Grafting polymers from cellulose nanocrystals via surface‐initiated atom transfer radical polymerization

Cellulose Nanocrystal Stabilized Liquid Metal Pickering Emulsion as Photothermal and Conductive Direct-Writing Ink

Gallium-based liquid metal (LM) has attracted great attention for constructing flexible electronic devices due to its excellent deformability and electrical conductivity. However, its large surface tension makes it difficult to be uniformly dispersed in polymers, which severely limits its wide applications. Hence, a surfactant-free approach is proposed to prepare stable LM microspheres against precipitation and coalesce by facile ultrasonication via cellulose nanocrystal (CNC) stabilized LM-in-water Pickering emulsion (PE), where CNCs are employed as Pickering emulsifiers due their partial wettability with both LM and water phases, strong electrostatic adsorption and hydrogen bonding interactions with LM. So far, reports about LM PE and CNC-stabilized inorganic material PE are still rare. CNC/LM PE is employed as direct-writing inks on various substrates for delicate patterns. The pristine CNC/LM patterns show excellent photothermal conversion due to localized surface plasma resonance effect of CNC/LM microspheres. After activation by friction sintering, the LM patterns are highly electric conductive (1666.7 S m-1) due to the formation of LM connection. The activated LM patterns also displayed excellent Joule heating (83.2 °C at 0.9 V) and electromagnetic interference (EMI) shielding ability (585.7 dB mm-1) in X-band range.

Surface-Vinylated Cellulose Nanocrystals as Cross-Linkers for Hydrogel Composites

Cellulose nanocrystal (CNC) fillers have been shown to significantly improve the performance of polymer composites and hydrogels, elevating both strength and toughness. Polymer grafting from the surface of the nanocrystals has been employed to enhance matrix-filler interactions and keep the fillers dispersed within the matrix. However, such approaches often rely on multistep syntheses and diligent process control. Here, we propose modifying the nanocrystal surface to carry vinyl moieties, turning the particles into cross-linking comonomers. Using allyl glycidyl ether in an aqueous modification route, we were able to decorate the CNCs with varying amounts of vinyl moieties. Subsequent dispersion in 2-hydroxy methacrylate and thermally initiated free radical polymerization yielded composite materials that showed superior mechanical performance compared to those obtained from monomeric cross-linkers and unmodified CNCs. The large discrepancies in the observed glass transition temperatures of the obtained materials suggest, however, that the impact of the fillers on the polymerization kinetics is significant and less easily explained.

Designing mechanically robust one-component nanocomposites via hyperbranched cellulose nanofibril grafted vegetable oil polymers

Achieving effective interfacial compatibility between hydrophilic cellulose nanofibrils (CNFs) and hydrophobic vegetable oil polymers (VOPs) remained a significant challenge. To address this issue, we developed a one-component nanocomposite (OCN) based on hyperbranched CNF-grafted VOPs. Rigid precursor initiator poly (vinylbenzyl chloride) (PVBC) was first grafted onto the CNF surface via phase-transfer catalysis, forming a branched macroinitiator (CNF-g-PVBC) with chlorine contents ranging from 4.4 to 9.1 wt%. Subsequently, vegetable oil based monomers (lauryl methacrylate, LMA) were directly grafted onto CNF-g-PVBC through sacrificing initiator-free surface-initiated atom transfer radical polymerization (SI-ATRP). Finally, a hyperbranched CNF-based one-component nanocomposite (OCN-CVOP) was successfully prepared. Nanoscale infrared spectroscopy and microscopy confirmed the highly uniform morphology of the OCN-CVOP films, highlighting the superior dispersion of CNFs within the VOP matrix. Notably, compared to pure VOPs, OCN-CVOP exhibited remarkably low glass transition temperature (∼-15 °C) and reduced viscosity, which was attributed to the hyperbranched architecture. Even at LMA contents as high as ∼70 wt%, OCN-CVOP demonstrated excellent mechanical performance, achieving a tensile strength of 3.6 ± 0.2 MPa and a toughness of 21.5 ± 2.9 MJ/m3. This innovative design successfully addressed the mechanical limitations of conventional VOPs, offering a sustainable approach for developing environmentally friendly, high-performance VOP materials with diverse application potential.

High thermal conductive and photothermal phase change material microcapsules via cellulose nanocrystal stabilized Pickering emulsion for solar harvesting and thermal energy storage

Phase change materials (PCMs) are promising for thermal energy storage due to their high latent enthalpy and constant phase change temperature. However, organic PCMs suffer from leaking, low thermal conductivity, and flammability. Herein, high thermal conductivity, photothermal and flame-proof docosane microcapsules with melamine-formaldehyde (MF) and polypyrrole (PPy) (C22-CMFP) were reported with cellulose nanocrystal (CNC) stabilized Pickering emulsion droplets as templates through in-situ polymerization. CNCs showed outstanding C22 Pickering emulsifying ability with the presence of NaCl and provided ideal templates for C22 microcapsules. The obtained C22-CMFP microcapsules displayed high enthalpy (205.7 J/g), C22 core ratio (86.1 %), and stability. The C22-CMFP microcapsules retained an outstanding enthalpy remaining ratio (98.9 %) after 100 times cooling/heating cycles and could tolerate 100 °C for 12 h without leaking due to the robust hybrid CMFP shell. PPy significantly improved the thermal conductivity and photothermal conversion efficiency of C22-CMFP microcapsules. The C22-CMFP microcapsules exhibited a high thermal conductivity of 0.683 W/(m·K). The maximum temperature of C22-CMFP microcapsules under light irradiation for 18 min was 60.4 °C. Moreover, C22-CMFP microcapsules showed superb flame-proof properties. This study provides a facile approach to fabricate high enthalpy, stable, thermal conductive, photothermal, and flame-proof PCM microcapsules for solar harvesting and thermal energy storage.

Synthesis, characterization and evaluation of cellulose-graft-poly(4-vinylpirydine), using cellulose from a new pretreatment process, for heavy metal removal from wastewater

The synthesis, characterization and evaluation of cellulose-graft-poly(4-vinylpirydine) for heavy metal removal from wastewater, is reported. Cellulose was obtained from a corn cob biomass using a recently developed gas-phase acid pretreatment process (GPAPP). The obtained corn cob cellulose (CCC) was functionalized by partial esterification of the superficial -OH groups with α-bromoisobutyryl bromide (BIBB) under mild conditions (room temperature and dimethyl formamide, DMF as solvent). The functionalized cellulose was characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM)/energy dispersive spectroscopy (EDS), thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). The BIBB-functionalized CCC was used as initiator for surface-initiated (SI) atom transfer radical polymerization (ATRP) of 4-vinylpyridine (4VP). Grafting of the polymer (p4VP) onto cellulose was confirmed by FTIR, TGA and XPS. The same procedure was carried out with microcrystalline cellulose (MCC) as a reference. The performance of the cellulose copolymers for the removal of lead and iron from water was evaluated. Removal percentages of 83 % in 30 min for lead and 79 % in 180 min for iron were obtained with MCC-g-p4VP. In contrast, removal percentages of 50 % were obtained in 30 min for lead and 30 % for iron in 180 min, respectively, when CCC-g-p4VP was used.

Click-Chemistry-Enabled Functionalization of Cellulose Nanocrystals with Single-Stranded DNA for Directed Assembly

Controlling the self-assembly of cellulose nanocrystals (CNCs) requires precise control over their surface chemistry for the directed assembly of advanced nanocomposites with tailored mechanical, thermal, and optical properties. In this work, in contrast to traditional chemistries, we conducted highly selective click-chemistry functionalization of cellulose nanocrystals with complementary DNA strands via a three-step hybridization-guided process. By grafting terminally functionalized oligonucleotides through copper-free click chemistry, we successfully facilitated the assembly of brushlike DNA-modified CNCs into bundled nanostructures with distinct chiral optical dichroism in thin films. The complexation behavior of grafted DNA chains during the evaporation-driven formation of ultrathin films demonstrates the potential for mediating chiral interactions between the DNA-branched nanocrystals and their assembly into chiral bundles. Furthermore, we discuss the future directions and challenges that include new avenues for the development of functional, responsive, and bioderived nanostructures capable of dynamic reconfiguration via selective complexation, further surface modification strategies, mitigating diverse CNC aggregation, and exploring environmental conditions for the CNC-DNA assembly.

SI-ATRP grafting of polymers from polydopamine-modified cellulose nanocrystals

This work reports on the possibility of using polydopamine (PDA) as a tool to immobilize bromoisobutyryl moieties at the surface of cellulose nanocrystals (CNCs) and initiate Surface Intitiated Atom Transfer Radical Polymerization (SI-ATRP) reactions from these sites. Two different strategies based on i) the stepwise modification of the CNCs with dopamine (DA) and α-bromoisobutyryl bromide (BiBB) (Protocol 1) and ii) the one-step treatment of the CNCs with a mixture of DA and BiBB-modified DA (Protocol 2), were compared. Only the CNC particles treated according to Protocol 1 guaranteed efficient anchoring of the SI-ATRP initiating sites in our experimental conditions (with limited impact on the CNCs crystalline structure), the coated layer being leached out by certain solvents in the case of Protocol 2. The brominated particles displaying the best performances were subsequently tested as potential ATRP macroinitiators, using methyl methacrylate (MMA) and styrene (St) as model monomers. Polymer-grafted particles were successfully obtained, with a grafting density twice as high for Sty as for MMA, demonstrating the validity of this strategy.

Nanocellulose-based hydrogels as versatile materials with interesting functional properties for tissue engineering applications

Tissue engineering has emerged as a remarkable field aiming to restore or replace damaged tissues through the use of biomimetic constructs. Among the diverse materials investigated for this purpose, nanocellulose-based hydrogels have garnered attention due to their intriguing biocompatibility, tunable mechanical properties, and sustainability. Over the past few years, numerous research works have been published focusing on the successful use of nanocellulose-based hydrogels as artificial extracellular matrices for regenerating various types of tissues. The review emphasizes the importance of tissue engineering, highlighting hydrogels as biomimetic scaffolds, and specifically focuses on the role of nanocellulose in composites that mimic the structures, properties, and functions of the native extracellular matrix for regenerating damaged tissues. It also summarizes the types of nanocellulose, as well as their structural, mechanical, and biological properties, and their contributions to enhancing the properties and characteristics of functional hydrogels for tissue engineering of skin, bone, cartilage, heart, nerves and blood vessels. Additionally, recent advancements in the application of nanocellulose-based hydrogels for tissue engineering have been evaluated and documented. The review also addresses the challenges encountered in their fabrication while exploring the potential future prospects of these hydrogel matrices for biomedical applications.

Development of functionalized poly(lactide) films with chitosan via SI-SARA ATRP as scaffolds for neuronal cell growth

Polylactic acid (PLA), a polymer derived from renewable resources, is gaining increasing attention in the development of biomedical devices due to its cost-effectiveness, low immunogenicity, and biodegradability. However, its inherent hydrophobicity remains a problem, leading to poor cell adhesion features. On this basis, the aim of this work was to develop a method for functionalizing the surface of PLA films with a biopolymer, chitosan (CH), which was proved to be a material with intrinsic cell adhesive properties, but whose mechanical properties are insufficient to be used alone. The combination of the two polymers, PLA as a bulk scaffold and CH as a coating, could be a promising combination to develop a scaffold for cell growth. The modification of PLA films involved several steps: aminolysis followed by bromination to graft amino and then bromide groups, poly(glycidyl methacrylate) (PGMA) grafting by surface-initiated supplemental activator and reducing agent atom transfer radical polymerization (SI-SARA ATRP) and finally the CH grafting. To prove the effective adhesive properties, conjugated and non-conjugated films were tested in vitro as substrates for neuronal cell growth using differentiated neurons from human induced pluripotent stem cells. The results demonstrated enhanced cell growth in the presence of CH.

From Nature-Sourced Polysaccharide Particles to Advanced Functional Materials

Polysaccharides constitute over 90% of the carbohydrate mass in nature, which makes them a promising feedstock for manufacturing sustainable materials. Polysaccharide particles (PSPs) are used as effective scavengers, carriers of chemical and biological cargos, and building blocks for the fabrication of macroscopic materials. The biocompatibility and degradability of PSPs are advantageous for their uses as biomaterials with more environmental friendliness. This review highlights the progresses in PSP applications as advanced functional materials, by describing PSP extraction, preparation, and surface functionalization with a variety of functional groups, polymers, nanoparticles, and biologically active species. This review also outlines the fabrication of PSP-derived macroscopic materials, as well as their applications in soft robotics, sensing, scavenging, water harvesting, drug delivery, and bioengineering. The paper is concluded with an outlook providing perspectives in the development and applications of PSP-derived materials.

Antibacterial polylactic acid fabricated via Pickering emulsion approach with polyethyleneimine and polydopamine modified cellulose nanocrystals as emulsion stabilizers

Antibacterial biodegradable plastics are highly demanded for food package and disposable medical plastic consumables. Incorporating antibacterial nanoagents into polymer matrices is an effective method to endow polymers with antibacterial activity. However, synthesis of sustainable antibacterial nanoagents with high antibacterial activity via facile approach and well dispersion of them in polymer matrices are still challenging. In this study, polyethyleneimine (PEI) was grafted on surface of cellulose nanocrystals (CNCs) via the oxidation self-polymerization of dopamine (DA) and the Michael addition/Schiff base reaction between DA and PEI. The resulted PEI and polydopamine modified CNCs (PPCs) showed substantially enhanced antibacterial activity and reduced cytotoxicity for NIH3T3 than PEI due to increased local concentration and anchoring of PEI. The minimum concentration of PPCs to achieve antibacterial rate of 99.99 % against S. aureus and E. coli were about 50 and 20 μg/mL, respectively. PPCs displayed outstanding emulsifying ability, and PPC coated polylactic acid (PLA) microspheres were obtained by drying PPC stabilized PLA Pickering emulsion, leading to a well dispersion of PPCs in PLA. PPC/PLA film prepared by hot-pressing displayed great antibacterial performance and enhanced mechanical properties. Therefore, this study proposed a facile approach to fabricate biocompatible antibacterial nanoagents and plastics.

Cylindrical brushes with ionized side chains: Scaling theory revisited

We revisit the classic scaling model of a cylindrical polyelectrolyte (PE) brush focusing on molecular brushes with stiff backbones and dispersions of polymer-decorated nanorods. Based on the blob representation we demonstrate that similarly to the case of planar PE brushes, separation of intra- and intermolecular repulsions between charges leads to novel scaling regimes for cylindrical PE brushes in salt-added solution and a sharper decrease in its thickness versus salt concentration dependence. These theoretical predictions may inspire further comprehensive experimental research and computer simulations of synthetic and biopolyelectrolyte cylindrical brushes.

Polymeric Materials Obtained by Extrusion and Injection Molding from Lignocellulosic Agroindustrial Biomass

This review presents the advances in polymeric materials achieved by extrusion and injection molding from lignocellulosic agroindustrial biomass. Biomass, which is derived from agricultural and industrial waste, is a renewable and abundant feedstock that contains mainly cellulose, hemicellulose, and lignin. To improve the properties and functions of polymeric materials, cellulose is subjected to a variety of modifications. The most common modifications are surface modification, grafting, chemical procedures, and molecule chemical grafting. Injection molding and extrusion technologies are crucial in shaping and manufacturing polymer composites, with precise control over the process and material selection. Furthermore, injection molding involves four phases: plasticization, injection, cooling, and ejection, with a focus on energy efficiency. Fundamental aspects of an injection molding machine, such as the motor, hopper, heating units, nozzle, and clamping unit, are discussed. Extrusion technology, commonly used as a preliminary step to injection molding, presents challenges regarding fiber reinforcement and stress accumulation, while lignin-based polymeric materials are challenging due to their hydrophobicity. The diverse applications of these biodegradable materials include automotive industries, construction, food packaging, and various consumer goods. Polymeric materials are positioned to offer even bigger contributions to sustainable and eco-friendly solutions in the future, as research and development continues.

Polyelectrolyte Cylindrical Brushes in Hairy Gels

We considered dispersions of cylindrical polyelectrolyte (PE) brushes with stiff backbones, and polymer-decorated nanorods with tunable solubility of the brush-forming PE chains that affected thermodynamic stability of the dispersions. We focused on thermo-induced and deionization-induced conformational transition that provokes loss of aggregative dispersion stability of nanorods decorated with weakly ionized polyions. A comparison between theoretical predictions and experiments enabled rationalization and semi-quantitative interpretation of the experimental results.

Adsorptive performance and mechanism exploration of l-lysine functionalized celluloses for enhanced removal of Pb(II) from aqueous medium

In this study, two novel biosorbents of l-lysine grafted cellulose (L-PCM, L-TCF) were prepared for Pb(II) removal from aqueous solutions. Various adsorption parameters were surveyed, such as adsorbent dosages, initial concentration of Pb(II), temperature and pH, using adsorption techniques. At normal temperature, less adsorbent can achieve better adsorption capacity (89.71 ± 0.27 mg g^-1 with 0.5 g L^-1 of L-PCM, 16.84 ± 0.02 mg g^-1 with 3.0 g L^-1 of L-TCF). The pH range of application for L-PCM was 4-12 and that of L-TCF was 4-13. The adsorption of Pb(II) by biosorbents went through the boundary layer diffusion stage and void diffusion stage. The adsorption mechanism was chemisorption based on multilayer heterogeneous adsorption. The pseudo-second-order model fitted the adsorption kinetics perfectly. The Freundlich isotherm model adequately described Multimolecular equilibrium relationship between Pb(II) and biosorbents; the predicted maximum adsorption capacities of the two adsorbents were 904.12 and 46.74 mg g^-1, respectively. The results showed that the adsorption mechanism was the electrostatic attraction between Pb(II) and -COOH and the complexation between Pb(II) and -NH₂. This work demonstrated that l-lysine modified cellulose-based biosorbents have great potential in the field of Pb(II) removal from aqueous solutions.

Self-healing waterborne polyurethane coatings with high transparence and haze via cellulose nanocrystal stabilized linseed oil Pickering emulsion

Protection coatings with self-healing ability can significantly enhance their anti-corrosion properties and service life. In this study, self-healing waterborne polyurethane (WPU) coatings with high transparence and haze were facile fabricated via cellulose nanocrystal (CNC) stabilized linseed oil (LO) Pickering emulsion. Sustainable CNCs displayed outstanding emulsifying ability and stability to stabilize LO Pickering emulsion. The size of LO Pickering emulsion droplets decreases with the CNC concentration, while the emulsion fraction and surface coverage by CNCs increase with CNC concentration, leading to a more stable Pickering emulsion. The self-healing rates of WPU coatings at varied time, temperature, CNC and catalyst concentration were investigated. Higher temperature, larger emulsion droplets, and with driers employed as catalysts generally lead to faster self-healing rate. The WPU self-healing coatings displayed much better abrasion resistance and mechanical properties than pristine WPU due to the incorporation of CNCs. Moreover, the WPU self-healing coatings show a high transparence and haze due to light scattering, and their applications as coatings of lamp covers and glass to achieve uniform light distribution and privacy protection with high light transmission were further demonstrated.

Thermoformable and transparent one-component nanocomposites based on surface grafted cellulose nanofiber

One-component nanocomposites based on poly(methyl methacrylate)(PMMA) and polystyrene (PS) grafted cellulose nanofiber (CNF) with high polymer graft percentage were fabricated. At relative ambient conditions, less active vinyl monomer, MMA, and styrene were grafted from CNF via surface-initiated Cu(0)-mediated reversible deactivation radical polymerizations (RDRP), and PMMA/PS grafted CNFs could reach a graft percentage as high as 7550 % and 3530 %, respectively. The one-component composite films were manufactured by simple hot-pressing subsequentially. Optical transparency, thermal stability, and glass transition temperature of one-component nanocomposites were enhanced dramatically in contrast with the bicomponent nanocomposite. The uniform fracture surface confirmed the uniform dispersity by morphological observation. Mechanical tests indicated that break elongation and tensile strength ascended notably, and tensile modulus slightly descended as the graft percentage increased for PS and PMMA grafted CNF one-component composite. It was concluded that for glassy graft chains, obtaining one-component nanocomposites with high enough graft chain length was essential to achieve moderated mechanical performance without compromising optical properties and thermal manufacturing ability.

Copolymer-Functionalized Cellulose Nanocrystals as a pH- and NIR-Triggered Drug Carrier for Simultaneous Photothermal Therapy and Chemotherapy of Cancer Cells

As a class of biocompatible and biodegradable naturally derived nanomaterials, cellulose nanocrystals (CNCs) with diverse surface functionalization have aroused considerable attention for a range of biomedical applications in drug or gene delivery, as a fluorescent nanoprobe, in cancer targeting, and in photothermal cancer therapy, among others. Herein, we construct the copolymer-functionalized CNCs as a pH- and near-infrared (NIR)-triggered drug carrier for simultaneous photothermal therapy and chemotherapy of cancer cells. Poly(ε-caprolactone)-b-poly(2-(dimethylamino)ethyl methacrylate) (PCL-b-PDMAEMA) was conjugated onto the surface of CNCs through ring-opening polymerization, followed by activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP). The resultant CNC-based drug carrier can encapsulate doxorubicin (DOX) as a therapeutic agent and indocyanine green (ICG) as an NIR dye in the PCL core and the PDMAEMA shell, respectively, via hydrophobic and electrostatic interactions. In addition to the intrinsic pH response, the release profile of DOX can also be controlled by the duration of laser irradiation due to collapse of the crystal structure of the PCL domain with the increase of temperature induced by photothermal conversion. The drug carrier can exhibit enhanced cytotoxicity toward HepG2, human hepatocyte carcinoma, cells upon laser irradiation, which can be attributed to the synergistic effect arising from NIR-triggered burst release of DOX and photothermal heating. The rod-like morphology of the CNC-based drug carrier may help accelerate the endocytosis in cell membranes compared with its common spherical counterpart. Based on the abovementioned advantages, copolymer-functionalized CNCs can serve as a promising candidate for effective cancer treatment.