An insulation board has been developed that is made from straw and has an excellent environmental profile. The boards were made at low density, 80-160 kg/m³ (5-10 lb/ft³) and have good thermal properties for an air-based insulation, meaning a conductivity of 0.036-0.048 W/m·K (thermal resistance of R4 to R3 per inch [Btu×in./h×ft² ·°F]^-1). The initial effort focused on boards suitable for northern Pakistan, where we have studied the needs and construction of schools and houses. A survey of possible fabrication methods included binding straw particles with such adhesives as PVA and sodium silicate, applied with such methods as spraying, foaming, and dipping. Small samples were formed at a range of densities to test structural and thermal properties. Experimental work showed it was difficult to compete commercially with existing insulation boards in North America or Pakistan. In the final phase of the project, boards were made with a thermosetting resin. Milled straw and resin were mixed in a blender and the boards formed in a hot press. The boards, made at a range of densities and resin contents, were tested thermally and structurally. Good mechanical properties were obtained at resin contents as low as 2% by weight. At densities of 128 and 160 kg/m³ (8 and 10 lb/ft³ ), these boards have thermal conductivities of 0.039-0.041 W/m·K (R-values of 3.7 and 3.45 per inch), respectively. The pressure required to compress the 160 kg/m 3 (10 lb/ft 3 ) boards to 10% of their original thickness is approximately 102 kPa (15 lb/in.²), and the modulus of rupture in bending is in the range of 340 kPa (50 lb/in.²). Removing the fine particles from the straw improved board strength markedly. The best boards had an estimated materials cost of 3.8¢ per unit of thermal resistance and surface area (m²·K/W)·m²), (2¢ per R-ft²), substantially less than the retail cost of the expanded polystyrene available in Pakistan or of any rigid board insulation sold in North America.

AUTHOR: Joseph A. Charlson, Leon R. Glicksman, Ph.D., Henry S. Harvey, Jr., Leslie K. Norford
CITATION: Thermal Performance of the Exterior Envelopes of Buildings VII
KEYWORDS: December, Florida, 1998
YEAR: 1998