Green Composites from Natural Resources

73Hemp and Hemp-Based Composites

traditional retting procedures (Vignon et al. 1996). For the steam explosion method,

semi-retted bast ber is removed from the woody core and impregnated with a weak

solution of sodium hydroxide under a vacuum. The bers are drained prior to loading

into a steam reactor and steamed at 200°C (1.5 MPa) for 90 seconds (Vignon et al.

1996). The pressure is released suddenly from the steam reactor, resulting in explo-

sive decompression. As the water in the bers rapidly vaporizes and increases in vol-

ume, the ber bundles are blown apart and separated at the middle lamella. During

the steam treatment, pectins, hemicelluloses, and lignin are partially degraded and

rendered soluble in the sodium hydroxide solution, ...