Synergistic effects of egg shell powder and halloysite clay nanotubes on the thermal and mechanical properties of abacá/polypropylene composites

The present study investigates the synergistic effects of halloysite clay nanotubes (HNTs) and eggshell powder (ESP) derived from bio-waste on the thermomechanical properties of composites consisting of natural abacá fiber (AF) and polypropylene (PP). First, nine composite sheets of AF/PP incorporating varying loadings of HNTs and ESP (0–6 wt%) were fabricated. The effects of HNTs and ESP on the fracture surfaces of the AF/PP composite using field emission scanning electron microscopy (FESEM) were examined. Subsequently, various experimental tests on the composite samples, including bending tests, differential scanning calorimetry (DSC), and cone calorimeter tests (CCT) were conducted. The results of the bending tests revealed a considerable improvement in the flexural properties of the samples containing HNTs. Specifically, the maximum flexural stress and flexural modulus of the composite containing 6 wt% HNT (H6E0) exhibited approximately 40% and 84% higher values, respectively, compared to the pure AF/PP composite (H0E0). Conversely, the incorporation of ESP had a detrimental effect on the flexural properties of the composites. Additionally, DSC analysis showed an improvement in the thermal behavior of the composite samples upon adding both ESP and HNTs. The results also revealed that while both HNT and ESP had positive effects on the melting temperature (Tm), the impact of ESP was more pronounced. Specifically, the experimental data indicated improvements of 0.9% and 2% in the Tm for the 6 wt% ESP-loaded composite (H0E6) and 6 wt% HNT/6 wt% ESP-loaded composite (H6E6) samples, respectively. Moreover, the CCT results showed that the composite sample containing 3 wt% HNT and 6 wt% ESP exhibited superior flame-retardant performance, indicating significantly improved flammability behavior of the AF/PP composites.