New thermal insulation fiberboards from cake generated during biorefinery of sunflower whole plant in a twin-screw extruder

• New thermal insulation fiberboards were manufactured using a heated hydraulic press.
• The starting material was a cake generated during the biorefinery of sunflower.
• Mold temperature, pressure applied, and molding time affected the fiberboard density.
• The least dense board (500 kg/m3) had the lowest thermal conductivity (88.5 mW/m K).
• These new medium-density materials could be used for thermal insulation of buildings.

The objective of this study was to manufacture new thermal insulation fiberboards by thermo-pressing. The starting material was a slightly deoiled cake (17.6% oil content), generated during the biorefinery of sunflower (Helianthus annuus L.) whole plant in a co-rotating (Clextral BC 45, France) twin-screw extruder. All fiberboards produced were cohesive mixtures of proteins and lignocellulosic fibers, acting respectively as binder and reinforcing fillers in what could be considered as a natural composite. The molding experiments were conducted using a 400 ton capacity heated hydraulic press (Pinette Emidecau Industries, France). The influence of molding conditions on board density, mechanical properties and heat insulation properties was examined. Molding conditions included mold temperature (140–200 °C), pressure applied (150–250 kgf/cm2) and molding time (40–76 s), and these greatly affected board density and thus the mechanical and heat insulation properties. Board density increased with increasingly extreme molding conditions, rising from 500 to 858 kg/m3. The mechanical properties increased at the same time (from 52 to 660 kPa for flexural strength at break, from 5.9 to 49.4 MPa for elastic modulus, from 0.5 to 7.7 kJ/m2 for Charpy impact strength, and from 19.2 to 47.1° for Shore D surface hardness). Conversely, heat insulation properties improved with decreasing board density, and the lowest thermal conductivity (88.5 mW/m K at 25 °C) was obtained with the least dense fiberboard. The latter was produced with a 140 °C mold temperature, a 150 kgf/cm2 pressure applied and a 40 s molding time. A medium mold temperature (160 °C) was needed to obtain a good compromise between mechanical properties (272 kPa for flexural strength at break, 26.3 MPa for elastic modulus, 3.2 kJ/m2 for Charpy impact strength, and 37.3° for Shore D surface hardness), and heat insulation properties (99.5 mW/m K for thermal conductivity). The corresponding board density was medium (687 kg/m3). Because of their promising heat insulation properties, these new fiberboards could be positioned on walls and ceilings for thermal insulation of buildings. The bulk cake also revealed very low thermal conductivity properties (only 65.6 mW/m K at 25 °C) due to its very low bulk density (204 kg/m3). It could be used as loose fill in the attics of houses.