Topic 2 properties of wood Flashcards
(32 cards)
Describe the microstructure of wood.
The microstructure of wood consists of bundles of tubular cells (or fibers) glued together by lignin, with the primary building block of these cells being cellulose. The cells are mainly aligned longitudinally.
Explain the difference between earlywood and latewood.
Earlywood cells are characterized by their larger diameter and thinner cell walls compared to latewood cells.
Define the primary building block of wood cells.
The primary building block of wood cells is cellulose.
How are the cells in wood aligned?
The cells in wood are mainly aligned longitudinally.
Describe the role of lignin in the microstructure of wood.
Lignin acts as a glue that holds the bundles of tubular cells (fibers) together in the microstructure of wood.
What distinguishes earlywood from latewood in terms of cell structure?
Earlywood has larger diameter cells with thinner walls, whereas latewood has smaller diameter cells with thicker walls.
Describe the primary function of tracheids in wood.
Tracheids are responsible for mechanical support and the transport of water and sap in wood.
Explain the difference in length of tracheids between softwoods and hardwoods.
Tracheids in softwoods tend to be 3 to 5 mm long, while in hardwoods, they are approximately 1 mm long.
What is the typical aspect ratio (L/d) of tracheids in softwoods?
The aspect ratio (length to diameter) of tracheids in softwoods is around 100.
Describe the microstructure of a wood cell.
Each wood cell has two main zones: a thin primary wall that forms first, followed by a three-layer secondary wall that provides most of the strength.
How are tracheids aligned within the wood structure?
Tracheids are longitudinally aligned cells within the wood.
Define the primary wall of a wood cell.
The primary wall is a thin layer that forms first during cell development.
Describe the secondary wall of a wood cell.
The secondary wall is a three-layer structure that provides most of the cell’s strength.
Explain the significance of the secondary wall in wood cells.
The secondary wall provides most of the mechanical strength to the wood cell.
Describe the three layers in the secondary wall of wood and their orientation.
The three layers are S1, S2, and S3. The thick S2 layer is almost parallel to the cell’s major axis, providing strength in the longitudinal direction. The thinner S1 and S3 layers are almost perpendicular to the cell axis, acting mainly perpendicular to the grain.
Explain the microstructure of wood cells and how they are bonded.
Wood cells are bonded to each other with a binder called lignin. The cell walls are framed with string-like microfibrils composed of millions of parallel, closed-packed cellulose molecules. These microfibrils are bound together in the cell wall by a hemicellulose and lignin matrix, similar to fibreglass construction.
Define the role of microfibrils in the cell wall structure of wood.
Microfibrils are string-like structures composed of parallel cellulose molecules that form the framework of the cell wall, providing structural strength and support.
Describe the composition of microfibrils in the cell wall.
Microfibrils are composed of millions of parallel, closed-packed cellulose molecules.
Explain the function of lignin in the wood cell structure.
Lignin acts as a binder that bonds the microfibrils together within the cell wall, providing rigidity and structural integrity.
Describe the analogy used to explain the binding of microfibrils in the cell wall.
The binding of microfibrils in the cell wall is similar to fibreglass construction, where fibers are embedded in a matrix to form a strong composite material.
Identify the orientation of the S2 layer in the secondary wall and its significance.
The S2 layer is almost parallel to the major axis of the cell, which provides strength in the longitudinal direction.
Explain why the S1 and S3 layers are oriented almost perpendicular to the cell axis.
The S1 and S3 layers are oriented almost perpendicular to the cell axis to act mainly perpendicular to the grain, contributing to the overall structural integrity of the wood.
Describe the main components of wood’s microstructure.
Wood’s microstructure mainly consists of cellulose (50% by weight), lignin (23-33% in softwood, 16-25% in hardwood), hemicellulose (15-20% in softwood, 20-30% in hardwood), and extractives such as tannins, oils, resins, wax, and gums (5-30%). Additionally, ash content includes minerals like calcium, phosphate, potassium, and silica.
Explain the role of cellulose in wood.
Cellulose forms ordered strands called fibrils, making up about 50% of wood by weight. It is a polymer formed from glucose and provides high-density structural support in the wood microstructure.
