Search

Interactions between dry cellulose were studied using model systems, cellulose beads, and cellulose films, using custom-built contact adhesion testing equipment. Depending on the configuration of the substrates in contact, Polydimethylsiloxane (PDMS) film, cellulose films spin-coated either on PDMS or glass, the interaction shows three distinct processes. Firstly, molecular interlocking is formed between cellulose and cellulose when there is a soft PDMS thin film backing the cellulose film. Secondly, without backing, no initial attraction force between the surfaces is observed. Thirdly, a significant force increase, ∆F, is observed during the retraction process for cellulose on glass, and there is a maximum in ∆F when the retraction rate is increased. This is due to the kinetics of a contacting process occurring in the interaction zone between the surfaces caused by an interdigitation of a fine fibrillar structure at the nano-scale, whereas, for the spin-coated cellulose surfaces on the PDMS backing, there is a more direct adhesive failure. The results have generated understanding of the interaction between cellulose-rich materials, which helps design new, advanced cellulose-based materials. The results also show the complexity of the interaction between these surfaces and that earlier mechanisms, based on macroscopic material testing, are simply not adequate for molecular tailoring. [Display omitted] [ABSTRACT FROM AUTHOR]

Non-sustainable single-use plastics used for food packaging needs to be phased out. Films made from cellulose nanofibrils (CNFs) are suitable candidates for biodegradable and recyclable packaging materials as they exhibit good mechanical properties, excellent oxygen barrier properties and high transparency. Yet, their poor water vapour barrier properties have been a major hindrance in their commercialisation. Here, we describe the preparation of 25 μm thick CNF films with significantly improved water vapour barrier properties after deposition of ultrathin polymeric and metallic coatings, parylene C and aluminium, respectively. When first adding a 40 nm aluminium layer followed by an 80 nm parylene layer, i.e. with a combined thickness of less than one percent of the CNF film, a water vapour transmission rate of 2.8 g m−2 d−1 was achieved at 38 °C and 90 % RH, surpassing a 25 μm polypropylene film (4–12 g m−2 d−1). This is an improvement of more than 700 times compared to uncoated CNF films, under some of the harshest possible conditions a packaging material will need to endure in commercial use. The layers showed a good and even coverage, as assessed by atomic force microscopy, and the parylene-coated surfaces were hydrophobic with a contact angle of 110°, providing good water repellency. [Display omitted] [ABSTRACT FROM AUTHOR]