Durability of poly(ɛ-caprolactone) modified wood under outdoor soil burial test

Abstract

This research explores the chemical modification of spruce wood to maintain its resistance and durability properties under soil conditions through ring-opening polymerization using both fresh and re-used ε-caprolactone solutions at concentrations of 70% and 100%. Durability of the modified wood was evaluated over 24 months through soil burial tests, and degradation was assessed via mass loss measurements, Fourier-transform infrared spectroscopy, and scanning electron microscopy (SEM) analyses. In addition, compression strength, modulus of rupture, and modulus of elasticity were determined after the soil burial test. Mass loss of 70% PCL modified samples and controls during the 24 months in soil was higher than that of 100% PCL modified samples due to fungi and termite attacks. SEM analysis revealed the presence of fungal hyphae in both the control and 70% PCL-modified samples, indicating that fungal degradation was more pronounced in these groups. Specifically, the middle lamella in these samples exhibited greater structural breakdown compared to the 100% PCL-modified samples, which showed higher resistance to fungal attack. 100% PCL modified samples were highly resistant to the termite attacks, with a slight visible sign of feeding by the termites in MOR and MOE samples, whilst the controls and some samples of 70% PCL modified samples were destroyed by termites. Parallel to findings on mass losses, strength losses were remarkably lower in 100% PCL modified samples than in controls and 70% PCL modified samples, even after termite attack. The results clearly showed that 100% PCL modification protects wood against soil degrading organisms; however, the re-use of ε-caprolactone solution more than three times negatively affected the success of the modification process and reduced the properties of modified wood.

Graphical abstract