issue 02/2021

Injection Moulding
PLA-WPC for injection moulding
How to disrupt FMCG-Packaging with wood and biopolymers
Using wood-based and fully renewable materials for
fast-moving consumer goods (FMCG) to reduce fossilbased
plastic consumption is the vision that drives
the team behind forewood. For this purpose, they have
developed a technology that enables WPC to be injection
moulded into thin-walled, complex packaging applications.
Wood-plastic composites, better known as WPC, is a wellknown
class of materials for various purposes. In their first
generation, they are used to manufacture extrusion profiles,
such as decking or window frames. Further developments
enable the use of WPC in injection moulding for large parts,
such as furniture. The original idea for WPC was primarily
based on economic considerations: non-cutting processing
makes it possible to manufacture products with a wooden
look much more cost-effectively. Accordingly, WPC products
were comparatively simple and did not need to meet any
special technical requirements. With the growing interest
in sustainability and environmental protection, the material
class WPC is also experiencing a revival. With the use of
wood flour as a filler, it is already possible to partially
replace fossil resources with renewable raw
materials without compromising the
known properties. The upcoming
generation of WPC combines
technical wood fibres with
bioplastics to generate up to
100 % biobased materials.
Forewood uses wood
fibres embedded in a
polymer matrix fully made
of biopolymers, such as
polylactic acid (PLA). Using
wood fibres instead of wood
flour improves the mechanical
properties of the composite.
The completely biobased and
biodegradable material consists
of more than 50 % wood and is
suitable for producing everyday products via injection
moulding. However, the successful processing of forewood
in injection moulding is significantly more challenging
than conventional plastics. The fundamental challenge
in processing WPC lies in the contrasting properties of
the two materials it contains. While wood is subject to
thermal decomposition at high temperatures, sufficiently
high temperatures are necessary for the melting process
of the involved polymer. This trade-off results in a narrow
processing window for forewood. There is a sweet spot
of process stability that requires a high level of control
over all processes involved. Processing temperatures
must be relatively low to produce high-quality products.
Otherwise, the appearance and the mechanical properties
of the product suffer, as the wood fibres’ advantages get
lost through thermal decomposition. Too high processing
temperatures also result in organoleptic changes to the
material. In addition to the injection moulding process, the
accompanying process steps are also specially designed for
forewood. The hydrophilic wood fibres require appropriate
pre-treatment to ensure a low residual moisture content.
The abrasive effect of the wood fibres influences the design
of the mould and injection unit. The selection and control of
these parameters and the overall process coordination are
crucial for high product quality.
With the rezemo wooden coffee capsule launched in 2018,
the basic feasibility, marketability, and customer acceptance
of FMCG made from forewood was proven. In this lighthouse
project, forewood fulfils several specific requirements.
The material complies with the food standard according
to EU No. 10/2011, has very good sealing properties, and
a sufficient barrier against oxygen. Permeation tests show
that a coffee shelf life of more than nine months is feasible.
Due to the wood fibres, higher stiffness and thermal stability
are achievable with forewood compared to pure PLA. As a
result, high strengths can be achieved even with low layer
thicknesses. In
concrete
terms:
20 bioplastics MAGAZINE [02/21] Vol. 16