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In this study, the impregnated fibre bundle test, a common method used by carbon and glass fibre manufacturers to determine the properties of fibres used in composites, was adapted for natural fibres and validated by a round robin test on one type of natural fibres, namely flax fibres. Five European laboratories have carried out in parallel the impregnated fibre bundle test, on the same batch of hackled flax (long fibres), to check the applicability and reliability of this modified method on natural fibres. The results were compared to the more traditional single fibre test on elementary fibres. The back-calculated fibre stiffness shows a very low scatter between the five laboratories of less than ±5% (59.8 ± 2.4 GPa, as measured between 0 and 0.1% strain). The fibre ultimate tensile strength of 527 ± 138 MPa has a higher scatter, compared to stiffness values, as this property is highly sensitive to imperfections and flaws.

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Over the last few years, polymer/clay nanocomposites have been an area of intensive research due to their capacity to improve the properties of the polymer resin. These nanocharged polymers exhibit a complex rheological behavior due to their dispersed structure in the matrix. Thus, to gain fundamental understanding of nanocomposite dispersion, characterization of their internal structure and their rheological behavior is crucial. Such understanding is also key to determine the manufacturing conditions to produce these nanomaterials by liquid composite molding (LCM) process. This paper investigates the mix of nanoclays particles in an unsaturated polyester resin using three different dispersion techniques: manual mixing, sonication, and high shear mixing (HSM). This paper shows that the mixing method has a significant effect on the sample morphology. Rheology, scanning electron microscopy (SEM), and differential scanning calorimetry (DSC) characterization techniques were used to analyze the blends morphology and evaluate the nanoclays stacks/polymer matrix interaction. Several phenomena, such as shear thinning and premature polymer gelification, were notably observed.

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