The species Melia composita has come to prominence only during the last decade and has been found suitable for several applications and end uses. However, being non-durable and difficult to treat some pre-treatment is required to improve preservative uptake. Hence the effect of microwave (MW) pre-treatment was studied on the samples of Melia composita wood in order to ameliorate its retention, depth of penetration and treatability class to ensure its sustainable use for a longer duration. The samples were exposed to MW radiation of different intensities and treated with 6% solutions of CCA, ZiBOC, CCB and Borax boric acid (BBA) preservatives by a dip diffusion method for 24 hours. Results showed a significant improvement in preservative uptake after dipping for 24 hours, in comparison with the controls. The highest retention was found in the samples treated with ZiBOC preservative after their MW exposure to 840 MJ·m–3. Wood anatomical analysis after MW modification was also performed in order to assess the changes taking place within the wood microstructure. The cross-sectional analyses of the controls and the treated specimens were briefed accordingly. Results of the anatomical study exhibited a significant improvement in the effective vessel diameters of the microwave irradiated specimens due to the clearance of the occlusions blocking the vessels with respect to the control samples, which aids in increasing wood permeability and results in higher retention and penetration.

Microwave modification can increase the permeability of wood by delaminating and rupturing its anatomical microstructures at their weak points. A high degree of intensity of microwave modification can cause significant structural damage to the microstructures of wood, resulting in poorer strength properties. The objective of this study was to evaluate the changes in the anatomical structure of Norway spruce (Picea abies (L.) Karst.) heartwood and sapwood after microwave modification in order to develop the most effective treatment in terms of applied energy without causing significant structural damage. Analysis with light and scanning electron microscopy were performed to evaluate the effect of microwave treatment for two different energy intensities, moderate and high intensity. The results indicated structural changes in the tracheid cells. Microscopy showed varying degrees of modification within the wood microstructure, with the heartwood samples showing a greater anatomical distortion compared to their sapwood counterparts. Furthermore, the samples were subjected to pycnometric density measurements, which indicated a reduction in skeletal and absolute density after microwave modification, for both high and moderate intensity treatment on sapwood and heartwood samples. With increasing microwave energy, a gradual increase in specific pore volume and porosity percentage of the samples were also detected.

The performance of treated wood in the field is ultimately affected by retention and penetration of preservative in wood. In the present study, a new preservative system ZiBOC and a commercially used preservative copper-chrome-arsenate (CCA) were used for evaluation of treatability of Melia composita by the vacuum pressure method at different pressure levels in unsealed and end sealed specimens. The retention and penetration levels of both the preservatives were significantly different at (P< 0.05) in sapwood, heartwood and pith zones. Melia composita exhibited treatability class 'C' (21 -42% penetration). The results revealed that longitudinal penetration in Melia composita was the dominant flow as examined by spot test for copper in unsealed and end sealed specimens.

Low permeability of many wood species due to their anatomical properties causes problems during timber drying as well as impregnating with preservatives and resins. Microwave (MW) treatment influences heartwood permeability and improves preservative uptake and distribution. In the present study, microwave treatment of chir pine (Pinus roxburghii) wood was done at 2,45 GHz frequency at different level of intensity and radiation time. The gas permeability of chir pine wood was measured in an in-house built apparatus. Preservative uptake was tested using acid copper chromate (ACC) preservative by a dipping process. The effect of radiation intensity and time on preservative uptake and air permeability were studied. The results revealed remarkable increase in longitudinal wood air permeability and preservative uptake with the increase of intensity and time of treatment. The results indicate that this technology can be tested and applied on pilot scale for application in wood preservation industry.

This study investigated the effect of microwave treatment on wood pH and termite resistance. Pinus roxburghii heartwood was exposed to four different microwave intensities at 2450 MHz frequency for 5 minutes. Preservative impregnation, pH variation and termite resistance of microwave-treated and control specimens were studied. Wood pH decreased from 4,6 (C1) to 3,9 (T4) and preservative uptake increased (i.e., 10,4 to 21,6 kg.m-3) with increasing microwave treatment intensities. However, microwave treatment had little effect on termite resistance.