Interfacial shear strength of flax fibers in thermoset resins evaluated via tensile tests of UD composites

A method of interfacial shear strength evaluation, based on the length distribution of fibers pulled out from the tensile fracture surface of an oriented flax-reinforced composite, is applied to composites with vinyl ester and acrylated epoxidized soy oil resin matrices. Two approaches for characterizing the strength of fibers with modified Weibull distribution, fiber fragmentation tests and fiber tension tests, are compared in the analysis of pull-out data. Interfacial shear strength is found to increase by a few percent when loading rate is increased from 1.33% to 8%/min. © 2012 Elsevier Ltd.</p

Apparent interfacial shear strength of short-flax-fiber/starch acetate composites

The paper deals with an indirect industry-friendly method for identification of the interfacial shear strength (IFSS) in a fully bio-based composite. The IFSS of flax fiber/starch acetate is evaluated by a modified Bowyer and Bader method based on an analysis of the stress-strain curve of a short-fiber-reinforced composite in tension. A shear lag model is developed for the tensile stress-strain response of short-fiber-reinforced composites allowing for an elastic-perfectly plastic stress transfer. Composites with different fiber volume fractions and a variable content of plasticizer have been analyzed. The apparent IFSS of flax/starch acetate is within the range of 5.5-20.5 MPa, depending on composition of the material. The IFSS is found to be greater for composites with a higher fiber loading and to decrease with increasing content of plasticizer. The IFSS is equal or greater than the yield strength of the neat polymer, suggesting good adhesion, as expected for the chemically compatible constituents

Investigation of Surface Properties of Hydrothermally Modified Soft Deciduous Wood

The determination of surface free energy of wood is an important parameter in applications such as coating, painting and gluing. The simplest technique for that is measurement of contact angle. This technique has been used for the investigation of the effect of heat treatment of wood on the surface free energy. Two wood species – aspen and grey alder – have been treated in a range of temperatures from 140 to 180°C. With the sessile drop technique, series of contact angle data have been collected and used to determine the corresponding surface energies and changes in wettability. The most commonly used approaches, Zisman, Owens–Wendt, Wu, equation of state and acid–base theories, were applied. The results demonstrate that heat treatment affects wettability and solid surface energy, in particular, from the Owens–Wendt and Wu theories. We know that at higher treatment temperatures, the polar component of the surface energy for both wood species decreases, while the dispersive component is almost constant. The experiments have been conducted while trying to fulfil the same measuring conditions, but in any case, it was not possible to reach the thermodynamic equilibrium conditions assumed by Young’s equation, due to chemical heterogeneity, surface roughness and capillarity. It is possible to improve the accuracy of results using a larger number of probe liquids