Issue 03/2016
bioplasticsMAGAZINE_1603
bioplasticsMAGAZINE_1603
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Injection moulding molding<br />
By:<br />
Mike Parker<br />
Product Development Manager<br />
GreenDot<br />
Cottonwood Falls, Kansas, USA<br />
Wood-plastic composites are also compatible with<br />
foaming agents, for example. The addition of these<br />
foaming agents can create a balsa-like material.<br />
This is a useful property when the finished product<br />
needs to be especially lightweight or buoyant. For the<br />
purpose of the injection molder though, this is yet<br />
another example of how the diversifying composition<br />
of wood-plastic composites may lead to there being<br />
more to consider than when these materials first<br />
came to market.<br />
Processing temperatures are one area where woodplastic<br />
composites differ significantly from conventional<br />
plastics. Wood-plastic composites generally process<br />
in temperatures around 10 K lower than the same,<br />
unfilled material. Most wood additives will begin to<br />
burn at around 200 °C.<br />
Shearing is one of the most common issues to<br />
arise when processing wood-plastic composites.<br />
When pushing a material that’s too hot through too<br />
small a gate, the increased friction has a tendency to<br />
burn the wood and leads to telltale streaking and can<br />
ultimately degrade the plastic. This problem can be<br />
avoided by running wood-plastic composites at a lower<br />
temperature, ensuring the gate size is adequate and<br />
removing any unnecessary turns or right angles along<br />
the processing pathway.<br />
An injection molding standard<br />
Wood-plastic composites aren’t just for decking<br />
anymore. They are being optimized for injection<br />
molding, which is opening them up to a vast array of<br />
new product applications, from furniture to car parts.<br />
The wide range of formulations now available can<br />
enhance the benefits of these materials in terms of<br />
sustainability, aesthetic diversity and features such<br />
as buoyancy or rigidity. Demand for these materials<br />
will only increase as these perks become better<br />
known.<br />
For injection molders, this means a number of<br />
variables specific to each formulation that must be<br />
accounted for. But it also means molders should<br />
expect a product that’s better suited to injection<br />
molding than feedstock that was designated primarily<br />
to be extruded into boards. As these materials<br />
continue to develop, injection molders should raise<br />
their standards for the characteristics they expect<br />
to see in the composite materials delivered by their<br />
suppliers.<br />
www.greendotpure.com<br />
bioplastics MAGAZINE [<strong>03</strong>/16] Vol. 11 21