Microscopic Insight into the Structure-Processing-Property Relationships of Core-Shell Structured Dialcohol Cellulose Nanoparticles

In the quest to develop sustainable and environmentally friendly materials, cellulose is a promising alternative to synthetic polymers. However, native cellulose, in contrast to many synthetic polymers, cannot be melt-processed with traditional techniques because, upon heating, it degrades before it melts. One way to improve the thermoplasticity of cellulose, in the form of cellulose fibers, is through chemical modification, for example, to dialcohol cellulose fibers. To better understand the importance of molecular interactions during melt processing of such modified fibers, we undertook a molecular dynamics study of dialcohol cellulose nanocrystals with different degrees of modification. We investigated the structure of the nanocrystals as well as their interactions with a neighboring nanocrystal during mechanical shearing, Our simulations showed that the stress, interfacial stiffness, hydrogen-bond network, and cellulose conformations during shearing are highly dependent on the degree of modification, water layers between the crystals, and temperature. The melt processing of dialcohol cellulose with different degrees of modification and/ or water content in the samples was investigated experimentally by fiber extrusion with water used as a plasticizer. The melt processing was easier when increasing the degree of modification and/or water content in the samples, which was in agreement with the conclusions derived from the molecular modeling. The measured friction between the two crystals after the modification of native cellulose to dialcohol cellulose, in some cases, halved (compared to native cellulose) and is also reduced with increasing temperature. Our results demonstrate that molecular modeling of modified nanocellulose fibers can provide fundamental information on the structure-property relationships of these materials and thus is valuable for the development of new cellulose based biomaterials.

Automated summary

Cellulose is a promising alternative to synthetic polymers in the development of sustainable and environmentally friendly materials. However, it cannot be melt-processed like many synthetic polymers. Chemical modification, such as dialcohol cellulose, can improve its thermoplasticity. A molecular dynamics study of dialcohol cellulose nanocrystals with different degrees of modification reveals that stress, interfacial stiffness, hydrogen-bond network, and cellulose conformations during mechanical shearing are highly dependent on the degree of modification, water layers, and temperature. Experimental investigation shows that increasing the degree of modification and/or water content makes the melt processing of dialcohol cellulose easier, which aligns with the conclusions from the molecular modeling.