Innovative low-density blocks from amaranth pith for the thermal insulation of buildings

Amaranth is an annual herb native to temperate and tropical regions. Cultivated by Native Americans for the nutritional properties of its seeds, the latter are very digestible and also an interesting source of starch and proteins. For the future, amaranth appears as a promising raw material for the biorefinery of whole plants, all parts of the plant being potentially usable for different food and non-food applications. This study especially aims to investigate the possible uses of pith from stems for material applications. For that, plants from the Amaranthus cruentus variety were cultivated in 2018 near Auch (Gers, France). Stems were manually harvested at plant maturity. Representing up to 90% w/w of the aerial part of amaranth plant, stems were then dried in a ventilated oven to facilitate their conservation. They are composed of a bark on their periphery and a pith fraction in their middle. The structure of stems was studied from ten samples, and the pith fraction was estimated manually to 27% w/w. Due to the difference in density between bark and pith fractions, a fractionation process associating grinding and blowing steps made possible the continuous separation between bark and pith. As for sunflower and corn, amaranth pith particles have an alveolar (i.e. a microporous) structure similar to that of expanded polystyrene, and they reveal a very low bulk density (e.g. 48-52 kg/m3 for 4-16 mm particle size, and 58-61 kg/m3 for 1.25-2.50 mm particle size), making them a promising raw material for the thermal insulation of buildings. Cohesive and low-density insulation blocks were successfully obtained from amaranth pith, primarily mixed with a starch-based binder, through compression moulding at ambient temperature. Different operating conditions were tested, especially including (i) the size distribution of amaranth pith particles, (ii) the binder content, and (iii) the filling level of the mould. All produced samples were then characterized in terms of (i) density, (ii) bending and compression properties, and (iii) thermal insulation properties (measured through the hot wire method). All insulation blocks revealed low density, ranging from 90 to 140 kg/m3. Such innovative materials could be sustainable and viable options for the thermal insulation of buildings

Impact of thermomechanical fiber pre-treatment using twin-screw extrusion on the production and properties of renewable binderless coriander fiberboards

The aim of this study consisted of manufacturing renewable binderless fiberboards from coriander straw and a deoiled coriander press cake, thus at the same time ensuring the valorization of crop residues and process by-products. The press cake acted as a natural binder inside the boards owing to the thermoplastic behavior of its protein fraction during thermopressing. The influence of different fiber-refining methods was evaluated and it was shown that a twin-screw extrusion treatment effectively improved fiber morphology and resulted in fiberboards with enhanced performance as compared to a conventional grinding process. The best fiberboard was produced with extrusion-refined straw using a 0.4 liquid/solid (L/S) ratio and with 40% press cake addition. The water sensitivity of the boards was effectively reduced by 63% through the addition of an extrusion raw material premixing operation and thermal treatment of the panels at 200 °C, resulting in materials with good performance showing a flexural strength of 29 MPa and a thickness swelling of 24%. Produced without the use of any chemical adhesives, these fiberboards could thus present viable, sustainable alternatives for current commercial wood-based materials such as oriented strand board, particleboard and medium-density fiberboard, with high cost-effectiveness

Innovative insulating materials from coriander (Coriandrum sativum L.) straw for building applications

Straw represents 60-80% of the aerial part of the coriander plant. Because of the increasing demand for vegetable oil from fruits for food, cosmetics or the chemical industry, the availability of straw will grow strongly in the future. Its high lignocellulose content (62%) makes this crop by-product an interesting raw material for producing bio-based building materials. Bulk materials can be obtained by refining the straw through twin-screw extrusion in the presence of water. The fiber aspect ratio of refined straw can be varied (22.9-26.5) by applying different liquid/solid ratios (0.4-1.0), leading to a variation in the tapped density of the resulting bulk material (110-61 kg/m3). For the lowest density, thermal conductivity is 47.3 mW/(m.K). Twin-screw refining can also be conducted from an aqueous borax solution. Refined straw thus becomes fire-proofed, making it usable as loose fill in housing. Insulation blocks of medium density, associating straw and a starch-based binder, can also be produced through compression molding. With a density of 155 kg/m3 and a thermal conductivity of 55.6 mW/(m.K), the optimal cohesive blocks (7.5 mm milled straw and 15% binder), cold-pressed at 87 kPa for 30 s, are promising alternatives for the thermal insulation of buildings (e.g., filling of walls, interior partitions, etc.)

The coriander straw, an original agricultural by-product for the production of building insulation materials

Straw represents 60-80% of the aerial part of coriander. It is cheap (90 €/ton including harvesting, bunching and transportation) and has an availability of 250 tons/year. However, the latter will grow strongly in the next five years due to the increasing use of vegetable oil from the fruits for food, cosmetics or the chemical industry. Due to its high lignocellulose content (62%), coriander straw is an interesting crop by-product for the production of bio-based building materials. Two types of insulating materials are presented here. Firstly, it is possible to produce bulk materials by thermo-mechano-chemical refining of straw with water using a twin-screw reactor. According to the applied liquid/solid ratio (0.4-1.0), it is possible to control the fiber aspect ratio of the refined straw (22.9-26.5) and thus the tapped density of the resulting bulk material (110-61 kg/m3). For the lowest density, the thermal conductivity was 47.3 mW/m K, corresponding to a 1.06 m2 K/W resistance for a 5 cm thickness of extrusion-refined straw. Twin-screw refining was also successfully conducted with an aqueous borax solution, allowing fire-proofing of the straw. When used as loose fill in housing, refined coriander straw is a promising solution for building insulation. Medium-density insulation blocks can also be manufactured using compression molding by combining coriander straw (milled or extrusion-refined) and a starch-based binder. The use of a milled straw (7.5 mm sieve) mixed with 15% binder, cold pressed (87 kPa, 30 s) and then dried, resulted in cohesive blocks with a 155 kg/m3 density and a 55.6 mW/m K thermal conductivity, corresponding to a 0.90 m2 K/W resistance for a 5 cm thickness. Similarly, such blocks could be used for the thermal insulation of buildings, including the filling of walls, interior partitions, etc

Stems from amaranth (Amaranthus cruentus), an original agricultural by-product for obtaining low-density insulation blocks and hardboards for building applications

Amaranthus cruentus is a promising raw material for the biorefinery of whole plant. Stems are composed of (i) a bark on their periphery (76% w/w), and (ii) a pith in their middle (24% w/w), both usable for material applications. It is possible to separate mechanically and continuously these two fractions thanks to a fractionation process developed recently, involving a grinding step plus a blowing one. The low density for pith particles makes them usable as thermal insulating materials inside buildings (in the form of insulation blocks molded with 10% starchy binder). The optimal insulation block is light and insulating while preserving good machinability and promising mechanical properties. The extrusion-refined bark was successfully used for the manufacture of hardboards (i.e., dense fiberboards) using hot pressing. The optimal hardboard is a viable option for replacing current wood-based building materials, e.g., floor underlayers, interior partitions, etc. According to NF EN 312 standard, this board is already usable for interior fittings (including furniture), in dry environment (P2 type board). With much improved water resistance (10% max for thickness swelling), it could be used as a P7 type board (board working under high stress, used in humid environment)

Characterization of volatile organic compound emissions from self-bonded boards resulting from a coriander biorefinery

In this study, the VOC emissions from a self-bonded coriander board originating from a coriander biorefinery, were investigated. These emissions mainly result from the presence of essential oil in the manufactured materials. Firstly, an extensive analysis of the essential oil obtained from French coriander fruits showed the presence of linalool as the major component (72%), with an absolute concentration in the essential oil of 412 g/L. A characterization of the enantiomeric distribution of linalool, which is important in terms of its bioactivity, resulted in an enantiomeric excess of (S)-linalool of 77%. Further, the presence of this volatile oil in the coriander boards was confirmed through identification of the terpenoid compounds in the VOC emission profile. The area specific emission rate of linalool and camphor was determined at 125 and 25 μgm−2 h−1, respectively, at 25 °C and 50% RH, while their emission was found to increase by a factor of 3 with an increase in temperature of 10 °C. The renewable self-bonded boards could thus present potentially interesting alternatives for less sustainable materials in the construction or agricultural industry, where they could provide a significant added value in terms of indoor air quality or storage of food and agricultural products

VOC and carbonyl compound emissions of a fiberboard resulting from a coriander biorefinery: comparison with two commercial wood-based building materials

Indoor air quality is a major public health issue. It is related to the choice of construction materials and associated with VOC emissions. Two wood-based commercial panels were tested: a medium-density fiberboard (MDF) and a chipboard (CH), and they were compared to a material produced from a coriander biorefinery (COR). Indicators chosen to compare the materials were physical properties (density, bending properties, surface hardness, thickness swelling, and water absorption) and VOC emissions. Emissions were evaluated in an environmental chamber at 23 °C, 31 °C, and 36 °C, and during 28 days. Carbonyl emissions on day 1 at 23 °C were 74, 146, and 35 μg m−2 h−1, respectively, for MDF, CH, and COR. Terpenic emissions were 12, 185, and 37 μg m−2 h−1, respectively. Higher temperature resulted in higher emissions which decreased over time, except for formaldehyde. VOC emissions depended largely on material and temperature. Formaldehyde emission was 300 to 600 times lower for coriander boards (< 0.2 μg m−2 h−1), making them significantly more environmentally friendly materials in comparison with MDF and chipboard. These results highlight the interest of coriander by-products as raw materials for producing fiberboards with low impact on indoor air quality

Amaranth, a model for the future biorefinery of whole plants

Amaranth is an annual herb native to temperate and tropical regions. It is a promising raw material for the biorefinery of whole plants. Looking at the large amounts of starch, proteins and squalene inside its seeds, the latter could find applications in many fields like the food, cosmetics and material industries. This study specifically investigated the possible uses of stems for material applications. Stems are composed of a bark on their periphery (90% w/w) and a pith fraction in their middle (10%). A fractionation process was developed for separating mechanically and continuously these two fractions. Due to their low density (47 kg/m3), pith particles could be used as thermal insulating materials inside buildings. For its part, grinded bark was successfully used for the manufacture of fiberboards using hot pressing. Looking at its usage properties, the optimal hardboard produced appeared as a viable option for replacing current commercial wood-based materials

Performance, durability and recycling of thermoplastic biocomposites reinforced with coriander straw

In this study, coriander straw fiber was effectively incorporated as a reinforcing filler in polypropylene and biobased low-density polyethylene composite materials through twin-screw extrusion compounding and injection molding. Maleic anhydride-grafted copolymers were added as a coupling agent and effectively provided fiber/matrix compatibilization. With a significant reinforcing effect, resulting in a 50% increase in the flexural and tensile strength (from 19 to 28 MPa and from 12 to 17 MPa, respectively, for polypropylene composites) as compared to the native polymer, coriander straw allowed the production of 40% filled thermoplastic biocomposites with adequate mechanical properties comparable to those of commercial wood fibers, excellent durability in terms of UV and hygrothermal weathering and high potential for recycling. At the same time, such coriander biocomposites show a favorable cost structure, with 28% reduction of the granule cost as compared to wood fiber composites

Fabrication de panneaux agglomérés de fibres à partir des anas collectés lors de l'extraction mécanique des fibres libériennes de la paille de lin oléagineux

Dans cette étude, des panneaux agglomérés de fibres ont été produits à partir d’anas collectés après extraction mécanique des fibres libériennes de paille de lin oléagineux. Les panneaux ont été mis en oeuvre par thermopressage. Leurs propriétés mécaniques et thermo-mécaniques ont été étudiées ainsi que leur comportement vis-à-vis de l’eau. L’influence d’un prétraitement thermo-mécanique des anas bruts à l’aide d’une extrudeuse bi-vis a été étudiée ainsi que l’ajout de lignine exogène. Tous les panneaux mis en oeuvre possèdent une tenue suffisante pour être manipulés à la main. Le panneau ayant obtenu les propriétés optimales a été obtenu à partir des anas extrudés et sans ajout supplémentaire de lignine. Au regard de ses caractéristiques et du standard NF EN 312, ce dernier remplit complètement les critères d’un panneau aggloméré de type P1 (panneau d’usage général utilisé en milieu sec)