Fabrication of fully bio-based malleable thermoset derived from cellulose, furfural and plant oil for advanced capacitive sensor.

Fabrication of sustainable bio-based malleable thermosets (BMTs) with excellent mechanical properties and reprocessing ability for applications in electronic devices has attracted more and more attention but remains significant challenges. Herein, the BMTs with excellent mechanical robustness and reprocessing ability were fabricated via integrating with radical polymerization and Schiff-base chemistry, and employed as the flexible substrate to prepare the capacitive sensor. To prepare the BMTs, an elastic bio-copolymer derived from plant oil and 5-hydroxymethylfurfural was first synthesized, and then used to fabricate the dynamic crosslinked BMTs through Schiff-base chemistry with the amino-modified cellulose and polyether amine. The synergistic effect of rigid cellulose backbone and the construction of dynamic covalent crosslinking network not only achieved high tensile strength (8.61 MPa) and toughness (3.77 MJ/m3) but also endowed the BMTs with excellent reprocessing ability with high mechanical toughness recovery efficiency of 104.8 %. More importantly, the BMTs were used as substrates to fabricate the capacitive sensor through the CO2-laser irradiation technique. The resultant capacitive sensor displayed excellent and sensitive humidity sensing performance, which allowed it to be successfully applied in human health monitoring. This work paved a promising way for the preparation of mechanical robustness malleable bio-thermosets for electronic devices.

Recyclable and mechanically tough nanocellulose reinforced natural rubber composite conductive elastomers for flexible multifunctional sensor.

The development of flexible wearable multifunctional electronics has gained great attention in the field of human motion monitoring. However, developing mechanically tough, highly stretchable, and recyclable composite conductive materials for application in multifunctional sensors remained great challenges. In this work, a mechanically tough, highly stretchable, and recyclable composite conductive elastomer with the dynamic physical-chemical dual-crosslinking network was fabricated by the combination of multiple hydrogen bonds and dynamic ester bonds. To prepare the proposed composite elastomers, the polyaniline-modified carboxylate cellulose nanocrystals (C-CNC@PANI) were used as both conductive filler to yield high conductivity of 15.08 mS/m, and mechanical reinforcement to construct the dynamic dual-crosslinking network with epoxidized natural rubber latex to realize the high mechanical strength (8.65 MPa) and toughness (29.57 MJ/m3). Meanwhile, the construction of dynamic dual-crosslinking network endowed the elastomer with satisfactory recyclability. Based on these features, the composite conductive elastomers were used as strain sensors, and electrode material for assembling flexible and recyclable self-powered sensors for monitoring human motions. Importantly, the composite conductive elastomers maintained reliable sensing and energy harvesting performance even after multiple recycling process. This study provides a new strategy for the preparation of recyclable, mechanically tough composite conductive materials for wearable sensors.

Biomimetic construction of environmental-tolerant composite hydrogels based on galactomannan for tough, flexible and conductive sensors.

Sustainable composite hydrogel materials with harsh environmental adaption and tolerance capability have received considerable interests but still remain as challenges. In this work, biomimetic strategy was adapted for construction of three-dimensional galactomannan (GM) hydrogels with intercalation of flexible polymer chains polyethyleneimine (PEI), biomacromolecules tannin acid (TA) and CeO2 nanoparticles (NPs). The hydrogels cross-linked with double-networks (DN) present not only pH-responsive water absorption property, but also boosted mechanical strength with highest toughness of 326 kJ/m3 and Young's modulus of 220 kPa. Self-healing and anti-freezing capabilities were revealed for the hydrogels by maintaining of fracture elongation (23 %) and fracture strength (250 kPa). TA, CeO2 NPs as well as the amide groups in PEI of the hydrogels introduced excellent bacterial prohibition performance on both Bacillus subtilis (B. subtilis) and Escherichia coli (E. coli). Also, due to the existence of the free ions, the hydrogels exhibited electric conductive properties, with wide-range high sensitivity and long-time conductive stability. In addition, various tensile strain degrees were related to the conductive resistance values, and the great recovery performance was proved by cyclic tensile-conductive tests for 3000 times. Therefore, the proposed GM-based hydrogels displayed great potentials as strain sensors that are adaptable and tolerant to various environmental conditions.

Tough and strong sustainable thermoplastic elastomers nanocomposite with self-assembly of SI-ATRP modified cellulose nanofibers.

The ingenious design of sustainable thermoplastic elastomers (STPEs) is of great significance for the goal of the sustainable development. However, the preparation of STPEs with good mechanical performance is still complicated and challenging. Herein, to achieve a simple preparation of STPEs with strong mechanical properties, two biobased monomers (tetrahydrofurfuryl methacrylate (THFMA) and lauryl methacrylate (LMA)) were copolymerized into poly (THFMA-co-LMA) (PTL) and grafted onto TEMPO oxidized cellulose nanofiber (TOCN) via one-pot surface-initiated atom transfer radical polymerization (SI ATRP). The grafting modified TOCN could be self-assembled into nano-enhanced phases in STPEs, which are conducive to the double enhancement of the strength and toughness of the STPEs, and the size of nano-enhanced phases is mainly affected by TOCN fiber length and molecular weight of grafting chains. Especially, with the addition of 7 wt% TOCN, tensile strength, tensile strain, toughness, and glass transition temperature (Tg) of TOCN based STPEs (TOCN@PTL) exhibited 140 %, 36 %, 215 %, and 6.8 °C increase respectively, which confirmed the leading level in the field of bio-based elastomers. In general, this work constitutes a proof for the chemical modification and self-assembly behavior of TOCN by one-pot SI ATRP, and provides an alternative strategy for the preparation of high-performance STPEs.

Self-strengthening and conductive cellulose composite hydrogel for high sensitivity strain sensor and flexible triboelectric nanogenerator.

Triboelectric nanogenerators (TENGs) as promising energy harvesting devices have gained increasing attention. However, the fabrication of TENG simultaneously meets the requirements of green start feedstock, flexible, stretchable, and environmentally friendly remains challenging. Herein, the hydroxyethyl cellulose macromonomer (HECM) simultaneously bearing acrylate and hydroxyl groups was first synthesized and used as a crosslinker to prepare the chemically and physically dual-crosslinked cellulose composite hydrogel for an electrode material of stretchable TENG. Meanwhile, the in-situ polymerization of pyrrole endowed the hydrogel with satisfactory conductivity of 0.40 S/m. More impressively, the synergies of the cellulose rigid skeleton and the construction of the dual-crosslinking network significantly improved the mechanical toughness, and the hydrogel exhibited excellent self-strengthening through cyclic compression mechanical training, the self-strengthening efficiency reached 124.7 % after 10 compression cycles. Given these features, the hydrogel was used as wearable strain sensors with extremely high sensitivity (GF = 3.95) for real-time monitoring human motions. Additionally, the hydrogel showed practical applications in stretchable H-TENG for converting mechanical energy into electric energy to light LEDs and power a digital watch, and in self-powered wearable sensors to distinguish human motions and English letters. This work provided a promising strategy for fabricating sustainable, eco-friendly energy harvesting and self-powered electronic devices.

One-pot and one-step preparation of "living" cellulose nanofiber hydrogel with active double-bond via chemical vapor deposition.

Due to the existence of water, it is still a challenge to conduct chemical modification on cellulose nanofiber (CNF) hydrogels with active double bonds. A simple one-pot and one-step method for constructing "living" CNF hydrogel with double bond was created at room temperature. The chemical vapor deposition (CVD) of methacryloyl chloride (MACl) was used to introduce physical-trapped, chemical-anchored and functional double bonds into TEMPO-oxidized cellulose nanofiber (TOCN) hydrogels. TOCN hydrogel could be fabricated within just 0.5 h, the minimum dosage of MACl could be reduced to 3.22 mg/g (MACl/TOCN hydrogel). Furthermore, the CVD methods showed high efficiency for mass production and recyclability. Moreover, the chemical "living" reactivity of the introduced double bonds were verified by the freezing and UV crosslinking, radical polymerization and thiol-ene click reaction. Compared with pure TOCN hydrogel, the obtained functionalized TOCN hydrogel exhibited remarkable improvements in mechanical properties, with enhancements of 12.34 times and 2.04 times, as well as an increase in hydrophobicity by 2.14 times and a fluorescence performance improvement of 2.93 times.

Strain-induced orientation facilitates the fabrication of highly stretchable and tough xylan-based hydrogel for strain sensors.

Stretchable and tough polysaccharide-based functional hydrogels have gained popularity for various applications. However, it still remains a great challenge to simultaneously own satisfactory stretchability and toughness, particularly when incorporating renewable xylan to offer sustainability. Herein, we describe a novel stretchable and tough xylan-based conductive hydrogel utilizing the natural feature of rosin derivative. The effect of different compositions on the mechanical properties and the physicochemical properties of corresponding xylan-based hydrogels were systematically investigated. Owing to the multiple non-covalent interactions among different components to dissipate energies and the strain-induced orientation of rosin derivative during the stretching, the highest tensile strength, strain, and toughness of xylan-based hydrogels could reach 0.34 MPa, 2098.4 %, and 3.79 ± 0.95 MJ/m3, respectively. Furthermore, by incorporating MXene as the conductive fillers, the strength and toughness of hydrogels were further enhanced to 0.51 MPa and 5.95 ± 1.19 MJ/m3. Finally, the synthesized xylan-based hydrogels were able to serve as a reliable and sensitive strain sensor to monitor the movements of human beings. This study provides new insights to develop stretchable and tough conductive xylan-based hydrogel, especially utilizing the natural feature of bio-based resources.

Biomimetic ultra-strong, ultra-tough, degradable cellulose-based composites for multi-stimuli responsive shape memory.

Fabrication of ultra-strong, ultra-tough, sustainable, and degradable bio-based composites is urgently needed but remains challenging. Here, a biomimetic sustainable, degradable, and multi-stimuli responsive cellulose/PCL/Fe3O4 composite with ultra-strong mechanical strength and ultra-high toughness was developed. To prepare the proposed composites, the soft poly(ε-caprolactone) (PCL) side chain was grafted onto the rigid cellulose backbone, then the cellulose graft copolymer (EC-g-PCL) reacted with rigid hexamethylenediamine modified Fe3O4 nanoparticle (Fe3O4-NH2) to construct the crosslinking network using MDI-50 as a crosslinker. Given by the construction of crosslinking network and the "hard" and "soft" interactive structure, the composites showed ultra-strong mechanical strength (25.7 MPa) and ultra-high toughness (107.0 MJ/m3), and the composite specimen could lift a weight of approximately 21,200 times its mass. The composites also exhibited rapid degradation ability with high degradation efficiency. In addition, the composites showed excellent thermal responsive shape memory property with a shape recovery ratio above 96 %. Most importantly, the Fe3O4 nanoparticles endowed the composites with photothermal conversion property, the composites exhibited superior NIR light-triggered shape memory capability. The EC-g-PCL/Fe3O4 composites with ultra-strong mechanical strength and ultra-high toughness have promising applications in heavy-lift, object transportation, and self-tightening knots.

Utilization of different wood-based microfibril cellulose for the preparation of reinforced hydrophobic polymer composite films via Pickering emulsion: A comparative study.

Pickering emulsion is a promising strategy for the preparation of hydrophobic polymer composite using hydrophilic nanocellulose. Herein, two types of microfibril cellulose, pure mechanical pretreated microfibril cellulose (P-MFC) and Deep eutectic solvents pretreated microfibril cellulose (DES-MFC), were used to fabricate reinforced hydrophobic polystyrene (PS) composites (MFC/PS) with the aid of Pickering emulsion. The results showed that both oil/water ratio and the content as well as surface hydrophilicity of MFC were playing an important role in emulsifying capacity. 8 % MFC/PS emulsion showed the smallest and most uniform emulsion droplets which is similar to nanofibril cellulose (NFC)/PS at the oil/water ratio of 3:1. The mechanical performance of MFC/PS composites verified that the reinforcement effect was closely related to the emulsifying capacity of MFC. Specially, when the content of P-MFC was 8 wt%, the composite exhibited the best mechanical properties with the tensile strength of 44.7 ± 4.4 MPa and toughness of 1162 ± 52.8 kJ/m3 and Young's modulus of 13.5 ± 0.8 GPa, which was comparable to NFC/PS composite. Moreover, the effective enhancement role of P-MFC in hydrophobic polymethyl methacrylate and polycarbonate composites were also realized via Pickering emulsion strategy. Overall, this work constituted a proof of concept of the potential application of P-MFC in nano-reinforced hydrophobic composite.

Synthesis of pH-Sensitive and Self-Fluorescent Polymeric Micelles Derived From Rosin and Vegetable Oils via ATRP.

Preparation and application of sustainable polymers derived from renewable resources are of great significance. The aim of this study is to synthesize a kind of sustainable polymeric micelles from rosin and vegetable oils via atom transfer radical polymerization (ATRP) and to investigate the doxorubicin delivery properties of these micelles. Dehydroabietic acid-based poly lauryl methacrylate (DA-PLMA) with narrow PDI of 1.13 was prepared in a well-controlled process using rosin as an ATRP initiator. Thereafter, carboxylic groups were introduced to form poly methacrylic acid (PMAA) moieties in DA-PLMA polymer via acid hydrolysis. The resulted DA-PLMA-PMAA could self-assemble in water to form pH-dependent polymeric micelles with a diameter of ∼65 nm and PDI as low as 0.105. Owing to the existence of rosin, DA-PLMA-PMAA micelles also showed self-fluorescence properties. In addition, Dox-loaded micelles were prepared in aqueous solution with the drug-loading capacity as high as 16.0% and showed sustained-release characteristics. These results demonstrate great promise for designing polymeric micellar from rosin and vegetable oils.

Ultra-strong hydroxypropyl cellulose/polyvinyl alcohol composite hydrogel by combination of triple-network and mechanical training.

To develop the hydrogels with high mechanical strength and excellent conductivity is always a challenging topic. In this study, the ultra-strong hydroxypropyl cellulose (HPC)/polyvinyl alcohol (PVA) composite hydrogels were prepared by combination of the triple-network and mechanical training. The proposed composite hydrogels were achieved by physically crosslinking HPC with PVA to form the first crosslinking network, in which the HPC fibers could decrease the crosslinking density of PVA matrix and generate a lot of water-rich porous area. Then, 2-hydroxyethyl acrylate (HEA), acrylamide (AM) and aluminium chloride diffused into the first network to fabricate the chemical crosslinking network and ionically cross-linked domains. The formation of triple-network enhanced the mechanical strength and toughness to 1.87 MPa and 339.09 kJ/m3, respectively. Especially, the crystalline domains of PVA chains could improve the hydrogel's fatigue resistance, and the orderly arrangement of the crystalline domains achieved through mechanical training process could further enhance the mechanical strength. The mechanical strength of pre-stretched composite hydrogel was increased up to 2.8 MPa. The composite hydrogels exhibit great applications in sensors, human-machine interactions, and wearable devices.

Integration of metal-free ATRP and Diels-Alder reaction toward sustainable and recyclable cellulose-based thermoset elastomers.

Well-defined sustainable and recyclable thermoset elastomers derived from cellulose, fatty acid and furfural were successfully prepared via photoinduced metal-free ATRP and Diels-Alder (DA) reaction. Firstly, metal free ATRP was applied to prepare a range of thermoplastic cellulose graft copolymers with furfural groups. Then, a modified epoxidized soybean oil bearing 6-maleimidohexanoic group (ESOM) as a crosslinker was employed to perform DA reaction with furfural groups in these cellulose graft copolymers, by which the copolymer formed the dynamic crosslinked network and achieved the thermoset elastomers. The dynamic crosslinked network formed by DA reaction not only could increase the chain entanglement that was associated with the improved flexibility and could contribute to enhancing the mechanical strength up to 166 %, but also endowed these thermoset elastomers with recyclability, excellent shape memory and self-healing property. These thermoset elastomers can be used as self-healing strain sensor and wearable sensing devices after compounding them with carbon nanotubes.

Two-Step 3 D-Printing Approach toward Sustainable, Repairable, Fluorescent Shape-Memory Thermosets Derived from Cellulose and Rosin.

Invited for this month's cover is the group of Jifu Wang at Biomass-derived Photopolymer Materials, Institute of Chemical Industry of Forest Products, CAF. The image shows the application of cellulose and rosin to fabricate a class of renewable, repairable, fluorescent, and shape-memory thermosets by a two-step 3 D-printing approach. The Full Paper itself is available at 10.1002/cssc.201902191.

Two-Step 3 D-Printing Approach toward Sustainable, Repairable, Fluorescent Shape-Memory Thermosets Derived from Cellulose and Rosin.

Efficiently converting biomass into multifunctional polymerized materials is a challenge to effect high-valued utilization of biomass resources. A two-step 3 D-printing approach has been developed to fabricate a class of robust, fluorescent shape-memory thermosets from cellulose and rosin-based photosensitive 3 D-printing resin solution. The stereolithography 3 D printing was first performed to form the first crosslinked network by UV-induced chain-growth polymerization, which fixed the shape of thermoset. Subsequently, isocyanate was applied to react with hydroxy in the monomer to form the second crosslinked network by thermally induced step-growth polymerization. The formation of a dual-cure network, leading to phase separation and increased crosslinking density, could greatly improve the mechanical and thermal properties of 3 D-printed thermosets and endow them with thermally triggered shape-memory properties and excellent repairability. The 3 D-printed thermosets are found to have strong luminescence resulting from aggregation-induced emission originating from rosin. In addition, these 3 D-printed thermosets could degrade in the presence of NaOH aqueous solution and in situ achieved a range of flexible conductive hydrogels that have important potential application in the flexible electronic materials and smart photoelectric materials.

Sustainable elastomers derived from cellulose, rosin and fatty acid by a combination of "graft from" RAFT and isocyanate chemistry.

Utilization of natural sustainable feedstock to fabricate polymers has attracted remarkable attention. In this work, we reported a strategy to prepare a series of grafted copolymers from rosin, fatty acids and ethyl cellulose. The process involved the preparation of EC-based macro-RAFT agent through a simple esterification reaction, followed by a "grafting from" reversible addition-fragmentation chain transfer polymerization (RAFT) of DAGMA (derived from rosin) and LMA (derived from fatty acid) to achieve a class of EC-g-P(DAGMA-co-LMA) graft copolymers with a tunable Tg tuned by the DAGMA/LMA molar ratio. Then, hexamethylene diisocyanate (HDI) was used to crosslink these graft copolymers. The mechanical and dynamic thermo-mechanical properties of tests showed that elastic recovery values of copolymers were enhanced to 90%, as compared to the un-crosslinked samples. Additionally, all these polymers showed an excellent UV absorption performance. This study provides a facile way to fabricate biobased elastomeric materials with improved mechanical properties.

Fabrication of UV-absorbent cellulose-rosin based thermoplastic elastomer via "graft from" ATRP.

Cellulose-rosin based thermoplastic elastomers with UV absorption properties were fabricated by a combination of rosin, poly(butyl acrylate) (PBA) and ethyl cellulose (EC) via "graft from" ATRP with the aid of EC-rosin macroinitiator (EC-g-(DA)-Br) prepared by a simple esterification reaction between EC, dehydroabietic acid (DA, one of rosin's resin acids) and 2-bromoisobutylryl bromide. The introduction of rosin affords these elastomers with UV absorption property. And the glass transition temperature of these EC-rosin grafted copolymers could be tuned by changing the content of PBA. Moreover, the introduction of PBA to EC endowed EC-g-(DA)-g-PBA with a good film-forming property and excellent thermoplastic elastomer behavior. All of these EC-rosin grafted copolymers showed an excellent UV absorption performance, and maintained outstanding UV absorption capability after continuous UV-irradiation or being heated to 115 °C for 1 h. As a result, these EC-rosin grafted copolymers have a potential application in coating materials with UV absorption property.

Sustainable thermoplastic elastomers derived from cellulose, fatty acid and furfural via ATRP and click chemistry.

Cellulose-based thermoplastic elastomers (TPEs) have attracted considerable attention because of their rigid backbone, good mechanical properties, renewable nature and abundance. In the present study, sustainable TPEs based on ethyl cellulose (EC), fatty acid and furfural were generated by the combination of ATRP and "click chemistry". To fabricate sustainable TPEs with higher toughness, a range of polymers, including mono random-copolymer poly(tetrahydrofurfuryl methacrylate-co-lauryl methacrylate) (P(THFMA-co-LMA), dual polymer side chains PTHFMA and PLMA, and mono-block copolymer PTHFMA-b-PLMA, were designed as side chains to fabricate EC brush copolymers with random, dual or block side chain architectures using the "grafting from" and "grafting onto" methods. The multi-armed structures, chemical compositions and phase separation of these EC brush copolymers were confirmed by FT-IR, 1H NMR, GPC, DSC, TEM and SEM. Overall, three types of EC brush copolymers all exhibited the desired mechanical properties of TPEs. In addition, the EC brush copolymers with dual/block side chain architectures showed higher tensile strength than that of the random polymers with similar compositions.

Toll-like receptor 4 signaling promotes invasion of hepatocellular carcinoma cells through MKK4/JNK pathway.

Toll-like receptor (TLR) 4-mediated signaling has been shown to be important to cell survival, invasion and metastasis in a variety of cancers. The present study aimed to explore the role and downstream pathways of TLR4 signaling in the invasion of hepatocellular carcinoma (HCC) cell lines. We found that LPS, the agonist of TLR4, notably enhanced the invasiveness of HCC cells and the expression of MMP2 and MMP9, as well as the production of IL-6 and TNFα. LPS treatment dramatically increased the TLR4 expression on HCC cells surface and MKK4/JNK activation, while knockdown of TLR4 inhibited the LPS-induced invasion and the phosphorylation of MKK4 and JNK. Furthermore, silencing of MKK4 or inhibition of JNK activity led to impaired invasiveness of HCCs, low expression level of MMPs and TLR4, as well as limited production of cytokines. However, LPS stimulation only triggered moderate activation of NF-кB. Silencing of NF-кB or NF-кB inhibitor had no obvious effect on the invasive ability of HCCs and TLR4 expression, but suppressed IL-6 and TNFα production. These findings suggested that LPS-TLR4 signaling enhanced the invasiveness of HCCs mainly through MKK4/JNK pathway.