Twin-Screw Extrusion Process to Produce Renewable Fiberboards

Podsumowanie

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.

Streszczenie

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.

Wprowadzenie

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 s....

Protokół

1. Prepare the raw materials

1. Use oleaginous flax shives, which are the result of a preliminary stage of mechanical extraction of the bast fibers from straw in an "all fiber" 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 extrude....

Wyniki

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 works^25,26,27, 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.......

Dyskusje

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.......

Materiały

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