The increased amount of plastic bags in our environment lead to discussions about whether or not plastic bags degrade in the short or long term (for example, the 450 year plastic bottle degradation live stream) and how much they harm our environment. Therefore, in the beginning of this year I started a plastic bag degradation experiment, using a piece of simple high density polyethylene (HDPE) bag and sea water.
The motivation – find out when bag degradation starts
For that I took a standard HDPE plastic
bag and cut a 240x160x0.1 mm part out. Then I filled an empty marmalade glass
with sea water right from the beaches of Sesimbra, Portugal (California Beach; close to our holiday rental). Then the glass filled with sea water and the HDPE bag was placed
in a storage room without the influence of sunlight.
 |
| HDPE Plastic Bag Degradation - The Experiment (up: the HDPE bag sample; down left: identification stamp on the bag; down right: glass with bag sample and sea water; start: January 2021; findoutaboutplastics.com). |
It is
a simple experiment and there are several scientific studies dealing with this topic.
One of them is from Mr. Telmo Ojeda [1] who investigated the degradability of
linear polyolefins under natural weathering conditions. Four different polymers
were used for the study: high density polyethylene (HDPE), linear low density
polyethylene (LLDPE), isotactic polypropylene (PP), oxo-biodegradable
HDPE/LLDPE blend (containing a
pro-oxidant additive to accelerate degradation).
They
found out that it took less than a year for polyolefin films, which have low or
no content of antioxidants to degrade by natural weathering. Mechanical
properties got lost due to the decrease in molar mass caused by oxidative
degradation. There are differences in terms of degradation speed of the
investigated polymers. HDPE and LLDPE films showed a more slow degradation, however
this degradation was significantly in a timeframe of few months. Rapid
degradation could be found with PP and oxo-bio HDPE/LLDPE blend. Since
pro-oxidant additives are present in the oxo-bio HDPE/LLDPE blend, acceleration
of degradation was accepted and could be proven. The PP film contained primary (sterically
hindered phenols) and secondary (phosphite) antioxidant additives, which slow
down the degradation process. However, the antioxidant additives, applied in
low concentration, could not prevent the rapid photo-oxidative
degradation. Secondary antioxidant
additives showed little influence to delay the abiotic degradation (photodegradation
and hydrolysis) in HDPE and LLDPE.
The
second study I selected was conducted by Napper and Thompson [2]. The
researchers investigated the degradation of biodegradable, oxo-biodegradable,
compostable, and HDPE bags over 3 years.
All
the materials were exposed to three different environments: open-air, buried in
soil, and immersed in sea water. The sea water has a tremendous impact on the
compostable bag, which disappeared within three months. The same bag material
was still present after 27 month of exposure in soil. However the mechanical
strength was so much reduced that it could not hold weight without cracking.
Interesting result was that all bag materials decompose into fragments after
nine month exposure to open-air.
Governments in different European countries react and made already laws to ban plastic bags. In Austria, for example, plastic bags for shopping are forbidden since 2020. In Austria, the plastic bag consumption sums up to 7000 to 8000 tons per year which represents around 1% of overall waste. Looking at the per head consumption of plastic bags per year, it has a CO2 equivalent of a 15 km passenger car ride [3].
Fact
is that plastic bags should not end up in our oceans nor in our environment in
general. We have a littering problem and not plastic problem. I hope this
conception is changing over the years ahead of us, since plastics are among the most
environmentally friendly materials out there [4,5].
I will
update you in 2022 on the degradation progress of the HDPE plastic bag immersed
in sea water.
Thanks
for reading and #FindOutAboutPlastics!
Greetings,
Herwig
Juster
Literature
[1]
Ojeda et.al., Degradability of linear polyolefins under natural weathering, 2011
[2] I.
E. Napper & R. C. Thompson, Environmental Deterioration of Biodegradable,
Oxo-biodegradable, Compostable, and Conventional Plastic Carrier Bags in the
Sea, Soil, and Open-Air Over a 3-Year Period,(2019)
[3] https://www.nachrichten.at/oberoesterreich/ein-sackerl-statt-einem-debatterl;art4,3159915
[4] https://fortune.com/2019/09/04/dow-ceo-plastic-waste/
[5] Chris DeArmitt - The Plastics Paradox: https://plasticsparadox.com/
