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Polymer Matrix Composites (PMC's):

Wood

Category Summary

Wood is a natural composite with a natural, organic, polymer matrix called lignin, the wood fibers (cellulose) make up the reinforcement component, also an organic polymer. Wood is the hard, tough substance that forms the trunk of trees. Wood has been used for thousands of years as fuel and construction material.
The markings, called grain, found on all types of wood, are caused by the structure of wood. Wood consists essentially of fine cellular tubes, which carry water and dissolved minerals from the roots to the leaves and which are arranged more or less vertically within the trunk. This usually forms straight-grained lumber. Many types of wood have prominent growth rings. Only a thin layer entirely surrounding the trunk grows, this called the cambium. In most trees, the wood formed early in season is lighter of colour than wood growing later in the year. New concentric sheaths are formed around the trunk of a tree each year, the year markings. As a tree grows older the central portion of the trunk, called heartwood, dies completely. Knots are areas of the trunk in which the base of a branch is embedded. When the wood is sawed into planks, knots become clear as somewhat circular discontinuities or irregularities in the grain structure. Knots are generally undesirable in lumber from the standpoint of appearance and their negative influence on the strength of the wood. The principle physical properties of wood are strength, hardness, stiffness and density. Dense types of wood are usually hard and strong. The term strength covers a number of different properties. Strength varies greatly with seasoning and with the direction of the grain; wood is much stronger when cut along the grain than when cut across it. Toughness is a measure of strength against sudden, repeated stress. Wood is naturally very durable. If not attacked by living things, it can last for hundreds or even for thousands of years. The most important threat for wood are fungi that cause so-called dry rot. The heartwood of a few species is naturally resistant to these fungi. Other types of natural resistance to various of other types of attack, have been discovered in other species. These types are usually very aromatic. It is suspected that they are protected by the resins and other chemicals they contain. Wood may need to be preserved by protecting it chemically against deterioration.

Category Details

Features

The features of wood depend strongly on the wood type:

  • Toughness

Classification

The wood types in Matbase are not classified by their mechanical, thermal or similar properties, but their natural durability measured in the period of time they can withstand degredation by wood-destroying fungi and maintain their structural integrity according to European norm EN350:

  • Class 1 - very durable: service life > 25 years
  • Class 2 - durable: service life 15-25 years
  • Class 3 - moderatly durable: service life 10-15 years
  • Class 4 - slightly durable: service life 5-10 years
  • Class 5 - not durable: service life < 5 years

Other classifications are:

  • Natural resistance to wood-destroying beetles (D = Durable / S = Susceptible)
  • Natural resistance to termites and marine borers (D = Durable / M = Moderatly durable / S = Susceptible)
  • Treatability of wood:

Class 1 - Easy to treat: the material absorbs preservatives completely and trough-and-trough
Class 2 - Moderately easy to treat
Class 3 - Difficult to treat
Class 4 - Extremely difficult to treat: the material is not penetratable with or absorbs little presarvatives

Classification Sources

CEN EN350-2

Idemat 2003

Wikipedia 2003

Health

Known health effects for this category.

Environment

Known environmental effects for this category.