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.