Issue 04/2023

56 bioplastics MAGAZINE [04/23] Vol. 18
Basics
Overcoming challenges in PHA
injection moulding
The plastics industry is increasingly aware of the need
to reduce the environmental impact of traditional
plastics and embrace more eco-friendly alternatives.
Biodegradable biopolymers, like PHAs, offer a promising
solution, but their unique properties pose challenges in the
injection moulding process. This article shall explore four
common challenges and how to overcome them.
Thermal Degradation:
PHAs have a limited processing window between their
thermal degradation and melting temperatures, making
them sensitive to temperature and residence time.
To address this, fine-tune the control (PID) settings for the
extruder and mould heating controller and reduce idle time
to a minimum. Additionally, be mindful of shear forces during
transportation from the extruder to the mould cavity by using
mould constructions that lower shear. Employ a tuned hot
runner for successful material transfer. Having experienced
operators is crucial to identifying and addressing visual
degradation or defects promptly.
Melt Flow and Crystallinity
Optimising melt parameters is vital for creating highquality
PHA products. Higher melt flow helps fill voids in the
mould cavity, but achieving the right balance of crystallinity is
essential. Some applications require partial crystallisation in
the mould, which necessitates higher mould temperatures.
However, excessive crystallinity can increase brittleness.
Finding the optimal strength and flexibility for the finished
part will involve trial and error based on the specific resin.
Consider using non-stick coatings on mould cavities to avoid
parts sticking to the mould.
Drying Process
Proper drying of PHAs is crucial since they can hold up to
1 % moisture when saturated, leading to further degradation.
The ideal processing moisture content is below 500 ppm.
Ensure to dry the resin above 70°C for at least four hours,
and use a calibrated moisture analyser to confirm it’s within
the processing window.
Purging
Adequate purging is vital during PHA processing. When
the material sits idle in the barrel or hot runner, degraded
material can build up. Choose an appropriate purge resin
with a melt flow and melting temperature that closely match
the PHA to cleanse degraded material and carbon deposits.
Skilled operators who can recognise these limitations will
minimise downtime and reduce waste.
Bioplastics, especially PHAs, hold great promise for a
sustainable future. It can be very tempting to mix PHA’s with
other biopolymers or even traditional polymers to broaden
processing windows. However, there is a great risk to
compromising their natural ability to be fully biodegradable or
even compostable. Generating or shedding toxic microplastic
that can harm the environment needs to be considered. And
the author strongly discourages the temptation to produce
products aimed at greenwashing exercises.
As more companies and consumers prioritise eco-friendly
products, PHAs and other bioplastics will become increasingly
important. To stay ahead of the curve, manufacturers should
embrace these materials and tackle their unique challenges.
Beyond Plastic takes pride in its 75+ years of combined
experience in various injection moulding processes.
And they are dedicated to creating a more sustainable
future by offering custom compounded alternatives to
conventional plastics using PHA.
www.beyondplastic.com
By:
Fred Pinczuk, CTO
Beyond Plastic
Commerce,
CA, USA