Valorization of Uruguayan Pinus elliottii Bark by Developing Sustainable Adhesives

Abstract

Pinus elliottii Engelm bark is a byproduct of Uruguay’s milling industry. As a circular economy strategy, it is burned in broilers for energy production. Aiming to increase the added value of the bark, this work analyzes the extraction of its tannins to use them in the development of formaldehyde-free adhesives, while evaluating whether it retains its calorific power for further energy production. The best extraction conditions (methanol at 65 °C for 2 h) were identified at a laboratory level after which they were scaled up to 50 L, which did not affect extraction yield. The Stiasny number remained above 65%, meaning the extractive was suitable for its use in adhesive formulations. The characterization of the extractives was completed with molecular weight distribution, FTIR-ATR, ABES and DSC. Finally, two formaldehyde-free adhesive formulations were developed using hexamine and glyoxal as hardeners. Their behaviors were compared through rheological analysis, DSC and ABES. It was determined that the adhesive formulations with hexamine at pHs of 8 and 10 are suitable for their use in the timber industry. It was noted that they react the best at a pressing temperature of 160 °C. After the extraction, the calorific power of the P. elliottii Engelm bark decreased by only 13%, thus remaining useful for energy production.