Towards improving the fibre-matrix adhesion in oleaginous flax fibre polylactide (PLA) composites
Topic(s) : Material science
Co-authors :
Alexander BEHRENS (GERMANY), Regine HIRSCHBERG (GERMANY), Sebastian DRABBEN (GERMANY), Pia BORELBACH , Jörg MÜSSIG (GERMANY)Abstract :
Sustainability from an ecological and economical point of view is of great importance towards mitigating climate change. Especially natural fibres have great reinforcing potential in more sustainable composites (Khan et al. 2022). Accordingly, flax shows excellent specific mechanical properties for lightweight composite applications whilst being an eco-friendly reinforcing material. However, flax varieties are classified into textile and oleaginous flax species, where the textile flax is cultivated towards higher quality fibres and higher amounts of fibres per plant. On the contrary, oleaginous flax is harvested for the linseed and cultivated accordingly. The worldwide cultivation area of oleaginous flax far outweighs the area for textile flax with an approx. area of 1.7 Mha (Ouoagne et al. 2017). Typically, after harvesting the seeds, the plant’s stem is unused (Rennebaum et al. 2002). Therefore, a huge sustainable valorisation potential lies in the unused crop of the oleaginous flax plant. Using the reinforcing properties of the oleaginous flax fibres in combination with a biodegradable polylactide (PLA) matrix provides a bio-based and recyclable composite with a wide field of possible applications.
However, to utilise the potential of the composite, the mechanical properties, which are heavily dependent on the adhesion between the fibre and the matrix, have to be determined (Müssig & Graupner 2021). The adhesion between fibre and matrix depends on the me-chanical, physical and chemical interaction. Whereas surface roughness is the main driving factor for mechanical adhesion, physical and chemical adhesion depends on the bonding between the two materials, which has proven difficult because of the polar fibres interacting with the nonpolar matrix (Xia et al. 2016). Whilst the adhesion properties between flax and polyolefins have been researched extensively, very little research has been conducted on the adhesion between flax and PLA. To improve the adhesion between fibre and matrix, either the fibre can be treated or the matrix can be altered. In this work, the fibre treatments with lignin and ethanol, as well as matrix compounds with different coupling agent concentrations have been examined.
Figure 1 shows the interlaminar shear strength between fibre and matrix. The ethanol treatment improved the fibre matrix adhesion significantly, whilst the coupling agent didn’t show any effect. Raman spectroscopy and SEM imaging have been conducted to understand better the underlying principle and why the commercially available adhesion promoter for PLA is hardly effective. Additionally, to observe the improved adhesion on a macro scale, injection moulded tensile specimens have been tested with ethanol treatment as well as without.
However, to utilise the potential of the composite, the mechanical properties, which are heavily dependent on the adhesion between the fibre and the matrix, have to be determined (Müssig & Graupner 2021). The adhesion between fibre and matrix depends on the me-chanical, physical and chemical interaction. Whereas surface roughness is the main driving factor for mechanical adhesion, physical and chemical adhesion depends on the bonding between the two materials, which has proven difficult because of the polar fibres interacting with the nonpolar matrix (Xia et al. 2016). Whilst the adhesion properties between flax and polyolefins have been researched extensively, very little research has been conducted on the adhesion between flax and PLA. To improve the adhesion between fibre and matrix, either the fibre can be treated or the matrix can be altered. In this work, the fibre treatments with lignin and ethanol, as well as matrix compounds with different coupling agent concentrations have been examined.
Figure 1 shows the interlaminar shear strength between fibre and matrix. The ethanol treatment improved the fibre matrix adhesion significantly, whilst the coupling agent didn’t show any effect. Raman spectroscopy and SEM imaging have been conducted to understand better the underlying principle and why the commercially available adhesion promoter for PLA is hardly effective. Additionally, to observe the improved adhesion on a macro scale, injection moulded tensile specimens have been tested with ethanol treatment as well as without.