The influence of the humidity on the mechanical properties of 3D printed continuous flax fibre reinforced poly(lactic acid) composites

The paper describes the influence provided by the humidity on the mechanical and failure properties of 3D printed composites made by continuous flax fibres reinforcing a poly-lactic acid matrix. The bulk in-plane shear, transverse and longitudinal samples considered here have 28%-31% fibre volume fraction and 3%-6% porosity. The longitudinal and transverse elastic moduli of the composites, together with their transverse and shear strengths show an almost exponential decay with the increase of the moisture content. The longitudinal strength remains however constant over the range of relative humidity considered in this work. A fractographic inspection shows that the exposure of the 3D printed composites to large relative humidity values facilitates the interlaminar fracture. The influence of the 3D printing process on the fracture and the mechanical properties is also described. Moreover, the paper provides a comprehensive benchmark of the properties of our 3D printed composites against analogous data from open literature.