HSC – Core Module 1: Production of Materials 2. Some scientists research the extraction of materials from biomass to reduce our dependence on fossil fuels Discuss the need for alternative sources of the compounds presently obtained from the petrochemical industry. Fossil fuels such as natural gas, coal and petroleum are non-renewable resources. Consumption of these resources has accelerated in the last 200 years and we face a future in which these fossil fuels will eventually run out. Alternative sources of carbon compounds must be developed to allow the economies of nations to grow. Cellulose represents one major source of carbon compounds. Cellulose contains the basic carbon chain structures that are needed to build compounds that are presently obtained from petrochemicals. Cellulose is a major concept of biomass. Biomass is a renewable resource. It is formed when green plants use carbon dioxide, water and solar energy for photosynthesis. It is a carbon-based matter, mainly from plants, that stores the chemical energy produced by photosynthesis. Biomass represents a massive quantity of a carbon based renewable resource. In the past, humans have utilized biomass for food or as wood for building materials; also they have exploited fossilized biomass in the form of coal. The great bulk of biomass is composed of carbohydrates (cellulose, hemi-cellulose starch and sugars); the remainder is lignin. Lignin consists of non-sugar-type molecules linked together in large sheet like structures. Lignin can be removed from the biomass, and the cellulose fibers that are recovered can be used to make paper and textiles. Biomass represents a very large energy resource. Only 7% of this resource is currently utilized. This may be due to the two main problems that occur in utilizing biomass: - Cost – Fossils fuels are currently much cheaper to produce than biomass fuels. Considerable energy is needed to plant, fertilise, harvest and process energy crops. Suitable Land – Fertile land is required to grow energy crops. In many placed the small amount of fertile land is solely devoted to the growth of food crops. Farming of energy crops also alters the local water table and the demand for soil nutrients. Therefore, overall there is a need to develop alternate sources of the compounds presently obtained from the petrochemical industry, and this is solely due to the fact that fossils fuels are non-renewable resources of energy. Another issue that is raised due to the use of fossil fuels is the pollution caused due to their combustion. Toxins and chemicals that are released from the incomplete and/or complete combustion of fossil fuels are detrimental to the environment. There are four main types of pollution that result from the combustion of fossil fuels: 1) Carbon pollution: Carbon monoxide is a colourless, odourless gas. It is toxic because it combines with the haemoglobin in red blood cells in preference to oxygen, reducing the ability of blood to transport oxygen. It is produced by incomplete combustion when the oxygen supply is limited. Eg: 2C8H18(l) + 17O2(g) 16CO(g) + 18H2O(l) If there is insufficient air for the complete combustion of fuel, then some soot (solid carbon) may be formed. Eg: C5H12(g) + 4O2(g) 3C(s) + 2CO(g) + 6H2O(g) Carbon monoxide production is prominent in petrol engines where the air to fuel ration is very minimal. Diesel engines and electricity generating stations have a high air to fuel ratio, and thus produced very little carbon monoxide, however, if badly designed they can produced a lot of soot. However, the production of carbon monoxide and soot can be minimised and this is by allowing the incorporation of excess air into the reaction. I.e. To ensure that the air to fuel ratio is high. In some engines this is not possible (such as petrol where ignition then becomes too difficult). Therefore, the minimization of these substances can be done using a catalyst in the exhaust pipe with is able to convert and carbon monoxide into carbon dioxide. 2) Sulfur pollutants Sulfur dioxide is formed by the combustion of sulfur in fossil fuels. This is mainly due to the impurities in the fuel – mostly from coal. When the combustion of coal occurs, the sulfur combines with the oxygen to produce sulfur dioxide which is a pungent gas that can cause breathing difficulties at low concentrations. S(s) + O2(g) SO2(g) Sulfur dioxide in the atmosphere then forms acid rain: 2SO2(s) + O2(g) 2SO3(g) SO3(s) + H2O(l) H2SO4(aq) The way to reduce the emission of sulfur dioxide into the atmosphere is to use low sulfur coals whenever possible. Also, sulfur dioxide can be removed from the exhaust gas at factories / power stations, but this is generally very expensive to do. 3) Particulates Particulates are very small droplets of liquids or small solid particles that result from the incomplete combustion of fuels. Vehicles produce limited amounts of particulates, but the main contributors are power generators and industrial factories. From oil and coal, the particulates rise from the incomplete combustion of the fuel. However, these particulates emitted from power stations and industrial factories can be minimised through the use of electrostatic precipitators. These devices can generate a high voltage, causing the small particulates to combine with one another to produce large amounts of substance, which are then easily filtered out of the exhaust gas. 4) Oxides of Nitrogen Oxygen – nitrogen reactions only occur at extremely high temperatures (above 1000 degrees Celsius), in order to produce nitric oxide: N2(g) + O2(g) 2NO(g) The next step occurs, when nitric oxide reacts with oxygen to produce nitrogen dioxide: 2NO(g) + O2(g) 2NO2(g) Petrol and diesel engines along with power stations and industrial factories are the main contributors. The main concern with the production of nitrogen dioxide is that under the influence of sunlight it can lead to the production of ozone, which is a very dangerous substance – it is known as a photochemical smog. Nitrogen oxides can cause respiratory problems and also contribute to the formation of acid rain. Laws are in place to minimise production of nitrogen oxides from petrol / diesel engines. Also relocation of power stations from population centres. Also using catalysts to remove oxides of nitrogen from exhaust gas of power stations. Finally lowering combustion temperatures to prevent the formation of those oxides. Extra: Pollution due to Carbon Dioxide – The Greenhouse Effect Carbon dioxide is not considered as a pollutant – this is mainly because it has no damaging affect on humans or any other living organism, and does not spoil any aspect of the environment. Carbon dioxide is a necessary substance on Earth and without it there would be no life. However, the excessive release of carbon dioxide into the atmosphere contributes to what is known as the greenhouse effect. This is when a layer (which is constantly increasing) of carbon dioxide and other gases surround the earth, causing the Earth to heat up since they reflect heat back to Earth. This is believed to cause significant climate changes such as rising levels of oceans. Combustion of fossil fuels is the most significant contributor to global warming and the only way to reduce the emission of carbon dioxide into the atmosphere is to reduce the need for fossil fuels, by creating more efficient vehicles / industries. Explain what is meant by a condensation polymer Condensation polymerisation is sometimes called ‘step growth’ polymerisation. The important aspects of this type of polymerisation are: monomers combine via a chemical process called condensation. A small molecular weight molecule (eg. Water) is eliminated at each condensation step. A condensation polymer is any type of polymer that is formed through condensation polymerisation. Describe the reaction involved when a condensation polymer is formed. Condensation reactions are reactions in which two molecules combine together with the elimination of a smaller molecule The formation of condensation polymers is more complex that the formation of addition polymers. Unlike addition polymers, in which all the atoms of the monomers are present in the polymer, two products result from the formation of condensation polymers, the polymer itself and another small molecule which is often, but not always, water. These polymers can form from a single kind of monomer, or, copolymers can form if two or more different monomers are involved. Most of the natural polymers are formed by condensation. Example 1 – Formation of polyester. Step 1 - Formation of an ester When an alcohol molecule reacts with carboxylic acid they combine to form a large molecule called an ester. Water molecules are eliminated in the process. Thus if methanol (CH 3OH) reacts with ethanoic acid (CH3COOH) in the presence of a catalyst, methyl ethanoate ester and water are formed. CH3COOH + CH3OH CH3COOCH3 + H2O Step 2 – Formation of polyester. To produce polyester, one monomer must be a dicarboxylic acid (i.e a hydrocarbon with two COOH groups) and the other monomer must be a diol (i.e a hydrocarbon with two OH groups). Dimers are formed in the fist step. Dimers can continue to add more monomers so that the chain grows in steps. Dicarboxylic acid + diol Note: General Terms: ester dimer + water Ester – an organic molecule containing the –COO- functional group Amine – an organic molecule containing the – NH2 functional group Carboxylic Acid – an organic molecule containing the –COOH functional group. Example 2 – Formation of Polyamide. Step 1 – Formation of amide When an amine molecule reacts with a carboxylic acid they combine to form a larger molecule called an amide. Water molecules are eliminated. Thus if aminoethane (CH3CH2NH2) reacts with propanoic acid (CH3CH2COOH), ethyl propanamide and water are formed. These simple condensation reactions, however, are insufficient to produce long chain polymers. In order to produce a polymer, each reactant must possess at least two functional groups so that the step growth process can continue. Step 2 – Formation of a polyamide To produce a polyamide, one monomer must be a dicarboxylic acid and the other must be a diamine (ie. A hydrocarbon with two amino groups). The chain grows by condensing with more monomers until a polymer is formed. Dicarboxylic Acid + Diamine Amide dimer + water Useful condensation polymers Polyethylene teraphthalate (PET) Many plastic containers are made from the PET polymer. PET is an example of polyester. This polymer is also used as a fibre in the manufacture of fabric for clothing. Polyesters are quick drying fibres that form fabrics that do not crease easily, making them ideal for drip-dry shirts. Terylene or Dacron are composed of PET fibres. Nylon Nylon is a strong, hardwearing fibre that does not absorb water very well. This hydrophobic nature allows for it to be used as rain wear. Nylon is a polyamide. There are several different types of nylon. Extra: Velcro was invented in 1957 by a Swiss engineer called George de Maestral. He observed how plant burrs stick to clocking and animal fur using their tiny hooks. He used nylon to develop a plastic product that would behave the same way as plant burrs. Nylon was commercially marketed in the U.S in 1938. It was first used to make women’s stockings. Initially production couldn’t keep up with demand Velcro is a plastic product developed from nylon. It is widely used in clothing, footwear, + sporting equipment describe the structure of cellulose and identify it as an example of a condensation polymer found as a major component of biomass Cellulose is a bio polymer formed by the condensation polymerisation of glucose monomers. Cellulose fibres are produced by plants to give their cell walls strength and shape. Humans have used cellulose for thousands of years to make paper and linen. Cotton fibre is another natural product composed of cellulose molecules. Cellulose can also be modified to produce filaments of rayon (otherwise known as artificial silk). Extra Note: Rayon is formed by digesting the cellulose fibre in sodium hydroxide solution followed by extrusion into acid. Modern rayon has fire retardants added, and this is known as viscose rayon. The formation and Structure of Cellulose The figures below show the structures of glucose. There are numerous OH groups in the glucose molecule. There are two structural forms of glucose called alpha-glucose and beta-glucose. It is the beta-glucose that leads to the formation of cellulose. During condensation polymerisation, beta-glucose monomers ink together by a beta 1,4-gycosidic bond to form a beta-maltose dimer. Maltose dimmers then continue to condense and the polymer chain increases in length. Ultimately up to 10000 glucose units will form the long, unbranched cellulose chain. Figure (c) shows this condensation polymerisation process and the structure of a section of cellulose polymer. This diagram shows that the CH2 OH groups on the C-5 position alternate on opposite sides of the chain. This alternating arrangement maintains a linear structure in the polymer. Cellulose is insoluble in water because its structure exposed very few OH groups to water molecules in the environment. identify that cellulose contains the basic carbon-chain structures needed to build petrochemicals and discuss its potential as a raw material Two important fields of research are the production of petrochemicals and the production of fuel gases. Production of Petrochemicals. Cellulose is a potential source of petrochemicals because of its long carbon chain structure. The flow chart below shows a proposed possible method of producing petrochemicals from cellulose, using ethylene as an intermediate. Bacteria that live in the intestines of termites and ruminants produce enzymes that break down cellulose into glucose monomers. Enzymic breakdown of cellulose if the first step in the production of petrochemicals. Alternatively, the cellulose can be broken down chemically via acid hydrolysis. The glucose produced can be fermented by yeast to form ethanol that can be readily dehydrated to yield ethylene. From ethylene a wide variety of petrochemicals (including polymers) are manufactured. This method of generating ethylene from cellulose via ethanol is much more expensive than the current methods of obtaining ethylene. Production of fuel gases Methane is an important fuel gas that can be generated by anaerobic fermentation of agricultural waste. Such waste includes manure and harvest residue. The anaerobic bacteria initially digest the biomass into organic acids, sugars and alcohols. In later stages, methane and CO2 are produced. The methane produced can be used directly as a fuel, which residues are used as fertilizers. Use available evidence to gather and present data from secondary sources and analyse progress in the recent development and use of a named biopolymer. This analysis should name the specific enzyme(s) used or organism used to synthesise the material and an evaluation of the use or potential use of the polymer produced related to its properties Synthetic biopolymers Non-biodegradable plastics are a major problem for our environment. When they are dumped in landfills, they remain there without significant decay for hundreds of years. In response to growing concern, biodegradable plastics are being developed PLA – Polyactic Acid. Polyactic acid is a biodegradable polymer that exhibits both strength and flexibility. The raw material is lactic acid, which is derived from starch waste obtained from potatoes or sorghum. The use of such waste lead to huge saving in the use of petroleum and petrol. The first step in the production of PLA involves the conversion of starch waste to simple sugars that are fermented by bacteria to produce lactic acid. Water splits out as the lactide dimer forms. The dimer undergoes further chain growth to from the PLA polymer. PLA polymers are similar to polystyrene in that they have high gloss and clarity. They also have high tensile stress. Like PET, PLA polymers resist greases and are readily heat-sealed. There is ongoing research into starch-based polymers such as PLA because of their potential to replace petrochemical plastics. In the future, these plastics could be used to make plastic bags, food packaging and disposable tableware. PHB – Polyhydroxybutyrate KNOW THIS ONE! Bacteria such as Clostridium, Pseudomonas and Syntrophomonas can be used to synthesis polyester polymers called PHA’s of polyhydroxyalkanoates. One of these is called PHB, or poly-4-hyrdoxybutyrate. PHB is a stiff brittle polymer that is rapidly degraded by bacteria to form carbon dioxide. This property is essential for future plastics as they would rapidly degrade in landfills. PHA plastics (also known as bacterial plastics), have low impact strength which is a disadvantage in many applications. The bacterium Ralstonia Eutrphus is used to produce a copolymer with PHB called PHBV (poly-3-hydroxybutyrate-poly-3-hydroxyvalerate). The bacteria are grown in a high glucose or highly acidic environment. The bacteria manufacture the polymer which is stored in their cell walls as granules. The polymer can be extracted and processed into plastic products. The cost of these bacterial plastics is much higher than that of petrochemical plastics. Research is being carried out to genetically modify bacteria to control the plastic that they form. In addition, gene splicing is being investigated as a means of transferring the PHA production capability to other common forms of bacteria. Properties of PHB Water insoluble. This differentiates PHB from most other biodegradable plastics, which are moisture sensitive. Good ultra-violet resistance but poor resistance to acids and bases. Biocompatible and hence is suitable for medical applications. Melting point 175°C and glass transition temperature 15°C. High Tensile strength Nontoxic Short Summary of Section: - Step-growth polymerisation is aslo called condensation polymerisaation. In condensation polymerisation a small molecule such as water is eliminated at each step of the condensation process. Polyesters are condensation polymers. They are formed when dicarboxylic acids condense with diols. Polyamides are condensation polymers. They are formed when dicarboxylic acids condense with diamines. Nylon is an example of this type of polymer. PET (or polyethylene terephthalate) is a very useful condensation polymer; used in plastic soft drink bottles. Cellulose is a condensation polymer of glucose Cellulose is a useful raw material. It can be used as a fuel or it can be converted to other polymers or petrochemicals. Like cellulose, many other biopolymers such as starch and protiens are condensation polymers Cellolosse is a major component of biomass. Cellulose is a polysaccaride composed of glucose monomers. Current reseach invovles utilising biomass for the production of biodegradable plastics and alternative fuels such as ethanol Polyactic acid and polyhydroxybutyrate are biodegradable biopolymers. Biodegradable polymers may evenually replace polymers derived from petroleum. Extra Information From Conquering Chemistry – HSC Course – Roland Smith The Need for new Sources of materials The raw materials for making most polymers are crude oil. This is a considerable concern as the world is going to use up all its available oil reservies within the next few decades. Currently there is pressure to reduce energy use and to develop alternative fuels, first because of the greenshouse problem and secondly because as supplies of oil diminish the cost will increase. Currently the petrochemical industry (mainly plastics) consume only about 3-5% of the total oil used in the world today. Ethanol is the prime candidte for an alternaive source of ethylene. Ethanol can be produced by fermentation of starch and sugars from a variety of agricultural crops and it can be easily converted into ethylene. However, cellolose is another source for making polymers. Cellulose is a major componenet of plant material. Glucose Structure Cellulose is a polymer of which the monomer units are glucose. It has 5 carbon atoms and an oxygen atom which form a puckered ring; there are OH groups on 5 of the C atoms. The side of the ring on which each OH group is positioned is important. When glucose molecules combine to form cellulose, the OH on the right hand C-atom of one molecule (as shown above) combines with the OH of the left hand carbon atom of the next glucose molecule, this forms the structure below: The important things to note: - for bonding to occur, alternate glucose units must be inverted - This bonding produces a very linear molecule. The geometry of the rings and the C-O-C bond angles cause this linearity Biopolymers that have been made from cellulose: - Cellophane: This is a form of rayon that is produced as a thin transparent film which is widely used for packaging Cellulose Nitrate: This a synthetically modified cellulose that was widely used for photographic and movie films; and was also used as an explosive. However due to high flammability it was replaced by other plastics Cellulose Acetate: This is much less flammable than cellulose nitrate and is still widely used; for example in overhead projector slides. In cellulose nitrate and acetate the three OH groups on each glucose unit of the cellulose molecule are replaced by –ONO2 (nitrate group) and –O-CO-CH3 (acetate group) respectively. The major problem with Petroleum based polymers There is a major problem with petroleum-based polymers: they are not biodegradable. This means that when they are discarded into the environment they are not decomposed naturally by the action of living organisms such as bacteria or fungi. One approach to building biodegradability into synthetic polymers has been to alternate biopolymer sections in the same polymer molecule: biological decay of the biopolymer leads to disintegration of the whole polymer. Another very recent approach has been to develop biopolymers that have similar properties to the synthetic polymers but which still retain biodegradability. A synthetic biodegradable polymer PHB – Poly (3-hyrdoxybutanoate): The three means that they hydroxy group is on the third carbon counting from the carboxylic acid group. The polymer is a polyester; and although PHB has quite a different chemical structure from polypropylene, its physical and mechanical properties are very similar. To produce PHB a culture of micro-organism such as Alcaligenes Eutrophus is placed in a suitable medium and fed nutrients so that it multiplies rapidly and grows into a large quantity. Then the ‘diet’ is changed to restrict the supply of a particular nutrient (such as nitrogen): under these conditions the organism is no longer able to increase its population but instead begins to make the desired polymer which it stores for later use as an energy source. The amount of PHB that the organism can produce is from 30-80% of its own dry weight. The organism is then harvested and the polymer separated out. PHB is much more expensive to make than oil based polymers with similar properties. However there is a slowly growing demand for it where biodegradability is a prime concern. Such applications include packaging of bottles, bags, wrapping film and also packaging for medical and hospital supplies. Extra – From Conquering Chemistry HSC Course Will Raw materials run out? The raw materials for making polymers come from crude oil (basically ethylene and propene). There is considerable concern that the world is going to use up all its available oil reserves within the next few decades. The majority of crude oil is used as fuel for cars, planes and trains. Currently there is pressure to reduce energy use and to develop alternative fuels, firstly because of the greenhouse problem and secondly because as supplies of oils diminish cost will increase. Ethanol is regarded as a possible solution – as it can be obtained from agricultural crops and is renewable. Despite a increase in oil prices, the petrochemical industry will be minimally affected because the cost of raw materials is a small proportion of the cost of finished products, and thus will still be able to afford oil. Regardless, it would be optimum if alternative methods of manufacturing polymers were to be developed. Ethanol is a prime candidate for an alternative source of ethylene. Ethanol can be produced by fermentation of starch and sugars from a variety of agricultural crops and it can be easily converted into ethylene. There is however another prime source – cellulose. Cellulose is a major component of plant material, whereas starch and sugars are minor components. Condensation Polymerisation Condensation polymers are polymers that form by the elimination of a small molecules (often water) when pairs of monomer molecules join together. Cellulose is a naturally occurring condensation polymer. The monomer from which it forms is glucose. Glucose: Also can be written as: The polymerisation occurs by the elimination of water molecules from between pairs of glucose molecules: Alternatively it can be written as: This is saying that n molecules of glucose combine to from one molecule of cellulose (which contains n glucose units) by eliminating (n-1) water molecules. A synthetic condensation polymer is nylon-6. This is a particular type of nylon formed from the monomer 6-aminohexanoic acid which has the structure: This can be written as: This molecule contains two functional groups, the amine group – NH2 and the carboxylic acid group - COOH. Full Structures Carboxylic acids react with amines: Where Ra and Rb are the rest of the molecule (commonly alkyl groups). For convenience this is often written as: Molecules of 6-aminohexanoic acid having both functional groups can react with one another to from a polymer. The polymerisation reaction is: The chemical bond that has formed here is the same as occurs when proteins form: a carboxylic acid group combines with an amine group to form what is known as an amide link ( ) In biochemical terms it is known as a peptide link. In nylon-g all the monomer units are identical. The generic name is polyamide. Proteins are condensation polymers made from amino acids. Amino acids are compounds with a group at one end and a group at the other. When proteins form amino acids, different amino acids are strung together sequentially in the one chain. The properties of the protein depend as much upon the sequence of amino acids as upon the number of them in the chain. The condensation polymer made from ethylene glycol and terephthalic acid is known as a polyester when used as a fiber and as PET [poly(ethylene teraphthalate)] when used for bottles. PET and nylon are main synthetic polymers in use today. PHB – Polyhydroxybutyrate – Polyhydroxybutanoate Bacteria can be used to synthesis polyester polymers called PHA’s or polyhydroxyalkanoates. One of these is called PHB, or poly-3-hyrdoxybutyrate. PHB is a stiff brittle polymer that is rapidly degraded by bacteria to form carbon dioxide. This property is essential for future plastics as they would rapidly degrade in landfills. PHA plastics (also known as bacterial plastics), have low impact strength which is a disadvantage in many applications. PHB – Poly (3-hyrdoxybutanoate): The three means that they hydroxy group is on the third carbon counting from the carboxylic acid group. The polymer is a polyester; and although PHB has quite a different chemical structure from polypropylene, its physical and mechanical properties are very similar. To produce PHB a culture of micro-organism such as Alcaligenes Eutrophus or Clostridium or Pseudomonas is placed in a suitable medium and fed nutrients so that it multiplies rapidly and grows into a large quantity. The bacteria are grown in a high glucose or highly acidic environment. Then the ‘diet’ is changed to restrict the supply of a particular nutrient (such as nitrogen): under these conditions the organism is no longer able to increase its population but instead begins to make the desired polymer which it stores for later use as an energy source. The amount of PHB that the organism can produce is from 30-80% of its own dry weight. The organism is then harvested and the polymer separated out. PHB is much more expensive to make than oil based polymers with similar properties. Research is being carried out to genetically modify bacteria to control the plastic that they form. In addition, gene splicing is being investigated as a means of transferring the PHA production capability to other common forms of bacteria. However there is a slowly growing demand for it where biodegradability is a prime concern. Such applications include packaging of bottles, bags, wrapping film and also packaging for medical and hospital supplies. Properties of PHB - Water insoluble. This differentiates PHB from most other biodegradable plastics, which are moisture sensitive. Good ultra-violet resistance but poor resistance to acids and bases. Biocompatible and hence is suitable for medical applications. Melting point 175°C and glass transition temperature 15°C. High Tensile strength Nontoxic Low impact strength Biopol – PHBV (Poly-3-hydroxybutyrate-poly-3-hydroxyvalerate) Polyhydroxyalkanoates (PHA’s) are naturally occurring polyesters produced as energy storage materials by many bacteria. The most common representative is Polyhydroxybutyrate (PHB) together with the copolymer containing hydroxyvalerate (PHBV). These microbial polyesters have unique physicochemical properties such as thermoplasticity, biodegradability, biocompatibility and piezoelectricity. Recently, it has become of industrial interest to evaluate these polyesters for a wide range of medical application. The microorganism Alcaligenes Eutrophus (also known as Ralstonia Eutrophus) is used as the producer. This organism uses inexpensive carbon sources, which is important in industrial-scale production. It high polymer production capacity and the polymer can be easily separated from cells. The Biosynthesis of the Polymers Biosynthesis occurs in two steps. Firstly, the growth of the cells is promoted since a high number of cells is needed for high polymer yield. In this step, the cells are grown until a late logarithmic phase. The second step is the production step in which the polymer production and deposition is encouraged by nutrient deficiencies (i.e., nitrogen, phosphate, etc.). The grown cells are collected and transferred to the production medium. Fructose can be used as a carbon source. The production is maximized by the addition of the extra carbon source (sucrose) at the late logarithmic phase Extraction and Purification of the Polymers After the cells are collected, they are lyophilized (freeze drying in a vacuum). The dried cells are extracted (from the cell walls of the bacteria as the polymer is stored as granules in here) and placed for 6 hours in chloroform to achieve the destruction of the cells and dissolution of the polymer. Purification of the polymers is done by precipitation of the polymer in alcohol. The precipitated polymer is collected by filtration and then finally dried at room temperature. The cost of these bacterial plastics is much higher than that of petrochemical plastics. Research is being carried out to genetically modify bacteria to control the plastic that they form. In addition, gene splicing is being investigated as a means of transferring the PHA production capability to other common forms of bacteria such as Escherichia coli.