Incorporating Cellulose Nanocrystals Research Articles

Obtaining Cellulose Nanocrystals from Olive Tree Pruning Waste and Evaluation of Their Influence as a Reinforcement on Biocomposites

The objective of this work is to improve the mechanical properties of polylactic acid (PLA) by incorporating cellulose nanocrystals (CNC) previously obtained from a cellulose pulp extracted from olive tree pruning (OTP) waste. Composites were manufactured by melt processing and injection moulding to evaluate the effect of the introduction of CNC with conventional manufacturing methods. This OTP-cellulose pulp was subjected to a further purification process by bleaching, thus bringing the cellulose content up to 86.1%wt. This highly purified cellulose was hydrolysed with sulfuric acid to obtain CNCs with an average length of 267 nm and a degradation temperature of 300 °C. The CNCs obtained were used in different percentages (1, 3, and 5%wt.) as reinforcement in the manufacture of PLA-based composites. The effect of incorporating CNC into PLA matrix on the mechanical, water absorption, thermal, structural, and morphological properties was studied. Maximum tensile stress and Young’s modulus improved by 87 and 58%, respectively, by incorporating 3 and 5%wt. CNC. Charpy impact strength increased by 21% with 3%wt. These results were attributed to the good dispersion of CNCs in the matrix, which was corroborated by SEM images. Crystallinity index, glass transition, and melting temperatures were maintained.

Interpenetrating and semi-interpenetrating network superabsorbent hydrogels based on sodium alginate and cellulose nanocrystals: A biodegradable and high-performance solution for adult incontinence pads

Superabsorbent hydrogels (SAHs) are essential in various applications, including hygienic products like adult incontinence pads. However, synthetic-based super absorbent polymers (SAPs) dominate the market despite being non-biodegradable. Alternatively, bio-based hydrogels, such as sodium alginate (SA)-based hydrogels, offer biodegradable alternatives. In this study, we aimed to enhance the practical applied properties of SA-based hydrogels by grafting SA with acrylic acid (AA) and incorporating cellulose nanocrystals (CNCs). Specifically, we investigated the potential of interpenetrating network (IPN) and semi-interpenetrating network (S-IPN) hydrogels as absorbent materials in adult incontinence pads. The fabricated SAHs were characterized by Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM). They were also evaluated for absorption and rheological properties. The results showed that in IPN/SAHs, the addition of CNCs decreased pore sizes, while in S-IPN/SAHs, CNC incorporation increased pore sizes. The S-IPN/SAHs exhibited a significantly higher free swelling capacity (FSC) with CNCs loading, reaching 142.29 g/g in 0.9 % NaCl solution and 817.4 g/g in distilled water. On the other hand, IPN/SAHs showed a higher storage modulus and lower loss modulus compared to S-IPN/SAHs. Notably, the superior samples from this study showed a 33 % reduction in SAP consumption compared to commercial SAPs, making them more cost-effective for adult incontinence pad manufacturers. Overall, our research demonstrates the potential of interpenetrating and semi-interpenetrating network superabsorbent hydrogels as high-performance absorbent materials. The results offer improved absorbency and cost savings for producers of adult incontinence pads, and bio-based hydrogels like SA-based hydrogels are promising biodegradable alternatives to synthetic-based SAPs.

Development of reduced graphene oxide (rGO) reinforced poly(lactic) acid/ cellulose nanocrystal composite through melt mixing: Effect of nanofiller on thermal, structural, biodegradation and antibacterial properties

The intent of this research work was to synthesised a synthetic polymer that is biodegradable, bioresorbable, and biocompatible, while also exhibiting favorable thermal characteristics. The present study reports the successful fabrication of bionanocomposites by incorporating Cellulose nanocrystals (CNCs) and Reduced graphene oxide (rGO) into host matrix (PLA) using the melt-mixing technique. Various weight percentages (wt%) of rGO were employed in the process and various characterization techniques, including BET analysis, XRD, FTIR and field emission scanning electron microscopy (FE-SEM) were used to verify the efficient fabrication of a number of nanoformulations and nanofiller’s effect. Introduction of CNC and rGO in PLA matrix increases the surface area as well as porosity of the composites, established by BET analysis. DSC results indicate that the assimilation of rGO into the polymer matrix improved thermal stability of the composite material and leads to boost in the degree of crystallinity which was supported by XRD analysis. TGA results found no noticeable change in glass transition temperature (Tg) due to the addition of Nanofiller (rGO). The wettability analysis was done by contact angle measurement to determine the hydrophilicity of the composite and it is shown that with the increasing amount of rGO, hydrophilicity increases and contact angle reaches to 69° for 0.75 wt% of rGO in composite in comparision to 100° Neat PLA. The rGO/CNC/PLA nanocomposites exhibit a unique antibacterial effectiveness against both the S. aureus (Gram-positive) and E. coli (Gram-negative) bacterial strains. The highest antimicrobial activity was obtained in the nanocomposite tested against S. aureus. Biodegradation through Lysozyme in PBS solution shows promising result after incorporation of nanofillers. Hence, the nanocomposite manufactured through melt mixing process has promising uses in the biomedical and food packaging industries.

Enhanced mechanical, barrier and antioxidant properties of rice protein/sodium alginate-based films by incorporating cellulose nanocrystals and rosemary extract

This study aimed to develop rice protein (RP)/sodium alginate (SA)-based biodegradable films with excellent properties by incorporating cellulose nanocrystals (CNCs) and rosemary extract. Effects of the RP/SA weight ratio and CNCs content on the physical properties of the films were investigated, and the improved performance was illustrated by Fourier Transform Infrared spectroscopy and molecular dynamics (MD) simulation. As the RP/SA weight ratio varied from 5:0–1:1, the tensile strength (TS) of the films was increased by 143%, water vapor permeability (WVP) and oil permeability were significantly reduced by 22% and 99.2%, respectively. As the CNCs content increased to 0.3%, the TS was enhanced by 51% and the WVP was reduced by 14%. The improved mechanical and barrier properties of the films were possibly attributed to the formation of a more homogeneous and compact structure observed by scanning electron microscopy. In addition, MD simulation results revealed that there were high number of hydrogen bonds and strong electrostatic interactions in the RP/SA/CNCs/RE system, which may also lead to the improvement of mechanical and barrier properties of films. Finally, the films effectively attenuated oil oxidation. The developed films with enhanced properties are potential food packaging materials.

Thermo-sensitive composite microspheres incorporating cellulose nanocrystals for regulated drug release kinetics

Thermo-sensitive composite microspheres (TPCP) were developed to achieve the on-demand release of drugs. The TPCP microspheres were synthesized using Oil-in-Water (O/W) emulsion evaporation technique and then impregnated with thermo-sensitive polyethylene glycol (PEG). The addition of cellulose nanocrystals (CNCs) significantly enhance thermal stability, crystallization ability, and surface hydrophilicity of TPCP microspheres due to heterogeneous nucleation effect and hydrogen bonding interaction, resulting in stable microsphere structure. The thermal degradation temperature (Tmax) increased by 13.8 °C, and the crystallinity improved by 20.9 % for 10 % TPCP. The thermo-sensitive composite microspheres showed the regulated cumulative release according to in vitro human physiological temperature changes. Besides, four release kinetics and possible release mechanism of TPCP microspheres were provided. Such thermo-responsive composite microspheres with control microsphere sizes and high encapsulation rate may have the potential to the development of on-demand and advanced controlled-release delivery systems.

Development of antimicrobial films with cinnamaldehyde stabilized by ethyl lauroyl arginate and cellulose nanocrystals

Antimicrobial films were developed by incorporating cellulose nanocrystals (CNC) and cinnamaldehyde-based Pickering emulsions into polyvinyl alcohol. The food-grade cationic surfactant, ethyl lauroyl arginate (LAE), was used to modify CNC for emulsion stability improvement. We contend that the LAE reduced the electrostatic repulsion by partially neutralizing the CNC surface charge and increased its packing density around the droplet interface. The CNC/LAE and cinnamaldehyde mixture formed an oil-in-water Pickering emulsion with an average droplet size of 5.54 µm. The emulsion-added films led to significant inhibition of microbial growth of E. coli, S. aureus, and B. cinerea. Moreover, there was no significant adverse effect on the films' mechanical properties, water vapor permeability, or solubility with 1% and 2% emulsions added. Lastly, the antimicrobial films with 2% emulsion inhibited the deterioration rate of strawberries by 52.2%. The CNC-LAE-cinnamaldehyde Pickering emulsions-added films demonstrate a promising application for antimicrobial food packagings.

Evaluation of the Antimicrobial, Thermal, Mechanical, and Barrier Properties of Corn Starch-Chitosan Biodegradable Films Reinforced with Cellulose Nanocrystals.

Packaging materials play an essential role in the preservation and marketing of food and other products. To improve their conservation capacity, antimicrobial agents that inhibit bacterial growth are used. Biopolymers such as starch and chitosan are a sustainable alternative for the generation of films for packaging that can also serve as a support for preservatives and antimicrobial agents. These substances can replace packaging of synthetic origin and maintain good functional properties to ensure the quality of food products. Films based on a mixture of corn starch and chitosan were developed by the casting method and the effect of incorporating cellulose nanocrystals (CNC) at different concentrations (0 to 10% w/w) was studied. The effect of the incorporation of CNC on the rheological, mechanical, thermal and barrier properties, as well as the antimicrobial activity of nanocomposite films, was evaluated. A significant modification of the functional and antimicrobial properties of the starch–chitosan films was observed with an increase in the concentration of nanomaterials. The films with CNC in a range of 0.5 to 5% presented the best performance. In line with the physicochemical characteristics which are desired in antimicrobial materials, this study can serve as a guide for the development this type of packaging for food use.

Highly Foldable, Super-Sensitive, and Transparent Nanocellulose/Ceramic/Polymer Cover Windows for Flexible OLED Displays.

Polymer cover windows are important components of flexible OLED displays but they easily generate wrinkles because of their weak folding resistance. Increasing the polymer thickness can improve the folding resistance but it decreases the touch sensitivity. Thus, fabricating highly foldable and supersensitive polymer cover windows is still challenging. Here, by incorporating cellulose nanocrystals (CNCs) and zirconia (ZrO2) into colorless polyimide (CPI), we developed a highly foldable and supersensitive hybrid cover window. Inspired by the theory of elasticity, we added rigid CNCs into CPI to improve the elastic modulus and hence the foldability. ZrO2 was introduced to improve dielectric properties, which leads to improved touch sensitivity. After these modifications, the elastic modulus of the cover windows was increased from 1432 to 2221 MPa, whereas its dielectric constant was increased from 2.95 to 3.46 (@1 × 106 Hz), resulting in significantly enhanced foldability and sensitivity. Meanwhile, because of the nano size of CNCs and ZrO2, the hybrid cover windows exhibit excellent optical properties with the transmittance of ∼88.1%@550 nm and haze of 2.39%. With improved and balanced mechanical, dielectric, and optical properties, these hybrid cover windows overcome current cover windows' defects and could be widely used in next-generation flexible displays.

All-natural and biocompatible cellulose nanocrystals films with tunable supramolecular structure

Herein, nanocomposites films were prepared via the facile casting method by incorporating cellulose nanocrystals (CNCs) with arabinogalactan (AG), galactomannan (GM) or konjac glucomannan (KGM) respectively. The introduced polysaccharides maintained the transparency of CNCs films and promoted the UV blocking properties. In addition, mechanical strength of the nanocomposite films was greatly improved after the combination of polysaccharides. The interactions of hydroxyl-abundant macromolecules, smoother and tighter morphological structures, as well as the disturbed crystal structure were proved to be responsible for the improved properties. Hydrophilic lattice planes of cellulose crystallites were determined to interact with polysaccharides resulting in lower crystallite sizes and crystallinity. The cell culture assay revealed that the films had no cytotoxicity and presented a satisfactory cytocompatibility, because of the polysaccharides from plant cell walls introduced into the films. Therefore, the biocompatible nanocomposites films can be tuned by the addition of polysaccharides, which show great potentials for materials modification in optical, packaging and biomedical fields.

Cellulose nanocrystal treatment of aligned short hemp fibre mats for reinforcement in polypropylene matrix composites

Oriented short hemp fibre mats were produced using dynamic sheet forming (DSF) incorporating cellulose nanocrystals (CNCs) to improve their integrity. The CNCs were found to act as a binder and improve mechanical strength of the mats as well as the strength of polypropylene matrix composites produced with the mats. Improved thermal stability was also obtained for composites by using CNC treatment of fibre mats.

Multifunctional Biosensors Made with Self-Healable Silk Fibroin Imitating Skin.

We report on robust silk fibroin (SF) gels fabricated by incorporating cellulose nanocrystals (SF/CNC) as a "tough" unit and photopolymerization of acrylamide as an "elastic" segment. The addition of CNC affects the refolding process of SF molecules controlled by nucleation via templating, resulting in a stable mesoscopic structure. The gel shows robust mechanical stability (88.8% of initial stress after 1000 compression cycles) and excellent adhesion to various materials. The connected gel can recover its ionic conductivity within 20 s and be stretched to a maximum strain of 498% after healing for 10 h with an efficiency of 95.2%. This multifunctional gel sensor can sensitively detect different toxic gases and small-scale and large-scale human motions in real-time. Its sensitivity is calculated as GF = 3.84 at 0-200% strain. Especially, the gel with 5 wt % thermochromic pigments as a visual temperature indicator can quickly reflect abnormal human body temperature according to the color change. Therefore, the strategy shows potential applications in flexible electrodes, biomimetic sensors, and visual biosensors.

Cellulose nanocrystal mediated fast self-healing and shape memory conductive hydrogel for wearable strain sensors

Electro-conductive hydrogel (ECH) with self-healing, shape memory and biocompatible properties is highly urgent for wearable strain sensors to prolonging their lifespan, endowing programmable shape control property, and improving affinity to skin during service. However, most of synthetic polymer-based ECH usually involve potential toxicity, long healing and shape drive time. Herein, a fast healable and shape memory ECH with excellent biocompatibility is reported for the first time by incorporating cellulose nanocrystals grafted phenylboronic acid (CNCs-ABA) and multiwalled carbon nanotubes (MWCNTs) into polyvinyl alcohol (PVA). CNCs-ABA is designed as dispersant and crosslinker in hydrogel. pH-induced dynamic borate bonds give hydrogel excellent shape recovery and fixity ratio of 82.1% and 78.2%, respectively. Meanwhile, 97.1% healing efficiency is obtained within 2 min depending on remarkable photothermal effect of MWCNTs and reversible microcrystallization. Double crosslinking networks endow excellent mechanical properties to hydrogel, whose tensile strength, strain and elastic modulus reach 227.0 kPa, 395.0% and 9.0 kPa, respectively. Furthermore, the synergistic effect of MWCNTs and NaOH enhance the conductivity of hydrogel with value of 3.8×10−2 S/m. In addition, the hydrogel can act as strain sensor for detecting human motion with superior biocompatibility and fast resistance response to applied strain, which is suitable for human health management.

Thermoplastic polyurethane-cellulose nanocomposite for transparent armour: Characterisation of adhesion and thermal aging

Environmental degradation of transparent thermoplastic polyurethane (TPU) is an issue of growing concern. Measured increased in the mechanical properties of nano-reinforced TPUs have been reported, however, limited research is available regarding their adhesive properties and resistance to environmental aging. By incorporating cellulose nanocrystals (CNCs) into a TPU via planetary ball milling, an increase to both the mechanical and adhesive properties was obtained. The TPU/CNC nanocomposite showed bond integrity and lap shear strengths were increased by 34% and 25% respectively relative to the unmodified nanocomposite, and further improvements in mechanical performance were seen. The TPU/CNC nanocomposite showed higher melting temperature and increased melting enthalpy indicating improved thermal aging resistance. The restriction of TPU segments and changes in chemical bond state and crystallinity were identified as key mechanisms driving performance improvements.

Thin film nanocomposite nanofiltration membrane incorporated with cellulose nanocrystals with superior anti-organic fouling affinity

Thin film nanocomposite (TFN) nanofiltration (NF) membranes were fabricated by incorporating cellulose nanocrystals (CNCs) in a polyamide (PA) layer.

Highly Efficient and Stable White Light-Emitting Diodes Using Perovskite Quantum Dot Paper.

Perovskite quantum dots (PQDs) are a competitive candidate for next‐generation display technologies as a result of their superior photoluminescence, narrow emission, high quantum yield, and color tunability. However, due to poor thermal resistance and instability under high energy radiation, most PQD‐based white light‐emitting diodes (LEDs) show only modest luminous efficiency of ≈50 lm W−1 and a short lifetime of <100 h. In this study, by incorporating cellulose nanocrystals, a new type of QD film is fabricated: CH3NH3PbBr3 PQD paper that features 91% optical absorption, intense green light emission (518 nm), and excellent stability attributed to the complexation effect between the nanocellulose and PQDs. The PQD paper is combined with red K2SiF6:Mn4+ phosphor and blue GaN LED chips to fabricate a high‐performance white LED demonstrating ultrahigh luminous efficiency (124 lm W−1), wide color gamut (123% of National Television System Committee), and long operation lifetime (240 h), which paves the way for advanced lighting technology.

Enhanced mechanical and oxygen barrier performance in biodegradable polyurethanes by incorporating cellulose nanocrystals with interfacial polylactide stereocomplexation

Using bio-derived cellulose nanocrystals (CNCs) to reinforce the mechanical properties of biodegradable polyurethanes (PUs) is a promising approach especially when attempting to fabricate fully sustainable materials with high performance. However, the way to efficiently improve the dispersion and interfacial strength of CNCs in PU matrices is still an open question. In the current work, poly-l-lactide (PlLA) grafted CNCs (CNC-g-l) and a PU elastomer with poly-d-lactide as partial soft segments (d-PU) were first prepared separately, and then the fully biodegradable PU nanocomposites were fabricated by solution blending of CNC-g-l and d-PU. The surface grafting of PlLA can improve the thermal stability of CNCs, but has marginal effect on that of the nanocomposites. The improved dispersion of CNCs and enhanced interfacial strength, as evidenced by scanning electron microscopy, wide-angle X-ray diffraction and rheology measurements, are achieved by the construction of interfacial polylactide stereocomplexation (sc-PLA). The optimal improvement in mechanical properties of the nanocomposites is realized when only 1 wt% CNC-g-l is incorporated in the d-PU matrix. With the assistance of interfacial sc-PLA, the nanocomposite can gain 40% reduction in oxygen transmission rate at the optimal CNC-g-l content of 5 wt%. This study may provide a new method to improve the dispersion and interfacial strength of CNCs in biodegradable PUs and achieve simultaneously mechanical and barrier performance enhancement.

Preparation and evaluation of oxygen scavenging nanocomposite films incorporating cellulose nanocrystals and Pd nanoparticles in poly(ethylene-co-vinyl alcohol)

There is current interest in active packaging, where the packaging material exhibits desirable functions in addition to containment of product. One of these functions is to reduce the oxygen content in the package in order to minimize product oxidation and spoilage, and prolong product shelf-life. In this work, we have developed novel nanocomposites, comprising cellulose nanocrystals and Pd nanoparticles embedded in an ethylene–vinyl alcohol copolymer (EVOH). The nanocellulose is a critical component in the nanocomposite because it acts not only as reducing agent for PdCl2 but also as support for the dispersion of Pd nanoparticles on EVOH film and enhances the physical properties of the EVOH. Pd nanoparticles react with oxygen to serve as oxygen scavenger. The cellulose nanocrystals have also been optionally oxidized, and the increased presence of carboxyl groups favored a better distribution of the Pd nanoparticles, thereby enabling improved oxygen absorption. These features make the nanocomposites promising candidates as active packaging materials. Included in this work are the preparation and the characterization of these materials.

Electrospun polyvinylidene fluoride-based fibrous nanocomposite membranes reinforced by cellulose nanocrystals for efficient separation of water-in-oil emulsions

A hydrophobic-oleophilic nanofibrous membrane was successfully produced by incorporating cellulose nanocrystals (CNC) into polyvinylidene fluoride (PVDF) via an electrospinning process. The effects of levels of CNC loading on membrane microstructure, mechanical properties, water and oil contact angle and efficacy of separating oil from water-in-oil emulsions were investigated. The results demonstrated that the incorporation of CNC improved the flux of emulsion separation of the fabricated fibrous membranes by optimizing microstructure and porosity. For water-in-toluene emulsions, a higher flux of 5842 L m−2 h−1 with high separation efficiency of 97% was obtained for membranes with CNC addition of 4 wt%, 4 times greater than that of pure PVDF membrane (1495 L m−2 h−1). Most importantly, as increasing CNC loading levels, membranes demonstrated good mechanical performance while being easily recycled, which is environmentally friendly, flexible and sustainable.

Unique thermo-responsivity and tunable optical performance of poly(N-isopropylacrylamide)-cellulose nanocrystal hydrogel films

A hybrid materials system to modulate lower critical solution temperature (LCST) and moisture content for thermo-responsivity and optical tunability was strategically developed by incorporating cellulose nanocrystals (CNCs) into a poly(N-isopropylacrylamide) (PNIPAm) hydrogel matrix. The PNIPAm/CNC hydrogel films exhibit tunable optical properties and wavelength bandpass selectivity as characterized by PROBE Spectroscopy and Dynamic Light Scattering (DLS). Importantly, the micro/nano structures of the PNIPAm/CNC hydrogel films were completely different when dried below and above the LCST. Below the LCST, PNIPAm/CNC hydrogel films exhibit transparency or semi-transparency due to the uniform bonding of hydrophilic PNIPAm and CNC through hydrogen bonds. Above the LCST, the hydrogel films engage in both hydrophobic PNIPAm and hydrophilic CNC interactions due to changes in PNIPAm conformation which lead to light scattering effects and hence opacity. Furthermore, the incorporation of CNC induces a ∼ 15 °C reduction of the LCST relative to pure PNIPAm hydrogel films.

Incorporating Cellulose Nanocrystals into the Core of Polymer Latex Particles via Polymer Grafting.

Surface-initiated atom transfer radical polymerization was used to graft hydrophobic poly(butyl acrylate) from cellulose nanocrystals (CNCs) resulting in compatibilized CNCs that were successfully incorporated inside the core of polymer latex particles. CNCs are anisotropic nanoparticles derived from renewable resources and have potential as reinforcing agents in nanocomposites. However, challenges due to the incompatibility between cellulose and hydrophobic polymers and processing difficulties, such as aggregation, have limited the performance of CNC nanocomposites produced to date. Here, CNCs were incorporated into the miniemulsion polymerization of methyl methacrylate by adding polymer-grafted CNCs to the monomer phase. A poly(methyl methacrylate)-CNC nanocomposite latex was subsequently produced in situ, whereby polymer-grafted CNCs (with optimized graft length) were located inside the latex particles, as shown by transmission electron microscopy. This work provides a method for controlling the location of CNCs in latex-based nanocomposites and may extend the use of CNCs in commercial adhesives and coatings.