Increasing Cellulose Nanocrystals Content Research Articles

Mechanical and shrinkage properties of cellulose nanocrystal modified alkali-activated fly ash/slag pastes

Alkali-activated materials based on fly ash (FA) and ground granulated blast furnace slag (GGBFS) offer lower carbon footprints but face challenges like low tensile strength and shrinkage susceptibility. This research explores the potential of cellulose nanocrystals (CNC) as additives to enhance the mechanical and shrinkage properties of alkali-activated fly ash/slag (AAFS) pastes to advance sustainable construction materials. A comprehensive examination is conducted on the impact of different contents of CNC (0.05 %, 0.1 %, 0.2 %, and 0.3 % by mass of FA + GGBFS) on the properties of AAFS pastes with two different alkaline activator contents (4 % and 8 % by mass of FA + GGBFS). It is found that incorporating 0.3 % CNC into AAFS pastes respectively improves the 28-day compressive and flexural strengths by 18.54 % and 60.87 % (8 % alkaline activator) and by 16.99 % and 50.12 % (4 % alkaline activator), and reduces the autogenous shrinkage and drying shrinkage by 26.42 % and 50.32 % (8 % alkaline activator) and by 11.74 % and 22.05 % (4 % alkaline activator). Also, the flexural/compressive strength ratio of AAFS pastes is increased with increasing CNC content. The microstructural analysis shows increased hydration product formation and a smoother, more compact morphology in CNC-modified samples, which together with water retention and distribution effect and nano-reinforcing effect of CNC explains the improvements in mechanical properties and volume stability. The research findings highlight the great potential of CNC as a reinforcing agent for sustainable construction materials, aligning with the demand from industries for eco-friendly alternatives to traditional cementitious materials.

3D-Printed Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)-Cellulose-Based Scaffolds for Biomedical Applications.

While biomaterials have become indispensable for a wide range of tissue repair strategies, second removal procedures oftentimes needed in the case of non-bio-based and non-bioresorbable scaffolds are associated with significant drawbacks not only for the patient, including the risk of infection, impaired healing, or tissue damage, but also for the healthcare system in terms of cost and resources. New biopolymers are increasingly being investigated in the field of tissue regeneration, but their widespread use is still hampered by limitations regarding mechanical, biological, and functional performance when compared to traditional materials. Therefore, a common strategy to tune and broaden the final properties of biopolymers is through the effect of different reinforcing agents. This research work focused on the fabrication and characterization of a bio-based and bioresorbable composite material obtained by compounding a poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) matrix with acetylated cellulose nanocrystals (CNCs). The developed biocomposite was further processed to obtain three-dimensional scaffolds by additive manufacturing (AM). The 3D printability of the PHBH-CNC biocomposites was demonstrated by realizing different scaffold geometries, and the results of in vitro cell viability studies provided a clear indication of the cytocompatibility of the biocomposites. Moreover, the CNC content proved to be an important parameter in tuning the different functional properties of the scaffolds. It was demonstrated that the water affinity, surface roughness, and in vitro degradability rate of biocomposites increase with increasing CNC content. Therefore, this tailoring effect of CNC can expand the potential field of use of the PHBH biopolymer, making it an attractive candidate for a variety of tissue engineering applications.

Characteristics of Sodium Alginate/Antarctic Krill Protein Composite Fiber Based on Cellulose Nanocrystals Modification: Rheology, Hydrogen Bond, Crystallization, Strength, and Water-Resistance.

The purpose of adding cellulose nanocrystals (CNCs) into sodium alginate (SA) and Antarctic krill protein (AKP) system is to use the ionic cross-linking of SA and AKP and the dynamic hydrogen-bonding between them and CNCs to construct multiple cross-linking structures, to improve the water-resistance and strength of SA/AKP/CNCs composite fiber. Based on the structural viscosity index in rheological theory, the ratio of spinning solution and temperature were optimized by studying the structural viscosity index of the solution under different CNCs content and temperature, then the composite fiber was prepared by wet spinning. We found that when the content of CNCs is 0.8% and 1.2%, the temperature is 45 °C and 55 °C, the structural viscosity is relatively low. Under the optimal conditions, the intermolecular hydrogen bonds decrease with the increase of temperature. Some of the reduced hydrogen bonds convert into intramolecular hydrogen bonds. Some of them exist as free hydroxyl; increasing CNCs content increases intermolecular hydrogen bonds. With the increase of temperature, the crystallinity of composite fiber increases. The maximum crystallinity reaches 27%; the CNCs content increases from 0.8% to 1.2%, the breaking strength of composite fiber increases by 31%. The water resistance of composite fiber improves obviously, while the swelling rate is only 14%.

Improving gas barrier properties of sugarcane‐based LLDPE with cellulose nanocrystals

AbstractThis study was aimed at improving the gas barrier property of sugarcane based LLDPE using cellulose nanocrystals (CNCs). Specifically, this study evaluated the effect of CNC content on the crystallinity, tortuosity factor, carbon dioxide permeability (PCO2), and/or oxygen permeability (PO2) of bio‐LLDPE sheets and films. All nanocomposites showed considerable improvement in gas barrier irrespective of the CNC content. The PCO2 coefficient of LLDPE sheets decreased by 36% by adding 10 wt% of CNCs into the sheet. Similarly, a significant decline in both PO2 (about 50%) and PCO2 (about 33%) coefficients of LLDPE films was obtained by adding 2.5 wt% of CNCs into the films. Nevertheless, no correlation was established between gas permeability and percent crystallinity of LLDPE sheet since the PCO2 coefficient decreased almost linearly with increasing CNC content whereas the percent crystallinity of LLDPE increased only up to 2.5% CNC content and remained constant thereafter. In contrast, the tortuosity factors calculated from the gas diffusion coefficients increased almost linearly with CNC contents and correlated well with the gas permeability improvement in bio‐LLDPE‐based nanocomposites. Consequently, the enhanced gas barrier in the nanocomposite was assigned to the tortuosity effect created by the impermeable CNCs rather than the changes in percent crystallinity.

Banana Rachis CNC/Clay Composite Filter for Dye and Heavy Metals Adsorption from Industrial Wastewater

This study demonstrates a successful processing and utilization of banana rachis cellulose nanocrystals (CNCs) dispersed clay composite filter which is capable of adsorbing dye and heavy metal ions namely Pb(II) and Cr(III) from industrial wastewater. The composite of different compositions was prepared by dispersing the cellulose nanocrystals, obtained by acid hydrolysis of banana rachis fibres, within the tri-ethyl amine treated clay. The CNC and treated clay were characterized by Fourier transform infrared (FTIR), X-ray diffractometry (XRD), and scanning electron microscopy (SEM) analyses. Industrial wastewater containing a basic yellow2 dye and two heavy metal ions, Pb(II) and Cr(III), was passed through the prepared filters set in a column. The dye and metal ions adsorption capability of the filters were analyzed by determining the dye and metal ions concentration into the water before and after passing through the composite filter. The concentration of dye and metal ions in water was determined by a UV-visible spectrophotometer and an atomic absorption spectrophotometer, respectively. It was found that the dye adsorption capacity of the composite filters was about 50 mg per gram of composite as well as Pb(II) and Cr(III) ions adsorption capacities of the composite filters were ˃10.0 mg and ˃12.4 mg respectively per gram of the composite when CNC content in the composite was ˃30 wt.%. It was also found that the metal ions adsorption capability of the composite filter was improved with increasing CNC content in the composites.

Preparation and Characterization of Cellulose Nanocrystals Reinforced Poly (vinyl alcohol) Based Hydrogels for Drug Delivery System

Structural property of most hydrogels is soft, resulting in low mechanical performance that limits their usage in the biomedical applications. For overcoming the drawback, cellulose nanocrystals (CNCs) were adopted in this study. Effects of CNCs on characteristics and drug delivery performance of poly (vinyl alcohol) based hydrogels were explored. FT-IR results showed that the fabricated hydrogels had semi-IPN (semi-interpenetrating polymer network) by formation of acetal and aldehyde bridge. Water absorption and swelling ratio decreased with increasing CNCs content, and the hydrogels with CNCs showed better viscoelastic performance than the without CNCs. Also, CNCs mostly improved the ability of the hydrogel to absorb the drug and the sustainability of the drug release. These results demonstrated that incorporating CNCs into the hydrogel systems can be a good alternative to improve drug delivery performance and mechanical property of the hydrogels.

Rheology, crystallization behavior, and mechanical properties of poly(butylene succinate-co-terephthalate)/cellulose nanocrystal composites

A series of biodegradable poly (butylene succinate-co-terephthalate) (PBST) with different aromatic units content was synthesized and then melt blended by adding cellulose nanocrystals (CNCs) to manufacture the full organic composites. A network-like structure of CNCs in PBST matrix was evaluated by rheometer. The storage modulus and complex viscosity at low frequency region were significantly enhanced with increasing CNC content. Meanwhile, the decreasing tanδ and flow index were attributed to the excellent interaction between PBST and CNCs. When PBST has a content of the aromatic unit exceeds 30 mol%, the crystallization temperatures increased with increasing CNC contents. On the other hand, when PBST has 30 mol% content of the aromatic unit, the cold crystallization temperatures decreased with increasing CNC contents. These above observation in crystallization properties suggested that the CNC make a role of heterogeneous nucleation in PBST matrix. The result of mechanical properties evaluated by dynamic mechanical analysis showed a good reinforcement effect of the addition of stiff CNC. The PBST/CNC composites were suitable for cell growth and might have a potential as biomedical materials, which is confirmed by MTT assay.

Chitosan Hydrogels Crosslinked by Genipin and Reinforced with Cellulose Nanocrystals: Production and Characterization

In this work, chitosan hydrogels crosslinked with genipin and reinforced with cellulose nanocrystals (CNC) were developed and characterized with the aim of future biomedical applications. CNC was produced by acid hydrolysis and characterized by atomic force microscopy (AFM). Chitosan/CNC nanocomposite hydrogels were produced with different CNC concentrations (w/w): 0%, 2%, 4%, and 6%. The genipin was used as a crosslinking agent in a genipin/chitosan molar proportion of 1:8. The hydrogels were characterized by porosity measurements, scanning electron microscopy (SEM), swelling test, and mechanical compression test. No significant differences were observed concerning the porosity of the hydrogels; however, a trend of decreasing porosity was observed with increasing CNC content. The SEM images showed a better pore structure as the CNC concentration increased. A decrease in the swelling degree with increasing CNC content in the chitosan/CNC nanocomposite hydrogel was verified in the swelling tests. An increase in the CNC concentration in the chitosan/CNC nanocomposite hydrogel caused a gradual increase in the maximum stress and maximum strain as observed in the compression tests, showing a significant difference between chitosan/CNC 6 wt % and neat chitosan hydrogel.

Effect of cellulose nanocrystals on crystallization, morphology and phase transition of polyamide 6

ABSTRACTNanocomposites comprised of polyamide 6 (PA6) and cellulose nanocrystals (CNC) were prepared by solvent casting and subsequent melt pressing. The role of cellulose nanocrystals on morphology, crystallization and conformation of the resulting PA6 nanocomposites were investigated using differential scanning calorimetry, thermogravimetric analysis and Fourier transform infrared (FTIR) spectroscopy. Scanning electron microscopic observation showed that the CNC were homogenously dispersed in the PA6 nanocomposites up to 5 wt% CNC. The thermal stability of the PA6 nanocomposites slightly decreased with the CNC loading. The addition of the CNC modified the non-isothermal crystallization behavior of the PA6 nanocomposites by increasing the crystallization temperature and the rate of nucleation. FTIR spectroscopic observation showed that the neat PA6 primarily crystallized in the more stable α crystalline form and that an α to metastable γ crystalline transformation occurred with increasing concentrations of the CNC in the PA6 matrix. The non-isothermal crystallization kinetics of these nanocomposites with increasing CNC content were investigated, and it was demonstrated that the amount of CNC plays a significant role in crystallization kinetics.

Sodium alginate/cellulose nanocrystal fibers with enhanced mechanical strength prepared by wet spinning

Sodium alginate/cellulose nanocrystal fibers were prepared using a wet spinning method to enhance the mechanical strength of sodium alginate fibers. Cellulose nanocrystals were prepared by sulfuric acid hydrolysis method. The particle diameter size was measured, and the morphology of cellulose nanocrystals was characterized by transmission electron microscopy and scanning electron microscopy. The structure and mechanical properties of sodium alginate/cellulose nanocrystal fibers were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and mechanical strength testing. The incorporation of cellulose nanocrystals significantly improved the strength of alginate fibers because of the uniform distribution of cellulose nanocrystals in the alginate matrix. The tensile strength and elongation at break of the alginate fibers increased from 1.54 to 2.05 cN/dtex and from 8.29% to 15.05% with increasing cellulose nanocrystals content from 0 to 2 wt%, respectively.

Effects of aspect ratio and crystal orientation of cellulose nanocrystals on properties of poly(vinyl alcohol) composite fibers

This work reports a study on the effects of different types and aspect ratios of cellulose nanocrystals (CNCs) on properties of poly (vinyl alcohol) (PVA) composite fibers. CNCs were extracted from wood pulp and cotton and reinforced into PVA to produce fibers by dry-jet-wet spinning. The fibers were collected as-spun and with the first stage drawing up to draw ratio 2. The elastic modulus and tensile strength of the fibers improved with increasing CNC content (5–15 wt. %) at the expense of their strain-to-failure. It was also observed that the mechanical properties of fibers reinforced with cotton CNC were higher than the fibers with wood CNC at the same amount of CNCs due to their higher aspect ratio. The degree of orientation along the spun fiber axis was quantified by 2D X-ray diffraction. As expected, the CNC orientation correlates to the mechanical properties of the fibers. Micromechanical models were used to predict the fiber performance and compare with experimental results. Finally, surface and cross-sectional morphologies of fibers were analyzed by scanning electron microscopy and optical microscopy.

Effect of cellulose nanocrystals on crystallization kinetics of polycaprolactone as probed by Rheo-Raman

The development of biocompatible polymer nano-composites that enhance mechanical properties while maintaining thermoplastic processability is a longstanding goal in sustainable materials. When the matrix is semi-crystalline, the nanoparticles may induce significant changes to crystallization kinetics and morphology due to their ability to act as nucleating agents. To fully model this behavior in a process line, an understanding of the relationship between crystallinity and modulus is required. Here, we introduce a scalable model system consisting of surface-compatibilized cellulose nanocrystals (CNC) dispersed into poly(ε-caprolactone) (PCL) and study the effects of nanoparticle concentration on isothermal crystallization kinetics. The dispersion is accomplished by exchange of the Na+ of sulfated cellulose nanocrystals by tetra-butyl ammonium cations (Bu4N+) followed by melt mixing via twin-screw extrusion. Crystallization kinetics are measured through the recently developed rheo-Raman instrument which extracts the relationship between the growth of the transient mechanical modulus and that of crystallinity. With extrusion and increasing CNC content, we find the expected enhancement of crystallization rate, but we moreover find a significant change in the relative kinetics of increase in modulus versus crystallinity. We analyze this via generalized effective medium theory which allows computation of a critical percolation threshold ξc and discuss the results in terms of a change in nucleation density and a change in the anisotropy of crystallization.

Pressure sensitive adhesive property modification using cellulose nanocrystals

The impact of cellulose nanocrystals (CNCs) as a property modifier for pressure sensitive adhesives (PSAs) was investigated. Stable CNC/poly(n-butyl acrylate-co-methyl methacrylate) latex nanocomposites with different CNC loadings ranging from 0.25 to 1wt% (based on monomer weight) were synthesized by both an in situ seeded semi-batch polymerization and a blending technique. The PSA films obtained from both techniques demonstrated a concurrent enhancement of shear strength, tack, and peel strength with increasing CNC content. However, the performance enhancement for the PSAs prepared via the in situ technique was substantially greater: increases of up to 3.8x for tack, 6x for peel strength and 20x for shear strength for the in situ technique compared to increases of up to 2.4x for tack, 1.5x for peel strength and 6.4x for shear strength for the blending technique. The difference in mechanical performance of the CNC/PSA films synthesized via the in situ technique vs. blending was a result of better interaction of CNCs with the polymer matrix during both latex synthesis and film formation.

Coaxial Electrospinning and Characterization of Core-Shell Structured Cellulose Nanocrystal Reinforced PMMA/PAN Composite Fibers.

A modified coaxial electrospinning process was used to prepare composite nanofibrous mats from a poly(methyl methacrylate) (PMMA) solution with the addition of different cellulose nanocrystals (CNCs) as the sheath fluid and polyacrylonitrile (PAN) solution as the core fluid. This study investigated the conductivity of the as-spun solutions that increased significantly with increasing CNCs addition, which favors forming uniform fibers. This study discussed the effect of different CNCs addition on the morphology, thermal behavior, and the multilevel structure of the coaxial electrospun PMMA + CNCs/PAN composite nanofibers. A morphology analysis of the nanofibrous mats clearly demonstrated that the CNCs facilitated the production of the composite nanofibers with a core-shell structure. The diameter of the composite nanofibers decreased and the uniformity increased with increasing CNCs concentrations in the shell fluid. The composite nanofibrous mats had the maximum thermal decomposition temperature that was substantially higher than electrospun pure PMMA, PAN, as well as the core-shell PMMA/PAN nanocomposite. The BET (Brunauer, Emmett and Teller) formula results showed that the specific surface area of the CNCs reinforced core-shell composite significantly increased with increasing CNCs content. The specific surface area of the composite with 20% CNCs loading rose to 9.62 m2/g from 3.76 m2/g for the control. A dense porous structure was formed on the surface of the electrospun core-shell fibers.

Thermo-Responsive Poly(N-Isopropylacrylamide)-Cellulose Nanocrystals Hybrid Hydrogels for Wound Dressing.

Thermo-responsive hydrogels containing poly(N-isopropylacrylamide) (PNIPAAm), reinforced both with covalent and non-covalent interactions with cellulose nanocrystals (CNC), were synthesized via free-radical polymerization in the absence of any additional cross-linkers. The properties of PNIPAAm-CNC hybrid hydrogels were dependent on the amounts of incorporated CNC. The thermal stability of the hydrogels decreased with increasing CNC content. The rheological measurement indicated that the elastic and viscous moduli of hydrogels increased with the higher amounts of CNC addition, representing stronger mechanical properties of the hydrogels. Moreover, the hydrogel injection also supported the hypothesis that CNC reinforced the hydrogels; the increased CNC content exhibited higher structural integrity upon injection. The PNIPAAm-CNC hybrid hydrogels exhibited clear thermo-responsive behavior; the volume phase transition temperature (VPTT) was in the range of 36 to 39 °C, which is close to normal human body temperature. For wound dressing purposes, metronidazole, an antibiotic and antiprotozoal often used for skin infections, was used as a target drug to study drug-loading and the release properties of the hydrogels. The hydrogels showed a good drug-loading capacity at room temperature and a burst drug release, which was followed by slow and sustained release at 37 °C. These results suggested that newly developed drugs containing injectable hydrogels are promising materials for wound dressing.

Preparation and characterization of nanocellulose reinforced semi-interpenetrating polymer network of chitosan hydrogel

Semi-interpenetrating polymer network hydrogels with improved mechanical properties and remarkable sensitivity toward pH changes were prepared using chitosan reinforced with cellulose nanocrystals (CNCs). Glutaraldehyde was used as a crosslinker because of its high reactivity toward the amine groups of chitosan. In this study, rod-shaped CNCs that were approximately 200–300 nm in length and 40–50 nm in width were prepared from microcrystalline cellulose via sulfuric acid hydrolysis. CNC ratios of 0, 0.5, 1, 1.5, 2, and 2.5% were selected to study the effects of CNCs on the mechanical properties and swelling behavior of the chitosan hydrogel. The crosslinking reaction between chitosan and glutaraldehyde was confirmed by the presence of a –C=N stretching group at 1548 cm−1 in the Fourier transform infrared spectrum of chitosan hydrogel. The crosslinking degree of the chitosan hydrogel was 83.6%. The X-ray diffraction patterns confirmed that adding CNCs induced a combination of amorphous and crystalline regions in the hydrogel matrix. Mechanical tests showed that the maximum compression of the chitosan hydrogel increased from 25.9 ± 1 to 50.8 ± 3 kPa with increasing CNC content from 0 to 2.5%. CNC-chitosan hydrogels exhibited excellent pH sensitivity and producing the maximum swelling ratio under acidic condition (pH 4.01). On the basis of the results of this study, we assume that the improved mechanical properties and excellent pH sensitivity of the CNC-chitosan hydrogels will expand their application scopes in various fields, such as tissue engineering, pharmaceuticals, and drug delivery.

Understanding mechanical characteristics of cellulose nanocrystals reinforced PHEMA nanocomposite hydrogel: in aqueous cyclic test

Cellulose nanocrystals (CNC) can be embedded within hydrogels to form tough and strong nanocomposite materials, which possess biomimetic properties from hydrogels including good biocompatibility, permeability and flexible mechanical characteristics. There are many potential applications for these strong nanocomposite hydrogels in medical devices, such as wound dressing or super absorbents. Whereas, the research on the mechanical properties of CNC reinforced nanocomposite remains at superficial level, and their nonlinear mechanical responses are rarely investigated in previous reports. Mechanical characteristics of CNC reinforced poly(2-hydroxyethyl methacrylate) (PHEMA) nanocomposite hydrogels, in terms of stress–strain correlations, fracture mechanism, and cyclic stretching responses, have been investigated in this work. Experimental results show that the modulus of the nanocomposite hydrogel tends to increase with increasing CNC content. Theoretical foundation for analysing the mechanical properties of hydrogels based on Mooney–Rivlin hyperelastic model, Voigt model and Reuss model has been developed and validated, which provides the prediction of the mechanical responses of CNC reinforced nanocomposite hydrogel to tension, especially the nonlinear responding behaviour.

Morphology, crystallization and rheological behavior in poly(butylene succinate)/cellulose nanocrystal nanocomposites fabricated by solution coagulation

Nanocomposites consisting of poly(butylene succinate) (PBS) and cellulose nanocrystals (CNC) were fabricated by solution coagulation method. Morphology analysis indicated that CNC dispersed well in PBS matrix and rheological analysis suggested that PBS and CNC showed strong interactions. Thermal analysis indicated that the nanocomposites showed slightly increased glass transition temperature, significantly enhanced crystallization temperature and different melting behavior, compared to neat PBS. Study on crystallization indicated that small loading of CNC could significantly increase overall crystallization rate of PBS, meanwhile the crystallization mechanism and crystal structure remained unchanged. The significant enhancement in overall crystallization was attributed to the increased nucleation ability by incorporation of well dispersed CNC nanoparticles. Tensile testing indicated that the tensile strength and modulus were gradually improved with increasing CNC content, while the elongation at break decreased and even brittle fracture occurred when the content of CNC increased to 1.0wt%.

Preparation and physical properties of tara gum film reinforced with cellulose nanocrystals

Cellulose nanocrystals (CNC) prepared from microcrystalline cellulose were blended in tara gum solution to prepare nanocomposite films. The morphology, crystallinity, and thermal properties of the CNC and films were evaluated by using transmission electron microscopy, X-ray diffractometry, and thermogravimetric analysis, respectively. The resultant CNC was rod-shaped with diameters of around 8.6nm. The effect of CNC content on physical and thermal properties of films was studied. The composite film tensile strength increased from 27.86 to 65.73MPa, elastic modulus increased from 160.98MPa to 882.49MPa and the contact angle increased from 55.8° to 98.7° with increasing CNC content from 0 to 6wt%. However, CNC addition increased the thermal stability slightly and CNC content above 6wt% decreased the tensile strength by CNC aggregation in the matrix. The nanocomposite film containing 6wt% CNC possessed the highest light transmittance, mechanical properties, and lowest oxygen permeability. CNC addition is a suitable method to modify tara gum matrix polymer properties.

Processing and Characterization of Cellulose Nanocrystals/Polylactic Acid Nanocomposite Films.

The focus of this study is to examine the effect of cellulose nanocrystals (CNC) on the properties of polylactic acid (PLA) films. The films are fabricated via melt compounding and melt fiber spinning followed by compression molding. Film fracture morphology, thermal properties, crystallization behavior, thermo-mechanical behavior, and mechanical behavior were determined as a function of CNC content using scanning electron microscopy, differential scanning calorimetry, X-ray diffraction, dynamic mechanical analysis, and tensile testing. Film crystallinity increases with increasing CNC content indicating CNC act as nucleating agents, promoting crystallization. Furthermore, the addition of CNC increased the film storage modulus and slightly broadened the glass transition region.