2.4. Tensile testing

Specimens to be tested were conditioned at a controlled temperature of 25 °C and humidity of 40–60%, during two weeks prior to testing. This allows sufficient time for secondary crystallisation of PHBV [1]. Standard procedures according to ASTM D638 (Type V specimens), were followed during tensile testing using an electromechanical Instron model 5584 (Instron Pty Ltd, USA) with a 1 kN load cell. Specimens were tested at constant cross-head displacement rate of 1 mm/min and clamped using pneumatic grips. The strain value across the narrow region of the specimen was monitored using a video-extensometer. A total of five specimens were tested for each extrusion run. Typical tensile stress versus strain curves observed for neat PHBV and wood–PHBV composites are shown in Fig. 1. The raw data files containing stress–strain values for each individual tested specimen are located in two separate folders ‘Raw Data for mechanical testing – Samples A’ and ‘Raw Data for mechanical testing – Samples B’ for neat PHBV material and wood–PHBV composites respectively. More specifically the raw data files include values for time (s), extension (mm), load (N), video axial strain (%) and tensile strength (MPa), as well as each specimen dimensions (width, thickness and gauge length) and the test date. In this work, tensile strength was calculated as the tensile stress at maximum load (in MPa). Tensile modulus (in GPa) was calculated by the linear trend from fitting between 0% and 2.0% strain, while strain (in % video axial strain) was measured at the point of maximum load. A summary of all the processed data for neat PHBV material and wood–PHBV composites is available in root folder in the files ‘Summary of mechanical testing – Samples A’ and ‘Summary of mechanical testing – Samples B’ for neat PHBV and wood–PHBV composites respectively.

Typical tensile curves observed for (a) neat PHBV, and (b) wood–PHBV (30 wt%) specimens.