Monday, August 3, 2015

WASTE MANAGEMENT OF PLASTICS MATERIAL


                                                                       
The World Environment Day is observed on 5th June every year, to conserve our environment. Plastic waste remains one of the biggest headaches globally. Piles of plastic waste have become a common site in towns, and the menace is rapidly spreading to the countryside. Plastics have become an indispensable part of our daily life. But repeated reprocessing of plastic waste, and its disposal creates environmental problems, pose health hazards, although plastics pose a hazard to the environment because they do not decay, plastics are preferred because they are cheap and versatile.
Health impacts of solid waste
The unhygienic use and disposal of plastics and its effects on human health has become a matter of concern. Colored plastics are harmful as their pigment contains heavy metals that are highly toxic. Some of the harmful metals found in plastics are copper, lead, chromium, cobalt, selenium, and cadmium. In most industrialized countries, colour plastics have been legally banned. Until recently no legislation was framed to deal specifically with issues connected with plastic waste management. The Government of Himachal Pradesh was one of the earliest to introduce legislation prohibiting the throwing or disposing of plastic articles in public places. The Union Ministry of Environment and Forests has recently notified the "Recycled Plastic Manufacture and Usage Rules, 1999''. These rules require that carry bags or containers used for purposes of storing shall be made of virgin plastic and be in natural shade or white. These items when made of recycled plastic and used for purposes other than storing and packaging of foodstuffs shall use pigments and colorants as per Indian Standards. Recycling of plastics shall also be undertaken strictly in accordance with specifications prescribed by the Bureau of Indian Standards, and shall carry a mark that the product is manufactured out of recycled plastic. The thickness of carry bags shall not be less than 20 microns. Finally and most importantly, Rule 4 prohibits all vendors from using carry bags or containers made out of recycled plastics for storing, carrying, dispensing or packaging of foodstuffs. In other words all vendors are required to use carry bags and containers manufactured to specifications prescribed in the 1999 Rules.
Sorting Of Wastes
Waste is separated into the following categories:

1.      kitchen wastes
2.      paper and cardboard
3.      glass
4.      aluminium
5.      other metals
6.      oils, fuels, other liquids
7.      wood
8.      batteries
9.      other materials, plastics, construction materials and obsolete items

Proper methods of waste disposal have to be undertaken to ensure that it does not affect the environment around the area or cause health hazards to the people living there. At the household-level proper segregation of waste has to be done and it should be ensured that all organic matter is kept aside for composting, which is undoubtedly the best method for the correct disposal of this segment of the waste. In fact, the organic part of the waste that is generated decomposes more easily, attracts insects and causes disease. Organic waste can be composted and then used as a fertilizer.
Waste Disposal Options:
Plastics material offer many waste disposal options because they are usually solid, handleable materials. They are recoverable in most cases after use for several disposal options. This includes:
1.                  Incineration
2.                  Recycling
3.                  Land fill
4.                  Composting
5.                  Reuse
6.                  Source of energy
7.                  Reclamation
Incineration
Qualified staff operate high-temperature two-chamber incinerators at all stations. Incinerator ash and residues are returned to disposal. Kitchen and medical waste, low grade paper and cardboard, contaminated low density polythene (rubbish bags) and solid human waste from field camps are incinerated. All fats and oils, plastics (including polyurethane foam, polystyrene), large quantities of timber boxing and out-of-date food are returned for waste management.
Disadvantages of incineration:
  1. Incineration destroys valuable resources.
  2. Burning fossil fuels like coal, oil and gas is causing increasing levels of carbon dioxide in our atmosphere, leading to climate change. Incineration contributes to climate change, because when materials are burnt more fossil fuel energy is used to replace them through mining, manufacturing, and transportation around the world. Energy from burning waste is not renewable.
  3. Incinerators need a steady stream of waste to keep them going. This means there is no incentive to reduce waste or recycle it.
  4. Incineration causes pollution from air emissions and toxic ash.
  5. Incineration is worse for climate change than recycling because new products have to be made to replace those destroyed.
  6. Incineration does not provide the thousands of new job opportunities that recycling does.
Re-Cycling
Many items are re-used on station, e.g. packing materials such as cardboard boxes and plastic sheeting, packing crate timber, 200 L drums either with the lid part opened (for metal waste, glass or incinerator ash) or intact for returning chemical waste (e.g. photographic chemicals). Official photography on stations is now substantially electronic (i.e. no wet processing). All stations sort wastes as indicated above for disposal to recyclers. Recycling is one of the most immediate and effective ways to protect the environment. By recycling instead of producing goods from raw materials, substantial amounts of energy and raw materials are saved. 40% of local authorities now provide facilities for recycling plastics, with a quarter of these involved in doorstep collection schemes which are the most successful in recovering plastic waste. The six most common types of plastic can all easily be recycled and have a much higher value than most recyclable materials. As the volume of recycled material increases markets will expand, making the material more attractive to industry and the benefits of recycling more apparent. Recycling and waste minimization businesses could employ over 100,000 more people than the landfill and incinerator businesses would make redundant. Hence we can:
• Buy products made of recycled plastic wherever possible.
• Recycle plastic plants can be established.
• Set up a community scheme. The Community Recycling Network can help
• Encourage recycling in your workplace/school/church, etc.
Landfill:
Friends of the Earth wants a ban on new landfill capacity until policies are in place to achieve the 60-80 per cent recycling rates achieved in other countries, because:
• Landfill waste valuable resources.
• Landfill contributes to climate change, because when materials are buried more fossil fuel energy is used to replace them through mining, manufacturing, and transportation around the world.
• Landfill produces methane, a powerful greenhouse gas which contributes to climate change.
• Landfill creates water pollution as liquid from landfill sites leaks into our water supply.
• Landfill can lead to land contamination.
• Landfill leads to increased traffic, noise, smell, smoke, dust and litter.
Composting:
Composting is predominantly biodegradation with the possibility of oxidation and hydrolysis. There is an opportunity for environmentally degradable plastics which are used in food application such as wrappers and utensils in these uses, plastics are contaminated with food residues and are suitable for composting without separation. Where recovery of current plastics is not economically feasible, viable, controllable or attractive, the plastics remain as litter and may be discarded at sea from naval vessels, may be used in farm and agricultural application such as pre emergency plant protection or  in hygienic application such as diapers, hospital garments and swabs etc.
Re-use
It makes sense and it saves energy to re-use rather than recycle, but it is currently more economical for manufacturers to produce new product rather than wash and re-fill packaging. The Body Shop will re-fill plastic bottles with the same product, and many small producers across the country also do this, showing that re-use can make economic sense.
• Re-use plastic bags, or better still avoid them by using a sturdy bag that will last for years.
• Re-use pots with lids for storage rather than buying new ones.
• In the garden, re-use plastic pots for raising seedlings and cut-down plastic bottles to protect them from slugs
• Give usable goods to charity shops, or hold car boot sales for charity with any plastic items that can be re-used.
• Ask suppliers if they will take back plastic items for re-use: for example, plant pots in garden centers.
• Use refillable toner cartridges.

A Source of Energy

Material recovery is by no means the only way to recycle plastics. Another option is to recover their thermal content, providing an alternative source of energy. An average typical value for polymers found commonly in house hold waste is 38 mega joules per kilogram (MJ/kg), which compares favorably to the equivalent value of 31 MJ/kg for coal. This represents a valuable resource raising the overall calorific value of domestic waste which can then be recovered through controlled combustion and re-used in the form of heat and steam to power electricity generators. Successful ventures in this field include plants, such as a major incinerator, which produces steam to power an electricity turbine. Waste containing plastics can also be reprocessed to yield fuel pellets, which have the added advantage of being storable.
It is sometimes claimed that incineration of municipal waste poses an environmental problem in the shape of atmospheric pollutants. Although the potential is there, modem incineration techniques ensure that actual emission levels are kept with-in internationally accepted safety limits. In fact, several countries, such as Sweden, Germany and the Netherlands, have recently affirmed their confidence in incineration by announcing plans to expand existing capacity.

Reclamation

The majority of municipal waste is still used as land fill, due to the very high cost of facilities for the sorting, separation and recycling of waste. As plastics are stable, both physically and chemically they in turn provide stability to the tips. This provides a safe and solid foundation upon which to build; thereby releasing land for development.

Conserving the Environment

The plastics industry is concerned that it should take appropriate care of resources and the environment. The advantages of plastics over other raw materials are apparent from the beginning of their life-cycle. Research shows that it often takes less energy to make products in plastics, and although most plastics depend on oil, coal or gas they are responsible for only a small fraction of the national consumption of these fuels. Energy savings can be made easily with plastics because plastics are lighter, easier to store and transport. Also the developments in the recycling of plastics, there are interesting advances in the production of degradable plastics for products which need only a limited life.

The Future

Plastics recycling are in the growth phase as the whole industry is still relatively young. A further development in recycling, which is being researched, is the recovery of the individual chemical components of plastics for re-use as chemicals, or for the manufacture of new plastics.
 


Tuesday, April 21, 2015

FAILURE ANALYSIS



To learn from every failure is the way to success. Every well experienced person is the one who learns maximum out of the failure by analyzing the cause of failure and exploring suitable remedy for each cause. Sir Thomas Alva Edison explored 1000 of procedures through which light bulb could not glow. Learning out of each way he found his way to glow the bulb. Thus learning from each failure and not repeating the same mistakes/blunders one can achieve the success.    
How to analyze the failure? One has to perform quick immediate postmortem on a project that has failed so as to prevent future failure as well as to get guideline for future testing and quality control.
Some of the areas to cover are:
1.       Scope:
The goals must be set on the basis of available infrastructure and all surrounding parameters influencing the project. Higher target or over ambitions may describe the feeling of failure. In other words, higher expectations than what is been deserved cannot be called failure.  
2.       Money:
Sufficient funding and that to when required is necessary for a project to be successful.
3.       The team of project:
The team members who have shared the experience of failure of the previous project should be given chance to try again because they also have learnt from the failure. If the project is launched for the first time just select the persons having experience of analyzing the failure in a positive manner.
4.       Vendors/suppliers:
The raw material should be of the desired quality. Raw material should be supplied in right quantity and at the right time. Supplier should be able to identify the problem and be able to troubleshoot them.  
5.       Structure:
The structure of the project should be simple and easily understood by the persons who have to execute it. Over complicated and messy project will fail due to its own complexity. The goals should not be intangible and imponderable.
6.       Timing:
There must be a right time to launch a new project. A team of fresher/trainees members cannot handle all to gather a new project. OR A rain water harvesting plant may not run in a desert or in summer. The environment surrounding the project, the people affected by or can affect the project, system; business conditions should be properly evaluated.   
7.       Information/data:
The reliability of the data used during the planning and goal setting of a project must be checked. Precise, recent, valid and timely data are useful for a project to be successful. If the data is collected especially for setting a goal for a project may be biased and the goals set on the basis of such data may be exaggerated.  
8.       Salvaging:
The previous failed project may be assessed for the extent of failure. Whether the project is a total failure and should be started from the beginning or can be started from a point where the situation went out of control should be analyzed.  
9.       Graphics:
Graphs and charts can be used to identify problems easily. Graphs and charts help to analyze the failure easily and promptly.
10.   Comparisons:
Comparison with a successful project of a similar kind may help to identify and rectify the problems causing failure.
11.   Motivation:
The project under consideration should have new idea or plan i.e. it should be profitable or of some benefit to the the people affected by or can affect the project. In other words there must be some motivational value of the project so that the people affected by or can affect the project will endeavor for its success. Nobody is willing to work on a futile project.   
12.   Use failure to be successful:
Planning a failure may be beneficial for further planning of a successful project at a low cost. When we are aware of causes of failure we are sure to take remedial actions against those causes. This in turn results in a full proof planning of a successful project.  

Tuesday, March 17, 2015

CLASSIFICATION OF BIODEGRADABLE POLYMERS



BIODEGRADABLE POLYMER
Dr.Mrs.G.D.SHAH ( Ph.D. Chemical Engg. M.E. POLYMER TECH.)
I/C HEAD OF PLASTICS ENGG.DEPT.
GOVT. POLYTECHNIC, AHMEDABAD GUJARAT, INDIA.

ABSTRACT
Biodegradable polymers can be classified into natural polymers, synthetic polymers and modified natural polymers. Various biodegradable polymers are described with respect to their composition, structure, properties and applicability.

 Today polymer industry is facing environmental problems. Most of the polymer does not degrade under standard environmental conditions. Yet it would be interesting to know about various polymers that degrade in biological environment. Also by increasing their use the environmental problems can be resolved to a certain extent.
CLASSIFICATION OF BIODEGRADABLE POLYMERS:
Biodegradable polymers can be divided into three broad classifications:
1.                  Natural polymers
2.                  Synthetic polymers
3.                  Modified Natural polymers
These classes may be further subdivided as:
1.                  Natural polymers or biopolymers
2.                  Synthetic polymers                  (a) Carbon chain backbone
             (b) Heteroatom chain backbones
3.                  Modified  Natural polymers
(a)    Blends and grafts
(b)   Chemically modified
(c)    Oxidation
(d)   Esterification
NATURAL POLYMERS OR BIOPOLYMERS:
They are produced naturally by all living organisms. They are environmentally acceptable degradable polymers. Most common natural polymers are:
1.         Polysaccharides           starch and cellulose
2.         Polyesters                    polyhydroxyalkanoates
3.         Proteins                       silk and poly (2-Glutamic acid)
4.         Hydrocarbons             natural rubbers
POLYSACCHARIDES:
They are largely limited to starch and cellulose derivatives for practical applications either in plastics or as a water-soluble polymers. Both these polymers are composed of D-Glycopyranoside repeating units to very high molecular weight, thousands of units. They differ in that starch is poly (1,4-2-D-Glucopyranoside) and cellulose is poly (1,4-B-D-Glucopyranoside). This difference in structure control biodegradation rates and properties of the polymers. Complex carbohydrates like microbially produced xanthan, curdlan, pullulan, hylauranic acid alginates, carageenan and guar are accepted biodegradable polymers. Xanthan is the prominent microbial polysaccharide and finds use in the food industry. It is also used as a thickener in many industrial applications.
PROTEINS:
They must be used as found in nature because they are not soluble or fusible without decomposition. They are widely used as fibbers e.g. wool, silk, gelatin (collagen) which is used as an encapsulate in the pharmaceutical and food industry. The structure of proteins is an extended chain of amino acid joined through amide linkages that are readily degraded by enzymes, particularly protease. Recent activity in poly (r-glatanic acid) with control of stereo chemistry. The inclusion of manganese ions may be important for future development in biodegradable water-soluble polymers with carboxyl functionality.
POLYESTERS:
They are produced by many bacteria as intracellular reserve material for use as a food source during periods of environmental stress. They are biodegradable, can be processed as plastic materials, are produced from renewable resources and can be produced by many bacteria in a range of composition. The thermoplastic polymers vary from soft elastomer to rigid brittle plastics in accordance with the structure of the pendent side-chain of the polyester. All the polyesters are 100% optically pure and are 100% isotactic. Longer side chain polyesters are produced by variety of bacteria, usually as copolymers and with low crystallinity, low melting points and low Tg. These polyesters are elastomeric and have excellent toughness and strength. They are inherently biodegradable. But as the chain length increases the rate of biodegradation is greatly reduced.
SYNTHETIC POLYMERS:
Synthetic polymers do not have natural origin, the plethora of enzymes available in nature for degrading natural polymers are not useful for synthetic polymers. Researches are carried out for synthetic polymeric structure that can be biodegraded. Some guidelines based on polymer structure, polymer physical properties and environmental conditions at the exposure sites have emerged for polymer structure. Following generalization can be made:
1.                A higher hydrophilic/hydrophobic ration is better for degradation.
2.                Carbon chain polymers are unlikely to biodegrade.
3.                Chain branching is deleterious to biodegradation.
4.                Condensation polymerization is more unlikely to biodegrade.
5.                Lower molecular weight polymers are more susceptible to biodegradation.
6.                Crystallinity reduces biodegradability.
Favorable polymer physical properties include water solubility and sample purity. Environmental conditions to be considered in evaluation o biodegradability are temperature, pH, moisture, oxygen, nutrients, suitable microbial population, concentration and test duration.
POLYMERS WITH CARBON BACKBONES:
These polymers may be represented by and is considered derivatives of PE. Where ‘n’ is the degree of polymerization and ‘R’ is the functional group. The functional groups and the molecular weight of the polymer control their properties that vary in hydrophobicity, solubility characteristics, Tg and crystalinity.
POLYETHYLENES:
Fungal and bacterial growth tests indicate that polyethylene and other high molecular weight carbon chain polymers do not support growth. Anomalous results were observed when plasticizers or low molecular weight impurities were added. It was also found that branching of hydrocarbon chains limits biodegradation. There is an increase in biodegradation with lower molecular weight because of the transportation of polymer across cell wall is more likely at lower molecular weight or it may be the mechanism of biodegradation or because of random or chain end cleavage prior to entering the cell. The slow biodegradation process in PE can be accelerated with surfactants or an oxidation process.
VINYL POLYMERS:
Their biodegradation requires an oxidation process and most of the biodegradable vinyl polymers contain an easily oxidisable functional group. To improve biodegradability of vinyl polymers, catalysts are added to promote their oxidation or photodegradation or both. Incorporation of photosensitive groups like ketones into the polymers is also attempted.
POLYVINYL ALCOHOL:
It is the most readily biodegradable of vinyl polymers. It is readily degraded in wastewater activated sludge. The microbial degradation of PVAL has been studied. Its enzymatic degradation by secondary alcohol peroxide isolated from soil bacteria of the pseudomonas strain is also studied. The initial step involves the enzymatic oxidation of the secondary alcohol groups in PVAL to ketone groups. Hydrolysis of ketone goups results in chain cleavage. Other bacterial strain, such as flavobacterium and azetobacter were effective in degrading PVAL.
PEK:
Controlled chemical oxidation of PVAL into PEK. It has similar structure to the intermediate formed as PVAL is biodegraded. PEK is found more susceptible to hydrolysis and biodegradation than PVAL. it is the polymeric form of acetoacetone, hence it forms metal chelate. Its water solubility, reactivity and biodegradability make it potentially useful material in biomedical, agricultural and water treatment areas. By using dyes as model it was found that PEK and PCL blends are excellent controlled release systems.
POLYVINYL ACETATE:
 PVAL is obtained from hydrolysis of polyvinyl acetate. Controlled hydrolysis of PVAc followed by oxidation provides degradation material having a wide range of properties and degradability. PVAc undergoes slow biodegradation in soil burial tests. The weight loss increases with the acetate content.
POLYACRYLATES:
Polyalkyl acrylates and polycyanoacrylates generally resist biodegradation. Weight loss in soil burial test is reported for copolymers of ethylene and propylene with acrylic acid, acrylonitirde and acrylamide poly alkyl 2-cyanoacrylates. Polymethyl 2- cyanoacrylate is the most degradable among the esters. The degradability decreases as the alkyl size increases. Poly iso beetyl 2- cyanoacrylate nano particles is degraded in two enzyme free media a pH 7 and pH12 in the presence of rat liver microsomes.Poly 2-hydroxy ethyl methacrylate is generally cross-linked with a small amount of ethylene dimethacrylate. It swells in water to form a hydrogel and is widely used in biomedical area due to its good biocompatibility.
HETEROATOM CHAIN BACKBONE POLYMERS:
Their linkages are quite frequently found in nature and they are more likely to biodegrade than hydrocarbon based polymers. They include polyesters, polyamides, polyethers, polyacetates and other condensation polymers.
POLYESTERS:
Aliphatic polyesters are the most easily biodegraded synthetic polymers known.

TABLE: Biodegradable polyesters in commercial development
PHA
polyhydroxyalkanoates
PHB
polyhydroxybutyrate
PHH 
polyhydroxyhexanoate
PHV     
polyhydroxyvalerate
PLA      
polylactic acid
PCL      
polycaprolactone
PBS 
polybutylene succinate
PBSA    
polybutylene succinate adipate
AAC     
Aliphatic-Aromatic copolyesters
PET       
polyethylene terephthalate
PBAT    
polybutylene adipate/terephthalate
PTMAT 
polymethylene adipate/terephthalate
PGA
polyglycolic acid
PLLA
poly (L- lactic acid)

The simplest poly (a-hydroxyacid), polyglycolic acid (PGA) has been successfully used as biodegradable suture. The partially crystalline polyester is generally obtained from the polymerisation of diglycolide with a tin catalyst. Also poly (L- lactic acid) PLLA is obtained from dilactide and is used as suture. Aromatic polyesters such as PET exhibit excellent material properties, they prove to be almost totally resistant to microbial attack. Aliphatic polyesters on the other hand are readily biodegradable, but lack good mechanical properties that are critical for most applications. All polyesters degrade eventually, with hydrolysis (degradation induced by water) being the dominant mechanism. Synthetic aliphatic polyesters are synthesised from diols and dicarboxylic acids via condensation polymerisation, and are known to be completely biodegradable in soil and water. These aliphatic polyesters are, however, much more expensive and lack mechanical strength compared with conventional plastics such as polyethylene.
POLYURETHANES:
Polyester based polyurethanes are more susceptible to degradation than those derived from polyether diols. As the flexibility of polyurethane increases, their susceptibility towards biodegradability increases. Polyamide urethane prepared from amino alcohols are easily degraded by substilin.
POLYAMIDES:
Nylon 6, Nylon 6,6  generally resist microbial and enzymatic attacks but oligomers of e-amino hexanoic acid are degraded by enzymes and microorganism. The loss of tensile strength of nylon in vivo is by 25% after 89 days and 83% after 726 days. Etching of a nylon fiber after 210 days in vivo is also seen. In vivo degradation of nylon is caused by hydrolysis and proteolytic enzyme catalysis. Incorporation of methyl, hydroxy and benzyl groups into polyamide chains improves the biodegradability. Biodegradability of polyamide esters decreases by shortening polyamide blocks and increasing polyamide content.
POLYUREAS:
Polyureas prepared from lysine esters with 1,6 hexane diisocyanate are readily degradable and is used in polymer drug application. The polyester urea from phenylamine containing hydrophobic benzyl group is readily hydrolyzed while unsubstituted polyester urea from glyline is not affected.
POLYANHYDRIDES:
Fibre forming polyanhydrides are very susceptible to hydrolysis. Poly[bis-(p-carboxyphenoxy)methane] – PCPM was examined as matrix material for controlled release of drugs and was found to erode slightly faster in vivo than in vitro buffer. The erosion of PCPM is mostly heterogenous surface erosion which gives a near zero order released rate.
POLY [AMIDE-ENAMINE] s:
Homogeneous erosion of hydrophilic biodegradable polymer matrix system undergo progressive loosening or swelling. Hence by surface erosion, a near zero order release can be obtained if diffusion release is small. Poly [amide-enamine]s are are found susceptible to hydrolysis and biodegradation.
POLYPHOSPHAGENE:
The polymer contains phosphorous nitrogen chains. They are readily hydrolyzed to give phosphoric acid and ammonia derivatives.

MODIFIED NATURAL POLYMERS:
Natural polymers are modified so that the environmentally acceptable polymer can be developed. Hence the modification should not interfere the biodegradation process. The modification includes blends with other natural and synthetic polymers, grafting of other polymeric composition and chemical modification to introduce some desirable functional group by oxidation or some other simple chemical reaction such as esterification or etherification.
STARCH:
Starch is made thermoplastic at elevated temperature in the presence of water as a plasticizer, allowing melt processing alone or in blends with other thermoplastic. Water lowers the melt transition temperature of starch so that processing can be done well below the degradation temperature.
STARCH-PE BLENDS:
The most important commercial application is the blending of PE with starch in presence or absebce of other additives. The starch –PE are compatibilized with:
1.                  Ethylene acrylic acid copolymer
2.                  Ethylene  vinyl alcohol polymers
3.                  Hydroxyacids
4.                  Urethanes
5.                  Polyamides
6.                  Polyvinyls
7.                  Cellulose acetate
8.                  Alkyds
9.                  Polycaprolactone

The product based on this chemistry are characterized by incomplete biodegradation, water sensitivity.
OTHER BLENDS:
The blending composition is limited only by number of polymers and the compatibility of the components.
1.                  PHA with cellulose acetate
2.                  PHA with PCL
3.                  PLA with PEG
4.                  Chitosan with Cellulose
5.                  PLA with inorganic fillers
6.                  PHA and aliphatic polyesters with inorganics
NATURALLY PRODUCED POLYMERS:
PHA
Polyhydroxyalkanoates (PHAs) are aliphatic polyesters naturally produced via a microbial
process on sugar-based medium, where they act as carbon and energy storage material in bacteria.They were the first biodegradable polyesters to be utilised in plastics.
PHB/PHV
The two main members of the PHA family are polyhydroxybutyrate (PHB) and polyhydroxyvalerate (PHV).Aliphatic polyesters such as PHAs, and more specifically homopolymers and copolymers of hydroxybutyric acid and hydroxyvaleric acid, have been proven to be readily biodegradable. Such polymers are actually synthesised by microbes, with the polymer accumulating in the microbes’ cells during growth. The most common commercial PHA consists of a copolymer PHB/PHV together with a plasticiser/softener and inorganic additives such as titanium dioxide and calcium carbonate. A major factor in the competition between PHAs and petroleum based plastics is in production costs. Opportunities exist however for obtaining cheaper raw materials that could reduce PHA production costs. Such raw materials include corn-steeped liquor, molasses and even activated sludge. These materials are relatively inexpensive nutrient sources for the bacteria that synthesise PHAs. The PHB homopolymer is a stiff and rather brittle polymer of high crystallinity, whose mechanical properties are not like polystyrene, though it is less brittle. PHB copolymers are preferred over general purposes as the degradation rate of PHB homopolymer is high at its normal melt processing temperature. PHB and its copolymers with PHV are melt processable semi-crystalline thermoplastics made by biological fermentation from renewable carbohydrate feedstocks. They represent the first example of a true biodegradeable thermoplastic produced via a biotechnology process. No toxic by-products are known to result from PHB or PHV.
PHBH
Poly-hydroxybutyrate-co-polyhydroxyhexanoates (PHBHs) resins are one of the newest type of naturally produced biodegradable polyesters. The PHBH resin is derived from carbon sources such as sucrose, fatty acids or molasses via a fermentation process. These are ‘aliphatic-aliphatic’ copolyesters, as disctint from ‘aliphatic-aromatic’ copolyesters. Besides being completely biodegradable, they also exhibit barrier properties similar to those exhibited by ethylene vinyl alcohol (see Section 3.1.2). Procter & Gamble Co. researched the blending of these polymers to obtain the appropriate stiffness or flexibility.
RESEARCH SCOPE:
1.                    Use of degradable polymers can be increased to protect environment.
2.                    The properties of degradable polymers should be compared with those of conventional synthetic polymers
3.                    The properties of degradable polymers that are not acceptable can be improved by adding suitable additives, changing the chemical structure, incorporating functional groups etc.
4.                    After modifying the degradable polymer for achieving strength, the degradability should be assessed.
5.                    The residue from the polymer after degradation should be assessed for its harmfulness to the environment.
REFERENCES:

1.      Leonard I. Nass, Encyclopedia of PVC vol.I Marcel Dekker, Inc., N.Y. and Basel 1976 pp385-592.
2.      Leonard I. Nass, Encyclopedia of PVC vol.II Marcel Dekker, Inc., N.Y. and Basel 1976 pp801-837.
3.      R. Gatcher and Muller, Plastics additives, Hanser Publishers, Munich Vienna N.Y. 1985. pp 251-335 and 601-617.
4.      P.D. Ritchie, Plasticizer, Stabilizers, and Fillers, London ILIFFE Books Ltd., 1972 pp 1-226.
5.      Baboolal Agrawal Handbook of Solvents and Plasticizers. Small Business Publications Delhi SBP series-68. pp 163-183.
6.      Abraham J. Domb, Joseph Kost and David M. Wiseman, Handbook of Biodegradable polymers SPE series Gordon and Breach Publishing group pp 1- 34 and 445-550.
7.      Mark and others, Encyclopedia of polymer science and engineering vol.2 pp 202-289.
8.       Kirk and Othmer, Encyclopedia of chemical technology vol.7 3rd edition Wieley-Interscience N.Y. 1984. pp 281-291.
9.      Kirk and Othmer, Encyclopedia of chemical technology vol. 19 3rd edition Wieley-Interscience N.Y. 1984. pp 968-996.
10.  J.E. Potts, Plastics Environmentally Degradable 3rd edition suppl. Vol. Union carbide corporation pp 626-668.
11.  Eugene Stevens, Green Plastics: An introduction to New science of biodegradable plastics.
12.  David L. Kalpan Biopolymers from renewable resources.
13.  Ching Chauncey, Kalpan David and Thomas Edwin L., Biodegradable Polymers and Packaging.
14.  G.F. Moore and S.M. Saunders, Advances in biodegradable polymers, Rapra tech. 1999.
15.   Johnson, H. 1989. Plastigone photodegradable film performance in California. Proc. Natl. Agr. Plastics Cong. 21:1-6.
16.  Smt. G.D.Shah, Seminar on Biodegradable polymers, Chemical Engg. Dept. M.S. University, Baroda. 2002. pp 48-150.
17.   Smt. G.D.Shah, dissertation: The study of Biodegradable Plastics, Chemical Engg. Dept. M.S. University, Baroda. 2002. pp 48-150.
18.  Environment Australia Biodegradable Plastics – Developments and Environmental Impacts OCTOBER, 2002 NOLAN-ITU Pty Ltd.