Acoustical properties of Lyocell, hemp, and flax composites

This study characterizes the acoustical behavior of natural fiber composites. Regenerated cellulose fibers (Lyocell), hemp fibers, and flax fibers were embedded in an epoxy-matrix. These unidirectional composites were tested for their logarithmic damping decrement, the resonance frequency, the ultrasound velocity, the dynamic and static modulus of elasticity, and bending strength and density. Glass-epoxy composites served as a reference. All tested cellulosic fibers showed a significantly higher damping at lower densities. The ultrasound velocity was in the range of the reference for Lyocell— and hemp—fiber composites. Taking the low density into account, the dynamic and static modulus of elasticity of the samples were relatively high compared to the glass reference. The specific acoustical properties of these natural fiber composites point at high value applications, e.g., devices that require high damping of the body structures.