A Study on Microwave Exposure Effects on Surface Coating Properties of Linden (Tilia cordata) and Spruce (Picea abies) Woods

Abstract

The quality performance of surface coatings are evaluated with emphasis on Microwave (Mw) irradiation, effects on both wood and oil modified alkyd-based varnish, separately. The surface pencil film hardness value of 2B (5 in metric) found for neat varnish coated linden and spruce control samples. It appears Mw exposure on both woods and varnish were effective for further increasing pencil hardness which are about 4 and 5 unit higher than controls. It is also noticeable that a clear improvement for cross-cut (adhesion) properties were realized with Mw treated varnish coated linden woods. Although cold liquid resistance of coating evaluations have conducted with 11 liquids, but coated surfaces were showed the lowest resistance, assessed grade 1 (considerably changes) for five of these liquids (juice, milk, ketchup, lemon juice, cola)  regardless of conditions or wood species. Therefore, results revealed some level correlation between Mw conditions and wood samples for six of the cold liquids involved in the examination. Mw treated spruce samples usually show 1 to 2 unit higher olive oil, vinegar, mayonnaise, ethyl alcohol resistance while no any improvement found for coffee and mineral water. Linden samples usually show 1 to 3 unit improving (higher) resistance against all these six cold liquids, regardless of Mw conditions. It is important to note that all Mw treated and varnish applied wood species subjected to olive oil, mayonnaise and ethyl alcohol show very high resistant properties (graded 4 and 5). Similar results are also realized with applying Mw irradiated vanish to both wood species. These variations and changes could be results of chemical structural changes, including cross-linking by esterification and etherification, promoted by Mw irradiation.