Biodeterioration-tests on wood/plastic composites - CHIMICA OGGI ...

patterns when feeding in groups using all resources to the
maximum (8). Although some preferences for certain wood
species may occur (9-11), all cellulose containing material can
be used as food and energy sources. Termites, therefore, feed
on any wooden material.
As termites, especially subterranean termites, search for
food, they may penetrate and damage many noncellulose
materials as well, including plastics, even if these do not
serve as food source and can not be digested (12). The
sharp mouth parts of worker termites can abrade or break
apart virtually any material and the high
reproductive rate in termites instantly replaces
workers with blunt mandibles.
It is therefore not surprising that most plastics
failed in <strong>tests</strong> for resistance to termites (13-
16). Nevertheless, differences exist between
different plastics and their susceptibility to
termite attack. Condensation-plastics like
polyesters appear more resistant than additionplastics
like polyethylene, polystyrene and
polyurethane (13). However, it is not only the
mechanical hardness of plastics that characterises
durability against termite attack, the surface
structure is just as important. Smooth, even
levelled surfaces, are more likely to prevent
termite attack, but the smallest cracks and
crevices or ruffled surfaces and edges provide
immediate access for termite mandibles. The
same holds true for WPCs. Once the surface
is broken, destruction is only a matter of time
and termite population density, unless the
material is protected by either an effective
termiticide or a repellent that prevents continuous
feeding. Although it was shown that drywood
termites are capable of attacking plastics (13),
it is considered unlikely that this group of
Wood/plastic
composites (WPC) are a
fairly new category of
materials on the market.
The authors point out
biological procedures to
characterise and specify
different WPC-materials.
While moisture is
essential for growths
of algae and fungi,
termites can also attack
dry materials.
Whether biocides
are needed for
protection of a materials
depends
on the environment
it will be exposed to
during its use.
termites would infest plastics to establish colonies as they do
in pure wooden structures. For WPCs this still needs to be
demonstrated.
USE CLASSES FOR WOODEN MATERIALS
Before deciding on measures to protect the WPC it is important
to decide where the material has to perform and to what
environment it will be exposed. In the field of wood protection,
the definition of use classes (former hazard
classes) was found to be useful and could now
also be applied to identify the intended use for
WPC-materials (17, 18). These use classes
cover the following general service situations:
Use class 1 for interior and covered, use class
2 for interior and not covered, use class 3 for
exterior above ground, use class 4 for exterior
in the ground or fresh water and use class 5
for use in salt water. Some minor subdivisions
in the use classes may occur.
TESTING OF WPCS FOR BIOLOGICAL
DURABILITY
In Europe, CEN with its Technical Committee
249, Working Group 13, has been working on
laboratory methods to characterise WPCs since
2003. Chapter 8.6 of the technical specification
TS 15534-1released in 2006, “Resistance against
biological agents” (19), deals with the different
forms of microbiological decay (Annex C: termites,
Annex D: wood destroying basidiomycetes,
Annex E: soft rotting micro-fungi, Annex F:
discolouring micro-fungi and algae).
Biocides