This document discusses the degradation of plastics over time. It examines research on the breakdown of various plastic materials, such as polyethylene bottles and polystyrene cups, when exposed to different environmental conditions like weather, sediment, and heat over periods of 2 years. The research found that plastic type and environment significantly impact degradation rates, with thermal aging causing faster breakdown than weather or water exposure. Most plastics showed chemical changes within 24 months, with polyurethane breaking down most quickly. Cigarette butts were also examined and found to degrade into paper and acetic acid. Understanding plastic degradation can help address the global pollution problem.

1. Plastalderen smuldrer
Yvonne Shashoua, Forskningsprofessor

2. I love realism. I don't like plastics - Michael Jackson, 1982
Plastic artefacts will be the most important witnesses to our
time- Biefer and Zgraggen, 1991
1920 1960 2015
2015 2018
1970
2021

3. ▪ what are plastics, chemically speaking?
▪ why do plastics break down and how are
their lifetimes measured?
▪ can research into degradation of heritage
plastics help us better understand plastic
pollution?
▪ and find solutions?

4. 1862-1940s :Semi- synthetic plastics
cellulose + nitric acid cellulose nitrate
(sustainable source)

5. 1920:cellulose acetate replaced
cellulose nitrate

6. ingredients for making cellulose acetate
+
triphenyl
phosphate-
fire retardant
+
diethyl
phthalate-
plasticizer
cellulose acetic
acid
+

7. 1945 – today: production of synthetic
plastics
plasticizers
antiageing
additives,
lubricants
colour
+

9. how long do plastics last?
hint: the first synthetic plastic is 70 years old
*based on predictions and modeling

10. 20 years
loss of original significance of cultural heritage
loss of function of product during use
loss of physical integrity after use-microplastics
2 years
1 year

12. plastics industry uses accelerated ageing to
test products within a convenient period
Q10 = 2 - rate of reaction doubles for every 10°C increase in temperature

13. darkening of PVC tubing
at 70°C over 4 months
new 1 month 2months 3 months 4 months
Physical bonding of plasticizers ( )
to PVC polymer
+

14. polyethylene fishing box absorbs
plasticizer from PVC worm in real time

15. rubber balloons from 1981-
oxidized to crumbs 1990

16. • how long does
plastic litter take to
degrade to
microplastics
(smaller than 5mm)?
• can all plastics form
microplastics?
• which environments
promote
microplastics?

17. Single Use Plastics studied since 2019
• LDPE bottles
• PP salad boxes
• PS cups /lids
• PVC tubing
• nylon strips
• PET cups
• natural rubber
cycle tyres
• PLA cups
petroleum-based new-generation
• polyurethane ether
sponges

18. accelerated thermal ageing
24 months at 70⁰C = ca. 50 years at 20⁰C
LDPE
PP
PS
PS
PVC
PET
PUR ether
PLA
formed MPs after 15 months
formed MPs after 16 months
PLA

19. plastics threaded on polypropylene ropes

20. Danish weather
dataloggers monitor
temperature, light levels and
oxygen
PUR foam yellowed
rubber tyre crazed
new
24 months

21. underwater and in sediment in Lynæs Havn
new after 24 months

22. after exposure for 12 months
in sediment 128cm below surface 90cm below surface
increasing oxygen
increasing light
increasing degradation

23. measure fragment dimensions (MP ≤ 5mm)
PP salad
boxes in
Danish
weather for 24
months
In oven at
70°C for 24
months

24. FTIR spectroscopy to examine changes in
chemical structure on ageing
new C=O group forms
in polystyrene after 2
years

25. new Danish weather
underwater 70°C

26. new Danish weather
70°C
underwater

27. 730 days Danish Weather
730 days heat aging
TDI
isomers
loss of flame retardant
GC-MS examines additives and degradation products
loss of antioxidant

28. polyurethane ether foam
new 4 weeks/70°C 21 days ultraviolet
Ethereal body by
Claus Carstensen
1986 2013

29. new heat light

30. ▪plastic type, colour and environment are significant factors for
rate of degradation
▪degradation in environments:
thermal ageing (70°C) >Danish weather > surface seawater >
under seawater >sediment
▪ PLA, PUR foam,PVC, PE, PS, PET and rubber showed chemical
degradation within 24 months
▪polyurethane sponges least stable
▪polyester and nylon are the most stable
Results

31. Skodprojektet
cigarette butts are the greatest source of
plastic pollution in Denmark
ca. 8 million butts on Danish streets daily
it costs 2kr per cigarette butt to clean up!
they contain water-soluble toxins

32. what are cigarette filters?
• filters for particles and tar from tobacco
• cellulose acetate fibres wrapped in a brown
paper

33. cellulose acetate produces acetic acid
and eventually becomes paper again
degradation rate doubles at pH 4

34. cigarette butts exposed to 8 environments
earth
air
seawater
pH 2
tap water
pH 7
soap water
pH 12
freezer
-20°C oven
70°C

35.  all plastics degrade
 it is essential to understand the causes
and rates of their degradation
 museums are a unique source of
knowledge and experience because we
preserve everything-including plastics!
 research into plastics in cultural heritage
can be transferred directly to plastics
pollution

36. I am grateful to
the Velux
Foundation and
KrogagerFonden
for their financial
support