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

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)

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

Low-density insulation blocks and hardboards from amaranth (Amaranthus cruentus) stems, a new perspective for building applications

Nowadays, amaranth appears as a promising source of squalene of vegetable origin for the cosmetic industry. Squalene represents up to 6% (w/w) of oil from seeds. It can be isolated from vegetable oil for subsequent use. This triterpene is highly appreciated in cosmetology, especially for the formulation of moisturing creams. Indeed, it has the ability to quickly penetrate the skin without leaving traces or oily sensations on it, and it blends well with other oils and vitamins. The squalene currently marketed is almost exclusively extracted from the liver of sharks, causing at the same time their overfishing. Thus, providing to the cosmetic industry a squalene of renewable origin is a major challenge for the cosmetic industry. As amaranth oil is one of the most concentrated vegetable oils in squalene, this is the reason why the amaranth plant has experienced renewed interest in recent years. In addition to the seeds, a stem is also produced during the amaranth cultivation. Representing up to 80% (w/w) of the plant aerial part, it is composed of a ligneous fraction, the bark, on its periphery, and a pith in its middle. In this study, a mechanical fractionation process was developed to separate continuously bark and pith. The use of both fractions to produce renewable materials for building applications was also investigated. On the one hand, the bark was succesfully used to produce hardboards, with the deoiled seeds acting as natural binder. Such boards are a viable alternative to commercial wood-based panels (e.g., plywood, chipboard, OSB or MDF). On the other hand, the pith was transformed with success into cohesive and machinable low-density insulation blocks revealing a thermal conductivity near from that of polystyrene