Microscopic identification of changes in beech (Fagus sylvatica L.) and pine (Pinus sylvestris L.) cell structure after drying using high-frequency energy of the microwave band

Abstract

High-frequency energy transfer represents a progressive technology with an increasing range of industrial application. One of the main advantages of microwave technology is the volumetric principle of energy transfer. Based on this fact, the gradients of moisture content and temperature are identical and when the wood is dried it helps transport moisture from porous material and it also helps and transport free water whit lumen of cells. From a practical viewpoint, microwave heating increases the quality of the dried material and reduces the necessary processing. The quality of a dry material is an essential input parameter for other technological procedures and it depends on the deformations created in its cell structure. Therefore, the monitoring of changes brought about during the drying process is necessary. The aim of this study was to identify the changes in the microscopic structure of the wood of beech (Fagus Sylvatica L.) and pine (Pinus Sylvestris L.) dried using the high-frequency energy of the microwave band. The microscopic structure of a material modified by microwaves was photographed by means of a low-vacuum microscope and then visually compared with the native structure. The results show that the structure of beech and pine wood during the time of the proposed drying regime does not differ considerably from the native structure. This outcome is documented in a digital form and it confirms the harmless character of microwave heating towards wood structure in the conditions of optimum drying parameters.