Agriculture Reference
In-Depth Information
Wood is a very complex material comprising primarily cellulose and lignin. This is
an important fact in WPC production because cellulose and lignin degrade >190 °C.
There are two significant mass-loss events in the thermogravimetric analysis of
water, with a 5% loss at lower temperature ranges and a possible 70% loss at high
temperature ranges due to the decomposition of cellulose and lignin. These values are
important in the pre-drying of wood flour before mixing with the polymer matrix.
The difficulty of non-satisfactory drying of the wood flour poses problems for WPC
producers when considering the temperature ranges for standard extruder operations.
Hence, a producer of WPC will be making a profile in which the constituent with the
highest weight percentage in a formula is likely to be undergoing thermally induced
decomposition as it enters the extrusion die. Preventing this decomposition (or at
least controlling it adequately) poses a great challenge in WPC extrusion. Common
quality-quality problems for WPC arising from thermal degradation of wood are
distortion of the extruded profile (known as 'dog boning' or 'swelling').
6.1.3 Market Potential for Wood Plastic Composites
WPC have been around for well over 25 years and have been made with various
agricultural wastes (though most are made with wood flour). Thus far, WPC are used
widely in decking, fencing, and outdoor applications. WPC developers and end users are
beginning to realise the great potential that WPC have for wider ranges of applications
and thinking 'outside the box' is greatly helping this cause. One application area for
WPC that is receiving increasing attention is its use within 'road furniture': guard
rails, sound barriers, traffic cones, mileage posts, sign posts, road-lane markers, snow
fences and crash barriers. Research has been initiated to work out the possibilities of
replacing currently used materials in many of these highway applications, particularly
with WPC utilising woody biomass. The relatively low-tech products related to highway
infrastructure could provide better opportunities for utilisation of significant volumes
of biomasses because they are harvested, processed and used locally.
A range of street-furniture products based on WPC utilising recycled wood and
recycled plastics are being marketed by companies in Australia and China and
include: bollards, street signs, park and street benches, tree stakes, bin enclosures,
parking aids, wheel stops, handrails and posts. Other, perhaps more exotic potential
applications being developed include electric-vehicle charging points made from 70%
cellulosic wood fibre and 30% PP being developed in Germany to protect cables, power
outlets and switchgear as replacements for steel. According to reports, the European
Commission in its latest industrial policy has announced six priority areas which
include bio-based products, as well as sustainable construction and raw materials.
A greater potential exists for bio-plastics and bio-based products, particularly if the
plastic content in a WPC were to be biodegradable.
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