JEC COMPOSITES MAGAZINE - Issue #110 - January/February 2017 - 25

WPC MANUFACTURlNG

Formula and tooling considerations for
manufacturing with wood-plastic composites

TONY SIMPSON
Board of Directors.
Green Dot Bioplastics

esigning and manufacturing products
based on a wood-plastic composite is a
remarkably similar process to working
with traditional plastics. There are some additional variables, though, that designers and
manufacturers should be aware of when such
a material is being selected for a product. For
manufacturers, understanding the effects of
different ratios and tooling configurations on
the process will help ensure a smooth project
from start to finish.
Effect on behaviour
The ratio of wood to plastic in the chosen
formula of a wood-plastic composite will

Organic materials such as starch and natural fibres act as substitutes for petroleum-based feedstock and reduce the amount of
greenhouse gas emissions associated with plastics production.
Biobased plastic resins can be made to behave similarly to traditional plastics in the manufacturing phase and preserve much of the
look and feel of purely petroleum-based plastics.

have some effect on its behaviour as it goes
through the production process. The percentage of wood present in the composite
has an effect on the melt flow index (MFI),
for example. As a rule, the more wood that is
added to the composite, the lower the MFI.
The percentage of wood will also have a bearing on the strength and stiffness of the final
product. Generally speaking, the more wood
that's added, the stiffer the product becomes.
Wood can make up as much as 70% of the total wood-plastic composite, but the resulting
stiffness comes at the expense of the ductility
of the final product, to the point where it may
even risk becoming brittle.
Higher concentrations of wood also shorten
machine cycle times by adding an element
of dimensional stability to the wood-plas-

tic composite as it cools in the mould. This
structural reinforcement allows the plastic to
be removed at a higher temperature than a
conventional plastic. At temperatures where
conventional plastics are still too soft to be removed from their moulds, composites made
with wood can successfully be ejected.
A relatively easy transition
If the product will be manufactured using existing tools, the gate size and general shape of
the moulding should factor into the discussion of optimal wood particle size. A smaller
particle will likely better serve tooling with
small gates and narrow extensions. If other
factors have already led designers to settle
on a larger wood particle size, then it may be
beneficial to redesign the existing tooling accordingly. But, given the existing options for
different particle sizes, this outcome should
be completely avoidable.
In general, the tooling considerations when
working with wood-plastic composites are
more or less the same as when working with
conventional plastics. Even when changes are
necessary, they can often be made as modifications to existing tooling, rather than fromscratch reboots. This compatibility makes
beginning to work with wood-plastic composites a relatively easy transition.

These wood-plastic composites blend fine wood particles with renewable, biodegradable, reclaimed, recycled,or virgin plastic materials to make firm, smooth pellets for convenient handling and further processing

No110 January-February 2017

More information
www.greendotbioplastics.com

/ jec composites magazine

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Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #110 - January/February 2017