Cellulose nanofibril (CNF)‐networks are modified by the addition of small amounts (below 10 wt%) of well‐defined cationic nanolatexes synthesized through reversible addition–fragmentation chain‐transfer‐mediated polymerization‐induced self‐assembly (PISA). Minute amounts of nanolatex inclusions lead to increased tensile and shear moduli, indicating that nanolatexes can act as bridging‐points between CNFs. At higher nanolatex content, this stiffening effect is lost, likely due to interactions between nanolatexes leading to plasticization. The influence of nanolatex content and size on interparticle distance is discussed and is used as a tool to understand the effects observed in macroscopic properties. Upon annealing, the stiffening effect is lost due to the softening of the nanolatexes, indicating that the core–shell morphology is a prerequisite for this effect. These systems form a versatile platform to develop fundamental insights into complex condensed colloidal systems, to ultimately aid in the development of new sustainable material concepts.

Fiber-based materials are attractive sustainable alternatives to fossil-based plastics, however, the lack of ductility (i.e., brittleness) limits their applicability in complex shapes as are often utilized for plastics. In this study, we hypothesize that it is possible to enhance the ductility of a cellulose-rich material by the incorporation of low molecular weight plasticizers (glycerol, urea, citric acid, and tannic acid). However, no significant effects could be observed after swelling in the presence of plasticizers. To enhance any potential effect, it was decided to employ ultrasonication to mechanically disintegrate the fiber and aid the sorption of plasticizer prior to formation of sheets from the treated fibers. Glycerol or urea in combination with ultrasonication resulted in both internal and external fibrillation of the fibers, and it could be observed that the resulting fines create a film at the surface of the fibers in the formed sheets. Tensile testing shows that this gives rise to a 100% increase in ductility compared to sheets from untreated fibers. The use of citric or tannic acid has the opposite effect, reducing ductility to a third of that of the reference sheet. This is suggested to be due to the formation of covalent cross-links in the treated fibers, which also leads to different internal and external fibrillation mechanisms, as observed by scanning electron microscopy. The exceptionally high improvement of the strain-at-break for sheets from the glycerol-and urea-treated fibers suggests that low molecular weight plasticizers affect the internal properties of the fiber wall as well as the interactions between the fine material forming in-between the fibers. The findings from the current study suggest that the proposed approach to obtain ductile cellulose-rich materials holds promise for the future, but it is also clear that more in-depth research is required to obtain a mechanistic understanding and release the full potential.