Cellular Makeup

 

 

 

Wood Cells

simplified structure of the cell wall showing orientation of microfibrils in each of the major wall layers

		yellow pine
from The Science and Technology of Civil Engineering Materials, J.F. Young, et al., Prentice Hall, 1998.		Koch, P. 1972b. Utilization of the southern pines. II. The raw material. USDA Forest Service Agricultural Handbook No. 420. 926 pp.

 

 

 

 

In summary, the mechanical properties of wood relate directly to the shape and size of its cells, and to the properties of the composite-like cell walls.  Loaded along the grain, the cell walls are loaded in simple tension or compression, and the properties scale as the density.  But across the grain, the cell walls bend, and then the properties depend on a power (3/2 to 2) of the density.  That, plus the considerable anisotropy of the cell wall material, explain the enormous difference between the modulus, strength and toughness along the grain and across it.  from Engineering Materials 2: An Introduction to Microstructures, Processing and Design, M.F. Ashby & D.R.H. Jones, Pergamon, 1994, p. 263.

 

Cell Wall

from Wood: Nature's Cellular, Polymeric Fibre-Composite,  J.M. Dinwoodie, The Institute of Metals, 1989, p. 13.

 

Category	Material	Structure	Approx. wt %
fibres	cellulose	crystalline	45
matrix	lignin	amorphous	20
	hemicellulose	semi-crystalline	20
	water	dissolved in the matrix	10
	extractives	dissolved in the matrix	5

from Engineering Materials 2: An Introduction to Microstructures, Processing
and Design, M.F. Ashby & D.R.H. Jones, Pergamon, 1994, p. 258.

 

Cellulose is the primary component of the cell wall.  Furthermore, it is the single most abundant organic chemical in nature.  It is one of the few natural compounds that retain the same structure regardless of whether its source is wood, cotton, grass, or a host of other plants.  Structurally cellulose is the simplest of the cell wall components -- a linear polymer of glucose units.  Biosynthetic polymerization is such that the basic polymeric unit of two combined glucose constituents is "stretched" to almost its maximum dimension.  The number of glucose units in a cellulose molecule (degree of polymerization) ranges from a few to as many as 15,000, depending on its location within the cell wall.
from Mechanics of Wood and Wood Composites, J. Bodig & B.A. Jayne, Krieger Publishing, 1993, p. 5.

(C₆H₁₀O₅)_n

Cellulose nanocrystals 'have strength of steel'

International Conference on Natural Fibers

 

Category	Material	Density (Mg m-3)	Modulus (GPa)	Strength (MPa)
fiber	carbon, type 1	1.95	390	2200
	carbon, type 2	1.75	250	2700
	e-glass	2.56	76	1400-2500
	cellulose	1.61	60	1200
	kevlar	1.45	125	2760
matrix	epoxies	1.2-1.4	2.1-5.5	40-85
	polyesters	1.1-1.4	1.3-4.5	45-85

 

 

Sapwood vs Heartwood

sapwood - store food, transport liquids, accepts wood preservative

heartwood - inactive cells, darker, more decay resistant

 

 

Earlywood (springwood) vs Latewood (summerwood)

growth rings with growing seasons

yellow pine	yellow pine	Valinhos, Brazil
Koch, P. 1972a. Utilization of the southern pines. I. The raw material. USDA Forest Service Agricultural Handbook No. 420. 733 pp.	Koch, P. 1972b. Utilization of the southern pines. II. The raw material. USDA Forest Service Agricultural Handbook No. 420. 926 pp.

Managed tree plantations (genetic engineering, thinning, protein and fertilization) has resulted in greater proportions of earlywood.  Difference in moduli found to be as high as seven.
"Mesostructure Elastic Properties in Loblolly Pine" by S. Cramer

 

 

Softwood vs Hardwood

softwood	hardwood
larger, longer cells water transported by cells	large-diameter vessels water transported by these vessels

 

yellow pine
Koch, P. 1972a. Utilization of the southern pines. I. The raw material. USDA Forest Service Agricultural Handbook No. 420. 733 pp. Koch, P. 1972b. Utilization of the southern pines. II. The raw material. USDA Forest Service Agricultural Handbook No. 420. 926 pp.
white ash
white Oak

 

see The Tree Collection for more cellular images