Synthesis and Characterizations of Eco-Friendly Organosolv Lignin-Based Polyurethane Coating Films for the Coating Industry.

Sara Bergamasco,Manuela Romagnoli,Florian Zikeli,Swati Tamantini,Giuseppe Scarascia Mugnozza,Vittorio Vinciguerra

doi:10.3390/polym14030416

Abstract

Three different formulations of bio-based polyurethane (PU), varying the weight ratio between Organosolv lignin and a commercial isocyanate, were synthesized. The coating formulations were characterized by SEM, pyrolysis-GC/MS, FTIR spectroscopy and FTIR mapping, which confirmed the successful formation of urethane bonds between commercial isocyanate and hydroxyl groups deriving from lignin. The coatings were applied on beech wood samples to measure color and contact angles, and eventually FTIR mapping of the coated wood samples was performed. FTIR mapping is an interesting tool to monitor the distribution of PU chemical bonds on the coating surface and to evaluate the homogeneity of the applied coating films. Increasing the lignin content of the PU coatings results in more red-yellow and darker tones, while the commercial PU coating is transparent. For a higher lignin concentration, the solid content as well as the weight gain of the applied coatings increase. A higher percentage of lignin in the prepared PU formulations leads to superficial cracks and therefore higher coating permeability compared to the commercial PU, but the prepared lignin-based PU coating still makes a raw wood surface significantly more hydrophobic. Apparently, additives such as film-formers with low surface tension to counteract cracks’ formation are necessary to improve the performance of lignin-based PU coatings.

Highlights

Wood materials and wood-based products are increasingly considered the materials of the future, fully in line with modern concepts of a bio-circular economy [1,2]
The intrinsic biodegradability of wood is the most important weakness, which limits a wider end use, and the improvement of wood durability is still one of the major challenges [3,4]. This challenge can be tackled by different means, such as thermo-treatments [5,6] or fossilbased and natural wood coatings with protective or biocidal functions [7,8,9,10]
The application of thermal or chemical modifications improved the performance of natural products

Summary

Introduction

Wood materials and wood-based products are increasingly considered the materials of the future, fully in line with modern concepts of a bio-circular economy [1,2]. The intrinsic biodegradability of wood is the most important weakness, which limits a wider end use, and the improvement of wood durability is still one of the major challenges [3,4]. This challenge can be tackled by different means, such as thermo-treatments [5,6] or fossilbased and natural wood coatings with protective or biocidal functions [7,8,9,10]. The application of thermal or chemical modifications improved the performance of natural products

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Methods

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Discussion

Conclusion