To achieve adequate mechanical properties in flax fibre-reinforced recycled polypropylene (rPP) composites, strong fibre-matrix adhesion is required. Typically, poor adhesion between flax and polypropylene (PP) is improved by using maleic anhydride-grafted PP (MAPP), in turn improving the mechanical properties of the composite. However, in rPP derived from mixed-source post-consumer waste, the interfacial shear strength (IFSS) remained constant at approx. 5 MPa, regardless of the MAPP concentration. In contrast, the MAPP showed an improvement in virgin PP, increasing the IFSS to 11.1 MPa. Differential scanning calorimetry (DSC) measurements revealed the presence of polyethylene (PE) in the rPP. A PP/PE blend showed an improvement in IFSS to 8.3 MPa, indicating that polymer contamination partially affects adhesion. Further chemical analysis using NMR (Nuclear Magnetic Resonance) and GC-MS (Gas Chromatography-Mass Spectrometry) revealed the presence of commonly used additives and their respective oxidation products, as well as terpenes, which are hypothesised to interfere with MAPP functionality. A masterbatch solution was implemented, compensating for the reduced mechanical performance of rPP-based composites, achieving a Young’s modulus of 2.18 GPa and a tensile strength of 30 MPa, compared to 2.24 GPa and 35 MPa for fibre-reinforced virgin materials, respectively, while maintaining a recyclate content of 67 %.
Facing challenges in the incorporation of flax fibres into recycled post-consumer polypropylene matrices
Giulia Ronconi;
2026
Abstract
To achieve adequate mechanical properties in flax fibre-reinforced recycled polypropylene (rPP) composites, strong fibre-matrix adhesion is required. Typically, poor adhesion between flax and polypropylene (PP) is improved by using maleic anhydride-grafted PP (MAPP), in turn improving the mechanical properties of the composite. However, in rPP derived from mixed-source post-consumer waste, the interfacial shear strength (IFSS) remained constant at approx. 5 MPa, regardless of the MAPP concentration. In contrast, the MAPP showed an improvement in virgin PP, increasing the IFSS to 11.1 MPa. Differential scanning calorimetry (DSC) measurements revealed the presence of polyethylene (PE) in the rPP. A PP/PE blend showed an improvement in IFSS to 8.3 MPa, indicating that polymer contamination partially affects adhesion. Further chemical analysis using NMR (Nuclear Magnetic Resonance) and GC-MS (Gas Chromatography-Mass Spectrometry) revealed the presence of commonly used additives and their respective oxidation products, as well as terpenes, which are hypothesised to interfere with MAPP functionality. A masterbatch solution was implemented, compensating for the reduced mechanical performance of rPP-based composites, achieving a Young’s modulus of 2.18 GPa and a tensile strength of 30 MPa, compared to 2.24 GPa and 35 MPa for fibre-reinforced virgin materials, respectively, while maintaining a recyclate content of 67 %.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
