New Aspects of Cellulose Acetate Biodegradation

Transcription

1 New Aspects of Cellulose Acetate Biodegradation Dirk HÖLTER, Philippe LAPERSONNE ST 13

2 Cellulose acetate is biodegradable or not? cellulose acetate, a non-biodegradable plastic C. Curtis et al., Tobacco Control (2016) 0, 1 5 non-biodegradable cellulose acetate filters 2 WHO 2017, Tobacco and its environmental impact: an overview Contrary to popular belief, cigarette butts are NOT biodegradable! Depending upon the degree of substitution cellulose acetate can be biodegradable

3 What means Biodegradable? There is no universal definition of 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) 3

4 No evaluation of biodegradability without defined frame conditions Almost common sense: biodegradation has to result in CO 2 (CH 4 ), H 2 O and biomass (+ N 2 and salts) but what s about: environmental conditions indicator for biodegradation the form of the tested samples passing criteria for biodegradability 4 standardized test conditions defined in standards or certification schemes

5 How does biodegradation of a polymer material work? General Process (simplified): 1. microbes (bacterias and fungi) colonize the surface of the material biofilm formation 1 2. enzymes from the microbes attack the material 3. material is transformed into CO 2 (anaerob also CH 4 ), water and biomass (+ N 2 and salts) the process can be supported by abiotic degradation 2, e.g. photo degradation or hydrolysis 5 1 H.-C. Flemming, Polym. Degrad. Stab. (1998) 59, N. Lucas, Chemosphere (2008) 19,

6 The special thing about cellulose acetate Cellulose Biofilm formation, deacetylating microbes are rate determing 6 Cellulose Acetate Synergistic degradation including deactylation and cellulose breakdown Cellulose acetate with degree of substitution (DS) ~ 2.5

7 What are enviromental conditions? External Parameters influencing biodegradation performance: general kind of environment (soil, water, compost ) present microbes and their numbers local conditions like humidity, temperature, ph, nutrients 7

8 Biodegradation tests 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) 8

9 Biodegradation in anaerobic conditions Cellulose (powder) Cellulose Acetate filter rods biogas plant landfill Cellulose acetate filter rods degrade very well under anaerobic conditions, even within the average retention time of an anaerobic digester of a biogasification plant 9 Smoked cigarette butts according to ISO 15985/ ASTM D at mesophilic conditions (37 +/- 2 C) (indicator: biogas release CO 2 /CH 4 )

10 Biodegradation in Water Cellulose (powder) 10 Cellulose Acetate (milled fibers) Cellulose Acetate (milled fibers) according to ISO (indicator: oxygen consumption) Cellulose acetate degrades in water, but shows a high variability even under very same conditions.

11 Biodegradation with Pre-exposed Water Cellulose (powder) Addition of 4% of water from former degradation test with cellulose acetate 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) Cellulose Acetate (milled fibres) according to ISO (indicator: oxygen consumption)

12 Biodegradation in Marine Water Cellulose (powder) 12 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

13 Biodegradation in Soil Cellulose (powder) 13 Cellulose acetate is also biodegradable in soil, can require several years depending on conditions Cellulose Acetate (milled fibres) according to ISO (indicator: oxygen consumption)

14 Biodegradation in Industrial Compost the general compostability under industrial conditions (> 50 C) was reported in literature 3 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 3 J. Puls, Steven A. Wilson, Dirk Hölter Degradation of Cellulose Acetate-Based Materials: A Review, J. Polym. Environ, (2001) 19,

15 How does cellulose acetate compared to other materials? 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 acetate 4, degrades better in industrial composting Polypropylene extremely slow degradation, can last centuries, seen as non-biodegradable 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) 15 4 J. J. Kolstad et al., Polym. Degrad. Stab. (2012) 97,

16 Can biodegradability be improved? 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 16

17 Successful route to accelerated biodegradation? 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 Test in water Cellulose 17 Cellulose acetate with additive Cellulose acetate Test in marine water Cellulose Cellulose acetate with additive Cellulose acetate

18 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 18

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