Fully biobased sustainable elastomers derived from chitin, lignin, and plant oil via grafting strategy and Schiff-base chemistry

Sustainable chitin-derived elastomers via grafting strategy with tunable mechanical and adhesion properties

With increasing environmental awareness and the pursuit of sustainable development goals, environmentally friendly sustainable thermoplastic elastomers (TPEs) derived from natural resources are highly desired to replace traditional TPEs. However, preparing sustainable TPEs with high mechanical properties and multifunctionality from biobased feedstocks remains a significant challenge. In this work, a series of chitin-graft-poly(acrylamide-co-2-ethylhexyl acrylate) (Chitin-g-P(AM-co-EHA)) copolymers were synthesized through reversible addition-fragmentation chain transfer (RAFT) polymerization. The tensile strength of Chitin-g-P(AM-co-EHA) copolymers can be tuned over a wide range from 1.0 to 7.3 MPa by adjusting the chitin and PAM contents. Benefiting from the brush-like architecture, Chitin-g-P(AM-co-EHA) copolymer exhibits improved mechanical properties over its linear counterparts. Moreover, these Chitin-g-P(AM-co-EHA) copolymers show good adhesion performance on different substrates. The shear strength can achieve 7.5 MPa for Chitin0.8-PAM50, which is high enough for commercial applications. The combination of chitin and grafting strategy can promote the development of strong chitin-based sustainable elastomers. This approach can be further utilized to design novel high-performance biobased elastomers and adhesives derived from natural resources.

Glutaraldehyde crosslinked ternary carboxymethylcellulose/polyvinyl alcohol/polyethyleneimine film with enhanced mechanical properties, water resistance, antibacterial activity, and UV-shielding ability without any UV absorbents

Despite the plethora of methods reported for fabricating ultraviolet (UV) shielding films using various UV absorbers to date, it remains a major challenge for the development of novel UV shielding films that simultaneously exhibit excellent transparency. In this work, a novel composite film (GA-x-CMC/PVA/PEI) is fabricated by integrating anionic carboxymethylcellulose (CMC), cationic polyethyleneimine (PEI), and polyvinyl alcohol (PVA) via electrostatic and hydrogen bond interactions and further cross-linking with glutaraldehyde (GA). Herein, PVA expands hydrogen bonding networks, reduces film haze, and enhances its mechanical strength. GA acts as a crosslinker in producing Schiff bases with PEI and acetals with CMC and PVA. The synthesized GA-x-CMC/PVA/PEI composite film possesses a notable amount of unsaturated -CH=N- bonds of Schiff base, resulting from the condensation of PEI and GA, which exhibit superior shielding efficiency against both UV-A and UV-B rays while maintaining exceptional transparency, visibility, and simultaneously enhancing mechanical properties and thermal stability. Notably, increasing the content of PEI leads to almost complete shielding of the entire UV spectrum (<400 nm) due to the increasing of the number of -CH=N- unsaturated bonds. Furthermore, the obtained film without any UV-shielding additives has exceptional mechanical properties, hydrophobicity, and antibacterial properties, rendering it a wide application prospect.

Wholly sustainable graft copolymers derived from cellulose, lignin, and hemicellulose for high-performance elastomers, adhesives, and UV-blocking materials

Sustainable elastomers derived from renewable biobased resources with excellent mechanical properties and varied functions are highly pursued to substitute traditional petroleum-based polymers yet challenging due to their limited macroscopic performance. In this work, we designed a series of wholly biobased cellulose-graft-poly(vanillin acrylate-co-tetrahydrofurfuryl acrylate) (Cell-g-P(VA-co-THFA) copolymer elastomers with cellulose as the rigid backbone, sustainable VA derived from lignin and soft THFA derived from hemicellulose as the hard and soft segments in the rubbery side chains. Moreover, the grafted side chains can be cross-linked to introduce an additional dynamic network structure via Schiff-base chemistry between the aldehyde and amino groups. The mechanical properties of Cell-g-P(VA-co-THFA) copolymer elastomers, including tensile strength, extensibility, elasticity, and toughness can be facilely manipulated by the VA/THFA feed ratio, cellulose content, and cross-linking density. These Cell-g-P(VA-co-THFA) copolymer elastomers are thermally stable and possess outstanding adhesion behavior and prominent UV-shielding performance. Besides dramatically enhanced mechanical properties, the cross-linked Cell-g-P(VA-co-THFA) counterparts exhibit remarkable shape memory behavior. This work provides a robust and convenient strategy for developing strong and versatile sustainable elastomers with different application demands by integrating different biomass feedstocks via elaborate molecular design.

Facile preparation of near-monodisperse oligocellulose and its elastomeric derivatives with tunable mechanical properties

Oligocellulose (OC) with low polydispersity indices has been produced in large quantities using an improved method of acid-assisted hydrolysis, in which long cellulose chains disintegrate in concentrated phosphoric acid at moderately elevated temperatures. The hydrolysis time has been reduced by three orders of magnitude without compromising the overall yield of the process or the quality of OC products. The efficient production of high-quality OCs in large quantities allows for developing OC-derived elastomeric materials. A series of OC-graft-poly(isobornyl methacrylate-random-n-butyl acrylate) [OC-g-P(IBOMA-r-BA)] elastomers have been synthesized via activators regenerated by electron transfer for atom transfer radical polymerization (ARGET ATRP). OC-g-P(IBOMA-r-BA) elastomers have tunable molecular architectures and phase morphologies toward desirable mechanical properties and thermal stability suitable for various applications. The methodologies of the OC production and the graft-polymers synthesis in this study would help advance technologies for broader applications of bio-based elastomers.

Strong and ultrafast stimulus-healable lignin-based composite elastomers with excellent adhesion properties

With the increased environmental issues, advanced high-performance and multifunctional polymeric materials derived from biomass have tremendous attention due to the great potential to replace their traditional petroleum-based counterparts. In this work, a series of lignin graft copolymers, lignin-graft-poly(n-butyl acrylate-co-acrylic acid) (Lig-g-P(BA-co-AA)), were rationally prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization. These lignin-based copolymers demonstrate good thermal stability and tunable glass transition temperature (Tg) values. The mechanical performance, including tensile strength, extensibility, Young's modulus, and toughness can be facilely adjusted by the BA/AA feed ratio and lignin content during polymerization. Owing to the extraordinary photothermal conversion ability of lignin, the Lig-B550 copolymer, containing 11.8 wt% lignin content, shows excellent stimulus-healing behavior within 1 min with a 97.1 % healing efficiency under near-infrared (NIR) laser irradiation. Moreover, the Lig-g-P(BA-co-AA) copolymers exhibit remarkable adhesion property, broadening their potential applications in the adhesive area. This grafting strategy is versatile and efficient, conferring the resultant lignin-based composite elastomers with dramatically enhanced mechanical properties and unprecedented photothermal behavior, which can inspire the further development of strong lignin-based sustainable elastomers.

Adsorption of methyl orange from aqueous solution with lignin-modified metal-organic frameworks: Selective adsorption and high adsorption capacity

The lignin-based metal-organic framework (UIO-g-NL) was prepared by a Schiff base reaction of aminated lignin and the zirconium cluster-based MOF (UIO-66-NH2) as an adsorbent of methyl orange (MO). The results showed that UIO-g-NL maintained the original crystal structure and aminated lignin was successfully introduced after functionalization. UIO-g-NL selectively adsorbed MO from a mixed solution 50 mg/L MO and 50 mg/L methylene blue (MB), with an adsorption efficiency of nearly 100%. In a mixed solution 250 mg/L MB and 250 mg/L MO, UIO-g-NL adsorbed both dyes with 1120.70 mg/g for MB and 961.54 mg/g for MO. Hydrogen bonding, π-π and NH-π interactions, and electrostatic attraction contribute to the MO adsorption by UIO-g-NL. In the MO/MB mixture, MO adsorption by UIO-g-NL follows the pseudo-second-order kinetic and Freundlich isotherm models, which is an endothermic, spontaneous, and feasible adsorption process. Furthermore, the MO adsorption efficiency of UIO-g-NL remained high (>90%) after six re-use cycles.

Sustainable Elastomers for Actuators: "Green" Synthetic Approaches and Material Properties

Elastomeric materials have great application potential in actuator design and soft robot development. The most common elastomers used for these purposes are polyurethanes, silicones, and acrylic elastomers due to their outstanding physical, mechanical, and electrical properties. Currently, these types of polymers are produced by traditional synthetic methods, which may be harmful to the environment and hazardous to human health. The development of new synthetic routes using green chemistry principles is an important step to reduce the ecological footprint and create more sustainable biocompatible materials. Another promising trend is the synthesis of other types of elastomers from renewable bioresources, such as terpenes, lignin, chitin, various bio-oils, etc. The aim of this review is to address existing approaches to the synthesis of elastomers using "green" chemistry methods, compare the properties of sustainable elastomers with the properties of materials produced by traditional methods, and analyze the feasibility of said sustainable elastomers for the development of actuators. Finally, the advantages and challenges of existing "green" methods of elastomer synthesis will be summarized, along with an estimation of future development prospects.

Green Routes for Bio-Fabrication in Biomedical and Pharmaceutical Applications

In the last decade, significant advances in nanotechnologies, rising from increasing knowledge and refining of technical practices in green chemistry and bioengineering, enabled the design of innovative devices suitable for different biomedical applications. In particular, novel bio-sustainable methodologies are developing to fabricate drug delivery systems able to sagely mix properties of materials (i.e., biocompatibility, biodegradability) and bioactive molecules (i.e., bioavailability, selectivity, chemical stability), as a function of the current demands for the health market. The present work aims to provide an overview of recent developments in the bio-fabrication methods for designing innovative green platforms, emphasizing the relevant impact on current and future biomedical and pharmaceutical applications.