Bio-Based Polyurethane Resins Derived from Tannin: Source, Synthesis, Characterisation, and Application

Abstract

Tannins are soluble, astringent secondary phenolic metabolites generally obtained from renewable natural resources, and can be found in many plant parts, such as fruits, stems, leaves, seeds, roots, buds, and tree barks, where they have a protective function against bacterial, fungal, and insect attacks. In general, tannins can be extracted using hot water or organic solvents from the bark, leaves, and stems of plants. Industrially, tannins are applied to produce adhesives, wood coatings, and other applications in the wood and polymer industries. In addition, tannins can also be used as a renewable and environmentally friendly material to manufacture bio-based polyurethanes (bio-PUs) to reduce or eliminate the toxicity of isocyanates used in their manufacture. Tannin-based bio-PUs can improve the mechanical and thermal properties of polymers used in the automotive, wood, and construction industries. The various uses of tannins need to be put into perspective with regards to possible further advances and future potential for value-added applications. Tannins are employed in a wide range of industrial applications, including the production of leather and wood adhesives, accounting for almost 90% of the global commercial tannin output. The shortage of natural resources, as well as the growing environmental concerns related to the reduction of harmful emissions of formaldehyde or isocyanates used in the production of polyurethanes, have driven the industrial and academic interest towards the development of tannin-based bio-PUs as sustainable alternative materials with satisfactory characteristics. The aim of the present review is to comprehensively summarize the current state of research in the field of development, characterization, and application of tannin-derived, bio-based polyurethane resins. The successful synthesis process of the tannin-based bio-PUs was characterized by Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), MALDI-TOF mass spectrometry, and gel permeation chromatography (GPC) analyses.

Enhancing Thermal and Mechanical Properties of Ramie Fiber via Impregnation by Lignin-Based Polyurethane Resin

“…Lignocellulosic biomass can be converted to liquid polyols through liquefaction processes or oxypropylation for polyurethane applications [14]. Bio-polyurethanes (Bio-PU) can also be obtained by using polyols from renewable materials such as lignin and tannin for various applications [15,16].…”

Performance of eco‐friendly particleboard from agro‐industrial residues bonded with formaldehyde‐free natural rubber latex adhesive for interior applications

“…[31,32] Tannins can be classified into two groups, those characterized by having a molecular structure composed of flavonoids, known as condensed tannins, and those consisting of gallic and ellagic acids with a sugar core, known as hydrolysable tannins. [28,33] Among these types, condensed tannins are the most relevant with 90% of wood adhesives market. [34] By contrast to lignin and tannin, natural rubber latex (NRL) is barely used as wood adhesives, thus it is important to develop NRL-based adhesive particularly for PB.…”

Modification of Ramie Fiber via Impregnation with Low Viscosity Bio-Polyurethane Resins Derived from Lignin

“…Polyurethane (PU) is a polymer composed of urethane bonds (NH–(C=O)–O) synthesized between isocyanate (NCO) and alcohol (OH) groups [ 9 ]. The process of synthesis and cross-link formation occurs when one monomer contains at least two isocyanates (diisocyanates), and the other monomer contains two alcohols (diols or polyols) [ 10 ].…”