) plant oil production. The side stream from this oil production is a high-protein crambe meal that has limited value, as it is not fit for food or feed use. However, it contains proteins that could potentially make it a suitable raw material for higher-value products. The purpose of this study was to find methods of making this side stream into extruded films, showing that products with a higher value can be produced. The study mainly considered the development of material compositions and methods of preparing and extruding the material. Wheat gluten was added as a supportive protein matrix material, together with glycerol as a plasticizer and urea as a denaturant. The extrudate was evaluated with respect to mechanical (tensile testing) and oxygen barrier properties, and the extrudate structure was revealed visually and by scanning electron microscopy. A denser, more homogeneous material had a lower oxygen transmission rate, higher strength, and higher extensibility. The most homogeneous films were made at an extruder die temperature of 125-130 &#176;C. It is shown here that a film can be extruded with promising mechanical and oxygen barrier properties, the latter especially after a final compression molding step.

Film Extrusion of Crambe abyssinica/Wheat Gluten Blends

The side stream from plant oil production of Crambe abyssinica has limited value. The purpose of this study was to find methods for extruding materials based on this side stream, demonstrating that products with a higher value can be produced. The extrudates were found to have promising properties.

Crambe abyssinica is a plant with potential for use in industrial (non-food) plant oil production. The side stream from this oil production is a ...

Fabrication and Mechanical Property Assessment of Fiber Composite Laminates

Measuring the Mechanical Properties of Glass Fiber Reinforcement Polymer Composite Laminates Obtained by Different Fabrication Processes

The traditional wet hand lay-up process (WL) has been widely applied in the manufacturing of fiber composite laminates. However, due insufficiency in the forming pressure, the mass fraction of fiber is reduced and lots of air bubbles are trapped inside, resulting in low-quality laminates (low stiffness and strength). The wet hand lay-up/vacuum bag (WLVB) process for the fabrication of composite laminates is based on the traditional wet hand lay-up process, using a vacuum bag to remove air bubbles and provide pressure, and then carrying out the heating and curing process. 
Compared with the traditional hand lay-up process, laminates manufactured by the WLVB process show superior mechanical properties, including better strength and stiffness, higher fiber volume fraction, and lower void volume fraction, which are all benefits for composite laminates. This process is completely manual, and it is greatly influenced by the skills of the preparation personnel. Therefore, the products are prone to defects such as voids and uneven thickness, leading to unstable qualities and mechanical properties of the laminate. Hence, it is necessary to finely describe the WLVB process, finely control steps, and quantify material ratios, in order to ensure the mechanical properties of laminates. 
This paper describes the meticulous process of the WLVB process for preparing woven plain patterned glass fiber reinforcement composite laminates (GFRPs). The fiber volume content of laminates was calculated using the formula method, and the calculated results showed that the fiber volume content of WL laminates was 42.04%, while that of WLVB laminates was 57.82%, increasing by 15.78%. The mechanical properties of the laminates were characterized using tensile and impact tests. The experimental results revealed that with the WLVB process, the strength and modulus of the laminates were enhanced by 17.4% and 16.35%, respectively, and the specific absorbed energy was increased by 19.48%.

Author Spotlight: Enhancing Fiber Composite Laminate Quality with the Wet Hand Lay-Up/Vacuum Bag Process 

This paper describes a fabrication process for fiber-reinforced polymer matrix composite laminates obtained using the wet hand lay-up/vacuum bag method.

The traditional wet hand lay-up process (WL) has been widely applied in the manufacturing of fiber composite laminates. However, due insufficiency in the ...

Twin-Screw Extrusion Process to Produce Renewable Fiberboards

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