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Biodegradation of compostable polymer materials under real conditions
Chapter 7
Biodegradation of compostable polymer materials under real conditions Chapter Outline References253
The current wide diffusion of compostable polymers has focused the attention on the allocation of compostable polymers for the direct recycling in composting processes [1–3]. Actually, the acknowledged current methods to estimate the biodegradability are mainly based on laboratory tests and measurements under controlled conditions, while scarce information are available on the effective transformation of compostable polymers in real composting facilities. The biodegradability validation criteria under composting conditions, such as the threshold percentage of biodegradation and disintegration, the time and temperature, and the ecotoxicity are described in the main norms and standard testing methods [3]. Commercial or municipal composting is a large scale operation, which generally employs turning and active aeration, except for static pile and some in-vessel composting systems. Since waste materials have different characteristics, operational parameters such as moving, mixing, and manipulation differ [1]. The material suitable for composting must meet certain quality criteria, such as compatibility with the composting process, displaying no negative effect on the quality of compost, and leaving no visible, distinguishable or toxic residues. In particular, the rate and extent of decomposition of the waste is a crucial factor in disposing of a biodegradable waste in industrial composting units. Currently, researchers are demonstrating that compostable packages can be composted in facilities that handle yard waste and manure as well as in those that handle food wastes. Therefore, more options to compost biodegradable polymers could be available if compostable polymers used in packaging applications were accepted by these compost facilities. The commercially available compostable products, made from PLA, sugarcane, or corn starch, biodegraded while in a commercial compost facility with other common yard waste compostable items [4]. Biodegradation of samples of a plate made from sugarcane, a tray made from potato-starch, a trash bag made Compostable Polymer Materials. https://doi.org/10.1016/B978-0-08-099438-3.00007-0 Copyright © 2019 Elsevier Ltd. All rights reserved.
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240 Compostable Polymer Materials
from corn starch, and a cup, fork, knife, straw, and clear clamshell container made from Nature-Works polylactic acid (PLA) was measured by disintegration studies over 20 weeks. The positive control materials included cellulose filter paper, Kraft paper and Avicell micro-cellulose. The PLA container, PLA cup, and PLA knife degraded at a similar rate as the Avicel cellulose control and were degraded completely in 7 weeks. The corn starch-based Biobag trash bag and sugarcane plate degraded at a similar rate as the Kraft paper control. The three materials degraded between 80% and 90% after 20 weeks. Three PLA packages, a bottle, a tray, and a deli container, were used to determine the degradation process under ambient exposure and under compost conditions [5]. The degradation of the PLA containers was monitored by visual inspection, GPC, DSC, and TGA. PLA trays and deli containers degraded before 30 days under composting conditions (T > 55 °C, >65% RH, pH ∼7.5). First order degradation kinetics was observed for the bottle and tray. A glass transition Tg reduction of 1 °C/day was found for PLA containers with 96% l-lactide, and a Tg average reduction of around 0.6 °C/day was found for PLA containers with 94% l-lactide. A method to study the compostability of biodegradable packages under real compost conditions has been outlined. The degradation of two commercially available biodegradable packages made of PLA was investigated and compared under real compost conditions and under ambient exposure, using visual inspection, gel permeation chromatography, differential scanning calorimetry and thermogravimetry analysis [6]. PLA bottles made of 96% l-lactide exhibited lower degradation than PLA delicatessen containers made of 94% l-lactide, mainly due to their highly ordered structure and therefore their higher crystallinity. Temperature, relative humidity and pH of the compost pile played an important role in the rate of degradation of the packages. PLA deli containers degraded in 30 days under composting conditions (temperature 60 °C, relative humidity (RH) 65%, pH 7.5). The biodegradation performance of polylactide (PLA) bottles under simulated composting conditions according to ASTM and ISO standards, and these results are compared with a novel method of evaluating package biodegradation in real composting conditions [7]. Two simulated composting methods were used in this study to assess biodegradability of PLA bottles: (a) a cumulative measurement respirometric (CMR) system and (b) a gravimetric measurement respirometric (GMR) system. Both CMR and GMR systems showed similar trends of biodegradation for PLA bottles and at the end of the 58th day the mineralization was 84.270.9% and 77.8710.4%, respectively. PLA bottle biodegradation in real composting conditions was correlated to their breakdown and variation in molecular weight. Molecular weight of 4100 Da was obtained for PLA bottles in real composting conditions on the 30th day (Figs 7.1 and 7.2). Study on the biodegradation behaviour of prototype packaging thermoformed from PLA-extruded film and plain PLA film under industrial composting conditions was performed [8]. Hydrolytic degradation in water was conducted for reference. The effects of composting duration on changes in molar mass, glass
Biodegradation of compostable polymer materials Chapter | 7 241
FIG. 7.1 Variation in molecular weight (●) and PDI (■) for PLA bottles in real composting conditions. (Reprinted from Kale G, Auras R, Singh S, Narayan R. Biodegradability of polylactide bottles in real and stimulated composting conditions. Polym Test 2007;26:1049.)
FIG. 7.2 Comparison of variation in molecular weight (■) due to biodegradation and percentage mineralization values for PLA bottles in CMR (●) and MODA (○) systems. (Reprinted from Kale G, Auras R, Singh S, Narayan R. Biodegradability of polylactide bottles in real and stimulated composting conditions. Polym Test 2007;26:1049.)
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FIG. 7.3 Change [%] in weight average molar mass of PLA product during incubation in a container and the composting pile. (Reprinted from Musioł M, Sikorska W, Adamus G, Janeczek H, Richert J, Malinowski R, Jiang G, Kowalczuk M. Forensic engineering of advanced polymeric materials. Part III – biodegradation of thermoformed rigid PLA packaging under industrial composting conditions. Waste Manag 2016;52:69.)
transition temperature and degree of crystallinity of the polymeric material were monitored using gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). The chemical structure of water soluble degradation products of the polymeric material was determined using nuclear magnetic resonance (NMR) and electrospray ionization mass spectrometry (ESI-MS). The results showed that the biodegradation process was less dependent on the thermoforming process of PLA and more dependent on the composting/ degradation conditions that were applied (Fig.7.3). The increase in the dispersity index, leading to the bimodal molar mass distribution profile, suggested an autocatalytic hydrolysis effect at the early stage of the composting process, during which the bulk hydrolysis mechanism dominantly operates. Both the prototype PLA-packaging and PLA rigid film samples were shown to have a gradual increase in opacity due to an increase in the degree of crystallinity. The biodegradability of poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) containing 3 mol% hydroxyvalerate (HV) was tested under composting conditions on both a pilot and a laboratory scale [9]. In the pilot-scale composting conditions, parameters such as pH value, temperature and the amounts of oxygen and CO2 produced were determined periodically. It was found that degradation phenomenon of PHBV in the pilot-scale composting conditions was similar with that in a laboratory scale, i.e. the degradation occurred with erosion from surface to the interior. The PHBV film was completely disintegrated in the pilot-scale composting test, and the degree of biodegradation was 81% in the laboratory-scale control composting test (Fig. 7.4). The FT-IR spectra of PHBV films collected from the compost at different degradation times are given in Fig. 7.5. It can be seen that PHBV films before and after degradation had similar absorption peaks, indicating that the chemical
Biodegradation of compostable polymer materials Chapter | 7 243
FIG. 7.4 The apparent morphology of PHBV film at different composting time. (Reprinted from Weng YX, Wang Y, Wang XL, Wang YZ. Biodegradation behaviour of PHBV films in pilot-scale composting conditions. Polym Test 2010;29:579.)
structure of PHBV films was not changed, which agreed with the conclusion from SEM. After12weeks, no residual PHBV film fragments could be found on the sieve (pore size of 2 mm) used to screen the compost. Therefore, the degree of biodegradation of PHBV films was 100% according to ISO16929. The effect of biodegradable and degradable plastics on the composting of green wastes, with special emphasis on compost quality was conducted [10]. After 1 week of composting, the biodegradable plastics (Mater-Bi) disappeared completely, while 2% of the original degradable plastic still remained after 8 weeks of composting. Molecular level the decomposition of specific starch-based thermoplastic mulching film for horticultural crops, combined with the simultaneous characterization of the organic biomasses for the attainment of mature compost for agricultural application, in a real on-farm composting system was determined [11]. The molecular characterization of original and final components of bulk compost and bio-polymer was analyzed by 13C CPMAS NMR spectroscopy and off-line thermochemolysis gas-chromatography–mass-spectrometry. The decomposing test was performed on starch-based thermoplastic bio- film for mulching application, developed in the Operative National Project PON Enerbiochem. The experiment was carried out in the on-farm composting facility built within the same project, at the Long Term Experimental field site of the
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FIG. 7.5 The FT-IR spectra of PHBV degraded at different time. (Reprinted from Weng YX, Wang Y, Wang XL, Wang YZ. Biodegradation behaviour of PHBV films in pilot-scale composting conditions. Polym Test 2010;29:579.)
University of Napoli, located at Castel-Volturno. Solid-state NMR spectroscopy and thermochemolysis revealed a noticeable variation of both polymeric components and molecular properties. The composting process showed the typical modifications associated with OM stabilization, that is characterized by the decrease of bio-labile compounds and the selective preservation of recalcitrant alkyl and aromatic molecules. In addition to classical protocols to test biodegradation of materials, the experiments by real composting process of this work followed by the analytical characterization of residues appear as an useful technique to elucidate the molecular properties of starch-based polymers, and to highlight that the composting process is a viable way to recycle the residues of biodegradable materials. The mechanisms of degradation of the PLA films in real composting conditions was investigated [12]. The studies on the degradation process of rigid films made from. PLA and its blend with a-PHB were conducted in an open-air industrial composting pile. The comparative laboratory experiments were carried out in
Biodegradation of compostable polymer materials Chapter | 7 245
the compost extracts, obtained from the industrial compost in order to estimate the role of microorganisms in addition to temperature and humidity. It was concluded that during the industrial composting process of PLA-based materials the abiotic hydrolysis occurred by the random scission of ester bonds and leaded to a successive reduction in the molar mass and increased in the dispersity index of the samples studied. After longer incubation time (70 days in composting pile and 35 days in extracts) the samples were disintegrated and then start to decomposed into the acidic water-soluble degradation products. The lack of change in the pH of the nonsterile extract indicates that the hydrolytic degradation in this environment is accompanied by the action of microorganisms. The degradation of PLA and its blend with (R,S)-PHB as rigid foils were studied under industrial composting conditions [13]. Incubation of these materials in water at 70 °C (hydrolytic degradation) was conducted as reference experiment. Gel permeation chromatography, electrospray mass spectrometry, nuclear magnetic resonance and differential scanning calorimetry were used to determine the progress of degradation during incubation in selected environments. The present results showed that PLA-based rigid foil degrades under industrial composting conditions. In the blends, (R,S)-PHB content was found to accelerate the degradation process under industrial composting conditions in comparison with the reference experiment. The biodegradabilities of the blends of poly(l-lactide) and cellulose acetate butyrate (CAB), and their blends without and with 20 % plasticizer (PEG1500, PEG6000 and Paraplex G40) added were determined under real aerobic composting conditions [14]. In the case of the PLA film it had fragmented by day 12 and had disappeared completely by day 30. This rapid degradation of PLA was attributed, at least in part, to the elevated temperature and humidity (45–70 °C, RH 40–55%) in the compost pile relative to the Tg of PLA of around 60 °C. The PLA/CAB/plasticizer blend films all degraded in real composting conditions at PLA contents of over 50 wt%. Moreover, the PEG-plasticized ternary blend films showed complete degradability at PLA ≥ 70 and CAB ≤30 wt%. The biodegradation course of the blown film based on the commercially available polymeric blend based on Polylactic acid, Bioflex1 219F, was studied through microscopical observations, weight loss measurements, testing of mechanical properties and investigation of structure by using Fourier transform infrared spectroscopy and differential scanning calorimetry [15]. The results show relatively good degradability of the samples in the composting environment. The weight loss was almost 30% after 6 weeks of composting. The significant drop of mechanical properties occurred already after 2 weeks of testing. Noticeable changes were also found in the structure of the polymer samples. It reveals degradation reactions connected with the cleavage of the polymeric chains, which was confirmed by the results from infrared spectroscopy. The degradation behavior of polymer compositions containing atactic poly[(R,S)3- hydroxybutyrate ] (a- PHB), poly[(dl)- lactide] (PLA) and aliphatic –aromatic copolyester of terephthalic copolyester and adipic acid with
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1,4-butanediol (BTA) in industrial composting pile was studied [16]. Test was performed for samples in form of monofilaments with diameter 1 mm and average length 10 cm. The macroscopic observations of surface changes, the weight loss and changes of molecular weight, polydispersity and compositions of samples were monitored during 14 days of composting process. In 2011, the practical application of organic waste bags made of compostable polymer ecovio® underwent large-scale testing in Bad Duerkheim district (Germany) in a joint pilot project involving the waste management company AWB and BASF [17]. Some 65,000 households each received ten compostable organic waste bags for collecting and disposing of organic waste in the organic waste bin. It was investigated how satisfied residents were with the bags and whether the bags could be processed into compost without any problems at the organic composting plant Gruenstadt owned by the waste management company GML. It was found that ecovio® bags completely degraded within three weeks and no effect on the quality of compost was observed. Several commercially available degradable plastic products in six different composting environments and a simulated marine environment was studied [18]. The biodegradable materials were placed in four compost environments, including, traditional windrow, in-vessel manure, in-vessel food waste, and in-vessel municipal solid waste. All of the compost facilities are commercial operations and produce compost for the public. The composting environments included a laboratory and actual facilities composting greenwaste, cow manure and straw, food waste, municipal solid waste, and an enclosed ―in-vessel‖ facility in the absence of oxygen. All of the products tested disintegrated satisfactorily in commercial composting operations within 180 days. Specifically, a minimum of 60% of the organic carbon converted to carbon dioxide by the end of the test period. For all products, the measured amounts of lead and cadmium in finished compost were less than one percent of maximum allowable levels. The polylactic acid (PLA) straws, polyhydroxyalkanoate (PHA) bags, Ecoflex bags, sugar cane plates and corn starch based trash bags released no toxic materials into the compost and successfully supported the growth of tomato seedlings after ten days. The biodegradation of plastic commercial bags was tested in real composting conditions [19]. Samples were placed in the compost pile operated by the Central Composting Plant in Brno, and were checked and visually assessed during the experiment which lasted 12 weeks. The rate of biodegradation has been analyzed by investigating the morphological properties using scanning electron microscopy (SEM). SEM images of bioplastics (based on starch and starch and polycaprolactone blend) before and after composting showed substantial changes in the surface of the material. Samples showed significant erosion on surface when subjected to the SEM analysis.
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Degradation process of polylactic acid PLA and poly(butylene adipate-co- terephthalate) PBAT blends in the form of films was studied [20]. The biodegradation tests were performed under industrial composting conditions in a pile and in a container system. Additionally, an abiotic degradation test was carried out under laboratory conditions. The selected materials allowed the determination of the effect of PLA content (17 and 40 mol%) in the films on their degradation process and a comparison of the degradation of materials with different thickness and the same molar content (40 mol%) of PLA. The changes of molar mass, molar-mass dispersity, composition and thermal properties of the samples were observed during an incubation period in degradation media and the resultant material was characterized by GPC, 1H NMR, TGA and DSC techniques, respectively. The obtained results indicate that both components of the blend are degraded, but at different rates. The differences in the degradation rate of the materials tested, with a similar content of the PLA component, could be caused by differences in their thickness and/or the presence of commercial additives used during the processing stage. Certified compostable foodware and packaging (CFP) at 10 and 20% by volume were examined in three composting practices in British Columbia, Canada to assess disintegration [21]. These facilities use four commercial composting practices: turned windrow, anaerobic digestion coupled with static pile and windrow curing, static pile with windrow curing, and in-vessel coupled with covered windrow. The disintegration of a mix of CFP products at varying concentrations for four types of compost operations: turned windrow, static pile, in-vessel and anaerobic digestion was studied. Seventeen typical CFP products (e.g. bowls, cups, spoons) were used in this study to represent an array of materials from unlined natural kraft paper, to natural fibres and cellulose, blended bio-polymers, and pure PLA biopolymer (97% l-lactide and 3% d- lactide). Laboratory studies were conducted to determine CFP amended with compost feedstocks at 1 and 2% by weight effects on microbial activity and community structure. Results showed disintegration varied significantly by CFP and facility type. Nearly 90% of poly-lactic acid based CFP completely disintegrated in the in-vessel and static pile, followed by turned windrow (63%) but only 30% of CFP in the anaerobic digestion operation. The disintegration of fibre based CFP was significantly lower than other CFP across composting practices. Increased concentration of CFP enhanced disintegration only in the static pile. Doubling the concentration of CFP (2 vs.1%) in laboratory conditions significantly increased microbial activity (150% of CO2 respiration) and abundance of microbial community groups, i.e. total phospholipid fatty acids, and those of gram-positive bacteria and fungi by 45, 330 and 28%, respectively. These results indicate that under ideal composting conditions CFP products are likely to disintegrate completely and higher concentrations may enhance their biodegradation. Summary of composting studies under real conditions is given in Table 7.1.
TABLE 7.1 Composting studies under real conditions of compostable polymers. Composting conditions Polymer
Form
Starch-based (MaterBi)
Bags
Corn starch-based (Biobag)
Temperature/ moisture
Time
Compost source
Results
References
>60 °C (first five days); 63.1% moisture
6 weeks
Green wastes
After one week of monitoring, all the strips of plastic have completely disappeared.
[10]
A trash bag
40–70 °C
20 weeks
Municipal compost facility
84% degradation after 20 weeks
[4]
Starch
Bag (thickness 0.2 mm)
nd
12 weeks
Three-month-old mature compost, which was provided by a full-scale aerobic composting
SEM images showed the biodegradation indicators such as fractures, breaches, cavities, and holes on the surface
[19]
Starch and polycaprolactone blends
Bag (thickness 0.2 mm)
nd
12 weeks
Three-month-old mature compost, which was provided by a full-scale aerobic composting
SEM images showed the biodegradation indicators such as fractures, breaches, cavities, and holes on the surface
[19]
Sugarcane
A plate
40–70 °C
20 weeks
Municipal compost facility
78% degradation after 20 weeks
[4]
Poly(lactide) (PLA)
l
Bottles Trays l Containers
65 ± 5 °C (initial) 63 ± 5% (initial) (T > 55 °C, >65% RH)
30 days
Cow manure, wood shavings, and waste feed (i.e. the feed that the cows left)
The degradation time of PLA trays and deli containers in a commercial facility was not more than 30 days, and in the case of the bottle was not more than 45 days.
[5]
l
Poly(lactide) (PLA)
Bottles
65 ± 5 °C (initial) 63 ± 5% (initial)
30 days
Cow manure, wood shavings, and waste feed (i.e. the feed that the cows left)
Molecular weight of 4100 Da was obtained for PLA bottles in real composting conditions on the 30th day.
[6]
Poly(lactide) (PLA)
l
65 ± 5 °C (initial) 63 ± 5% (initial)
30 days
Cow manure, wood shavings, and waste feed (i.e. the feed that the cows left)
PLA deli containers degraded in <30 days under composting conditions. PLA bottles made of 96% l-lactide exhibited lower degradation than PLA delicatessen (‘deli’) containers. made of 94% l-lactide
[7]
Film
EN ISO 14855.
6 weeks
EN ISO 14855.
The weight loss was almost 30% after 6 weeks of composting.
[15]
Spoons Knives l Lids l Cups l Containers
48 °C–65 °C 35–55%
120 days
Municipal Compost Facility; The facility accepts green yard waste, which includes lawn clippings, leaves, wood, sticks, weeds, and pruning.
After 90 days, the PLA spoons, knives, and lids had completely disintegrated. PLA containers, and PLA cups had noticeable biodegradation and were broken into fragments. After 120 days, PLA forks, spoons, knives, and lids, sugar were completely biodegraded and no fragments were found. Small fragments of PLA cups, PLA container were visible.
[18]
Bottles Deli containers
l
PLA based blend (Bioflex) Polylactic acid (PLA)
l l
Continued
TABLE 7.1 Composting studies under real conditions of compostable polymers.—cont’d Composting conditions Polymer
Form
Polylactic acid (PLA)
l
Time
Compost source
Results
References
Cups Forks l Spoons l Knives l Clamshell containers l Lids l Straws
48 °C–64 °C 35–55%
120 days
In-vessel Compost Facility; dairy manure and rice straw
After 120 days, the materials that completely degraded included PLA forks, spoons, knives, and lids, sugar cane lids and plates. Small fragments of PLA cups and PLA container, and corn starch trash bags were visible. Approximately, three PLA cup and container fragments were found (250 PLA cups and 160 clamshell containers were buried in a compost facility).
[18]
Cup Knife l Clamshell container
40–70 °C
20 weeks
Municipal compost facility
100% degradation in 7 weeks
[4]
Films
45–70 °C, 40–55%
90 days
Vegetable waste, wood chips, coconut shells, fruit peels and old composts
The rate of biodegradability decreased with increasing amount (30%) of CAB. PLL film had fragmented by day 12 and had disappeared completely by day 30.
[14]
l
Polylactic acid (PLA)
Temperature/ moisture
l l
Blends of poly(l- lactide) and cellulose acetate butyrate (CAB)
Blends of polylactide (PLA) with poly[(R,S)- 3-hydroxybutyrate] ((R,S)-PHB)
Rigid films
52, 54 and 59 °C at the 7th, 21st and 70th day of the experiment, respectively.
70 days
Leaves (40%), branches (30%) and grass (30%) + the kitchen waste
After 70 days in composting pile the samples were disintegrated.
[12]
Blends of polylactide (PLA) with poly[(R,S)- 3-hydroxybutyrate] ((R,S)-PHB)
Foils
59 °C – composting pile 60 °C – in a container
70 days
Industrial composting
PLA-based rigid foils degraded in the container during first 2 weeks and in composting pile after 70 days.
[13]
Blends of polylactic acid (PLA) and poly(butylene adipate- co-terephthalate) (PBAT)
Films (PLA content: 17 and 40% mol); Disposable bag (PLA content: 40% mol)
60–61 °C
21 days
Industrial composting conditions in two systems: a static composting open-air pile and a KNEER container system
Macro-and microscopic visual evaluation of the samples during the degradation process indicated erosion as well as tarnishing of the film’s surface beginning from the 21st day of incubation in both composting systems. Both films with 17 and 40% of PLA in their blends during degradation showed similar morphological changes that occurred predominately on the sample surface. The thicker samples showed little change for 21 days.
[20]
Continued
TABLE 7.1 Composting studies under real conditions of compostable polymers.—cont’d Composting conditions Polymer
Form
Poly(hydroxybutyrate- co-hydroxyvalerate) (PHBV)
Films
Polyhydroxyalkanoates (PHA) (Mirel)
Bags
Temperature/ moisture
Time
Compost source
Results
References
35–75 °C (temperature variations according to ISO16929) The temperature reached 73 °C after 3 days and then decreased to about 60 °C after 4-day degradation. The period in which the temperature was higher than 40 °C, was about 36 days.
12 weeks
Cabbage, apple, fresh apple pericarp, wood scrap, rabbit feedstuff, mature compost and distilled water
After 12 weeks, no residual PHBV film fragments could be found on the sieve (pore size of 2 mm) used to screen the compost. Therefore, the degree of biodegradation of PHBV films was 100% according to ISO16929.
[9]
55–70 °C
180 days
In-vessel Food-waste Compost Facility
After 180 days the materials completely degraded.
[18]
Biodegradation of compostable polymer materials Chapter | 7 253
References [1] Kale G, Kijchavengkul T, Auras R, Rubino M, Selke SE, Singh SP. Compostability of bioplastic packaging materials: an overview. Macromol Biosci 2007;7:255. [2] Kijchavengkul T, Auras R. Perspective compostability of polymers. Polym Int 2008;57:793. [3] Briassoulis D, Dejean C, Picuno P. Critical review of norms and standards for biodegradable agricultural plastics. Part II: composting. J Polym Environ 2010;18:364. [4] Greene J. Biodegradation of compostable plastics in green yard-waste compost environment. J Polym Environ 2007;15:269. [5] Kale G, Auras R, Singh S. Degradation of commercial biodegradable packages under real composting and ambient exposure conditions. J Polym Environ 2006;14:317. [6] Kale G, Auras R, Singh S. Comparison of the degradability of poly(lactide) packages in composting and ambient exposure conditions. Packag Technol Sci 2007;20:49. [7] Kale G, Auras R, Singh S, Narayan R. Biodegradability of polylactide bottles in real and stimulated composting conditions. Polym Test 2007;26:1049. [8] Musioł M, Sikorska W, Adamus G, Janeczek H, Richert J, Malinowski R, Jiang G, Kowalczuk M. Forensic engineering of advanced polymeric materials. Part III – biodegradation of thermoformed rigid PLA packaging under industrial composting conditions. Waste Manag 2016;52:69. [9] Weng Y-X, Wang Y, Wang X-L, Wang Y-Z. Biodegradation behaviour of PHBV films in pilot- scale composting conditions. Polym Test 2010;29:579. [10] Unmar G, Mohee R. Assessing the effect of biodegradable and degradable plastics on the composting of green wastes and compost quality. Biores Technol 2008;99:6738. [11] Spaccini R, Todisco D, Drosos M, Nebbioso A, Piccolo A. Decomposition of bio-degradable plastic polymer in a real on-farm composting process. Chem Biol Technol Agric 2016;3(4):1. [12] Sikorska W, Musiol M, Nowak B, Pajak J, Labuzek S, Kowalczuk M, Adamus G. Degradability of polylactide and its blend with poly[(R,S)-3-hydroxybutyrate] in industrial composting and compost extract. Int Biodeterior Biodegrad 2015;101:32. [13] Musioł M, Sikorska W, Grażyna Adamus G, Janeczek H, Kowalczuk M, Rydz J. (Bio)degradable polymers as a potential material for food packaging: studies on the (bio)degradation process of PLA/(R,S)-PHB rigid foils under industrial composting conditions. Eur Food Res Technol 2016;242:815. [14] Kunthadong P, Molloy R, Worajittiphon P, Leejarkpai T, Kaabbuathong N, Punyodom W. Biodegradable plasticized blends of poly(L-lactide) and cellulose acetate butyrate: from blend preparation to biodegradability in real composting conditions. J Polym Environ 2015;23:107. [15] Sedlarik V, Saha N, Sedlarikova J, Saha P. Biodegradation of blown films based on poly(lactic acid) under natural conditions. Macromol Symp 2008;272:100. [16] Sikorska W, Dacko P, Sobota M, Rydz J, Musioł M, Kowalczuk M. Degradation study of polymers from renewable resources and their compositions in industrial composting pile. Macromol Symp 2008;272:132. [17] http://www.plasticsportal.net/wa/plasticsEU∼pl_PL/portal/show/content/products/biodegradable_plastics/ecovio_bmb. Available September 6, 2017. [18] Performance evaluation of environmentally degradable plastic packaging and disposable food service ware – final report June 2007, produced by CSU. Chico Research Foundation. [19] Adamcová D, Radziemska M, Zloch J, Dvořáčková H, Elbl J, Kynický J, Brtnický M, Vaverková MD. SEM Analysis and degradation behavior of conventional and bio-based plastics during composting. Acta Univ Agric Silvic Mendelianae Brunensis 2018;66:349.
254 Compostable Polymer Materials [20] Musioł M, Sikorska W, Janeczek H, Wałach W, Hercog A, Johnston B, Rydz J. (Bio)degradable polymeric materials for a sustainable future – Part 1. Organic recycling of PLA/PBAT blends in the form of prototype packages with long shelf-life. Waste Manag 2018;77:447. [21] Zhang H, McGill E, Ohep Gomez C, Carson S, Neufeld K, Hawthorne I, Smukler SM. Disintegration of compostable foodware and packaging and its effect on microbial activity and community composition in municipal composting. Int Biodeterior Biodegraderior Biodegrad 2017;125:157.
Biodegradation of compostable polymer materials under real conditions Chapter Outline References253
The current wide diffusion of compostable polymers has focused the attention on the allocation of compostable polymers for the direct recycling in composting processes [1–3]. Actually, the acknowledged current methods to estimate the biodegradability are mainly based on laboratory tests and measurements under controlled conditions, while scarce information are available on the effective transformation of compostable polymers in real composting facilities. The biodegradability validation criteria under composting conditions, such as the threshold percentage of biodegradation and disintegration, the time and temperature, and the ecotoxicity are described in the main norms and standard testing methods [3]. Commercial or municipal composting is a large scale operation, which generally employs turning and active aeration, except for static pile and some in-vessel composting systems. Since waste materials have different characteristics, operational parameters such as moving, mixing, and manipulation differ [1]. The material suitable for composting must meet certain quality criteria, such as compatibility with the composting process, displaying no negative effect on the quality of compost, and leaving no visible, distinguishable or toxic residues. In particular, the rate and extent of decomposition of the waste is a crucial factor in disposing of a biodegradable waste in industrial composting units. Currently, researchers are demonstrating that compostable packages can be composted in facilities that handle yard waste and manure as well as in those that handle food wastes. Therefore, more options to compost biodegradable polymers could be available if compostable polymers used in packaging applications were accepted by these compost facilities. The commercially available compostable products, made from PLA, sugarcane, or corn starch, biodegraded while in a commercial compost facility with other common yard waste compostable items [4]. Biodegradation of samples of a plate made from sugarcane, a tray made from potato-starch, a trash bag made Compostable Polymer Materials. https://doi.org/10.1016/B978-0-08-099438-3.00007-0 Copyright © 2019 Elsevier Ltd. All rights reserved.
239
240 Compostable Polymer Materials
from corn starch, and a cup, fork, knife, straw, and clear clamshell container made from Nature-Works polylactic acid (PLA) was measured by disintegration studies over 20 weeks. The positive control materials included cellulose filter paper, Kraft paper and Avicell micro-cellulose. The PLA container, PLA cup, and PLA knife degraded at a similar rate as the Avicel cellulose control and were degraded completely in 7 weeks. The corn starch-based Biobag trash bag and sugarcane plate degraded at a similar rate as the Kraft paper control. The three materials degraded between 80% and 90% after 20 weeks. Three PLA packages, a bottle, a tray, and a deli container, were used to determine the degradation process under ambient exposure and under compost conditions [5]. The degradation of the PLA containers was monitored by visual inspection, GPC, DSC, and TGA. PLA trays and deli containers degraded before 30 days under composting conditions (T > 55 °C, >65% RH, pH ∼7.5). First order degradation kinetics was observed for the bottle and tray. A glass transition Tg reduction of 1 °C/day was found for PLA containers with 96% l-lactide, and a Tg average reduction of around 0.6 °C/day was found for PLA containers with 94% l-lactide. A method to study the compostability of biodegradable packages under real compost conditions has been outlined. The degradation of two commercially available biodegradable packages made of PLA was investigated and compared under real compost conditions and under ambient exposure, using visual inspection, gel permeation chromatography, differential scanning calorimetry and thermogravimetry analysis [6]. PLA bottles made of 96% l-lactide exhibited lower degradation than PLA delicatessen containers made of 94% l-lactide, mainly due to their highly ordered structure and therefore their higher crystallinity. Temperature, relative humidity and pH of the compost pile played an important role in the rate of degradation of the packages. PLA deli containers degraded in 30 days under composting conditions (temperature 60 °C, relative humidity (RH) 65%, pH 7.5). The biodegradation performance of polylactide (PLA) bottles under simulated composting conditions according to ASTM and ISO standards, and these results are compared with a novel method of evaluating package biodegradation in real composting conditions [7]. Two simulated composting methods were used in this study to assess biodegradability of PLA bottles: (a) a cumulative measurement respirometric (CMR) system and (b) a gravimetric measurement respirometric (GMR) system. Both CMR and GMR systems showed similar trends of biodegradation for PLA bottles and at the end of the 58th day the mineralization was 84.270.9% and 77.8710.4%, respectively. PLA bottle biodegradation in real composting conditions was correlated to their breakdown and variation in molecular weight. Molecular weight of 4100 Da was obtained for PLA bottles in real composting conditions on the 30th day (Figs 7.1 and 7.2). Study on the biodegradation behaviour of prototype packaging thermoformed from PLA-extruded film and plain PLA film under industrial composting conditions was performed [8]. Hydrolytic degradation in water was conducted for reference. The effects of composting duration on changes in molar mass, glass
Biodegradation of compostable polymer materials Chapter | 7 241
FIG. 7.1 Variation in molecular weight (●) and PDI (■) for PLA bottles in real composting conditions. (Reprinted from Kale G, Auras R, Singh S, Narayan R. Biodegradability of polylactide bottles in real and stimulated composting conditions. Polym Test 2007;26:1049.)
FIG. 7.2 Comparison of variation in molecular weight (■) due to biodegradation and percentage mineralization values for PLA bottles in CMR (●) and MODA (○) systems. (Reprinted from Kale G, Auras R, Singh S, Narayan R. Biodegradability of polylactide bottles in real and stimulated composting conditions. Polym Test 2007;26:1049.)
242 Compostable Polymer Materials
FIG. 7.3 Change [%] in weight average molar mass of PLA product during incubation in a container and the composting pile. (Reprinted from Musioł M, Sikorska W, Adamus G, Janeczek H, Richert J, Malinowski R, Jiang G, Kowalczuk M. Forensic engineering of advanced polymeric materials. Part III – biodegradation of thermoformed rigid PLA packaging under industrial composting conditions. Waste Manag 2016;52:69.)
transition temperature and degree of crystallinity of the polymeric material were monitored using gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). The chemical structure of water soluble degradation products of the polymeric material was determined using nuclear magnetic resonance (NMR) and electrospray ionization mass spectrometry (ESI-MS). The results showed that the biodegradation process was less dependent on the thermoforming process of PLA and more dependent on the composting/ degradation conditions that were applied (Fig.7.3). The increase in the dispersity index, leading to the bimodal molar mass distribution profile, suggested an autocatalytic hydrolysis effect at the early stage of the composting process, during which the bulk hydrolysis mechanism dominantly operates. Both the prototype PLA-packaging and PLA rigid film samples were shown to have a gradual increase in opacity due to an increase in the degree of crystallinity. The biodegradability of poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) containing 3 mol% hydroxyvalerate (HV) was tested under composting conditions on both a pilot and a laboratory scale [9]. In the pilot-scale composting conditions, parameters such as pH value, temperature and the amounts of oxygen and CO2 produced were determined periodically. It was found that degradation phenomenon of PHBV in the pilot-scale composting conditions was similar with that in a laboratory scale, i.e. the degradation occurred with erosion from surface to the interior. The PHBV film was completely disintegrated in the pilot-scale composting test, and the degree of biodegradation was 81% in the laboratory-scale control composting test (Fig. 7.4). The FT-IR spectra of PHBV films collected from the compost at different degradation times are given in Fig. 7.5. It can be seen that PHBV films before and after degradation had similar absorption peaks, indicating that the chemical
Biodegradation of compostable polymer materials Chapter | 7 243
FIG. 7.4 The apparent morphology of PHBV film at different composting time. (Reprinted from Weng YX, Wang Y, Wang XL, Wang YZ. Biodegradation behaviour of PHBV films in pilot-scale composting conditions. Polym Test 2010;29:579.)
structure of PHBV films was not changed, which agreed with the conclusion from SEM. After12weeks, no residual PHBV film fragments could be found on the sieve (pore size of 2 mm) used to screen the compost. Therefore, the degree of biodegradation of PHBV films was 100% according to ISO16929. The effect of biodegradable and degradable plastics on the composting of green wastes, with special emphasis on compost quality was conducted [10]. After 1 week of composting, the biodegradable plastics (Mater-Bi) disappeared completely, while 2% of the original degradable plastic still remained after 8 weeks of composting. Molecular level the decomposition of specific starch-based thermoplastic mulching film for horticultural crops, combined with the simultaneous characterization of the organic biomasses for the attainment of mature compost for agricultural application, in a real on-farm composting system was determined [11]. The molecular characterization of original and final components of bulk compost and bio-polymer was analyzed by 13C CPMAS NMR spectroscopy and off-line thermochemolysis gas-chromatography–mass-spectrometry. The decomposing test was performed on starch-based thermoplastic bio- film for mulching application, developed in the Operative National Project PON Enerbiochem. The experiment was carried out in the on-farm composting facility built within the same project, at the Long Term Experimental field site of the
244 Compostable Polymer Materials
FIG. 7.5 The FT-IR spectra of PHBV degraded at different time. (Reprinted from Weng YX, Wang Y, Wang XL, Wang YZ. Biodegradation behaviour of PHBV films in pilot-scale composting conditions. Polym Test 2010;29:579.)
University of Napoli, located at Castel-Volturno. Solid-state NMR spectroscopy and thermochemolysis revealed a noticeable variation of both polymeric components and molecular properties. The composting process showed the typical modifications associated with OM stabilization, that is characterized by the decrease of bio-labile compounds and the selective preservation of recalcitrant alkyl and aromatic molecules. In addition to classical protocols to test biodegradation of materials, the experiments by real composting process of this work followed by the analytical characterization of residues appear as an useful technique to elucidate the molecular properties of starch-based polymers, and to highlight that the composting process is a viable way to recycle the residues of biodegradable materials. The mechanisms of degradation of the PLA films in real composting conditions was investigated [12]. The studies on the degradation process of rigid films made from. PLA and its blend with a-PHB were conducted in an open-air industrial composting pile. The comparative laboratory experiments were carried out in
Biodegradation of compostable polymer materials Chapter | 7 245
the compost extracts, obtained from the industrial compost in order to estimate the role of microorganisms in addition to temperature and humidity. It was concluded that during the industrial composting process of PLA-based materials the abiotic hydrolysis occurred by the random scission of ester bonds and leaded to a successive reduction in the molar mass and increased in the dispersity index of the samples studied. After longer incubation time (70 days in composting pile and 35 days in extracts) the samples were disintegrated and then start to decomposed into the acidic water-soluble degradation products. The lack of change in the pH of the nonsterile extract indicates that the hydrolytic degradation in this environment is accompanied by the action of microorganisms. The degradation of PLA and its blend with (R,S)-PHB as rigid foils were studied under industrial composting conditions [13]. Incubation of these materials in water at 70 °C (hydrolytic degradation) was conducted as reference experiment. Gel permeation chromatography, electrospray mass spectrometry, nuclear magnetic resonance and differential scanning calorimetry were used to determine the progress of degradation during incubation in selected environments. The present results showed that PLA-based rigid foil degrades under industrial composting conditions. In the blends, (R,S)-PHB content was found to accelerate the degradation process under industrial composting conditions in comparison with the reference experiment. The biodegradabilities of the blends of poly(l-lactide) and cellulose acetate butyrate (CAB), and their blends without and with 20 % plasticizer (PEG1500, PEG6000 and Paraplex G40) added were determined under real aerobic composting conditions [14]. In the case of the PLA film it had fragmented by day 12 and had disappeared completely by day 30. This rapid degradation of PLA was attributed, at least in part, to the elevated temperature and humidity (45–70 °C, RH 40–55%) in the compost pile relative to the Tg of PLA of around 60 °C. The PLA/CAB/plasticizer blend films all degraded in real composting conditions at PLA contents of over 50 wt%. Moreover, the PEG-plasticized ternary blend films showed complete degradability at PLA ≥ 70 and CAB ≤30 wt%. The biodegradation course of the blown film based on the commercially available polymeric blend based on Polylactic acid, Bioflex1 219F, was studied through microscopical observations, weight loss measurements, testing of mechanical properties and investigation of structure by using Fourier transform infrared spectroscopy and differential scanning calorimetry [15]. The results show relatively good degradability of the samples in the composting environment. The weight loss was almost 30% after 6 weeks of composting. The significant drop of mechanical properties occurred already after 2 weeks of testing. Noticeable changes were also found in the structure of the polymer samples. It reveals degradation reactions connected with the cleavage of the polymeric chains, which was confirmed by the results from infrared spectroscopy. The degradation behavior of polymer compositions containing atactic poly[(R,S)3- hydroxybutyrate ] (a- PHB), poly[(dl)- lactide] (PLA) and aliphatic –aromatic copolyester of terephthalic copolyester and adipic acid with
246 Compostable Polymer Materials
1,4-butanediol (BTA) in industrial composting pile was studied [16]. Test was performed for samples in form of monofilaments with diameter 1 mm and average length 10 cm. The macroscopic observations of surface changes, the weight loss and changes of molecular weight, polydispersity and compositions of samples were monitored during 14 days of composting process. In 2011, the practical application of organic waste bags made of compostable polymer ecovio® underwent large-scale testing in Bad Duerkheim district (Germany) in a joint pilot project involving the waste management company AWB and BASF [17]. Some 65,000 households each received ten compostable organic waste bags for collecting and disposing of organic waste in the organic waste bin. It was investigated how satisfied residents were with the bags and whether the bags could be processed into compost without any problems at the organic composting plant Gruenstadt owned by the waste management company GML. It was found that ecovio® bags completely degraded within three weeks and no effect on the quality of compost was observed. Several commercially available degradable plastic products in six different composting environments and a simulated marine environment was studied [18]. The biodegradable materials were placed in four compost environments, including, traditional windrow, in-vessel manure, in-vessel food waste, and in-vessel municipal solid waste. All of the compost facilities are commercial operations and produce compost for the public. The composting environments included a laboratory and actual facilities composting greenwaste, cow manure and straw, food waste, municipal solid waste, and an enclosed ―in-vessel‖ facility in the absence of oxygen. All of the products tested disintegrated satisfactorily in commercial composting operations within 180 days. Specifically, a minimum of 60% of the organic carbon converted to carbon dioxide by the end of the test period. For all products, the measured amounts of lead and cadmium in finished compost were less than one percent of maximum allowable levels. The polylactic acid (PLA) straws, polyhydroxyalkanoate (PHA) bags, Ecoflex bags, sugar cane plates and corn starch based trash bags released no toxic materials into the compost and successfully supported the growth of tomato seedlings after ten days. The biodegradation of plastic commercial bags was tested in real composting conditions [19]. Samples were placed in the compost pile operated by the Central Composting Plant in Brno, and were checked and visually assessed during the experiment which lasted 12 weeks. The rate of biodegradation has been analyzed by investigating the morphological properties using scanning electron microscopy (SEM). SEM images of bioplastics (based on starch and starch and polycaprolactone blend) before and after composting showed substantial changes in the surface of the material. Samples showed significant erosion on surface when subjected to the SEM analysis.
Biodegradation of compostable polymer materials Chapter | 7 247
Degradation process of polylactic acid PLA and poly(butylene adipate-co- terephthalate) PBAT blends in the form of films was studied [20]. The biodegradation tests were performed under industrial composting conditions in a pile and in a container system. Additionally, an abiotic degradation test was carried out under laboratory conditions. The selected materials allowed the determination of the effect of PLA content (17 and 40 mol%) in the films on their degradation process and a comparison of the degradation of materials with different thickness and the same molar content (40 mol%) of PLA. The changes of molar mass, molar-mass dispersity, composition and thermal properties of the samples were observed during an incubation period in degradation media and the resultant material was characterized by GPC, 1H NMR, TGA and DSC techniques, respectively. The obtained results indicate that both components of the blend are degraded, but at different rates. The differences in the degradation rate of the materials tested, with a similar content of the PLA component, could be caused by differences in their thickness and/or the presence of commercial additives used during the processing stage. Certified compostable foodware and packaging (CFP) at 10 and 20% by volume were examined in three composting practices in British Columbia, Canada to assess disintegration [21]. These facilities use four commercial composting practices: turned windrow, anaerobic digestion coupled with static pile and windrow curing, static pile with windrow curing, and in-vessel coupled with covered windrow. The disintegration of a mix of CFP products at varying concentrations for four types of compost operations: turned windrow, static pile, in-vessel and anaerobic digestion was studied. Seventeen typical CFP products (e.g. bowls, cups, spoons) were used in this study to represent an array of materials from unlined natural kraft paper, to natural fibres and cellulose, blended bio-polymers, and pure PLA biopolymer (97% l-lactide and 3% d- lactide). Laboratory studies were conducted to determine CFP amended with compost feedstocks at 1 and 2% by weight effects on microbial activity and community structure. Results showed disintegration varied significantly by CFP and facility type. Nearly 90% of poly-lactic acid based CFP completely disintegrated in the in-vessel and static pile, followed by turned windrow (63%) but only 30% of CFP in the anaerobic digestion operation. The disintegration of fibre based CFP was significantly lower than other CFP across composting practices. Increased concentration of CFP enhanced disintegration only in the static pile. Doubling the concentration of CFP (2 vs.1%) in laboratory conditions significantly increased microbial activity (150% of CO2 respiration) and abundance of microbial community groups, i.e. total phospholipid fatty acids, and those of gram-positive bacteria and fungi by 45, 330 and 28%, respectively. These results indicate that under ideal composting conditions CFP products are likely to disintegrate completely and higher concentrations may enhance their biodegradation. Summary of composting studies under real conditions is given in Table 7.1.
TABLE 7.1 Composting studies under real conditions of compostable polymers. Composting conditions Polymer
Form
Starch-based (MaterBi)
Bags
Corn starch-based (Biobag)
Temperature/ moisture
Time
Compost source
Results
References
>60 °C (first five days); 63.1% moisture
6 weeks
Green wastes
After one week of monitoring, all the strips of plastic have completely disappeared.
[10]
A trash bag
40–70 °C
20 weeks
Municipal compost facility
84% degradation after 20 weeks
[4]
Starch
Bag (thickness 0.2 mm)
nd
12 weeks
Three-month-old mature compost, which was provided by a full-scale aerobic composting
SEM images showed the biodegradation indicators such as fractures, breaches, cavities, and holes on the surface
[19]
Starch and polycaprolactone blends
Bag (thickness 0.2 mm)
nd
12 weeks
Three-month-old mature compost, which was provided by a full-scale aerobic composting
SEM images showed the biodegradation indicators such as fractures, breaches, cavities, and holes on the surface
[19]
Sugarcane
A plate
40–70 °C
20 weeks
Municipal compost facility
78% degradation after 20 weeks
[4]
Poly(lactide) (PLA)
l
Bottles Trays l Containers
65 ± 5 °C (initial) 63 ± 5% (initial) (T > 55 °C, >65% RH)
30 days
Cow manure, wood shavings, and waste feed (i.e. the feed that the cows left)
The degradation time of PLA trays and deli containers in a commercial facility was not more than 30 days, and in the case of the bottle was not more than 45 days.
[5]
l
Poly(lactide) (PLA)
Bottles
65 ± 5 °C (initial) 63 ± 5% (initial)
30 days
Cow manure, wood shavings, and waste feed (i.e. the feed that the cows left)
Molecular weight of 4100 Da was obtained for PLA bottles in real composting conditions on the 30th day.
[6]
Poly(lactide) (PLA)
l
65 ± 5 °C (initial) 63 ± 5% (initial)
30 days
Cow manure, wood shavings, and waste feed (i.e. the feed that the cows left)
PLA deli containers degraded in <30 days under composting conditions. PLA bottles made of 96% l-lactide exhibited lower degradation than PLA delicatessen (‘deli’) containers. made of 94% l-lactide
[7]
Film
EN ISO 14855.
6 weeks
EN ISO 14855.
The weight loss was almost 30% after 6 weeks of composting.
[15]
Spoons Knives l Lids l Cups l Containers
48 °C–65 °C 35–55%
120 days
Municipal Compost Facility; The facility accepts green yard waste, which includes lawn clippings, leaves, wood, sticks, weeds, and pruning.
After 90 days, the PLA spoons, knives, and lids had completely disintegrated. PLA containers, and PLA cups had noticeable biodegradation and were broken into fragments. After 120 days, PLA forks, spoons, knives, and lids, sugar were completely biodegraded and no fragments were found. Small fragments of PLA cups, PLA container were visible.
[18]
Bottles Deli containers
l
PLA based blend (Bioflex) Polylactic acid (PLA)
l l
Continued
TABLE 7.1 Composting studies under real conditions of compostable polymers.—cont’d Composting conditions Polymer
Form
Polylactic acid (PLA)
l
Time
Compost source
Results
References
Cups Forks l Spoons l Knives l Clamshell containers l Lids l Straws
48 °C–64 °C 35–55%
120 days
In-vessel Compost Facility; dairy manure and rice straw
After 120 days, the materials that completely degraded included PLA forks, spoons, knives, and lids, sugar cane lids and plates. Small fragments of PLA cups and PLA container, and corn starch trash bags were visible. Approximately, three PLA cup and container fragments were found (250 PLA cups and 160 clamshell containers were buried in a compost facility).
[18]
Cup Knife l Clamshell container
40–70 °C
20 weeks
Municipal compost facility
100% degradation in 7 weeks
[4]
Films
45–70 °C, 40–55%
90 days
Vegetable waste, wood chips, coconut shells, fruit peels and old composts
The rate of biodegradability decreased with increasing amount (30%) of CAB. PLL film had fragmented by day 12 and had disappeared completely by day 30.
[14]
l
Polylactic acid (PLA)
Temperature/ moisture
l l
Blends of poly(l- lactide) and cellulose acetate butyrate (CAB)
Blends of polylactide (PLA) with poly[(R,S)- 3-hydroxybutyrate] ((R,S)-PHB)
Rigid films
52, 54 and 59 °C at the 7th, 21st and 70th day of the experiment, respectively.
70 days
Leaves (40%), branches (30%) and grass (30%) + the kitchen waste
After 70 days in composting pile the samples were disintegrated.
[12]
Blends of polylactide (PLA) with poly[(R,S)- 3-hydroxybutyrate] ((R,S)-PHB)
Foils
59 °C – composting pile 60 °C – in a container
70 days
Industrial composting
PLA-based rigid foils degraded in the container during first 2 weeks and in composting pile after 70 days.
[13]
Blends of polylactic acid (PLA) and poly(butylene adipate- co-terephthalate) (PBAT)
Films (PLA content: 17 and 40% mol); Disposable bag (PLA content: 40% mol)
60–61 °C
21 days
Industrial composting conditions in two systems: a static composting open-air pile and a KNEER container system
Macro-and microscopic visual evaluation of the samples during the degradation process indicated erosion as well as tarnishing of the film’s surface beginning from the 21st day of incubation in both composting systems. Both films with 17 and 40% of PLA in their blends during degradation showed similar morphological changes that occurred predominately on the sample surface. The thicker samples showed little change for 21 days.
[20]
Continued
TABLE 7.1 Composting studies under real conditions of compostable polymers.—cont’d Composting conditions Polymer
Form
Poly(hydroxybutyrate- co-hydroxyvalerate) (PHBV)
Films
Polyhydroxyalkanoates (PHA) (Mirel)
Bags
Temperature/ moisture
Time
Compost source
Results
References
35–75 °C (temperature variations according to ISO16929) The temperature reached 73 °C after 3 days and then decreased to about 60 °C after 4-day degradation. The period in which the temperature was higher than 40 °C, was about 36 days.
12 weeks
Cabbage, apple, fresh apple pericarp, wood scrap, rabbit feedstuff, mature compost and distilled water
After 12 weeks, no residual PHBV film fragments could be found on the sieve (pore size of 2 mm) used to screen the compost. Therefore, the degree of biodegradation of PHBV films was 100% according to ISO16929.
[9]
55–70 °C
180 days
In-vessel Food-waste Compost Facility
After 180 days the materials completely degraded.
[18]
Biodegradation of compostable polymer materials Chapter | 7 253
References [1] Kale G, Kijchavengkul T, Auras R, Rubino M, Selke SE, Singh SP. Compostability of bioplastic packaging materials: an overview. Macromol Biosci 2007;7:255. [2] Kijchavengkul T, Auras R. Perspective compostability of polymers. Polym Int 2008;57:793. [3] Briassoulis D, Dejean C, Picuno P. Critical review of norms and standards for biodegradable agricultural plastics. Part II: composting. J Polym Environ 2010;18:364. [4] Greene J. Biodegradation of compostable plastics in green yard-waste compost environment. J Polym Environ 2007;15:269. [5] Kale G, Auras R, Singh S. Degradation of commercial biodegradable packages under real composting and ambient exposure conditions. J Polym Environ 2006;14:317. [6] Kale G, Auras R, Singh S. Comparison of the degradability of poly(lactide) packages in composting and ambient exposure conditions. Packag Technol Sci 2007;20:49. [7] Kale G, Auras R, Singh S, Narayan R. Biodegradability of polylactide bottles in real and stimulated composting conditions. Polym Test 2007;26:1049. [8] Musioł M, Sikorska W, Adamus G, Janeczek H, Richert J, Malinowski R, Jiang G, Kowalczuk M. Forensic engineering of advanced polymeric materials. Part III – biodegradation of thermoformed rigid PLA packaging under industrial composting conditions. Waste Manag 2016;52:69. [9] Weng Y-X, Wang Y, Wang X-L, Wang Y-Z. Biodegradation behaviour of PHBV films in pilot- scale composting conditions. Polym Test 2010;29:579. [10] Unmar G, Mohee R. Assessing the effect of biodegradable and degradable plastics on the composting of green wastes and compost quality. Biores Technol 2008;99:6738. [11] Spaccini R, Todisco D, Drosos M, Nebbioso A, Piccolo A. Decomposition of bio-degradable plastic polymer in a real on-farm composting process. Chem Biol Technol Agric 2016;3(4):1. [12] Sikorska W, Musiol M, Nowak B, Pajak J, Labuzek S, Kowalczuk M, Adamus G. Degradability of polylactide and its blend with poly[(R,S)-3-hydroxybutyrate] in industrial composting and compost extract. Int Biodeterior Biodegrad 2015;101:32. [13] Musioł M, Sikorska W, Grażyna Adamus G, Janeczek H, Kowalczuk M, Rydz J. (Bio)degradable polymers as a potential material for food packaging: studies on the (bio)degradation process of PLA/(R,S)-PHB rigid foils under industrial composting conditions. Eur Food Res Technol 2016;242:815. [14] Kunthadong P, Molloy R, Worajittiphon P, Leejarkpai T, Kaabbuathong N, Punyodom W. Biodegradable plasticized blends of poly(L-lactide) and cellulose acetate butyrate: from blend preparation to biodegradability in real composting conditions. J Polym Environ 2015;23:107. [15] Sedlarik V, Saha N, Sedlarikova J, Saha P. Biodegradation of blown films based on poly(lactic acid) under natural conditions. Macromol Symp 2008;272:100. [16] Sikorska W, Dacko P, Sobota M, Rydz J, Musioł M, Kowalczuk M. Degradation study of polymers from renewable resources and their compositions in industrial composting pile. Macromol Symp 2008;272:132. [17] http://www.plasticsportal.net/wa/plasticsEU∼pl_PL/portal/show/content/products/biodegradable_plastics/ecovio_bmb. Available September 6, 2017. [18] Performance evaluation of environmentally degradable plastic packaging and disposable food service ware – final report June 2007, produced by CSU. Chico Research Foundation. [19] Adamcová D, Radziemska M, Zloch J, Dvořáčková H, Elbl J, Kynický J, Brtnický M, Vaverková MD. SEM Analysis and degradation behavior of conventional and bio-based plastics during composting. Acta Univ Agric Silvic Mendelianae Brunensis 2018;66:349.
254 Compostable Polymer Materials [20] Musioł M, Sikorska W, Janeczek H, Wałach W, Hercog A, Johnston B, Rydz J. (Bio)degradable polymeric materials for a sustainable future – Part 1. Organic recycling of PLA/PBAT blends in the form of prototype packages with long shelf-life. Waste Manag 2018;77:447. [21] Zhang H, McGill E, Ohep Gomez C, Carson S, Neufeld K, Hawthorne I, Smukler SM. Disintegration of compostable foodware and packaging and its effect on microbial activity and community composition in municipal composting. Int Biodeterior Biodegraderior Biodegrad 2017;125:157.