No abstract

The large-scale entry of bio-based polymers, such as poly(hydroxybutyrate-co-valerate) (PHBV), in applications commonly occupied by petroleum-based plastics is heavily limited by their poorer mechanical properties, thus, hindering efforts to reduce harmful plastic waste. Prior work to improve these properties has involved short natural fibre reinforcements, which do not produce substantial improvements. In this work, PHBV was simultaneously reinforced with unidirectional flax and toughened with poly(butylene adipate-co-terephthalate) (PBAT) or epoxidized natural rubber (ENR) to produce well-rounded composites. Toughened unidirectional composites were prepared by cryogenic grinding, powder layup and compression moulding. Unidirectional flax addition resulted in 4-fold increases in tensile properties, 3-fold increases in flexural properties and 20-fold increases in impact properties, whilst producing minimal change in the thermal properties. PBAT and ENR phases appeared well bonded to the PHBV within the composite. The addition of PBAT did not cause any significant changes in thermal or mechanical properties. The addition of ENR, however, reduced the tensile modulus and the flexural properties but produced a significant increase in impact strength, attributed to the coarse particle size of ENR. Unidirectional flax reinforcement of PHBV widens the scope of application of PHBV considerably where mechanical properties are of concern, while ENR has significant potential as a bio-based toughening agent for biocomposites.

Nanoindentation is a commonly used method to measure the hardness of surfaces with thin layers, and is especially useful in studying the change in mechanical properties of ion irradiated materials. This research compares two different methods of nanoindentation to study the changes in hardness resulting from ion irradiation of SS316 alloy. The samples were irradiated by He2+ ions at beam energies of 1, 2, and 3 MeV, respectively. The first method involves the indentation of the irradiated surface perpendicular to it using the continuous stiffness mode (CSM), while the second applies the indents on an oblique surface, accessing an inclined cross-section of the irradiated material. Finite element modelling has been used to further illuminate the deformation processes below the indents in the two methods. The hardness profiles obtained from the two nanoindentation methods reveal the differences in the outcomes and advantages of the respective procedures, and provide a useful guideline for their applicability to various experimental conditions. It is shown through an in depth analysis of the results that the ‘top-down’ method is preferable in the case when the ion irradiation energy, or, equivalently, the irradiated depth is small, due to its greater spatial resolution. However, the oblique cross section method is more suitable when the ion irradiation energy is >1 MeV, since it allows a more faithful measurement of hardness as a function of dose, as the plastic field is much smaller and more sensitive to local hardness values.