Lignin, a major component of lignocellulose, is the largest source of aromatic building blocks on the planet and harbors great potential to serve as starting material for the production of biobased products. Despite the initial challenges associated with the robust and irregular structure of lignin, the valorization of this intriguing aromatic biopolymer has come a long way: recently, many creative strategies emerged that deliver defined products via catalytic or biocatalytic depolymerization in good yields. The purpose of this review is to provide insight into these novel approaches and the potential application of such emerging new structures for the synthesis of biobased polymers or pharmacologically active molecules. Existing strategies for functionalization or defunctionalization of lignin-based compounds are also summarized. Following the whole value chain from raw lignocellulose through depolymerization to application whenever possible, specific lignin-based compounds emerge that could be in the fu...

Bright Side of Lignin Depolymerization: Toward New Platform Chemicals

Spectroscopy is the study of matter interacting with electromagnetic radiation (e.g., light). The electromagnetic spectrum in Figure 1 illustrates the many different types of electromagnetic radiation, including gamma rays (γ-rays), X-rays, ultraviolet (UV) radiation, visible light, infrared (IR) radiation, microwaves, and radio waves. The frequency (ν) and wavelength (λ) ranges associated with each form of radiant energy are also indicated in Figure 1.

Introduction to Spectroscopy

Adsorption of mercury ions from synthetic and real wastewater aqueous solution by functionalized multi-walled carbon nanotube with both amino and thiolated groups

Covalent immobilization of proteins on carbon nanotubes using the cross-linker 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide--a critical assessment.

The growing use of carbon and glass fibres has increased awareness about their waste disposal methods. Tonnes of composite waste containing valuable carbon fibres and glass fibres have been cumulating every year from various applications. These composite wastes must be cost-effectively recycled without causing negative environmental impact. This review article presents an overview of the existing methods to recycle the cumulating composite wastes containing carbon fibre and glass fibre, with emphasis on fibre recovery and understanding their retained properties. Carbon and glass fibres are assessed via focused topics, each related to a specific treatment method: mechanical recycling; thermal recycling, including fluidised bed and pyrolysis; chemical recycling and solvolysis using critical conditions. Additionally, a brief analysis of their environmental and economic aspects are discussed, prioritising the methods based on sustainable values. Finally, research gaps are identified to highlight the factors of circular economy and its significant role in closing the life-cycle loop of these valuable fibres into re-manufactured composites.

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A review on the recycling of waste carbon fibre/glass fibre-reinforced composites: fibre recovery, properties and life-cycle analysis

Self-healing of cross-linked PU via dual-dynamic covalent bonds of a Schiff base from cystine and vanillin

Vanillin can be obtained from waste of lignocellulosic bioresources with various methods.1−3 Such vanillin was used as chain extender [divanillin-ethanol amine conjugate (DV-EA)] after its dimerization and further modification with ethanolamine in the synthesis of biobased polyurethane, thereby increasing wt % of biocontents in the final polymer. 1,4-Butanediol often used as a general chain extender in polyurethane synthesis was replaced partially with DV-EA. The generated polyurethane hard segment consists of DV-EA polyol and MDI (methylene diisocyanate) units or 1,4-butanediol and MDI units, respectively. The properties of the DV-EA-based polyurethane were investigated with differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analyzer (DMA), X-ray diffraction spectroscopy (XRD), and universal testing machine (UTM). The results showed that this advanced polyurethane has 128% of Young’s modulus and 147% of increased strain compared to those of control, while its st...

Development of High Performance Polyurethane Elastomers Using Vanillin-Based Green Polyol Chain Extender Originating from Lignocellulosic Biomass

A bio-derived dihydroxylimine hardener, Van2HMDA, for the curing of epoxy resin was prepared from vanillin (Van) and hexamethylene-1,6-diamine (HMDA) by Schiff base formation. The epoxy resin of diglycidyl ether of bisphenol A was cured with Van2HMDA in the presence of the catalyst, 2-ethyl-4-methylimidazole (EMI). The crosslinked epoxy resin showed thermal-healing properties at elevated temperatures. Moreover, the crosslinked epoxy resin can be reshaped by heating via imine metathesis of the hardener units. The imine metathesis of Van2HMDA was confirmed experimentally. Stress-relaxation properties of the epoxy resin crosslinked with Van2HMDA were investigated, and the activation energy obtained from Arrhenius plots of the relaxation times was 44 kJ/mol. The imine bonds in the epoxy polymer matrix did not undergo hydrolysis after immersing in water at room temperature for one week. However, in the presence of acid, the crosslinked polymer was easily decomposed due to the hydrolysis of imine bonds. The hydrolysis of imine bonds was used for the ecofriendly recycling of crosslinked polymer. It is inferred that thermal-healing, reshaping, and reprocessing properties can be implemented in the various crosslinked epoxy resins with the bio-derived dihydroxylimine hardener, albeit the recycled epoxy resin is of inevitably lower quality than the original material.

Dai-Soo Lee

Papers

Self-healing of cross-linked PU via dual-dynamic covalent bonds of a Schiff base from cystine and vanillin

Development of High Performance Polyurethane Elastomers Using Vanillin-Based Green Polyol Chain Extender Originating from Lignocellulosic Biomass

Thermal Healing, Reshaping and Ecofriendly Recycling of Epoxy Resin Crosslinked with Schiff Base of Vanillin and Hexane-1,6-Diamine

Liquid crystalline epoxy resin with improved thermal conductivity by intermolecular dipole–dipole interactions

Immobilization of avidin on the functionalized carbon nanotubes