The potential of flax shives as reinforcements for injection moulded polypropylene composites

• Published in: Industrial crops and products 2020-06, Vol.148, p.112324, Article 112324
• Main Authors: Nuez, Lucile, Beaugrand, Johnny, Shah, Darshil U., Mayer-Laigle, Claire, Bourmaud, Alain, D’Arras, Pierre, Baley, Christophe
• Format: Article
• Language: English
• Subjects: Bioengineering; Biomaterials; Flax shives; Food engineering; Injection moulding; Life Sciences; Mechanical properties; Morphology; X-ray diffraction
• ISSN: 0926-6690; 1872-633X
• DOI: 10.1016/j.indcrop.2020.112324

•The impact of granulometry flax shives was assessed in injected PP biocomposites.•Morphology, crystallinity and biochemical composition of flax shives were analysed.•Mechanical results vary according to flax shive aspect ratio and volume fraction.•A model was established to evaluate the role of hollow reinforcing flax cell walls. Flax shives (FS) represent approximately 50 % in weight of dry flax stems, making it the main by-product of the flax scutching industry. Being an available and low-added value lignocellulosic resource, flax shives are an interesting candidate for thermoplastic composite reinforcement. In this study, raw flax shives were fragmented by knife milling using two grids of 500 and 250 μm respectively, while a third batch, with a targeted particle size below 50 μm, was obtained by an attrition beads mill. The fragmentation methods used do not modify the biochemical composition of FS but do reduce their crystallinity due to both crystalline cellulose allomorph conversion and amorphization. The poly-(propylene) and 4%-wt maleic anhydride modified poly-(propylene) injection moulded composites produced with these reinforcing materials have a maximum tensile strength that evolves linearly with particle aspect ratio after processing. The tensile Young’s modulus of the composites reinforced by coarser particles is 3268 ± 240 MPa, which is almost 90 % that obtained for a reference 1mm flax fibre reinforced composite. Furthermore, a basic micromechanical model was applied highlighting the reinforcing capacity of cell wall-like small tubular structures (e.g. flax shives). This study underlines the reinforcing potential of low-value by-product flax shives for value-added composite applications.