Introduction

The progress of mankind from the earliest days of
the eolithic age tothe present days of nuclearage can
be closely associated with a great deal of dependence
on wood.
The primitive man who lived in dense forests used
woodfor shelter,fuel, weapons and tools. In due course
of time, wood came to be used as a major structural
material for the construction of boats,vehicles and bridges.

Later when ores of metals were discovered, wood was
still needed as a fuel forsmelting the ores and for
working metals. The phenomenaladvances made
by manin the field of science and technology have made
available to him numerous materials for a multitude
of diverse and sophisticated requirements.Among them
wood still retains a prominent place not only in its natural
form, but also in a variety of scientificallymodified forms.
Wood and wood based products including paper, films and
other wood pulp products constitute the mainstay of our
civilised life.
Wood being a renewable resource,it does make sense not
only in continuing but also in increasing our dependence
on wood inpreference to othernon-renewable resources.

Wood, however,has certain limitations imposed by its
composition and structure.It is made up of fibres oriented
in one direction and,therefore, has most of its strength and
stiffness distributed in that direction. As a result
wood tends to crack and split easily along the direction
of the fibres. Secondly, wood is made up of hygroscopic
substance and therefore tends to absorb and give up moisture
from and into the surrounding air simultaneously undergoing
dimensional changes.On account of the anisotropic nature of
wood such moisture induced dimensional changes are
non-uniform, leading to warping and cracking.

Limitations as a Sheet Material

Wood is traditionally used in building construction
and other structural applications, in furniture and
in building interiors,essentially in two forms:

(a) As “structural lumber” e.g. beams, rafters, battens etc.

(b) As “panels” or sheet materials.

The disadvantages arising from the composition and
structure of wood becomes critical when it is used in
the form of “panels” on account of the high surface area
to volume ratio.

A wide range of reconstituted panel products like
Plywood, Blockboard, Particle Board, Medium
Density Fibreboard (MDF), have therefore, been developed
by the wood panel industry as superior substitutes to solid
timber panels, in terms of dimensionalstability and
resistance to splitting and cracking.