ABSTRACT For many years, the use of natural polymers for the fabrication of packaging materials has been an interesting alternative to replace non-biodegradable polymers which are normal components of these materials. The core problem of these starch based plastics is their hydrophilic character and the fact that they tend to become brittle with ageing. Unmodified starch is too much hydrophilic to be used as food packaging material. Chemical modification must be carried out in order to make them hydrophobic.
These modifications are grafting, alkylation-especially esterification including acetylation. The purpose of the project is to prepare acetylated starches/starch esters of different Degree of Substitution using different concentrations of acetic anhydride for modifying the native starch. The testing of samples is done by testing various properties of the obtained samples such as Degree of Substitution, Solubility, Swelling Power, Light Transmittance and Water Binding Capacity. INDEX 1. Introduction ………………………………………………………7 2. Literature Survey…………………………………………………. 9 3.
Biodegradation………………………………………………….. 14 4. Biopolymers…………………………………………………….. 21 5. Starch……………………………………………………………. 24 6. Physiochemical Properties of Modified Starch…………………. 28 7. Experiment………………………………………………………35 8. Results…………………………………………………………… 40 9. Discussion………………………………………………………. 42 10. Conclusion………………………………………………………. 47 11. Future Scenario of Biodegradable Polymers……………………. 48 12. References………………………………………………………. 49. Chapter 1 INTRODUCTION Plastic is the general term for a wide range of synthetic or semi-synthetic polymerization products.
They are composed of organic condensation or addition polymers and may contain other substances to improve performance or economics. There are many natural polymers generally considered to be “plastics”. Plastics can be formed into objects or films or fibers. Their name is derived from the fact that many are malleable, having the property of plasticity Plastic can be classified in many ways, but most commonly by their polymer backbone (polyvinyl chloride, polyethylene, polymethyl methacrylate, and other acrylics, silicones, polyurethanes, etc. ).
Other classifications include thermoplastic, thermoset, elastomer, engineering plastic, addition or condensation or polyaddition (depending on polymerization method used), and glass transition temperature or Tg. Plastics are durable and degrade very slowly. In some cases, burning plastic can release toxic fumes. Also, the manufacturing of plastics often creates large quantities of chemical pollutants. For many years, the use of natural polymers for the fabrication of packaging materials has been an interesting alternative to replace non-biodegradable polymers (polyethylene, polypropylene) which are normal components of these materials.
The latter should not be used for short term packaging such as bags, agriculture mulching, bottles, and fast food goods. Natural polymers contribute to the decrease of waste coming from plastics. Research has been done on biodegradable plastics that break down with exposure to sunlight (e. g. ultra-violet radiation), water (or humidity), bacteria, enzymes, wind abrasion and some instances rodent pest or insect attack are also included as forms of biodegradation or environmental degradation.
It is clear some of these modes of degradation will only work if the plastic is exposed at the surface, while other modes will only be effective if certain conditions are found in landfill or composting systems. Starch powder has been mixed with plastic as a filler to allow it to degrade more easily, but it still does not lead to complete breakdown of the plastic. Some researchers have actually genetically engineered bacteria that synthesize a completely biodegradable plastic, but this material is expensive at present e. . BP’s Biopol. BASF make Ecoflex, fully biodegradable polyester for food packaging applications. A potential disadvantage of biodegradable plastics is that the carbon that is locked up in them is released into the atmosphere as a greenhouse gas carbon dioxide when they degrade, though if they are made from natural materials, such as vegetable crop derivatives or animal products, there is no net gain in carbon dioxide emissions, although concern will be for a worse greenhouse gas, methane release. Of course, incinerating on-biodegradable plastics will release carbon dioxide as well, while disposing of it in landfills will release methane when the plastic does eventually break down. The core problem of these starch based plastics is their hydrophilic character and the fact that they tend to become brittle with ageing. Unmodified starch is too much hydrophilic to be used as food packaging material. Chemical modification must be carried out in order to make them hydrophobic. These modifications are grafting, alkylation-especially esterification including acetylation.
In this project acetylation of starch is used to modify the native starch. Various samples of acetylated starches are prepared by adding different concentrations of acetic anhydride to native starch. The properties of the obtained samples such as degree of substitution, solubility, swelling power, light transmittance and water binding capacity are determined and compared with that of native starch. Chapter 2 LITERATURE SURVEY Plastics are not biodegradable and therefore cause environmental pollution.
People experimented with plastics based on natural polymers for centuries. In the nineteenth century a plastic material based on chemically modified natural polymers was discovered: Charles Goodyear discovered vulcanization of rubber (1839) and Alexander Parkes, English inventor (1813—1890) created the earliest form of plastic in 1855. He mixed pyroxylin, a partially nitrated form of cellulose (cellulose is the major component of plant cell walls), with alcohol and camphor. This produced a hard but flexible transparent material, which he called “Parkesine. The first plastic based on a synthetic polymer was made from phenol and formaldehyde, with the first viable and cheap synthesis methods invented by Leo Hendrik Baekeland in 1909, the product being known as Bakelite. Subsequently poly (vinyl chloride), polystyrene, polyethylene (polyethene), polypropylene (polypropene), polyamides (nylons), polyesters, acrylics, silicones, polyurethanes were amongst the many varieties of plastics developed and have great commercial success. The development of plastics has come from the use of natural materials (e. g. chewing gum, shellac) to the use of chemically modified natural materials (e. g. , natural rubber, nitrocellulose, collagen) and finally to completely synthetic molecules (e. g. , epoxy, polyvinyl chloride, polyethylene). In 1959, Koppers Company in Pittsburgh, PA had a team that developed the expandable polystyrene (EPS) foam cup. On this team was Edward J. Stoves who made the first commercial foam cup. The experimental cups were made of puffed rice glued together to form a cup to show how it would feel and look. The chemistry was then developed to make the cups commercial.
Today, the cup is used throughout the world in countries desiring fast food, namely, the United States, Japan, Australia, and New Zealand. Freon was never used in the cups. Researchers at the University of Illinois at Urbana have been working on developing biodegradable resins, sheets and films made with zein (corn protein). Recently, however, a new type of biodegradable resin has made its debut in the United States, called Plastarch Material (PSM). It is heat, water, and oil resistant and sees a 70% degradation in 90 days.
Biodegradable plastics based on polylactic acid (once derived from dairy products, now from cereal crops such as maize) have entered the marketplace, for instance as polylactates as disposable sandwich packs. Various institutes in the world are trying to develop biodegradable polymers but only few had succeeded. So we can say that the research is going on all over the world to get rid of the problem of biodegradation. One of the institutes which have developed the biodegradable polymer is the Symphony Institute. Symphony’s material is the first example of 100% degradable polyethylene.
The plastic, known as SPITEK, has the same mechanical properties and processing characteristics as regular polyethylene and so can be used in the same way to make products. However, it has a special ingredient – up to 3% of a degradable compostable plastic (DCP) additive made under license from its developers EPI. This additive acts as a catalyst for the degradation of the polyethylene, kick starting the process when conditions dictate Symphony claims that its new plastic could effectively increase the capacity of landfill sites by as much as 20 to 30% by breaking down in a short time and allowing other materials to degrade.
The SPI-TEK material can be engineered to degrade in as little as 60 days or as long as 5 to 6 years, depending on the application. The level of the proprietary EPI DCP additive effectively determines the rate of degradation and the shelf life of products made from the polyethylene. Degradation is initiated by a number of factors – sunlight, heat and stress from pulling and tearing can all start the process, which then continues even if the material is in landfill or under water. Another step which had been taken is by Japan which had done the research work in the biodegradable plastics.
Japanese scientists and engineers are focusing on natural polymers from renewable resources, synthetic polymers, and bacterially produced polymers such as polyhydroxyalkanoates, poly (amino acids), and polysaccharides. The major polymers receiving attention are the PHBV copolymers, Biopol (R), poly (lactic acid) from several sources, polycaprolactone, and the new synthetic polyester, Bionolle (R). In their present state of development, these polymers all have major deficiencies that inhibit their acceptance for large-scale applications.
Bayer in Japan had currently tested a new polyester amide biodegradable plastic that it claims is 100% biodegradable and recyclable, and yet also has excellent properties including a high tensile strength. The plastic has additional green credentials as it is produced without solvents, chlorine or any aromatic ingredients. BAK 1095 is a semi-crystalline, largely transparent thermoplastic that breaks down into carbon dioxide, water and biomass under composting conditions.
Its degradation rate is comparable to that of other organic materials that are composted, and yet its physical properties are similar to those of typical polyolefins such as LDPE. It suggests that potential applications will be in areas such as horticulture, agriculture or the food sector, in which plastics must be used in conjunction with compostable waste. Since the mid-1970s, polymer-starch blends with acceptable physical properties have been developed. Starch has been used commercially as a biodegradable additive for polyethylene (Kim, Pometto, Johnson, &
Fratzke, 1994) and dry granular starch (Griffin, 1974) has been used as fillers to improve the biodegradability of plastics. One of the problems inherent in films prepared with the use of starch and gelatinized starch is the reduction of mechanical properties because of the incompatibility between hydrophobic plastics and hydrophilic starch. Chemical modification of starches could improve the interfacial contact between starch granule and polymer. Griffin (1977) proposed a process for making low density polyethylene (LDPE) blown films containing native or modified starches.
Swanmson, Westhoff, and Doane (1988) examined the effect of starch modification on LDPE films and found that the mixture of LDPE and poly (ethylene-co-acrylic acid)(EAA) polymers filled with hydroxypropyl or acetyl derivatives of starch had a higher elongation and often had a higher tensile strength than native starch-filled films. Otey,Westhoff, and Russell(1977) used a mixture of polyvinyl alcohol(PVA) and modified starch to develop water-soluble packaging plastics. Crosslinking of starch reinforces the granule by chemical bonds that act as bridges between molecules.
Crosslinked starch maintains a higher viscosity and shows less viscosity breakdown (Wurzburg, 1987). Crosslinking can prove to be a valuable tool for providing maximum film strength (Wurzburg, 1987). Cross linking of the starch can also modify the paste properties of the swollen granule, altering the texture and rheology of the paste (Kim & Lee, 1996). It can also reduce the sensitivity of the swollen granule paste to acidic conditions and shear force (Rutenberg & Solarek, 1984). Cross linking can be utilized to improve the film forming pastes of starch pastes.
Thus cross linked starches are used in the preparation of starch xanthates for water treatment ion-exchangers, stilt materials for micro-encapsulated coatings and anti-blocking agents for film in the food industry, textile industry and paper industry (Rutenberg & Solarek, 1984; Wurzburg, 1987). The use of starch-filled degradable plastics has been increasing in many countries. An example is the regulatory requirement in Korea to use household waste. Unfortunately, starch filled plastic bags are often easily torn when garbage is put into the bag.
Therefore it is necessary to improve the mechanical properties of the degradable starch –filled plastics. There is not much research on degradable film prepared with modified starch. New environmental regulations, societal concerns, and a growing environmental awareness of the non degradability of the plastics and their increasing use led to a world-wide search for better biodegradable polymers. The aim of this review is to discuss the prospects and promises of these environmental friendly biodegradable polymers (Samaresh Ghosh and Ajit K.
Banthia) Recycling of plastics in India is not organized in a well planned manner. The packaging films like PE, PP, are the largely consuming plastics materials which should be effectively recycled, unless properly not recycled; there will be large environmental pollution and more difficulty for the solid waste management and its disposal during land filing. Since these polymers are not inherently photo-degradable or bio-degradable and it will take millions of years to degrade into small fragments.
Hence, the incorporation of bio-degradable polymeric additives like starch is more important which accelerate their disintegration and degradation of the plastics materials within a short period of time. Starch is an inexpensive and abundantly available natural resource, which decomposes very quickly in the presence of water. The unawareness and illiteracy among the masses in disposing the waste plastic into the proper container and lack of proper training to manage it have posed this man made material as material of adverse nature to environment due to its non biodegradable nature.
The biodegradability of the plastics which became a serious issue, is not at all required in the application of cables, underground piping, plastic capsules used for preserving the glory, history and culture, and plastic currency, etc. The application plurality and versatility of this class of material have gone up in multiple order in replacing wood, glass, paper and conventional metals. 2-hydroxyethyl methacrylate (2-HEMA) was graft copolymerized with sodium salt of partially carboxymethylated starch (Na-PCMS). Thus, prepared graft copolymer (2- HEMA-g-Na-PCMS) and pure Na-PCMS were evaluated for their biodegradable character.
The lycopodia fungi were utilized as microorganisms and sucrose solution as the growth medium. Biodegradation medium was prepared from fungus Lycopodia sucrose solution. Percent weight loss and SEM photographs showed biodegradation in this graft copolymers and Na-PCMS in order of 32% and 80% respectively. Results were compared with the biodegradation data obtained with biodegraded samples. {Biodegradation of 2-Hema-g-Na-PCMS a polymeric matrix synthesized from natural modified carbohydrates – Prashant D. Pandya, Nirmal K. Patel, and Vijay Kumar Sinha) Chapter 3 BIODEGRADATION . 1 BIODEGRADATION “Biodegradation” as the name suggests is the combination of two words bio means something related to living thing and degradation means to decompose bigger products into smaller products. So we can sum it up to mean that it is the degradation of large molecule to the smaller weight molecule in the presence or with the help of microorganisms. The biodegradation of plastics involves the action of sunlight or an extra cellular enzyme, which is transported from the microbial cell to the plastic by aqueous media. 3. 2 NON BIODEGRADABILITY OF POLYMERS
The one important question arises is why the polymers are not biodegradable? The solution to this is that the biodegradability of the polymers is based on the functionality of the monomers. In the bifunctional monomer consist of two binding sites at the extreme end of the chain, it produces a linear chain polymers. In such polymers, all the monomers are connected with another by covalent bonds. Various chains are also connected by the vander Wall’s forces of attraction. Some polymers have polyfunctinal groups, which combine to form three-dimensional network.
So many of the polymers have the strong forces of attraction which is very difficult to destroy and due to such forces these are not biodegradable. 3. 3 PRESENT SCENARIO In the today’s World if we see the present scenario then we can imagine that how much we are playing with our environment. We are using lots of tones of non-biodegradable plastics. If we see the consumption of the main leading countries of the world we can imagine that how much our environment gets polluted in a year. China generates about 16 million tones, India 4. million tones and the UK 1 million tones, of which more than 800,000 tones is waste polyethylene. Millions of tones of plastic waste, including refuse sacks, carrier bags and packaging, are buried in landfill sites around the world each year. Other disposal routes are possible for these materials, such as recycling and incineration, but as much of the waste plastic is mixed up with other materials in the domestic and industrial waste streams, separation is costly particularly for small items such as carrier bags. 3. 4 LIKELY SOLUTION
One solution that major leading countries are trying is to produce the biodegradable polymers which can create the revolution in the plastics industry. So the research work is going all over the world to get the biodegradable polymers, which would help better to stabilize the environment, not to harm it. The biodegradable polymers as well as degradation products must be environmentally compatible causing no deleterious effects on the environment. Biodegradables, only one option under consideration, will compete with recycling, incineration, pyrolysis, and burial.
Biodegradables may never develop into a major commercial opportunity in World. Biodegradable plastics could satisfy such niche markets as fast-food wrappers, agricultural films, personal hygiene products, and marine and freshwater applications. Water-soluble polymers could achieve much broader acceptance as expectations rise that the biodegradability of these water-soluble polymers, which are disposed of into the environment, will be mandated in a few years. 3. 5 POLYMER DEGRADATION The challenge posed to chemists and biochemists is to determine to what extent polymers biodegrade.
Several chemists, biochemists, polymer manufacturers and independent testing groups have taken up this challenge. However, there is some disagreement as to what constitutes a biodegradable polymer. Polymer manufacturers are willing to accept break down of a polymer structure into smaller fragments that still contain the polymer. Conversely, environmentalists will not stop short of complete degradation into the monomer units or mineralization into products usable by organisms. This conflict has created a need for a standard system for determining the degree to which polymers can biodegrade.
One proposed system includes the following: measuring physicomechanical changes (changes in morphology and physical properties), chemical changes and products formed, and weight loss. When comparing the degree to which different polymers biodegrade, several factors must be taken into consideration. The first of these factors is the environment. Polymers may be tested in a natural or simulated environment. Simulated testing environments can be normal or accelerated. These are utilized to determine whether the polymer begins to degrade following disposal or while it is still in its intended use.
The next aspect of biodegradable polymers, which is considered, is polymer concentration. The polymer may have a high or low mass weight compared to its volume. Finally, the environmental effects of the polymer must be considered. A polymer that biodegrades is of little value if the products that form are found to contaminate water supplies or be toxic to living organisms in the environment. 3. 6 TYPES OF DEGRADATION There are several different types of degradation that can occur in the environment. These include biodegradation, photo degradation, oxidation, and hydrolysis.
Often, lay people will lump all of these processes together and call them biodegradation. However, most chemists and biologists will agree that biodegradation involves enzymatically promoted break down caused by living organisms, usually microorganisms. The tests of biodegradable polymers are carried out in two types of environments: aerobic and anaerobic. The biodegradation that occurs in each is characterized by total carbon conservation. 3. 6. 1 Aerobic Degradation In this the larger molecules containing carbon are degraded into smaller atoms with the help of microorganism in the presence of air.
In this the total mass, which is converted and formed, is constant and the equation is given below. For the aerobic environment, the equation is the following: Ct = CO2 + H2O + Cr + Cb Where Ct is the total carbon contained in the polymer. Following biodegradation, the carbon from the polymer will appear in one of three end products: CO2, which is a product of the respiration of the micro-organisms; Cr which is any residue of the polymer that is left or any by-product that is formed; and Cb which is the biomass produced by the micro-organisms through reproduction and growth. 3. 6. 2 Anaerobic Degradation
In this also the larger molecules containing carbon are degraded into smaller atoms with the help of microorganism but in the absence of oxygen under the earth at higher atmosphere. This process takes very long time; it may take as much as even 100 years. In the case of anaerobic biodegradation, carbon dioxide, methane, and humus are the degradation products. For the anaerobic environment, the total carbon equation is the following:- Ct = CO2 + CH4 + H2O + Cr + Cb where Ct, Cr, and Cb represent the same forms of carbon as above. Since oxygen is not present, however, methane is also a possible product of anaerobic respiration. . 7 HOW DOES THE DEGRADATION PROCESS WORK The catalyst causes carbon-carbon bonds in the polyethylene backbone to be broken, reducing the molecular weight and durability of the material. Tests have shown a reduction in molecular weight from a quarter of a million to less than 4,000, at which point the material can be digested by microorganisms in the soil and water. The final products of the degradation process are simply carbon dioxide and water. The DCP additive is neither water soluble nor toxic, making the material safe for disposal in landfill sites such as the flushing bio-reactor systems that are widely used in the UK.
These systems introduce pressurized water flows into the layers of waste material, feeding oxygen and microorganisms down to the degrading rubbish. The material will also degrade under other conditions, not just in the composting-type conditions of a landfill site. Figure 1 shows the effect of photo and thermal degradation on a carrier bag made from the new polyethylene compared to standard plastic. The bag degrades to mulch in just 55 days. Extensive tests such as this one and tests on buried material were carried out on the new polyethylene to prove its degradability, including testing with Pira International. Figure 1. Photo and thermal degradation of polyethylene carry bags made from standard polyethylene (bottom) and biodegradable polyethylene (top). Pictures show (left to right) at 0, 30 and 55 days exposure. | 3. 8 DEVELOPMENT OF BIODEGRADABLE POLYMERS One group that utilizes this system of comparison is Larry Krupp and William Jewell at Cornell University in Ithaca, New York (3). Their study was conducted on thin films of various polymers that contained varying amounts of starch (Table I). In 1989, these polymers were claimed to be biodegradable by their respective manufacturers.
The bioreactors in this are made of cylindrical polyethylene tanks with gas-tight covers; the aerobic reactor containing aerobic microbes and the anaerobic containing anaerobic microbes. In each case, the microbes were fed a 1:1 mixture of a-cellulose and field dried, milled sorghum twice per week for 115 days to establish the bioreactors. The aerobic reactor was operated at 37o C with humid air supplied at a rate of l ft3/hr and recycled at 1. 6 ft3/min. for sufficient oxygen transfer. Biogas was collected in gas collection bags and analyzed twice per week for CO2 content and dissolved oxygen.
The anaerobic reactor was operated at 58o C with no intake of air. It was also equipped with biogas collection bags and analyzed twice per week for CO2 and CH4. Both reactors were analyzed twice per week for temperature, pH, ammonia nitrogen, and alkalinity. The conditions after which the bioreactors were operated were intended to provide accelerated, simulated environments that parallel those found in such disposal possibilities as landfills (anaerobic) and litter (aerobic). In the aerobic reactor, the amount of oxygen supplied to the reactor, used by the microbes, and dissolved in the air within the bioreactor are mportant factors for the determination of the amount of biodegradation. By knowing the amount of polymer that is being tested, one can determine the amount of oxygen needed by the microbes to break down the polymer. If this reaction proceeds to completion, then the amount of oxygen needed is known as the theoretical Biochemical Oxygen Demand (BOD). By analyzing the amount of carbon dioxide and oxygen, the percentage of theoretical BOD can be determined and thus the extent of biodegradation can be calculated. The films were placed in the aerobic and anaerobic reactors simultaneously for four weeks using a hot water bath as the control.
The tests mentioned above were conducted during this time, and following exposure to the bioreactors, the films were measured for mass lost. Polyethylene films that contained starch showed no evidence of anything other than biodegradation of the starch component. In addition, based upon mass loss, most of the materials tested were affected identically by the aerobic and anaerobic bacteria. The polyhydroxybutyrate and polyhydroxyvalerate (PHB/PHV) film readily biodegraded. After four weeks of exposure in the bioreactors, the film had a mass loss of 90-l00%. At the same time, little mass was lost after being exposed to the hot water bath.
In addition, the film exerted a BOD that was 61% of the theoretical BOD (compared to around 70% for the cellulose sorghum mixture). This study, along with others, points to some conclusions about the biodegradability of polymers. The first conclusion is that naturally occurring polymers biodegrade and chemically modified natural polymers may biodegrade depending on the extent of modification. Next, synthetic addition polymers, like those described in the beginning, with carbon as the only atom in the backbone do not biodegrade at molecular weights above 500.
If an addition polymer contains atoms other than carbon in the backbone, it may biodegrade depending on any attached functionality groups. Synthetic condensation polymers are generally biodegradable to different extents depending on chain coupling (ester > ether> amide > urethane), morphology (amorphous > crystalline), molecular weight (lower > higher), and hydrophilic is faster than hydrophobic. However, if a polymer is water soluble, that does not necessarily mean that it is biodegradable. Chapter 4 BIOPOLYMERS Biopolymers are a class of polymers produced by living organisms.
Starch, proteins and peptides, DNA, and RNA are all examples of biopolymers, in which the monomer units, respectively, are sugars, amino acids, and nucleotides. For many years, the use of natural polymers for the fabrication of packaging materials has been an interesting alternative to replace non-biodegradable polymers (polyethylene, polypropylene) which are normal components of these materials. The latter should not be used for short term packaging such as bags, agriculture mulching, bottles, and fast food goods. Natural polymers contribute to the decrease of waste coming from plastics.
Also, they increase the value of agriculture raw materials, thanks to the transformation industry of large cultural plants. These natural polymers are claimed to be biodegradable in their native state even if some of them such as lignin, have relatively long life time. The most used natural polymers are proteic, lipide and glucosic compounds: gelatin, collagen, casein, albumin, fibrinogen and elastine; oil and fats; cellulose and derivatives: cellophane, nitrocellulose, cellulose acetate or ether, starch. 3. 1 BIOPOLYMERS VERSUS POLYMERS
A major but defining difference between polymers and biopolymers can be found in their structures. Polymers, including biopolymers, are made of repetitive units called monomers. Biopolymers inherently have a well defined structure: The exact chemical composition and the sequence in which these units are arranged is called the primary structure. Many biopolymers spontaneously fold into characteristic compact shapes, which determine their biological functions and depend in a complicated way on their primary structures. Structural biology is the study of the structural properties of the biopolymers.
In contrast most synthetic polymers have much simpler and more random (or stochastic) structures. This fact leads to a molecular mass distribution that is missing in biopolymers. In fact, as their synthesis is controlled by a template directed process in most in vivo systems all biopolymers of a type (say one specific protein) are all alike: they all contain the same sequence and number of monomers and thus all have the same mass. This phenomenon is called monodispersity in contrast to the polydispersity encountered in synthetic polymers. As a result biopolymers have a polydispersity index of 1. . 2 BIOPOLYMERS AS MATERIALS Some biopolymers- such as polylactic acid, naturally occurring zein, and poly-3-hydroxybutyrate can be used as plastics, replacing the need for polystyrene or polyethylene based plastics. Some plastics are now referred to as being ‘degradable’, ‘oxy-degradable’ or ‘UV-degradable’. This means that they break down when exposed to light or air, but these plastics are still primarily (as much as 98 per cent) oil-based and are not currently certified as ‘biodegradable’ under the European Union directive on Packaging and Packaging Waste (94/62/EC).
Biopolymers, however, will break down and some are suitable for domestic composting. 3. 3 BIOPOLYMERS AS PACKAGING MATERIALS Biopolymers (also called renewable polymers) are produced from biomass for use in the packaging industry. Biomass comes from crops such as sugar beet, potatoes or wheat: when used to produce biopolymers, these are classified as non food crops. These can be converted in the following pathways: Sugar beet > Glyconic acid > Polyglonic acid
Starch > (fermentation) > Lactic acid > Polylactic acid (PLA) Biomass > (fermentation) > Bioethanol > Ethene > Polyethylene Many types of packaging can be made from biopolymers: food trays, blown starch pellets for shipping fragile goods, thin films for wrapping. 3. 4 PROPERTIES OF BIOPOLYMERS Biopolymers have the following useful properties which make them different from synthetic polymers. 3. 4. 1 Renewable, sustainable, and can be carbon neutral Biopolymers are renewable, because they are made from plant materials which can be grown year on year indefinitely. These plant materials come from gricultural non food crops. Therefore, the use of biopolymers would create a sustainable industry. In contrast, the feedstocks for polymers derived from petrochemicals will eventually run out. In addition, biopolymers have the potential to cut carbon emissions and reduce CO2 quantities in the atmosphere: this is because the CO2 released when they degrade can be reabsorbed by crops grown to replace them: this makes them close to carbon neutral. 3. 4. 2 Biodegradable and some are also compostable Some biopolymers are biodegradable: they are broken down into CO2 and water by microorganisms.
In addition, some of these biodegradable biopolymers are compostable: they can be put into an industrial composting process and will break down by 90% within 6 months. Biopolymers that do this can be marked with a ‘compostable’ symbol, under European Standard EN 13432 (2000). Packaging marked with this symbol can be put into industrial composting processes and will break down within 6 months (or less). An example of a compostable polymer is PLA film under 20? m thick: films which are thicker than that do not qualify as compostable, even though they are biodegradable.
A home composting logo may soon be established: this will enable consumers to dispose of packaging directly onto their own compost heap. The standards for such a home composting logo have not yet been developed. Chapter 5 STARCH 5. 1 ABOUT STARCH Starch is the major carbohydrate reserve in plant tubers and seed endosperm where it is found as granules, each typically containing several million amylopectin molecules accompanied by a much larger number of smaller amylose molecules. By far the largest source of starch is corn (maize) with other commonly used sources being wheat, potato, tapioca and rice.
Amylopectin (without amylose) can be isolated from ‘waxy’ maize starch whereas amylose (without amylopectin) is best isolated after specifically hydrolyzing the amylopectin with pullulanase . Genetic modification of starch crops has recently led to the development of starches with improved and targeted functionality. REPRENSTATIVE PARTIAL STRUCTURE OF AMYLOPECTIN Starch is an inexpensive and abundantly available natural resource, which decomposes very quickly in presence of water. Thus starch is commonly used for making biodegradable polymers.
Amylose and Amylopectin are the 2 forms of sucrose which have corresponding ? -1,4 and ? -1,6 linkages. These starch components acts as a useful element in the biodegradable polymers as these can be broken easily, that’s why starch is added to many polymers. STARCH MOLECULE ? -1,4 and ? -1,6 linkage 5. 2 CHARCTERISTICS OF STARCH BASED PLASTICS Sugar polymer can be linear or branched and are typically joined with glycosidic bonds. However, the exact placement of the linkage can vary and the orientation of the linking functional groups is also important, resulting in ? – and ? -glycosidic bonds.
In addition, many saccharide units can undergo various chemical modification, such as amination, and can even form parts of other molecules, such as glycoproteins.. The reason starch is added to the polymers is that some microorganisms utilize starch, a polymer of glucose, as a nutrient source and secrete enzymes to break it down for consumption. These enzymes act on the polymer, provided the polymer is able to be broken down. Starch is added to polymers in two basis ways. The first method of starch addition is the attachment of acrylic acid segments at various locations on the polymer chain.
The acid segments hydrogen bond with the starch, allowing the mixture of components. The second way starch is added is to graft a polyethylene molecule to a starch molecule. This grafted molecule readily reacts with pure polyethylene or starch to produce a copolymer. Starch has been used commercially as a biodegradable additive for polyethylene. Gelatinized starch, modified starch, oxidized polyethylene and dry granular starch has been used as fillers to improve the biodegradability of plastics.
One of the problems inherent in films prepared with dry granular starch and gelatinized starch is the reduction of mechanical properties because of the incompatibility between plastics and starch. Accordingly, starch granule has been chemically modified to overcome some of the incompatibility between hydrophobic plastics and hydrophilic starch. Chemical modification of starches could improve the interfacial contact between starch granule and polymer. The use of starch-filled degradable plastics has been increasing in many countries.
An example is the regulatory requirement in Korea to use for household waste. Unfortunately, starch-filled plastic bags are easily torn when garbage is put into the bag. Synthetic condensation polymers are generally biodegradable to different extents depending on chain coupling (ester > ether> amide > urethane), morphology (amorphous > crystalline), molecular weight (lower > higher), and hydrophilic is faster than hydrophobic. However, if a polymer is water soluble, that does not necessarily mean that it is biodegradable. 5. 3 EFFECT OF CROSSLINKING
Crosslinking of starch reinforces the granule by chemical bonds that act as bridges between molecules. Crosslinked starch maintains a higher viscosity and shows less viscosity breakdown. Crosslinking can prove to be a valuable tool for providing maximum film strength. Crosslinking of the starch can also modify the paste properties of the swollen granule, altering the texture and rheology of the paste. It can also reduce the sensitivity of the swollen granule paste to acidic conditions and shear force. Crosslinking can be utilized to improve the film forming properties of starch pastes.
Thus, crosslinked starches are used in the preparation of starch xanthates for water treatment ion exchangers, silt materials for micro-encapsulated coatings and anti-blocking agents for film in the food industry, textile industry and paper industry. Chapter 6 PHYSIOCHEMICAL PROPERTIES OF MODIFIED STARCH 6. 1 SWELLING POWER Swelling power is determined after heating the starch in excess water and is the ratio of the wet weight of the (sediment) gel formed to its dry weight. It will depend on the processing conditions (temperature, time, stirring, and centrifugation) and may be thought of as its water binding capacity.
A swelling power test was developed for selecting wheat suitable for the manufacture of Japanese white noodles. The test is rapid, uses less than 0. 4 g of sample and is applicable to starch, flour, whole meal or Quadrum at Junior flour samples. Swelling power values correlated significantly (P < 0. 01) with peak paste viscosity monitored on the Rapid Visco Analyser and with noodle eating quality. Paste viscosity of flour or starch is considered an important characteristic governing noodle quality. The swelling power test provides a suitable predictive method for identifying noodle quality wheat in the early stages of a breeding programme. . 2 SOLUBILITY Solubility is a characteristic physical property referring to the ability for a given substance, the solute, to dissolve in a solvent. It is measured in terms of the maximum amount of solute dissolved in a solvent at equilibrium. The resulting solution is called a saturated solution. Also, the equilibrium solubility can be exceeded under various conditions to give a so-called supersaturated solution, which is metastable. In a solution, the solvent is often a liquid, which can be a pure substance or a mixture. The species that dissolves (the solute) can be a gas, another liquid, or a solid.
Solubilities range widely, from infinitely soluble such as ethanol in water, to poorly soluble, such as silver chloride in water. The term insoluble is often applied to poorly soluble compounds, though strictly speaking there are very few cases where there is absolutely no material dissolved. The solubility of a solute is the maximum quantity of solute that can dissolve in a certain quantity of solvent or quantity of solution at a specified temperature. 6. 2. 1 Factors that affect solubility 6. 2. 1. 1 The nature of the solute and solvent — While only 1 gram of lead II) chloride can be dissolved in 100 grams of water at room temperature, 200 grams of zinc chloride can be dissolved. The great difference in the solubilities of the of these two substances is the the result of differences in their natures. 6. 2. 1. 2 Temperature — Generally, an increase in the temperature of the solution increases the solubility of a solid solute. A few solid solutes, however, are less soluble in warmer solutions. For all gases, solubility decreases as the temperature of the solution rises. 6. 2. 1. 3 Pressure — For solids and liquid solutes, changes in pressure have practically no effect on solubility.
For gaseous solutes, an increase in pressure increases solubility and a decrease in pressure decrease solubility. (When the cap on a bottle of soda pop is removed, pressure is released, and the gaseous solute bubbles out of solution. This escape of a gas from solution is called effervescence. ) 6. 2. 2 Factors determining rate of solution Rate of solution is a measure of how fast a substance dissolves. Some of the factors determining the rate of solution are: * | * Size of the particles | * | * Stirring | * | * Amount of solute already dissolved | | * Temperature 6. 3 DEGREE OF SUBSTITUTION DS is defined as the average number of sites per glucose unit that possess a substituent group. Starch esters having an intermediate DS of 0. 5-1. 8 are prepared in aq one step process by reacting starch with high treatment levels of organic acid anhydride and high concentration of alkaline reagent. 6. 4 LIGHT TRANSMITTANCE| Diagram of Beer-Lambert Law of transmittance of a beam of light as it travels through a cuvette of width l. Transmittance is the fraction of incident light at a specified wavelength that passes through a sample.
Where I0 is the intensity of the incident light and I is the intensity of the light coming out of the sample. The transmittance of a sample is sometimes given as a percentage. Transmittance is related to absorbance A as Or, using the natural logarithm From the above equation and the Beer-Lambert law, the transmittance is thus given by , Where ? is the attenuation coefficient and x is the path length. The term “transmission” refers to the physical process of light passing through a sample, whereas transmittance refers to the mathematical quantity. 6. 4. 1 Spectroscopy
Animation of the dispersion of light as it travels through a triangular prism Light Transmittance is measured by a Spectrometer. Spectrometry refers to when a spectroscopic technique is used to assess the concentration or amount of a given species. In those cases, the instrument that performs such measurements is a spectrometer or spectrograph. Spectroscopy/spectrometry is often used in physical and analytical chemistry for the identification of substances through the spectrum emitted from or absorbed by them. The type of spectroscopy depends on the physical quantity measured.
Normally, the quantity that is measured is intensity, either of energy absorbed or produced. 6. 5 WATER BINDING CAPACITY Hydration is a general term concerning the amount of bound water but it is poorly defined. Even what is meant by ‘bound’ is very difficult to explain exactly and has been defined ‘non-bulk’ water. Using a simplistic approach to polysaccharide hydration, water can be divided into ‘bound water’, subcategorized as being capable of freezing or not, and ‘unbound water’, subcategorized as being trapped or not. Unbound’ water freezes at the same temperature as normal water (< 0°C dependent on cooling rate). However some water may take up to 24 hr to freeze. ‘Bound freezable’ water freezes at a lower temperature than normal water, being easily supercooled. It also exhibits a reduced enthalpy of fusion (melting). Although the inability to freeze is often used to determine bound water, freezing may not be a good measure of hydration as it concerns the water content of the glassy state; not aqueous hydration. However alternative determinants of ‘bound’ water, such as the use of NMR are also problematic as NMR determines inding dynamics (rates of dissociation involving dissociation activation energy) rather than thermodynamics (free energy changes). 1. Bound water; divided into non-freezing and freezing. Unbound water; divided into trapped and bulk. 2. Bound water; divided into tightly bound (removed by freeze-drying) and loosely bound (removed by centrifugation). Unbound water (removed by filtration). In practical experience, the effects of water on polysaccharide and polysaccharide on water are complex and become even more complex in the presence of other materials, such as salts.
Water competes for hydrogen bonding sites with intramolecular and intermolecular hydrogen bonding, certainly will determine the carbohydrate’s flexibility and may determine the carbohydrate’s preferred conformation(s) There is a high entropic cost (up to about 20. 8 kJ mol-1 at 25°C for a totally ‘frozen’ molecule) when water is bound and this must be reclaimed, for example, by the formation of stronger or extra hydrogen bonds. Chapter 7 EXPERIMENTS 7. 1 PREPARATION OF ACETYLATED STARCH SAMPLES 7. 1. 1 Materials Starch (corn starch) used was made by Sukhjit Starch and Chemicals Limited, Phagwara (Punjab. . Acetic anhydride was purchased from High Media. Pyridine, Ethanol, potassium hydroxide, Hydrochloric acid, and phenolphthalein indicator used were all reagent grade chemicals made by S. D. Fine Chemicals Limited, Bombay. 7. 1. 2 Equipments Used Beakers, Conical flask, Burette, Three-necked round bottom flask equipped with mechanical stirrer, A Reflux condenser, Immersion thermometer, Oven and Petri-dish. 7. 1. 3 Chemicals Used * Native Starch * Acetic Anhydride * Pyridine * Iso Propanol * Methanol 7. 1. 4 Procedure
Starch esters of different DS were prepared by using different concentrations of acetic anhydride. In each case, 20 g of a dried starch was added to a reaction flask followed by 100 ml of pyridine and then the flask was heated to 900C for 2 h to pre-activate the starch. A reflux-condenser was also used to prevent the loss of organic liquid. After the pre activation for 2 h, the temperature was decreased to 75 0C and acetic anhydride was added drop-wise, and then the reaction was continued for a further 22 h to ensure equilibrium between the starch and the acetic anhydride.
After carrying out the reaction for the given time, the content in the reaction flask was coagulated by adding 100 ml of Iso Propanol. The product was filtered and washed with methanol three times. Finally, it was dried in an oven at 700C for 24 h. 7. 1 DETERMINATION OF ACETYL (%) & DEGREE OF SUBSTITUTION (DS) 7. 2. 1 Equipments Used Beakers, Conical flask, and Burette. 7. 2. 2 Chemicals Used * Powdered sample of starch acetate * 75% Ethanol * 0. 5 N KOH * 0. 5 N HCl * Phenolphthalein Indicator 7. 2. 3 Procedure DS is defined as the average number of sites per glucose unit that possess a substituent group. acetyl content and degree of substitution were determined by placing a dried sample of powdered starch acetate (1 g) in a 250 ml flask and 75% EtOH (50 ml) was added. The solution was stirred at 50 0C for 30 min, and cooled to room temperature, 0. 5 N KOH (40 ml) was added with swirling. The flask was stoppered and then allowed to stand 72 h with occasional swirling. The excess of alkali was back titrated with 0. 5 N hydrochloric acid using phenolphthalein as an indicator. The solution was allowed to stand 2 h. Then any additional alkali which might leach from the sample was titrated.
A blank was titrated in parallel. Blank and sample were titration volumes in millilitre, sample weight was in gram. 7. 2. 4 Calculations Where, Va is volume of HCl for blank in L. Vb is volume of HCl Macetyl is molecular wt = 43 g/mol. m = wt. of dry sample in g. 7. 2 DETERMINATION OF SWELLING POWER AND SOLUBILITY 7. 3. 1 Equipments Used Centrifuge Tubes, Water Bath, Centrifuge and Oven. 7. 3. 2 Procedure The value of swelling power and solubility for native starch and acetylated starches were determined according to the modified method described by Tsai, Li, and Lii (1997). 0. g of starch was weighed into centrifuge tube with cap to which 10 ml distilled water was added. Then the starch suspension was incubated in a water bath at different temperatures from 650C to 950C with a working churn and kept at constant temperature for an hour. Subsequently, the tube was cooled to room temperature. Then these tubes were centrifuged at 3000 r/min for 20 min. Precipitated paste was separated from supernatant and had been weighed (Wp). Both phases were dried at 105 °C for 24 h and the dry solids in precipitated paste (Wps) and supernatant (Ws) were calculated.
SP is the ratio of the weight of swollen starch granules after centrifugation (g) to their dry mass (g). 7. 3. 3 Calculations The SOL is the percentage of dry mass of solubles in supernatant (Ws) to the dry mass of whole starch sample (W0). 7. 3 LIGHT TRANSMITTANCE (%) 7. 4. 1 Equipments Used Water bath, Spectrophotometer and Refrigerator 7. 4. 2 Procedure The value of light transmittance (%) was measured by the method described by Craig et al. (1989). An aqueous suspension of starch (1%) was heated in a water bath at 90 0C for 1 h with constant stirring.
The starch suspension was cooled for 1 hr at 300C, and light transmittance was measured at 640 nm against a water blank in a spectrophotometer (La Motte smart single beam spectrophotometer, wave length 350 – 1000 Nm). The samples were stored for five days at 40C in a refrigerator and transmittance was measured at 640 nm every 24 h. 7. 5 DETERMINATION OF WATER BINDING CAPACITY 7. 5. 1 Equipments Used Conical flasks, Agitator and Centrifuge 7. 5. 2 Procedure The procedure described by Sugimoto et al. (1986) was used with slight modification. Starch (1. 0g) was added to 15ml distilled water in a conical flask.
The flask was agitated for 1hr, and then centrifuged for 15min. at 16000 rpm. The water was decanted and allowed to further drain for 10min and weighed. The amount of water held by the starch was determined. The binding capacity was calculated from the formula: Bound water (g) x 100/1. 0. Chapter 8 EXPERIMENTAL RESULTS Table 8. 1: Acetyl content (%) and degree of substitution (DS) of the native starch and Acetylated starch samples. Sample| Starch (g)| % acetic anhydried| Pyridine (ml)| % Acetyl content| DS| 1| 20| 0| 100| 00| 00| 2| 20| 0. 6| 100| 1. 935| 0. 074| 3| 20| 1. 5| 100| 13. 76| 0. 598| 4| 20| 2. 5| 100| 25. 5| 1. 256| 5| 20| 3. 5| 100| 27. 95| 1. 450| 6| 20| 5. 5| 100| 33. 75| 1. 8967| Table 8. 2: Swelling power of native starch and acetylated starch samples with 10 ml tubes. Sample| SP at 650C g/g| SP at 750C| SP at 850C| SP at 950C| NS| 3. 09| 11. 43| 11. 78| 12. 26| 1. 5% acetic anhydride| 4. 18| 10. 46| 11. 01| 11. 18| 2. 5% acetic anhydride| 4. 130| 4. 57| 5. 00| 5. 56| 3. 5% acetic anhydride| 4. 35| 4. 386| 4. 426| 5. 37| 5. 5% acetic anhydride| 3. 574| 3. 623| 4. 68| 3. 75| Table 8. 3: Solubility index of native starch and acetylated starch samples. Sample| SP at 650C g/g| SP at 750C| SP at 850C| SP at 950C| NS| 10. 6| 12. 07| 10. 47| 17. 58| 1. 5% acetic anhydride| 22. 18| 23. 07| 23. 27| 24. 57| 2. 5% acetic anhydride| 9. 21| 5. 12| 6. 54| 6. 33| 3. 5% acetic anhydride| 12. 85| 7. 89| 7. 887| 6. 92| 5. 5% acetic anhydride| 7. 94| 6. 29| 17. 20| 44. 50| Table 8. 4: Effect of acetylated anhydride levels on % light transmittance of corn starch. Sample| 0 Day| 1 day| 2nd day| 3rd day| 4th day| 5th day| 6th day| NS| 1. 3| 1. 1| 0. 9| 0. 8| 0. 7| 0. 6| 0. 6| 1. 5% acetic anhydride| 3. 4| 2. 2| 2. 2| 2. 1| 2. 1| 2. 0| 2. 0| 2. 5% acetic anhydride| 12. 8| 11. 4| 11. 25| 11. 25| 11. 20| 9. 5| 9. 4| 3. % acetic anhydride| 15. 4| 12. 2| 11. 7| 11. 6| 11. 20| 10. 9| 10. 8| 5. 5% acetic anhydride| 73. 6| 72. 4| 64. 7| 64. 1| 59. 1| 59. 0| 59. 0| Table 8. 5: Water binding capacity of native starch and acetylated starch samples. Sample| WBC of Acetic anhydried| NS| 89. 76| 1. 5% acyl| 139. 57| 2. 5% acyl| 104. 33| 3. 5% acyl| 116. 70| 5. 5% acyl| 89. 73| Chapter 9 DISCUSSION 9. 1 DEGREE OF SUBSTITUTION The starch esters with different DS were prepared by using different concentrations of acetic anhydride. The DS of starch esters were determined by using titration method and results are summarized in Table 8. . It was observed, acetyl content (%) and DS of acetylated starch progressively increased with the level of acetic anhydride under same reaction conditions. % acetyl content and DS varied from 1. 935 – 33. 75 % and 0. 074 to 1. 8967, respectively. 9. 2 PHYSIOCHEMICAL PROPERTIES 9. 2. 1 Swelling Power Swelling power of native and acetic acid modified starches were determined over the temperature range 65-95 0C. Results showed that the swelling power of native and acetylated starches increased with the increase in temperature from 65 0C to 95 0C.
The acetylated starch at low DS values (0. 334) showed higher swelling power than native starch. But at higher DS values, the swelling power values of acetylated starch samples decreased than native starch sample values. The value of swelling power was minimum for DS 1. 8967 at 65 0C. 9. 3 Solubility Solubilities of native and acetic acid modified starches were determined over the temperature range 65-95 0C. The solubilities of all the starches also increased with the increase in temperature and the value was maximum at 95 0C for all the starches. The solubility of starches with DS 1. 56 at temperature 75 0C was minimum among all the starches. 9. 4 Light transmittance (%) Light transmittance provides the information on the behavior of starch paste when light passes through it and depends upon the swollen and non swollen granule remnants. The influence of refrigerated storage days on paste clarity of native and acetylated starch samples are presented in table. The transmittance of all the suspensions of native and acetylated starches decreased with increase in storage period. 9. 5 Water – binding capacity (WBC) Water binding capacity is the amount of water held by the starch.
WBC of native and acetylated starches is shown in table 5. Two domains of hydration can be observed from the values. At low DS values, acetylated starch showed higher WBC values than their native starch. The value of WBC for native starch is 89. 76g/100g and increased to 139. 57 g/100g when starch was acylated with 1. 5% acetic anhydride. The value decreased with acylation of 2. 5% and 3. 5% butyric anhydride but still higher than native starch value. Results further showed that at higher values of DS the water binding capacity of acylated starch samples decreased than native starch.
Chapter 10 CONCLUSION The starch esters with different DS were prepared by using different concentrations of acetic anhydride. By comparison of physiochemical properties of the acetylated starch with that of native starch it was observed that acetyl content (%) and DS of acetylated starch progressively increased with the level of acetic anhydride under same reaction conditions. The acetylated starch at low DS values showed higher swelling power than native starch. But at higher DS values, the swelling power values of acetylated starch samples decreased than native starch sample values.
The solubilities of all the starches also increased with the increase in temperature and the value was maximum at 95 0C for all the starches. The transmittance of all the suspensions of native and acetylated starches decreased with increase in storage period. At low DS values, acetylated starch showed higher WBC values than their native starch. Results further showed that at higher values of DS the water binding capacity of acetylated starch samples decreased than native starch. Chapter 11 FUTURE SCENARIO OF BIODEGRADABLE POLYMERS
From the above discussion we can say that the future of biodegradable polymers is very bright. Natural polymers or synthetic polymers based on naturally occurring monomers look to be the best for future development. However, some work must be done before these polymers can take the place of the synthetic polymers now in use. The natural polymers now known often lack some of the properties that make current synthetic polymers so popular, such as water resistance and other physical properties in addition to the relatively low cost of synthetic polymer production.
Clearly there is some way to go before these new degradable materials gain a large enough share of the market to make a significant impact on the amount of waste plastic hanging around and therefore the space available in landfill sites. The latest example of use of biodegradable plastic on Government and Public scale is Sydney Olympics; 40 million articles were made from biodegradable polymers used for packing and food serving purposes. So from the above discussion we can come to the point that we are compromising with the environment for the use of non-biodegradable polymers.
To use the polymers we have to overcome the limitations of the present polymers, to make the environment safe and free. At present the public does not vastly accept the polymers which had been developed, so the community of scientists has to further put emphasis on the development of the biodegradable polymers. And one day will come when we will be totally using the biodegradable polymers and the whole world is waiting for that day. REFERENCES Characteristics of crosslinked potato starch and starch-filled linear low- density polyethylene films— Meera Kim, Suna-Ja Lee) * Biodegradation of 2-Hema-g-Na-PCMS a polymeric matrix synthesized from natural modified carbohydrates (Prashant D. Pandya, Nirmal K. Patel, and Vijay Kumar Sinha) * Polymer processing aid—A wonder product for extrusion techniques( Manoj M. Ghule) * Polymers: a new horizon in modern industry (Dr. S. Banerjee , Dr. P. K. Dutta) * Compatibilizers for polymer blends: A literature review(C. K. Nere & Dr.
R. N. Jagtap) * Biodegradable Polymers: Prospective and Promising Scenario(Samaresh Ghosh and Ajit K. Banthia) * Biodegradation in plastics: An overview (F. Yasmeen, D. P. Mishra, V. S. Kale, S. T. Mhaske) * Enzymatic degradation and deacetylation of native and acetylated starch-based extruded blends( Alain Copinet, Christophe Bliard, Jean Paul Onteniente and Yves Couturier) * www. sciencedirect. com/starch modification/acetic anhydride * www. google. co. in/plastics/biodegradable plastics * www. wikipedia. co. in/plastics/history
