Technological Investigation of Prosopis leavigata Wood from Northeast Mexico

This study describes the anatomical properties of Prosopis laevigata trees found in northeast Mexico. The chemical composition and the topochemical distribution of lignin and phenolic compounds are described along with the deposition of extractives in pit canals, parenchyma cells, and the fiber S2 layer using UV microspectrophotometry (UMSP). The main physical and mechanical characteristics of trees from four different areas of northeast Mexico are presented. The natural durability of wood samples from various regions is determined through use of the soil-bed test ENpr 807. The durability of extractive-free wood specimens toward basidiomycetes is investigated as is the growing inhibition of Coniophora puteana and Trametes versicolor caused by extractives obtained by using hot water, ethanol-water, acetone-water, and cyclohexane. The shear strength of the wood after being glued with melamine formaldehyde (MF) and Polyvinyl acetate (PVAc) is measured. The effect of artificial weathering is also discussed. The Prosopis genus normally grows on arid and semi-arid land. It is used as a source of fodder for domestic animals, of flour for human consumption, and as a source of gums, mulch or compost. It also plays an important role in the production of honey. The wood is used to produce parquet lumber, furniture and decorative hand-crafted items; however, its main use is still as a source of fuel. The importance of the Prosopis species, both within Mexico and around the globe, is presented in Chapter 1. Its use, distribution and ecological importance are also discussed. An anatomical description and an analysis of its chemical composition are given in Chapters 2 and 3, respectively. The size, proportion and distribution of the wood s fiber structure, of its vessels and of its ray parenchyma cells are discussed and compared with those of other Prosopis species. The chemical wood composition reveals a holocellulose content of between 61.7 - 64.5% and a Klason lignin content of between 29.8 - 31.4% within the heartwood tissue. A large percentage of extractive compounds (14.1 to 16.0 %) are found within the wood, including catechin, epicatechin and taxifolin. The characteristics of the trees and, consequently, the properties of the wood are influenced by weather conditions in its natural habitats. Chapter 4 deals with the physical and mechanical properties, including density, swelling and shrinkage, as well as the modulus of elasticity, and the modulus of rupture and hardness. The results reveal that this wood is very stable with regard to dimensional changes and that it has medium to high wood strength. Differences in properties of wood grown in different areas are also presented. P. laevigata wood is highly resistant to decay. As described in Chapter 5, its heartwood has a very low mass loss and a dynamic modulus of elasticity loss after 32 weeks of soil contact. Low mass loss (0.4 to 1.5 %) is also found after 16 weeks of exposure to the basidiomycetes Coniophora puteana, Trametes versicolor, Irpex lacteus and Pleurotus ostreatus in a modified EN 113.The natural durability is classified as Class 1 (very durable) according to European Standard EN 350-1. Extractives have a moderate to large effect on C. puteana and T. versicolor growth after dissolving in a malt-agar medium; the extractives are most effective at 1000 ppm concentration. Artificial weathering and bonding properties are presented in Chapters 6 and 7. The wood has high stability with respect to dimensional changes and displays a great resistance to artificial weathering. The general appearance of P. laevigata changed from brown to white; Delta C (change of colour) increased from 5.6 to 9.6 and there were fewer crack formations than in Fagus sylvatica species but more than in Tectona grandis. Shear strength results obtained after gluing Prosopis wood (normally used for indoor applications) with Melamine Formaldehyde (MF) adhesives under wet condition demonstrate that Prosopis is suited for use in outdoor application. In summary, it must be emphasised that the density, the wood stability with regard to moisture changes and artificial weathering, the high natural durability, and, finally, the high amount of shear strength after bonding are parameters which point to an almost limitless number of indoor and outdoor applications for this wood. The analyses of the properties of P. laevigata wood as well as those of feasible wood uses done in this study have revealed some very important elements worthy of further research and development within the forestry and wood sciences.