Improved properties of high-density polyethylene by integrating high content of bio-fillers based on green nanolignin for applications in plastic industry

• The study examines polyethylene composites with high amounts of two modified nanolignins as green, bio-based fillers. • The developed methodology achieves good dispersion of high lignin loadings. • Adding nanolignin improves mechanical, thermal, and antioxidant properties. • Tests at 15–35 % filler show strong mechanical gains, up to 60 % at 35 %. A study on the processability and physical and mechanical properties of different thermoplastic-based green nanocomposite materials for applications in injection processes is presented: commercial high-density polyethylene acting as the polymeric matrix and high contents of two types of modified nanolignins serving as bio-based fillers. It is a novel procedure to obtain good dispersibility of high loadings of bio-fillers in polyethylene which is difficult to achieve according to literature. The inclusion of green fillers brings property enhancements that are normally seen with expensive nanofillers like carbon nanotubes or graphene: improvement of mechanical properties while keeping good thermal stability and antioxidant properties has been obtained. To compare the effect of the inclusion of the two different nanofillers at 15, 25 and 35 % wt loadings on the characteristics of polyethylene, physical, mechanical, and morphological tests were performed. Injection pellets were fabricated and used to fabricate coupons to evaluate the mechanical features by performing both flexural and tensile tests. Remarkable enhancements (up to 60 % with respect to the neat polymer) of certain mechanical properties were observed for composites with 35 % wt loading of nanofillers. Moreover, investigating the effect of the bio-based nanolignins inclusion at high loadings on both crystallization and melting temperature suggested the robust thermal stability of the presented composites. As nanolignin is a renewable filler-type, it will bring properties like low-cost, low toxicity and partially replace petroleum-based stabilizers or other additives. Polyethylene with nanolignin becomes a “partially bio-based” high-performance material without changing the polymer backbone. Polyethylene composites containing high loads of modified nanolignin can be prepared to achieve good dispersibility. The addition of nanolignin significantly improves mechanically, with mechanical gains up to 60 % at 35 % loading. The composites also maintain strong thermal stability. Because nanolignin is renewable and low-cost, it helps create a high-performance, partially bio-based polyethylene without altering the polymer’s structure.