The results show that the tensile stress is decreased with increased triacetin content and this trend was even more visible in PLA/flax composites. The addition of triacetin showed a positive effect on the elongation to break for pure PLA and PLA/flax composites, which was expected because of the softening effect. The highest triacetin addition (15%) clearly shows a negative effect for PLA/flax composites, both the stress and stiffness are strongly decreased