Sulapac® key feature: Designed to reduce plastic pollution

Sulapac materials can be digested by naturally occurring microorganisms. They biodegrade in the sense that they do not leave permanent microplastics behind.*  54–68 %  biodegradation into CO2, water and biomass has been measured in 364 days in the marine environment (ASTM D6691, 86oF/ 30oC) for Sulapac Universal and Sulapac Flow materials. The biodegradability properties originate from the unique combination of raw materials.

*Not considered degradable in California.

 

Background

Microplastics refers to small plastic particles, commonly accepted to measure a size of 5 mm or less in at least one external dimension. Currently there is no precise internationally standardized definition of a microplastic. Sulapac® has adopted the definition used by European Chemical Agency, ECHA [1,2], according to which:

“Microplastics means a material consisting of solid polymer containing particles, to which additives or other substances may have been added, and where ≥ 1% w/w of particles have (i) all dimensions 1nm ≤ x ≤ 5mm, or (ii), for fibers, a length of 3nm ≤ x ≤ 15mm and length to diameter ratio of >3. Polymers that occur in nature that have not been chemically modified (other than by hydrolysis) are excluded (as are polymers that are (bio)degradable).”

There are different views on how fast a material has to biodegrade in order to be excluded from the definition. To keep our microplastics definition solid in all contexts we also include small synthetic, biodegradable polymer particles in it. However, we make a difference between permanent microplastics, which resist biodegradation and thus accumulate in nature and biodegradable microplastics, which do not accumulate as they are converted into CO2, water and biomass by naturally occurring microbes.

Based on their origin microplastics can be classified into i) primary microplastics, which are small plastic particles that have originally been fabricated to be micro-size and intentionally added in products such as cosmetics and paints and  ii) secondary microplastics, which mean microplastics releases (particle emissions) formed due to wearing of macroscopic plastics [1, 2].

Microplastics originate from various sources. Any man-made polymer in plastics, fibers, tires, paints, cosmetics etc. can be a source of microplastics. If the particles are permanent, meaning resistant to biodegradation, they accumulate as microplastic pollution.

Remarkable amounts of microplastic pollution has been found all around the globe in seas, lakes, rivers, soil, urban and countryside atmosphere indoors & outdoors. WWF has estimated that we all ingest about 5 grams of microplastics every week, which equals to the size of one credit card. [3]

The potential environmental and human health risks of permanent microplastic particles are associated to (a) small size (typically microscopic) making them readily available for ingestion, and (b) resistance to normal environmental degradation, which will lead in to a long presence and accumulation in the environment after their initial release [4]. It has been observed that it’s possible that accumulating microplastics collect harmful chemicals and pathogens on their large surface area [5, 6]. There is also evidence that microplastics can contribute to disruption of the gut microbiome & inflammation in tissue. However, precise understanding of the fate and impacts of microplastics is still lacking. Fortunately, a lot of research is on-going.

To mitigate the issue of microplastics, actions on many levels are needed. Better waste management is important but not enough, as microplastic emissions can occur also during production & use phases, F.ex. when opening plastics packaging [7, 8]. Substitution of conventional plastics with materials that biodegrade and thus don’t leave permanent microplastics behind, can play an important role in the mitigation of microplastics accumulation.

 

Biodegradation mechanism of biodegradable biopolymers

Biodegradation of biopolymers and wood-biopolymer-composites are complex processes involving multiple steps and pathways. In the first step the macromolecules are broken down to monomers and oligomers. Oligomers/ monomers (Cpolymer) can pass through the cell membrane and thus can be taken up by the microorganisms, in which the subsequent metabolic activity breaks them down into metabolic end products such as carbon dioxide and water, while a portion of the carbon is converted into biomass. [9-11].

  1. Polymer → n Cpolymer (macromolecules break down by enzymes/ hydrolysis)
  2. n Cpolymer → Cbiomass (uptake of monomers/oligomers and beginning of metabolism)
  3. Cbiomass → CO2 + H2O (mineralization)

Biodegradation is an important decay mechanism of biological materials in nature. One of its functions is to recycle carbon and nutrients back to soil and environment in the forms of biomass and mineral salts. The whole carbon cycle would be very different, if all the carbon in the biological materials in nature would be converted 100% into CO2 (or methane), without any biomass formation

 

Key feature

Sulapac materials biodegrade in nature in the sense that they do not leave permanent microplastics behind. In other words, if leaked to the nature or worn in use, Sulapac materials do not accumulate, and thus, are not capable of collecting harmful chemicals or pathogens that can enrich along the food chain.

As all other biopolymers, such as collagen and native cellulose, Sulapac materials disintegrate first into tiny particles. However, in contrast to conventional plastics, after disintegration Sulapac materials biodegrade on molecular level into CO2 (CH4 if no oxygen is present), water and biomass in open environments within a similar time frame as naturally occurring biological materials such as wood and tree leaves.

Various tree leaves have shown to disintegrate and biodegrade in nature in 0.5–5 years depending on the tree species and environment [12-14].

The risks associated with a material that lasts 1-5 years in the environment, versus one that lasts 500 years, are completely different. [15]

 

Criteria

Several standardized test methods for biodegradation of materials in open environments exist. As sea water is considered to be the most difficult environment for biodegradation, we have chosen the test method ASTM D6691 “Standard Test Method for Determining Aerobic Biodegradation of Plastic Materials in the Marine Environment by a Defined Microbial Consortium or Natural Sea Water Inoculum”.

Anaerobic conditions are also considered as a difficult environment for biodegradation. For testing Sulapac materials in these conditions we have used ASTM D5511 “Standard Test method for Determining Anaerobic Biodegradation of Plastic Materials Under High-Solids Anaerobic-Digestion Conditions”. This method simulates an accelerated biodegradation process that takes place in a landfill because it is a stationary (no mixing) and dry (20 to 40 % solids) fermentation under optimal conditions.

In ASTM D6691 and ASTM D5511 tests the samples are in a powdered (disintegrated / microplastic) form and their molecular level degradation into CO2/CH4, H2O and biomass is measured. The reference material in these tests is native cellulose powder, and the biodegradation of the samples is calculated as the relative biodegradation percentage with respect to cellulose. [16, 17]

 

Validation

On the basis of the ASTM 6691 testing results we know that the relative biodegradation in sea water at 86oF (30oC) has proceeded to 54–68 % for Sulapac Flow and Sulapac Universal materials in 364 days. This proves that

  • sea water contains microbes which can digest Sulapac materials
  • biodegradation on molecular level to CO2, water & biomass occurs
  • in addition to wood also the biopolymers have started to biodegrade

 

Tosin et al [18] have demonstrated that if a polymer material for which biodegradation has been proven would be tested in a form of nanoplastics, the total biodegradation process would be extremely fast, lasting 10-20 days at maximum, with a time frame similar to that required by the OECD for the classification of “readily biodegradable chemicals” [19]. This shows, that the chemical permanence time of truly biodegradable materials is very short, and that these materials do not generate persistent microplastics (because as erosion increases the surface area of an item, this increases the biodegradation rate to levels similar to those required by the OECD for chemicals to be defined as readily biodegradable).

ASTM D5511 results for Sulapac Universal show that at 160 days, 68 % relative biodegradation is reached in anaerobic conditions at 99 oF  (37 oC) (accelerated landfill conditions). When comparing this result to ASTM D5511 results obtained by Kolstad et al [20] for PLA and oak leaves it can be stated that Sulapac Universal biodegrades on landfills over 10 times faster than semi crystalline PLA and about 2 times faster than oak leaves.

It should be added that Sulapac materials have been successfully tested by a third-party laboratory according to EN 13432/ ASTM D6400 protocol (industrial composting), which in addition to disintegration and biodegradation also tests that the degradation products are not ecotoxic and do not exceed the threshold values for heavy metals. [21, 22].

References

  1. Annex to the annex xv restriction report Proposal for a restriction- Intentionally added microplastics, European Chemical Agency, ECHA, 2019.
  2. https://echa.europa.eu/fi/-/echa-proposes-to-restrict-intentionally-added-microplastics
  3. No Plastic in Nature: Assessing Plastic Ingestion from Nature to People, analysis for WWF by Dalberg & University of Newcastle, Australia. https://wwf.panda.org/wwf_news/press_releases/?348337/Revealed-plastic-ingestion-by-people-could-be-equating-to-a-credit-card-a-week
  4. Note on substance identification and the potential scope of a restriction on uses of ‘microplastics’, Version 1.1, ECHA, 2018.
  5. Rios, L.M., Jones, P.R., Moore, C. and Narayan, U.V. Quantitation of persistent organic pollutants adsorbed on plastic debris from the Northern Pacific Gyre’s ‘eastern garbage patch’. Journal of Environmental Monitoring 12(12), 2226-2236. (2010)
  6. Gallo,, Fossi, C., Weber, R., Santillo, D., Sousa, J., Ingram, I., Nadal, A. and Romano, D. (2018). Marine litter plastics and microplastics and their toxic chemicals components: the need for urgent preventive measures. Environmental sciences Europe 30(1), 13.
  7. Winkler et al., Does mechanical stress cause microplastic release from plastic water bottles?, Water Research, Vol. 166, 2019, 115082.
  8. Sobhani, Z., et al. Microplastics generated when opening plastic packaging, Scientific Reports volume 10, Article number: 4841 (2020)
  9. Vroman et al., Biodegradable Polymers, Materials (Basel). 2009 Jun; 2(2): 307–344.
  10. Tosin et al., Biodegradation kinetics in soil of a multi-constituent biodegradable plastic, Polymer Degradation and Stability, 166 (2019), 213-218.
  11. Kjeldsen, A. et al., A review of Standards for Biodegradable Plastics, Industrial Biotechnology Innovation Centre (IBioIC), UK, 2019.
  12. Hasanuzzaman and Hossain M. Leaf Litter Decomposition and Nutrient Dynamics Associated with Common Horticultural Cropland Agroforest Tree Species of Bangladesh. International Journal of Forestry Research,Volume 2014; Article ID 805940.
  13. Gustafson F. Decomposition for the leaves of some forest leaves under field conditions. American Society of Plant Biologists, 1943.
  14. Webster, J.R, Benfield, E.F., Vascular plant breakdown in freshwater ecosystems  Rev. Ecol. Syst. 1986. 17:567-94.
  15. Collin Ward, a marine chemist at Woods Hole Oceanographic Institution,  https://phys.org/news/2020-06-lifetimes-plastics.amp?__twitter_impression=true
  16. ASTM D6691, Standard Test Method for Determining Aerobic Biodegradation of Plastic Materials in the Marine Environment by a Defined Microbial Consortium or Natural Sea Water Inoculum.
  17. ASTM D5511, Standard Test Method for Determining Anaerobic Biodegradation of Plastic Materials Under High-Solids Anaerobic-Digestion Conditions
  18. Tosin et al., Biodegradation kinetics in soil of a multi-constituent biodegradable plastic, Polymer Degradation and Stability, 166 (2019), 213-218.
  19. OECD, https://www.oecd-ilibrary.org/environment/test-no-301-ready-biodegradability_9789264070349-en
  20. Kolstad et al. Polymer Degradation and Stability 97 (2012) 1131-1141
  21. CEN EN 13432:2000, Requirements for packaging recoverable through composting and biodegradation – Test scheme and evaluation criteria for the final acceptance of packaging.
  22. ASTM D6400 Standard Specification for Compostable Plastics
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