Environmental Degradability of Polycaprolactone Under Natural Conditions

E3S Web of Conferences 10, 00048 (2016) DOI: 10.1051/e3sconf/20161000048 SEED 2016 Environmental degradability of polycaprolactone under natural conditions Katarzyna Krasowskaa, Aleksandra Heimowska and Magda Morawska Gdynia Maritime University, Department of Chemistry and Industrial Commodity Science, Morska 81-87 str.,Gdynia, Poland Abstract. The aim of this work was an estimation of susceptibility of biodegradable poly(-caprolactone) (PCL) to environmental degradation in different natural environments. The commercial poly(-caprolactone) film, the trade name “CAPA 680”, was degraded in the compost, pond, open and harbour area of the Baltic Sea. Characteristic parameters of all natural environments were monitored during the incubation of polymer samples and their influence on degradation of PCL was discussed. Susceptibility of PCL to degradation in natural environments was evaluated based on changes of weight, crystallinity and polymer surface morphology. The rate of environmental degradation of PCL depended on the incubation place, environmental conditions and decreased in order: compost>harbour area of the Baltic Sea>open area of the Baltic Sea>pond. 1 Introduction materials and fragmentation. Most polymers are too large to pass through cellular membranes, so they must In recent decades world consumption of polymers has be depolymerized to smaller molecules before they can increased exponentially. Polymers are used in many be adsorbed and degraded within microbial cells. areas, especially in the packaging, agriculture, medicine The monomers, dimers and oligomers of a polymer's etc. In the process of consuming products humans repeating units are much easily degraded generate plastic waste, which are responsible and mineralized, because they can be assimilated through for the problem of environmental pollution. Nowadays, the cellular membrane and then further degraded plastics which are not incinerated, landfilled or recycled by cellular enzymes. Under oxygen conditions, aerobic are found in the nature and they polluting for example microorganisms are mostly responsible for degradation seas, rivers, oceans, lakes, beaches, forests etc. of polymer. Biomass, carbon dioxide and water Very often the natural environment must serve as a waste are the final products of deterioration. As opposite to this, repository, either by absorbing or recycling them under anoxic conditions, anaerobic microorganisms play into useful or at least harmless substances. When the main role in polymer destruction. The primary the waste products exceed the environment's ability products are methane, water and biomass [1, 2]. to absorb them, the result is water, soil and air pollution. In the case of environmental degradation under The increase in volume of synthetic non-degradable natural conditions very often synergistic action various polymers, particularly in the form of one-trip packaging, factors including temperature, pH, humidity, aeration, presented a potential threat to the natural environment. sunlight, macroorganisms, microorganisms and enzymes The plastic packaging litter is not only the aesthetically leads to degradation of biodegradable polymers. undesirable but it causes the possibility of risk for people, Biodegradable polymers have been found to degrade animals, birds on the land and in the water. more rapidly if a combination of microbes is used rather Recently the increasing attention is paid to attempt than one specific microbe. Thus the presence of large rational replacement commonly used synthetic polymers varieties of microbes in the natural environment support by biodegradable polymers. The use of biodegradable faster biodegradation [3, 4]. polymers in consumer products should not lead An example of a biodegradable polymer which to the generation of toxic or otherwise environmentally undergoes microbial degradation, both in contact unacceptable chemicals in the natural environment. with living organisms, and in terms of the natural Biodegradable polymers are susceptible to biological environment is poly(-caprolactone), which can degrade degradation, resulting in the disintegration in several biotic environments, including sea, river and mineralization under the action of living organisms. and lake water, sewage sludge, farm soil and compost [5- The initial breakdown of a polymer, which is the first 12]. step of biological degradation process can result According to the literature degradation of from physical and biological forces, which can cause poly(-caprolactone) in a living environment can result mechanical damage such as cracking of polymeric a Corresponding author: [email protected] © The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons Attribution License 4.0 (http://creativecommons.org/licenses/by/4.0/). E3S Web of Conferences 10, 00048 (2016) DOI: 10.1051/e3sconf/20161000048 SEED 2016 of simple chemical hydrolysis of ester bonds or from enzymatic attack or both [13]. Chemical hydrolysis can be resulted in decreasing of molecular weight. Enzymatic degradation takes place only on the polymer surface, and therefore is associated usually with erosion process and may be quantitatively characterized by weight loss and fragmentation of the sample. At the result the polymer is disintegrated in the natural environment. Obviously, disintegradability does not indicate on total sample degradation. The small particles of the sample are constantly degraded and bioassimilated by microorganisms present in the environment, until the samples would be completely converted to carbon dioxide and water. The aim of this work was an estimation of susceptibility Figure 1. The cross-section of compost pile prepared in natural of poly(-caprolactone) (PCL) to environmental environment degradation in different natural environments. The results of PCL degradation in compost, pond, open and harbour The PCL samples were put into the special perforated area of the Baltic Sea are compared. basket and buried of 1 m in depth of the compost pile. The perforated structure of basket allowed for free access of macro, micro-organisms and enzymes existing 2 Experimental in this environment to degraded material. The characteristic parameters of the compost such as: 2.1 Material temperature, pH, moisture content, activity of dehydrogenases were measured during environmental The commercial poly(-caprolactone) film (PCL, Mw= degradation process of PCL samples and are shown 80000) with the trade name “CAPA 680” used in Table 1 [9]. in this work was kindly supplied by Solvay (England). Table 1. Characteristic parameters of compost 2.2 Environments Parameters moisture Activity of Months temperature pH content dehydrogenases The incubation of PCL samples took place in the several [oC] environments under natural weather depending [%] [mol mg-1 d.m.] conditions, such as: the compost, pond, open and harbour June 17.6 7.8 42.4 0.0197 area of the Baltic Sea. For comparison degradation July 18.2 5.8 45.8 0.0568 of PCL samples was also performed under the laboratory August 19.2 6.3 43.5 0.0485 conditions in a liquid medium containing sea water with the sodium azide (NaN3) and in a liquid medium 2.2.2 The Baltic Sea water containing pond water with NaN3. The incubation of PCL samples took place in two 2.2.1 The compost pile places of the Baltic Sea under natural conditions: - in the open area of the Baltic Sea in Łeba, on the west The compost pile was prepared under natural conditions side of the western breakwater, in the waters of the East of municipal waste treatment plant in Gdynia. It consisted current which allow for constant flow, of the dehydrated sewage sludge, burnt lime and straw. - in the harbour area of the Baltic Sea in Gdynia Harbour Burnt lime (0.45kgCaO/1kg dry mass of compost) on the Norwegian Pier near the ship of the Polish Ship was added to ravage phatogenic bacterium and eggs Salvage Company. parasites, to deacidificate sewage sludge and to convert The PCL samples were located in a special basket made sludge to compost. The straw was added to maintain of perforated galvanized steel, which was suspended from the higher temperature of the compost pile and to loosen a rope at 2 m depth under the surface of the sea. the structure of the compost pile. The compost pile The perforated baskets structure allowed for free prepared under natural conditions was not adequately movement of seawater and the access of micro-organisms aerated, so it was expected that a combination and enzymes dissolved in the water to degraded material. of conditions from aerobic at the upper part of pile, The places of environmental degradation of PCL microaerophilic in the middle part and facultative in the open and harbour area of the Baltic Sea are shown anaerobic at the bottom of the pile could occur on Figure 2. for microorganisms growth [2]. The Figure 1 represents cross-section of compost pile in natural environment. 2 E3S Web of Conferences 10, 00048 (2016) DOI: 10.1051/e3sconf/20161000048 SEED 2016 Figure 2. The places of environmental degradation of PCL in the Baltic Sea Figure 3. The scheme of the pond construction The temperature, pH, oxygen and salt content The characteristic parameters of the pond such of the Baltic Sea were monitored during environmental as: temperature, pH were measured during environmental degradation process of PCL samples. The characteristic degradation process of PCL samples and are shown parameters of the sea water in the open and harbour area in Table 4 [15]. according

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