Hemp yarn reinforced composites - III. Moisture content and dimensional changes

Based on a comprehensive set of experimental data it is demonstrated that the moisture properties of aligned hemp fibre yarn/thermoplastic matrix composites are showing low moisture sorption capacity and low dimensional changes. Using a reference humidity of 65% RH, and a common span of ambient humidity levels of 33% and 85% RH, the relative moisture content of composites with a high fibre fraction is ranging from −0.009 at 33% RH and +0.016 at 85% RH, and this lead to relative transverse hygral strains in the range of only −0.007 to +0.011. The axial hygral strain is practically zero. The moisture content of the composites is shown to be well predicted by a mixtures relationship using the measured moisture contents of the constituents. The dimensional changes of the composites are well predicted by micromechanical models of the transverse and axial hygral strains.