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Basics Avoiding confusion between biodegradable and compostable By: Pau Balaguer Project manager ITENE Research Center Paterna, Spain The terms biodegradable and compostable can be quite confusing words. Both words define biological processes but these concepts have often been misused in the field of marketing, leading to confusion. Any new products claimed to be compostable should be certified according to standardized testing methods and need to be identified with well-recognized logos promoted by several well-positioned entities. In recent years and mainly in the packaging sector, there has been a rising trend in replacing traditional plastics such as polyethylene and polypropylene by biodegradable materials in order to reduce the generation of packaging waste. With this regard certain bioplastics and cellulosic materials can be used. Bioplastics encompasses a whole family of materials which differ from conventional plastics insofar as that they are biobased, biodegradable, or both (fig. 1). Biobased means that the material or product is (partly) derived from renewable resources. According to their origin, biobased polymers can be grouped into three classes [2, 3]: (i) Polymers extracted directly from biomass, (ii) polymers synthesized from monomers obtained from biomass, and (iii) polymers produced by microorganisms. The first type of biobased polymers includes those based on polysaccharides (starch, cellulose…), and proteins (wheat gluten, soy protein, gelatin…). The second group of biopolymers covers a wide range of materials, such as poly (lactic acid) (PLA), produced from lactic acid obtained by fermentation of, for example, sugar cane; biopolyethylene (BioPE), from the polymerization of ethylene produced from bioethanol; and bio-polyurethanes, incorporating polyols of vegetable origin. The third type refers to biopolymers that are produced directly by microorganisms, such as polyhydroxyalkanoates (PHA) [4]. However, not all of them are biodegradable. The term biodegradable refers to a chemical process during which microorganisms that are available in the environment convert materials into natural substances such as water, carbon dioxide and biomass. There are diverse environments for biodegradation of materials, such as soil, water, marine environment, digester plants, household composting units, and industrial composting facilities. Regarding packaging waste, composting appears to be a feasible solution for its recovery reducing the need for final disposal (e. g. in landfill) of used packaging of those materials that meet specific requirements. To be considered as compostable a material or product have to undergo degradation by biological processes during composting to yield carbon dioxide, water, inorganic compounds, and biomass at a rate consistent with other known compostable materials, and must not leave any (visible or invisible) or even toxic residues. Following the definition of the terms biodegradable and compostable, any product can be biodegradable, but what really matters is the time frame in which a material is biodegraded and in which environment. Compostable thus restricts the term fixing both aspects, and deals with other important aspects such as material characteristics, disintegration degree, and quality of the resulting compost. Then it is important to remark that all compostable materials are biodegradable, but not all biodegradable materials are compostable. Many unsubstantiated claims to biodegradability and compostability were made in the past as a consequence of Figure 1. Biobased and biodegradable plastics [1] FROM RENEWABLE RESOURCES Figure 2. Compostability logos given by Vinçotte and DIN-Certco: OK COMPOST and Seedling and by DIN-Certco: Industrial Compostable. The Seedling is a trademark owned by European Bioplastics NOT DEGRADABLE bio-PE, bio-PA cellulose-acetate bio-polyisoprene PLA PHA (PHB...) TPS Celluloseregenerates BIODEGRADABLE / COMPOSTABLE no bioplastics PE-LD, PE-HD PP, PA, PS PVC, EVOH, oxo-fragmentable blends certain Co- Polyesters (e.g. PBAT), Polycaprolacton, PVA,... FROM FOSSIL RAW MATERIALS 42 bioplastics MAGAZINE [<strong>03</strong>/16] Vol. 11
Basics the lack of well-identified environmental requirements, and inexistence of well-established testing methods. However, since year 2000 there are standard methodologies to evaluate the suitability of a material for its organic recovery by composting. EN 13432 [5] is one of the most recognized standard norms that defines the procedure and the criteria to determine the compostability of a material. Logos (fig. 2) and certificates issued by several certification bodies such as DIN CERTCO and VINÇOTTE in Europe, BPI in USA, and JBPA in Japan, allow demonstrating the conformity of final products, materials, intermediates, and additives with the specified criteria in the standard compostability norms. Moreover, false and misleading environmental claims are being pursue by diverse organizations, such as Federal Trade Commission in the USA, which imposed recently a USD 450,000 civil penalty [6]. In order to obtain the different compostability logos the testing must be conducted in laboratories which are recognized by the certification bodies [7, 8]. Compostability testing The different tests to be performed in order to determine if a material, intermediate, additive or product can be recovered through composting according to EN 13432 [5] (and if applicable, in connection with ASTM D 6400 [9], ISO 18606 [10], ISO 17088 [11], EN 14995 [12]) are compiled in table 1 and described in the next subsections. Material characterization: Each product shall be identified and characterized including at least: 1. Information and identification of the constituents, 2. presence of regulated metals (Zn, Cu, Ni, Cd, Pb, Hg, Cr, Mo, Se, As, Co [13]) and other hazardous substances to the environment (F), and 3. content in total dry and volatile solids. Biodegradation Biodegradability is determined by measuring the carbon dioxide produced by the sample under controlled composting conditions following ISO 14855-1:2012 [16]. For this the sample is mixed with compost and placed in bioreactors at 58 °C under continuous flow of humidified air. At the exit the CO 2 concentration is measured and related to the theoretical amount that could be produced regarding the carbon content of the sample. The biodegradability should be determined for the whole material and individually for the constituents present at levels between 1 and 10 % [17]. The minimum duration of the test is 45 days, in which a positive control (cellulose) has to be biodegraded at least in a 70 %, and the maximum duration set out in the standard is 6 months, in which the sample has to be biodegraded in a 90 % to be considered as biodegradable in compost [18]. Figure 3 shows the different phases observed during biodegradation tests. Phase A corresponds to the lag time sometimes observed for initiate the biodegradation; Phase B corresponds to the active biodegradation of molecules into CO 2 and H 2 O; Phase C is the plateau zone reached after biodegradation has taken place, and D determines the ultimate level of biodegradation. After the first 45 days, continuation of the biodegradation test could be necessary or not depending on the biodegradation rate of the material and the phase achieved. Figure 3. Typical biodegradation curve. Biodegradation, % 100 90 80 70 60 50 40 30 20 10 0 0 A A Lag phase B Degradation phase C Stationary phase D Degree of biodegradation B 4 8 12 16 20 24 28 32 36 40 44 Time, days C D Table 1. Summary description of tests to be performed under EN 13432:2000. Test Standard Test duration Sample weight Chemical characterization of material: - Dry and volatile solids - Regulated metals (Zn, Cu, Ni, Cd, Pb, Hg, Cr, Mo, Se, As, Co [13]) - Hazardous substances (F) - Infrared transmission spectrum Biodegradation under industrial composting conditions Disintegration under ind. composting conditions and physico-chemical Pilot-scale properties of compost (total dry solids, volatile solids, pH, N-NH 4 , N-NO 2 , N-NO 3 , N, P, K, Mg, salt content, density, and maturity level) Ecotoxicity in 2 plant species: - Garden cress (Lepidium sativum) - Summer barley (Hordeum vulgare) EN 13432:2000 PT-04-63 EN 13432:2000 ISO 14855-1:2012 EN 13432:2000 ISO 16929:2013 2 weeks 20 g in powder 6 weeks – 6 months 100 g in powder 12 weeks 2 kg in final form, 14 kg in powder Lab-scale ISO 20200:2004 [15] 90 days (+ 90 days) 500 g in final form EN 13432:2000 OECD 208 (2006) 3 weeks, after disintegration test (compost samples from pilot-scale disintegration) bioplastics MAGAZINE [<strong>03</strong>/16] Vol. 11 43
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