Aiming for biodegradable and ecofriendly products

Physical and chemical methods of pollution control were always in the forefront because they were easy to understand, easy to control and were reproducible. Biodegrad ation, the real mechanism of nature of balancing the material, was always found to be incompletely understood, unpredictable and uncontrollable if we have to adapt it in the form of biological treatment methods. A better option then is to modify our materials, processes and products in such a way that we can rely upon the biodegradation in nature and recalcitrance, bioaccumulation problems are overcome. We are slowly changing our philosophy and are not merely targeting for clean-up or removal of pollutant but are aiming for prevention of pollution or facilitating biodegradation. 
Manufacturing processes are rapidly changing and biodegradable products are fast replacing man-made, difficult to degrade products. After understanding the nature, its role, its sup eriority and by knowing the fact that biodegradation is the ultimate fate of any material that enters into environment, it was inevitable for us to change our psychology - industrial ecology - industrial ecosystem - industrial metabolism - going close to nature. Objectives then are to improve upon the method of production, searching for alternative raw materials, recycling, conversion to suitable forms of certain wastes, so that we do not add any material, waste in nature which nature cannot take care of.
Biodegradation mechanisms which occur in the soil, aquatic environment though slow are important for us as they do not involve any cost of treatment when it occurs naturally, and are safer and bring about complete degradation and not mere conversion . Hence incorporating biodegradability or aiming for biodegradability is an obvious approach while carrying out production of different items. The agricultural products, food products, commodities hereafter will carry a label of ecofriendly in most of th e countries. The trend is to spread to every material and product. The consumables, coal, oil, petrol, synthetic fibre, plastic which are polluting / non-biodegradable will be replaced slowly by the one which is non-polluting / biodegradable.

General structure of PHA and some representative members

Polyhydroxyalkonates (PHAs) are polyesters of various hydroxyalkonates that are synthesized and intracellularly accumulated by num erous micro-organisms as energy reserve material. More than 100 different monomer units have been identified as the constituents of PHAs. This creates the possibility of producing biodegradable polymers with wide range of properties. PHB, Poly (3-hydroxybutyrate) is the best characterized PHA. PHB has lowest molecular weight and is most common in nature. Their molecular weight can be upto 2 million (i.e. 20000 monomers per polymer molecule). The monomer units of PHA are all in D-(-) configuration owing to the stereospecificity of the biosynthetic enzymes.

n = 1	R = hydrogen	Poly (hydroxy propionate)
	R = methyl	Poly (3-hydroxybutyrate)
	R = ethyl	Poly (3-hydroxyvalerate)
	R = propyl	Poly (3-hydroxyhexanoate)
	R = pentyl	Poly (3-hydoxyoctanoate)
	R = nonyl	Poly (3-hydroxy doedcanoate)
n = 2	R = hydrogen	Poly (4-hydroxybutyrate)
	R = methyl	Poly (4-hydroxyvalerate)
n = 3	R = hydrogen	Poly (5-hydroxyvalerate)
	R = methyl	Poly (5-hydroxyhexanoate)
n = 4	R = hexyl	Poly (6-hydroxydodecanoate)

There are three enzymes present in A.eutrophus for PHA biosynthesis (Fig.3). These are - PHA synthase, beta ketothiolase and reductase. Natural producers also have PHA depolymerase that degrades the polymer and uses the breakdown metabolites for cell growth

BIOPOL - PHB Accumulation in Micro-organisms

PHB material was first described in 1926 by Lemoigne. PHB is a very common and widespread storage material in many micro-organisms. PHB has been found to be a very basic polymer of variety of chemically similar polymers, the polyhydroxyalkonates. Poly - beta hydroxy butyrate (PHB) accumulates as energy reserve material in many micro-organisms like Alcaligenes, Azotobacter, Bacillus, Nocardia, Pseudomonas, Rhizobium etc. PHB has physical properties comparable with polypropylene (PP). Poly - beta hydroxy butyrate (PHB) consists repeat units of CH(CH₃)-CH₂ -CO-O. The difference is that PP shows insignificant degradation while PHB shows complete degradation. PHB sinks while PP floats. Therefore, degradation is easy at sediment. Alcaligenes eutrophusand Azotobacter beijerinckii can accumulate upto 70% of their dry weight of PHB. These micro-o rganisms can produce the polymer in environment of N and P limitation. Minimum 40-50% of the dry weight of this polymer is required for making the process commercially viable. Extraction of PHB is done by using solvents like halogenated hydrocarbons and purification is done. Moulding and extrusion of dried cells directly is possible when PHB contents are high. A lot of work is done on engineering polymeric properties of PHB. However PHB is suitable for specialized areas like biomedical use and speciality coatings. 

PHB Accumulation in Micro-organisms

Organisms with PHB accumulation	% of dry weight of the cell
Alcaligenes eutrophus	96
Azospirillum	75
Azotobacter	73
Baggiatoa	57
Leptothrix	67
Methylocystis	70
Pseudomonas	67
Rhizobium	57
Rhodobacter	80

Industrial Production of PHA

A subsidiary of ICI Ltd. in Great Britain produces Biopol from Alcaligenes eutrophus (H16). Either PHB homopolymer or copolymers of PHB and B-hydroxyvalerate can be produced by these cells depending on the substrate or substrate mixture used for growth and production. For industrial applications it is desirable to control the incorporation of different repeating units i nto the polymer in order to produce polyesters with specific material characteristics because their physical and chemical properties depend strongly on copolymer composition. Tailor-made copolymers can be made for this purpose by the use of controlled conditions. If a defined mixture of nutrients for certain type of microorganisms is supplied for growth, a defined and reproducible copolymer is formed. Biochemically there are 2 different ways of achieving polymer formation in microbes 

Parallel process has been demonstrated in R.rubrum and P.oleovorans. During cell growth, however part of the polymer forming potential is lost because of its utilization of substrate to maintain the cell's metabolism. In serial process of industrial polymer production micro-organisms are first grown on C source to obtain large biomass, then the medium is depleted of a n essential nutrient and polymer forming substrate is added. This is converted directly to polymers and essentially only little growth occurs. This approach is used for large scale PHA production by A. eutrophus.

List of limiting components leading to PHA formation

• Ammonia - Alcaligenes eutrophus, also others
• Carbon - Spirillum spp., Hypomicrobium spp.
• Iron, Mg - Pseudomonas spp.
• Mn, O₂ - Azospirillum, Rhodobacter spp.
• PO₄ - Rhodospirillum, Rhodobacter spp.
• Potassium sulfate Bacillus, Rhodospirillum, Rhodobacter etc.

Biopol of ICI is produced by using Alcaligenes eutrophus. Polymer separation and purification is accomplished by using a proprietary aqueous wash process followed by drying. PHB is too stiff and brittle for most applications, so the ICI add s a small amount of simple organic acid to the sugar feed stock to make the plastic stronger and more flexible. In technical terms, bacteria then produce co-polymers composed of PHB with varying amounts of hydroxyvalerate (HV). In this way ICI can produce a range of thermoplastic polymers which can be processed with conventional techniques to make bottles, mouldings, fibres and films. High grade Biopol is being made for medical applications, including woven patches for use inside the body to protect tissue s from scarring after surgery. After the wound is healed, enzymes in the blood dissolve away the patch. ICI's biodegradable plastic (thermoplastic Biopol) has found its North American applications as a blow-molded bottle and injection-molded caps for hair c are products. The Berlin Packaging corporation, Chicago will produce bottles and caps. Biopol currently sells for $ 8-10 per lb but is expected to sell for $ 4 per lb. The ICI company has currently a capacity of 600,000 lb per year in Billingham, UK. Annual production of 11 billion lbs is predicted by late 1990s. Biotehnologische Forschungsgesellschaft mbH in Austria produces PHB on a technical scale from cells of Alcaligenes latus with sucrose as a carbon source. 

Biopol has been used in Germany since 1990 to make the bottles of Wella's Sanara Shampoo. Biopol's US launch came in 1995, in the form of bottles for Brocanto International's Evanesce shampoo and material is being tested in the UK for cosmetic containers.
Japan also has shown interest in Biopol. Biopol has been introduced there in 1991 as a container for Ishizawa Kenkyujo's Earthic Alga shampoos and conditioners. Now three more hair care companies of Japan have started using Biopol containers and shortly Kai will use it for disposable razor with B iopol handle. Rubbish bags, disposable nappies, paper plates, cups coated with thin plastic film can be made with Biopol and will get degraded when thrown in landfill. Biopol shampoo bottle disappears in two years in typical dung.
With development in yields, productivity, use of newer strains PHB concentration and productivity of 100 g.l^-1 and 2.5 g.l^-1 h^-1 can be reached.
Chemi Linz AG began to develop a process for PHB production by fermentation in 1980s. Their polymer group Petrochemia Danubia (PCD) carries out the fermentation process through btF, a biotechnological research unit. The PCD process is different in that it uses Alcaligenes lactus as the producing organism and sucrose as the substrate. PHB formation is growth associated and nutrient limitation is not used to induce polymer accumulation. Solvent extraction is used to extract the product. It is a PHB homopolymer which is made. PCD-Polymere, an Austrian polyolefin producer developed a production process for PHB and processing technology for injection moulding and blow moulding. An Austrian biotechnology research company has developed a process for PCD-Polymere.
The fermentation process is based on a unique bacterial strain Alkaligenes latus. The strain is isolated from soil in California and Au stralia. It produces PHB in large amounts (80% of cell dry weight) during unlimited growth. Proprietary fermentation process developed is scaled upto 10 m3 of fermentation volume. In a fed batch mode more than 1 ton of PHB can be produced in less than a week. These fermentations are carried out in common stirred tank reactors, but other reactors like air lift or bubble column may also be used to get similar good results. The fermentation is carried out in mineral salts medium, sucrose or glucose as source of carbon. If precursors like propionic acid are added then co-polymers of PHB/HV can be produced as well as co-polymers of 3HB/4HB (3-hydroxybutyrate-co-4hydroxybutyrate) if 1,4 butanediol is added as precursor.
After fermentation cells are harvested, was hed with tap water and a concentrated suspension of 200 g/l is prepared. This suspension is directly used for the extraction process. The cell suspension is treated with solvent (methylene chloride). After this extraction step solvent is separated by cent r ifugation. The dissolved PHB is precipitated in water, recovered as white powder and dried. After one extraction step and one precipitation step PHB of 99% purity is obtained. This powder is directly used for compounding and further processing. Biomass can be recovered after the extraction process. It was tested as soil enhancer.
PCD-Polymere films and fibres are under development. Good results were obtained for injection moulding and blow moulding parts. PCD also helps others to develop further the technology.
The cost of producing PHB can be substantially reduced if methanol is used as substrate. Methanol is one of the cheapest noble substrates available, and has several advantages as fermentation substrate (purity, solubility, availability etc.) and is non-food substrate. Methanol can be easily obtained from natural gas and may also be obtained from biomass if necessary.
Methylobacterium extorquens is the isolate (gram negative, motile, pink pigmented bacterium can be used. Average PHB contents are found to be 25-30% of dry weight. It was also capable of producing PHV with the ratio of PHV to PHB of 0.2. Good process control was essential in the development of high cell-density fed-batch fermentation process for PHB production from methanol. Biomass leve l of 120 g/l and PHB levels of 60 g/l could be reached.

Production of PHA in Genetically Engineered Bacteria

Now PHA can also be produced efficiently and with novel properties in genetically engineered bacteria. Recombinant E.coli harboring multicopy plasmid carrying A.eutrophus PHA biosynthesis genes is developed. PHB concentration of 80 g.l-1 and 2.0 g.l-1h-1 is obtained. Metabolix researchers have transferred proprietary genes for PHA production into the safe and widely used industrial microbial strain, Escherichia coli, where the new genes result in rapid production of high levels of polymer. This strain, E. coli, K12, is already the source of a number of FDA approved food additives and medical products. The raw materials for the transgenic fermentations are widely available sugars like glucose, which are derived from renewable plant crops. Transgenic fermentation systems have several advantages over the non-engineered systems. As a result, the economics of PHA production are now more favourable than at any previous time. Better polymer yields, easier recovery, and production of new copolymers are all enabled by the use of E.coli -- the tried and true workhorse of the biotechnology industry. Faster growth means that engineered E.coli can produce PHA in just 24 hours, c ompared to three days or more for non-engineered strains. High levels of polymer, up to 90% of cell weight, are also achievable, so less carbon substrate is wasted to make extraneous biomass, and polymer isolation becomes more straightforward. Finally, E.coli has the best understood genetics and biochemistry of any organism in the world, so that further metabolic engineering (e.g. to produce new polymer compositions) is possible.

Advantages of using recombinant E.coli for production of PHA :

• Wide range of substrates (lactose, xylose, sucrose) can be used. Therefore whey, agricultural wastes and byproducts and molasses which are cheaper raw materials can be used.
• Engineered E.coli can produce PHB in 24 hours while non-engineered producers take 3 days.
• It is easier and less costly to purify polymers from recombinant E.coli than from A.eutrophus, since E.coli becomes fragile due to accumulation of biopolymer.
• Recombinant E.coli does not possess PHA depolymerase as what natural PHA producers possess. Hence synthesized PHA is not degraded by producer recombinant E.coli.
• Molecular weight of PHB produced by fermentation of recombinant E.coli can be controlled by modulating activity of PHA synthase enzyme. Average Molecular weight of PHA produced by recombinant E.coli is 4 X 10³ kDa, Average Molecular weight of PHA produced by A.eutrophus is 6 X 10² to 1.2 X 10³ kDa. Molecular weight decreases by increase in enzyme activity.
• Polydispersity index can be controlled by modulation of synthase activity.

Factors (e) and (f) thus affect polymer properties and processibility and well defined characteristics can be obtained. Newer applications such as stronger biodegradable fibre will be possible due to higher molecular weight of PHAs. Commercial product ion with recombinant bacteria will be very soon demonstrated.
Price factor -
The major drawback in commercialisation of PHA is the high cost of production. The cost of raw material itself accounts for 40%-50% of the total production cost. Looking to this various systems using different carbon sources are being explored. This includes use of whey, mollasses, acids from wastes by anaerobic treatment and then their conversion to PHA etc. The use of recombinant E.coli or genetically engineered plants will have their own economics reducing the price.
Commercial applications and wide use of PHAs is hampered due to its price. Today price with natural producer like A.eutrophus is US $16 per kg. This is about 18 time more expens ive than polypropylene. For PHA to be commercially viable price should come to US $3-5 per kg. With recombinant E.coli as producer of PHA, price can be reduced to US $4 per kg. which is close to other biodegradable plastic materials such as polylactides an d aliphatic polyesters. With transgenic plants producing PHA price comes to only US 20 cents per kg. Most important aspect is its biodegradable nature helps to overcome the problem of environmental hazard. And the value of clean environment will otherwise also outweigh conventional plastics on price factor in favour of more and more use of PHA.

Production of PHA by genetically engineered plants

Biopol is made in industrial fermentor by bacteria that converts sugars (refined from corn or beet) into polymer. But US scientists recently announced an important step towards making biodegradable plastic directly in plants. Genetically engineered Arabidopsis thaliana a type of cress was used for the purpose. Costs can be reduced tenfold if the plastics are produced by plants. With transgenic plants producing PHA pr ice comes to US 20 cents per kg. which is close to that of starch. Potatoes can be genetically engineered to make and store plastics instead of starch in their tubers. The idea of producing PHAs in transgenic plants was first described by MIT researchers in a 1989 patent application. By the mid-1990s several research groups had successfully produced PHB in various plants, ranging from Arabidopsis thaliana, an experimental research plant to commercial oilseed crops and even cotton. Full scale commercial dev e lopment of transgenic PHA crops is still 5-7 years away. The cost of plant-derived PHAs will depend upon several factors, such as plant crop used, content of PHAs, price of crop, location, scale, ease of extraction. If yields of PHAs are 20-50% of the crop then price of PHAs can be competitive with synthetic plastics. 1 m hectares ( 10 X 10m²) of farmland would produce 375000t of plastic. This quantity of plastic is only 5% of the US demand of plastic packaging market. Metabolic engineering efforts are on for Arabidopsis, Canola, Brassica, soybeans, corn and potato. 

Chris Somerville of the US Department of Energy's plant research laboratory at Michigan state University led a team collaborating with the James Madison University in Virginia to modify the cress. The investigators inserted two foreign genes into cress, taken from bacteria Alcaligenes eutrophus which makes PHB naturally. Agrobacterium tumefaciens is used as Trojan horse bacterium to transfer two genes to cress plant Arabidopsis thaliana. Plants produced 20-100 mcg / gram of plant tissue , PHB. Production should be raised 100 fold to com mercialize it. One potential problem is plants become sick. This is perhaps because new genes divert carbon away from the essential metabolites to PHB production. But if these genes are introduced in beet, potato plants which have too much excess of energy-storing carbon such as starch, such diversion of carbon to PHB is not damaging. However, USA only can think of PHB instead of starchy food. Genetically-engineered Arabidopsisplants so far have produced small amounts of pure PHB. But it is expected that co-polymers of PHB-HV can be made directly in crops.
Oilseed crops are most amenable targets for seed-specific PHA production. Since both oil and PHA are derived from acetyl-CoA, it is diversion of acetyl CoA to PHB accumulation. Plastids of plants are targeted for PHB synthesis by engineered genes. Arabidopsis thaliana is closely related to oil producing crop rapeseed which in fact is a target crop for PHB production on agricultural scale. Rapeseed, Sunflower and soyabean are the crops which can be genetically transformed to produce PHA. ZENECA Seeds and Monsanto are working on it. Monsanto will commercialise it by 2003 AD. Monsanto is trying to improve the performance of this bioplastic. The bioplastic will be initially used to produce paper coating and a film for food packaging.
Although PHB can be made by plants with little genetic work, for making PHBV four genes of bacterial origin were needed to be engineered into the rapeseed plant to make them produce PHBV by modification of two separate metabolic pathways. This was because, plants do not produce valeric acid which is required to produce PHBV. Gruys and his team from Monsanto, in St. Louis, Missouri have done this state-of-the-art work. Three genes are used from Ralstonia eutropha (formerly named as Alcaligenes eutrophus) and accomplish three final steps in the polymer pathway. Fourth gene for making valeric acid comes from E.coli.
The Monsanto team estimate that polymer concentration need to be around 15% dry weight to make extraction and processing economic. While today it is just 3%. Thus lot of research is needed before final commercialisation.
In a surprise move Monsanto also declared to its shareholders that it had no plans to produce bioplastics in genetically engineered plants though there were impressive successes. They are ready to give their technology to others on license.
The Forest Genetics Research Institute (Suwon, Korea), a subsidiary of the South Korean Ministry of Agriculture and Forestry, has developed a process to produce PHB in the chloroplasts of genetically engineered aspen trees (poplars). Two genes from Alcaligenes eutrophus have been transferred to poplar plant cells. PHB present in chloroplasts can be obtained from leaves. Leaves are dried, crushed to fine powder and then bioplastic is extracted with chloroform.
The Massachusetts Institute of Technology (MIT) has been awarded two patents in USA covering the production of biodegradable plastics in plants. These are seventh and eighth in a series exclusively to Metabolix (Cambridge, Mass). Metabolix is developing a range of technologies for PHA production including enzyme catalysed polymerisation and fermentation routes.
It has also been shown by Metabolix Inc. that transfer of the proprietary PHA genes into plants results in accumulation of PHA polymers in the new host. Current research aims to optimize expression of these genes and target polymer synthesis to easily processable tissues like the seeds or tubers. Polymer extracted from these sources is expected to compete directly on a price-performance basis with current nonrenewable pl astics. Full scale plant crop production is expected in four to ten years.
The polymers produced in plants are structurally identical to those from bacteria, so that processors can develop applications using fermented material in expectation of using plant- derived PHAs in the future. PHAs are also a useful industrial source of chiral building blocks for the chemical industry. Stereochemically pure monomers (R -3-hydroxyacids and their derivatives) are readily available by depolymerization of the PHA polymer s. Monomer derivatives have been supplied to customers by Metabolix under research agreements.

Physical Properties important for Processing of Bioplastics

PHA comprising medium-chain monomers (6 or more carbon length) are more elastomeric and may contain unsaturated carbon bonds. They are more conducive for coating and film materials, and offer greater possibilities for chemical modifications. The short-chain and medium-chain PHA arise from different biosynthetic routes and therefore are made by different microorganisms. The composition of culture medium (particularly carbon substrate), influences the microbial polymer (e.g. range of polymers formed, molecular weight, crystallinity) which in turn determines the physical properties (e.g. mechanical and tensile strength). Poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) is a copolymer comprised of short-chain monomers of 4-5 carbon length).
The properties of PHA polymers range from stiff, highly crystalline materials like PHB to rubbery elastomers like polyhydroxyoctonate (PHO) to other PHAs , which are completely amorphous, tacky substances.
Biopol is a copolymer where hydroxybutyrate and hydroxyvalerate units are incorporated randomly along the chain. Adding controlled amounts of organic acid may vary the hydroxyvalerate content.
There are two causes of variation in grades. (i) the level of hydroxyvalerate units and (ii) the presence of plastizer. The hydroxyvalerate copolymer has a Tmin the range of 173-180 degree centi. and Tg about 5 degree centi. The hydroxyvalerate content is about 5-12%. The ethyl side chain of the valerate unit will reduce chain packing and lower crystalline melting point, modulus and tensile strength and at the same time increase flexibility, impact strength and ductility. Higher the hydroxyvalerate content, lower is the crystallization rate. All commercial grades contains nucleating agent to facilitate crystallization and shorten processing cycles during the moulding operations. The use of plasticizers has similar effect as that of increasing the hydroxyvalerate content. It depresses Tg and therefore improves impact strength and ductility at lower temperatures. These polymers have good resistance to oils but are hydrolysed by acids and bases. Because of the enhanced crystallinity due to the presence of nucleating agents, the biodegradation commences at the surface of the polymer.
Processing of Bioplastics -
Presence of nucleating agents (which facilitate crystallization) or the use of plasticiser shortens the processing cycles during the moulding operations. There are two main points about processing of PHBV bioplastics -
(i) The limited thermal stability of the polymer and so it degrades rapidly above 195 degree centi. (ii) The need to optimise conditions to allow a maximum crystallization rate (which reduces cycle times). The maximum rate of crystallization is reported to be at about 55-60 degree centi. which is significantly closer to Tg than the Tm. Processing temperatures should not exceed 180 degree centi. and duration of time when the material is in melt state should be kept minimum. At the end of a run the processing equipment should be purged with polyethylene. When blow moulding the blow-pin and the mould should be at about 60 degree centi. to optimise crystallisation rates. Similarly injection moulds are recommended at 55-65 degree centi.
The low-hydroxyvalerate, unplasticised grades are most critical to process, requiring the higher processing temperatures. Conditions are slightly less critical with the higher hydroxyvalerate containing and plasticised grades. 

In addition to producing PHAs in dry powder form for melt processing, Metabolix is also developing PHA latexes. These materials have unique film forming properties, which are finding application in higher performance applications as well as in more traditional commodity uses. Metabolix company supplies PHA samples to companies under research and development agreements. 

Evaluatiuon of different extraction and cell rupture methods for PHA isolation from Rhodospirillum rubrum

	Hot Chloroform Extraction	Lysozyme Sonication	French Press	Hypochlorite
PHA content (% dry weight)	13.6	13.6	13.6	13.6
Isolated PHA (% dry weight)	12.5	9.7	7.7	12.1
Recovery %	92	71	58	89
Mw (x 10-6)	1.5	0.92	0.65	0.94
Mn (x 10-6)	1.1	0.36	0.46	0.37
Mw / Mn (Polydispersity)	1.4	2.6	1.4	2.5

Market for Biodegradable Material -
During the early 1990s, annual production of PHAs was just several hundred tonnes. In 1996 Zeneca, the main producer has stopped producing PHBV and sold the assets to Monsanto and Astra. Currently, the market for biodegradable material is largest in Scandi navia and other European countries, where companies are willing to pay up to pounds 4 per kg for PHAs. The estimate given in table below is based on the development of a composting infrastructure, which is now becoming highly developed in many parts of Eu rope, particularly in Germany, Holland and Belgium.
Western European market estimates for biodegradable plastics (tonnes per annum) -

Applications	Conventional Resins	Biodegradable Resins
Waste Disposal Bags for Composting	-	30 000
Disposable Fast Food Utensils	100 000	50 000
Hygiene Films	110 000	20 000
Paper Coatings	420 000	40 000
Agricultural Sector	65 000	30 000
Total	695 000	170 000
Source - BASF

Properties of PHB

1. PHB is water insoluble and relative ly resistant to hydrolytic degradation. This differentiates PHB from most other currently available biodegradable plastics, which are either water soluble or moisture sensitive.
2. PHB shows good oxygen permeability.
3. PHB has good ultra-violet resistance but has poor resistance to acids and bases.
4. PHB is soluble in chloroform and other chlorinated hydrocarbons.
5. PHB is biocompatible and hence is suitable for medical applications.
6. PHB has melting point 175⁰C., and glass transition temperature 15⁰C.
7. PHB has tensile strength 40 MPa which is close to that of polypropylene.
8. PHB sinks in water while polypropylene floats. But sinking of PHB facilitates its anaerobic biodegradation in sediments.
9. PHB is nontoxic.

Parameter	Polypropylene (pp)	PHB
Melting point Tm [0C]	171-186	171-182
Glass Transition Temperature Tg [0C]	-15	5-10
Crystallinity [%]	65-70	65-80
Density [g cm-3]	0.905 - 0.94	1.23 - 1.25
Molecular weight Mw (x10-5)	2.2 - 7	1 - 8
Molecular weight distribution	5 - 12	2.2 - 3
Flexural modulus [GPa]	1.7	3.5 - 4
Tensile strength [MPa]	39	40
Extension to break [%]	400	6 - 8
UV resistance	poor	good
Solvent resistance	good	poor
Oxygen permeability [cm3m-2atm-1d-1]	1700	45
Biodegradability	-	good
US Annual production M. tonnes	1.8	not determined
Other	due to low density floats in aquatic system	due to more density goes to the sediment in aquatic system.

Bioplastics are making commercial and scientific progress continuously. W. R. Grace was the American company which carried out t he work on PHB as early as 1960s. The work was then curtailed because at that time the techniques available for extraction were not able to provide a product thermally stable in processing. The development of PHB was begun by ICI in 1975-6 as a response t o increase in oil prices. ICI started marketing BIOPOL in 1982. ICI, the UK chemical group, has opened a plant at Billingham in North-east of England to make 300 tonnes of Biopol a year, which it says is the first fully biodegradable commercial plastic. The company plans to raise its annual production of this Nature's plastic to 5000 tonnes very soon. At present, Biopol costs about pounds 10 per kg., 20 times more than conventional plastic. Costs can be reduced to some extent by scaling up of the product ion. Even at its current price, ICI has plenty of buyers for limited amounts of Biopol hat they produce.
Australia's A$1 billion raw sugar industry is going to follow Brazilian researchers into new industry producing plastic from sugarcane. Australia's sugar to plastic plans are based on technology held by Procter & Gamble Co. which uses sugarcane genes to produce a plant which produces the polymer poly(3-hydroxybutyrate) (PHB).
Brazilian sugar industry, through the largest industry co-operative Copersucar, is well advanced in an ambitious non-genetic project to produce PHB by using bacteria to convert sugar to plastic.

Different approaches

• (I) modification of existing material,
• (II) chemical co-polymerisation of known biodegradable material,
• (III) use of biopolymers for making plastics.  
• 
  

(I) Partially biodegradable shopping bags are already manufactured from thin matrix of conventional polythene filled in with starch. After the bag has been thrown away, microorganisms eat away starch, leaving polythene film structure which soon disintegrates. Fertec (Ferruzzi, Ricercae Technologia) of Italy and Warner Lambert of the US are developing fully biodegradable starch-based plastics. Starch forms upto 50% by weight of the Fertec material and remaining is the synthetic polymer. Material shows partial biodegr adability in Warburg test. Warner Lambert's starch-based plastic is called Novon and contains 80% starch. Additives like plasticizers are used to make the material tougher and to improve processing. Novon is biodegradable in accelerated landfill, controlled compost, aerobic and anaerobic aquatic environments. Warner's starch-based plastic can be used for capsules for drugs, disposable single-use items like cups and food trays. The company has 25000 tonnes per annum production capacity from 1992. At present, biodegradable plastic represents just a tiny market compared with the conventional petrochemical material whose production amounts to >100 million tonnes per year. Bioplastics will comparatively prove cheaper when oil prices will continue to hike up.
(II) 'Bioceta' is the new biodegradable plastic which is cellulose diacetate-based product. It has been developed by Rhone Poulenc's Belgium subsidiary, Tubiz plastics. Bioceta uses additives which both plasticize and accelerate degradation by micro-organisms. The Sekisui chemical company has developed a new biodegradable plastic by co-polymerisation of two different biodegradable chemicals based on aliphatic polyester derivatives. The plastic has both good properties and complete biodegradability. The biodegradability and properties of new plastic can be adjusted to a larger extent by controlling the conditions of polymerization. It is thermoplastic and can be recycled. The plastic can be used effectively for agriculture, for goods packaging, but high-value add ed plastic can also be produced using the co-polymer. The plastic was developed in co-operation with the Government Industrial Research Institute, Osaka. Plastic is based on polyester which is decomposed by means of enzymes such as lipase to H₂O + CO₂ causing no secondary contamination as in other degradable plastics. According to firm s claim, this plastic is stronger than polyethylene, has a higher melting point (over 90⁰C) than the ordinary polyester resin and have fastest biodegradability. A film of 100 micron thickness of this plastic is totally decomposed in soil in just two months. Biodegradable plastic film comparable in strength to the general purpose polyethylene has been developed in Japan by the Agency of Industrial Science and Technology's (AIST) Fermentation Research Institute. The film has tensile strength of 200 kg/cm and is produced from a mixture of polycaprolactone (PCL) which is completely biodegradable and special compatible polyolefin. The mixture has a PCL content of 50-80% by weight a nd is formed with higher proportion of biodegradable PCL towards the surface, thus promoting high biodegradability while retaining the strength of special polyolefin. If buried in soil for a year, the film is degraded by micro-organisms into a powder with particles ranging from 1-10 microns. It releases no harmful gases when incinerated and has calorific value of 8000 k.cal per kg which is 80% of ordinary films. Co-polymers of succinic acid, glycerol and polyethylene glycol are found to be 100% biodegradable in 90 days in soil. They have glass transition temperature (Tg), 21}
(III) Bioplastics - Biopolymers obtained from growth of micro-organisms or from plants which are genetically-engineered to produce such polymers are likely to replace currently used plastics at least in some of the fields. Poly - hydroxy butyrate and polylactic acid are the kind of polymers which are used as materials of bioplastics.
This WebSite will concentrate on biopolymers the real Bioplastics - Biodegradable and of complete natural origin.

Conclusion Of Plastic Pollution

Thus, while tackling the issues related to environmental protection and cleanliness, we started with attack on symptoms rather than causes of pollution (Measurement of pollution and Treatment technologies). Then subsequently we gave stress on Environmental Impact Assessment (EIA) and could work on better planning and better control. And today we have started to attack the root cause of pollution - prevention of pollution. We are talking about clean technologies. We are aiming for biodegradable and ecofriendly products and processes. Bioplastics is only a part of the large efforts that we are determined to make. Bioplastics is a reality and is a practical truth. Our willingness and improvement in technologies will give it a wider success.