Basic knowledge of trees and wood

Trees and trees are living organisms, composed of crowns, trunks, and tree roots. The trunk is the main body of the tree, consisting of bark, forming layer, xylem (secondary xylem, ie wood), and marrow.

The trees are composed of axially and radially arranged cells with porosity, wet and dry shrinkage, low thermal conductivity and electrical conductivity, easy processing, easy cracking, perishable, flammable, porous, three-dimensional structure, anisotropic Organic biocomposites. It is divided into coniferous and broad-leaved tree materials. The former is called soft material and the latter is hard.

(1) Porosity

Trees 1. Wood-based porous materials (with tracheids, ducts, fibers, etc.).

Trees 2. Impact 1) Low thermal conductivity, such as water pine roots and balsa wood as water stoppers; (2) Mechanically resilient, wood can absorb a considerable amount of energy when subjected to heavy loads and impacts, and the horizontal stripes are more constrained; (3) easy to saw; (4) have a certain buoyancy; (5) high porosity, high storage air, easy growth of rot fungi; (6) easy chemical processing, anti-corrosion, drying treatment, wood modification; (7) Keep paint and adhesive.

(2) Anisotropy

Trees 1. Due to the three-dimensional structure (cells are not regular geometric figures; cell walls are also non-homogeneous).

Trees 2. Influence: Conductive and thermal conduction: longitudinal = 2 times transverse; wet expansion and contraction: longitudinal = a few tenths to several hundredths of the chord direction, chord direction = 2 times radial; causing wood warping; Quantity = 20 times horizontal stripes; striated tensile resistance = 40 times horizontal stripes; striated compression = 5 to 10 times horizontal stripes; the anti-stretching tensile strength is strongest, and the cleavage is the weakest.

(3) Variability

Tree cell size, compositional properties, and changes occur to mutate chemical and physical properties.

Trees 1. In-plant variability is related to tree development, ie, juvenile wood and mature wood. (1) Axial: The length and density of the tree base→top tubular molecule become shorter after increasing to a certain length. (2) Radial: medullary heart → bark tubular molecular length and density gradually increase to a certain stage or stabilize or continue to increase or decrease.

Trees 2. Inter-strain variability - mainly due to site conditions. Shady slope (shade) sun slope (sunny); low depression, hilly land; soil fertile, barren (not fertile); plant density material varies greatly.

(4) The thickness of the cell wall reflects the density of the wood, that is, the weight and intensity of the marked wood. The weight (or density) of the wood is also affected by the amount of cells.

Trees 1. Coniferous trees have a small change due to more than 90% of the tracheids.

Trees 2. The density of broad-leaved tree fibers (especially wall thickness) increases.