Enhancing Mechanical Performance of High-Lignin-Filled Polypropylene via Reactive Extrusion

Area of Science:

• Materials Science
• Polymer Science
• Sustainable Materials

Background:

• Polypropylene (PP) is a widely used plastic with significant environmental impact.
• Lignin, a byproduct of papermaking, presents an opportunity for sustainable material development.
• High-lignin-filled PP composites are explored as eco-friendlier alternatives.

Purpose of the Study:

• To investigate the incorporation of high lignin content (acetic acid lignin and Kraft lignin) into polypropylene.
• To evaluate the effect of maleic anhydride-grafted polypropylene (MAPP) as a compatibilizer on blend performance.
• To assess the mechanical properties, cost-effectiveness, and environmental benefits of lignin-filled PP composites.

Main Methods:

• Twin-screw extrusion and injection molding were used to prepare PP/lignin blends.
• Maleic anhydride-grafted polypropylene (MAPP) with varying maleic anhydride (MA) content and melt flow index (MFI) was employed as a compatibilizer.
• Mechanical testing (modulus, heat deflection temperature) and cost/greenhouse gas (GHG) emission analysis were conducted.

Main Results:

• Kraft lignin (KL) showed better dispersity in PP compared to acetic acid lignin (AAL).
• Optimal compatibilization was achieved with MAPP containing ≥0.8 wt.% MA and MFI of 60-100 g/10 min.
• PP/KL blends with 40 wt.% lignin and 10 pph compatibilizer exhibited mechanical properties comparable to neat PP, with increased modulus and heat deflection temperature (HDT).

Conclusions:

• High-lignin-filled PP composites, particularly with KL and optimized MAPP, offer a viable sustainable alternative to neat PP.
• These blends achieve comparable mechanical performance while reducing production costs by ~20% and GHG emissions by ~40%.
• This research promotes lignin valorization and contributes to cost-effective, eco-friendly plastic material development.