Compression of straw to high densities in closed cylindrical dies

Abstract The literature on the compression of straw and grass was reviewed and experiments conducted on the compression of straw in closed dies. Pressure-density relationships for straw were established. Wafers relaxed after removal from the die, to densities which were 25–45% of their compressed densities. At densities of 350 kg/m3 the wafers were durable and could be formed at pressures in a range 12–31 MPa. The optimum moisture content for wafer formation was 10–20% (w.b.); above about 25% (w.b.) it was difficult to form satisfactory wafers. Less pressure was required to form wafers of given density in small dies. Increasing the quantity of straw in a die resulted in an increase in wafer density. Different modes of mechanical loading had no practical advantage. Specific energies for water formation ranged from 11 to 24 MJ/t. Chopping the straw generally resulted in wafers of low durability. Oil seed rape straw formed the densest wafers and barley straw the least dense.