Document Type : Research Article
Authors
Department of Cellulose Industry Engineering, Faculty of Natural Resources, Behbahan Khatam Alanbia University of Technology, Behbahan, Iran
Abstract
Introduction
As a very important and widely used construction material, wood is easily decomposed by biological agents such as bacteria, fungi and termites. However, some wood species are more resistant to these destructive factors, while others are very susceptible to destruction. The aim of this study was to investigate the effective factors on the resistance of the wood of four species of poplar, maple, chinaberry and Cypress against the attacks of the subterranean termite Microcerotermes diversus Silvestri. Since the tropical provinces of Iran, including Khuzestan, are among the regions where different species of termites are considered as the main factors in the destruction of lignocellulosic materials, therefore, knowing resistant woods, which in their natural and untreated state can have high durability compared to the attacks of this insect can help to choose better wood for making wooden products and structures.
Materials and Methods
To check the natural durability of the four mentioned species, first, wooden samples were selected and cut from healthy trunks without visible defects. Then, with the aim of collecting termites to conduct selective and non-selective feeding tests, an abandoned palm grove was considered in Dodangeh village, located 20 km from Behbahan city, and then beech wood with dimensions of 2.5 x 4 x 20 cm were planted in the soil as bait for two weeks. After this period of time, the bait sticks were removed from the soil and transferred to the laboratory. Then, the cut wood was subjected to M. diversus termite infestation according to AWPA-EI:06 2008 standard obtained from baits. After the desired period of time, the chemical and physical properties of wood such as the percentage of extractive materials, specific gravity, lignin and cellulose content of each species were calculated according to the standard.
Results and Discussion
The results showed that the percentage of extractive substances in maple species has a significant difference compared to other species and is lower than other species, while the highest amount of extractive substances is related to Cypress. Among the investigated species, cypress exhibited the highest lignin content, while poplar displayed the lowest. Notably, both cypress and poplar significantly differed in lignin content compared to the other two species. Cellulose analysis revealed a significantly higher percentage in spruce compared to all other species (p< 0.05). Conversely, no significant differences in cellulose content were observed between the remaining three species. The lowest amount of specific mass belongs to spruce and the highest It belongs to the maple species. This difference is significant at the 95% level. The results of selective, non-selective and field tests of termite feeding on wooden samples are shown in figure number five. The results show that Cypress and chinaberry samples showed the lowest percentage of weight loss and poplar and maple samples showed the highest weight loss.
Conclusion
What increases the natural durability of wood species against termite attacks and other destructive factors are wood anatomy, wood density, lignin and cellulose content, moisture content, and the composition of extractive materials in the wood. Examining the extractives of the researched species, it can be seen that maple has the lowest percentage of extractives and Cypress has the highest amount, and this problem can have a serious effect on the intensity of termite attacks. Extractive substances play a critical role in enhancing wood's natural resistance to destructive agents, particularly insects. Their significance is evident in certain durable wood species. Removing these extractives renders the wood susceptible to decay. Furthermore, the weight loss observed in both selective and non-selective decay tests, along with field trials, demonstrates a clear correlation with the content of lignin and cellulose in the wood. By increasing the percentage of lignin, the desirability of wood for termites decreases, and on the other hand, with the addition of cellulose percentage, the desirability of the species for termites increases. Lignin is a polymer that, as the second component of wood after cellulose, plays an important role in wood, and due to its phenolic groups, it is considered a toxic substance for destructive agents and has repellent properties. When lignin coats the cell wall, it forms a more impermeable matrix, making the cellulose less accessible and making the wood more resistant to biodegradation. In this research, the highest amount of lignin belongs to Cypress and the lowest amount belongs to poplar, and a significant difference between the amount of lignin in these two species is observed. Physical characteristics such as specific mass is also considered as determining factors of durability against termite attacks, and species with lower and lighter specific mass are more likely to be attacked by termites. According to the obtained results, poplar is different from other species in terms of specific gravity and is considered a lighter species, and this issue, along with the high percentage of cellulose, which is the material preferred by termites, can increase the vulnerability of this species. Based on the obtained results, the effect of factors such as chemical composition and physical characteristics of the studied species on the intensity of subterranean termite attacks M. diversus and according to the mentioned parameters, Cypress species was the most resistant and poplar was the weakest species to the attack of this termite species.
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