New Aspects of Cellulose Acetate

Biodegradation Dirk HÖLTER, Philippe LAPERSONNE

ST 13

09.10.2017

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Cellulose acetate is biodegradable – or not?

CORESTA SSPT 2017 – ST 13 2

… cellulose acetate, a non-biodegradable plastic …

… non-biodegradable cellulose acetate filters …

Contrary to popular belief, cigarette butts are NOT biodegradable!

C. Curtis et al., Tobacco Control (2016) 0, 1–5

WHO 2017, Tobacco and its environmental impact: an overview

http://www.no-smoke.org

Depending upon the degree of substitution cellulose acetate

can be biodegradable http://opensourceecology.org/wiki/Cellulose_acetate

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What means “Biodegradable”?

• UN definition (1997)

“matter capable of decomposing rapidly under natural conditions”

• Wikipedia (09/2017)

“is the disintegration of materials by bacteria, fungi, or other biological means”

• IUPAC recommendation (2012)

“Qualifier for a substance or device that undergoes biodegradation (= degradation

caused by enzymatic process resulting from the action of cells)”

CORESTA SSPT 2017 – ST 13 3

There is no universal definition of “biodegradable”

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Almost common sense:

biodegradation has to result in CO2 (CH4), H2O and biomass (+ N2 and salts)

but what’s about:

• environmental conditions

• indicator for biodegradation

• the form of the tested samples

• passing criteria for biodegradability

CORESTA SSPT 2017 – ST 13 4

No evaluation of biodegradability without defined frame conditions

→ standardized test conditions

defined in standards or

certification schemes

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CORESTA SSPT 2017 – ST 13 5

General Process (simplified):

1. microbes (bacterias and fungi) colonize the surface of the

material → biofilm formation1

2. enzymes from the microbes attack the material

3. material is transformed into CO2 (anaerob also CH4), water and

biomass (+ N2 and salts)

→ the process can be supported by abiotic degradation2, e.g.

photo degradation or hydrolysis

How does biodegradation of a polymer material work?

1H.-C. Flemming, Polym. Degrad. Stab. (1998) 59, 309-315 2N. Lucas, Chemosphere (2008) 19, 429-442

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CORESTA SSPT 2017 – ST 13 6

Biofilm formation, „deacetylating“ microbes are rate determing

Synergistic degradation including deactylation and cellulose breakdown

Cellulose acetate with degree of substitution (DS) ~ 2.5

Cellulose

Cellulose

Acetate

The special thing about cellulose acetate

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CORESTA SSPT 2017 – ST 13 7

External Parameters influencing biodegradation performance:

• general kind of environment (soil, water, compost …)

• present microbes and their numbers

• local conditions like humidity, temperature, pH, nutrients …

What are enviromental conditions?

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CORESTA SSPT 2017 – ST 13 8

Degradation tests on the following slides

• were performed with Cellulose Acetate having a DS of ~2.5 like it is used

for filter tow production

• the tests were made on our behalf by the internationally acknowledged lab

OWS (Organic Waste Systems, Belgium)

Biodegradation tests

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CORESTA SSPT 2017 – ST 13 9

Cellulose acetate filter rods degrade very well under anaerobic conditions, even within the average retention time of an anaerobic digester of a biogasification plant

according to ISO 15985/ ASTM D.5511-12

at mesophilic conditions (37 +/- 2 °C)

(indicator: biogas release – CO2/CH4)

biogas plant landfill

Biodegradation in anaerobic conditions

Cellulose (powder)

Smoked

cigarette butts

Cellulose Acetate filter rods

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CORESTA SSPT 2017 – ST 13 10

Biodegradation in Water

Cellulose (powder)

Cellulose Acetate

(milled fibers) Cellulose Acetate

(milled fibers)

Cellulose acetate degrades in water, but shows a high variability even under very same conditions.

according to ISO 14851

(indicator: oxygen consumption)

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CORESTA SSPT 2017 – ST 13 11

Shorter lag phase and less variation between replicates with pre-exposed water, demonstrates the influence of the microbial composition at beginning of the test (probably more deacetylating microbes present)

Biodegradation with Pre-exposed Water

Cellulose (powder)

Cellulose Acetate

(milled fibres)

according to ISO 14851

(indicator: oxygen consumption)

→ Addition of 4% of water from former degradation test with cellulose acetate

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CORESTA SSPT 2017 – ST 13 12

Biodegradation in Marine Water

Cellulose (powder)

Cellulose Acetate

(milled fibres)

according to ASTM D.6691

(indicator: oxygen consumption)

Cellulose acetate is degradable in marine water, we found reduced variation between replicates compared to tests in water

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CORESTA SSPT 2017 – ST 13 13

Biodegradation in Soil

Cellulose (powder)

Cellulose acetate is also biodegradable in soil, can require several years depending on conditions

Cellulose Acetate

(milled fibres)

according to ISO 17556

(indicator: oxygen consumption)

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• the general compostability under industrial conditions (> 50 °C) was

reported in literature3 and also found in own tests in the past

• usually the cycle time of an industrial composting plant is too short for

full disintegration and degradation of filter tow or filters made thereof

• probably hydrolysis plays a more important role in composting,

compared to other environments

CORESTA SSPT 2017 – ST 13 14

Biodegradation in Industrial Compost

3J. Puls, Steven A. Wilson, Dirk Hölter „Degradation of Cellulose Acetate-Based Materials: A Review“, J. Polym. Environ,

(2001) 19, 152-165

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• Paper/Viscose

→ consist predominantly of cellulose, readily biodegradable in most environments

• PLA (polylactic acid)

→ at temperatures < 50 °C standard types biodegrade by far slower than cellulose acetate4, degrades better in industrial composting

• Polypropylene

→ extremely slow degradation, can last centuries, seen as non-biodegradable

CORESTA SSPT 2017 – ST 13 15

How does cellulose acetate compared to other materials?

• the biodegradability of cellulose acetate is closer to cellulose than to most other polymer materials including PLA

• but somewhat too slow to receive acknowledged certificates on biodegradability (e.g. from Vinçotte)

4J. J. Kolstad et al., Polym. Degrad. Stab. (2012) 97, 1131-1141

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16

Different strategies for acceleration have been discussed like

• increase of material surface

• decreasing degree of acetylation

• adding hydrolyzing agents

• adding enzymes or microbes

• adding nutrients microbes

• adding biodegradable softeners

CORESTA SSPT 2017 – ST 13

Can biodegradability be improved?

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17 CORESTA SSPT 2017 – ST 13

Successful route to accelerated biodegradation?

Test in water Test in marine water

Cellulose Cellulose

Cellulose

acetate

Cellulose

acetate

Cellulose acetate

with additive

Cellulose acetate

with additive

• in own tests significant improvement could be achieved improvement by

incorporation of slightly alkaline metal oxides into the cellulose acetate matrix

• requirements for external certifications could be met

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Conclusion

• cellulose acetate as it is used in cigarette filters proved to be biodegradable in all microbially active model environments including marine water

• cellulose acetate shows higher variations of test results compared to other materials, probably caused by necessity of biofilm formation of at least two different kind of microbes

• biodegradation is mostly too slow to fulfill requirements of standards or certificates

• biodegradation can be significantly accelerated by incorporation of additives like slightly alkaline metal oxides into the cellulose acetate matrix in order to meet certification/standard requirements

CORESTA SSPT 2017 – ST 13 18

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www.rhodia-acetow.com

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