Effect of SiO₂ nanoparticles on the melt-crystallization kinetics and mechanical behavior of polypropylene

This study investigates the effect of SiO₂ nanoparticles on polypropylene's (PP) crystallization kinetics and mechanical properties. SiO2 nanoparticles notably improve PP's thermal and mechanical performance by serving as nucleating agents, especially at lower concentrations. Differential scanning calorimetry (DSC) revealed that SiO₂ nanoparticles delayed crystallization onset, prolonged induction times, and altered nucleation behavior. Using the Johnson–Mehl–Avrami-Kolmogorov (JMAK) model, it was observed that nanoparticles increased crystallization rates through enhanced heterogeneous nucleation. Conversely, aggregation restricted molecular mobility at higher nanoparticle loadings, adversely influencing crystallization and mechanical properties. Mechanical tests indicated that 0.5 wt% SiO₂ significantly improved tensile strength (33.58 MPa) and elongation at break (41.3%). Excessive SiO₂ loading led to nanoparticle agglomeration, reducing mechanical performance due to diminished stress transfer efficiency. Scanning electron microscopy (SEM) and Raman spectroscopy confirmed uniform nanoparticle dispersion and strong nanoparticle-polymer interactions at lower concentrations, whereas higher concentrations induced phase separation and structural inconsistencies. Furthermore, activation energy calculations using isoconversional methods, including Ozawa–Flynn–Wall (OFW) and Kissinger–Akahira–Sunose (KAS) models, demonstrated a progressive increase in activation energy with crystallization progress, indicating diffusion-limited crystallization at higher SiO₂ concentrations. The Mo model further confirmed SiO₂ nanoparticles' ability to lower the cooling rate necessary for achieving specific crystallinity levels. Overall, these findings highlight the potential of SiO₂ nanoparticles as effective additives for enhancing PP's mechanical performance and crystallization kinetics at optimal concentrations. The study provides valuable insights into the role of nanoscale fillers in polymer engineering, paving the way for advanced polypropylene-based nanocomposites with tailored thermal and mechanical properties.