Cellulose nanofibers (CNFs) hold great potential as sustainable reinforcement fillers with excellent mechanical, thermal, and chemical properties. However, in polyolefin nanocomposite materials, the rational control of dispersion and the improvement of interfacial strength remain challenging. Herein we propose the tuning of the interface between CNF and high-density polyethylene by the design of polymer dispersants on the basis of surface free energy and the glass transition temperature. The former is related to the wettability against the polymer matrix and is therefore critical to the dispersion of CNF whereas the latter is related to the interfacial strength between CNF and HDPE. As a result of this investigation, we discovered a suitable dispersant for CNFs, poly(dicyclopentenyloxyethyl methacrylate)-block-poly(2-hydroxyethyl methacrylate), which played a pivotal role in achieving both a uniform dispersion of CNF and greatly improved mechanical properties, including a 4-fold increase of the Young's modulus over that of neat HDPE with 10 wt % CNF loading.

Production of nanocomposites from macro-scale materials in situ in a melting compounder is highly desirable yet challenging. In this study, we develop a highly efficient approach for the preparation of cellulose nanofiber (CNF)-reinforced highdensity polyethylene (HDPE) composite materials from asreceived wood pulp fibers, in which nanofibrillation-assisting plasticizers (urea and urea derivatives) and a diblock copolymer dispersant are used. The most effective plasticizer is urea, which plays a crucial role in producing CNF with less fragmentation during the kneading step, owing to the plasticization/nanofibrillation and the reaction with hydroxyl groups of cellulose fibers into a carbamate. The diblock copolymer as a dispersant enables the stabilization of the appropriate dispersion of the produced CNF in nonpolar HDPE. The resulting composites exhibit significantly improved mechanical properties, including a 6.9-fold increase in the Young's modulus with 10 wt % loading of wood pulp fibers over that of neat HDPE.

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