How to Make Polystyrene Biodegradable - Literature review Example

Institution : xxxxxxxxxxx Title : How to make polystyrene biodegradable Tutor : xxxxxxxxxxx Course : xxxxxxxxxxx @2010 Introduction Biodegradation is the chemical process that involves breakdown of substances via the physiological processes into the environment. The process has been commonly used in organic materials but recent studies have identified processes that can biodegrade synthetic materials. Polystyrene is one of the materials that have been difficult to biodegrade. It has adverse effect in the environment since when disposed, it cannot be broken down even by the biological processes. More environmental friendly methods of disposing polystyrene have been identified for use in its disposal. This essay discusses different processes by which polystyrene can be biodegraded to reduce its negative impact on the environment. One of the processes of biodegrading polystyrene is thermal degradation of polystyrene in the presence of hydrogen by catalyst in solution. This is explained by Balakrishnan, Guria, & Chandan, (2007). This process involves biodegrading polystyrene at low temperatures of 170 to 40.C. This is done in presence of hydrogen and the catalyst used is iron(III) oxide. This is to study the effect of the temperature and catalyst. The time taken to degrade the molecules is calculated by viscosity average method. The results indicated that the presence of hydrogen enhances biodegradation and also that the degradation chain breaks at the temperature of 170 to 40.C. The process of thermal degradation of polystyrene was also done by Karmore & Madras (2001) where they used an acid catalyst of p-toluene sulfonic acid (p-TSA). Degradation was carried out at different temperatures ranging from 150–170°C and different molarities of the acid. Gel permeation chromatography was used to determine the rate of reaction in the samples tested. The results indicated that the rate of degradation increased with the presence of the acid catalyst. The total activation energy that was obtained at the end with changing temperatures was found to be 22 kcal/mol. The other method is Photo-oxidative degradation of polystyrene which was done by Osawa, Konoma, Song, & Cen, (2006). In this process polystyrene is degraded using photo-oxidative process. Films of commercial polystyrene measuring 0.1 and 0.5 mm thick were photo irradiated in both single and multiple layers using different methods such as infrared, ultraviolet, gel chromatography and chemiluminescence. The most photo irradiation occurred with chemiluminescence since it was able to photo-oxidate from the surface of the film. To add on this, Hrdlovic, Pavlinec & Jellinek, (2003) found out that presence of sulfur dioxide in the polystyrene films enhanced the rate of photo oxidation. This was found to be faster due to where the sulfur dioxide is located in the near the folds of the crystalline areas of the polystyrene films that when it is located in the amorphous regions. When the same process was done with nitrogen dioxide instead of sulfur dioxide, the rate was found to be low but would increase with increased crystallinity. Kinetics of the degradation of polystyrene in supercritical acetone is also another method described by Oh, Han, Kwak, Bae, & Lee, (2007). This was done using the nonisothermal weight loss technique where heating was done at the rate of 3, 5 and 7.C per minute. This process was meant to obtain the rate of weight loss according to temperature change which was then analysed in a basic method based on Arrhenius form. This was aimed at obtaining parameters such as the total activation energy and the total reaction order. A comparison was then done using the parameters that were obtained from the experiment to those that were obtained when degradation of polystyrene was done using atmospheric nitrogen. This experiment found out that biodegradation of polystyrene in acetone requires little activation energy as compared to degradation in atmospheric nitrogen. The same experiment was done by Hwang, Kim, Bae, & Kumazawa, H., (2007) where degradation was also done in acetone but at different temperatures. This was to find out the factor that can act as a catalyst for the degradation in acetone. Degradation was done for duration of thirty minutes at different temperatures to find out which one completes first. This was measured by the amount of components of polystyrene released after the thirty minutes. It was found that the sample with the highest temperature completed first. This was an indication that temperature can act as a catalyst in degradation of polystyrene in acetone. Another method is thermal decomposition of polystyrene in supercritical methanol. This experiment was done by Shin & Bea, (2008) to compare the degradation of polystyrene in supercritical methanol compared to degradation of other monomers. The experiment was done with samples of polystyrene in methanol at temperatures ranging from 340 to 420. C. Pressure was also adjusted during the experiment varying from ten to thirty Mpa. As the experiment continued, the selectivity of monomers of polystyrene was declining as compared to others. The rate of decomposition of the monomers was reasoned by comparing the selectivity of the liquid products. The liquid with faster declining selectivity of monomers was found to be the one with high rate of decomposition. The process of degradation of polystyrene in supercritical liquids such as methanol can be formulated following the first order kinetic law where the rate of decomposition is directly proportional to concentration of reactants. This is because as the polystyrene monomers continued to decline, the concentration decreased in the liquid. Polystyrene can also be made biodegradable by blending it with biodegradable polyesters. This method was explained by Biresaw & Carriere, (2004). Investigations were done by blending polystyrene with d,l-polylactic acid (PLA), polycaprolactone (PCL), and Eastar Bio Ultra (EBU). The blends with increment of 25 percent were measure on various aspects such as yield strain, yield stress and modulus. The tensile properties of the resulting blend of polystyrene and biodegradable polyester was found to be ranging within similar values as the pure components. This indicated a relationship between tensile properties of pure biodegradable polyester and the blend of biodegradable polystyrene. The tensile properties of resulting polystyrene could therefore be attributed to the additional properties of the biodegradable polystyrene. However, according to Hamad, Kaseem, & Deri, (2003), these biodegradable polyesters must have characteristics that make them compatible with polystyrene. The compatibility is determined by measuring the interfacial tension of the resulting blend. However, the compatibility of d, l-polylactic acid (PLA), polycaprolactone (PCL), and Eastar Bio Ultra (EBU) is different. This was evaluated using the imbedded fibre retraction method. This found significant difference in compatibility of each with polystyrene. This difference results in morphological, mechanical and thermal properties of the resulting blend. However, this method has not gained 100 percent evidence on its effectiveness. Another method that can be used to biodegrade polystyrene is by use of starch as filler in increasing the biodegradability. In the experiment conducted by Jasso, Gonzalez-Ortiz, Contreras, Mendizabal, & Mora, (2000), two sample of commercial polystyrene one with starch and another without were set for degradation in aerated intense activated sludge. After staying in the sludge for a period of thirty days, various aspects were measured. Rigidity was found to be high in the sample that lacked starch. Starch was found to cause rigidity in the other sample. Degradation was observed by considering loss of strength. In the sample containing starch, substantial loss of strength was observed. The ultimate starch was also observed to increase as the material was kept in the sludge with starch. However, decrease in polymer mass was observed in both samples. The main action in this case is the attack of the polystyrene by the bacteria that has grown in the sludge. Starch attracts the bacteria which eventually attacks the polymer hence biodegrading it. Starch has therefore been found as in important additive in the process of biodegrading plastics through cultured micro organisms. This method however requires a lot if time to achieve complete degradation since the strength may return after starch has declined which decreases the rigidity. This therefore means that polystyrene has to remain in the sludge until it decomposes completely. This is because removal of starch decreases its rigidity. Another method of improving biodegradability of polystyrene is the abiotic and biotic degradation of oxo-biodegradable foamed polystyrene. This is explained by Ojeda, Freitas, Dalmolin, Dal Pizzol, Vignol, Melnik , Jacques, Bento, & Camargo, (2009). It involves addition of pro-oxidant substances in their structural formulations. The resulting formulation is called oxo-biodegradable. This is a plastic that contains very small amounts of metal to act as catalysts in the degradation process when the plastic is subjected to environmental conditions. After subjection, it produces water, carbon dioxide and biomass. The experiment described in the article was to examine the biotic and abiotic degradation of foamed polystyrene that has been formulated with Cobalt and Manganese as pro-oxidant additives. The formulated plates were subjected to heat and ultraviolet radiation to cause artificial weathering. Residues from the oxidized surfaces which detached from the samples were then incubated in a stable compost waste at 58 °C. This could also be incubated in aqueous medium containing minerals at 25 °C. On observation, it was found that the molar masses of material that was eroded in the samples activated with the pro-oxidant had reduced significantly. This was after comparing it with the molar masses of the initial samples. There was also incorporation of oxygen into the degradation chain during the process. For the incubation period of two months, the samples biodegraded and yielded mineral values of 2 to 5 percent. Similar samples that were incubated in medium that did not contain pro-oxidants were also observed but did not indicate changes in molecular masses. This method has been found to be effective and environmental friendly. This is because the residues that accumulate in the soil were found not having any negative impact to the environment. In Australia, these products have been tested for ecotoxicity and found to meet the requirements of the FDA. Mor & Sivan, (2008) also discovered another method of biodegrading polystyrene that involves formation of Biofilm which helps in partial biodegradation of polystyrene by the actinomycete Rhodococcus ruber. The biofilm used is produced by C208 strain of actinomycete Rhodococcus ruber and it used in biodegrading films of polystyrene. The experiment described by the article aims at examining the physiological characteristics of biofilm that are responsible for its actions and its ability to biodegrade polystyrene. Assessment of the biomass of the biofilm was done by use of a modified crystal violet staining or by checking the protein content of the biofilm. When the Rhodococcus ruber is cultured on flakes of polystyrene, the cells of bacteria adheres to the surface of polystyrene forming a biofilm. The growth pattern of the bacteria on polystyrene exhibited a pattern that is similar to planktonic culture. Further, the rate at which biofilm was respiring was also similar to the rte of biofilm growth. Incubation of the biofilm for a period of 8 weeks indicated substantial loss of polystyrene weight. This therefore indicated an increased affinity of C208 strain of actinomycete to polystyrene which further results in partial biodegradation of polystyrene. Biodegradability of polystyrene could also be improved by inserting a pyridine group in its formulation. This was explained by Peng & Shen, (1999) where method of copolymerization was used to prepare Poly (styrene-co-4-vinylpyridine) (PS-co-VP). This is polystyrene that contained large amounts of pyridinium group. Polystyrene containing small amounts of N-benzyl-4-vinylpyridinium chloride (PS-co-VPC) was also prepared using method of quaternization of PS-co-VP. The polystyrene which contained a significant amount of pyridinium group indicated substantial amount of biodegradation when it was kept in aeration tank of sewage works. Other control polymers that did not contain pyridinuim group did not indicate any sign of degradation. Reduction in molecular weight was shown to increase with increase in the amount of pyridinium group. Aalam, Pauss, & Lebeault, (2007) also explains how styrene, the bi product of polystyrene could be biodegraded to produce carbon and energy. This was done by subjection to a certain bacteria community in a two phase aqueous-organic medium. Since styrene is slightly soluble in water, it was stabilised by use of silicon oil. This was also to prevent it from becoming toxic into the environmental micro organisms. In a chemostat culture whose pH was controlled, styrene was found to be biodegraded at dilution rates of 0.05 to 0.20 h–1. The strain of bacteria Pseudomonas aeruginosa was found to degrade styrene at the activity level of 293 mg·g–1·h–1. This was also evidenced by Pelizzon, Bestetti, Galli, Benigni, & Orsini, (2006), where a strain of Pseudomonas putida collected from the soil was allowed to oxidate styrene. This led to identification of 2-phenyl-2-propen-1-ol and 1, 2-dihydroxy-3-isopropenyl-3-cyclohexene indicating their presence in -methylstyrene during the metabolism process. The bacteria also oxidized styrene releasing 1, 2-dihydroxy-3-isopropenyl-3-cyclohexene. Conclusion Biodegradation is very important especially to materials that are environmental unfriendly like polystyrene. This helps in reducing its negative impacts to the environment. Biodegradation can be achieved by various means some of which do not change it completely but they turn it to products that are friendly to the environment. This is therefore important and research is needed on more methods that can biodegrade polystyrene completely. Bibliography Balakrishnan, R., Guria, K., & Chandan, 2007 ‘Thermal degradation of polystyrene in the presence of hydrogen by catalyst in solution’, Polymer Degradation and Stability, Vol 92, Issue 8, Pp. 1583-1591. Hrdlovic, P.,Pavlinec , J.,& Jellinek,H., (2003)Degradation of polymers and morphology: Photo-oxidative degradation of isotactic polystyrene in presence of sulfur dioxide as function of polymer crystallinity,Journal of Polymer Science Part A-1: Polymer Chemistry, Volume 9, Issue 5,pages 1235–1245. Osawa, Z., Konoma,F., Song Wu and Cen, J., 2006, Photo-oxidative degradation of polystyrene: Comparison of chemiluminescence with other analytical methods’, Polymer Photochemistry, Volume 7, Issue 5, 1986, Pages 337-347. Oh,S, Han, D., Kwak H., Bae S., & Lee, K., 2007 ‘Kinetics of the degradation of polystyrene in supercritical acetone’, Polymer Degradation and Stability, vol 92, Issue 8, Pp 1622-1625. Hwang, G., Kim, K., Bae, S., & Kumazawa, H., (2007), Degradation of high density polyethylene, polypropylene and their mixtures in supercritical acetone , Korean Journal of Chemical Engineering, Volume 18, Number 3, 396-401. Satyanarayana, D., & Chatterji, P., (2003). “Biodegradable polymers: challenges and strategies,” Journal of Macromolecular Science, vol. C33, (3), pp. 349–368. Shin, H., & Bea, S., 2008, Thermal decomposition of polystyrene in supercritical methanol, Journal of Applied Polymer Science, vol, 108, Issue 6, pages 3467–3472. Biresaw, G, Carriere, CJ, 2004, ‘Compatibility and mechanical properties of blends of polystyrene with biodegradable polyesters’, Composites, vol 35 part A, Pp. Jasso, C., Gonzalez-Ortiz, L., Contreras, J., Mendizabal, E., & Mora, J., (2000).The degradation of high impact polystyrene with and without starch in concentrated activated sludge, Polymer Engineering and Science, Vol 6(2). P 245-261. Ojeda, T., Freitas, A., Dalmolin, E., Dal Pizzol, M., Vignol, L., Melnik , J., Jacques ,R, Bento, F., Camargo, F., 2009, ‘Abiotic and biotic degradation of oxo-biodegradable foamed polystyrene’ Polymer Degradation and Stability, vol 94, pp. 2128–2133. Mor, R., & Sivan, A., (2008). Biofilm formation and partial biodegradation of polystyrene by the actinomycete Rhodococcus ruber, Biodegradation of polystyrene, Volume 19, Number 6, 851-858. Peng, X., & Shen, J., 1999, Preparation and biodegradability of polystyrene having pyridinium group in the main chain This article is not included in your organization's subscription. However, you may be able to access this article under your organization's agreement with Elsevier. , European Polymer Journal, Volume 35, Issue 9, Pages 1599-1605. Aalam, S., Pauss, A., & Lebeault, J., 2007, High efficiency styrene biodegradation in a biphasic organic/water continuous reactor, Applied Microbiology and Biotechnology , Volume 39, Number 6, 696-699. Otake, Y., et al. (1995), Biodegradation of low-density polyethylene, polystyrene, polyvinyl chloride, and urea formaldehyde resin buried under soil for over 32 years. Journal of Applied Polymer Science, 56: 1789–1796. Pelizzon, F., Bestetti, G., Galli, E., Benigni, C., & Orsini, F., (2006), Biotransformation of styrenes by a Pseudomonas putida, Journal of Applied Microbiology and Biotechnology, Volume 39, (6), 696-699, Read More

This was found to be faster due to where the sulfur dioxide is located in the near the folds of the crystalline areas of the polystyrene films that when it is located in the amorphous regions. When the same process was done with nitrogen dioxide instead of sulfur dioxide, the rate was found to be low but would increase with increased crystallinity. Kinetics of the degradation of polystyrene in supercritical acetone is also another method described by Oh, Han, Kwak, Bae, & Lee, (2007). This was done using the nonisothermal weight loss technique where heating was done at the rate of 3, 5 and 7.

C per minute. This process was meant to obtain the rate of weight loss according to temperature change which was then analysed in a basic method based on Arrhenius form. This was aimed at obtaining parameters such as the total activation energy and the total reaction order. A comparison was then done using the parameters that were obtained from the experiment to those that were obtained when degradation of polystyrene was done using atmospheric nitrogen. This experiment found out that biodegradation of polystyrene in acetone requires little activation energy as compared to degradation in atmospheric nitrogen.

The same experiment was done by Hwang, Kim, Bae, & Kumazawa, H., (2007) where degradation was also done in acetone but at different temperatures. This was to find out the factor that can act as a catalyst for the degradation in acetone. Degradation was done for duration of thirty minutes at different temperatures to find out which one completes first. This was measured by the amount of components of polystyrene released after the thirty minutes. It was found that the sample with the highest temperature completed first.

This was an indication that temperature can act as a catalyst in degradation of polystyrene in acetone. Another method is thermal decomposition of polystyrene in supercritical methanol. This experiment was done by Shin & Bea, (2008) to compare the degradation of polystyrene in supercritical methanol compared to degradation of other monomers. The experiment was done with samples of polystyrene in methanol at temperatures ranging from 340 to 420. C. Pressure was also adjusted during the experiment varying from ten to thirty Mpa.

As the experiment continued, the selectivity of monomers of polystyrene was declining as compared to others. The rate of decomposition of the monomers was reasoned by comparing the selectivity of the liquid products. The liquid with faster declining selectivity of monomers was found to be the one with high rate of decomposition. The process of degradation of polystyrene in supercritical liquids such as methanol can be formulated following the first order kinetic law where the rate of decomposition is directly proportional to concentration of reactants.

This is because as the polystyrene monomers continued to decline, the concentration decreased in the liquid. Polystyrene can also be made biodegradable by blending it with biodegradable polyesters. This method was explained by Biresaw & Carriere, (2004). Investigations were done by blending polystyrene with d,l-polylactic acid (PLA), polycaprolactone (PCL), and Eastar Bio Ultra (EBU). The blends with increment of 25 percent were measure on various aspects such as yield strain, yield stress and modulus.

The tensile properties of the resulting blend of polystyrene and biodegradable polyester was found to be ranging within similar values as the pure components. This indicated a relationship between tensile properties of pure biodegradable polyester and the blend of biodegradable polystyrene. The tensile properties of resulting polystyrene could therefore be attributed to the additional properties of the biodegradable polystyrene. However, according to Hamad, Kaseem, & Deri, (2003), these biodegradable polyesters must have characteristics that make them compatible with polystyrene.

The compatibility is determined by measuring the interfacial tension of the resulting blend.

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