a laboratory scale, many polymer/CNC nano composites have been prepared and were demonstrated to exhibit a significant improvement in mechanical properties over the parent polymers. However, the technological exploitation of CNCs as reinforcing filler will hinge on the question if or how well such laboratory-scale results can be achieved by technologically viable processes. Unfortunately, systematic studies that correlate processing, structure, and mechanical properties of CNC nanocomposites are rare. In a previous study we demonstrated that once CNCs are well dispersed in amphiphilic polymers such as poly(vinyl acetate) [11] or hydrophobic polymers such as low-density polyethylene (LDPE), [16] they can be subsequently reprocessed via melt-mixing and retained similar dispersion and mechanical reinforcement, as long as highshear mixing, which caused mechanical degradation of the CNCs, was avoided.It appears to be particularly difficult to fabricate composites of the rather polar CNCs in hydrophobic polymer matrices such as LDPE, as the polarity differenceThe preparation of nanocomposites of low-density polyethylene (LDPE) and cellulose nanocrystals (CNCs) isolated from cotton or produced in situ by the dispersion of microcrystalline cellulose (MCC) is reported. The hydrophobic matrix polymer and the rather polar filler particles appear to be difficult to mix, but it is shown here that composites with significantly improved mechanical characteristics and of homogeneous appearance can be produced using an organic-solvent-free two-step process. This is achieved by first mixing an aqueous slurry of an LDPE powder with an average particle size of <600 μm with aqueous suspensions of CNCs or MCC and removing most, but not all, of the water. Compounding such water-plasticized mixtures in a roller-blade mixer and subsequent compression-molding afford highly transparent films, whose room-temperature storage modulus is increased by a factor of 2.5 upon incorporation of 15% w/w CNCs or MCC. The results demonstrate that LDPE/nanocellulose composites with improved mechanical properties can be produced by an organic solvent-free process that appears to be scalable to industrial production scale.

Surface mechanochemistry of nanocelluloses modified with a dynamic covalent mechanophore is investigated, and self-healing composites with the celluloses are developed.

Cellulose nanocrystals (CNCs) are mechanically rigid, toxicologically benign, fiber-like nanoparticles. They can easily be extracted from renewable biosources and have attracted significant interest as reinforcing fillers in polymers. We here report the modification of CNCs with the 2-ureido-4[1H]pyrimidinone (UPy) motif as an adaptive compatibilizer, which permits the dispersion of UPy-modified CNCs in nonpolar as well as polar media. In toluene, the UPy motifs appear to form intra-CNC dimers, so that the particles are somewhat hydrophobized and well-dispersible in this nonpolar solvent. By contrast, the UPy motifs dissociate in DMF and promote dispersibility through interactions with this polar solvent. We have exploited this adaptiveness and integrated UPy-modified CNCs into nonpolar and polar host polymers, which include different poly(ethylene)s, a polystyrene-block-polybutadiene-block-polystyrene elastomer and poly(ethylene oxide-co-epichlorohydrin). All nanocomposites display an increase of stiffness and strength in comparison to the neat polymer, and some compositions retain a high elongation at break, even at a filler content of 15% w/w.