Here, a highly flexible and anisotropic strain sensor based on sustainable biomass‐derived materials is fabricated through a facile, low‐cost, and scalable approach. The commercially available crepe paper made of the abundant and renewable cellulose is converted into a conductive network by carbonization. The fabricated strain sensor based on this carbonized crepe paper (CCP) exhibits high flexibility, fast response time (<115 ms), high durability (>10 000 cycles), and negligible hysteresis. Especially, the CCP strain sensor shows dramatically different gauge factors (10.10 and 0.14, respectively) between tensile bending perpendicular and parallel to the fibers direction. This anisotropic sensing performance is inherited from the crepe paper's unique anisotropic structure, i.e., aligned cellulose fibers and a corrugated surface, which is well maintained in the CCP. In addition, the CCP strain sensors' practical use in detecting complex human motions and controlling a 2‐degree‐of‐freedom machine is demonstrated, indicating their potential applications in multidimensional wearable electronics and smart robots.

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Ionic liquid (IL) is one of the pretreatment processes gaining considerable interests to remove the native recalcitrance of lignocellulose. But the cellulose crystalline transformation during the pretreatment and their correlations with enzymatic digestibility have not been fully elucidated. Microcrystalline cellulose (Avicel) and holocellulose, which have differential sources and original crystallinity, were respectively pretreated with 1-butyl-3-methylimidazolium chloride ([C4min]Cl). Cellulose crystalline variations as well as chemical and morphological changes were determined. Crystallinity of different materials was proved to influence the effects of pretreatment and following enzymatic digestibility. Recrystallized cellulose Iβ was revealed from slight initial cellulose Iα of Avicel, which was accomplished via formation of intermediate paracrystalline phases. The conversion yield of IL pretreated Avicel displayed no obvious changes, mainly resulted from initial high crystalline order and the recrystallization behavior. Recalcitrance of holocellulose was destroyed during cellulose allomorph transformation and hemicelluloses extraction, contributing to significant increase of glucose yield up to 92.20%. Explicit comprehension on cellulose supramolecular structure may help provide more efficient process for bioconversion after IL pretreatment.

The insufficient resolution of conventional methods has long limited the structural elucidation of cellulose and its derivatives, especially for those with relatively low crystallinities or in native cell walls. Recent 2D/3D solid-state NMR studies of 13C uniformly labeled plant biomaterials have initiated a re-investigation of our existing knowledge in cellulose structure and its interactions with matrix polymers but for unlabeled materials, this spectroscopic method becomes impractical due to limitations in sensitivity. Here, we investigate the molecular structure of unlabeled cotton cellulose by combining natural abundance 13C-13C 2D correlation solid-state NMR spectroscopy, as enabled by the sensitivity-enhancing technique of dynamic nuclear polarization (DNP), with statistical analysis of the observed and literature-reported chemical shifts. The atomic resolution allows us to monitor the loss of Iα and Iβ allomorphs and the generation of a novel structure during ball-milling, which reveals the importance of large crystallite size for maintaining the Iα and Iβ model structures. Partial order has been identified in the “disordered” domains, as evidenced by a discrete distribution of well-resolved peaks. This study not only provides heretofore unavailable high-resolution insights into cotton cellulose but also presents a widely applicable strategy for analyzing the structure of cellulose-rich materials without isotope-labeling. This work was part of a multi-technique study of ball-milled cotton described in the previous article in the same issue.

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Twenty-two superbase-derived ionic liquids (SILs) (16 novel) including 16 1,8-diazabicyclo[5.4.0]­undec-7-enium carboxylate (DBU-SILs) and 6 1,5-diazabicyclo[4.3.0]­non-5-enium carboxylate (DBN-SILs) were facilely synthesized by coupling superbase cations with different carboxylic anions for cellulose dissolution. Systematic investigations revealed that the combination of the electron-donating groups, small steric hindrance groups, and short-chain groups in carboxylate anions with a larger ring in superbase cations facilitated cellulose dissolution. The regenerated cellulose films produced from seven SILs ([DBUH]­[CH3CH2OCH2COO], [DBUH]­[CH3OCH2COO], [DBUH]­[CH2CHCOO], [DBUH]­[CH3COO], [DBUH]­[CH3CH2COO], [DBNH]­[CH3CH2OCH2COO], and [DBNH]­[CH3OCH2COO]) with excellent cellulose solubility exhibited similar chemical structures, a high degree of polymerization, sufficient thermostability, smooth morphology, and high mechanical strength. Moreover, room-temperature SILs with low viscosity displayed a promising opportunity for large-scale production of renewable packaging. Particularly, in addition to hydrogen bond destruction by the joint action of anions and cations, the interactions on (200) and (110) crystal planes of cellulose such as intermolecular hydrogen bonds (O6–H···O3, O6–H···O2, and O2–H···O6) and van der Waals forces were destroyed preferentially and violently by the SILs. This work presented an available protocol in designing novel ILs for commercial processing of cellulose.