Effect of pectin extraction method on properties of cellulose nanofibers isolated from sugar beet pulp

In this study, the effect of pectin extraction method on the properties of cellulose nanofibers (CNFs) isolated from sugar beet pulp (SBP) was studied. Pectin was extracted by the industrially practiced method by sulfuric acid hydrolysis or by enzymatic hydrolysis using a cellulase/xylanase enzymes mixture. The CNFs were then isolated by high-pressure homogenization and investigated in terms of their chemical composition, crystallinity, size, degree of polymerization, and re-dispersion in water after freeze-drying. The mechanical properties and surface characteristics of CNF films were also studied. The results showed that fibrillation of the de-pectinated SBP was more efficient for the acid hydrolyzed SBP. CNFs from the acid-hydrolyzed SBP had a slightly wider diameter, higher crystallinity, viscosity, and α-cellulose content but a lower degree of polymerization than CNFs from the enzyme-hydrolyzed SBP. Owing to the presence of more residual hemicelluloses in the CNFs from the enzyme-hydrolyzed SBP, the CNFs had higher re-dispersion ability in water. CNF films from enzyme-hydrolyzed SBP displayed slightly better mechanical properties and higher water contact angle than acid-hydrolyzed CNF films. Graphic abstract

Impact of the Enzyme Charge on the Production and Morphological Features of Cellulose Nanofibrils

The available research does not allow specific relationships to be established between the applied enzymatic-mechanical treatment, the degree of polymerization, and the characteristics of the cellulose nanofibrils (CNFs) produced. This work aims to establish specific relationships between the intensity of enzymatic treatment, the degree of polymerization of the cellulose, the morphology of CNFs, and the tensile strength of the CNF films. It is determined that the decrease in the degree of polymerization plays an essential role in the fibrillation processes of the cell wall to produce CNFs and that there is a linear relationship between the degree of polymerization and the length of CNFs, which is independent of the type of enzyme, enzyme charge, and intensity of the applied mechanical treatment. In addition, it is determined that the percentage of the decrease in the degree of polymerization of CNFs due to mechanical treatment is irrespective of the applied enzyme charge. Finally, it is shown that the aspect ratio is a good indicator of the efficiency of the fibrillation process, and is directly related to the mechanical properties of CNF films.

Influence of Lactic Acid Surface Modification of Cellulose Nanofibrils on the Properties of Cellulose Nanofibril Films and Cellulose Nanofibril–Poly (Lactic Acid) Composites

In this study, cellulose nanofibrils (CNFs) were modified by catalyzed lactic acid esterification in an aqueous medium with SnCl2 as a catalyst. Films were made from unmodified and lactic acid-modified CNF without a polymer matrix to evaluate the effectiveness of the modification. Ungrafted and lactic acid-grafted CNF was also compounded with poly(lactic acid) (PLA) to produce composites. Mechanical, water absorption, and barrier properties were evaluated for ungrafted CNF, lactic acid-grafted CNF films, and PLA/CNF composites to ascertain the effect of lactic acid modification on the properties of the films and nanocomposites. FTIR spectra of the modified CNF revealed the presence of carbonyl peaks at 1720 cm−1, suggesting that the esterification reaction was successful. Modification of CNF with LA improved the tensile modulus of the produced films but the tensile strength and elongation decreased. Additionally, films made from modified CNF had lower water absorption, as well as water vapor and oxygen permeability, relative to their counterparts with unmodified CNFs. The mechanical properties of PLA/CNF composites made from lactic acid-grafted CNFs did not significantly change with respect to the ungrafted CNF. However, the addition of lactic acid-grafted CNF to PLA improved the water vapor permeability relative to composites containing ungrafted CNF. Therefore, the esterification of CNFs in an aqueous medium may provide an environmentally benign way of modifying the surface chemistry of CNFs to improve the barrier properties of CNF films and PLA/CNF composites.

Preparation and characterization of graphene oxide and cellulose nanofibers/ polyvinyl alcohol nanocomposite film

Polyvinyl alcohol (PVA) is well-known in the packaging industry, especially in the food and medical fields with the ability to be completely biodegradable and easily soluble in cold water therefore products made from it are the environmentally friendly materials. However, the disadvantages of this polymer as quick dissolubility in water, poor moisture retention, weak mechanical properties reduce its applications. In this study, PVA, reinforced by “green” components at the nanometer-level such as nanocellulose fibers (CNF), graphene oxide (GO) nanosheets showed improvements in properties. Mechanical properties of all of nanocomposite films showed improvements in stress at break and modulus. Especially, reinforced GO and CNF films increased almost doubled and improved more 40% in modulus than the pure PVA film and films reinforced by only GO or CNF. When immersed in water (neutral pH) at room temperature, graphene oxide-reinforced films not only had effective improvements in swelling time but also supported to decrease water retension of film added CNF. The combined reinforcement also indicated a benefit in reducing the rate of water vapor loss of the film as well as the efficiency in declining the moisture absorption of the nanocomposite films. The PVA films reinforced by nanocellulose fibers and graphene oxide sheets overcomed some of the PVA's shortcomings. This helped expanding its applications in the field of environmentally friendly nanocomposite films.

Alteration of the Optical and Mechanical Characteristics of Cellulose Nanofibre Films Under Thermal Treatment

Nanocelluloses and their different designs, such as films and nanopapers, have gained considerable interest in many application areas due to their unique properties. For many purposes, such as for packaging and electronics, the thermal stability of nanocellulose materials is a crucial characteristic. In this study, the effects of heat treatment (100ºC, 150ºC and 200ºC) on the optical and mechanical properties of 2,2,6,6-tetramethylpiperidinyl-1-oxy radical-oxidised cellulose nanofibre (TO-CNF) films were investigated, especially the alteration of the colour, complex refractive index and birefringence of the films. Exposing TO-CNF films to high temperatures (> 150ºC) induced permanent transformations in the CNF structure, leading to an increase in the refractive index, decreases in the birefringence and crystallinity index, colour darkening and significant deterioration of the mechanical properties.

Cellulose nanofibrils manufactured by various methods with application as paper strength additives

Recycled paper and some hardwood paper often display poorer mechanical properties, which hinder its practical applications and need to be addressed. In this work, cellulose nanofibrils (CNFs) obtained by a combined process of enzymatic hydrolysis and grinding (EG-CNFs), grinding and microfluidization (GH-CNFs) or TEMPO-mediated oxidation and grinding (TE-CNFs) were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Moreover, CNFs were made into films on which some characterizations including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and UV–Vis transmittance spectroscopy were implemented. Results showed that CNF fibrillation was promoted as times of passes increased in microfluidization, and CNFs pretreated by enzyme possessed shorter length. Crystallinity of CNFs was related to CNF manufacturing methods, while CNF films’ transparency was correlated to CNF diameter distributions. Moreover, CNFs were applied with different dosages on recycled and hardwood paper. Lengths of CNFs, strength of CNF network, and pulp properties were critical factors affecting the mechanical strength of CNFs-enhanced paper. GH-CNFs showed better strengthened effect on tensile strength of paper than TE-CNFs and EG-CNFs. The best overall improvement was achieved at GH-CNF10 dosage of 5.0 wt% on hardwood paper. The increment of tensile index, burst index, and folding endurance were 108.32%, 104.65%, and 600%, respectively. This work aims to find out the relationship between production methods and morphologies of CNFs and how the morphological characteristics of CNFs affecting the mechanical performance of paper when they are added as strength additives.

Effect of The Enzyme Charge On The Production And Morphological Characteristics of Cellulose Nanofibrils

The effect of cellulase enzymes on the degree of polymerization of cellulose and the mechanical fibrillation process has been widely reported. However, the available information does not allow to establish specific relationships between the applied enzymatic-mechanical treatment, the degree of polymerization, and the characteristics of the cellulose nanofibrils (CNFs) produced. This work aims to establish specific relationships between the intensity of enzymatic treatment, the degree of polymerization of the cellulose, the morphology of CNFs, and the tensile strength of the films. It was determined that the decrease in the degree of polymerization plays an important role in the fibrillation processes of the cell wall to produce CNFs and that there is a linear relationship between the degree of polymerization and the length of CNFs, which is independent of the type of enzyme, enzyme charge, and intensity of the applied mechanical treatment. In addition, it was determined that the percentage of decrease in the degree of polymerization of CNFs due to mechanical treatment is irrespective of the applied enzyme charge. Else ways, it was shown that the aspect ratio is a good indicator of the efficiency of the fibrillation process, and the degree of polymerization in not. Finally, it was shown that the resistance of CNF films is positively related to the degree of polymerization up to a maximum value which corresponds to the maximum of the aspect ratio.

Induction and quantification of fiber alignment in cellulose nanofibril films

Cellulose nanofibrils (CNF) have been explored as an emerging naturally sourced material for use in the preparation of new biomaterials. CNF fibrils have a high aspect ratio with fibril lengths of ~ 1 µm and diameters of 20–40 nm. The assembly of CNF impacts both bulk mechanical properties as well as localized cellular interaction. The ability to reproducibly tune CNF fiber alignment is an active area of CNF-based biomaterial research. Here, we present a simple CNF fibril alignment strategy based on application of constant unilateral force on thin CNF films drying on a flexible substrate. CNF fibril alignment/orientation was characterized using both Polarized Light Microscopy (PLM) and conventional Scanning Electron Microscopy (SEM) approaches. CNF is optically birefringent; therefore, calculation of the birefringence orientation index (BOI) can infer the extent of CNF fibril alignment with a non-destructive, cost-effective technique. CNF fibril alignment is markedly increased with application of 10.2 N force as assessed by both SEM and PLM analysis. SEM imaging resolved individual CNF and the alignment was analyzed using OrientationJ, an ImageJ plugin, to extract fibril angle whereas PLM microscopy provided a BOI value. Both the fibril alignment and BOI score were in agreement; therefore, it is acceptable to infer fibril organization with PLM techniques. Furthermore, the addition of nanoparticle hydroxyapatite did not diminish the CNF fibril alignment as assessed by both PLM and SEM highlighting the utility of the CNF film fabrication technique. In summary, the application of unilateral force on thin CNF films adhered to latex, is an elegant, scalable, and cost-effective technique for generating CNF films with reproducible fibril alignment.