وبلاگ دانشجویان مهندسی چوب دانشگاه تهران

Microfibril angle (MFA) is perhaps the easiest ultrastructural variable

to measure for wood cell walls, and certainly the only such variable that

has been measured on a large scale. Because cellulose is crystalline, the

X-ray scanning devices such as SilviScan have produced large datasets

for a range of timber species using increment core samples. In conifers,

microfibril angles are large in the juvenile wood and small in the mature

wood. MFA is larger at the base of the tree for a given ring number from

the pith, and decreases with height, increasing slightly at the top tree. In

hardwoods, similar patterns occur, but with much less variation and much

smaller microfibril angles in juvenile wood. MFA has significant heritability,

but is also influenced by environmental factors as shown by its

increased values in compression wood, decreased values in tension wood

and, often, increased values following nutrient or water supplementation.

Adjacent individual tracheids can show moderate differences in MFA

that may be related to tracheid length, but not to lumen diameter or cell

wall thickness. While there has been strong interest in the MFA of the

properties. Such investigations have been limited by the much greater

difficulty of measuring angles for these wall layers. MFA, in combination

with basic density, shows a strong relationship to longitudinal modulus

of elasticity, and to longitudinal shrinkage, which are the main reasons

for interest in this cell wall property in conifers. In hardwoods, MFA is

of more interest in relation to growth stress and shrinkage behaviour

Key words: Microfibril angle, cellulose microfibrils, X-ray diffraction,

.