ABSTRACT In this study, virgin/recycled HDPE and polypropylene (PP) blends containing 0–30 wt.% post‐consumer recycled fraction, together with fully recycled references, were melt‐processed and comparatively investigated to evaluate the effects of recycled incorporation on thermal stability, viscoelastic response, and melt swelling behavior. Thermogravimetric analysis showed that increasing recycled content reduced early degradation stability, with T2% decreasing from 458.7°C to 390.1°C in HDPE systems and from 418.8°C to 386.8°C in PP systems, while Tmax remained relatively stable. Differential scanning calorimetry revealed nearly unchanged melting temperatures but a marked reduction in crystallinity in both polymer families. Dynamic mechanical analysis indicated composition‐dependent shifts in relaxation behavior and reduced storage modulus stability at higher recycled fractions. Die swell measurements demonstrated a pronounced decline in melt recovery, decreasing from +29.1% to +14.0% in HDPE blends and from +34.0% to −1.43% in PP systems. Overall, the results show that moderate recycled incorporation preserves the principal thermal transition profile, whereas crystallinity, viscoelastic softening behavior, and post‐extrusion dimensional recovery become progressively more sensitive with increasing recycled content.
Özkan et al. (Fri,) studied this question.