Microwave (MW) pretreatment was used to increase the impregnability of Oriental spruce sapwood (Picea orientalis (L.) Link.). Wood samples with moisture contents of 55% and 83% were subjected to different MW energy treatments (1156 MJ/m3 and 1542 MJ/m3). Additionally, the mechanical properties of the treated wood samples were tested to determine the degradation caused by exposure to the MW radiation. According to the test results, the average preservative material retention rates increased by 47.5% and 70% for the samples with initial moisture contents of 55% and 83%, respectively, compared to the reference samples. The mechanical properties of the MW pretreated wood samples decreased within the range of 1.7% to 2.9% in the case of the compression strength; changed within the range of (+)1.9% to (-)6.1% in case of the bending strength; and changed within the range of (+)0.9% to (-)6.2% in case of the modulus of elasticity (MOE). The application of MW energy at different power settings on the samples with similar moisture levels was determined to have no impact on the mechanical properties of treated wood.

In the microwave (MW) pre-treatment process, a constant MW energy intensity of 2158 MJ/m³ was applied by using 925 W (3700 sec.), 1295 W (2640 sec.) and 1850 W (1850 sec.) powers. Tanalith-E preservative material was used to determine the increase in impregnability of MW pre-treated wood. The mechanical properties of the treated wood specimens were tested to determine the degradation caused by exposure to the MW radiation. Additionally, scanning electron microscope (SEM) was used to determine the changes in wood microstructure with the effect of microwave pre-treatment. According to the impregnations, the average preservative material retention rates increased 62% for the specimens with MW groups, compared to the reference specimens. The mechanical properties of the MW pre-treated specimens decreased by (average) 5% in compression strength, 12% in the bending strength and 16% in the modulus of elasticity. SEM observations of the reference specimens showed that there were many aspirated bordered pits before MW pre-treatment. After the MW pre-treatment, parts of the pit membranes were damaged. The torus ruptured and cracked, while the structure of the micro-fibrils on the margo remained intact. In the observations of the intercellular microstructure of wood, it was observed that micro cracks with a width of 1–10 μm were formed.

There are various methods for nondestructive imaging of the internal structure of wood. A microwave nondestructive method based on the dielectric properties of a medium is an area of great interest for predicting wood strength in the worldwide wood industry, but the reliable prediction of strength in wood still has not been solved in a satisfying manner. Hence, answering the question of how dielectric properties of the wood are related to strength may improve the efficiency of models for predicting structural performance of wood by microwaves. Relationships were evaluated in this work between dielectric parameters (dielectric constant, loss factor, and loss tangent) and the strength properties of wood. Samples were prepared from fir and oak wood. Dielectric measurement was performed at a frequency of 9.8 GHz using Von Hippel’s Transmission Line Method. Wood density and some mechanical properties were then determined according to related ISO standards. The results showed that there were good relationships between the dielectric parameters and the MOR, MOE, IBS, and CS, especially for oak wood. The dielectric parameters were promising to predict wood strength with a high accuracy for oak but not fir, and the dielectric constant had a higher precision degree than the loss tangent and loss factor.

In recent years, due to increasing concerns about the environment and sustainable production, the effective utilization of wastes has become important. In this regard, it has become essential to obtain products with distinct properties by utilizing different types of biomass together. The world’s annual apricot production is approximately 4 million tonnes. The apricot seeds can be used to produce seed oils; however, remaining residue (apricot seed pulp) from this process is considered as waste. In this study, the co-pyrolysis of waste from the essential oil industry (apricot seed pulp, ASP, and by-products of the paper pulp industry (calcium lignosulfonate, CLS, and sodium lignosulfonate, SLS)) was carried out using mixtures at different temperatures (400–700 °C) and different ratios (4:1, 1:1, 1:4). The effects of temperature and ratio on the yields, composition, and HHV of biochars were investigated. Among biochars obtained from co-pyrolysis, the maximum HHVs of 26.91 MJ·kg⁻¹ and 25.64 MJ·kg⁻¹ were obtained for 5ASP-5CLS-400 biochar and 8ASP-2SLS-400 biochar, respectively. The results showed that the addition of ASP to CLS led to an increase in the HHVs of biochars when compared to the HHVs of biochars obtained from the pyrolysis of CLS. The use of two different types of waste has led to the production of biochars with different properties due to the synergistic effect in the pyrolysis. As a result, biochars with diverse properties, which have the potential to be utilized in various applications, were produced from different types of wastes.