Thermoplastic composites reinforced with natural fibers are attracting increasing interest because of their recyclability and lower environmental impact than conventional thermosetting composites. Among these materials, polypropylene-flax composites are promising for lightweight applications, although reliable joining remains challenging because of the low surface energy and chemical inertness of polypropylene. This study investigates adhesive bonding as a low thermal-impact alternative to thermal and ultrasonic welding. A partially bio-derived epoxy adhesive was benchmarked against a conventional toughened epoxy, while two surface preparation methods, mechanical abrasion (sanding) and peel-ply treatment, were evaluated. Joint performance was assessed by single-lap joint (SLJ) testing and surface morphology by three-dimensional optical profilometry. Surface preparation had a dominant influence on joint performance. Sanded specimens exhibited lap shear strengths of 1.65–1.80 MPa, whereas peel-ply-treated specimens achieved 4.98–5.30 MPa. Peel-ply-treated joints also absorbed substantially higher energy (up to approximately 1.74 J) than sanded specimens (0.13–0.21 J). Two-factor ANOVA confirmed that surface preparation significantly affected lap shear strength, whereas adhesive formulation had no statistically significant effect. Peel-ply treatment produced a more homogeneous surface with intermediate roughness (Sa ≈ 9 µm, Sq ≈ 10 µm), whereas sanding generated greater roughness but higher topographical heterogeneity. Failure analysis revealed predominantly adhesive failure for sanded joints and light fiber-tear failure for peel-ply-treated specimens. The bio-based epoxy achieved joint performance comparable to the conventional adhesive, demonstrating its potential as a sustainable alternative for bonding polypropylene-flax composites.
Evaluation of bio-based epoxy adhesive for joining polypropylene-flax composites
Moffa G.;Parodo G.;Sorrentino L.;Turchetta S.;
2026-01-01
Abstract
Thermoplastic composites reinforced with natural fibers are attracting increasing interest because of their recyclability and lower environmental impact than conventional thermosetting composites. Among these materials, polypropylene-flax composites are promising for lightweight applications, although reliable joining remains challenging because of the low surface energy and chemical inertness of polypropylene. This study investigates adhesive bonding as a low thermal-impact alternative to thermal and ultrasonic welding. A partially bio-derived epoxy adhesive was benchmarked against a conventional toughened epoxy, while two surface preparation methods, mechanical abrasion (sanding) and peel-ply treatment, were evaluated. Joint performance was assessed by single-lap joint (SLJ) testing and surface morphology by three-dimensional optical profilometry. Surface preparation had a dominant influence on joint performance. Sanded specimens exhibited lap shear strengths of 1.65–1.80 MPa, whereas peel-ply-treated specimens achieved 4.98–5.30 MPa. Peel-ply-treated joints also absorbed substantially higher energy (up to approximately 1.74 J) than sanded specimens (0.13–0.21 J). Two-factor ANOVA confirmed that surface preparation significantly affected lap shear strength, whereas adhesive formulation had no statistically significant effect. Peel-ply treatment produced a more homogeneous surface with intermediate roughness (Sa ≈ 9 µm, Sq ≈ 10 µm), whereas sanding generated greater roughness but higher topographical heterogeneity. Failure analysis revealed predominantly adhesive failure for sanded joints and light fiber-tear failure for peel-ply-treated specimens. The bio-based epoxy achieved joint performance comparable to the conventional adhesive, demonstrating its potential as a sustainable alternative for bonding polypropylene-flax composites.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
