Dielectric properties of copper-ethanolamine treated Chinese fir (Cunninghamia lanceolata Hook.)

Abstract

In order to clarify the interaction between copper and wood substances in wood treated with copper containing water-borne wood preservatives, the dielectric constant ɛ′ and dielectric loss factor ɛ″ of untreated wood and wood treated with four concentration levels of copper-ethanolamine (Cu-EA) solutions were determined within a temperature range from −100 to 40°C and a frequency range from 100 to 1 MHz. Three dielectric relaxation processes were observed in the ɛ″ spectrum; among them R-I is based on the reorientation of methylol groups in the amorphous region of wood cell walls and R-II is related to wood extractives. R-III appeared in Cu-EA treated wood, and its magnitude decreases with the concentration of Cu-EA solutions used in this experiment. This relaxation process was considered to be based on the reorientation of copper-ethanolamine-wood complexes in wood cell walls. At low copper retention, the hydrogen in the complex can form hydrogen bonding with adjacent hydroxyl groups, which results in a strong bonding state between copper and wood; at high copper retention, the numerous copper-ethanolamine complexes not only hinder them from forming hydrogen bonding with adjacent wood molecules due to steric hindrance, but also weaken the interaction between wood molecules themselves, which corresponds to reducing ɛ″ values of both R-I and R-III processes. The results explain the fact of increasing copper leaching in wood treated with high concentration copper-based water-borne preservatives.