Science behind compostable plastics ASTM standards

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1 January 26, 2011 Science behind compostable plastics ASTM standards Presentation at USCC 19 th Annual conference Ramani Narayan University Distinguished Professor Ramani Narayan, Michigan State University

2 BIOBASED PLASTICS & PRODUCTS Organic (carbon based) materials that contain in whole or part biogenic (biological) carbon -- replacing petro/fossil carbon with bio/renewable carbon beginning of life ASTM D6866 H 2 C CH 2 n H 2 C CH PE PP CH 3 n CH C CH 3 O PLA O n Narayan

3 Carbon footprint reduction strategy using bio content END-OF-LIFE OPTIONS FOR PLASTICS & BIOBASED PLASTICS/PRODUCTS) What happens to product after use when it enters the waste stream Design for biodegradability (in what disposal environment?) Composting COMPOSTABLE PLASTICS! anaerobic digestion Marine soil Recycling Energy recovery (Collection, Buy back, mail back programs) Misleading and Deceptive biodegradability/compostability claims Beware! Narayan 3

4 COMPOSTABLE PLASTICS Plastics that will completely biodegrade under composting environment Functions as food for the microorganisms present in the compost environment Completely assimilated/utilized by the microorganisms present in the disposal environment -- composting Narayan

5 Carbon footprint reduction strategy using bio content Biodegradability A misused and abused term QUESTION Can microorganisms present in the disposal environment utilize/assimilate the plastic carbon substrate the biotic process What extent in what time frame Need complete microbial assimilation and removal from the environmental compartment in a short time period otherwise may have environmental and health consequences Degradable, partial biodegradable not acceptable serious health and environmental consequences Phil. Trans. Royal. Soc. (Biology) July 27, 2009; 364 Narayan 5

6 What does Biodegradable Mean? Can the microorganisms in the target disposal system (composting, soil, anaerobic digestor) assimilate/utilize the carbon substrate as food source completely and in a short defined time period? Environment soil, compost, waste water plant, marine Polymer chains with susceptible linkages Hydrolytic Oxidative Enzymatic STEP 1 Biodegradation(Step 2): Only if all fragmented residues consumed by microorganisms as a food & energy source as measured by evolved CO 2 in defined time and disposal environment Oligomers & polymer fragments Complete microbial assimilation defined time frame, no residues STEP 2 CO 2 + H 2 O + Cell biomass Narayan

7 Carbon footprint reduction strategy using bio content Biodegradability/microbial utilization fundamentals Microorganisms extract chemical energy for use in their life processes by the aerobic oxidation of glucose and other utilizable substrates BIODEGRADBLE PLASTICS, food waste, paper, forest residues biological matter AEROBIC Glucose/C-bioplastic + 6 O 2 6 CO2 + 6 H2O; DG 0 = -686 kcal/mol ANAEROBIC Glucose/C-bioplastic 2 lactate; DG 0 = -47 kcal/mol CO 2 + CH 4 CO 2 is the quantitative measure of the ability of the microrganisms present in the disposal environment to utilize/assimilate the test C-bioplastic, which is the sole C-source available for the microorganisms biodegradation or bioassimilation Ramani Narayan, Michigan State University 7

8 More Biodegradation/Bioassimilation Facts The aerobic oxidation process (a highly specialized cellular phenomenon) requires the participation of three metabolically interrelated processes: 1. Tricarboxylic acid cycle (TCA cycle) 2. Electron transport 3. Oxidative phosphorylation All of the processes take place inside the cell For these processes to occur: The substrates needs to be transported inside the cell Thus, molecular weight, hydrophobic/hydrophilic balance, other molecular and structural features govern transport across cell membrane into the cell for utilization of the C-substrate. Ramani Narayan, Michigan State University

9 % C conversion to CO2 (% biodegradation) Carbon footprint reduction strategy using content Measuring biodegradability biodegradation degree O 2 CO plateau phase biodegradation phase Compost & Test Materials lag phase Time (days) Ramani Narayan, Michigan State University ASTM D5338; ISO 14855; EN

10 Carbon footprint reduction strategy using bio content Biodegradability Test Methods End-of-life strategy using naturally occurring microorganisms in the selected disposal environment End-of-life composting ASTM D5338 ISO EN method + specification End-of-life Aqueous systems ISO OECD 301 End-of-life Anaerobic biogasification ASTM D 5511 ISO (aqueous) NWIP N1144 (slurry phase) Must provide results from the test methods could be zero or 50 or 100 percent --- till curve reaches plateau Narayan

11 Specification Standard for Compostable Plastic -- ASTM D6400 Microbial Utilization (D5338): Demonstrate microbial utilization as measured by evolved carbon dioxide, 90% carbon conversion to CO2 Same rate as natural materials Leaves, paper, grass & food scraps Time days or less; if radiolabeled polymer is used 365 days or less Narayan

12 Specification Standard for Compostable Plastic --ASTM D6400 (contd) Disintegration ISO or ISO or under full scale regular industrial composting conditions for disintegration 90% of material should have gone through a 2mm sieve ISO 16929, Plastics Determination of the degree of disintegration of plastic materials under defined composting conditions in a pilotscale test ISO 20200, Plastics Determination of the degree of disintegration of plastic materials under simulated composting conditions in a laboratory-scale test Safety No phytotoxicity (impacts on plants) using OECD Guide 208 No ecotoxicity Regulated (heavy) metals less than 50% of EPA (USA, Canada) prescribed threshold Narayan

13 SET-UP FOR 2-L BIODEGRADABILITY EXPERIMENTS ASTM D5338 (45 sample vessels in parallel) solenoid valve manifold carbon dioxide analyzer flow restrictor humidifier sample vessel controlled temperature incubator Narayan computer I/O board

14 FEEDBACK CONTROLLED PILOT-SCALE COMPOSTING SET-UP ISO RTD insulating jacket oxygen analyzer carbon dioxide analyzer humidification column compressed air RTD thermal mass flow controller I/O board computer Narayan

15 Carbon footprint reduction strategy using bio content SPECIFICATION STANDARDS Biodegradability under composting conditions Specification Standards ASTM D6400, D6868 Specification Standards EN (European Norm) Specification Standards ISO (International Standard) Biodegradability under marine conditions Specification Standard D 7021 ASTM Standards require testing for eco and phyto toxicity, and regulated metals, thereby ensuing meeting the NOSB requirement that compost produced do not contribute to contamination of crops, soil, or water by plant nutrients, pathogenic organisms, heavy metals, or residues of prohibited substances Narayan 15

16 Aliphatic-aromatic copolyester O C O C O O O CH 2 O C CH 2 C m n x y z Terephthalic acid Diol Aliphatic diacid T m ~ C Copolyester Completely Biodegradable (microbial assimilation) under composting conditions C-14 label on aromatic ring carbon for monitoring biodegradability Ramani Narayan, Michigan State University Cooperation with Eastman Chemical

17 Ramani Narayan, Michigan State University, Aliphatic-aromatic copolyester

18 COMPOSTING PROCESS Microorganisms Oxygen/Air Moisture Nutrients N,P,K,... ORGANIC/COMPOSTABLE MATERIAL (carbon source) Chemical degradation Biodegradation* HEAT kcal/mol energy Breakdown Products death microbial biomass CO 2 + H O 2 Polymerization Ramani Narayan, Michigan State University, HUMUS/ COMPOST * C-substrates utilized by microorganisms for energy to drive its life processes

19 Lignin Microorganisms Cellulose microbial metabolism Degradations OH OH CO 2 + amino acids, proteins, polypeptides Polymer Polymer Formation of Humic Substances During Composting Nucleophilic addition Quinoidal chemistry OH OH OH O OH O R 1 N H oxidative coupling OH O R 1 N H Polymer Polymer Ramani Narayan, Michigan State University,

20 Pilot-Scale Composting of PE-Coated Packaging C packaging materials C inoculum (1752 g) (147 g) INPUT 5% Plastic COMPOST BIOREACTOR C co2 (1205 g) OUTPUT 34% Plastic C plastic C cellulosic C biomass (234 g) (323 g) (124 g) Ramani Narayan, Michigan State University,

21 Ramani Narayan, Michigan State University,

22 Pilot Scale Composting of paper-yard waste C/N Time (days) DH% Ramani Narayan, Michigan State University,

23 COMPOSTABLE PLASTICS MEETING NOSB DEFINITIONS AND REQUIREMENTS Biodegradable plastic products that meet ASTM D6400 (Standard Specification for Compostable Plastics), and ASTM D6868 (Standard Specification for biodegradable plastics used as coatings on paper and other compostable substrates) are required to be: completely consumed (assimilated) by the microbes present in compost. They function as food for the microorganisms providing it with energy to drive their life processes, and thereby promoting the regular composting process. At the end of the compost period there is no biodegradable plastic/product remaining, they are all consumed by the microorganisms in the composting process. Compostable plastics (completely biodegradable plastics under composting conditions) meeting ASTM D6400, D6868 specifications satisfy the feedstock requirements defined by the NOSB, and the compost task force they become part of the microorganisms because they are transported into the microbial cells where they are oxidized to CO2, releasing energy for the microbial life processes. The ASTM Specification Standards require that all of the substrate carbon is consumed by the microorganisms. Ramani Narayan, Michigan State University

24 COMPOSTABLE PLASTICS MEETING NOSB DEFINITIONS AND REQUIREMENTS petitioning for inclusion in the National list of allowable substance to be used in manufacture of organic products is not applicable and moot. The biodegradable plastic/product does not exist anymore after the composting process it is all used up as biological fuel by the microorganisms for its life processes. The compost that is generated comes from the plant and other organic matter used in the composting process and will meet the basic fundamental definition and requirements set by the NOSB. Ramani Narayan, Michigan State University

25 Carbon footprint reduction strategy using bio content Problems with incomplete and partial biodegradation Thompson, R.C. et al Lost at sea: Where is all the plastic? Science 304, 838, 2004 plastic pieces can attract and hold hydrophobic elements like PCB and DDT up to one million times background levels. As a result, floating plastic is like a poison pill From Algalita Marine Research Foundation PCBs, DDE, and nonylphenols (NP) were detected in high concentrations in degraded polypropylene (PP) resin pellets collected from four Japanese coasts. Plastic residues function as a transport medium for toxic chemicals in the marine environment. Takada et al Environ. Sci. Technol. 2001, 35, Blight, L.K. & A.E. Burger Occurrence of plastic particles in seabirds from the Eastern North Pacific. Mar. Poll. Bull. 34: Phil. Trans. Royal. Soc. (Biology) July 27, 2009; 364 Ramani Narayan, Michigan State University 25