Abstract
The nano- to microscale structures at the interface between materials can define the macroscopic material properties. These structures are extremely difficult to investigate for complex material systems, such as cellulose-rich materials. The development of new model cellulose materials and measuring techniques has opened new possibilities to resolve this problem. We present a straightforward approach combining micro-focusing grazing-incidence small-angle X-ray scattering and atomic force microscopy (AFM) to investigate the structural rearrangements of cellulose/cellulose interfaces in situ during drying. Based on the results, we propose that molecular interdiffusion and structural rearrangement play a major role in the development of the properties of the cellulose/cellulose interphase; this model is representative of the development of the properties of joint/contact points between macroscopic cellulose fibers.
Highlights
Natural raw materials such as protein, silk, or wood have attracted increasing attention in the development of environmentally friendly products.[1−5] Cellulose, mainly extracted from plants, has gained particular attention owing to its natural abundance, renewability, low cost, biodegradability, and excellent mechanical properties.[6−9] On an industrial scale, it has been converted into paper, packaging materials, filaments, and textiles; it is being used as a carrier in chromatography, separation technology, and life science applications.[10−17] The mechanical properties of these materials are strongly determined both by the supramolecular structure of cellulose and the molecular interaction between the cellulose surfaces and other materials, especially in the wet state where the joints are developed and consolidated during drying.[4,5]
We have fabricated millimeter-sized cellulose gel beads as model surfaces by precipitating cellulose/lithium chloride (LiCl)/N,N-dimethylacetamide (DMAc) solution into a nonsolvent.[21−25] These gel beads have been used as a model system for investigating the swelling behavior of the wet, delignified wood cellulosic fiber wall.[24]
Similar drying behavior was previously observed for drying water-swollen cellulose gel beads,[21,22] suggesting that the drying kinetics of the filament is the same as that of the bead
Summary
Natural raw materials such as protein, silk, or wood have attracted increasing attention in the development of environmentally friendly products.[1−5] Cellulose, mainly extracted from plants, has gained particular attention owing to its natural abundance, renewability, low cost, biodegradability, and excellent mechanical properties.[6−9] On an industrial scale, it has been converted into paper, packaging materials, filaments, and textiles; it is being used as a carrier in chromatography, separation technology, and life science applications.[10−17] The mechanical properties of these materials are strongly determined both by the supramolecular structure of cellulose and the molecular interaction between the cellulose surfaces and other materials, especially in the wet state where the joints are developed and consolidated during drying.[4,5] Despite extensive research in this field, structural information of the molecular processes controlling these interactions is very limited.[18,19] This is partially due to the lack of well-characterized cellulose model surfaces and partially due to the lack of high-resolution measurement techniques capable of characterizing the structure of the interfaces and interphase throughout the joining process. The 2D μGISAXS patterns of the filament/thin film interface and thin-film surface at scan step 19 (Figure S3c,d) exhibit clear differences. The surface roughness and morphologies of the prepared cellulose thin films, dried beads, and the corresponding edges of the interface after separating the beads from thin films were measured by an atomic force microscope MultiMode 8 (Bruker, Santa Barbara, CA, USA) setup using the SCANASYST mode with a SCANASYST-AIR cantilever. They were measured in the dry state in the air under ambient conditions
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