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    Biological Degradation

    Biological Degradation

    The biological degradation is the natural way of wood degradation, which is occurred by different environment factors like moisture, water, fungi, acid, ultraviolet ray, etc.

    From: Reference Module in Materials Science and Materials Engineering, 2018

    Related terms:

    HydrolysisBiodegradationLigninProteinWastewaterEnvironmental PollutantChemical DepolymerizationPlasticizer

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    Assessing the moisture resistance of adhesives for marine environments

    W. Broughton, in Adhesives in Marine Engineering, 2012

    7.3.4 Biodegradation

    Biological degradation is not a common form of degradation as most polymers are resistant to microbiological attack by algae. It is the chemical additives and pigments that are usually susceptible to microbial attack (Campo, 2007), which tends to occur on exposed surfaces due to oxidation of the additives. Polyurethanes in particular are sensitive to microbial attack, although polyether polyurethanes are more resistant to biological degradation than polyester polyurethanes (Brown and Greenwood, 2002; Chanda and Roy, 2009). Polymers that have good water and weather resistance generally have greater resistance to microbial attack. Geographical location and seasonal effects are important because microorganism growth is more rapid in warm, humid climates than cold, dry climates.

    Resistance to mould, algae, fungi and bacteria can be improved by including antimicrobial additives (also known as fungicides or biocides), uniformly distributed throughout the adhesive during the compounding process or alternatively by applying a suitable protective coating and/or sealant around the exposed edges of the adhesive joint. Antimicrobials can provide protection against mould, mildew, fungi and bacterial growth, which can cause discoloration, embrittlement and sometimes product failure. These additives are known to be highly toxic, and care needs to be taken in handling and storage of these materials. The effectiveness of antimicrobials depends on their ability to migrate to the edges of the bonded structure where microbial attack initially occurs. Antimicrobials are usually carried in plasticisers, which are mobile. It is important for the adhesive system to be able to replenish any surface loss caused through leaching or erosion, but only sufficiently to maintain protection. High mobility can cause significant leaching of the antimicrobial through weathering, compromising its ability to protect the adhesive joint from the surrounding environment. Silicone rubbers have good resistance to microbial attack, hence their use as sealants.

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    Improving bonding in hostile chemical environments

    W. Broughton, in Advances in Structural Adhesive Bonding, 2010

    19.2.6 Biological degradation

    Biological degradation is not a common form of degradation as most polymers are resistant to microbiological attack by fungi or bacteria. It is the chemical additives and pigments that are usually susceptible to microbial attack (Campo, 2007), which tends to occur on exposed surfaces owing to oxidation of the additives. Polyurethanes in particular are sensitive to microbial attack, although polyether polyurethanes are more resistant to biological degradation than polyester polyurethanes (Brown and Greenwood, 2002; Chanda and Roy, 2009). Polymers that have good water and weather resistance generally have greater resistance to microbial attack. Geographical location and seasonal effects are important because microorganism growth is more rapid in warm, humid climates than cold, dry climates.

    Resistance to mould, fungi and bacteria can be improved by including antimicrobial additives (also known as fungicides or biocides), uniformly distributed throughout the polymer (or adhesive), during the compounding process or alternatively by applying a suitable protective coating and/or sealant around the exposed edges of the adhesive joint. Antimicrobials can provide protection against mould, mildew, fungi and bacterial growth, which can cause discoloration, embrittlement and sometimes product failure. These additives are known to be highly toxic and care needs to be taken in handling and storing these materials. The effectiveness of antimicrobials depends on their ability to migrate to the edges of the bonded structure where microbial attack initially occurs. Antimicrobials are usually carried in plasticizers, which are mobile. It is important for the adhesive system to be able replenish any surface loss caused through leaching or erosion, but only sufficient to maintain protection. High mobility can cause significant leaching of the antimicrobial via weathering which compromises its ability to protect the adhesive joint from the surrounding environment. As silicone rubbers have good resistance to microbial attack, they are used as sealants.

    Microbial testing generally consists of exposing materials to an outdoor environment in geographical locations where weather conditions are favourable to microbial growth (see ASTM G 21 and ISO 846). The angle of exposure to sunlight and weather conditions will influence the extent and duration of microbial attack. An alternative approach (known as soil burial) is to bury specimens for set periods of time and then to exhume and examine the specimens for the effects of microbial attack. The conditions involved in soil burial tests have been optimized to ensure maximum degradation (Brown and Greenwood, 2002).

    स्रोत : www.sciencedirect.com

    Biodegradation

    Biodegradation

    From Wikipedia, the free encyclopedia

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    For the journal, see Biodegradation (journal).

    This article's lead section may be too short to adequately summarize the key points. Please consider expanding the lead to provide an accessible overview of all important aspects of the article.

    Yellow slime mold growing on a bin of wet paper

    Biodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi.[a][2]

    Contents

    1 Mechanisms

    2 Factors affecting biodegradation rate

    3 Plastics

    4 Biodegradable technology

    5 Biodegradation vs. composting

    6 Environmental and social effects

    7 Etymology of "biodegradable"

    8 See also 9 Notes 10 References

    10.1 Standards by ASTM International

    11 External links

    Mechanisms[edit]

    The process of biodegradation can be divided into three stages: biodeterioration, biofragmentation, and assimilation.[3] Biodeterioration is sometimes described as a surface-level degradation that modifies the mechanical, physical and chemical properties of the material. This stage occurs when the material is exposed to abiotic factors in the outdoor environment and allows for further degradation by weakening the material's structure. Some abiotic factors that influence these initial changes are compression (mechanical), light, temperature and chemicals in the environment.[3] While biodeterioration typically occurs as the first stage of biodegradation, it can in some cases be parallel to biofragmentation.[4] Hueck,[5] however, defined Biodeterioration as the undesirable action of living organisms on Man's materials, involving such things as breakdown of stone facades of buildings,[6] corrosion of metals by microorganisms or merely the esthetic changes induced on man-made structures by the growth of living organisms.[6]

    Biofragmentation of a polymer is the lytic process in which bonds within a polymer are cleaved, generating oligomers and monomers in its place.[3] The steps taken to fragment these materials also differ based on the presence of oxygen in the system. The breakdown of materials by microorganisms when oxygen is present is aerobic digestion, and the breakdown of materials when oxygen is not present is anaerobic digestion.[7] The main difference between these processes is that anaerobic reactions produce methane, while aerobic reactions do not (however, both reactions produce carbon dioxide, water, some type of residue, and a new biomass).[8] In addition, aerobic digestion typically occurs more rapidly than anaerobic digestion, while anaerobic digestion does a better job reducing the volume and mass of the material.[7] Due to anaerobic digestion's ability to reduce the volume and mass of waste materials and produce a natural gas, anaerobic digestion technology is widely used for waste management systems and as a source of local, renewable energy.[9]

    In the assimilation stage, the resulting products from biofragmentation are then integrated into microbial cells.[3] Some of the products from fragmentation are easily transported within the cell by membrane carriers. However, others still have to undergo biotransformation reactions to yield products that can then be transported inside the cell. Once inside the cell, the products enter catabolic pathways that either lead to the production of adenosine triphosphate (ATP) or elements of the cells structure.[3]

    Aerobic biodegradation formula

    Anaerobic degradation formula

    Factors affecting biodegradation rate[edit]

    Average estimated decomposition times of typical marine debris items. Plastic items are shown in blue.

    In practice, almost all chemical compounds and materials are subject to biodegradation processes. The significance, however, is in the relative rates of such processes, such as days, weeks, years or centuries. A number of factors determine the rate at which this degradation of organic compounds occurs. Factors include light, water, oxygen and temperature.[10] The degradation rate of many organic compounds is limited by their bioavailability, which is the rate at which a substance is absorbed into a system or made available at the site of physiological activity,[11] as compounds must be released into solution before organisms can degrade them. The rate of biodegradation can be measured in a number of ways. Respirometry tests can be used for aerobic microbes. First one places a solid waste sample in a container with microorganisms and soil, and then aerates the mixture. Over the course of several days, microorganisms digest the sample bit by bit and produce carbon dioxide – the resulting amount of CO2 serves as an indicator of degradation. Biodegradability can also be measured by anaerobic microbes and the amount of methane or alloy that they are able to produce.[12]

    It's important to note factors that affect biodegradation rates during product testing to ensure that the results produced are accurate and reliable. Several materials will test as being biodegradable under optimal conditions in a lab for approval but these results may not reflect real world outcomes where factors are more variable.[13] For example, a material may have tested as biodegrading at a high rate in the lab may not degrade at a high rate in a landfill because landfills often lack light, water, and microbial activity that are necessary for degradation to occur.[14] Thus, it is very important that there are standards for plastic biodegradable products, which have a large impact on the environment. The development and use of accurate standard test methods can help ensure that all plastics that are being produced and commercialized will actually biodegrade in natural environments.[15] One test that has been developed for this purpose is DINV 54900.[16]

    स्रोत : en.wikipedia.org

    Biological Degradation of Polymers in the Environment

    Polymers present to modern society remarkable performance characteristics desired by a wide range of consumers but the fate of polymers in the environment has become a massive management problem. Poly

    Home > Books > Plastics in the Environment

    OPEN ACCESS PEER-REVIEWED CHAPTER

    Biological Degradation of Polymers in the Environment

    WRITTEN BY John A. Glaser

    Submitted: April 11th, 2018Reviewed: February 11th, 2019Published: May 13th, 2019

    DOI: 10.5772/intechopen.85124

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    Plastics in the Environment

    Edited by Alessio Gomiero

    FROM THE EDITED VOLUME

    Plastics in the Environment

    Edited by Alessio Gomiero

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    Abstract

    Polymers present to modern society remarkable performance characteristics desired by a wide range of consumers but the fate of polymers in the environment has become a massive management problem. Polymer applications offer molecular structures attractive to product engineers desirous of prolonged lifetime properties. These characteristics also figure prominently in the environmental lifetimes of polymers or plastics. Recently, reports of microbial degradation of polymeric materials offer new emerging technological opportunities to modify the enormous pollution threat incurred through use of polymers/plastics. A significant literature exists from which developmental directions for possible biological technologies can be discerned. Each report of microbial mediated degradation of polymers must be characterized in detail to provide the database from which a new technology developed. Part of the development must address the kinetics of the degradation process and find new approaches to enhance the rate of degradation. The understanding of the interaction of biotic and abiotic degradation is implicit to the technology development effort.

    Keywords

    polymersplasticsdegradationmicrobial degradationbiofilmsextent of degradation

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    1. Introduction

    In 1869, the first synthetic polymer was invented in response to a commercial $10,000 prize to provide a suitable replacement to ivory. A continuous string of discoveries and inventions contributed new polymers to meet the various requirements of society. Polymers are constructed of long chains of atoms, organized in repeating components or units often exceeding those found in nature. Plastic can refer to matter that is pliable and easily shaped. Recent usage finds it to be a name for materials called polymers. High molecular weight organic polymers derived from various hydrocarbon and petroleum materials are now referred to as plastics [1].

    Synthetic polymers are constructed of long chains of smaller molecules connected by strong chemical bonds and arranged in repeating units which provide desirable properties. The chain length of the polymers and patterns of polymeric assembly provide properties such as strength, flexibility, and a lightweight feature that identify them as plastics. The properties have demonstrated the general utility of polymers and their manipulation for construction of a multitude of widely useful items leading to a world saturation and recognition of their unattractive properties too. A major trend of ever increasing consumption of plastics has been seen in the areas of industrial and domestic applications. Much of this polymer production is composed of plastic materials that are generally non-biodegradable. This widespread use of plastics raises a significant threat to the environment due to the lack of proper waste management and a until recently cavalier community behavior to maintain proper control of this waste stream. Response to these conditions has elicited an effort to devise innovative strategies for plastic waste management, invention of biodegradable polymers, and education to promote proper disposal. Technologies available for current polymer degradation strategies are chemical, thermal, photo, and biological techniques [2, 3, 4, 5, 6]. The physical properties displayed in Table 1 show little differences in density but remarkable differences in crystallinity and lifespan. Crystallinity has been shown to play a very directing role in certain biodegradation processes on select polymers.

    Polymer Abbreviation Density (23/4°C) Crystallinity (%) Lifespan (year)

    Polyethylene PE 0.91–0.925 50 10–600

    Polypropylene PP 0.94–0.97 50 10–600

    Polystyrene PS 0.902–0.909 0 50–80

    Polyethylene glycol terephthalate PET 1.03–1.09 0–50 450

    Polyvinyl chloride PVC 1.35–1.45 0 50–100+

    Table 1.

    Selected features of major commercial thermoplastic polymers [7].

    Polymers are generally carbon-based commercialized polymeric materials that have been found to have desirable physical and chemical properties in a wide range of applications. A recent assessment attests to the broad range of commercial materials that entered to global economy since 1950 as plastics. The mass production of virgin polymers has been assessed to be 8300 million metric tons for the period of 1950 through 2015 [8]. Globally consumed at a pace of some 311 million tons per year with 90% having a petroleum origin, plastic materials have become a major worldwide solid waste problem. Plastic composition of solid waste has increased for less than 1% in 1960 to greater than 10% in 2005 which was attributed largely to packaging. Packaging plastics are recycled in remarkably low quantities. Should current production and waste management trends continue, landfill plastic waste and that in the natural environment could exceed 12,000 Mt of plastic waste by 2050 [9].

    स्रोत : www.intechopen.com

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