Sustainable, High-Performance, and Biodegradable Plastics Made from Chitin

A high-performance biodegradable plastic was made from a chitin KOH/urea solution. The solution was transferred into a hydrogel by cross-linking using epichlorohydrin and ethanol immersion, and a chitin bioplastic was finally prepared by drying in a mold at 40 °C. The solution concentration positively impacts viscosity, crystallinity, and smoothness. A 4% chitin bioplastic exhibits high barrier properties, flame retardancy, high-temperature resistance, mechanical properties (tensile strength up to 107.1 MPa), and soil degradation properties. The chitin bioplastic can be completely degraded by microorganisms in 7 weeks. In addition, biosafety tests suggest that chitin is safe for cells and crops (wheat and mung beans). The chitin bioplastic was further applied to containers, straws, cups, and photoprotection, and it was found that the water resistance and transparency were comparable to those of commercial polypropylene plastics. Due to the excellent performance, safety, and sustainability of the chitin bioplastic, it is expected to become a good substitute for conventional fossil fuel-based plastics.

High-tensile regenerated cellulose films enabled by unexpected enhancement of cellulose dissolution in cryogenic aqueous phosphoric acid

We have demonstrated, for the first time, high-efficient non-destructive and non-derivative dissolution of cellulose could be achieved in cryogenic aqueous phosphoric acid. Cellulose from different sources and of varying degree of polymerization from 200 (MCC) to 2200 (cotton fabric) could be dissolved completely to afford solutions containing 5 wt%-18 wt% cellulose, from which ultra-strong and tough cellulose films of tensile strength as high as 707 MPa could be obtained using water as the coagulant. These solutions can be stored at -18 °C for extended time without noticeable degradation while desired degree of polymerization is also attainable by tuning the storage conditions. The findings of this work call for renewal attention on phosphoric acid as a promising cellulose solvent for being non-toxic, non-volatile, easy to handle, and cost-effective.

Simultaneous toughening and strengthening of chitin-based composites via tensile-induced orientation and hydrogen bond reconstruction

Chitin, an abundant, biodegradable, and biocompatible polysaccharide, is one of the most ideal eco-friendly alternatives to petroleum-based plastics. However, the applications of chitin-based materials are hindered by their low processability and brittleness induced by strong hydrogen bonds. Herein, a tensile-induced orientation and hydrogen bond reconstruction strategy was developed to fabricate a chitin nanowhiskers/poly(vinyl alcohol) composite film with high strength and toughness. After stretching and hydrogen bond reconstruction, the tensile strength and elongation at break of the composite film increased from 38.6 to 115.2 MPa and 9.37% to 40.7%, respectively. Furthermore, strengthening and toughening mechanisms were also studied, which were attributed to the effects of the intra-layer orientation and interlayer sliding, respectively.

In situ growth of amino-functionalized ZIF-8 on bacterial cellulose foams for enhanced CO2 adsorption

Zeolitic imidazolate frameworks (ZIFs) hold great potential for carbon capture, while a major challenge for the practical application of ZIFs is the development of convenient three-dimensional bulk materials. Here, sustainable and biodegradable bacterial cellulose (BC) was used as the substrate for ZIF growth. Amino-functionalized ZIF-8 (ZIF-8-NH₂) was prepared within BC substrate via an in situ growth approach. ZIF crystals were wrapped uniformly over cellulose fibers and the chelating effect between metal (zinc) ions and hydroxyl groups makes the composites have high interface affinity and compatibility. The resulting foams presented a high CO₂ adsorption capacity of 1.63 mmol/g (25 °C, 1 bar). Moreover, ZIF-8-NH₂@BC foams are facile to be regenerated by heating at 80 °C. This work provides a new avenue to construct ZIF/cellulose composites for gas treatment applications.

Spiral Honeycomb Microstructured Bacterial Cellulose for Increased Strength and Toughness

Natural materials, such as nacre and silk, exhibit both high strength and toughness due to their hierarchical structures highly organized at the nano-, micro-, and macroscales. Bacterial cellulose (BC) presents a hierarchical fibril structure at the nanoscale. At the microscale, however, BC nanofibers are distributed randomly. Here, BC self-assembles into a highly organized spiral honeycomb microstructure giving rise to a high tensile strength (315 MPa) and a high toughness value (17.8 MJ m-3), with pull-out and de-spiral morphologies observed during failure. Both experiments and finite-element simulations indicate improved mechanical properties resulting from the honeycomb structure. The mild fabrication process consists of an in situ fermentation step utilizing poly(vinyl alcohol), followed by a post-treatment including freezing-thawing and boiling. This simple self-assembly production process is highly scalable, does not require any toxic chemicals, and enables the fabrication of light, strong, and tough hierarchical composite materials with tunable shape and size.

Novel bio-inspired three-dimensional nanocomposites based on montmorillonite and chitosan

In this study, inspired by nacre-like structural natural shells, novel three-dimensional (3D) nanocomposites based on natural nanoplatelets of montmorillonite (MMT) and polysaccharide of chitosan (CS) were prepared with solution intercalation and self-assembly process. The CS-intercalated-MMT nanoplatelets units acted as "bricks" and CS molecules acted as "mortar", arranging in fairly well-ordered layered structure. With addition of glutaraldehyde (GA) and Pd²⁺ cations, synergistic toughening and strengthening effects of covalent and ionic bonds could be achieved. The best mechanical properties of the prepared 3D nanocomposites were observed as 5.6 KJ/m² (impact strength), 3.3 GPa (flexural modulus), and 65.8 MPa (flexural strength), respectively, which showed higher toughness but lower flexural properties than natural pearl mussel shells. Nevertheless, both the impact and flexural properties of the prepared 3D nanocomposite were much higher than the other natural shell, i.e. green grab shell. Besides conventional methods characterizations, the nacre-like structure of the artificial 3D nanocomposite was further evidenced with positron annihilation lifetime spectroscopy characterizations. This work might facilitate a versatile platform for developing green 3D bionanocomposites with fairly good mechanical properties.