Interfacial Mechanisms of Water Vapor Sorption into Cellulose Nanofibril Films as Revealed by Quantitative Models

Humidity is an efficient instrument for facilitating changes in local architectures of two-dimensional surfaces assembled from nanoscaled biomaterials. Here, complementary surface-sensitive methods are used to collect explicit and precise experimental evidence on the water vapor sorption into (2,2,6,6-tetramethylpiperidin-1-yl)­oxyl (TEMPO) oxidized cellulose nanofibril (CNF) thin film over the relative humidity (RH) range from 0 to 97%. Changes in thickness and mass of the film due to water vapor uptake are tracked using spectroscopic ellipsometry and quartz crystal microbalance with dissipation monitoring, respectively. Experimental data is evaluated by the quantitative Langmuir/Flory–Huggins/clustering model and the Brunauer–Emmett–Teller model. The isotherms coupled with the quantitative models unveil distinct regions of predominant sorption modes: specific sorption of water molecules below 10% RH, multilayer build-up between 10 to 75% RH, and clustering of water molecules above 75% RH. The study reveals the sorption mechanisms underlying the well-known water uptake behavior of TEMPO oxidized CNF directly at the gas–solid interface

Accessibility of Cell Wall Lignin in Solvent Extraction of Ultrathin Spruce Wood Sections

Wood is a naturally occurring composite, comprising cellulose, hemicellulose, and lignin. The tightly arranged cell wall components make the fibers resistant against chemical and microbial degradation. This natural resisting power of fibers is a technical obstacle during the degradation of cellulose into sugars. Therefore, removal of cell wall lignin is necessary in order to make the cellulose accessible. In this study, ultrathin sections of Norway spruce (Picea abies) branch wood were examined using Raman and transmission electron microscopy (TEM) before and after extracting the sections with 1,4-dioxane without resin embedding in order to study the accessibility of native lignin. The progress of extraction of lignin was followed by measuring its Raman scattering intensity at the ∼1600 cm^–1 band. It was found that lignin was extracted not only from the compound middle lamellae but also from other layers of the cell wall. Changes in the contrast of TEM images confirmed a decrease in lignin concentration after solvent extraction. Observed ruptures in the S₁ layer indicated that extraction weakened this layer in particular

A Systematic Study of Noncross-linking Wet Strength Agents

Cellulosic fibers are inherently hydrophilic, and the modification of them to withstand moisture is important both commercially and scientifically. The usual methods are based on the cross-linking chemistry of reactive groups such as epichlorohydrins. Here, we present that it is possible to attain paper with wet strength from a combination of polymers that lack cross-linking chemistry, namely, carboxymethyl cellulose (CMC) and Polybrene. To accomplish this, we first altered the surface charge of the fibers by adsorption of CMC. Subsequent adsorption of Polybrene, forming the fibers as paper sheets, and drying yielded paper with wet strength properties. The wet strengthening was further investigated by (i) varying the molecular weight of the CMC, (ii) varying the cationic polyelectrolyte, and (iii) synthesizing polymers called ionenes to study the structural properties behind the wet strength of Polybrene. The results showed that (i) drying was necessary to obtain wet strength, (ii) wet strength seemed to be a surface effect, (iii) high <i>M</i>_w CMC played an important role in the development of wet strength, and (iv) only asymmetric ionenes ([3,6] and [6,12]-ionenes) could attain wet strength while symmetric [3,3] and [6,6]-ionenes failed to show wet strength properties

A Systematic Study of Noncross-linking Wet Strength Agents

Cellulosic fibers are inherently hydrophilic, and the modification of them to withstand moisture is important both commercially and scientifically. The usual methods are based on the cross-linking chemistry of reactive groups such as epichlorohydrins. Here, we present that it is possible to attain paper with wet strength from a combination of polymers that lack cross-linking chemistry, namely, carboxymethyl cellulose (CMC) and Polybrene. To accomplish this, we first altered the surface charge of the fibers by adsorption of CMC. Subsequent adsorption of Polybrene, forming the fibers as paper sheets, and drying yielded paper with wet strength properties. The wet strengthening was further investigated by (i) varying the molecular weight of the CMC, (ii) varying the cationic polyelectrolyte, and (iii) synthesizing polymers called ionenes to study the structural properties behind the wet strength of Polybrene. The results showed that (i) drying was necessary to obtain wet strength, (ii) wet strength seemed to be a surface effect, (iii) high <i>M</i>_w CMC played an important role in the development of wet strength, and (iv) only asymmetric ionenes ([3,6] and [6,12]-ionenes) could attain wet strength while symmetric [3,3] and [6,6]-ionenes failed to show wet strength properties

Assessment of the Alga <i>Cladophora glomerata</i> as a Source for Cellulose Nanocrystals

Nanocellulose is isolated from cellulosic fibers and exhibits many properties that macroscale cellulose lacks. Cellulose nanocrystals (CNCs) are a subcategory of nanocellulose made of stiff, rodlike, and highly crystalline nanoparticles. Algae of the order Cladophorales are the source of the longest cellulosic nanocrystals, but manufacturing these CNCs is not well-studied. So far, most publications have focused on the applications of this material, with the basic manufacturing parameters and material properties receiving little attention. In this article, we investigate the entirety of the current manufacturing process from raw algal biomass (Cladophora glomerata) to the isolation of algal cellulose nanocrystals. Yields and cellulose purities are investigated for algal cellulose and the relevant process intermediates. Furthermore, the effect of sulfuric acid hydrolysis, which is used to convert cellulose into CNCs and ultimately determines the material properties and some of the sustainability aspects, is examined and compared to literature results on wood cellulose nanocrystals. Long (>4 μm) CNCs form a small fraction of the overall number of CNCs but are still present in measurable amounts. The results define essential material properties for algal CNCs, simplifying their future use in functional cellulosic materials

Strong and Stiff: High-Performance Cellulose Nanocrystal/Poly(vinyl alcohol) Composite Fibers

The mechanical properties of rodlike cellulose nanocrystals (CNCs) suggest great potential as bioderived reinforcement in (nano)­composites. Poly­(vinyl alcohol) (PVOH) is a useful industrial material and very compatible with CNC chemistry. High performance CNC/PVOH composite fibers were produced coaxial coagulation spinning, followed by hot-drawing. We showed that CNCs increase the alignment and crystallinity of PVOH, as well as providing direct reinforcement, leading to enhanced fiber strength and stiffness. At 40 wt % CNC loading, the strength and stiffness reached 880 MPa and 29.9 GPa, exceeding the properties of most other nanocellulose based composite fibers previously reported

Thermoresponsive Nanocellulose Hydrogels with Tunable Mechanical Properties

Cellulose microfibrils physically bound together by soft hemicellulose chains form the scaffolding that makes plant cell walls strong. Inspired by this architecture, we designed biomimetic thermoreversible hydrogel networks based on reinforcing cellulose nanocrystals (CNC) and thermoresponsive methylcellulose (MC). Upon dissolving MC powder in CNC aqueous dispersions, viscoelastic dispersions were formed at 20 °C, where the storage modulus (<i>G</i>′) is tunable from 1.0 to 75 Pa upon increasing the CNC concentration from 0 to 3.5 wt % with 1.0 wt % MC. By contrast, at 60 °C a distinct gel state is obtained with <i>G</i>′ ≫ <i>G</i>″, <i>G</i>′ ∼ ω⁰, with an order of magnitude larger <i>G</i>′ values from 110 to 900 Pa upon increasing the CNC concentration from 0 to 3.5 wt % with constant 1.0 wt % MC, due to the physical cross-links between MC and CNCs. Therefore, simply mixing two sustainable components leads to the first all-cellulose thermoreversible and tunable nanocellulose-based hydrogels

Noncovalent Dispersion and Functionalization of Cellulose Nanocrystals with Proteins and Polysaccharides

Native cellulose nanocrystals (CNCs) are valuable high quality materials with potential for many applications including the manufacture of high performance materials. In this work, a relatively effortless procedure was introduced for the production of CNCs, which gives a nearly 100% yield of crystalline cellulose. However, the processing of the native CNCs is hindered by the difficulty in dispersing them in water due to the absence of surface charges. To overcome these difficulties, we have developed a one-step procedure for dispersion and functionalization of CNCs with tailored cellulose binding proteins. The process is also applicable for polysaccharides. The tailored cellulose binding proteins are very efficient for the dispersion of CNCs due to the selective interaction with cellulose, and only small fraction of proteins (5–10 wt %, corresponds to about 3 μmol g^–1) could stabilize the CNC suspension. Xyloglucan (XG) enhanced the CNC dispersion above a fraction of 10 wt %. For CNC suspension dispersed with carboxylmethyl cellulose (CMC) we observed the most long-lasting stability, up to 1 month. The cellulose binding proteins could not only enhance the dispersion of the CNCs, but also functionalize the surface. This we demonstrated by attaching gold nanoparticles (GNPs) to the proteins, thus, forming a monolayer of GNPs on the CNC surface. Cryo transmission electron microscopy (Cryo-TEM) imaging confirmed the attachment of the GNPs to CNC solution conditions

Microwave hydrolysis, as a sustainable approach in the processing of seaweed for protein and nanocellulose management

The nature of marine biomass is very complex for a material scientist due to the large seasonal variation in the chemical composition that makes it difficult to prepare standardized products. A systematic investigation of the interaction of microwave irradiation with seaweed from Norway and Caribbean region was performed, covering a broad temperature range (130 → 170 ◦C) and without and with addition of ℽ-valerolactone (GVL) in ratios of 1:4 and 1:2. The temperatures above 150 ◦C and without addition of GVL led to the closure of mass balances up to 90 % that includes polysaccharides, “pseudo-lignin” fraction, fatty acids, and proteins. Fucoidan and mannose represented >50 % of all detected polysaccharides in ascophyllum nodosum (AN), while aegagropila linnaei (AL) contained mostly glucose. The presence of arabinose and rhamnose in the upper surface of the cell wall hinders the glucose release during microwave treatment. The differences in the polysaccharide composition among both algae samples hindered the definition of a parameters set that can be used in microwave treatment of various seaweed species. A large fraction of protein (> 95 %) remained in the seaweed solid residue. Higher amount of protein was determined in AL, which was dominated by leucine and lysine. Another potential barrier to the application of seaweed in industry is the limited knowledge on the chemical composition of “pseudo-lignin” and extractives. The total amino acid analysis was identified as the most accurate to characterize the protein yield and composition. The results showed that microwave treatment of seaweed is indeed a viable method for producing bioactives in the temperature range 120–150 ◦C, and proteins and nanocellulose at temperatures above 170 ◦C without using GVL. The microwave temperature and seaweed type played a dominating role in the mass closure balances leading to >95 % identified compound.</p

Fast, easy, and reproducible fingerprint methods for endotoxin characterization in nanocellulose and alginate-based hydrogel scaffolds

Nanocellulose- and alginate-based hydrogels have been suggested as potential wound-healing materials, but their utilization is limited by the Food and Drug Administration (FDA) requirements regarding endotoxin levels. Cytotoxicity and the presence of endotoxin were assessed after gel sterilization using an autoclave and UV treatment. A new fingerprinting method was developed to characterize the compounds detected in cellulose nanocrystal (CNC)- and cellulose-nanofiber (CNF)-based hydrogels using both positive- and negative-ion mode electrospray ionization Fourier transform ion cyclotron resonance mass spectroscopy (ESI FT-ICR MS). These biobased hydrogels were used as scaffolds for the cultivation and growth of human dermal fibroblasts to test their biocompatibility. A resazurin-based assay was preferred over all other biocompatibility methodologies since it allowed for the evaluation of viability over time in the same sample without causing cell lysis. The CNF dispersion of 6 EU mL−1 was slightly above the limits, and it did not affect the cell viability, whereas CNC hydrogels induced a reduction of metabolic activity by the fibroblasts. The chemical structure of the detected endotoxins did not contain phosphates, but it encompassed hydrophobic sulfonate groups, requiring the development of new high-pressure sterilization methods for the use of cellulose hydrogels in medicine.</p