Hydrophobic Cellulose Nanocrystals Research Articles

Non-covalent interaction induces controlled reinforcement of thermoplastic elastomer composites homologously incorporated with hydrophobized cellulose nanocrystals

Surface hydrophobization of cellulose nanocrystal (CNC) is developed through Pickering emulsion method and esterification-grafting, consequentially enhancing its thermal properties and hydrophobicity, and tensile modulus in thermoplastic elastomer composites. n-Tetradecenylsuccinic anhydride (TDSA) provides a high level of compatibility owing to the structural homology by non-covalent interactions between CNC-graft-TDSA and poly(styrene)-block-poly(isoprene)-block-poly(styrene) (SIS). Theoretical calculations supports the molecular-level insight on how the nanofiller and SIS interacts. Density functional theory calculations and the energy decomposition analysis reveal the stabilization free energy of −2.59 kcal mol−1 gained through hydrophobic and OH–π interactions, which is assigned as the key component for the superior mechanical properties. At the filler contents of 0.6–2.5 vol %, the moduli of the TPE nanocomposites gradually strengthen while retaining thermoplasticity, without sacrificing the ultimate tensile characteristics of SIS, although it is below the calculated φc of 5.9 vol % (critical percolation threshold) for filler-filler interactions. Origin of the controlled boost in filler-matrix binding is rationalized by pronounced hydrophobic interactions in isoprene-rich rubbery phase (86 wt % in SIS). Interestingly, at 5.1 vol % near to filler-filler interactions, even though reinforcements in storage/initial modulus, and toughness increase by up to 14/4.0-, and 1.2-fold, the tensile stress at break only decreases by 27 %.

Hydrophobic enzymatic cellulose nanocrystals via a novel, one-pot green method

Cellulose nanocrystals (CNCs) are a rapidly growing bionanomaterial with remarkable properties that have been harnessed in various applications, including mechanical reinforcement, biomedical materials, and coatings. However, for non-water-based applications, hydrophobization of CNCs while preserving their integrity is crucial. In this study, we propose a new eco-friendly, one-pot surface esterification method for hydrophobizing enzymatic CNCs in aqueous suspension without solvent exchange. By establishing an appropriate set of reaction conditions, it was possible to create a miscibility gradient that enabled a low-cost, and renewable fatty acid to be utilized as an acyl donor and solvent, allowing direct hydrophobic modification of the as-produced aqueous suspension of enzymatic CNC. FT-IR and AFM-IR analyses confirmed the formation of ester groups, while 13C NMR confirmed the emergence of carboxyl groups. XPS revealed a high degree of surface substitution (0.39) in the modified CNC, while a substantial increase in contact angle (from 40 to approximately 90°) quantitatively confirmed the high efficiency of the enzymatic CNC's hydrophobic modification. Additionally, important properties such as morphology remained practically unchanged, except for a slight increase in thermal stability and crystallinity of the CNCs. Therefore, hydrophobic enzymatic CNCs were successfully produced via a simple, scalable, and environmentally friendly approach without compromising their properties. These hydrophobic CNCs have the potential to enhance nanocomposite compatibility, improve packaging performance for electronics and foods, optimize adhesion in coatings, and offer advancements in cosmetics and drug delivery. However, comprehensive studies are needed to confirm their applicability across these sectors.

Highly Stretchable, Repairable, and Tough Nanocomposite Hydrogel Physically Cross-linked by Hydrophobic Interactions and Reinforced by Surface-Grafted Hydrophobized Cellulose Nanocrystals.

Highly stretchable, repairable, and tough nanocomposite hydrogels are designed by incorporating hydrophobic carbon chains to create first-layer cross-linking among the polymer matrix and monomer-modified polymerizable yet hydrophobic nanofillers to create second-layer strong polymer-nanofiller clusters involving mostly covalent bonds and electrostatic interactions. The hydrogels are synthesized from three main components: hydrophobic monomer DMAPMA-C18 by reacting N-[3-(dimethylamino)propyl]methacrylamide] (DMAPMA) with 1-bromooctadecane, monomer N,N-dimethylacrylamide (DMAc), and monomer-modified polymerizable hydrophobized cellulose nanocrystal(CNC-G) obtained by reacting CNC with 3-trimethoxysily propyl methacrylate. The polymerization of DMAPMA-C18 and DMAc and physical cross-linking due to the hydrophobic interactions between C18 chains make DMAPMA-C18/DMAc hydrogel. The additional introduction of CNC-G brings more interactions into the final hydrogel (DMAPMA-C18/DMAc/CNC-G): the covalent bonds between CNC-G and DMAPMA-C18/DMAc, hydrophobic interactions, electrostatic interactions between negatively charged CNC-G and positively charged DMAPMA-C18, and hydrogen bonds. The optimum DMAPMA-C18/DMAc/CNC-G hydrogel exhibits excellent mechanical performance with elongation stress of 1085 ± 14kPa, strain of 4106 ± 311%, toughness of 3.35×104 kJ m-3 , Young's modulus of 844kPa, and compression stress of 5.18MPa at 85% strain. Besides, the hydrogel exhibits good repairability and promising adhesive ability (83-260kN m-2 toward various surfaces).

Polylactic Acid Cellulose Nanocomposite Films Comprised of Wood and Tunicate CNCs Modified with Tannic Acid and Octadecylamine.

Herein, a one-pot strategy was used to prepare hydrophobic cellulose nanocrystals (CNCs) surface-modified with tannic acid and octadecylamine. By this strategy, CNCs derived from wood (W-CNC) and tunicates (T-CNC) were modified in situ and incorporated into a polylactic acid (PLA) matrix using two methods, without first drying the CNCs. Films of PLA-CNC nanocomposites were prepared both by solution casting and by wet compounding in a thermo-kinetic mixer, followed by melt extrusion. Various properties of these PLA nanocomposites were evaluated herein, along with an assessment of how these properties vary with the type of CNC reinforcement. Cast films with a hybrid mixture of wood and tunicate CNCs displayed improved mechanical properties compared to either wood or tunicate CNCs, but extruded films did not show this hybrid effect. The water vapor permeability of the extruded nanocomposite films with 1% CNCs was reduced by as much as 60% compared to the PLA films. The composite films also showed enhanced biodegradation compared to neat PLA films. These results demonstrate that wet compounded PLA composites produced with wood or tunicate CNCs modified using a one-pot, water-based route have improved barrier and biodegradation properties, indicating a potential for packaging applications without having to dry the CNCs.

Multifunctional Gold Nanoparticle-Conjugated Cellulose Nanoonions Alleviate Aβ42 Fibrillation-Induced Toxicity via Regulation of Oxidative Stress and Ion Homeostasis.

Inhibition of hen egg white lysozyme (HEWL) and Aβ42 fibrillation have been established as the main models for the treatment of systemic lysozyme amyloidosis and Alzheimer's disease (AD), respectively. Several antiamyloidogenic nanomaterials have been developed over the period; however, their intracellular mechanism of action is still not well understood. In this context, plant-based, gold-conjugated, injectable, hydrophilic cellulose nanoonions (CNOs), viz., DH-CNO (∼60 ± 5 nm) and LC-CNO (∼55 ± 12 nm), were developed from their respective hydrophobic cellulose nanocrystals (DH-CNC and LC-CNC) using a single-step chemical template-mediated process. This unique nanocellulose architecture was chemically and morphologically characterized by various spectroscopic and microscopic techniques. Further, the different biophysical studies documented marked the inhibition/disintegration potential of gold-conjugated LC-CNO against HEWL and Aβ42 peptide aggregation. It was further observed that inhibition of protein fibrillation could be achieved within ∼10 min when the same materials were used under photoirradiation conditions. In vitro protein aggregation studies using HEK293 cells suggested that gold-conjugated LC-CNO could effectively reduce the cellular toxicity via regulation of oxidative stress and ion homeostasis. The outcome of the present study will help in designing cellulose-based novel functional nanochaperones against various neurodegenerative diseases.

Hydrophobized cellulose nanocrystals enhance xanthan and locust bean gum network properties in gels and emulsions

Locust bean/xanthan gum (LBG/XG) synergistic networks have previously been well studied, with evidence that junction zones between the two polymers result in hydrophobic domains. Here we report on the effect of both hydrophilic and hydrophobic cellulose nanocrystals (CNCs) on the rheological properties of the individual gums, the gum networks, and emulsion gels consisting of the gum network and corn oil. We also take advantage of differences in the autofluorescent spectra for each of the components to map their distribution within the gel and emulsion gel systems. Whilst both types of CNC confer thermal stability to the systems, hydrophilic CNCs induce minor changes in rheological properties of synergistic gels and prove to be detrimental to the stability of the emulsion gels. In contrast, hydrophobic CNCs associate with the LBG/XG network, affecting the rheological response. Their inclusion in the emulsion gel system results in smaller, more homogeneously distributed oil droplets with a resultant increase in the storage modulus by an order of magnitude compared to the CNC-free and hydrophilic CNC systems. We conclude that hydrophobic CNCs play a critical role in stabilising LBG/XG network gels and emulsions.

Hydrophobization of Cellulose Nanocrystals for Aqueous Colloidal Suspensions and Gels.

Surface hydrophobization of cellulose nanomaterials has been used in the development of nanofiller-reinforced polymer composites and formulations based on Pickering emulsions. Despite the well-known effect of hydrophobic domains on self-assembly or association of water-soluble polymer amphiphiles, very few studies have addressed the behavior of hydrophobized cellulose nanomaterials in aqueous media. In this study, we investigate the properties of hydrophobized cellulose nanocrystals (CNCs) and their self-assembly and amphiphilic properties in suspensions and gels. CNCs of different hydrophobicity were synthesized from sulfated CNCs by coupling primary alkylamines of different alkyl chain lengths (6, 8, and 12 carbon atoms). The synthetic route permitted the retention of surface charge, ensuring good colloidal stability of hydrophobized CNCs in aqueous suspensions. We compare surface properties (surface charge, ζ potential), hydrophobicity (water contact angle, microenvironment probing using pyrene fluorescence emission), and surface activity (tensiometry) of different hydrophobized CNCs and hydrophilic CNCs. Association of hydrophobized CNCs driven by hydrophobic effects is confirmed by X-ray scattering (SAXS) and autofluorescent spectroscopy experiments. As a result of CNC association, CNC suspensions/gels can be produced with a wide range of rheological properties depending on the hydrophobic/hydrophilic balance. In particular, sol-gel transitions for hydrophobized CNCs occur at lower concentrations than hydrophilic CNCs, and more robust gels are formed by hydrophobized CNCs. Our work illustrates that amphiphilic CNCs can complement associative polymers as modifiers of rheological properties of water-based systems.

Thermosensitive supramolecular and colloidal hydrogels via self-assembly modulated by hydrophobized cellulose nanocrystals

Utilization of reversible non-covalent interactions is a versatile design strategy for the development of stimuli responsive soft materials. In this study, hydrophobic interactions were harnessed to assemble water-soluble macromolecules and nanoparticles into a transient hybrid network forming thermosensitive hydrogels with tunable rheological properties. Hybrid hydrogels were built of biopolymer derived components: cellulose nanocrystals (CNCs), nanoparticles of high aspect ratio, and hydroxypropyl methylcellulose (HPMC). To enable polymer/CNC assembly via hydrophobic interactions, the surface of highly hydrophilic CNCs was modified by binding octyl moieties (octyl-CNCs). The amphiphilicity of octyl-CNCs was confirmed by surface tension measurements. The molecular and particulate amphiphiles assemble into hybrid networks, which result in stiffer and stronger hydrogels compared to HPMC hydrogels and hydrogels reinforced with hydrophilic CNCs. Hybrid hydrogels retain the ability of HPMC hydrogels to flow under applied shear stress. However, significantly higher viscosity was achieved for HPMC/octyl-CNCs compared with HPMC/CNCs hydrogels. The inherent thermal response of rheological properties of HPMC hydrogels was further amplified in combination with octyl-CNCs due to temperature-induced polymer/nanoparticle association via hydrophobic interactions. Saturation transfer difference NMR spectroscopy demonstrated the growth of network-bound water with an increase in temperature, which correlates with the increase of stiffness and viscosity of hydrogels upon heating. Rheological properties of these hybrid hydrogels are defined by the content of the soluble polymer and the CNCs, and it is shown that they can be finely adjusted for a required application.Graphical abstract

Synergy of Silane and Polyacrylate Treatments to Prepare Thermally Stable and Hydrophobic Cellulose Nanocrystals

Cellulose nanocrystals (CNCs) were modified by surface grafting with silane and polyacrylate without disturbing the material morphologies. The modified CNCs exhibited improved hydrophobicity and th...

Mechanically Robust Gels Formed from Hydrophobized Cellulose Nanocrystals.

Cellulose nanocrystals (CNCs) that bind to each other through associative hydrophobic interactions have been synthesized by modifying sulfated CNCs (sCNCs) with hydrophobic moieties. These octyl-CNCs form gels at significantly lower concentrations than parent sCNCs, producing extremely strong hydrogels. Unlike sCNCs, these octyl-CNCs do not form ordered liquid crystalline phases indicating a random association into a robust network driven by hydrophobic interactions. Furthermore, involvement of the octyl-CNCs into multicomponent supramolecular assembly was demonstrated in combination with starch. AFM studies confirm favorable interactions between starch and octyl-CNCs, which is thought to be the source of the dramatic increase in gel strength.

Cellulose nanocrystals modified with a triazine derivative and their reinforcement of poly(lactic acid)-based bionanocomposites

In order to improve the thermal stability of cellulose nanocrystals (CNCs) and to weaken their hydrophilicity, extensive research has been conducted to graft hydrophobic molecular chains on CNC surfaces to cover and/or replace hydroxyl and sulfate ester groups. According to our previous research, it was proposed that triazine derivative is an ideal candidate to modify CNCs. In this study, triazine derivative-grafted CNCs were synthesized and incorporated into poly(lactic acid) (PLA) nanocomposites as a reinforcing filler. The synthesis of triazine derivative was confirmed by FT-IR and the characterization of modified CNCs was determined by TEM, FT-IR,13C NMR, EDX, TGA and contact angle measurements. It was found that the triazine derivative was successfully grafted onto the CNC surfaces. The thermal stability of the modified CNCs was improved, and hydrophobic CNCs were obtained. Moreover, the properties of CNC/PLA composites were investigated by SEM, UV–Vis spectrophotometer and DSC, and the mechanical properties of composites were measured. The compatability of the modified CNCs with the PLA matrix was improved, and the mechanical properties of PLA composites were improved without serious destruction of their transmittance.

Bio-inspired hydrophobic modification of cellulose nanocrystals with castor oil

This work presents an efficient and environmentally friendly approach to generate hydrophobic cellulose nanocrystals (CNC) using thiol-containing castor oil (CO-SH) as a renewable hydrophobe with the assist of bio-inspired dopamine at room temperature. The modification process included the formation of the polydopamine (PDA) buffer layer on CNC surfaces and the Michael addition reaction between the catechol moieties of PDA coating and thiol groups of CO-SH. The morphology, crystalline structure, surface chemistry, thermal stability and hydrophobicity of the modified CNC were charactered by TEM, XRD, FT-IR, solid-state 13C NMR, XPS, TGA and contact angle analysis. The modified CNC preserved cellulose crystallinity, displayed higher thermal stability than unmodified CNC, and was highly hydrophobic with a water contact angle of 95.6°. The simplicity and versatility of the surface modification strategy inspired by adhesive protein of mussel may promote rapid development of hydrophobic bio-based nanomaterials for various applications.

Synthesis and Characterization of Microencapsulated Phase Change Materials with Poly(urea-urethane) Shells Containing Cellulose Nanocrystals.

The main objective of this study is to develop microencapsulation technology for thermal energy storage incorporating a phase change material (PCM) in a composite wall shell, which can be used to create a stable environment and allow the PCM to undergo phase change without any outside influence. Surface modification of cellulose nanocrystals (CNCs) was conducted by grafting poly(lactic acid) oligomers and oleic acid to improve the dispersion of nanoparticles in a polymeric shell. A microencapsulated phase change material (methyl laurate) with poly(urea-urethane) (PU) composite shells containing the hydrophobized cellulose nanocrystals (hCNCs) was fabricated using an in situ emulsion interfacial polymerization process. The encapsulation process of the PCMs with subsequent interfacial hCNC-PU to form composite microcapsules as well as their morphology, composition, thermal properties, and release rates was examined in this study. Oil soluble Sudan II dye solution in methyl laurate was used as a model hydrophobic fill, representing other latent fills with low partition coefficients, and their encapsulation efficiency as well as dye release rates were measured spectroscopically in a water medium. The influence of polyol content in the PU polymer matrix of microcapsules was investigated. An increase in polyol contents leads to an increase in the mean size of microcapsules but a decrease in the gel content (degree of cross-linking density) and permeability of their shell structure. The encapsulated PCMs for thermal energy storage demonstrated here exhibited promising performance for possible use in building or paving materials in terms of released heat, desired phase transformation temperature, chemical and physical stability, and concrete durability during placement.

Tung Oil Wood Finishes with Improved Weathering, Durability, and Scratch Performance by Addition of Cellulose Nanocrystals.

The main aim of this study is to verify whether cellulose nanocrystal (CNCs)-reinforced tung oil (TO) composites are effective for wood finishes and offer enhanced mechanical and weathering performance owing to the high strength, stiffness, and barrier properties of CNCs. To achieve even dispersion of CNC particles in a polymeric coating film, surface hydrophobization of the CNCs was carried out by grafting poly(lactic acid) oligomers and oleic acid. These new TO coating formulations contain 0 (controlled sample) to 10 wt % of hydrophobized cellulose nanocrystals (hCNCs). The coating performance (degree of wrinkle, leveling, and instantaneous filling) of the hCNC-TO finishes as well as their coating properties (topography, optical properties, mechanical properties, and gas permeability) were investigated in this study. The influence of the hCNC content in the tung oil composite coatings was examined using scratch/impact resistance tests and oxygen transmission rate (OTR) measurements. An increase in the hCNC content led to an increase in scratch/impact resistance as well as a slight decrease in the color-b change, gloss, surface roughness, and OTR value of their film coatings. The hCNC-TO composites for wood coatings presented here showed enhanced performance for utilization in wood-working processes in terms of desired mechanical properties (scratch and impact resistance), weathering performance (color stability), and easy production without any deterioration in surface gloss and roughness after the addition of hCNC to a TO matrix. The hCNC enhanced coating system is a promising candidate for substantial protection of wood surfaces in demanding settings.

Green One-Pot Synthesis of Surface Hydrophobized Cellulose Nanocrystals in Aqueous Medium

The surface hydrophobization of cellulose nanocrystals (CNCs) by fatty acids (FAs), biodiesel, or plant oils was conducted via a green process using an organic solvent less one-pot method. In the process, an aqueous lactic acid syrup served as a reactive solvent to provide a stable and well-dispersed water suspension of CNC and participate in esterification reactions, producing an intermediate product of polylactic acid (PLA) oligomer grafted CNCs (CNC-g-PLA). This reactive solvent and intermediate product system allows for an in situ solvent exchange from water to lactic acid without prior drying of the CNC and a subsequent efficient esterification reaction of CNC with carboxylic acids or esters having a long hydrocarbon chain (FAs). Another advantage of the proposed process is the possibility to reuse the reagents in the subsequent reaction in order to reduce the production cost. The grafting efficiency of the CNC-g-PLA-FA samples covalently grafted with PLA and FAs were characterized by Fourier transfo...

Nanocomposites of Hydrophobized Cellulose Nanocrystals and Polypropylene

Cellulose nanocrystals (CNCs) are high-strength sustainable nanomaterials, the incorporation of which to a host polymer matrix can potentially lead to nanocomposites with superior mechanical properties. However, the mismatch in surface energy of CNCs and common structural polymers is a challenge that needs to be overcome to prevent the aggregation of CNCs and ensure the robust integration of CNCs into a polymer matrix. Herein, we report an approach involving the functionalization of CNCs with maleated-anhydride polypropylene (MAPP) through diethylenetriamine (DETA) linkers to significantly enhance the compatibility between CNCs and polypropylene. Polypropylene/modified CNC nanocomposites displayed 74% and 76% increase in elastic modulus in comparison to neat polypropylene and polypropylene/untreated CNC nanocomposites, respectively. The tensile strength was also higher for nanocomposites withmodified CNC than neat polypropylene, as well as nanocomposites with untreated CNCs. The tensile strength at 5.5% strain of polypropylene/modified CNCnanocomposites was 32% and 28% larger that of polypropylene and polypropylene/untreated CNC nanocomposites, respectively. Finally, such CNC-based nanocomposites have a lower density than many competitive systems resulting in opportunities to propagate this environmentally-responsible technology to nanocomposites used in additive manufacturing, automotive applications, construction materials and consumer products.

One-pot preparation of hydrophobic cellulose nanocrystals in an ionic liquid

The facile one-pot preparation of hydrophobic cellulose nanocrystals (CNCs) from wood pulpboard in an ionic liquid is reported in the present paper. This process employed a so-called amorphous cellulose solvent system capable of dissolving the majority of the amorphous regions in cellulose while maintaining the crystalline domains essentially intact, and consisting of tetrabutylammonium acetate with dimethylacetamide. These solvents were mixed at a mass ratio of 1:9 in conjunction with acetic anhydride to prepare CNCs via surface acetylation. The rod-like morphology and nanometer-scale dimensions of the resulting CNCs were ascertained by atomic force microscopy and transmission electron microscopy. Successful surface acetylation while maintaining an intact crystalline core was confirmed by Fourier transform infrared, 13C CP/MAS NMR and X-ray photoelectron spectroscopy in addition to X-ray diffraction. Finally, the thermal stability and hydrophobic behavior of the hydrophobic CNCs were characterized using thermal gravimetric analysis and water contact-angle measurements, respectively.

Hydrophobic modification of cellulose nanocrystal via covalently grafting of castor oil

Hydrophobic cellulose nanocrystals (CNs) have been prepared by grafting isocyanate-terminated castor oil, a kind of natural vegetable oil, onto their surface. The existence of castor oil component in the modified cellulose nanocrystals was verified by Fourier transform infrared spectroscopy, solid-state C-13 NMR spectra and X-ray photoelectron spectroscopy. At the same time, X-ray diffraction and transmission electron micrographs further proved that the crystalline structure and large aspect ratio of cellulose nanocrystals were essentially preserved after chemical grafting. Furthermore, the surface of modified cellulose nanocrystals appeared to be hydrophobic as indicated by contact angle measurements. The value of the polar component of surface energy decreased from 21.5 mJ/m(2) to almost zero via grafting castor oil. These novel hydrophobic castor oil-grafted cellulose nanocrystals appear as valuable alternatives to formulate bionanocomposites with non-polar polymers for optimized performances.

Hydrophobic cellulose nanocrystals modified with quaternary ammonium salts

An environmentally friendly procedure in aqueous solution for the surface modification of cellulose nanocrystals (CNCs) using quaternary ammonium salts via adsorption is developed as inspired by organomodified layered silicates. CNCs with a high carboxylate content of 1.5 mmol g−1 were prepared by a new route, direct hydrochloric acid hydrolysis of 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidized nanofibrillated cellulose from a softwood pulp, and characterized by atomic force microscopy (AFM) and X-ray diffraction (XRD). Four quaternary ammonium cation surfactants bearing long alkyl, phenyl, glycidyl, and diallyl groups were successfully used to modify CNCs carrying carboxylic acid groups as characterized by Fourier transform infrared spectroscopy (FTIR). The modified CNCs can be redispersed and individualized in an organic solvent such as toluene as observed by scanning transmission electron microscopy (STEM). One may envision removing excess surfactant to obtain CNC with a monolayer of surfactant. The toluene suspension of the modified CNCs showed strong birefringence under crossed polars but no further chiral-nematic ordering was observed. The model surface prepared by the CNCs modified with quaternary ammonium salts bearing C18 alkyl chains showed a significant increase in water contact angle (71°) compared to that of unmodified CNCs (12°). This new series of modified CNCs can be dried from solvent and have the potential to form well-dispersed nanocomposites with non-polar polymers.