Natural high-performance materials have inspired the exploration of novel materials from protein building blocks. The ability of proteins to self-organize into amyloid-like nanofibrils has opened an avenue to new materials by hierarchical assembly processes. As the mechanisms by which proteins form nanofibrils are becoming clear, the challenge now is to understand how the nanofibrils can be designed to form larger structures with defined order. We here report the spontaneous and reproducible formation of ordered microstructure in solution cast films from whey protein nanofibrils. The structural features are directly connected to the nanostructure of the protein fibrils, which is itself determined by the molecular structure of the building blocks. Hence, a hierarchical assembly process ranging over more than six orders of magnitude in size is described. The fibril length distribution is found to be the main determinant of the microstructure and the assembly process originates in restricted capillary flow induced by the solvent evaporation. We demonstrate that the structural features can be switched on and off by controlling the length distribution or the evaporation rate without losing the functional properties of the protein nanofibrils.

The three-dimensional (3D) microstructure of sustainable and biodegradable protein foam absorbents is correlated to their liquid absorption characteristics using X-ray microtomography. The physicochemical relationships between the protein material pore size and liquid penetration and distribution allow for understanding how the pores' interconnectivity impacts the absorption, particularly considering capillary-driven transport phenomena within the thin nano cell walls. The foams were made via lyophilization of protein solutions containing cellulose nanofibers to emphasize the impact of the processing on the foam microstructure. The results show gaseous and solid phases of the foams covering ca. 1000 pores, providing information that cannot be obtained using traditional 2D analysis (SEM). A correlation with the channel tortuosity was established based on the statistical ac-curacy of the diameter and number of pores per mm(3). The relationship between absorption kinetics and physical parameters enables the designing of biofoams with functionality also resembling commercial synthetic products that currently generate a high amount of nondegradable waste in our society.

2,2,6,6-Tetramethylpiperidin-1-yl oxyl (TEMPO)-oxidized beta-chitin nanofibrils (T-ChNF) are novel nanofibrils of high strength and stiffness and can also enhance the adsorption of chitosan in materials for biomedical applications. This study presents the preparation, structure, and properties of T-ChNF based on squid pens. Our nanofibrils have a zeta potential of -25.3 mV at neutral pH and a carboxylic content of 0.17 mmol/g, making hydrocolloid suspension stable at alkaline and neutral pH. It was demonstrated that positively charged chitosan could be adsorbed on the negatively charged surface of T-ChNF, leading to charge neutralization. The key to strong squid pen T-ChNF is the initial raw squid chitin properties and the high degree of acetylation (DA = 99.9%). The T-ChNF diameter is similar to 4.4 nm, and the length is in the micrometer range. The length and diameter are similar to those of squid pen beta-chitin fibrils prepared under mild conditions. These qualities of fibrils resulted in high-strength (176 MPa) chitin films prepared using the rapid vacuum filtration and drying technique. T-ChNF-based films are ductile, flexible, and transparent.

Metal organic frameworks (MOFs) are porous crystalline materials that can be designed to act as selective adsorbents. Due to their high porosity they can possess very high adsorption capacities. However, overcoming the brittleness of these crystalline materials is a challenge for many industrial applications. In order to make use of MOFs for large-scale liquid phase separation processes they can be immobilized on solid supports. For this purpose, nanocellulose can be considered as a promising supporting material due to its high flexibility and biocompatibility. In this study a novel flexible nanocellulose MOF composite material was synthesised in aqueous media by a novel and straightforward in situ one-pot green method. The material consisted of MOF particles of the type MIL-100(Fe) (from Material Institute de Lavoisier, containing Fe(III) 1,3,5-benzenetricarboxylate) immobilized onto bacterial cellulose (BC) nanofibers. The novel nanocomposite material was applied to efficiently separate arsenic and Rhodamine B from aqueous solution, achieving adsorption capacities of 4.81, and 2.77 mg g^‒1, respectively. The adsorption process could be well modelled by the nonlinear pseudo-second-order fitting.

The α-chitin nanofibril is an alternative to nanocellulose as a building-block for strong films and other nanomaterials. The hypothesis of high film strength for films based on mildly treated insect cuticles was tested. Fibrils from the cuticle of Ruspolia differens (a long-horned bush cricket grasshopper locally known as senene) are disintegrated by a mild process, subsequently characterized by transmission electron microscopy, NMR, Fourier transform infrared spectroscopy, and XRD, and used to prepare strong and transparent films. A mild process (with 20% NaOH treatment for 2 weeks and at room temperature) was used to largely remove the strongly bound protein associated with chitin. The purpose was to reduce chitin degradation. The native structure of chitin was indeed well preserved and close to the native state, as is supported by data for degree of acetylation, molar mass, crystallinity, and crystallite dimensions. The diameter of the smallest chitin fibrils was as small as 3-7 nm (average 6 nm) with lengths larger than or around 1 μm. A stable and well-dispersed colloidal chitin fibril suspension in water was achieved. A nanostructured chitin film prepared by filtration showed high optical transmittance (∼90%) and very high tensile strength (220 MPa). The high tensile strength was attributed to the well-preserved chitin structure, high intrinsic fibril strength, and high colloidal stability of the fibril suspension. Strong, transparent insect chitin films offer interesting alternatives to nanocellulose films because of different resource origins, surface chemistries, and potential antimicrobial properties.

Chitin nanofibrils (ChNF) are interesting high-value constituents for nanomaterials due to the enormous amount of waste from the seafood industry. So far, the reported ChNFs are substantially modified and chemically degraded (shortened) during extraction from the organisms. Here, highly individualized and long native-state ss-chitin nanofibrils from Illex argentinus squid pens are prepared. A mild treatment was developed to preserve the molar mass, aspect ratio, degree of acetylation and crystallite structure. The fibrils show a uniform diameter of 2-7 nm, very high aspect ratio (up to 750), high degree of acetylation (DA = 99%), and high molar mass (843 500 dalton). The powder X-ray diffraction analysis showed the preserved crystallite structure after protein removal. These " high quality" ChNFs were used to prepare nanostructured films via vacuum filtration from stable hydrocolloids. The effects of well-preserved " native" fibrils on morphology, and film properties (mechanical and optical), were studied and compared with earlier results based on coarser and shorter, chemically degraded chitin fibrils.

Microfibrillated cellulose (MFC) is an important industrial nanocellulose product and material component. New MFC grades can widen the materials property range and improve product tailoring. Microfibrillated lignocellulose (MFLC) is investigated, with the hypothesis that there is an optimum in lignin content of unbleached wood pulp fibre with respect to nanofibril yield. A series of kraft fibres with falling Kappa numbers (lower lignin content) was prepared. Fibres were beaten and fibrillated into MFLC by high-pressure microfluidization. Nano-sized fractions of fibrils were separated using centrifugation. Lignin content and carbohydrate analysis, total charge, FE-SEM, TEM microscopy and suspension rheology characterization were carried out. Fibres with Kappa number 65 (11% lignin) combined high lignin content with ease of fibrillation. This confirms an optimum in nanofibril yield as a function of lignin content, and mechanisms are discussed. MFLC from these fibres contained a 40–60 wt% fraction of nano-sized fibrils with widths in the range of 2.5–70 nm. Despite the large size distribution, data for modulus and tensile strength of MFLC films with 11% lignin were as high as 14 GPa and 240 MPa. MFLC films showed improved water contact angle of 84–88°, compared to neat MFC films (< 50°). All MFLC films showed substantial optical transmittance, and the fraction of haze scattering strongly correlated with defect content in the form of coarse fibrils. Graphic abstract: [Figure not available: see fulltext.]

Conductive natural rubber (NR) nanocomposites were prepared by solvent-casting suspensions of reduced graphene oxide(rGO) or carbon nanotubes (CNTs), followed by vulcanization of the rubber composites. Both rGO and CNT were compatible as fillers in the NR as well as having sufficient intrinsic electrical conductivity for functional applications. Physical (thermal) and chemical reduction of GO were investigated, and the results of the reductions were monitored by X-ray photoelectron spectroscopy for establishing a reduction protocol that was useful for the rGO nanocomposite preparation. Field-emission scanning electron microscopy showed that both nanofillers were adequately dispersed in the main NR phase. The CNT composite displays a marked mechanical hysteresis and higher elongation at break, in comparison to the rGO composites for an equal fraction of the carbon phase. Moreover, the composite conductivity was always ca. 3-4 orders of magnitude higher for the CNT composite than for the rGO composites, the former reaching a maximum conductivity of ca. 10.5 S/m, which was explained by the more favorable geometry of the CNT versus the rGO sheets. For low current density applications though, both composites achieved the necessary percolation and showed the electrical conductivity needed for being applied as flexible conductors for a light-emitting diode. 

The development of fully natural wheat gluten foams showing rapid and high uptake of water, sheep blood, and saline solution, while maintaining high mechanical stability in the swollen state, is presented. Genipin was added as a natural and polar cross-linker to increase the polarity of the protein chains, whereas cellulose nanofibers (CNFs) were added as a reinforcement/stiffener of the foams, alone or in combination with the genipin. The presence of only genipin resulted in a foam that absorbed up to 25 g of water per gram of foam and a more than 15 g uptake in only 8 min. In contrast, with CNF alone, it was not possible to maintain the mechanical stability of the foam during the water uptake and the protein foam disintegrated. The combination of CNF and genipin yielded a material with the best mechanical stability of the tested samples. In the latter case, the foam could be compressed repeatedly more than 80% without displaying any structural damage. The results revealed that a strong network had formed between the wheat gluten matrix, genipin, and cellulose in the foam structure. A unique feature of the absorbent/foam, in contrast to commercial superabsorbents, was that it was able to rapidly absorb nonpolar liquids (here, n-heptane) due to the open-cell structure. The capillary-driven absorption due to the open-cell structure, the high liquid absorption in the cell walls, and the mechanical properties (both in dry and swollen states) of these natural foams make them interesting as a sustainable replacement for a range of petroleum-based foam materials, including absorbent hygiene products such as sanitary pads.