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88-465: The R.C. aircraft is usually, though not always, built with the body consisting of a lightweight plastic material such as PVC gutter downspout or an aluminium rail. The wings are made of an equally light material such as foam or coroplast . The remaining components added to the plane are virtually the same as can be found in any other R.C. aircraft of similar size. This concept of building simple radio controlled airplanes using cheap materials without

176-424: A polymer blend , such as high impact polystyrene . Large companies may do their own compounding prior to production, but some producers have it done by a third party. Companies that specialize in this work are known as Compounders. The compounding of thermosetting plastic is relatively straightforward; as it remains liquid until it is cured into its final form. For thermosoftening materials, which are used to make

264-415: A combination of impermeable liners several metres thick, geologically stable sites and collection systems to contain and capture this leachate. It can then be treated and evaporated. Once a landfill site is full, it is sealed off to prevent precipitation ingress and new leachate formation. However, liners must have a lifespan, be it several hundred years or more. Eventually, any landfill liner could leak, so

352-512: A conductivity of up to 80 kS/cm in stretch-oriented polyacetylene , has been achieved, it does not approach that of most metals. For example, copper has a conductivity of several hundred kS/cm. Biodegradable plastics are plastics that degrade (break down) upon exposure to sunlight or ultra-violet radiation ; water or dampness; bacteria; enzymes; or wind abrasion. Attack by insects, such as waxworms and mealworms, can also be considered as forms of biodegradation. Aerobic degradation requires that

440-630: A finished plastic may be non-toxic, the monomers used in the manufacture of its parent polymers may be toxic. In some cases, small amounts of those chemicals can remain trapped in the product unless suitable processing is employed. For example, the World Health Organization 's International Agency for Research on Cancer (IARC) has recognized vinyl chloride , the precursor to PVC, as a human carcinogen. Some plastic products degrade to chemicals with estrogenic activity. The primary building block of polycarbonates, bisphenol A (BPA),

528-400: A good choice for beginners. Good trainer planes and gliders can be made from SPADs. SPAD modelers make equally good advanced planes that can be made with corrugated plastic. They include: RC Airplane Combat, 3D Flying, and are preferred in places where the flyers would normally not risk a more expensive plane and yet want the same flying characteristics of balsa planes. For making a SPAD plane,

616-408: A large molecular weight, they are biochemically inert. Plastic products contain a variety of additives, however, some of which can be toxic. For example, plasticizers like adipates and phthalates are often added to brittle plastics like PVC to make them pliable enough for use in food packaging, toys, and many other items. Traces of these compounds can leach out of the product. Owing to concerns over

704-417: A material with inconsistent properties, which can be unappealing to industry. For example, mixing different colored plastics with different plastic colorants together can produce a discolored or brown material and for this reason plastic is usually sorted by both polymer type and color before recycling. Absence of transparency and reporting across the value chain often results in lack of knowledge concerning

792-500: A mixture of private and state-owned enterprises. Roughly half of all production takes place in East Asia, with China being the largest single producer. Major international producers include: Historically, Europe and North America have dominated global plastics production. However, since 2010 Asia has emerged as a significant producer, with China accounting for 31% of total plastic resin production in 2020. Regional differences in

880-486: A new disease caused solely by plastics, was discovered in seabirds. The birds identified as having the disease have scarred digestive tracts from ingesting plastic waste. "When birds ingest small pieces of plastic, they found, it inflames the digestive tract. Over time, the persistent inflammation causes tissues to become scarred and disfigured, affecting digestion, growth and survival." Pure plastics have low toxicity due to their insolubility in water, and because they have

968-692: A particular purpose. Examples include thermoplastics , thermosets , conductive polymers , biodegradable plastics , engineering plastics and elastomers . One important classification of plastics is the degree to which the chemical processes used to make them are reversible or not. Thermoplastics do not undergo chemical change in their composition when heated and thus can be molded repeatedly. Examples include polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC). Thermosets, or thermosetting polymers, can melt and take shape only once: after they have solidified, they stay solid. If reheated, thermosets decompose rather than melt. In

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1056-674: A pattern of more regularly spaced atoms, such as high-density polyethylene (HDPE), polybutylene terephthalate (PBT), and polyether ether ketone (PEEK). However, some plastics are partially amorphous and partially crystalline in molecular structure, giving them both a melting point and one or more glass transitions (the temperature above which the extent of localized molecular flexibility is substantially increased). These so-called semi-crystalline plastics include polyethylene, polypropylene, polyvinyl chloride, polyamides (nylons), polyesters and some polyurethanes. Intrinsically Conducting Polymers (ICP) are organic polymers that conduct electricity. While

1144-519: A turnover of more than 360 billion euros per year. In China in 2016 there were over 15,000 plastic manufacturing companies, generating more than US$ 366 billion in revenue. In 2017, the global plastics market was dominated by thermoplastics – polymers that can be melted and recast. Thermoplastics include polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS) and synthetic fibers, which together represent 86% of all plastics. Plastic

1232-594: A variety of shapes: films, fibers, plates, tubes, bottles and boxes, among many others. Plasticity also has a technical definition in materials science outside the scope of this article; it refers to the non-reversible change in form of solid substances. Most plastics contain organic polymers. The vast majority of these polymers are formed from chains of carbon atoms, with or without the attachment of oxygen, nitrogen or sulfur atoms. These chains comprise many repeating units formed from monomers . Each polymer chain consists of several thousand repeating units. The backbone

1320-440: A viable and abundant source of materials and energy . In the developing world, waste pickers often scavenge for still-usable materials. In commercial contexts, companies have also discovered landfill sites, and many have begun harvesting materials and energy. Well-known examples include gas-recovery facilities. Other commercial facilities include waste incinerators which have built-in material recovery. This material recovery

1408-921: A wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be molded , extruded or pressed into solid objects of various shapes. This adaptability, plus a wide range of other properties, such as being lightweight, durable, flexible, and inexpensive to produce, has led to their widespread use. Plastics typically are made through human industrial systems. Most modern plastics are derived from fossil fuel-based chemicals like natural gas or petroleum ; however, recent industrial methods use variants made from renewable materials, such as corn or cotton derivatives. Between 1950 and 2017 9.2 billion metric tons of plastic are estimated to have been made; more than half of this has been produced since 2004. In 2020, 400 million tons of plastic were produced. If global trends on plastic demand continue, it

1496-551: Is CO 2 . The gas also contains about 5% molecular nitrogen (N 2 ), less than 1% hydrogen sulfide (H 2 S), and a low concentration of non-methane organic compounds (NMOC) , about 2700 ppmv . Landfill gases can seep out of the landfill and into the surrounding air and soil. Methane is a greenhouse gas , and is flammable and potentially explosive at certain concentrations, which makes it perfect for burning to generate electricity cleanly. Since decomposing plant matter and food waste only release carbon that has been captured from

1584-403: Is a global treaty to protect human health and the environment from chemicals that remain intact in the environment for long periods, become widely distributed geographically, accumulate in the fatty tissue of humans and wildlife, and have harmful impacts on human health or on the environment. Other additives proven to be harmful such as cadmium , chromium , lead and mercury (regulated under

1672-531: Is an estrogen-like endocrine disruptor that may leach into food. Research in Environmental Health Perspectives finds that BPA leached from the lining of tin cans, dental sealants and polycarbonate bottles can increase the body weight of lab animals' offspring. A more recent animal study suggests that even low-level exposure to BPA results in insulin resistance, which can lead to inflammation and heart disease. As of January 2010,

1760-555: Is as packaging materials, but they are used in a wide range of other sectors, including: construction (pipes, gutters, door and windows), textiles ( stretchable fabrics , fleece ), consumer goods (toys, tableware, toothbrushes), transportation (headlights, bumpers, body panels , wing mirrors ), electronics (phones, computers, televisions) and as machine parts. In optics, plastics are used to manufacture aspheric lenses. Additives are chemicals blended into plastics to change their performance or appearance, making it possible to alter

1848-488: Is burned, especially when burning is uncontrolled or takes place in low- technology incinerators, as is common in many developing countries. Incomplete combustion can cause emissions of hazardous substances such as acid gases and ash which can contain persistent organic pollutants (POPs) such as dioxins . A number of additives identified as hazardous to humans and/or the environment are regulated internationally. The Stockholm Convention on Persistent Organic Pollutants (POPs)

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1936-496: Is estimated that annual global plastic production will reach over 1.1 billion tons by 2050. The success and dominance of plastics starting in the early 20th century has caused widespread environmental problems, due to their slow decomposition rate in natural ecosystems. Most plastic produced has not been reused, or is incapable of reuse, either being captured in landfills or persisting in the environment as plastic pollution and microplastics . Plastic pollution can be found in all

2024-585: Is not required, the plastic can optionally be decorated with vinyl sheets which are available in any signboard making shop at very cheap price. The hinges for the control surfaces can be made by sheering one of the twinwalls of the plastic sheet and no special hinging device is required. SPAD Modelers use corrugated plastic sheets of various thickness, such as 2 millimeter (like the flying wings [3] or electric gliders for which 2mm sheet are preferred) and 4 millimeter. These sheets are generally used by signboard makers and many times, when these sheets are discarded,

2112-446: Is not sold as a pure unadulterated substance, but is instead mixed with various chemicals and other materials, which are collectively known as additives. These are added during the compounding stage and include substances such as stabilizers , plasticizers and dyes , which are intended to improve the lifespan, workability or appearance of the final item. In some cases, this can involve mixing different types of plastic together to form

2200-414: Is performed by simply remelting and reforming used plastic into new items. Additives present risks in recycled products, as they are difficult to remove. When plastic products are recycled, it is highly likely that the additives will be integrated into the new products. Waste plastic, even if it is all of the same polymer type, will contain varying types and amounts of additives. Mixing these together can give

2288-548: Is possible through the use of filters ( electro filter , active-carbon and potassium filter, quench, HCl-washer, SO 2 -washer, bottom ash -grating, etc.). In addition to waste reduction and recycling strategies, there are various alternatives to landfills, including waste-to-energy incineration, anaerobic digestion , composting , mechanical biological treatment , pyrolysis and plasma arc gasification . Depending on local economics and incentives, these can be made more financially attractive than landfills. The goal of

2376-671: Is rapidly displaced by CO 2 in the effluent gas. Hydrolysis of the biodegradable fraction of the solid waste begins in the acid formation phase, which leads to rapid accumulation of volatile fatty acids (VFAs) in the leachate. The increased organic acid content decreases the leachate pH from approximately 7.5 to 5.6. During this phase, the decomposition intermediate compounds like the VFAs contribute much chemical oxygen demand (COD). Long-chain volatile organic acids (VOAs) are converted to acetic acid (C 2 H 4 O 2 ), CO 2 , and hydrogen gas (H 2 ). High concentrations of VFAs increase both

2464-518: Is the first stage by which wastes are broken down in a landfill. These are followed by four stages of anaerobic degradation. Usually, solid organic material in solid phase decays rapidly as larger organic molecules degrade into smaller molecules. These smaller organic molecules begin to dissolve and move to the liquid phase, followed by hydrolysis of these organic molecules, and the hydrolyzed compounds then undergo transformation and volatilization as carbon dioxide (CO 2 ) and methane (CH 4 ), with rest of

2552-403: Is the longest decomposition phase. The rate of microbiological activity slows during the last phase of waste decomposition as the supply of nutrients limits the chemical reactions, e.g. as bioavailable phosphorus becomes increasingly scarce. CH 4 production almost completely disappears, with O 2 and oxidized species gradually reappearing in the gas wells as O 2 permeates downwardly from

2640-448: Is the part of the chain that is on the main path , linking together a large number of repeat units. To customize the properties of a plastic, different molecular groups called side chains hang from this backbone; they are usually hung from the monomers before the monomers themselves are linked together to form the polymer chain. The structure of these side chains influences the properties of the polymer. Plastics are usually classified by

2728-712: The Landfill Allowance Trading Scheme has been established for local authorities to trade landfill quotas in England. A different system operates in Wales where authorities cannot 'trade' amongst themselves, but have allowances known as the Landfill Allowance Scheme. U.S. landfills are regulated by each state's environmental agency, which establishes minimum guidelines; however, none of these standards may fall below those set by

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2816-646: The Los Angeles Times reported that the US Food and Drug Administration (FDA) is spending $ 30 million to investigate indications of BPA's link to cancer. Bis(2-ethylhexyl) adipate , present in plastic wrap based on PVC, is also of concern, as are the volatile organic compounds present in new car smell . The EU has a permanent ban on the use of phthalates in toys. In 2009, the US government banned certain types of phthalates commonly used in plastic. Because

2904-473: The Minamata Convention on Mercury ), which have previously been used in plastic production, are banned in many jurisdictions. However they are still routinely found in some plastic packaging including food packaging. The use of the additive bisphenol A (BPA) in plastic baby bottles is banned in many parts of the world, but is not restricted in some low-income countries. In 2023, plasticosis ,

2992-593: The United States Environmental Protection Agency (EPA). Permitting a landfill generally takes between five and seven years, costs millions of dollars and requires rigorous siting, engineering and environmental studies and demonstrations to ensure local environmental and safety concerns are satisfied. The status of a landfill's microbial community may determine its digestive efficiency. Bacteria that digest plastic have been found in landfills. One can treat landfills as

3080-574: The biochemical oxygen demand (BOD) and VOA concentrations, which initiates H 2 production by fermentative bacteria, which stimulates the growth of H 2 -oxidizing bacteria. The H 2 generation phase is relatively short because it is complete by the end of the acid formation phase. The increase in the biomass of acidogenic bacteria increases the amount of degradation of the waste material and consuming nutrients. Metals, which are generally more water-soluble at lower pH, may become more mobile during this phase, leading to increasing metal concentrations in

3168-803: The landfill gas utilization and generation of electricity . Landfill gas monitoring alerts workers to the presence of a build-up of gases to a harmful level. In some countries, landfill gas recovery is extensive; in the United States, for example, more than 850 landfills have active landfill gas recovery systems. A Solar landfill is a repurposed used landfill that is converted to a solar array solar farm . Landfills in Canada are regulated by provincial environmental agencies and environmental protection legislation. Older facilities tend to fall under current standards and are monitored for leaching . Some former locations have been converted to parkland. In

3256-462: The polymerization of their starting materials ( monomers ); which are almost always petrochemical in nature. Such facilities are normally large and are visually similar to oil refineries , with sprawling pipework running throughout. The large size of these plants allows them to exploit economies of scale . Despite this, plastic production is not particularly monopolized, with about 100 companies accounting for 90% of global production. This includes

3344-412: The 1950s. Others estimate a cumulative human production of 8.3 billion tons of plastic, of which 6.3 billion tons is waste, with only 9% getting recycled. Landfill A landfill is a site for the disposal of waste materials. It is the oldest and most common form of waste disposal , although the systematic burial of waste with daily, intermediate and final covers only began in the 1940s. In

3432-566: The 20th century, but gained wide use in the 1960s and 1970s, in an effort to eliminate open dumps and other "unsanitary" waste disposal practices. The sanitary landfill is an engineered facility that separates and confines waste. Sanitary landfills are intended as biological reactors ( bioreactors ) in which microbes will break down complex organic waste into simpler, less toxic compounds over time. These reactors must be designed and operated according to regulatory standards and guidelines (See environmental engineering ). Usually, aerobic decomposition

3520-494: The EU, over 400 additives are used in high volumes. In a global market analysis, 5,500 additives were found. At a minimum, all plastic contains some polymer stabilizers which permit them to be melt-processed (molded) without suffering polymer degradation . Other additives are optional and can be added as required, with loadings varying significantly between applications. The amount of additives contained in plastics varies depending on

3608-718: The European Union, individual states are obliged to enact legislation to comply with the requirements and obligations of the European Landfill Directive . The majority of EU member states have laws banning or severely restricting the disposal of household trash via landfills. Landfilling is currently the major method of municipal waste disposal in India. India also has Asia's largest dumping ground in Deonar, Mumbai. However, issues frequently arise due to

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3696-485: The Greek πλαστικός ( plastikos ), meaning "capable of being shaped or molded ;" in turn, it is from πλαστός ( plastos ) meaning "molded." As a noun , the word most commonly refers to the solid products of petrochemical-derived manufacturing. The noun plasticity refers specifically here to the deformability of the materials used in the manufacture of plastics. Plasticity allows molding , extrusion or compression into

3784-561: The North American Free Trade Agreement or NAFTA region) accounts for 21% of global plastic consumption, closely followed by China (20%) and Western Europe (18%). In North America and Europe, there is high per capita plastic consumption (94 kg and 85 kg/capita/year, respectively). In China, there is lower per capita consumption (58 kg/capita/year), but high consumption nationally because of its large population. The largest application for plastics

3872-516: The United States Environmental Protection Agency (US EPA) revealed that out of 3,377 chemicals potentially associated with plastic packaging and 906 likely associated with it, 68 were ranked by ECHA as "highest for human health hazards" and 68 as "highest for environmental hazards". As additives change the properties of plastics they have to be considered during recycling. Presently, almost all recycling

3960-486: The additives' function. For example, additives in polyvinyl chloride (PVC) can constitute up to 80% of the total volume. Pure unadulterated plastic (barefoot resin) is never sold, even by the primary producers. Additives may be weakly bound to the polymers or react in the polymer matrix. Although additives are blended into plastic they remain chemically distinct from it, and can gradually leach back out during normal use, when in landfills, or following improper disposal in

4048-415: The age of landfill, type of waste, moisture content and other factors. For example, the maximum amount of landfill gas produced can be illustrated a simplified net reaction of diethyl oxalate that accounts for these simultaneous reactions: 4 C 6 H 10 O 4 + 6 H 2 O → 13 CH 4 + 11 CO 2 On average, about half of the volumetric concentration of landfill gas is CH 4 and slightly less than half

4136-514: The alarming growth rate of landfills and poor management by authorities. On and under surface fires have been commonly seen in the Indian landfills over the last few years. Landfilling practices in the UK have had to change in recent years to meet the challenges of the European Landfill Directive . The UK now imposes landfill tax upon biodegradable waste which is put into landfills. In addition to this

4224-510: The atmosphere through photosynthesis, no new carbon enters the carbon cycle and the atmospheric concentration of CO 2 is not affected. Carbon dioxide traps heat in the atmosphere, contributing to climate change . In properly managed landfills, gas is collected and flared or recovered for landfill gas utilization . Poorly run landfills may become nuisances because of vectors such as rats and flies which can spread infectious diseases . The occurrence of such vectors can be mitigated through

4312-534: The birth of the plastic industry in the 1950s, global production has increased enormously, reaching 400 million tonnes a year in 2021; this is up from 381 million metric tonnes in 2015 (excluding additives). From the 1950s, rapid growth occurred in the use of plastics for packaging, in building and construction, and in other sectors. If global trends on plastic demand continue, it is estimated that by 2050 annual global plastic production will exceed 1.1 billion tonnes annually. Plastics are produced in chemical plants by

4400-690: The chemical profile of the final products. For example, products containing brominated flame retardants have been incorporated into new plastic products. Flame retardants are a group of chemicals used in electronic and electrical equipment, textiles, furniture and construction materials which should not be present in food packaging or child care products. A recent study found brominated dioxins as unintentional contaminants in toys made from recycled plastic electronic waste that contained brominated flame retardants. Brominated dioxins have been found to exhibit toxicity similar to that of chlorinated dioxins. They can have negative developmental effects and negative effects on

4488-448: The chemical structure of most plastics renders them durable, they are resistant to many natural degradation processes. Much of this material may persist for centuries or longer, given the demonstrated persistence of structurally similar natural materials such as amber . There are differing estimates of how much plastic waste has been produced in the last century. By one estimate, one billion tons of plastic waste have been discarded since

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4576-802: The chemical structure of the polymer's backbone and side chains. Important groups classified in this way include the acrylics , polyesters , silicones , polyurethanes , and halogenated plastics . Plastics can be classified by the chemical process used in their synthesis, such as condensation , polyaddition , and cross-linking . They can also be classified by their physical properties, including hardness , density , tensile strength , thermal resistance , and glass transition temperature . Plastics can additionally be classified by their resistance and reactions to various substances and processes, such as exposure to organic solvents, oxidation , and ionizing radiation . Other classifications of plastics are based on qualities relevant to manufacturing or product design for

4664-452: The commodity plastics, with many having exceptional properties. Engineering plastics are more robust and are used to make products such as vehicle parts, building and construction materials, and some machine parts. In some cases they are polymer blends formed by mixing different plastics together (ABS, HIPS etc.). Engineering plastics can replace metals in vehicles, lowering their weight and improving fuel efficiency by 6–8%. Roughly 50% of

4752-418: The compacted waste and the cover material is called a daily cell. Waste compaction is critical to extending the life of the landfill. Factors such as waste compressibility, waste-layer thickness and the number of passes of the compactor over the waste affect the waste densities. The term landfill is usually shorthand for a municipal landfill or sanitary landfill. These facilities were first introduced early in

4840-513: The developing world, the applications of plastic may differ; 42% of India's consumption is used in packaging. In the medical field, polymer implants and other medical devices are derived at least partially from plastic. Worldwide, about 50 kg of plastic is produced annually per person, with production doubling every ten years. The world's first fully synthetic plastic was Bakelite , invented in New York in 1907, by Leo Baekeland , who coined

4928-666: The effects of such leachates , the EU has restricted the use of DEHP (di-2-ethylhexyl phthalate) and other phthalates in some applications, and the US has limited the use of DEHP, DPB , BBP , DINP , DIDP , and DnOP in children's toys and child-care articles through the Consumer Product Safety Improvement Act . Some compounds leaching from polystyrene food containers have been proposed to interfere with hormone functions and are suspected human carcinogens (cancer-causing substances). Other chemicals of potential concern include alkylphenols . While

5016-401: The environment. Additives may also degrade to form other toxic molecules. Plastic fragmentation into microplastics and nanoplastics can allow chemical additives to move in the environment far from the point of use. Once released, some additives and derivatives may persist in the environment and bioaccumulate in organisms. They can have adverse effects on human health and biota. A recent review by

5104-407: The finite limits of fossil fuel reserves and to rising levels of greenhouse gases caused primarily by the burning of those fuels, the development of bioplastics is a growing field. Global production capacity for bio-based plastics is estimated at 327,000 tonnes per year. In contrast, global production of polyethylene (PE) and polypropylene (PP), the world's leading petrochemical-derived polyolefins,

5192-436: The ground around landfills must be tested for leachate to prevent pollutants from contaminating groundwater . Rotting food and other decaying organic waste create decomposition gases , especially CO 2 and CH 4 from aerobic and anaerobic decomposition, respectively. Both processes occur simultaneously in different parts of a landfill. In addition to available O 2 , the fraction of gas constituents will vary, depending on

5280-525: The ground during an earthquake . Once full, the area over a landfill site may be reclaimed for other uses. Operators of well-run landfills for non-hazardous waste meet predefined specifications by applying techniques to: They can also cover waste (usually daily) with layers of soil or other types of material such as woodchips and fine particles. During landfill operations, a scale or weighbridge may weigh waste collection vehicles on arrival and personnel may inspect loads for wastes that do not accord with

5368-568: The host resin. Masterbatch granules can be mixed with cheaper bulk polymer and will release their additives during processing to give a homogeneous final product. This can be cheaper than working with a fully compounded material and is particularly common for the introduction of color. Companies that produce finished goods are known as converters (sometimes processors). The vast majority of plastics produced worldwide are thermosoftening and must be heated until molten in order to be molded. Various sorts of extrusion equipment exist which can then form

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5456-427: The landfill bioreactor strata gradually decreases. Microbial populations grow, density increases. Aerobic biodegradation dominates, i.e. the primary electron acceptor is O 2 . The O 2 is rapidly degraded by the existing microbial populations. The decreasing O 2 leads to less aerobic and more anaerobic conditions in the layers. The primary electron acceptors during transition are nitrates and sulphates since O 2

5544-469: The landfill can be significant and can be mitigated by wheel washing systems . Pollution of the local environment , such as contamination of groundwater or aquifers or soil contamination may occur, as well. When precipitation falls on open landfills, water percolates through the garbage and becomes contaminated with suspended and dissolved material, forming leachate. If this is not contained it can contaminate groundwater. All modern landfill sites use

5632-451: The landfill's waste-acceptance criteria. Afterward, the waste collection vehicles use the existing road network on their way to the tipping face or working front, where they unload their contents. After loads are deposited, compactors or bulldozers can spread and compact the waste on the working face. Before leaving the landfill boundaries, the waste collection vehicles may pass through a wheel-cleaning facility. If necessary, they return to

5720-459: The leachate. The acid formation phase intermediary products (e.g., acetic, propionic, and butyric acids) are converted to CH 4 and CO 2 by methanogenic microorganisms. As VFAs are metabolized by the methanogens, the landfill water pH returns to neutrality. The leachate's organic strength, expressed as oxygen demand, decreases at a rapid rate with increases in CH 4 and CO 2 gas production. This

5808-604: The majority of products, it is necessary to melt the plastic in order to mix-in the additives. This involves heating it to anywhere between 150–320 °C (300–610 °F). Molten plastic is viscous and exhibits laminar flow , leading to poor mixing. Compounding is therefore done using extrusion equipment, which is able to supply the necessary heat and mixing to give a properly dispersed product. The concentrations of most additives are usually quite low, however high levels can be added to create Masterbatch products. The additives in these are concentrated but still properly dispersed in

5896-470: The modeler (usually a beginner) can copy the dimensions of a well known balsa trainer and makes the SPAD plane using the same dimensions and adapting to the building techniques of a SPAD plane. The plane can also be built from plans or can be scratch built (usually, the modeler draws his/her own plans and makes the plane, though this is mostly attempted by experienced modelers) Plastic Plastics are

5984-486: The modelers have a choice to use them to build model airplanes. The choice of propulsion can be either internal combustion engine or electric motors as with balsa counterparts. Corrugated plastic planes are simpler alternative to the traditional balsa wood based R.C. aircraft for a variety of situations. Most of the SPAD airplanes do not use balsa which saves considerable cost. They withstand crashes better than balsa counterparts because of their resilience and hence are

6072-450: The nervous system and interfere with mechanisms of the endocrine system. Many of the controversies associated with plastics actually relate to their additives, as some compounds can be persistent, bioaccumulating and potentially harmful. The now banned flame retardants OctaBDE and PentaBDE are an example of this, while the health effects of phthalates are an ongoing area of public concern. Additives can also be problematic if waste

6160-462: The past, waste was simply left in piles or thrown into pits (known in archeology as middens ). Landfills take up a lot of land and pose environmental risks. Some landfill sites are used for waste management purposes, such as temporary storage, consolidation and transfer, or for various stages of processing waste material, such as sorting, treatment, or recycling. Unless they are stabilized, landfills may undergo severe shaking or soil liquefaction of

6248-709: The plastic be exposed at the surface, whereas anaerobic degradation would be effective in landfill or composting systems. Some companies produce biodegradable additives to enhance biodegradation. Although starch powder can be added as a filler to allow some plastics to degrade more easily, such treatment does not lead to complete breakdown. Some researchers have genetically engineered bacteria to synthesize completely biodegradable plastics, such as polyhydroxy butyrate (PHB); however, these were still relatively costly as of 2021. While most plastics are produced from petrochemicals, bioplastics are made substantially from renewable plant materials like cellulose and starch. Due both to

6336-571: The plastic into almost any shape. For thermosetting materials the process is slightly different, as the plastics are liquid to begin with and but must be cured to give solid products, but much of the equipment is broadly similar. The most commonly produced plastic consumer products include packaging made from LDPE (e.g. bags, containers, food packaging film), containers made from HDPE (e.g. milk bottles, shampoo bottles, ice cream tubs), and PET (e.g. bottles for water and other drinks). Together these products account for around 36% of plastics use in

6424-464: The preferred choice for the mass production everyday objects. Their biggest single application is in packaging, with some 146 million tonnes being used this way in 2015, equivalent to 36% of global production. Due to their dominance; many of the properties and problems commonly associated with plastics, such as pollution stemming from their poor biodegradability , are ultimately attributable to commodity plastics. A huge number of plastics exist beyond

6512-413: The properties of plastics to better suit their intended applications. Additives are therefore one of the reasons why plastic is used so widely. Plastics are composed of chains of polymers. Many different chemicals are used as plastic additives. A randomly chosen plastic product generally contains around 20 additives. The identities and concentrations of additives are generally not listed on products. In

6600-528: The term "plastics". Dozens of different types of plastics are produced today, such as polyethylene , which is widely used in product packaging , and polyvinyl chloride (PVC), used in construction and pipes because of its strength and durability. Many chemists have contributed to the materials science of plastics, including Nobel laureate Hermann Staudinger , who has been called "the father of polymer chemistry ," and Herman Mark , known as "the father of polymer physics ". The word plastic derives from

6688-762: The thermosetting process, an irreversible chemical reaction occurs. The vulcanization of rubber is an example of this process. Before heating in the presence of sulfur, natural rubber ( polyisoprene ) is a sticky, slightly runny material; after vulcanization, the product is dry and rigid. Around 70% of global production is concentrated in six major polymer types, the so-called commodity plastics . Unlike most other plastics these can often be identified by their resin identification code (RIC): Polyurethanes (PUR) and PP&A fibers are often also included as major commodity classes, although they usually lack RICs, as they are chemically quite diverse groups. These materials are inexpensive, versatile and easy to work with, making them

6776-533: The time-consuming and painstaking process of working with balsa wood and iron-on plastic coating was popularized by a web site created in the late 1990s, spadtothebone.net. [1] While this web site, and the many original plans and articles still exist, the main gathering place for Spad enthusiasts on the web today resides at rcgroups. [2] . R/C Report magazine author Frank Costa covered Spads from April 2003 to July 2004. SPADs are preferred to other materials because they are cheaper and are easy to work with, painting

6864-531: The troposphere. This transforms the oxidation–reduction potential (ORP) in the leachate toward oxidative processes. The residual organic materials may incrementally be converted to the gas phase, and as organic matter is composted; i.e. the organic matter is converted to humic -like compounds. Landfills have the potential to cause a number of issues. Infrastructure disruption, such as damage to access roads by heavy vehicles, may occur. Pollution of local roads and watercourses from wheels on vehicles when they leave

6952-432: The use of daily cover . Other potential issues include wildlife disruption due to occupation of habitat and animal health disruption caused by consuming waste from landfills, dust, odor, noise pollution , and reduced local property values. Gases are produced in landfills due to the anaerobic digestion by microbes. In a properly managed landfill, this gas is collected and used. Its uses range from simple flaring to

7040-444: The volume of modern cars is made of plastic, but this only accounts for 12–17% of the vehicle weight. High-performance plastics are usually expensive, with their use limited to specialized applications which make use of their superior properties. Many plastics are completely amorphous (without a highly ordered molecular structure), including thermosets, polystyrene, and methyl methacrylate (PMMA). Crystalline plastics exhibit

7128-518: The volume of plastics production are driven by user demand, the price of fossil fuel feedstocks, and investments made in the petrochemical industry. For example, since 2010 over US$ 200 billion has been invested in the United States in new plastic and chemical plants, stimulated by the low cost of raw materials. In the European Union (EU), too, heavy investments have been made in the plastics industry, which employs over 1.6 million people with

7216-404: The waste depend on how well microbial populations function in syntrophy , i.e. an interaction of different populations to provide each other's nutritional needs.: The life cycle of a municipal landfill undergoes five distinct phases: As the waste is placed in the landfill, the void spaces contain high volumes of molecular oxygen (O 2 ). With added and compacted wastes, the O 2 content of

7304-435: The waste remaining in solid and liquid phases. During the early phases, little material volume reaches the leachate , as the biodegradable organic matter of the waste undergoes a rapid decrease in volume. Meanwhile, the leachate's chemical oxygen demand increases with increasing concentrations of the more recalcitrant compounds compared to the more reactive compounds in the leachate. Successful conversion and stabilization of

7392-416: The weighbridge for re-weighing without their load. The weighing process can assemble statistics on the daily incoming waste tonnage, which databases can retain for record keeping. In addition to trucks, some landfills may have equipment to handle railroad containers. The use of "rail-haul" permits landfills to be located at more remote sites, without the problems associated with many truck trips. Typically, in

7480-399: The working face, the compacted waste is covered with soil or alternative materials daily. Alternative waste-cover materials include chipped wood or other "green waste", several sprayed-on foam products, chemically "fixed" bio-solids, and temporary blankets. Blankets can be lifted into place at night and then removed the following day prior to waste placement. The space that is occupied daily by

7568-497: The world's major water bodies , for example, creating garbage patches in all of the world's oceans and contaminating terrestrial ecosystems. Of all the plastic discarded so far, some 14% has been incinerated and less than 10% has been recycled. In developed economies, about a third of plastic is used in packaging and roughly the same in buildings in applications such as piping , plumbing or vinyl siding . Other uses include automobiles (up to 20% plastic ), furniture, and toys. In

7656-726: The world. Most of them (e.g. disposable cups, plates, cutlery, takeaway containers, carrier bags) are used for only a short period, many for less than a day. The use of plastics in building and construction, textiles, transportation and electrical equipment also accounts for a substantial share of the plastics market. Plastic items used for such purposes generally have longer life spans. They may be in use for periods ranging from around five years (e.g. textiles and electrical equipment) to more than 20 years (e.g. construction materials, industrial machinery). Plastic consumption differs among countries and communities, with some form of plastic having made its way into most people's lives. North America (i.e.

7744-644: Was estimated at over 150 million tonnes in 2015. The plastic industry includes the global production, compounding , conversion and sale of plastic products. Although the Middle East and Russia produce most of the required petrochemical raw materials, the production of plastic is concentrated in the global East and West. The plastic industry comprises a huge number of companies and can be divided into several sectors: Between 1950 and 2017, 9.2 billion tonnes of plastic are estimated to have been made, with more than half this having been produced since 2004. Since

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