Microdistribution of chromated copper arsenate preservative in rubberwood (Hevea brasiliensis Muell. Arg.)

Rubberwood is popular for making indoor furniture since rubberwood is relatively abundant and sustainable. Currently more than 60% of the total annual rubberwood produced by rubber plantation is used as fuelwood. Rubberwood has the potential for both indoor and outdoor application. For exterior applications, preservative treatment is needed to extend the service life of rubberwood. The objectives of this study are to (1) assess treatability of rubberwood with chromated copper arsenate (CCA) preservative, (2) evaluate the natural decay resistance and efficacy of CCA on rubberwood, and (3) study the microdistribution of CCA components in rubberwood cells. The treatability of rubberwood was determined by measuring the penetration and retention of CCA type C preservative after a full-cell treatment. Natural decay resistance and efficacy of CCA treatment on rubberwood was estimated using a laboratory soilblock test according to AWPA E 10-91. The microdistribution of chromium, copper and arsenic in CCA-treated rubberwood was studied using scanning electron microscope in conjunction with energy dispersive X-ray analyzer (SEM-EDXA). As expected, longitudinal permeability was found to be better than the radial and the tangential permeability. The penetration and retention in the radial direction was about 3 times better than in the tangential direction. Longer pressure period increased penetration and retention of CCA type C in rubberwood. Complete penetration was achieved after 4 hours of pressure (1240 kPa) treatment. A pre-treatment steaming improved the treatability of rubberwood regardless of the anatomical direction. The average weight loss by white rot and brown rot was about 1.5 times higher than that of soft rot. A linear relationship was found between the weight loss and the incubation period for all the six test fungi. A CCA retention of 4.1 kg/m3 reduced weight loss to about 10% and retention of 14.5 kg/m3 reduced the weight loss of all test fungi at less than 2%. Vessels contained high level of chromium, copper, and arsenic compared to fibers. Chromium level was the highest, followed by arsenic and then copper in rubberwood cells. After the full cell treatment, fibers contained about 0.42%, 0.63%, and 1.02% of copper after treatment with 4.1 kg/m3, 10.5 kg/m 3, and 14.5 kg/m3 of CCA, respectively. Highest levels of Cr, Cu, and As were recorded in fiber-to-vessel cell corner (FV_CC ) and Fiber-to-vessel middle lamella (FV_ML) and the lowest was recorded in S₂ layer of fiber. Linescan analyses showed that higher count rates of carbon, oxygen, chromium, copper, and arsenic were found in the middle lamella compared to the fiber S₂ layer in CCA-treated rubberwood. The increase of the solution strength in chromium, copper, and arsenic corresponds to an increase in Cr, Cu, and As level in wood cells.