w-‘a: 1:“.- .33.”, 1.5!. as: g... .1» v3.9.3. . i235: 2.51:. :s‘ In: :1 osflh: n3 traxtfiih; a . . . t q -~- 2'5"} til!-q-\ruqflug-channfi‘vnvuql1“(It lllllllllllllllllllllllll , LIBRARY M'Chlgan State nlverslty mama l This is to certify that the dissertation entitled “Biodegradation of Poly(2-Methy1 Phenylene Oxide) in Solid State Fermentations presented by Yilan Ling has been accepted towards fulfillment of the requirements for M.S. degree in Chemical Engineering Major professor Date W 18L "1‘14 MSU is an Affirmative Action/Equal Opportunity Instirution 0-12771 PLACE IN RETURN BOX to remove this checkout from your record. 1'0 AVOID FINES return on or before date due. DATE DUE DATE DUE DATE DUE LJl mEl—l WV l MSU Is An Affirmative Action/Equal Opportunity Institution WWJ BIODEGRADATION OF POLY(2-METHYL PHENYLENE OXIDE) IN SOLID STATE FERMENTATIONS By Yilan Ling A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Chemical Engineering 1994 ABSTRACT BIODEGRADATION OF POLY(2-IV[ETHYL PI-IENYLENE OXIDE) IN SOLID STATE FERMENTATIONS By Yilan Ling The increasing environmental concerns with the disposal of solid waste has prompted the increased push for the design and analysis of biodegradable polymers. Poly(2-methyl phenylene oxide), PMPO, was made in the laboratory using 2,2-isoproproxy ethyl pyridine complexed to copper chloride as a catalyst with a 75% yield based on the monomer, and a rolling drum composter was used to determine the biodegradability of PMPO in a controlled environment. The sample was placed with a mixture of grasses and leaves to simulate common yard waste and provide an optimal media for the composting bacteria. Samples were run at polymer to organic material ratios of 1/10, 1/ 17, 1/25, 1/200, and 1/400. The optimal ratio was 1/200 that degraded an average of 50-60% over three forty-day runs based on dry-weight analysis. Using size-exclusion chromatography the polymer gave a bimodal distribution. The high molecular weight peak decreased in size from the initial molecular weight of the polymer and the low molecular weight peak remained constant at an average molecular weight of 350 g/mol. The degradation based on the overall molecular weight change is 30% and the degradation based on the loss of area of the high molecular weight polymer peak is 50-60%. ACKNOWLEDGEMENTS There are several people I would like to thank for both their help and support in completing this project. First, I would like to thank my advisor, Dr. Eric Grulke, for his helpfiil guidance and patience; Dr. Patrick Oriel for great conversations and suggestions. I must also thank Rod Andrews and Keyi Wang for helping me in the lab. I must thank Marshall Bredwell for his love, support, and patience. He has to deal with me through the ups and downs of the completion of the project. He was a tremendous help for proof-reading and graphical layout of this thesis. He has been very WOI‘IdCl’fiJl through it all and I must sincerely thank him for putting up with me. Finally, I must thank my parents, Zuning Bian and Guanhong Ling, god father, Zhenping Xiong, and grandmother, Heimang Hu, for their love and support. They have always been behind me and given great deal of advice. iii TABLE OF CONTENTS List of Figures Chapter 1: Introduction Chapter 2: Literature Review A. Composting B. Microbial Activity C. Solid State Fermentation Model 1 Kinetic Model 2. Moisture Content 3. Carbon Dioxide Removal 4 Degradation Mechanism 5 Degradation Products D. Polymer Biodegradation 1. Degradation Methods 2. Biodegradation Tests E. Poly(phenylene ethers) Chapter 3: Materials and Methods A. Polymer Productions B. Composter Construction and Design C. Sample Preparation D. Sample Analysis iv vi 1] 17 23 31 31 32 35 36 Chapter 4: Results A. Polymer Production B. Composter System Design C. HPLC, Bimodal and Dry Weight Analysis Chapter 5: Discussion A. Polymer Production B. Rolling Drum Composter C. Sample Preparation D. HPLC Analysis 1. System Difficulty 2. Column Choice 3. Extraction Technique 4. Bimodal Peak Analysis E. Dry Weight Analysis F. Comparison of Results Chapter 6: Suggestions For Improvement and Future Work A. Composting System B. Analysis Techniques C. Biodegradation Appendices Bibliography 39 39 39 4O 48 48 48 50 53 6O 61 63 63 63 63 65 71 Table/Figure Title 2-1 2-2 2-3 2-4 2-5 2-6 2-7 3-8 3-9 4—14 4—15—20 5-21 LIST OF FIGURES Substrate Flow Diagram Bacteria and Temperature Bacterial Activity Diagram Poly(2-methyl phenylene oxide) Structure Poly(2,6-dimethyl phenylene oxide) Structure Poly(2,6-dimethyl phenylene oxide) Mechanism Diagram Poly(Z-methyl phenylene oxide) Mechanism Diagram Rolling Drum Composter System Analysis Flow Chart Polystyrene Standards Degradation Molecular Weight Degradation (HPLC Analysis) Mass Degradation (Dry Weight Analysis) Bimodal Peak Comparison HPLC Traces HPLC Detector vi Page 24 24 27 29 34 38 4o 41 42 43 44 45 52 5-22 5-23 A24 A25 A26-27 A28 A29 A30 Polystyrene Structure Methylated/Hydroxylated PMPO Polystyrene Standards Calibration Curve HPLC Flow Rate Optimization FTIR Sample Methanol FTIR Chloroform F TIR o-Cresol F TIR vii 55 58 65 66 67 69 69 7O CHAPTER 1: INTRODUCTION Composting is a practice that thousands of people in the United States do each and every year. Just about every home that has a garden makes use of a 'compost pile’; a place where organic materials are thrown to sit and 'rot'. Once this rotting has occurred, what is left is a rich, fertile soil which can be used as a fertilizer in gardens for later years. What happens in a household compost pile is what many people believe happens in landfills. What actually occurs is not at all what happens in a compost pile. The waste thrown into landfills is buried and remains intact and undergoes little degradation for many years. Considering that plastics take up almost 30% of the volume of solid municipal waste, 320 billion pounds per year‘, there is much focus on the biodegradability of plastics that are being used in industry. Such an emphasis on biodegradability has led cities such as New York and Berkeley, California, to either ban plastic containers used in fast food or to require them to be made of biodegradable materials‘. Strong emphasis has been placed on developing environmentally sound plastics, while retaining desirable physical properties such as strength and moldability needed for consumer use. Poly(2-methyl phenylene oxide), PMPO, is polymer which comes from a family of polymers that include polymers such as Noryl engineering resins, the poly(phenylene ethers). Poly(2,6-dimethyl phenylene oxide), PDMPO, has good physical properties and is biodegradable due to the ether linkages. Theoretically, by reducing the methyl substitution on the aromatic ring, the biodegradability of the polymer should increasez. 2 Biodegradability of a polymer is detennined by how well the composting bacteria can consume the polymer as a substrate or food source. The highest rate of decomposition is caused by the thermophilic bacteria in the composting cycle. While the metabolic pathway for the biodegradation of PMPO is not known, it most likely follows a similar pathway to other well- elucidated degradation metabolisms, such as lignin and cellulose. Therefore the optimal reactor will operate in the higher temperature range, 60°C, where the thermophilic bacteria operate. The reactor is a solid state fermentation reactor, a rolling drum type, that uses a drum with the polymer sample and a composting media (of grass and leaves) as its reaction vessel. The vessel is rotated to insure a homogeneous mixture throughout the entire composting period. The temperature and humidity of the vessel are controlled. Two different analysis schemes were used in the study for biodegradability. Techniques such as liquid scintillation and infrared spectroscopy were not used due to lack of equipment and safety risks, but size-exclusion chromatography and dry-weight analysis were performed. The size-exclusion chromatography was performed on a HPLC instrument and the amount of biodegradation was based on the initial molecular weight of the polymer sample. The dry weight analysis was based on the initial sample and all samples were normalized using that basis. CHAPTER 2: LITERATURE REVIEW Composting: The word "compost" comes from two Latin roots, one meaning "together" and the other meaning "to bring". Compost is the bringing together of organic material and microbes that feed on and utilize the organic material. The modern practice of composting is simply the speeding up of the natural process. All things will decompose if given enough time, and composting is intended to shorten the time necessary for the decomposition. The degradation of organic material is accomplished by the biological activity of microbes which feed on the organic material in the compost. They use the compost as their source of "food". The material that is used for compost is any type of organic waste. Such things as weeds, grasses, leaves, yard wastes, and even animal feces and food wastes are ideal material for the compost. Many household gardeners have something in their backyard called a "compost pile". This is where wastes are placed and allowed to be degraded by bacteria into a rich material full of such useful fertilizer compounds as phosphorus and nitrogen. Composting can also be used to speed up the biodegradation processes of many synthetic compounds like many polymers and some toxic chemicals and wastes. Since composting can be done on a very large scale, it can be used as a commercial technique to dispose of various synthetic materials. Wastes in a composting system can travel many different routes. The organic material may end up as new biomass, become excreted as products of metabolic pathways such as C02, or remain as the starting material (Figure 2-1). S b trate Bacteria . . New Biomass (lilogmer) » lDelgrade/U “1126 Excreted By-Products o ymer Remain as Polymer Figure 2-1: Substrate Flow Diagram Organic materials in a compost pile undergo attack by the myriad of micro-organisms present in the pile. The organic materials undergo biological oxidation via microbial activity and metabolism through a number of biological pathways. These bacteria use the organics as a carbon source and propagate their growth. Microorganisms have the ability to utilize carbon from a broad range of sources; for example some microorganisms use carbon monoxide, some microorganisms can utilize poly-ch]orinated-biphenyls. Compounds such as lignin and cellulose undergo degradation in elucidated and well-characterized pathways, while many synthetic compounds undergo degradation in yet unknown manners. What pathway is utilized and what the final degradation product is depends on the carbon source and the microorganism“. There is a large amount of research to determine the biochemical pathway through which many synthetic compounds are degraded. If it is understood how a compound is degraded by a microorganism and which microorganism processes or utilizes the synthetic compound, engineers can optimize composting conditions in order to maximize the degradation of that compound. This also allows seeding of a commercial composter with 5 bacteria which degrade the compound of interests. Eventually, genetically engineered bacteria can be used in controlled composting systems that have been metabolically optimized to provide the greatest level of degradation. Finally, by elucidating the metabolic pathways through which the compounds degrade, the by-products of the degradation can be determined. Many degradations can produce toxic by-products which are not analyzed for and are not expected. Oxygen is a key nutrient to composting6. Oxygen is necessary for the aerobic bacteria to perform their job. The composting bacteria take in oxygen and use it as a terminal electron acceptor. They release many by-products such as water, heat, carbon dioxide, and odor in the production of mature compost. They also produce by-products from the carbon sources that they utilize. The toxicity of the by-products has not yet been detemiined. The ultimate goal of composting is to take in organic and synthetic materials and degrade them to environmentally acceptable end products. There are basically five different types of commercial reactors used in composting (or solid state fermentation, SSF)? The first is a stationary tray reactor. It basically consists of shallow trays that have been filled evenly with solid substrate. The trays are then stacked one on top of another or in tiers. The tower is then aerated and temperature and humidity are controlled. The second type of SSF reactor is a tunnel reactor. It consists of a well-insulated, large-air—flow container with only one bed of a thin or thick layer, which is throughflown by a conditioned air flow in the vertical direction. The tunnel can be filled or unloaded automatically, and the solid substrate can be loosed or mixed with a moveable treating machine. Another type of reactor, a paddle-type reactor, consists of a horizontal drum with 6 rotating paddles that gently mix the substrate. Conditioned air is blown through the reactor over the solid substrate bed. The rotary drum type of reactor consists of a drum mounted on rollers and driven slowly. The drum is also inclined in the vertical direction, to allow the material to flow through the reactor. Finally, a tower fermenter is used in SSF. It consists of stacks of rotating trays that transfer the material from the top of the reactor to the bottom of the reactor with conveyors. Stationary tray and tunnel reactors are basically stationary layer reactors and batch systems while rotary drum, paddle and tower fermenters are basically mixed layer reactors and continuous systems.6 Composting Phase Temperature Range Primary Bacteria Mesophilic Phase 20°C - 45°C mesophilic Eubacteria mesophilic Actinomycetes mesophilic fungi Thermophilic Phase 45°C - 70°C Bacillus ssp. Streptomyces ssp. Ihermoactinomyces ssp. Asperigillusfilmigatus Cooling Phase 45°C - 20°C Asperigillusfilmigatus Actinomycetes ssp. Fungal Invasion MeSOphilic Recolonization Maturation Phase 20°C Minor Changes in Mesophilic Bacterial Population Temperature ((°C) g 44» so § ‘5. 2e 0 a '3 8‘ 1101) g Figure 2-2: Bacteria and Temperature7 /\ Thermophilllie Phase Cooling Phase Mannafion P/ Time ===€> Figure 2-3: Bacterial Activity Diagram7 Microbial Activity: The bacterial activity within a compost pile is very high. The flora of a compost pile is very diverse and depends on the stage of maturity of the compost (Table 2-2). The composting process can be divided into four major phases that are temperature dependant (Figure 2-3). The process consists of a mesophilic phase, a thermophilic phase, a cooling phase, and a maturation phase. In the meSOphilic phase, the composting process is started by meSOphilic bacteria (20°C - 45°C). In colder temperatures, there may be some composting done by psychrophilic bacteria before the mesophilic bacteria take over. When the mesophilic bacteria undergo aerobic respiration, the temperature of the pile rises. The bacteria that are primarily present during this phase of composting are the mesophilic Eubacteria, the mesophilic Actinomycetes, and the mesophilic multicellular fiingi7. As the temperature increases due to active respiration by the mesophiles, there is a shift in the bacterial population. The mesophiles die off in the pile as the temperature increases to 70°C and during this time they are replaced by thermophilic bacteria. The thermophilic bacteria fiinction at a higher temperature range than the mesophilic bacteria and they can resist elevations in temperature much longer than can the mesophiles. The dominant species in the thermophilic range of composting is Bacillus species”. Bacterial species also present in the compost are Streptomyces ssp. and Thermoactinomyces ssp. A fimgus, Asperigillus fiimigatus", is also found to be present in this phase as well. The rate of degradation during the thermophilic range is much higher than the rate of degradation in the mesophilic range and has greater carbon dioxide production. The cooling phase of the composting process is where the available carbon for growth 9 becomes limiting. This causes a decrease in the microbial population, because the bacterial food source has become depleted. Since the microbial population declines, the heat production from the bacterial activity declines as well; thereby lowering the temperature of the pile. In this phase the mesophilic bacteria begin to recolonize the compost. Fungal invasion also occurs in this phase because their spores can withstand high temperatures and because of their ability to utilize lignin and other waxy components from food (carbon sources which bacteria cannot normally utilize)7. The primary denizens of the compost pile in this phase are A. fumigatus and Actinomyces ssp.8 The final phase of composting in terms of bacterial activity is the maturation phase where the mesophilic bacteria and the fungi continue to metabolize all that has not yet been metabolized in the compost pile. The activity in this stage is very low considering the small amount of organic carbon remaining. Finally the compost cools back to ambient temperature. As shown before, temperature is a very important factor in the composting of materials. Temperature gradients can be seen throughout a static compost pile. The temperature will be the greatest at the center and will decrease towards the outer levels of the pile. Temperature is a primary control factor for commercial composters. Since the greatest bacterial activity, organic material oxidation, and degradation are done in the thermophilic phase, the emphasis is placed on maintaining a high thermophilic bacterial population, and maintaining that phase for as long as possible. Temperatures greater than 60°C in composters lead to rapid thermal deactivation of bacterial activity. The amount of metabolic heat that is produced in composting is on the order of 3200 kcal/kg dry matter and a temperature gradient of 3°C/cm in the fennentation9. This heat must be dissipated, since microbial growth 10 is sensitive to temperature and it affects spore germination, growth, product formation, and sporulation9. Commercial composters use an air-blowing system to control temperature. The compost is loaded onto a conveyor and is stirred and mixed while a large quantity of air is blown onto the system. The air acts as a cooling medium, keeping the ever-rising temperature of the compost below its critical temperature of bacterial deactivation. The temperature and flow rate of the air are the control variables in commercial systems. Also by blowing air on the compost, oxygen is supplied in excess for the oxidation of the compost and for the aerobic respiration of the bacteria. 11 Solid State Fermentation Model: Heat transfer in solid-state fermentation is an extremely critical factor. Many techniques of heat removal in a system have been developed. As mentioned before, an important and heavily used technique is the blowing of air on to the fermentation bed. Other methods are based on the stirring of the fermentation media, which can reduce the heterogeneity of the system. Mathematical models have been developed in an attempt to describe the heat transfer in a solid substrate fermentation9’m. This allows for an examination of the fundamental heat transfer in a static SSF system and to specifically assess the importance of the convection and conduction for heat dissipation. The model is based on two parts; a) a set of ordinary differential equations that describe the physiological process (biomass production, substrate consumption, and carbon dioxide formation) as a fimction of temperature in the reactor; and b) an energy balance which takes into account the accumulation, conduction, convection, and generation phenomena through dimensionless numbers. This model allows the prediction of carbon dioxide formation and a measure of continuous microbial metabolism. This model also gives the temporal and spatial distribution of microbial activity throughout the system. However this model was not solved in this project due to the difficulty of measuring critical variables such as biomass and substrate content. Also, the solids were well-mixed and the temperature was at steady-state. The model can be expressed as a kinetic model with the following set of equations9: 12 Kinetic Model: Ld a" . , (621* . ii?) .. e . F,Da,,,ig at R2 Pe ar2 rBr BZ ' g a 91 where: dC R = J = Yco s 9 dt 2 1 RS : —_Ci_$ : —RX +m¢ dt YX/S X Rx : fl _ 1“‘lrriaxx(1 - _) d) dt max subject to: Atr= 1; 13? = Bi(T- 1) 6r At r = 0 fl = 0 6r T. At: t = O T = —1 Tb 13 where: r,z = radial, axial coordinates, dimensionless t = t'/ (I) = time, dimensionless (I) = L/u [=] time, L = reactor length, u = velocity T = temperature, dimensionless X = biomass m = maintenance energy S = sugar content CO2 = carbon dioxide [4 = specific growth rate me = maximum biomass concentration Ym, YCOZ = yield coefficient Bi = Biot number Pe = Peclet number DaIII = Damkéhlar number F dm = dry mass fraction The constants that are necessary to solve the above set of equations are dependent on the bacteria type and are determined from experimental data in some cases, and are estimated in other cases. Because of the low diffusion rate of biomass and glucose in solid media, the mass balance is not considered. The heat accumulation is considered as the main limitation of microbial growth in SSF because of experimental work showing severe limitation in growth at elevated temperatures”. The model simulates the biomass growth and sugar consumption inside the bioreactor. Moisture Content: Another major control factor in SSF is the control of moisture content in the reactor. It is also a primary optimizing factor for SSF reactors°. This is because the moisture content of the substrate affects the firngal and microbial growth, the enzyme activity, the accessibility of the substrate to the bacteria, and the regulation of product formation. The moisture content in the substrate pores also influences the mass transfer rate of oxygen and carbon l4 dioxide and the rate of heat dissipation. Too little moisture in the substrate reduces the enzyme activity and the accessibility to nutrients due to low substrate swelling. If the moisture content is too high, the void spaces become filled with water and the gas phase is forced out. As a result, aeration and degassing is hindered, which favors anaerobic process conditions. These inhibit the growth of the high-rate metabolizing thermophilic bacteria that are the primary culprits in the degradation of composting substrate. The most suitable method for moisture content control is the control of the relative humidity of the air supplied for aeration. This is difficult to control due to water formation by microbial activity, and moisture content absorption by the substrate. Carbon Dioxide Removal: Another control factor is the removal of carbon dioxide. The carbon dioxide percentage in the air in the reactor should be lower than 10% to prevent inhibition of the lignin degradation metabolism.°‘ll Therefore, the air supplied to the composter must be great enough for heat removal, oxygen supply, and to remove the carbon dioxide generated in the reactor. The limiting factor with the oxygen supply or carbon dioxide removal may be the interparticle mass transfer or the intraparticle diffusion°. The interparticle mass transfer is the transfer of oxygen or carbon dioxide from the void fractions within the solid phase to the growing microorganisms on the substrate surface. The intraparticle diffusion is the diffusion of the gaseous phase within the solid substrate. The most effective control for oxygen is to monitor the oxygen level within the substrate mass and take appropriate corrective action when the oxygen concentration drops to an unacceptable value. Due to the lack of 15 appropriate sensors for measuring oxygen concentration within the moist solids, the oxygen concentration in the exhaust air must be used for control. Degradation Mechanisms: The method by which bacteria degrade synthetic materials is not well known. The method of degradation is different for each strain of bacteria and for each substrate. For example, the lignocellulose-degrading bacteria that are common to composting systems biologically cleave the residues of certain degradable plastics. Other bacteria can degrade materials like cellulose and cellulose-like materials through normal aerobic pathways. Certain fungi, the white rot fiingi, can degrade xenobiotic compounds like 2,4-D (2,4- dichlorOphenoxyacetic acid) and 2,4,5-T (2,4,5-trichlorophenoxyacetic acid) which are common pesticides7. The biological pathways through which many of these compounds are degraded have not yet been elucidated. A technique exhibited by certain bacteria and fungi consists of the secretion of extracellular enzymes into the biological environment which break down the cellulose into oligo- and monosaccharides that can be absorbed into the cell for fiirther and later degradation. Another type involves the bonding of the bacteria to substrate to be degraded by certain regions on the cellular exterior membrane and the subsequent degradation of the material. There is usually a large variety of species in a bacterial degradation system. This is due to the fact that the degradation product from one type of cell might be the ideal substrate for another type of bacteria. This is called a domino type of degradation and allows for higher levels of biodegradation. l6 Mdation Products: In some cases, the compound that is to be degraded is not always converted into some biologically sound form. Sometimes, the material is not degraded at all°, but rather volatilized into the atmosphere by the excessive heat produced in a composting process. The material is still present in the environment and is still toxic. Other cases have found that one toxic material has been converted into another that is not utilizable by other bacteria as a substrate. This also causes problems with the testing and analyzing of the composting residues. The new toxic material may not be able to be identified by current analysis techniques being run on the composting system. l7 Polymer Biodegradation: Plastics take up 30% of the volume of municipal solid waste. This amounts to 320 billion pounds per year of plastics solid waste, which will increase to 380 billion pounds per year by the year 2000, 85% of which are disposed of in landfills‘. Three particular polymers account for 90% of all plastic found in municipal waste; polyethylene 38%, polyvinylchloride 31%, and polystyrene 21%”. These three polymers are heavily used in the packaging industry”. One third of all the landfills in the nation will fill up and close within the next five years, and their high cost, $100/ton’, force the consideration of new techniques for the disposal of polymers. Recycling and biodegradable plastics are the two biggest thrusts. Legislation has been enacted to force the use of new plastics and recycling1 for example, the use of polyethylene terephthalate bottles for recycling. Another example is the banning of plastic food packaging in Suffolk County in New York, targeting fast food packages made of polystyrene. Also in Berkeley, California, all fast food restaurant containers must be biodegradable. The poisoning of our natural environment by plastics is shown by the analysis of a crude oil sample from Chevron's Red Wash basin. It was analyzed as 5% low molecular weight polyethylene”. There is a lot of developments going on in the area of biodegradable polymers for use in the commercial industry”. The term "biodegradable" is defined as the ability of the molecular components of a material to be broken down into smaller molecules by living organisms, so that the carbon contained in the material can ultimately be returned to the biosphere. Many degradable polymers don't degrade under environmental conditions while l8 degrading well in the controlled environment of the laboratory. Photodegradable plastics, with weak linkages in the hydrocarbon backbone, with wonderful degradation, are of no purpose when buried in a landfill. Other problems include biodegradable plastics that do not biodegrade in landfill conditions and the non-degradable portions of many polymers do not degrade. Mdation Methods: There are many techniques to monitor and measure the levels of degradation. The change in molecular weight is a primary technique in measuring degradation. Size-exclusion chromatography (SEC) is used for measuring molecular weight changes, infrared spectrophotometry (IR) is used to monitor changes in the carbonyl index, and liquid scintillation (LS) is used in studies measuring the evolution of 1“C02. Other techniques in measuring the degradation levels are the monitoring the changes in the physical properties of the polymer. Properties such as tensile strength, modulus, and stress-strain curves decrease during degradation. Biodegradation Tests: The key to testing the biodegradability of commercial polymers is the testing of biodegradability in an environment similar to what it will be in nature. Therefore, many of the biodegradability tests performed have not done an entire fate analysis of the polymer, and the information on the polymer’s biodegradability is suspect. BiodegradatiOn studies fall into two categories; water soluble and water insoluble. Testing of water soluble polymers is simpler and has been done for many years, i.e. with detergent additives. These tests include biological l 9 oxygen demand, carbon dioxide evolution, semi-continuous active sludge tests, and the aforementioned l“C tests. The water insoluble tests are much more difficult to perform and include bacterial and fungal growth ratings, physical form and weight losses of the polymer, and the 1“C tests. Many one component polymers, such as polyethylene, are not biodegradable to any extent. This is especially true for addition polymers with carbon-carbon backbones. Polyethylene degradation has been seen to be 0.5% per year; powdering to increase surface area has only increased this slightly”. Polyvinyl alcohol is the only carbon-carbon backbone polymer to biodegrade rapidly. It is found that linkages other than carbon-carbon are more readily degradable. Polyacetals, developed by Monsanto, are considered biodegradable, as are polyesters and polyamides. One common technique to increase the biodegradability of polymers is to use a biodegradable filler with a non-degradable polymer base. This gives the desirable degradablity of the biodegradable polymers combined with the physical strength and toughness of the non-degradable polymers. The key to making usefirl polymers with suitable physical properties and required rates of degradation is to prepare what is known as a compatible blend. An incompatible blend is where two distinct phases form when the primary polymer is mixed with the biodegradable component. To determine the compatibility of the polymers, the refractive index of the film or the singularity of a glass transition temperature is used. This limits the amount of biodegradable "filler" that can be added to the polymer due to rapid loss of desirable physical properties. Large regions of biodegradable (discontinuous) phase 20 will lead to rapid loss of strength, while increasing the biodisintegration of the bulk material. Compatible blends, where the biodegradable component could be added at the molecular level, will lead to uniform loss of physical properties during degradation. Compatible blends have had more gradual changes in physical properties than incompatible blends where the loss of physical properties is very rapid. Compatible blends will also increase the degradation of the bulk material rather than degradation of the "biodegradable region" in an incompatible blend. Single phase polymers (compatible blends) can dissolve in water and presumably might be attacked by microorganisms. Most of these compatible blends have hydrolyzable linkages that include ester and amide types. These polymers do not blend well with the more hydrophobic polymers used in packaging applications such as polyethylene and polypropylene? Polymer blends, particularly olefins with biodegradable polymers are being used as an approach to packaging plastics. The problem with these blends is that only certain regions biodegrade, leaving the non-biodegradable sections intact. While this does cause the polymer to lose form and volume, allowing for polymer to be put into the same landfill; it does not eliminate the problem. The polymer is still present in the environment. The polymer degrades in proportion to the fraction of degradable filler. One study examined the degradation or rather the susceptibly of various commercial polymers to bacterial attack”. The only polymers that showed significant degradation, or bacterial growth, were a polyvinyl chloride with a soybean oil plasticizer and polyurethane. All the other samples, which included polyvinyl acetate, polyethylene food wrap, polypropylene, polystyrene, polyethylene 21 terephthalate, and nylon 66, showed little bacterial growth. Another result of this study was the determination that with biodegradable "fillers", it was the filler that was degraded and resulted in the bacterial growth and the polymer backbone was not degraded at all. A study on how certain bacteria of the Streptomyces ssp. can degrade lignin, the second most abundant plant polymer after cellulose, was performed”. The polymer basically consists of carbon-carbon monomers and ether linkages. The study examined the biochemicals and enzymes excreted and proposed a mechanism of degradation for the lignin polymer. The results suggested that the catabolism of the polymer involves substantial initial cleavage of the ether linkages concomitant with other lignin oxidation reactions. This is a good sign for the degradation of ether linkages for polymers. Carbon-carbon linkage polymers have a difficult time degrading while the ether linkages, carbon-oxygen, biodegrade much more easily, since the bacterial enzyme only works on C=O linkages. The ether linkages are what are broken in the above example rather than the carbon-carbon linkages, although it takes less energy to break carbon-carbon linkages than it does to break a carbon- oxygen linkage. The oxygen withdraws electrons and makes the molecule more polarized and gives it greater ionic character. This makes it easier to break apart the molecule or polymer. The effects of polymer morphology are significant to the biodegradability of the polymer. Straight chain polymers are more easily utilized by microorganisms than their branched companions. A study12 showed that high growth rates were obtained when the bacteria were utilizing straight chain hydrocarbons in comparison to bacteria utilizing branch polymers. It was also seen that increasing molecular weight makes the polymer less and less 22 degradable. This makes sense because by having smaller and smaller pieces, greater surface area for microbial attack is created. 23 Poly(phenylene ethers): Poly(Z-methyl 1,4-phenylene oxide) (Figure 2-4) is the polymer chosen for this study. Poly(2-methyl 1,4-phenylene oxide), PMPO, is a synthetic polymer based on the known microbial degradation of many simple aromatic compounds by oxidative ring cleavage following hydroxylationz. The monomer of this molecule, o-cresol, is a compound that is known to be biodegradable", which leads to the belief that PMPO might be biodegradable as long as bonds between monomers can be broken. Much of the basis of the engineering properties, such tensile strength and modulus, of this material is based on the physical properties of poly(2,6-dimethyl 1,4-phenylene oxide) (PDMPO) (Figure 2-5). Since PMPO has less substitution on the aromatic ring, and therefore fewer branches, biodegradability should be greater than that of PDMPO. The biodegradability was comparedz, and it was seen that the biodegradation rate of PDMPO is significantly lower than that of PMPOZ. It has also been determined that the biodegradation of PMPO occurs independently of its molecular weightz. Degradation might occur through a cell-associated mechanism where the degrading bacteria use specialized areas on the cell’s exterior to bind to the substrate. This strategy conserves enzymes and prevents the loss of enzyme products into the surrounding fluid. PMPO belongs to the class of poly(phenylene ethers) polymers. There are several commercial poly(phenylene ethers) on the market. The largest commercial use of these polymers is in Noryl engineering resins, which are alloys of poly(2,6-dimethyl-l,4-phenylene ether) and polystyrene. This polymer, PDMPO, is produced from 2,6-dimethylphenol rather than the o-cresol (o-methylphenol) for PMPO. PDMPO has a high impact strength, a glass 24 «Steam A023 goers—E .maaoEEéJK—om "m4” 2sz :0 a10 of °i £0 0 I ‘3‘ £0 on: ‘3‘ £0 0 I O 9.5225 32.8 0:01:29 .mfioiévbom 31a ouswrm £0 I :0 OI Q°©°Qo©>é 2 5 transition temperature of 205°C, and a crystalline melting point of 267°C. The polymer has a high weight average molecular weight of 40,000 and a number average molecular weight of 18,000 and is therefore suitable for injection molding. It is a linear thermoplastic polymer with a free hydroxyl group on the head of each polymer chain. This hydroxyl group is what allows the unique properties of the polymer, such as the grafting of polystyrene and comb- type terpolymers. The physical properties of the polymer are that it is a hard, ductile material with high heat deflection temperature under load. It maintains its ductability to very low temperatures, has a low coefficient of linear expansion, low creep under mechanical load, and retention of high tensile and modulus values at elevated temperatures. It is compatible with polystyrene in all proportions. Blending is desired due to difficulties with injection molding and high melt viscosity. Blending with high impact polystyrene improves the processability and impact properties. The polymer can also be blended with polyamides, such as nylon—6,6 which improves melt flow and resistance to organic solvents‘g'lg. The polymerization techniques used in the production of PDMPO is based on the oxidative coupling of 2,6-disubstituted phenols with hydrogen atoms in the 4 position. The mechanism of how this polymerization occurs is as follows. If there are "free" phenoxy radicals generated in solution, then carbon-carbon linking will predominate, and since the linkages in poly(phenylene ethers) are primarily carbon-oxygen, the assumption is made that "free" phenoxy radicals do not exist. The mechanism visualized is stated by Hayzo’z‘. It consists of a copper complex catalyst being coordinated to a phenol in the initial step. In the first step in the reaction, the copper catalyst reacts with the phenol to give a copper complex 26 in which the phenoxide ion is directly coordinated to the copper. Through electron transfer, a phenoxy radical could be generated, but still complexed to the copper. It would then be carbon-oxygen coupled. This mechanism is diagramed in Figure 2-6. It shows the formation of the first attachment of monomer from the radicals and the formation of inorganic copper. This does not include the termination reaction where two reactive intermediates encounter and the polymer chain growth is ceased. 27 CH3 H3C CH3 ITIR ITIR O + Cl“ CU'OH —-> C1- CU‘O I I NR NR 2,6 - Dimethylphenol CH3 Cl CI CI I I I RN-CU —NR RN—Cu —NR RN—Cu —NR 6: I I l , :O . i=5 9 H30 I CH3 H3C‘l CH3 H3C .CH3 Figure 2-6: Poly(2,6-dimethyl phenylene oxide) Mechanism Diagram 28 The method of production of PMPO uses a different catalyst system. The difficulty with using the method presented by Hay21 is that the open ortho position causes high levels of carbon-carbon linkages (undesirable for biodegradability) and low molecular weights. Greater selectivity could be obtained if bulkier ligands were used in the reaction. Bulky ligands physically hinder the reaction at the ortho position. Attempts were made21 using ligands such as 2-n-amypyridine, 2-n-tridecylpyridine, and 2-(2-(5-nonyl))pyridine. These attempts yielded higher molecular weights, but non-linear polymers, which meant brittle films that crOsslinked and became insoluble. High molecular weight PMPO was prepared with a new catalyst system that used CuCl with 2,2-i50propoxy ethyl pyridine. The bulky coordination complex (on the copper catalyst) reduced the carbon-carbon coupling at the 6- position”. The proposed mechanism for this system is presented in Figure 2-7. In this polymerization mechanism, the oxidation of mono-ortho-substituted phenols is very complex. Under the oxidative polymerization of the phenol, reactions at the ortho position might be repressed by increasing the size ligand and physically blocking any reaction from occurring at the unsubstituted ortho position. Even though high molecular weights have been produced, on the order of those produced for poly(2,6-dimethyl-1,4-phenylene ether), there is some branching. This indicates that the reaction at the unsubstituted ortho position has been greatly reduced but not completely halted. 29 OH CH3 CH3 NR NR + Cl- C:u- -OH —-> Cl- C:u -0 NR NR o-Cresol (2-methylphenol) NR =O- Clu- CI .OJ 0.\ CUNR: —> .C-r:|-L<:>=O:: Cu-Cl + Cu (I) CH3 RN Cl ’. NR 0 CH3 I CHZCHZOCHCH3 2,2-isopropoxy ethyl pyridine Figure 2-7: Poly(Z-methyl phenylene oxide) Mechanism Diagram 30 Composting is a technique that can be used to enhance the biodegradation of polymers; If the polymer can be utilized by the flora of the compost, the polymer will be consumed as substrate and converted to new biomass or as products from various metabolic pathways. Composting is done commercially with large scale reactors such as tower and rolling drum fermenters. Certain variables are key control variables in the fermentation system: moisture content, carbon dioxide removal, oxygen supply, and temperature. The temperature of a composting system can give the phase that the system is in. The temperature also determines what bacterial species are present in the system. As the composting system is allowed to sit the compost will go through four phases; meSOphilic, thermophilic, cooling, and maturation. The bacterial and firngal populations will vary depending on the temperature. The most active phase of composting where the highest rates of degradation are measured is the thermophilic phase. Therefore, most commercial reactors operate in this range. Mathematical models have been developed to describe the dynamics of composting. While none of the models were employed in this study, they can describe the temperature, growth, product production, and substrate consumption of the system. New polymerization techniques have been developed for the polymerization of biodegradable polymers. One of these polymers is poly(2—methyl phenylene oxide) and the methods used to examine the biodegradability of it in a rolling drum composter are described in the next section. CHAPTER 3: MATERIALS AND METHODS Poly(Z—methyl-l,4-phenylene oxide) Production: The polymer was prepared using o-cresol (Aldrich Chemical Company) as a monomer (F.W. = 108.14, (1 = 1.048, b.p. = 191 °C, m.p. = 32 - 34 °C, 98% purity) and was used without further purification. Oxygen gas (Airco, Inc.) was passed for 10 - 15 minutes into a reaction mixture that contained 3 grams of copper chloride (Aldrich Chemical Company), 50 mL of 2-(2-isopropoxyethyl)-pyridine (Aldrich Chemical Company) and 150 mL of toluene (Aldrich Chemical Company). After treatment of the system by the oxygen, an o-cresol solution was added dropwise through a funnel into the solution. The o-cresol solution was prepared by dissolving 32.4 grams of o-cresol into 200 mL of toluene. Oxygen was added to the system constantly throughout the addition of the o-cresol solution and throughout the remainder of the reaction. During the reaction, the temperature was controlled below 50°C by adjusting the dr0pwise addition rate of the o-cresol solution. The reaction was performed in a three-neck 500 mL round bottom flask, with one port used for addition of the o-cresol solution, one port for a thermometer, and one port used for the addition of oxygen gas. A magnetic stirrer kept the reaction well mixed during the entire process at a moderate agitation rate. Water was removed from the system by the addition of 18 grams of anhydrous magnesium sulfate (Aldrich Chemical Company). After the complete addition of the monomer solution, the reaction was kept going for two hours. The product was precipitated by pouring the reaction mixture into two liters of methanol with one mL of 1 normal hydrochloric acid. The product was allowed to precipitate and was collected in a 31 32 Buchner funnel by suction filtration. The precipitate is a dark orange-brown solid that was a sludge on precipitation. The polymer was dried for five minutes over the suction and allowed to air dry overnight. A light yellow-brown powder was the result. Composter Construction and Design: A rolling drum composter was constructed to perform the solid state fermentation. The design consists of a drum which is 5 inches in diameter, 10 inches long, and 0.5 thick and constructed of a rubber. It has a removable screen at one end of the drum to allow the passage of air and water in and out of the system. The screen needed to be made of a porous type of material, and in this case, denim was used. The screen required replacement every ten or so days due to rot caused by the bacteria and the extreme conditions of the fermentation vessel. The drum was placed on a set of roll bars that were attached to an electric motor. The motor turned the roll bars and caused the drum to spin at a relatively slow rate (30 - 60 rpm) and caused the material inside to be well-mixed and uniform in composition. The entire drum, roll bar, and electric motor unit were placed inside a controlled environment chamber. Inside this chamber, the temperature and humidity were controlled. The environmental chamber has ports for water and an air feed and for water and air exhaust. The drum and motor unit were manufactured at the Division of Engineering Research's Machine Shop and the controlled environmental chamber was manufactured by Blue M, model #VP-lOOAT-l. The air supplied to the environmental chamber was heated and had water added to it before entering the chamber. This was done to help reduce the load on the heating and humidity units in the controlled environment chamber and to help reduce fluctuations in the temperature and humidity. This was done by passing air through silicon tubing into an oven 33 where the air was heated to approximately 60°C and passed through two consecutive gas washing bottles containing water. The oven (Blue M) had holes drilled into the top for inlet and outlet ports. The warm, moist air was then passed into the controlled environmental chamber through the gas inlet port. The chamber was set at 60°C and 95% humidity. These were monitored inside the chamber by a thermocouple and humidity gauge. The controlled environment chamber was hooked up to the cold water outlet on the sink. This helped to remove heat that was built up in the chamber due to the action of the motor. The air and water were obtained from house line with no filtering or treatment. The flow rate of the air was monitored using a rotameter. No monitoring was done on the outlet air flow of the chamber. The entire system was assembled in the laboratory and a schematic diagram of the system is presented in Figure 3-8. 34 Samoa—=80 EEG w:_=o~— "Tm charm ban—i .523? _ _ beam 54 L 3.3.30 ohaauoafioh an: .0835! ,III SS .53 \ an. . 83cm Mam—.33 new 1.? Ea L233— :33m .55: IE1 :o>O Samoa—Sou 35 Sample Preparation: The material used for most of the composting runs was a mixture of grass clipping and leaves. The optimal carbon/nitrogen ratio for composting substrates was assumed to be 31%7, which corresponds to 16.7 grams of grass and 8.3 grams of leaves for a 25 gram sample. The two components were placed into a high speed blender (Waring, Inc.) along with 0.125 grams of prepared polymer pellets and mixed together thoroughly at approximately 10,000 rpm. The polymer/compost mixture was placed into the rolling drum reactor and the temperature and humidity within the reactor were controlled at 60°C and 95% humidity. The drum was set to roll at 40 revolutions per minute, thereby insuring a uniform mixture of polymer and composting media. Samples of 4 grams were taken every five days during the experiment. Much of the sample weight was water. At the time of taking the samples, 5 mL of water was added to the rolling drum reactor to maintain the 95% humidity and compensate for water lost in the air that left the reactor. The samples were then placed in pre-weighed dry glass beakers and allowed to dry in the oven overnight to remove all of the moisture from the sample. The dried sample was treated with three successive additions of chloroform to insure complete removal of the polymer from the sample, followed by filtration to remove the solid grass and leave remains. This chloroform/polymer mixture was treated with five times the volume of methanol (Baker, HPLC grade). This caused the polymer to precipitate out of solution. The polymer was recovered by centrifiigation (Sorvall, Inc.) at 10,000 rpm for twenty minutes. The sample was suspended in a small amount of methanol and placed in an aluminum drying pan and 36 allowed to dry overnight in an oven (Blue M, Inc.). The sample was weighed for dry weight analysis. Samples of the supernatant from the centrifiigation were sent to the Division of Engineering Research at Michigan State University for analysis by FTIR to see whether or not polymer remained in the solution (see Figure 3-9). Sample Analysis: The sample was analyzed by both dry weight and HPLC. Dry weight analysis was performed as mentioned above. For HPLC analysis, the samples were redissolved in chloroform at a concentration of 0.25 mg/ 100 mL of solvent (0.25%). The HPLC system used was a Waters HPLC system (Millipore Inc., Vineland, NJ) equipped with a Waters 600 Multisolvent Delivery System, a Waters 410 Differential Refractometer, and a Waters 490 Multiwavelength Detector. The column used was an Ultrastyragel column (Waters - Millipore Inc., Vineland, NJ) for gel permeation. The column is high resolution with a nominal particle size of 7pm and a pore size of 1000 angstroms. The detectors of the system are monitored by a data acquisition system attached to a personal computer. The HPLC system was first cleaned with nitric acid to remove residues, followed by water, methanol, and then finally followed by chloroform to purge the system of any impurities. The column itself was washed only with chloroform. Standards were run on the system to calibrate for sample HPLC runs. The standards were polystyrene and were premade and purchased. The flow rate for the runs was determined from an analysis to determine the optimal separation and was found to be 1.0 mL/min. The redissolved samples were injected into the system after being filtered through a 0.22 pm filter (Bio-Rad Inc.) at a flow rate of 1.0 mL/min. For evaluating the number-average molecular weight, the following equation was 117 Z n‘M, 2 It used. n = k A where ki is the response coefficient and A,- is the area under each division. There are two possible mechanisms for calculating the number average molecular weight. The first mechanism is that if 19 is only proportional to Ai and not a fiinction of chemical groups, then the following equation results: 24M. EA 1 117: However, for this case, k,- is also related to molecular weight since different organic groups respond to light differently, the following equation is adopted for estimating the number- average molecular weight: An analysis flow chart for the biodegradation studies is presented in Figure 3-9. 38 Grass/Leaves(2:1) - Bacteria PMPO (0.5 weight %) Temp Control ’ C stin S ste Wagon... .4 (ravines m Humidity Control I Sample Every 5 Days I Dry Weight Chloroform » I E .on I ‘ Filtration (F iltrate) Methanol . l Precipitation l Centrifugation l Filter Precipitate Supernatant HPLC Anal ' W ' t Anal ' ysrs Dry ergh ysrs FTIR Figure 3-10: Analysis Flow Chart CHAPTER 4: RESULTS Polymer Production: The polymer was produced in the manner described in the materials and methods section. The polymer generated was a light yellow-brown powder. The average molecular weight, determined from HPLC analysis in comparison with polystyrene standards, was 4900 g/mol. The average yield from the polymer production was 72.5% and a theoretical yield of 32.4 g from 32.4 g of limiting reactant (monomer). Composter System Design: The rolling drum composter was constructed in the DER machine shop. The rolling drum system kept a constant mixing rate that allowed a semi-homogeneous mixture within the chamber. The denim screens on the drum allowed for the penetration of oxygen and moisture into the system while keeping the fermentation media contained within. The temperature control system functioned adequately and well with minimal fluctuations, :t 2°C; monitored by both internal sensors and an external thermocouple. The humidity control for the reactor kept the humidity in the reactor at least 75% throughout the experimentation period. Water addition was necessary to compensate for moisture lost to the environment and due to condensation in the chamber. 39 4o HPLC and Dry Weight Analysis: The molecular weight of the degraded polymer was determined from analysis by HPLC. This was done in comparison to polystyrene standards. The standards were run under the same conditions (pressure and flow rate) as the sample analysis. The polystyrene samples are presented in Figure 4-10 and Figure A-24. The optimum flow rate was determined to be 1 ml/min based on the separation and resolution of the PMPO samples. The data are presented in Figure A-25. Figure 4-10: Polystyrene Standards 41 The optimum polymer to substrate ratio was determined to be 1/200. Five different degradation ratios were examined, and they are presented in Figure 4-11. MW 14.28% 5075 - 4350 21.74% 17.08% 4883 ~ 4049 26.27% 17.06% 5075 ~ 4209 29.66% 33.87% 4880 ~ 3228 55.92% 31.42% 4875 ~ 3343 52.49% 33.12% 4877 ~ 3262 56.37% no data' 4956 - ???? no data Figure 4-11: Degradation ('— indicates too little polymer to obtain data) Polymer degradation is represented as molecular weight reduction as a fiinction of time for HPLC analysis in Figure 4-12 and represented as a reduction in polymer weight as a fiinction of time in dry weight analysis in Figure 4-13. 42 QONHFIOI oomuwldl oomuwlol mwuvlll wen—lei 33+ Amara—554 Unruly 5353239 2385 3.3232 as-.. 2%; m o lilieilllla - 00.0000 1 - oodomm - - oodoow I T 00603. oodoom oodomm oawa :0 1H5!9M Jalnoaiow 43 oowuwldl OONHFIOI oomnvlol mNHFLal Curl? own—.101 ov T 392.254 2335 De :e_.a—E..won 8&2 ”2-9 9.sz mm — _ gen 0 N or o— 1»— v.0 I md I 0.0 I No I ad I md 0 Ode 1° °/o1M 44 In the HPLC analysis, a bimodal distribution is observed (see Figures 4-15 through 4-20). The higher molecular weight peak is identified as Peak #1 and the lower molecular weight peak is identified as Peak #2. A ratio of the area of peak #1 to peak #2 was calculated. This is presented in Figure 4-14. verage 5566 i 2% 450 i 3% 5209 i 9% 347 i 2% 3840 i10% 357 i 5% 37363: 15% 336i4o/o 3721 21:17% 246i9% Figure 4—14: Bimodal Peak Comparison (Data taken from Run #6 in Figure 4-1 1) 45 ta: - 9:: 63. 2:? c E - 04:: "E-.. 2%.: 46 mu b5 .. use: an-.. 2:3... 8 b5 .. 01:: ”S-.. 2:3... 47 3 b5 - 04:: 5N-.. 2&2 9.. an - one: "a-.. 9...»:— CHAPTER 5: DISCUSSION Polymer Production The average molecular weight of the polymer in the beginning of the experiment was determined from HPLC analysis in comparison with polystyrene standards. The average molecular weight was 4900 g/mol. This corresponds to an average of 45 monomers per polymer chain. The possible structure for this polymer is given in Figure 2-4 in the previous Chapter 2. The average yield from the polymer production runs was 72.5% based on the monomer and a theoretical yield of 32.4 grams when starting with 32.4 grams of the monomer. The yield compares well with literature values using R groups on the copper catalyst of n-amyl and n-tridecyl pyridine of 76% and 78% respectively.20 Rolling Drum Composter: The humidity control for the system was not adequate for the requirements of the experiment. A fair amount of fluctuation occurred in the humidity during the forty day runs, but that was not critical in our experiment because the goal was just to maintain high humidity. The major difficulty was in maintaining the high humidity. Even though the air feed to the system was made as moist as possible, the air and water flows out of the system kept requiring that more water be added to the system. The water was added every ten days when the samples were withdrawn. Five milliliters was added each time directly to the rolling drum and its contents. This kept the humidity in the system above 75% for the majority of the experimentation period. The temperature control on the chamber worked well. Since the air was preheated 48 4 9 before entering the chamber, less stress was placed on the heating system and much better control was obtained. The heat accumulated due to the activity of the rolling drum was removed by the cooling system in the environmental chamber. The temperature was monitored by a thermocouple as well and the internal temperature sensors. The temperature was maintained at 60°C i 2°C. The mass balances on the reactor were done and are presented below. (mass) + (mass) (mass) gas entering gas produced _ gas leaving *(humidityout) (mass) airout *(humiditye)+~(mas$ (masS .. alrin liqadded = It was found that these mass balances could not be solved with the data taken. The variables needed would be the air flow rate leaving the reactor and some measure of the liquid flow rate out of the reactor. If these variables could be measured, the closure on the balances could be determined. 50 Sample Preparation: The sample was prepared to give an optimal carbon/nitrogen ratio for the composting bacteria. Composting bacteria are very sensitive to the composition of their substrates, and when studying biodegradation in controlled environments, the maximum composting rate is desired. Therefore the substrate and media components were Optimized to have the highest rate of degradation possible. The thermophilic composting bacteria (bacteria with the highest rate of reaction - Figure 2-3), prefer a media having a carbon/nitrogen ratio of 26% to 35%7. It is in this range where they are the most efficient in their degrading action. (That is why many organic gardening shops offer what they call "compost activators"; to help optimize and supply nutrients that the ordinary compost pile does not have.) Maple leaves have a carbon/nitrogen ratio of 60%, too high for optimal composting, and grass clippings have a carbon/nitrogen ratio of 20%, too low for optimal composting7. Therefore a combination of these two components commonly found in ordinary compost piles will give a good solid substrate. The optimal percentage was based on averaging the two extremes of the range and 31% carbon was used as the optimal percentage. In order to insure good, solid mixing, a blender was used. This is critical to the experiment. It is very important to start with and have throughout the experiment a homogenous mixture. When withdrawing samples, a representative sample is desired, and different zones within the reactor should be avoided. The molecular weight of poly(2-methyl-1,4-phenylene oxide) was found to be 4900 g/mol. This is the starting molecular weight and all measurements of biodegradation are taken from this point. A study to determine the optimum ratio between polymer and composting 51 material was done. The cases studied were 1:10, 1:17, 1:25, 1:200, and 1:400 by weight. In the first three cases the experimental data show little biodegradation. This was seen by both dry weight analysis and HPLC analysis. There was little significant degradation during the forty days of the run; the overall biodegradation percentages ranged from only 20%-3 0% for dry-weight analysis and approximately 15% for HPLC analysis. The 1:200 runs showed a weight reduction of over 50% and a loss of over 30% in the average molecular weight. The 1:400 run failed since there was too little polymer in the composting mixture; no polymer could be recovered in the extraction procedure. All later runs were done with a 1:200 ratio since this provided the best results. 52 5:359 .528:— UwE: :NIm PEwE cwhdm mmoxo 4 hmOIm mwh4 1 q / II I 9.: .4 I ' l- l I 1 q . \ - ‘ I V \ r I .= ‘ //\ r 1 ‘ f’\ I , — ‘. 1' / I . ‘r I I / -' . 1 . . , , I . 72 _ l l '. ,' \V \l i- I I I \ / ; 1 : a 1 l : r. _ ' I ’ .- I I / i L _ 1 1 I I l 4’2 " \ q I ‘1 A/ i m)- 1 I ,1 . . I I: — / II V 2 . I is.» I III ;‘ I g ‘I ~ 1 1 I : 1— !, l j .' ' I , ,. . I I” ‘ ‘ f ' I ;I . 1' l V I! i C 24 —. j .' . . .' l 1 i 21 i . I g I 14 i» I ? j = 4 \/ 1,! J L i 1' '9 6 "If I I 1' I I I I I T I I I I I I I I I I I A 31561. _- Inc: I»: on 1200 son X 1676 4.866 656 2 96 6 73 112 4'5 I 661511?! REF 4989 1.69 71 2889 166.57 3976 189 2 3869 11.6 9 "5354 18 6 2946 18 B 223-1 21 '3 2594 92 6 252% 6’9 5 2228 1151-1 7 26144 '38 6 147-8 41 6 1426 46 Z 1226 71 a 11.14 56 3 1839 6 7 758 12 4 666 38 9 END 16 PEI-MEI FOUND Figure A27: FTIR - Sample ‘0 .1. ‘J I \‘ A N 69 25.8.9515 - y: umN< PSME “9: IE 5.0.8“ I ‘u I. ’— 3.0”.uhll '- l g 'n l I I. I ’4 I I. .- l l J I h<3 oo- 80. con. 81. 8.. 8: 82 _ . _ . _ . _ n. n. .. o. a a . a mm m 3.012! 83.9 .822 01.: 3 m5... .: «:22 “rm: 8 0.08.3 9: 3% .E E 95. u :8. 2E ggnggggggngggvgg _ . 0 his. . . . . . . . . n ad -.u a." ..N flu fin ad u.“ 8 s. + 8 .3856 .5313. m5 @280 BIBLIOGRAPHY BIBLIOGRAPHY Thayer, A.M., Plastics Recycling Eflorts Spurred by Concerns About Solid Waste, Chemical and Engineering News, 67(55), 1989, pp. 7-15. Lia-Xia, L., Grulke, EA, and P]. Oriel, Synthesis and Microbial Degradation of Poly(Z-methylphenylene oxide), Journal of Applied Polymer Science, 777?. Grajek, W., Production of Protein by Thermophillic Fungi fiom Sugar-Beet Pulp in Solid-State Fermentation, Biotech. and Bioeng, 32, 1988, pp. 25 5-259. Ramachandra, M., Crawford, D.L., and Pometto III, A.L., Extracelluar Enzyme Activities aiiring Lignocellulose Degradation by Streptomyces ssp. .° A Comparative Study of Wild-Tm and Genetically Manipulated Strains, Applied and Environmental Microbiology, 53(12), 1987, pp. 2754-2760. Abdullah, A.L., Tengerdy, RIP, and Murphy, V.G. , Optimization of Solid Substrate Fermentation of Wheat Straw, Biotech. and Bioeng, 27, 1985, pp. 20-27. Weiland, P., Treatment of Lignocellulostics with White Rot Fungi: Principles of Solid State Fermentation, Elsevier Applied Science, New York, 1986, pp. 64-75. Fogarty, A.M., and Tuovinen, O.H., Microbial Degradation of Pesticides in Yard Waste Composting, Microbiological Reviews, 55(2), 1991, pp. 225-233. Strom, P.F. , Identification of Thermophillic Bacteria in Solid- Waste Composting, Applied and Environmental Microbiology, 50, 1985, pp. 906-913. 71 10. 11. 12. 13. 14. 15. 72 Saucedo-Castafieda, G., Gutierrez-Rojas, M., Bacquet, G., Raimbault, M., and Viniegra—Gonzalez, G., Heat Transfer Simulation in Solid State Fermentation, Biotech. and Bioeng., 35, 1990, pp. 802-808. Lai, M.N., Wang, H.H., and Chang, F.W., Thermal Difi‘usivity of Solid Mash of Sorghum Brewing -A Solid State Fermentation, Biotech. and Bioeng., 34, 1989, pp. 1337-1340. Schuchardt, F ., and Zadrazil, F., Treatment of Lignocellulostics with White Rot Fungi: A 352 L Fermenter for Solid State Fermentationof Straw by White-Rot Fungi, Elsevier Applied Science, New York, 1986, pp. 77-89. Potts, J E Clendinning, R.A., Ackart, W.B., and Niegisch, W.D., The Biodegradability of Synthetic Polymers, MW, Plenum Press, New York, 1973, pp. 61-79. Glass, J .E., Plastic Degradability and Agricultural Product Utilization, from A_' .1... ..__ h ' Pl Ir'B9Q'3192...‘ .__._ i' 'on, American Chemical Society, 1990, pp. 52-57. Abbe, B., Biodegradable product industry advances, Ag Industrial Materials and Products, New Uses Council, St. Louis, Dec. 1993. Swifi, G. , Degradability of Commodity Plastics and Specialty Polymers: An Overview, from Agrjgulmral and Smthetig Polmers; Biodegradability and Man, American Chemical Society, 1990, pp. 2-12. 16. 17. 18. 19. 20. 21. 22. 23. 24. 7 3 Lee, B., Pometto, A.L., Fratzke, A, and Bailey, T.B., Bi i n f D l Plasfic Pgbmhylme by Phgnerochaete and Streptomyces Species, App]. and Envim. Micro, 57(3), 1991, pp. 678-685. Buswell, J.A.,J. Bacteriol, 124, 1077-1083, 1975. Encyclopedia of Polymer Science and Engineering, Vol. 13, Wiley and Sons, New York, 1988. Karasz, FE, and O'Reilly, J .M., Thermal Properties of Poly(2, 6-Dimethyl phenylene ether), J. Polym. Sci. Polym. Lett. Ed, 3, 1965, 561-563. Hay, A. S . , The SPE International Award Address - 1975: Polymerization by Oxidative Coupling - A Historical Review, Polymer Engineering and Science, 16(1), 1976, pp. 1-9. Hay, A. S., and Endres, G.F ., Polymerization by Oxidative Coupling. VI. Oxidation of Q—Cresol, J. Polym. Sci. Polym. Lett. Ed, 3, 1965, 887-889. Bailey, W.J., Kuruganti, V.K., and Angle, J .S., Biodegradable Polymers Produced by F ree-Radical Ring-Opening Polymerization, W W, American Chemical Society, 1990, pp. 149-166. Gould, J.M., Gordon, S.H., Dexter, LB, and Swason, C.L., Biodegradation of Starch-Containing Plastics, A ri l r h i P l r ' Bi '° andjltihzatm, American Chemical Society, 1990, pp. 65-75. Ingle, J .D., and Crouch, S.R., MW, Prentice-Hall, New Jersey, 1988. n 111171387158 IV. 01’3’19 :1 .11. I H N U E T on ..I S N Am C I H C I ”