User:Polymersrock/draft article: Difference between revisions
Polymersrock (talk | contribs) edited formatting of Specific Testing Methods subsection |
Polymersrock (talk | contribs) added a lot of information to the mechanisms section and reordered the information that was already included in the article before |
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Biodegradable additives attract microorganisms to the polymer through [[quorum sensing]] after [[biofilm]] creation on the [[plastic]] product. Additives are generally in [[masterbatch]] formation that use carrier resins such as [[polyethylene]], [[polypropylene]], [[polystyrene]] or [[polyethylene terephthalate]]. |
Biodegradable additives attract microorganisms to the polymer through [[quorum sensing]] after [[biofilm]] creation on the [[plastic]] product. Additives are generally in [[masterbatch]] formation that use carrier resins such as [[polyethylene]], [[polypropylene]], [[polystyrene]] or [[polyethylene terephthalate]]. |
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Chemical and physical properties of plastics play important roles in the process of biodegradation. Biodegradable additives can influence the mechanism of biodegradation by changing these chemical and physical properties.<ref name=":2" /> |
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== Mechanism of biodegradation == |
== Mechanism of biodegradation == |
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There are several different mechanisms and conditions in which microorganisms can carry out the process of plastic degradation. In general, the process of plastic biodegradation results in a considerable decrease in molecular weight leading to a loss of structural integrity of the plastic. |
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This section will discuss the various mechanisms of biodegradation and microbic degradation. There are a few common mechanisms that are cited throughout the literature: anaerobic, aerobic, direct, indirect. |
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| ⚫ | In most cases, plastic is made up of [[hydrophobic]] [[Polymer|polymers]]. Chains must be broken down into constituent parts for the energy potential to be used by [[microorganisms]]. These constituent parts, or [[monomers]], are readily available to other [[bacteria]]. The process of breaking these chains and dissolving the smaller molecules into solution is called [[hydrolysis]]. Therefore, hydrolysis of these high-molecular-weight polymeric components into their constituent oligomers, dimers, and monomers is the necessary first step in both aerobic and anaerobic biodegradation. Through hydrolysis, the complex organic molecules are broken down into simple sugars, [[Amino acid|amino acids]], and [[Fatty acid|fatty acids]]. Enzyme-based microbial degradation can occur under two conditions: aerobic and anaerobic. Common enzymes involved in microbial plastic biodegradation include lipase, proteinase K, pronase, and hydrogenase, among others.<ref name=":4">{{Cite journal|last=Ghosh|first=Swapan Kumar|last2=Pal|first2=Sujoy|last3=Ray|first3=Sumanta|date=2013-7|title=Study of microbes having potentiality for biodegradation of plastics|url=http://link.springer.com/10.1007/s11356-013-1706-x|journal=Environmental Science and Pollution Research|language=en|volume=20|issue=7|pages=4339–4355|doi=10.1007/s11356-013-1706-x|issn=0944-1344}}</ref> The efficacy of these enzymes will depend on which plastic they are degrading. |
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=== Aerobic === |
=== Aerobic === |
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Under [[aerobic]] conditions, the microorganisms will use oxygen as an electron acceptor. The resulting products will be carbon dioxide (CO<sub>2</sub>) and water (H<sub>2</sub>O).<ref name=":3">{{Cite journal|last=Shah|first=Aamer Ali|last2=Hasan|first2=Fariha|last3=Hameed|first3=Abdul|last4=Ahmed|first4=Safia|date=2008-5|title=Biological degradation of plastics: A comprehensive review|url=https://linkinghub.elsevier.com/retrieve/pii/S0734975008000141|journal=Biotechnology Advances|language=en|volume=26|issue=3|pages=246–265|doi=10.1016/j.biotechadv.2007.12.005}}</ref> |
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=== Anaerobic |
=== Anaerobic=== |
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Under anaerobic conditions, the lack of oxygen requires that the bacteria use a different source for an electron acceptor. Common electron acceptors used by anaerobic bacteria are sulfate, iron, nitrate, manganese and carbon dioxide. The resulting products under anaerobic conditions will be carbon dioxide (CO<sub>2</sub>), water (H<sub>2</sub>O), and methane (CH<sub>4</sub>).<ref>{{Cite journal|last=Ahmed|first=Temoor|last2=Shahid|first2=Muhammad|last3=Azeem|first3=Farrukh|last4=Rasul|first4=Ijaz|last5=Shah|first5=Asad Ali|last6=Noman|first6=Muhammad|last7=Hameed|first7=Amir|last8=Manzoor|first8=Natasha|last9=Manzoor|first9=Irfan|date=2018-3|title=Biodegradation of plastics: current scenario and future prospects for environmental safety|url=http://link.springer.com/10.1007/s11356-018-1234-9|journal=Environmental Science and Pollution Research|language=en|volume=25|issue=8|pages=7287–7298|doi=10.1007/s11356-018-1234-9|issn=0944-1344}}</ref> |
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source<ref name=":4">{{Cite journal|last=Ghosh|first=Swapan Kumar|last2=Pal|first2=Sujoy|last3=Ray|first3=Sumanta|date=2013-7|title=Study of microbes having potentiality for biodegradation of plastics|url=http://link.springer.com/10.1007/s11356-013-1706-x|journal=Environmental Science and Pollution Research|language=en|volume=20|issue=7|pages=4339–4355|doi=10.1007/s11356-013-1706-x|issn=0944-1344}}</ref> |
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source<ref name=":4" /> |
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<nowiki>**</nowiki>The below information is from the original article: |
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A simple chemical equation of the process is: |
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[[Acetate]] and hydrogen produced in the first stages can be used directly by [[Methanogen|methanogens]]. Other molecules, such as volatile fatty acids (VFAs) with a chain length greater than that of acetate must first be [[Catabolise|catabolised]] into compounds that can be directly used by methanogens. |
[[Acetate]] and hydrogen produced in the first stages can be used directly by [[Methanogen|methanogens]]. Other molecules, such as volatile fatty acids (VFAs) with a chain length greater than that of acetate must first be [[Catabolise|catabolised]] into compounds that can be directly used by methanogens. |
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The terminal stage of anaerobic biodegradation is the biological process of [[methanogenesis]]. Here, methanogens use the intermediate products of the preceding stages and convert them into methane, carbon dioxide, and water. These components make up the majority of the [[biogas]] emitted. Methanogenesis is sensitive to both high and low [[PH|pHs]] and occurs between pH 6.5 and pH 8. The remaining, indigestible material the microbes cannot use and any dead bacterial remains constitute the digestate.<ref>{{cite web|url=http://www.biosphereplastic.com/uncategorized/what-is-biodegradation/|title=Biodegradable Plastic by Additives|date=|publisher=BioSphere Biodegradable Plastic|accessdate=2012-08-30}}</ref> |
The terminal stage of anaerobic biodegradation is the biological process of [[methanogenesis]]. Here, methanogens use the intermediate products of the preceding stages and convert them into methane, carbon dioxide, and water. These components make up the majority of the [[biogas]] emitted. Methanogenesis is sensitive to both high and low [[PH|pHs]] and occurs between pH 6.5 and pH 8. The remaining, indigestible material the microbes cannot use and any dead bacterial remains constitute the digestate.<ref>{{cite web|url=http://www.biosphereplastic.com/uncategorized/what-is-biodegradation/|title=Biodegradable Plastic by Additives|date=|publisher=BioSphere Biodegradable Plastic|accessdate=2012-08-30}}</ref> |
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Some microorganisms can directly consume plastic fragments and use the carbon as a nutritional source.<ref name=":4" /> |
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Microbes involved in the breakdown of fossil-based plastics typically used an indirect mechanism in which microbial enzymes break down the plastic. Through indirect action, the metabolic products of the microorganism will affect the properties of the plastic, resulting in degradation.<ref name=":4" /> |
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== Types of biodegradable Additives == |
== Types of biodegradable Additives == |
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[[File:Plastic waste at Batlapalem, Andhra Pradesh.jpg|thumb|As seen in this image, large areas of land are currently covered in plastic waste. Biodegradable additives will help speed up the biodegradation process of some plastics so that these plastic pile ups will be less frequent. ]] |
[[File:Plastic waste at Batlapalem, Andhra Pradesh.jpg|thumb|As seen in this image, large areas of land are currently covered in plastic waste. Biodegradable additives will help speed up the biodegradation process of some plastics so that these plastic pile ups will be less frequent. ]] |
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Plastics are ubiquitous in everyday life and are produced in huge quantities each year. Many common plastics, such as polyethylene, polypropylene, polystyrene, poly(vinyl chloride), and poly(ethylene terephthalate), that can be found in most consumer products are not biodegradable.<ref>{{Cite journal|last=Tokiwa|first=Yutaka|last2=Calabia|first2=Buenaventurada|last3=Ugwu|first3=Charles|last4=Aiba|first4=Seiichi|date=2009-08-26|title=Biodegradability of Plastics|url=http://www.mdpi.com/1422-0067/10/9/3722|journal=International Journal of Molecular Sciences|language=en|volume=10|issue=9|pages=3722–3742|doi=10.3390/ijms10093722|issn=1422-0067}}</ref> These, and other, non-biodegradable plastics accumulate in the environment, which is threat to both human and animal health and leads to harmful changes in our planet. |
Plastics are ubiquitous in everyday life and are produced in huge quantities each year. Many common plastics, such as polyethylene, polypropylene, polystyrene, poly(vinyl chloride), and poly(ethylene terephthalate), that can be found in most consumer products are not biodegradable.<ref name=":2">{{Cite journal|last=Tokiwa|first=Yutaka|last2=Calabia|first2=Buenaventurada|last3=Ugwu|first3=Charles|last4=Aiba|first4=Seiichi|date=2009-08-26|title=Biodegradability of Plastics|url=http://www.mdpi.com/1422-0067/10/9/3722|journal=International Journal of Molecular Sciences|language=en|volume=10|issue=9|pages=3722–3742|doi=10.3390/ijms10093722|issn=1422-0067}}</ref> These, and other, non-biodegradable plastics accumulate in the environment, which is threat to both human and animal health and leads to harmful changes in our planet. |
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Current solutions to dealing with the amount of plastic being thrown away include burning the plastics and dumping them into large fields or landfills. Burning plastics leads to significant amounts of air pollution, which is harmful to human health. When dumped into fields or landfills, plastics can cause changes in the pH of the soil, leading to infertile land once the plastics are degraded.<ref name=":4" /> |
Current solutions to dealing with the amount of plastic being thrown away include burning the plastics and dumping them into large fields or landfills. Burning plastics leads to significant amounts of air pollution, which is harmful to human health. When dumped into fields or landfills, plastics can cause changes in the pH of the soil, leading to infertile land once the plastics are degraded.<ref name=":4" /> |
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Revision as of 23:47, 30 April 2019
Most plastics contain various additives to improve certain characteristics of the polymer, such as ductility, hardness, and durability.[1] Biodegradable additives are additives that enhance the biodegradation of polymers by allowing microorganisms to utilize the carbon within the polymer chain itself.
Biodegradable additives attract microorganisms to the polymer through quorum sensing after biofilm creation on the plastic product. Additives are generally in masterbatch formation that use carrier resins such as polyethylene, polypropylene, polystyrene or polyethylene terephthalate.
Chemical and physical properties of plastics play important roles in the process of biodegradation. Biodegradable additives can influence the mechanism of biodegradation by changing these chemical and physical properties.[2]
Mechanism of biodegradation
There are several different mechanisms and conditions in which microorganisms can carry out the process of plastic degradation. In general, the process of plastic biodegradation results in a considerable decrease in molecular weight leading to a loss of structural integrity of the plastic.
In most cases, plastic is made up of hydrophobic polymers. Chains must be broken down into constituent parts for the energy potential to be used by microorganisms. These constituent parts, or monomers, are readily available to other bacteria. The process of breaking these chains and dissolving the smaller molecules into solution is called hydrolysis. Therefore, hydrolysis of these high-molecular-weight polymeric components into their constituent oligomers, dimers, and monomers is the necessary first step in both aerobic and anaerobic biodegradation. Through hydrolysis, the complex organic molecules are broken down into simple sugars, amino acids, and fatty acids. Enzyme-based microbial degradation can occur under two conditions: aerobic and anaerobic. Common enzymes involved in microbial plastic biodegradation include lipase, proteinase K, pronase, and hydrogenase, among others.[3] The efficacy of these enzymes will depend on which plastic they are degrading.
Aerobic
Under aerobic conditions, the microorganisms will use oxygen as an electron acceptor. The resulting products will be carbon dioxide (CO2) and water (H2O).[4]
Anaerobic
Under anaerobic conditions, the lack of oxygen requires that the bacteria use a different source for an electron acceptor. Common electron acceptors used by anaerobic bacteria are sulfate, iron, nitrate, manganese and carbon dioxide. The resulting products under anaerobic conditions will be carbon dioxide (CO2), water (H2O), and methane (CH4).[5]
A simple chemical equation of the anaerobic process is: C6H12O6 → 3CO2 + 3CH4
Acetate and hydrogen produced in the first stages can be used directly by methanogens. Other molecules, such as volatile fatty acids (VFAs) with a chain length greater than that of acetate must first be catabolised into compounds that can be directly used by methanogens.
The biological process of acidogenesis results in further breakdown of the remaining components by acidogenic (fermentative) bacteria. Here, VFAs are created, along with ammonia, carbon dioxide, and hydrogen sulfide, as well as other byproducts. The process of acidogenesis is similar to the way milk sours.
The third stage of anaerobic digestion is acetogenesis. Simple molecules created through the acidogenesis phase are further digested by Acetogens to produce largely acetic acid, as well as carbon dioxide and hydrogen.
The terminal stage of anaerobic biodegradation is the biological process of methanogenesis. Here, methanogens use the intermediate products of the preceding stages and convert them into methane, carbon dioxide, and water. These components make up the majority of the biogas emitted. Methanogenesis is sensitive to both high and low pHs and occurs between pH 6.5 and pH 8. The remaining, indigestible material the microbes cannot use and any dead bacterial remains constitute the digestate.[6]
Direct Action
Some microorganisms can directly consume plastic fragments and use the carbon as a nutritional source.[3]
Indirect Action
Microbes involved in the breakdown of fossil-based plastics typically used an indirect mechanism in which microbial enzymes break down the plastic. Through indirect action, the metabolic products of the microorganism will affect the properties of the plastic, resulting in degradation.[3]
Types of biodegradable Additives
Starch
Experiments have been done on the feasibility of using starch as a biodegradable additive.[7]
Bioaugmentation
Experiments have been done on bioaugmentation - the addition of certain microbial strains to plastics - and its role in increasing biodegradability.[8]
Testing of biodegradable additives
Testing methods
This section will include certain tests for crystallinity, morphology, etc.
Testing environments/conditions
Soil Burial
source[7]
Compost[8]
Specific Testing Methods
The following testing methods have been approved by the American Society for Testing and Materials:
- ASTM D5511-12 testing is for the "Anerobic Biodegradation of Plastic Materials in a High Solids Environment Under High-Solids Anaerobic-Digestion Conditions"[9]
- ASTM D5526-12 testing is for the "Standard Test Method for Determining Anaerobic Biodegradation of Plastic Materials Under Accelerated Landfill Conditions"[10]
- ASTM D5210-07 testing is for the "Standard Test Method for Determining the Anaerobic Biodegradation of Plastic Materials in the Presence of Municipal Sewage Sludge"[11]
Laboratories performing ASTM testing methods
- Eden Research Labs
- Respirtek
- NE Laboratories
- National Science Foundation (NSF)
Environmental Impact
Plastics are ubiquitous in everyday life and are produced in huge quantities each year. Many common plastics, such as polyethylene, polypropylene, polystyrene, poly(vinyl chloride), and poly(ethylene terephthalate), that can be found in most consumer products are not biodegradable.[2] These, and other, non-biodegradable plastics accumulate in the environment, which is threat to both human and animal health and leads to harmful changes in our planet.
Current solutions to dealing with the amount of plastic being thrown away include burning the plastics and dumping them into large fields or landfills. Burning plastics leads to significant amounts of air pollution, which is harmful to human health. When dumped into fields or landfills, plastics can cause changes in the pH of the soil, leading to infertile land once the plastics are degraded.[3]
Because of the substantial growth in plastic consumption, biodegradable additives are becomingly increasingly necessary to increase the rate of degradability of common plastics. Current research is focused on finding new biodegradable additives and determining their impacts in the degradation process.
References
- ^ Selke, Susan; Auras, Rafael; Nguyen, Tuan Anh; Castro Aguirre, Edgar; Cheruvathur, Rijosh; Liu, Yan (2015-03-17). "Evaluation of Biodegradation-Promoting Additives for Plastics". Environmental Science & Technology. 49 (6): 3769–3777. doi:10.1021/es504258u. ISSN 0013-936X.
- ^ a b Tokiwa, Yutaka; Calabia, Buenaventurada; Ugwu, Charles; Aiba, Seiichi (2009-08-26). "Biodegradability of Plastics". International Journal of Molecular Sciences. 10 (9): 3722–3742. doi:10.3390/ijms10093722. ISSN 1422-0067.
{{cite journal}}: CS1 maint: unflagged free DOI (link) - ^ a b c d Ghosh, Swapan Kumar; Pal, Sujoy; Ray, Sumanta (2013-7). "Study of microbes having potentiality for biodegradation of plastics". Environmental Science and Pollution Research. 20 (7): 4339–4355. doi:10.1007/s11356-013-1706-x. ISSN 0944-1344.
{{cite journal}}: Check date values in:|date=(help) - ^ Shah, Aamer Ali; Hasan, Fariha; Hameed, Abdul; Ahmed, Safia (2008-5). "Biological degradation of plastics: A comprehensive review". Biotechnology Advances. 26 (3): 246–265. doi:10.1016/j.biotechadv.2007.12.005.
{{cite journal}}: Check date values in:|date=(help) - ^ Ahmed, Temoor; Shahid, Muhammad; Azeem, Farrukh; Rasul, Ijaz; Shah, Asad Ali; Noman, Muhammad; Hameed, Amir; Manzoor, Natasha; Manzoor, Irfan (2018-3). "Biodegradation of plastics: current scenario and future prospects for environmental safety". Environmental Science and Pollution Research. 25 (8): 7287–7298. doi:10.1007/s11356-018-1234-9. ISSN 0944-1344.
{{cite journal}}: Check date values in:|date=(help) - ^ "Biodegradable Plastic by Additives". BioSphere Biodegradable Plastic. Retrieved 2012-08-30.
- ^ a b Santonja-Blasco, L.; Contat-Rodrigo, L.; Moriana-Torró, R.; Ribes-Greus, A. (2007-11-15). "Thermal characterization of polyethylene blends with a biodegradable masterbatch subjected to thermo-oxidative treatment and subsequent soil burial test". Journal of Applied Polymer Science. 106 (4): 2218–2230. doi:10.1002/app.26667.
- ^ a b Castro-Aguirre, E.; Auras, R.; Selke, S.; Rubino, M.; Marsh, T. (2018-8). "Enhancing the biodegradation rate of poly(lactic acid) films and PLA bio-nanocomposites in simulated composting through bioaugmentation". Polymer Degradation and Stability. 154: 46–54. doi:10.1016/j.polymdegradstab.2018.05.017.
{{cite journal}}: Check date values in:|date=(help) - ^ "ASTM D5511-12". ASTM International. Retrieved 2012-06-30.
- ^ "ASTM D5526-12". ASTM International. Retrieved 2012-06-30.
- ^ "ASTM D5210-07". ASTM International. Retrieved 2012-06-30.