Sustainable epoxy composites from biogenic fillers: Mechanical and thermal characterization of flower heads of milk thistle (Cynara cardunculus) reinforced composites

This study explores the development and characterization of sustainable epoxy composites reinforced with biogenic fibers extracted from the flower heads of Cynara cardunculus (milk thistle). Composites containing 6 % and 12 % fiber content by weight were fabricated using the hand lay-up technique with LY556 epoxy resin and HY951 hardener. Mechanical testing revealed that the 12 % CC/epoxy composite exhibited superior tensile stress (61.07 MPa) compared to the 6 % counterpart (48.07 MPa), although its tensile modulus was reduced. Thermal stability was assessed through thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), indicating improved degradation resistance in higher fiber content composites. FTIR analysis confirmed the presence of key functional groups related to cellulose and lignin, validating an effective fiber-resin interaction. Scanning electron microscopy (SEM) revealed good fiber dispersion and interfacial adhesion, with signs of fiber pullout and breakage under load. Water absorption tests showed increasing moisture uptake over time, with higher absorption in composites with more fiber content. These results demonstrate the potential of milk thistle fibers as a viable reinforcement in sustainable epoxy-based composites, with promising thermal and mechanical performance for eco-friendly applications.