Mechanical, rheological, physical, and thermal proprieties of poly (lactic acid) composites reinforced by walnut and apricots shells flour

In this work, flour of apricots shells (AS) and walnut shells (WS) was valorized for the preparation of various composites, employing poly (lactic acid) as the polymeric matrix. The composites were successfully prepared using the cast-solution method. Fourier transform infrared (FTIR) spectroscopy revealed no significant changes in peak positions, indicating that the incorporation of WS and AS in PLA did not result in any notable alterations to the chemical structure of PLA. Tensile testing demonstrated an increase in both tensile modulus and tensile strength, while the elongation at break decreased for most composites. The composite containing 4% AS exhibited a maximum tensile modulus of 1680.32 MPa, whereas the composite loaded with 2% WS showed a maximum tensile modulus of 1862.10 MPa. The composite loaded with 4% WS displayed the minimum tensile modulus (708.40 MPa), and the composite loaded with 7% AS showed the minimum elongation at break (2.2%), compared to pure PLA. The melt flow index reached its lowest value in the composites loaded with 7% AS and 2% WS. Moisture absorption decreased after the incorporation of AS and WS, and was almost negligible in the composites loaded with 2% WS, 4% AS, and 7% AS. Thermal analyses indicated an increase in thermal stability for all composites after the incorporation of AS and WS. Crystallinity rate increased in all composites loaded with AS, in comparison with pure PLA, while it decreased in the composites loaded with WS, for the heating cycles.