It was like one of those days when you actually have done far better than you did, you go home and think, Kash.... but then it's a bit too late. After the efforts you give in .... u didnt fair well.... what do you do??? I promise myself to turn it around, no matter what!
Saturday, 26 November 2011
Tuesday, 15 November 2011
EFFECT OF POLYMERS ON MARINE ECO SYSTEM
EFFECT OF POLYMERS ON MARINE ECO SYSTEM
A project by:- Dhruv Sapra, B.Tech, Delhi Technological University aka Delhi College of engineering
EFFECT OF POLYMERS ON MARINE ECO SYSTEM
Introduction
Plastic materials have revolutionized the consumption of durable goods. The production and consumption of plastic is by increasing a factor of manifold. The plastics have numerous desirable properties for materials used in products ranging from different types of water bottles to numerous microprocessor packages. Synthetic polymers, commonly known as plastics, have been entering the marine environment in quantities paralleling their level of production over the last half century. However, in the last two decades of the 20th Century, the deposition rate accelerated past the rate of production, and plastics are now one of the most common and persistent pollutants in ocean waters and beaches worldwide.
Between 1960 and 2000, the world production of plastic resins increased 25-fold, while recovery of the material remained below 5%. Between 1970 and 2003, plastics became the fastest growing segment of the US municipal waste stream, increasing nine-fold, and marine litter is now 60-80% plastic, reaching 90-95% in some areas. While undoubtedly still an eyesore, plastic debris today is having significant harmful effects on marine biota. Albatross, fulmars, shearwaters and petrels mistake floating plastics for food, and many individuals of these species are affected; in fact, 44% of all seabird species are known to ingest plastic. Sea turtles ingest plastic bags, fishing line and other plastics, as do 26 species of cetaceans. In all, 267 species of marine organisms worldwide are known to have been affected by plastic debris, a number that will increase as smaller organisms are assessed. The number of fish, birds, and mammals that succumb each year to derelict fishing nets and lines in which they become entangled cannot be reliably known; but estimates are in the millions.
Plastic debris is categorized into two categories: macro, >5 mm and micro, <5 mm. While macro-debris may sometimes be traced to its origin by object identification or markings, micro-debris, consisting of particles of two main varieties, (1) fragments broken from larger objects, and (2) resin pellets and powders, the basic thermoplastic industry feedstock, are difficult to trace. Ingestion of plastic micro-debris by filter feeders at the base of the food web is known to occur, but has not been quantified. Ingestion of degraded plastic pellets and fragments raises toxicity concerns, since plastics are known to adsorb hydrophobic pollutants. The potential bioavailability of compounds added to plastics at the time of manufacture, as well as those adsorbed from the environment are complex issues that merit more widespread investigation. The physiological effects of any biological compounds desorbed from plastics by marine biota are being directly investigated, since it was found 20 years ago that the mass of ingested plastic in Great Shearwaters was positively correlated with PCBs in their fat and eggs. Colonization of plastic marine debris by sessile organisms provides a vector for transport of alien species in the ocean environment and may threaten marine biodiversity. There is also potential danger to marine ecosystems from the accumulation of plastic debris on the sea floor. The accumulation of such debris can inhibit gas exchange between the overlying waters and the pore waters of the sediments, and disrupt or smother inhabitants of the benthos. The extent of this problem and its effects have recently begun to be investigated. A little more than half of all thermoplastics will sink in seawater.[0]
How Plastics are entering into the marine ecosystem
Plastic materials have revolutionized the consumption of durable goods. The production and consumption of plastic is by increasing a factor of manifold. The plastics have numerous desirable properties for materials used in products ranging from different types of water bottles to numerous microprocessor packages. A plastic material can reach the marine ecosystem through various means whether it is fishing related activities or travellers dumping their wastes onto the beaches or through the river streams carrying plastic material.
No good estimate of the amount of plastic waste annually introduced into the marine environment is available. But, plastic waste results mainly from fishing-related activities, and from beaches. These days many fishing gears are being, made up of plastics, including nets, pots, and the traps.
Earlier, the fishing nets were made of natural materials like cloth or metal, even if the fisherman dumped their trash overboard or lost a net, it would sink to the bottom or biodegrade easily. But plastic nets used these days’ remains floating on the surface. The derelict fishing gear items pose an entanglement risk to marine species of all types. Designed to trap and catch marine life, derelict fishing gear debris continues to entangle and trap target and non- target organisms. Discarded fishing nets can continue to catch huge number of fishes.
Plastics which are used in packaging and in gear fabrication are mainly found on the surface of the seas and oceans. These are thrown during the fishing related activities as well as by the sailors.
Large streams also tend to transport excess plastic wastes to other areas creating a mobile contamination problem.
The consumer wastes found on the beaches are derived from the tourism activities on the beaches by various tourists.
Plastics can also reach the ocean through water disposal from plastic industries, plastic garbage from ships, landfills, and litter on the beaches. The plastics can stick to marine life and affect their breathing or swimming.
Plastic are often mistaken for food by marine animals (plastic bags look a lot like jelly fish) sea birds and even the ocean smallest feeders can be misled by tiny plastic fragments which are indistinguishable from plankton. Plastics can fill the digestive system of these animals causing them to starve. Small plastic fragments can be mistaken as food by fish or other sea life which can kill them by filling up or damaging their stomach or other digestive organs.
Plastic objects make it into the main sewer system, and the water treatment plants are carried by the excessive rain right out to the sea. In New York and New Jersey beaches in 1988, the medical wastes were floating up onshore. When heavy rains arrived , the litter accumulated on the streets and in storm sewers, were carried to the sea through combined sewers and were blown back onto the shores.
In our day to day life, we use several products such as face wash and perfumes etc. These products consists of micro plastics which can easily travel through the city wastewater facilities evading capture by filters due to the miniscule size and end up going straight into the ocean. These micro plastics are being ingested by planktonic organisms at the base of the food chain and are then pushed up to the higher levels of the food chain (such as micro plastics transferred to fur seals feeding on copepods).
The boaters and the mariners travel to various destinations around the globe using the sea route often discard their wastes into the sea.
The ocean also carries the litter or trash to many places through its currents and starts to concentrate the plastic waste on a particular area.
Plastic soda rings and the plastic pellets are often mistaken by sea turtles as authentic food. Clogging their intestines, missing out on vital nutrients, turtles starve to death.
The plastic waste taken as food by these marine animals enters their food chain and thus causing a relatively more adverse effect then usually thought. The new born child may have deformities since their birth or may die just after the birth. Seabirds mistake the pellets for fish eggs, small crab and the other prey, and sometimes even feeding the pellets to their young ones. Despite the fact that only 0.05% of plastic pieces from surface waters are pellets, they comprise about 70% of the plastics eaten by seabirds. These small plastic particles have been found in the stomachs of 63 of the world’s approximately 250 species of seabirds.
MAIN SOURCES OF POLLUTION: Introduction of different type of pollutants to the marine ecosystem can be mainly categorized as follows:
· Direct discharge
Pollutants enter rivers and the sea directly from urban sewerage and industrial waste discharges, sometimes in the form of hazardous and toxic wastes. Inland mining for copper, gold. etc., is another source of marine pollution. Most of the pollution is simply soil, which ends up in rivers flowing to the sea. However, some minerals discharged in the course of the mining can cause problems, such as copper, a common industrial pollutant, which can interfere with the life history and development of coral polyps.
· Land runoff
Surface runoff from farming, as well as urban runoff and runoff from the construction of roads, buildings, ports, channels, and harbors , can carry soil and particles laden with carbon, nitrogen, phosphorus, and minerals. This nutrient-rich water can cause fleshy algae and phytoplankton to thrive in coastal areas; known as algal blooms, which have the potential to create hypoxic conditions by using all available oxygen .Polluted runoff from roads and highways can be a significant source of water pollution in coastal areas.
· Ship pollution
Ships can pollute waterways and oceans in many ways. Oil spills can have devastating effects. While being toxic to marine life, polycyclic aromatic hydrocarbons (PAHs), the components in crude oil, are very difficult to clean up, and last for years in the sediment and marine environment. Discharge of cargo residues from bulk carriers can pollute ports, waterways and oceans. In many instances vessels intentionally discharge illegal wastes despite foreign and domestic regulation prohibiting such actions. It has been estimated that container ships lose over 10,000 containers at sea each year (usually during storms). Ships also create noise pollution that disturbs natural wildlife, and water from ballast tanks can spread harmful algae and other invasive species.
· Atmospheric pollution
Climate change is raising ocean temperatures and raising levels of carbon dioxide in the atmosphere. These rising levels of carbon dioxide are acidifying the oceans. This, in turn, is altering aquatic ecosystems and modifying fish distributions, with impacts on the sustainability of fisheries and the livelihoods of the communities that depend on them. Healthy ocean ecosystems are also important for the mitigation of climate change.
· Deep sea mining
Deep sea mining is a relatively new mineral retrieval process that takes place on the ocean floor. Ocean mining sites are usually around large areas of poly metallic nodules or active and extinct hydrothermal vents at about 1,400 - 3,700 meters below the ocean’s surface. The vents create sulfide deposits, which contain precious metals such as silver, gold, copper, manganese, cobalt, and zinc. The deposits are mined using either hydraulic pumps or bucket systems that take ore to the surface to be processed. As with all mining operations, deep sea mining raises questions about environmental damages to the surrounding areas.
Because deep sea mining is a relatively new field, the complete consequences of full scale mining operations are unknown. However, experts are certain that removal of parts of the sea floor will result in disturbances to the benthic layer, increased toxicity of the water column and sediment plumes from tailings. Removing parts of the sea floor disturbs the habitat of benthic organisms, possibly, depending on the type of mining and location, causing permanent disturbances. Aside from direct impact of mining the area, leakage, spills and corrosion would alter the mining area’s chemical makeup.
· Acidification
The oceans are normally a natural carbon sink, absorbing carbon dioxide from the atmosphere. Because the levels of atmospheric carbon dioxide are increasing, the oceans are becoming more acidic. The potential consequences of ocean acidification are not fully understood, but there are concerns that structures made of calcium carbonate may become vulnerable to dissolution, affecting corals and the ability of shellfish to form shells
· Eutrophication
Eutrophication is an increase in chemical nutrients, typically compounds containing nitrogen or phosphorus, in an ecosystem. It can result in an increase in the ecosystem's primary productivity(excessive plant growth and decay), and further effects including lack of oxygen and severe reductions in water quality, fish, and other animal populations. The biggest culprit are rivers that empty into the ocean, and with it the many chemicals used as fertilizers in agriculture as well as waste from livestock and humans. An excess of oxygen depleting chemicals in the water can lead to hypoxia and the creation of a dead zone.
· Plastic Debris
Marine debris is mainly discarded human rubbish which floats on, or is suspended in the ocean. The mass of plastic in the oceans may be as high as one hundred million metric tons. Discarded plastic bags, six pack rings and other forms of plastic waste which finish up in the ocean present dangers to wildlife and fisheries. Aquatic life can be threatened through entanglement, suffocation, and ingestion. Fishing nets, usually made of plastic, can be left or lost in the ocean by fishermen. Known as ghost nets, these entangle fish, dolphins, sea turtles, sharks, dugongs, crocodiles, seabirds, crabs, and other creatures, restricting movement, causing starvation, laceration and infection, and, in those that need to return to the surface to breathe, suffocation. Many animals that live on or in the sea consume flotsam by mistake, as it often looks similar to their natural prey.
Plastics accumulate because they don't biodegrade in the way many other substances do. They will photo degrade on exposure to the sun, but they do so properly only under dry conditions, and water inhibits this process. In marine environments, photo degraded plastic disintegrates into ever smaller pieces while remaining polymers, even down to the molecular level. When floating plastic particles photo degrade down to zooplankton sizes, jellyfish attempt to consume them, and in this way the plastic enters the ocean food chain. Many of these long-lasting pieces end up in the stomachs of marine birds and animals, including sea turtles, and black-footed albatross.
· Toxins
Apart from plastics, there are particular problems with other toxins that do not disintegrate rapidly in the marine environment. Examples of persistent toxins are PCBs, DDT, pesticides, furans, dioxins, phenols and radioactive waste. Heavy metals are metallic chemical elements that have a relatively high density and are toxic or poisonous at low concentrations. Examples are mercury, lead, nickel, arsenic and cadmium. Such toxins can accumulate in the tissues of many species of aquatic life in a process called bioaccumulation. They are also known to accumulate in benthic environments, such as estuaries and bay mud : a geological record of human activities of the last century.
· Noise
Marine life can be susceptible to noise or sound pollution from sources such as passing ships, oil exploration seismic surveys, and naval low-frequency active sonar. Sound travels more rapidly and over larger distances in the sea than in the atmosphere. Marine animals, such as cetaceans, often have weak eyesight, and live in a world largely defined by acoustic information. This applies also to many deeper sea fish, who live in a world of darkness. Noise also makes species communicate louder, which is called the Lombard vocal response. Whale songs are longer when submarine-detectors are on. If creatures don't "speak" loud enough, their voice can be masked by anthropogenic sounds. These unheard voices might be warnings, finding of prey, or preparations of net-bubbling. When one species begins speaking louder, it will mask other specie voices, causing the whole ecosystem to eventually speak louder.
Effect of plastics on the marine ecosystem
Beaches, Coast, Sea Floor, Shorelines
Sewage, toxic chemicals, pulp mill and manufacturing wastes, fertilizers, soaps, detergents, litter and refuse disposal, radioactive wastes, plastics, oil spills and leaks, runoff, and insecticides are contaminating our ocean and freshwater sources on a daily basis - far in excess of what the natural filtering and recycling systems can sustain. As some hazardous chemicals are banned worldwide and/or locally, many other new chemicals are developed that continue the harm. [1]
With large quantities of plastics, making their way into the shores and beaches, the plastic spill washing up the beaches is easily visible. On every beach found in the world, plastic debris can be found in one form or another. All over the world the statistics are ever growing, just staggeringly. Last year, an estimated 150,000 tons of marine plastic debris washed up onto the shores of Japan and 300 tons a day on India’s shores. [2]
The Hawaiian Archipelago, extending from the southernmost island of Hawaii 1,500 miles northwest to Kure Atoll, is among the longest and most remote island chains in the world. The 19 islands of the archipelago, including Midway atolls, receive massive quantities of plastic debris, shot out from the Pacific gyres. Some of the plastic litter is decades old. Some beaches are buried under 5 to 10 feet of plastic trash, while other beaches are riddled with “plastic sand,” millions of grain-like pieces of plastic that are practically impossible to clean up. One of the reasons marine debris accumulates in these islands is the movement of debris within the North Pacific Subtropical Convergence Zone (STCZ), as we have explained supra. [2]
Researchers Barnes and Milner (2005) list five studies which have shown increases in accumulation rates of debris on mid to high latitude coasts of the southern hemisphere. Surveys of shorelines around the world, reported by Greenpeace, have recorded the quantity of marine debris either as the number of items per km of shoreline or the number of items per square meter of shoreline. The highest values reported were for Indonesia (up to 29.1 items per m) and Sicily (up to 231 items per m). It’s been reported by Greenpeace that an estimated 70 percent of the mass of fragmented plastic present in the open oceans of the world does sink to the deep-sea bed. A limited body of literature exists, though, concerning these small to microscopic particles (micro debris) mirroring the little research addressed to marine litter on the sea floor. [2]
Ecosystem Changes
The changes inflicted on the ecosystem are another effect of the plastic tide that goes beyond visual is its potentiality to change entire ecosystems.
Plastic is not just an aesthetic problem. It can actually change entire ecosystems. Several documentations done in this field lead to the conclusion that: plastic debris which floats on the oceans, acts as rafts for small sea creatures to grow and travel on. This represents a potential threat for the marine environment should an alien species become established. It is postulated that the slow speed at which plastic debris crosses oceans makes it an ideal vehicle for this. The organisms have plenty of time to adapt to different water and climatic conditions. [2]
Coral Reefs
Derelict fishing gear can be destructive to coral reefs. Corals are in fact animals, even though they may exhibit some of the characteristics of plants and are often mistaken for rocks. In scientific classification, corals fall under the phylum Cnidaria and the class Anthozoa. They are relatives of jellyfish and anemones. [2]
Nets and lines become snagged on coral and subsequent wave action causes coral heads to break off at points where the debris was attached. Once freed, debris can again snag on more coral and the whole process is repeated. This cycle continues until the debris is removed or becomes weighted down with enough broken coral to sink. Eventually, derelict fishing gear may become incorporated into the reef structure. [2][3][4]
Plastic bags can kill coral by covering and suffocating them, or by blocking sunlight needed by the coral to survive. During 2001, so many plastic bags were regularly seen in the Gulf of Aqaba, off the coast of Jordan, that the Board of Aqaba Special Economic Zone issued a law banning the production, distribution, and trade of plastic bags within the areas under their jurisdiction [2].
A study on the biological impacts of marine debris on coral reefs in the Florida Keys’ reported that the most common debris in the area was hook and line gear and debris from lobster traps (It was predominantly these types of derelict fishing gear that caused damage to the reef. This debris was found to cause damage or mortality to many invertebrates including sponges and corals. As a consequence, it was suggested that the overall biological impacts from marine debris on the Florida Key reefs may be considerable. [3][5]
Economics
Marine litter cause serious economic losses to various sectors and authorities. Among the most seriously affected are coastal communities (increased expenditures for beach cleaning, public health and waste disposal), tourism (loss of income, bad publicity), shipping (costs associated with fouled propellers, damaged engines, litter removal and waste management in harbors), fishing (reduced and lost catch, damaged nets and other fishing gear, fouled propellers, contamination), fish farming and coastal agriculture. [2]
In a 2007 Fortune Magazine article about India, it was written that the costs of river pollution to the economy are enormous. Waterborne diseases are India’s leading cause of childhood mortality. Shreekant Gupta, a professor at the Delhi School of Economics who specializes in the environment, estimates that lost productivity from death and disease resulting from river pollution and other environmental damage is equivalent to about 4 percent of gross domestic product. [2]
Our Oceans and coastlines are under unprecedented plastics waste attack. It’s coming back at us in many ways. It’s a dire problem that only received serious scientific and public attention in the early 90’s, as we know, but all along the perpetrators have simply and clearly been identified. [2]
Case Study
One of the most hazardous of the environmental condition due to Marine Pollution is "Great Pacific Garbage Patch" which is discussed as below:
The Great Pacific Garbage Patch, also described as the Pacific Trash Vortex, is a gyre of marine litter in the central North Pacific Ocean located roughly between 135°W to 155°W and 35°N to 42°N. The patch extends over an indeterminate area, with estimates ranging very widely depending on the degree of plastic concentration used to define the affected area.
Figure: The Garbage Patch is located within the North Pacific Gyre, one of the five major oceanic gyres
The Patch is characterized by exceptionally high concentrations of pelagic plastics, chemical sludge, and other debris that have been trapped by the currents of the North Pacific Gyre. Despite its size and density, the patch is not visible from satellite photography, since it consists primarily of suspended particulates in the upper water column. Since plastics break down to ever smaller polymers, concentrations of submerged particles are not visible from space, nor do they appear as a continuous debris field. Instead, the patch is defined as an area in which the mass of plastic debris in the upper water column is significantly higher than average.
Discovery
The existence of the Great Pacific Garbage Patch was predicted in a 1988 paper published by the National Oceanic and Atmospheric Administration (NOAA) of the United States. The prediction was based on results obtained by several Alaska-based researchers between 1985 and 1988 that measured neustonic plastic in the North Pacific Ocean. This research found high concentrations of marine debris accumulating in regions governed by ocean currents. Extrapolating from findings in the Sea of Japan, the researchers hypothesized that similar conditions would occur in other parts of the Pacific where prevailing currents were favorable to the creation of relatively stable waters. They specifically indicated the North Pacific Gyre.
Charles J. Moore, returning home through the North Pacific Gyre after competing in the Transpac sailing race in 1997, came upon an enormous stretch of floating debris. Moore alerted the oceanographer Curtis Ebbesmeyer, who subsequently dubbed the region the "Eastern Garbage Patch" (EGP). The area is frequently featured in media reports as an exceptional example of marine pollution. Moore's claim of having discovered a large, visible debris field is, however, a mischaracterization of the polluted region overall, since it consists primarily of particles that are generally invisible to the naked eye.
Formation
It is thought that, like other areas of concentrated marine debris in the world's oceans, the Great Pacific Garbage Patch formed gradually as a result of marine pollution gathered by oceanic currents. The garbage patch occupies a large and relatively stationary region of the North Pacific Ocean bound by the North Pacific Gyre (a remote area commonly referred to as the horse latitudes). The gyre's rotational pattern draws in waste material from across the North Pacific Ocean, including coastal waters off North America and Japan. As material is captured in the currents, wind-driven surface currents gradually move floating debris toward the center, trapping it in the region.
Figure: The north Pacific Garbage Patch on a continuous ocean map
The size of the patch is unknown, as large items readily visible from a boat deck are uncommon. Most debris consists of small plastic particles suspended at or just below the surface, making it impossible to detect by aircraft or satellite. Instead, the size of the patch is determined by sampling. Estimates of size range from 700,000 square kilometres (270,000 sq mi) to more than 15,000,000 square kilometres (5,800,000 sq mi) (0.41% to 8.1% of the size of the Pacific Ocean), or, in some media reports, up to "twice the size of the continental United States".Such estimates, however, are conjectural based on the complexities of sampling and the need to assess findings against other areas.
Net-based surveys are less subjective than direct observations but are limited regarding the area that can be sampled (net apertures 1–2 m and ships typically have to slow down to deploy nets, requiring dedicated ship's time). The plastic debris sampled is determined by net mesh size, with similar mesh sizes required to make meaningful comparisons among studies. Floating debris typically is sampled with aneuston or manta trawl net lined with 0.33 mm mesh. Given the very high level of spatial clumping in marine litter, large numbers of net tows are required to adequately characterize the average abundance of litter at sea. Long-term changes in plastic meso-litter have been reported using surface net tows: in the North Pacific Subtropical Gyre in 1999, plastic abundance was 335 000 items km2 and 5.1 kg km2, roughly an order of magnitude greater than samples collected in the 1980s. Similar dramatic increases in plastic debris have been reported off Japan. However, caution is needed in interpreting such findings, because of the problems of extreme spatial heterogeneity, and the need to compare samples from equivalent water masses, which is to say that, if an examination of the same parcel of water a week apart is conducted, an order of magnitude change in plastic concentration could be observed.
Further, although the size of the patch is determined by a higher-than-normal degree of concentration of pelagic debris, there is no specific standard for determining the boundary between the "normal" and "elevated" levels of pollutants to provide a firm estimate of the affected area.
In August 2009, the Scripps Institution of Oceanography/Project Kaisei SEAPLEX survey mission of the Gyre found that plastic debris was present in 100 consecutive samples taken at varying depths and net sizes along a 1,700 miles (2,700 km) path through the patch. The survey also confirmed that, while the debris field does contain large pieces, it is on the whole made up of smaller items that increase in concentration toward the Gyre's centre, and these 'confetti-like' pieces are clearly visible just beneath the surface.
Sources of pollutants
There is strong scientific data concerning the origins of pelagic plastics. The figure that an estimated 80% of the garbage comes from land-based sources and 20% from ships is derived from an unsubstantiated estimate. Ship-generated pollution is a source of concern, since a typical 3,000-passenger cruise ship produces over eight tons of solid waste weekly, a major amount of which ends up in the patch, as most of the waste is organic Pollutants range in size from abandoned fishing nets to micro-pellets used in abrasive cleaners Currents carry debris from the west coast of North America to the gyre in about six years and debris from the east coast of Asia in a year or less. An international research project led by Dr. Hideshige Takada of Tokyo University studying plastic pellets, or nurdles, from beaches around the world may provide further clues about the origins of pelagic plastic.
Plastic photo degradation in the ocean
The Great Pacific Garbage Patch has one of the highest levels known of plastic particulate suspended in the upper water column. As a result, it is one of several oceanic regions where researchers have studied the effects and impact of plastic photo degradation in the neustonic layer of water.[20] Unlike debris, which biodegrades, the photo degraded plastic disintegrates into ever smaller pieces while remaining a polymer. This process continues down to the molecular level.
As the plastic flotsam photo degrades into smaller and smaller pieces, it concentrates in the upper water column. As it disintegrates, the plastic ultimately becomes small enough to be ingested by aquatic organisms that reside near the ocean's surface. Thus, plastic waste enters the food chain through its concentration in the neuston.
Some plastics decompose within a year of entering the water, leaching potentially toxic chemicals such as bisphenol A, PCBs, and derivatives of polystyrene.
Weight of plastics through water column
Charles Moore has estimated the mass of the Great Pacific Garbage Patch at 100 million tons.
Density of neustonic plastics
The patch is not a visibly dense field of floating debris. The process of disintegration means that the plastic particulate in much of the affected region is too small to be seen. In a 2001 study, researchers (including Charles Moore) found concentrations of plastic particles at 334,721 pieces per km2 with a mean mass of 5,114 grams (11.27 lbs) per km2, in the neuston. Assuming each particle of plastic averaged 5 mm x 5 mm, this would amount to only 8 m2 per km2 due to small particulates. Nonetheless, this represents a very high amount with respect to the overall ecology of the neuston. In many of the sampled areas, the overall concentration of plastics was seven times greater than the concentration of zooplankton. Samples collected at deeper points in the water column found much lower concentrations of plastic particles (primarily monofilament fishing line pieces).
Size and visibility
Although many media and advocacy reports have suggested that the patch extends over an area larger than the continental U.S., recent research sponsored by the National Science Foundation suggests the affected area may be twice the size of Hawaii,[25][26] while a recent study concluded that the patch might be smaller. This can be attributed to the fact that there is no specific standard for determining the boundary between the "normal" and "elevated" levels of pollutants and what constitutes being part of the patch. The size is determined by a higher-than-normal degree of concentration of pelagic debris in the water. Recent data collected from Pacific albatross populations suggest there may be two distinct zones of concentrated debris in the Pacific
The patch is not easily visible because it consists of very small pieces, almost invisible to the naked eye most of its contents are suspended beneath the surface of the ocean, and the relatively low density of the plastic debris at, in one scientific study, 5.1 kilograms of plastic per square kilometer of ocean area
Effect on wildlife
Some of these long-lasting plastics end up in the stomachs of marine birds and animals, and their young including sea turtles and the Black-footed Albatross. Besides the particles' danger to wildlife, the floating debris can absorb organic pollutants from seawater, including PCBs, DDT, and PAHs. Aside from toxic effects, when ingested, some of these are mistaken by the endocrine system as estradiol, causing hormone disruption in the affected animal. These toxin-containing plastic pieces are also eaten by jellyfish, which are then eaten by larger fish. Many of these fish are then consumed by humans, resulting in their ingestion of toxic chemicals. Marine plastics also facilitate the spread of invasive species that attach to floating plastic in one region and drift long distances to colonize other ecosystems
Research has shown that this plastic marine debris affects at least 267 species worldwide and a few of the 267 species reside in the North Pacific Gyre
Research and cleanup
Figure: Plastics-harvesting nets mounted on a vessel
In April 2008, Richard Sundance Owen, a building contractor and scuba dive instructor, formed the Environmental Cleanup Coalition to address the issue of North Pacific pollution. ECC collaborates with other groups to identify methods to safely remove plastic and persistent organic pollutants from the oceans.
The JUNK raft project was a trans-Pacific sailing voyage from June to August 2008 made to highlight the plastic in the patch, organized by the Algalita Marine Research Foundation.
Project Kaisei is a project to study and clean up the garbage patch launched in March 2009. In August 2009, two project vessels, the New Horizon and the Kaisei, embarked on a voyage to research the patch and determine the feasibility of commercial scale collection and recycling.[41]
The SEAPLEX expedition, a group of researchers from Scripps Institution of Oceanography, spent 19 days on the ocean in August, 2009 researching the patch. Their primary goal was to describe the abundance and distribution of plastic in the gyre in the most rigorous study to date. Researchers were also looking at the impact of plastic on mesopelagic fish, such as lantern fish. This group utilized a fully capable dedicated oceanographic research vessel, the 170 ft (52 m) long New Horizon
ADAPTATION AND MITIGATION :
Much anthropogenic pollution ends up in the ocean. The 2011 edition of the United Nations Environment Programme Year Book identifies as the main emerging environmental issues the loss to the oceans of massive amounts of phosphorus, "a valuable fertilizer needed to feed a growing global population", and the impact billions of pieces of plastic waste are having globally on the health of marine environments. Bjorn Jennssen (2003) notes in his article, “Anthropogenic pollution may reduce biodiversity and productivity of marine ecosystems, resulting in reduction and depletion of human marine food resources”. There are two ways the overall level of this pollution can be mitigated: either the human population is reduced, or a way is found to reduce the ecological footprint left behind by the average human. If the second way is not adopted, then the first way may be imposed as world ecosystems falter.
WHAT HAS BEEN OBSERVED SO FAR –
The scenario is as follows - Between 2000 to 2030 :
1) Global GHG increase by 25-90% with fossil fuel as dominant energy source.
2) Warming of 0.2°C per decade
3) Warming greatest over land & high Northern latitudes; least over Southern Ocean & parts of North Atlantic Ocean.
4)Contraction of snow cover, increase in thaw depth over most permafrost areas, decrease in sea ice extent, Arctic sea ice cover may disappear by late 21st century.
5)Increase of hot extremes, heat waves, heavy precipitation.
6)Increase in tropical cyclone intensity.
The Changing Ocean Environment:
Global warming should be called ocean warming, as more than 80% of the added heat resides in the ocean. Clear alterations to the ocean have already been detected from observations. The magnitude and patterns of these changes are consistent with an attribution to human activities and not explained by natural variability alone. Global average land and ocean surface temperatures increased at a rate of about 0.2°C/decade over the last few decades (Hansen et al., 2006), and ocean temperatures down to 3000 m (10,000 feet) depth are also on the rise. Averages rates of sea-level rise over the last several decades were 1.8±0.5 mm/y, with an even larger rate (3.1±0.7 mm/y) over the most recent decade. Higher precipitation rates are observed at mid to high latitude and lower rates in the tropics and subtropics. Corresponding changes have been measured in surface water salinities. One of the most striking trends is the decline in Arctic sea-ice extent, particularly over the summer. September Arctic ice-cover from 2002-2006 was 18% lower than pre-1980 ice-cover (http://www.arctic.noaa.gov/detect/ice-seaice.shtml), and some models predict near ice-free conditions by 2040. Recent studies of the Greenland ice sheet highlight an alarming increase in surface melting over the summer, and percolation of that melt water to the base of the ice sheet where the melt-water could lubricate ice flow and potentially greatly accelerate ice loss and sea-level rise. These new findings have not been full incorporated into projected sea-level rise estimates, which thus may be underestimated.
Over half of human carbon dioxide emissions to the atmosphere are absorbed by the ocean and land biospheres (Sarmiento and Gruber, 2002), and the excess carbon absorbed by the ocean results in increased ocean acidity. The physical and chemical mechanisms by which this occurs are well understood. Once carbon dioxide enters the ocean, it combines with water to form carbonic acid and a series of acid-base products, resulting in a lowering of pH values. The amount and distribution of human-generated carbon in the oceans are well determined from an international ocean survey conducted in the late 1980s and early 1990s. The rate of ocean carbon uptake is controlled by ocean circulation. Most of the excess carbon is found in the upper few hundred meters of the ocean (upper 1200 feet) and in high-latitude regions, where cold dense waters sink into the deep ocean. Surface water pH values have already dropped by about 0.1 pH units from preindustrial levels and are expected to drop by additional 0.14-0.35 units by the end of the 21st century.
ADAPTATION IN MARINE ECOSYSTEMS
Vulnerability to climate change is determined by economic, social and environmental factors. Resilience of the marine ecosystems likely to be exceeded by combination of climate change, associated disturbances (eg. ocean acidification) & other global change drivers (eg. pollution) -- species extinction -- coral bleaching -- decrease in primary productivity; -- Arctic & small island communities have increased vulnerability.
Adaptation (activities to reduce impacts of climate change) can reduce vulnerability. Adaptive capacity is related to social & economic development but unevenly distributed across societies.
Climate Adaptation, Mitigation, and Ocean Management
Mitigation is the Management of Ecosystem Resources reduce emissions, climate change impacts & biodiversity loss. Given the potential for significant negative impacts of climate change and ocean acidification on living marine resources, we need to develop comprehensive local, national and international ocean management strategies that fully incorporate climate change and acidification trends and uncertainties. The strategies should follow a precautionary approach that accounts for the fact that ocean biological thresholds are unknown. The strategies should include improved scientific information for decision support, adaptation to reduce negative climate change and acidification impacts, and mitigation to decrease the magnitude of future climate change and acidification.
Currently the United States and other countries invest significant resources in monitoring the ocean and improving scientific understanding on many of the physical, chemical and biological processes relevant to climate change and acidification. However, this wealth of data and information is typically not in a form that is easily accessible by ocean resource managers and other stakeholders, ranging from private citizens and small-businesses to large corporations, NGOs and national governments. For example, even state-of-the-art climate projections typically resolve climate patterns at relatively coarse spatial resolutions and include either relatively simple ocean biology or no ocean biology at all. In contrast, decision makers need information tailored to specific local fisheries and ecosystems. The national climate modelling centres should be encouraged to create on a routine basis targeted ocean biological-physical forecasts on seasonal to decadal time-scales, building on nested regional models, probabilistic and ensemble modelling of uncertainties, and downscaling methods developed for related applications (e.g., agriculture, water-resources). The utility of such forecasts and their uncertainties will be maximized if stakeholders are involved in their design from the onset and if the model results are translated into more accessible electronic forms that are widely distributed to the public.
A second challenge is to create more adaptive ocean management strategies that emphasize complete and transparent discussion on the risks and uncertainties from climate change and ocean acidification. Some amount of climate change and acidification is unavoidable because of past greenhouse emissions, and even under relatively optimistic scenarios for the future, substantial further ocean impacts should be expected at least through mid-century and beyond. Decisions will need to be made in the face of uncertainty, relying on for example the precautionary principle to limit future risk.
Climate change trends are growing in magnitude, but will still be gradual compared with natural interannual variability; management policies must include both types of variations and uncertainties. Empirical approaches developed from historical data cannot be used in isolation because climate change will shift the baseline for ocean biological systems. Serious efforts should be directed at reducing other human factors such as overfishing and habitat destruction to allow more time ecosystems and social systems to adapt. Mechanisms such as marine reserves, that protect specified geographical locations, need to account for the fact that ecosystem boundaries will shift under climate change. Procedures also need to be in place to monitor over time the effectiveness of ocean conservation and management policies, and that information and improved future climate forecasts should be used to modify and adapt management approaches.
The third challenge is to pursue climate mitigation approaches that limit the emissions of carbon dioxide and other greenhouse gases to the atmosphere or that remove fossil-fuel carbon dioxide that is already in the atmosphere. Stabilizing future atmospheric carbon dioxide at moderate levels to minimize climate change impacts will require a mix of approaches, and no single mechanism will solve the entire problem. Emissions of carbon dioxide can be reduced through energy conservation and transition to alternative, non-fossil fuel based energy sources (wind, solar, nuclear, biofuels). Attention also needs to be placed in the near-term on limiting other greenhouse gases such as chlorofluorocarbons, which may provide additional time to tackle the more challenging issues associated with carbon. Progress is being made on approaches that would remove carbon dioxide at power plants so that it can be sequestered in subsurface geological reservoirs (e.g., old oil and gas fields, salt domes).
Mitigation approaches have also been proposed using ocean biology, but these methods should only be pursued if critical questions are resolved on their effectiveness and environmental consequences. Biological mitigation strategies are based on the fact that plants and some marine microbes naturally convert carbon dioxide into organic matter during photosynthesis. Enhancing biological carbon removal can reduce atmospheric carbon dioxide if the additional organic matter is stored away from the atmosphere for multiple decades to a century or longer. The deep-ocean is one such reservoir because it exchanges only slowly with the surface and atmosphere.
Thus one potential mitigation method would be to fertilize the surface ocean phytoplankton so that they produce and export more organic carbon into the deep ocean. In many areas of the ocean, phytoplankton grow is limited by the trace element iron, which is very low in surface waters away from continents and dust sources. About a dozen scientific experiments have been conducted successfully showing that adding iron to the surface ocean causes a phytoplankton bloom and temporary drawdown in surface water carbon dioxide. But there remain outstanding scientific questions about whether iron resulted in any enhanced long-term carbon storage in the ocean.
As with any other mitigation approach on land or in the sea, the scientific and policy communities need to work closely to assure that the following questions are answered for large-scale commercial ocean fertilization. Is the method effective in removing carbon from the atmosphere, can the removal be validated, and how long will it remain sequestered? Could the method result in unintended consequences such as enhanced emissions of other, more powerful greenhouse gases (in the case of iron fertilization potentially nitrous oxide and perhaps methane)? What are the broad ecological consequences, and could carbon mitigation efforts conflict with maintaining living marine resources and fisheries? Systematic approaches to verify effectiveness and environmental impacts need to be put in place to assure a level playing field for commercial mitigation and carbon credit trading systems.
Conclusion
As we have studied various aspects of the problem of Marine pollution due to plastics, and given the condition we are in, and studying the pattern while predicting the future, we have realized the damage done to the greatest physical resource on the earth, the oceans , these actions cannot be reversed but the ways in present can be mended to weave a better tomorrow, formulation of related laws by the government and the related authorities, better resource management, improved recycling, finding alternatives to synthetic non biodegradable polymer waste, maximum utilization by prolonging usability of polymers and taking a moral responsibility as individuals, that are a few ways to make up for the harm that we have already done.
References
I. [0] Source: Algalita Marine Research Foundation, 148 N. Marina Drive, Long Beach, CA 90803, USA. cmoore@algalita.org
II. Source for "How plastics are entering the marine ecosystem?" is from the following links(25-10-2010):
· http://www.plasticdebris.org/
· http://saveourseas.com/threats/pollution
· http://www.brighthub.com/engineering/marine/articles/37397.aspx
· http://marinedebris.noaa.gov/info/plasticdet.html
· http://www.buzzle.com/articles/effects-of-plastic-pollution.html
· http://www.lurj.org/article.php/vol3n2/plastic.xml
· http://conference.plasticdebris.org/whitepapers/Anthony_Andrady.doc
· http://www.whoi.edu/science/B/people/kamaral/plasticsarticle.html
III. "Main sources of pollution" is studied from Wikipedia article on "marine pollution" dated 25th october,2011
IV. Mitigation and adaptation is sourced from :(date-1st November 2011) http://en.wikipedia.org/wiki/Adaptation_to_global_warming
V. REFERENCES for Effect of plastics on the marine ecosystem:
[1]. http://www.eco-pros.com/humanimpact.htm as on 25 October 2011.
[2]. http://coastalcare.org/2009/11/plastic-pollution/ as on 25 October 2011.
[3].http://www.unep.org/regionalseas/marinelitter/publications/docs/plastic_ocean_report.pdf. as on 25 October 2011.
[4]. NOACC, 2005.
[5]. Chiappone (et al. 2002).
VI. The article on Great Pacific Garbage Patch is sourced from Wikipedia dated 2nd November 2011
POLYMERISATION IN HETEROGENEOUS SYSTEMS
POLYMERISATION
IN
HETEROGENEOUS
SYSTEMS
-Dhruv Sapra , B.Tech, Delhi Technological university
POLYMERISATION IN HETEROGENEOUS SYSTEMS
Introduction
Polymerization is a process of reacting monomer molecules together in a chemical reaction to form three-dimensional networks or polymer chains. There are many forms of polymerization and different systems exist to categorize them. During the lectures in the class we discussed the various forms of polymerization and studied it's kinetics, with the assumption of pure monomers or we considered just simple solutions of monomer and polymer in a solvent. But certain other types of polymerizing systems are of great interest interests because they offer practical advantages in industrial applications. The polymer systems are broadly divided as Homogeneous and Heterogeneous for the purpose of their study on the basis of the phase in which the monomer and the polymer exists.
The homogeneous polymerization techniques involve pure monomer or homogeneous solutions of monomer and polymer is a solvent. There are two such systems:
· Bulk system:
Polymerization in bulk, perhaps the most obvious method of synthesis of polymers, is widely practiced in the manufacture of condensation polymers, where the reactions are only mildly exothermic, and most of the reaction occurs when the viscosity of the mixture is still low enough to allow ready mixing, heat transfer, and bubble elimination. Control of such polymerizations is relatively easy.
Bulk polymerization of vinyl monomers is more difficult, since the reactions are highly exothermic and, with the usual thermally decomposed initiators, proceed at a rate that is strongly dependent on temperature This, coupled with the problem in heat transfer incurred because viscosity increases early in the reaction, leads to
difficulty in control and a tendency to the development of localized "hot spots" and "runaways" " Except in the preparation of castings, for example, of poly(methy1 methacrylate), bulk polymerization is seldom used commercially for the manufacture of vinyl polymers.
Some of polymers prepared using Bulk polymerization are:
Polycaproamide (Nylon 6), LDPE, PET
· Solution system:
Polymerization of vinyl monomers in solution is advantageous from the standpoint of' heat removal (e..g., by allowing the solvent to reflux) and control, but has two potential disadvantages. First, the solvent must be selected with care to avoid chain transfer and, second, the polymer should preferably be utilized in solution, as in the case of poly(viny1 acetate) to be converted to poly(viny1 alcohol) and some acrylic ester finishes, since the complete removal of solvent from a polymer is often difficult to the point of impracticality, and is indeed a very expensive affair commercially.
Some of polymers prepared using Solution polymerization are:
HDPE, Polypropylene, Polystyrene, poly (acrylic acid), polyacrylamide
Heterogeneous polymerization techniques involve heterogeneous solutions of monomer and polymer in a solvent. These systems can be either emulsions, dispersions, suspensions or interfacial. Let us now discuss each of these polymerizations in detail.
Polymerization from Gaseous Monomers
The polymerization of gaseous monomers can take place with the formation of a liquid phase (polymer melt) or a solid polymer. In each case the polymerization of ethylene provides the most important industrial example.
The high-pressure polymerization of ethylene to branched polyethylene takes place by a free-radical mechanism in the presence of a liquid phase, at temperatures above the melting point of the polymer.. The polymerization is carried only to low conversion, with the remaining ethylene recovered when the pressure is lowered and recycled.
The low-pressure polymerization of' ethylene to linear polyethylene takes place by coordination polymerization using a catalyst suspended in gaseous ethylene in a fluid-bed reactor. The ethylene polymerizes to the solid phase, with the small amount of the catalyst required remaining in the solid polymer.
If the polymerization takes place with the formation of the solid polymer, then due to the solid-gas interface, it becomes an example of Interfacial polymerization.
Some of the polymers that undergo this polymerization include:
Polyethylene, Polypropylene
Emulsion Polymerization
Emulsion polymerization is a type of radical polymerization that usually starts with an emulsion incorporating solvent(usually water), monomer, initiator, and surfactant. These latex particles are typically 100 nm in size, and are made of many individual polymer chains.
Process
· the monomer has only a very limited (but finite) solubility in the
solvent (e.g. styrene in water). Most of it is present initially in
dispersed droplets (hence the term “emulsion” polymerisation); one
role of the (anionic) surfactant is to help stabilise these droplets, by
adsorbing at the droplet / water interface. However, some of the
monomer is present in the water phase – this is important !
Schematic diagram of emulsion polymerization
· the surfactant is present at a concentration > its c.m.c. that is critical micelles concentration(at the reaction temperature). Therefore, most of it is present as micelles,
again in the water phase.
Note: some of the monomer will be solubilized in the micelles – also important !
thus the monomer is actually distributed in 3 locations :
droplets > aqueous solution (small amount) > micelles [1]
· the initiator is soluble (and therefore present) in the water phase. The initial locus of polymerisation is, therefore, again in the aqueous solution (as in dispersion polymerisation), i.e. that is the first monomer to polymerise.
"Redox" Initiation
The decomposition of peroxide-type initiators in aqueous systems is greatly accelerated by the presence of a reducing agent. This acceleration allows the attainment of high rates of radical formation at low temperatures in emulsion systems.
A typical redox system is that of ferrous iron and hydrogen peroxide In the absence of a polymerizable monomer the peroxide decomposes to free radicals as follows:
Another widely used peroxide-type initiator is the persulfate ion. With a reducing agent R the reaction is
The reducing agent is often the thiosulfate ion,
or the bisulfite ion,
Many other redox initiator systems have been used.
· The growing, oligomeric free-radical chains, e.g. 2-SO4Am ·, beyond a certain value of m (typically 5 to 10), will co-micellise in with the existing micelles from the added anionic surfactant. The primary locus of polymerisation now switches to the micelles, where the
solubilised monomer can now begin to polymerise.
· as polymerisation (in the micelles) continues, particles form, as in dispersion polymerisation, and the distribution of monomer, as represented by the sequence labelled [1] above, is gradually pulled to the right. Polymerisation continues in the growing particles until all the monomer in the droplets and free solution is exhausted.
· the size of the final particles is controlled by the number of micelles present (i.e. the initial surfactant concentration); this is much greater than in dispersion polymerisation – hence the smaller particles.
Smith-Ewart Kinetics
(Smith 1948a,b).. In an ideal emulsion system, free radicals are generated in the aqueous phase at a rate of about lO-I3 per cubic centimeter per second. There are about lOI4 polymer particles per cubic centimeter. Simple calculations show that termination of the free radicals in the aqueous phase is negligible and that diffusion currents are adequate for the rapid diffusion of free radicals into the polymer particles-on the average, about one per particle every 10 sec It can also be calculated from the known termination rate constants that two free radicals within the same polymer particle would mutually terminate within a few thousandths of a second. Therefore each polymer particle must contain most of the time either one or no free radicals. At any time half of the particles (on the average) contain one free radical, the other half none.. The rate of polymerization per cubic centimeter of emulsion is
where N is the number of polymer particles per cubic centimeter. Since the monomer concentration is approximately constant, the rate depends principally on the number of particles present and not on the rate of generation of radicals.
The degree of polymerization also depends upon the number of' particles:
where p is the rate of generation of radicals. Unlike Vp, Xn is a function of the rate of free-radical formation. In bulk polymerization rate can be increased only by increasing the rate of initiation; this, however, causes a decrease in the degree of polymerization In emulsion polymerization the rate may be increased by increasing the number of polymer particles If the rate of initiation is kept constant, the degree of polymerization increases rather than decreases as the rate rises Since the number of polymer particles is determined by the number of soap micelles initially present, both rate and molecular weight increase with increasing soap concentration. The Smith-Ewart kinetics require that
where [E] is the soap or emulsifier concentration.
Deviations from Smith - Ewart kinetics
The above kinetic scheme is highly idealized, though valuable for its simplicity. It explains adequately only a small portion of the vast literature on emulsion polymerization, though it works well for monomers such as styrene, butadiene, and isoprene, whose water solubility is very low, less than 0.1%. Among the circumstances under which the Smith-Ewart kinetics fails to apply quantitatively are the following:
a. Larger particles (>O 1 - 0 15 km in diameter), which can accommodate more than one growing chain simultaneously
b. Monomers with higher water solubility (1--lo%), such as vinyl chloride, methyl methacrylate, vinyl acetate, and methyl acrylate Here initiation in the aqueous phase, followed by precipitation of polymer, becomes important. These particles may absorb emulsifier, decreasing [E] and thus N, or they may serve as sites for polymerization, increasing N.
c. Chain transfer to emulsifier This often takes place in large enough amount to suggest that growing chains are localized near the surfaces of the particles, where the soap exists.
Inverse emulsion systems
Emulsion polymerization can also be carried out in systems using an aqueous solution of a hydrophilic monomer, such as acrylic acid or acrylamide, emulsified in a continuous oil phase using an appropriate water-in-oil emulsifier Either oil- or water-soluble initiators can be used The mechanism seems to be that of normal emulsion polymerization, but the emulsions are often less stable.
Mini Emulsion systems
A miniemulsion is a special case of emulsion. A miniemulsion is obtained by shearing a mixture comprising two immiscible liquid phases, one surfactant and one co-surfactant (typical examples are hexadecane or acetyl alcohol).
The shearing proceeds usually via ultrasonication of the mixture or with a high-pressure homogenizer, which are high-shearing processes.
Stable droplets are then obtained, which have typically a size between 50 and 500 nm. The miniemulsion process is therefore particularly adapted for the generation of nano-materials. There is a fundamental difference between traditional emulsion polymerisation and a miniemulsion polymerisation.
Advantages of emulsion polymerization include:
§ High molecular weight polymers can be made at fast polymerization rates. By contrast, in bulk and solution free radical polymerization, there is a tradeoff between molecular weight and polymerization rate.
§ The continuous water phase is an excellent conductor of heat and allows the heat to be removed from the system, allowing many reaction methods to increase their rate.
§ Since polymer molecules are contained within the particles, viscosity remains close to that of water and is not dependent on molecular weight.
§ The final product can be used as is and does not generally need to be altered or processed.
Disadvantages of emulsion polymerization include:
§ Surfactants and other polymerization adjuvant remain in the polymer or are difficult to remove
§ For dry (isolated) polymers, water removal is an energy-intensive process
§ Emulsion polymerizations are usually designed to operate at high conversion of monomer to polymer. This can result in significant chain transfer to polymer.
§ Cannot be used for condensation, ionic or Ziegler-Natta polymerization usually.
Polymers produced by emulsion polymerization can be divided into three rough categories.
§ Synthetic rubber
§ Some grades of styrene-butadiene (SBR)
§ Some grades of Polybutadiene
§ Fluoroelastomer (FKM)
§ Plastics
§ Some grades of PVC
§ Some grades of polystyrene
§ Some grades of PMMA
§ Acrylonitrile-butadiene-styrene terpolymer (ABS)
§ PTFE
§ Dispersions (i.e. polymers sold as aqueous dispersions)
§ polyvinyl acetate copolymers
§ Styrene-butadiene
§ VAE (vinyl acetate - ethylene copolymers)
Suspension Polymerization
Suspension polymerization (also known as pearl polymerization, bead polymerization and granular polymerization) is a polymerization process that uses mechanical agitation to mix the monomer or mixture of monomers in a liquid phase such as water, polymerizing the monomer droplets while they are dispersed by continuous agitation. This process is used in the production of most PVC, a widely used plastic, as well as Sodium polyacrylate, a superabsorbent polymer used in disposable diapers.
Suspension polymerization consists of an aqueous system with monomer as a dispersed phase and results in polymer as a dispersed solid phase.
Method:
A reactor fitted with a mechanical agitator is charged with a water insoluble monomer and initiator (+ a chain-transfer agent to control molecular weight).
Droplets of monomer (containing the initiator and chain-transfer agent) are formed (50 – 200 µm). These sticky droplets are prevented by the addition of a protective colloid (PVA). Near the end of polymerization, the particles are hardened, are then recovered by filtration, and followed by washing step.
Advantages:
• Excellent heat transfer because of the presence of the solvent.
• Solvent cost and recovery operation are cheap.
Disadvantages:
• Contamination by the presence of suspension and other additives low polymer purity.
• Reactor cost may higher than the solution cost.
E.g. PVC, PSAN, Poly (vinylidene chloride –VC)
Precipitation Polymerization
In the preparation of a polymer insoluble in its monomer, or in polymerization in the presence of a non solvent for the polymer, marked deviations from the kinetics of homogeneous radical polymerization may occur. The normal bimolecular termination reaction is not effective, as the result of trapping or occlusion of radicals in the un swollen, tightly coiled precipitating polymer. The theory has been confirmed by the demonstration of the presence of radicals in the polymer both by chemical methods and by electron paramagnetic resonance. The lifetime of the trapped radicals is many hours at room temperature, and if polymer containing such radicals is heated in the presence of monomer to a temperature where the mobility of the radicals is increased, extremely rapid polymerization takes place
Kinetics
The polymerization of vinyl chloride in bulk or in the presence of a non solvent (Mickley 1962) follows a rate equation of the form
where the first term inside the braces arises from the normal rate equation for polymerization in the homogeneous liquid phase, and the second term represents the increment in rate due to polymerization in the precipitated polymer particles.
The function f (P) is proportional to the polymer concentration [PI at low conversion and to [P]2/3 at later times. Radical occlusion occurs, but the depth of radical penetration into the polymer particles is small, limiting radical activity to thin surface layers in larger particles present at higher conversions Termination occurs primarily in the liquid phase, probably as a result of transfer to monomer within the polymer particles, and subsequent diffusion of the monomer radicals to the liquid phase In contrast, transfer to monomer in the polymerization of acrylonitrile is so slow that permanent radical occlusion occurs.
Advantages
1) It requires more temperature and heat control.
2) They have low viscosity because of which they can dilute slurry.
3) No surfactant is required.
Some of the polymers going with precipitation polymerization include:
Polyvinyl chloride,
Dispersion Polymerization
It produces colloidal “latex” particles in the size range : 0.1 to 1mm
Ingredients- monomer, initiator and solvent.
a. The polymer is insoluble in the solvent, although the monomer is (just) soluble, e.g. styrene and water/methanol mixed solvent.
b. The initiator (e.g. K2S2O8 → 2 SO4 - , ~ 70°C) is soluble in the solvent and must possess a charge (when the solvent is aqueous or polar),e.g.
NOTE:
These “living”, low molar mass polymer chains (“oligomers”) closely resemble anionic surfactant molecules, and will therefore micellise, above their critical micelle concentration (c.m.c.) – at the temperature of the reaction , i.e. ~ 70°C.
These micelles will swell with monomer, and so the locus of polymerisation now switches to the micelles.
c. If electrolyte is added (e.g. NaCl) then this reduces the electrostatic repulsion between the particles, and some coagulation of the particles takes place. Whilst the particles are still “soft” (i.e. swollen with monomer), then coalescence of these coagulated particles occurs. This leads finally to particles with a greater average size.
d. In non-polar or semi-polar solvents, charge-stabilization of the growing particles is likely to be ineffective, and an alternative mechanism is required to achieve stabilisation of these particles to coagulation, and hence to gross precipitation. In this case “steric stabilisation” is employed, in which the surfaces of the particles are covered in a layer of attached, solvent-soluble polymer chains.
Polymer that is produced by dispersion polymerization include Polystyrene
Difference between dispersion and precipitation polymerisation:
A distinction should be made between precipitation and dispersion polymerization, due to the similarities. A dispersion polymerization is actually a type of precipitation polymerization, but the difference lies in the fact that precipitation polymerizations give larger and less regular particles, as a result of little or no stabilizer present.
The main difference between dispersion and precipitation polymerisation is the locus of polymerisation. In dispersion polymerisation the particles are the main locus of polymerisation, whereas in precipitation polymerisation the continuous phase is the locus of polymerisation because the medium or the monomer does not swell the precipitated polymer.
This also means that there is a continuous nucleation and the particles are irregularly shaped. A typical example is the polymerisation of acrylonitrile in bulk.
During precipitation the environment of the polymer chain changes dramatically, and if the radical on the chain is still active, termination can be delayed, which means that precipitation polymerisation leads to higher molecular masses as compared to dispersion polymerisation. Precipitation polymerisation can be used to obtain particles measuring 0.5-5um in size.
Solid Phase Polymerization
A large number of olefin and cyclic monomers can be polymerized from the crystalline solid state. Among those that react rapidly under these conditions are styrene, acrylonitrile, methacrylonitrile, formaldehyde, trioxane, 0-propiolactone, diketene, vinyl stearate and vinyl carbazole.
Polymerization always appears to be associated with defects in the monomer crystals, most likely line defects; otherwise, it would be required that the monomer and the polymer be isomorphous, that is, that they have the same crystal structure, lattice parameters, and so on This seems extremely unlikely and has not been observed.
References:
Ø Articles on the different types of polymerization available on wikipedia dated 1/11/11.
Ø http://www.chembbs.com.cn/bbs/File/UserFiles/UpLoad/20090914033604sw.pdf
Ø http://repository.ui.ac.id/contents/koleksi/11/e6780dd3999c39fd995a386e9cddd71cd3a1abe8.pdf
Ø Book on Polymer Chemistry by Odian pg 350
Ø http://www.scribd.com/doc/19063903/14/Suspension-polymerisation?query=suspension
Ø Textbook of polymer chemistry By Fred W.Billmeyer, third edition, chapter six.
Ø http://www.cheric.org/PDF/MMR/MR12/MR12-2-0233.pdf - for the section of Precipitation polymerisation.
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