Food pollution, white pollution, air pollution
Types of pollutants in food
Food pollution can be divided into three main categories according to the nature:
①Biological pollution: food contaminated by bacteria, molds and toxins they produce, as well as the eggs of parasitic worms, which can cause people to get food poisoning The food is contaminated with bacteria, molds and the toxins they produce, as well as parasite eggs, which can cause people to get food poisoning, suffer from infectious and parasitic diseases, or make the food rot, etc.
② chemical pollution: food containing toxic chemicals, and pesticide pollution is a major source of chemical pollution of food.
③ radioactive contamination: refers to the food absorption of man-made radionuclides higher than the natural radioactive background. Radioactive contaminants in food are mainly iodine and strontium.
What are the types of white pollution?
I. Classification, Composition and Properties of Plastics and Manufacturing Processes
Plastic is a synthetic polymer material with a wide range of uses, and plastic products abound in our daily lives. From the toiletries we use after getting up, breakfast tableware, to work and study stationery, rest with the seat cushions, mattresses, as well as televisions, washing machines, computer shells, as well as the night to bring us the light of a variety of shapes of lamps and lanterns ...... plastics with its excellent performance gradually replaced many of the materials and materials that have been used for decades and centuries, as well as the use of plastics in our daily life. Plastic has gradually replaced many materials and utensils that have been used for decades and centuries with its excellent performance, and has become an indispensable assistant in people's life. Plastic set of metal hardness, lightweight wood, glass transparency, ceramic corrosion resistance, rubber flexibility and toughness in one, so in addition to daily necessities, plastic is more widely used in aerospace, medical equipment, petrochemical, machinery manufacturing, national defense, construction and other industries.
One, the classification of plastics
There are many types of plastics, so far the world into the production of plastics about three hundred kinds. Plastic classification methods, commonly used in two kinds:
1, according to the nature of the plastic heat is divided into thermoplastic and thermosetting plastics
Thermoplastic molecular structure are linear structure, when heated, softening or melting, can be molded into a certain shape, and harden after cooling. In the heat to a certain extent and re-soften, after cooling and harden, this process can be repeated many times. Such as polyvinyl chloride, polyethylene, polystyrene and so on. Thermoplastic molding process is relatively simple, can be continuous production, and has a fairly high mechanical strength, so the development is very fast.
Thermoset plastics molecular structure is the body structure, in the heat also occurs when the softening, can be molded into a certain shape, but heat to a certain extent or add a small amount of curing agent, on the hardening of the stereotypes, and then will not soften the heat and change the shape. Thermosetting plastics processed after molding, heat is no longer softened, and therefore can not be recycled, such as phenolic plastics, aminoplastics, epoxy resins, etc. belong to this type of plastic. Thermosetting plastic molding process is more complex, so continuous production has some difficulties, but its heat resistance is good, not easy to deformation, and the price is relatively inexpensive.
2, according to the different uses of plastics are divided into general-purpose plastics and engineering plastics
General-purpose plastics refers to the production of large, low-priced plastics with a wide range of applications, including polyolefins, polyvinyl chloride, polystyrene, phenolic plastics and aminoplastics five varieties. Many products used in people's daily life are made of these general-purpose plastics.
Engineering plastics are plastics that can be used as engineering structural materials and replace metal to make machine parts. For example, polyamide, polycarbonate, polyformaldehyde, ABS resin, PTFE, polyester, polysulfone, polyimide and so on. Engineering plastics with low density, high chemical stability, good mechanical properties, superior electrical insulation, easy processing and molding characteristics, widely used in automotive, electrical appliances, chemical, mechanical, instrumentation, instrumentation and other industries, but also in cosmic navigation, rockets, missiles and other aspects.
Two, the composition of plastic
We usually use the plastic is not a pure substance, it is made of many materials formulated. One of the polymer (or synthetic resin) is the main component of plastic, in addition, in order to improve the performance of plastic, but also in the polymer to add a variety of auxiliary materials, such as fillers, plasticizers, lubricants, stabilizers, coloring agents, etc., in order to become a good performance of plastic.
1, synthetic resins
Synthetic resins are the most important component of plastics, its content in plastics is generally 40% to 100%. Because of the large content, and the nature of the resin often determines the nature of the plastic, so people often see the resin as a synonym for plastic. For example, polyvinyl chloride resin and polyvinyl chloride plastics, phenolic resins and phenolic plastics mixed together. In fact, resin and plastic are two different concepts. Resin is a raw unprocessed polymer, it is not only used in the manufacture of plastics, but also coatings, adhesives and synthetic fibers raw materials. In addition to a very small number of plastics containing 100% resin, the vast majority of plastics, in addition to the main component of resin, but also need to add other substances.
2, filler
Filler, also known as filler, it can improve the strength and heat resistance of plastic, and reduce costs. For example, phenolic resin can greatly reduce the cost of adding wood flour, so that phenolic plastics become one of the cheapest plastics, but also significantly improve mechanical strength. Fillers can be divided into two categories of organic fillers and inorganic fillers, the former such as wood flour, rags, paper and a variety of fabric fibers, etc., the latter, such as glass fibers, diatomaceous earth, asbestos, carbon black, etc..
3, plasticizers
Plasticizers can increase the plasticity and flexibility of plastics, reduce the brittleness of plastics easy to process molding. Plasticizers are generally miscible with the resin, non-toxic, odorless, light, heat-stable high-boiling organic compounds, the most commonly used is phthalate esters. For example, the production of polyvinyl chloride plastic, if you add more plasticizers can be obtained soft polyvinyl chloride plastic, if you do not add or add less plasticizers (dosage < 10%), the hard polyvinyl chloride plastic.
4, stabilizers
In order to prevent synthetic resins in the processing and use of the process of light and heat decomposition and destruction, to extend the service life, to add stabilizers in plastics. Commonly used stearate, epoxy resin and so on.
5, colorants
Colorants can make plastics have a variety of bright, beautiful colors. Commonly used organic dyes and inorganic pigments as colorants.
6, lubricants
The role of the lubricant is to prevent the plastic in the molding does not stick to the metal mold, at the same time can make the surface of the plastic smooth and beautiful. Commonly used lubricants are stearic acid and its calcium and magnesium salts.
In addition to the above additives, plastics can also be added to the flame retardant, foaming agent, antistatic agent, etc., to meet the different requirements of use.
Three, the characteristics of plastic
1, plastic has plasticity
As the name suggests, plastic is a material that can be molded. The so-called plasticity of plastic is a solid plastic can be softened by heating methods, and then put the softened plastic in the mold, let it cool down and re-solidify into a certain shape of the solid. This property of plastic also has certain defects, that is, easy to soften and deform when exposed to heat, and some plastics will be deformed even with higher temperature water, so plastic products should not be in contact with boiling water in general.
2, plastic with elasticity
Some plastics are like synthetic fibers, with a certain degree of elasticity. When it is stretched by external forces, the curled molecules are straightened by the flexibility, but once the tension is canceled, it will return to the original curled state, which makes the plastic with elasticity, such as polyethylene and polyvinyl chloride film products. But some plastics are not elastic.
3, plastic has high strength
Plastic is not as hard as metal, but compared with glass, ceramics, wood, etc., or has a relatively high strength and wear resistance. Plastic can be made into strong gears and bearings on the machine.
4, plastic has corrosion resistance
Plastic is not like metal in the moist air will rust, not like wood in the wet environment will rot or be microbial erosion, in addition to plastic corrosion resistant to acids and alkalis. Therefore, plastics are often used as water and liquid pipelines in chemical plants, doors and windows in buildings, and so on.
5, plastic has insulating
Plastic molecular chain is atoms to *** valence bonding combined, the molecules can not be ionized, but also in the structure of the transfer of electrons, so the plastic has insulating properties. Plastic can be used to make the wrapping of wires, electric sockets, the shells of electrical appliances and so on.
6. Plastic manufacturing process
The first step in the manufacture of the vast majority of plastics is the production of synthetic resins (obtained by the polymerization of monomers), and then according to the needs of the resin (sometimes adding a certain amount of additives) further processed into plastic products. There are a few varieties (such as plexiglass) whose resin synthesis and plastic molding is carried out simultaneously.
II. White pollution caused by land sloughing causes
With the development of the economy, scientific and technological progress, people's material and cultural living standards continue to improve, the amount of plastic products is increasing day by day. The extensive use of plastic products, does bring people a lot of convenience, but also brought a lot of social problems. People visualize it as "white pollution".
White trash natural degradation rate is too slow, long-term retention in the soil can not be decomposed, so that the soil permeability deterioration, water is not easy to infiltrate, reducing the growth of microorganisms, affecting the transfer of heat, resulting in the alkalization of the soil, a series of physicochemical properties of the changes in the soil colloid destruction, resulting in soil compaction. Because the plastic film is not easy to breathe, and not easy to decompose, so it is turned into the soil, will affect the degree of soil permeability, thus affecting the crop root growth.
III. Plastic on the merits of human development
Plastic is one of the major inventions of mankind in the 20th century, once in the shell of electronic products in the manufacture of sweat and tears. In recent years, plastics have gradually entered the interior of electronic products, began to become an important raw material for the manufacture of certain electronic components. Epoxy molded plastic is one of the integrated circuits with high degree of structural materials, plastic packaging methods for the production of large-scale integrated circuits, ultra-large-scale integrated circuits, special large-scale integrated circuits at home and abroad has been widely used and has become mainstream. China's epoxy mold plastic industry, although a late start, only in 1992 began to really large-scale production, but at present China's annual production scale of epoxy mold plastic has reached 10,000 tons or so, more than 95% of the integrated circuit products are used in the form of plastic packaging. Compared with the metal package or ceramic package, plastic package is still the most important form of packaging. At present, the production of plastic packaging products accounted for more than 90% of the world's total packaging production. In order to comply with the rapid development of semiconductor integrated circuit design and process technology needs, plastic sealing mold type is also constantly pushing the new. China is a large consumer of integrated circuits (accounting for 15% of the international market), but is the production of integrated circuits is a small country (accounting for 0.8% of the world output), about 80% of China's integrated circuits rely on imports. Since 1997, China's epoxy molding plastic demand has been a sustained high growth trend, product demand exceeds supply. Especially recently, the State Council to encourage the development of software and integrated circuit industry, a number of policies introduced, greatly driving the development of the plastic packaging industry
Data shows that the current total market demand for plastic sealing material is about 7,000 to 8,000 tons, is expected to be the total market demand for 2005 is about 1.5 million to 20,000 tons, of which the super-large-scale integrated circuits with the epoxy sealing material is expected to annual demand for 4,000 tons or so. For about 4000 tons. Plastic to become the protagonist of a new generation of electronic chips in 2000 after the rise of conductive plastics. For many years, silicon crystals have been in the field of electronic materials in the leader of the dominant position, but in fact, the use of silicon crystals to manufacture chips is very complex, manufacturing costs are very expensive, so the price of semiconductor chips over the years has been high. To this end, scientists are trying to find alternatives to silicon crystals to manufacture electronic chips, and the emergence of plastic chips to the electronics industry for a revitalization. As we all know, plastic is not a conductor but an insulator. But scientists found that the special treatment of organic polymers also have the function of transmission of electric current, and then developed a new plastic semiconductor. Compared with silicon chips, plastic chips are very inexpensive, only 1% to 10% of the price of silicon chips, very competitive market. It is predicted that by 2004, the global average sales of plastic chip industry will reach 10 billion U.S. dollars, plastic chips will become a new generation of chips with great potential for future development. At present, a number of IT industry giants have announced the establishment of a plastic chip specialized research institutions, they have developed a few hundred electronic components integrated plastic chip samples, to explore the mass production of less integrated plastic chips. Of even greater interest is the fact that robots controlled by microcomputers equipped with plastic chips are more flexible and easier to maneuver than robots with silicon chips. Experts expect that with the emergence of more and more highly integrated plastic chips, plastic chips in the near future to be able to compete with silicon chips. Belong to the high-tech field of modern electronic communications industry is also missing lightweight, transparent, tough and insulating plastic. The successful development of plastic optical fiber has brought new hope to the rapid development and popularization of optical communication. Optical fiber is a channel for directional transmission of light, but also an important device in the electronic communication transmission system. Before the introduction of plastic optical fiber are inorganic optical fiber, but with the development of the electronic communications industry, plastic optical fiber quickly occupy a place. Nowadays, the materials used as plastic optical fibers are polymethyl methacrylate, polystyrene, polycarbonate, fluorine plastic, silicone resin and so on. These materials determine the plastic optical fiber is light and soft, anti-flexing, high impact strength, inexpensive, anti-irradiation, easy to process, the ability to form optical fiber, and so on, and thus favored. As an ideal transmission medium for short-distance communication networks, plastic optical fiber has an important position in future data transmission in home intelligence, office automation, industrial control networking, vehicle-mounted airborne communication networks, military communication networks and multimedia devices. Through plastic optical fiber, we can achieve intelligent home appliances (home PC, HDTV, telephone, digital imaging equipment, home security equipment, air conditioning, refrigerators, stereos, etc.) networking, to achieve home automation and remote control and management, to improve the quality of life; through the plastic optical fiber, we can also realize the networking of office equipment, high-speed transmission of data to greatly improve the efficiency of the workplace to achieve telecommuting and so on; in the Light-sensitive detectors and indicators with plastic optical fiber can make the light-sensitive head easy to reach the measurement point, plastic optical fiber image transmitter can transmit bright color images. All of the above makes us have reason to believe that, with the development of science and technology, the application of plastics is more and more extensive, and the development of its market will be more and more broad. Industry LinksEngineering plastics, especially specialized engineering plastics, are attracting more and more attention because of their low density, high strength, corrosion resistance, good insulation, vibration resistance, abrasion resistance, easy processing, high production efficiency and energy saving. During the past 20 years, the development of consumer electronics has driven the development of the entire engineering plastics industry. Among them, the most important and largest production of nylon and polyester (PET and PBT), the main application areas are concentrated in the electrical and electronic industry, such as a variety of connectors, switches, coil boxes, power communication equipment and so on. According to statistics, in 1998, the Asia-Pacific region's total nylon and polyester consumption of 43.7 million tons, while in 2002 this figure reached 58.5 million tons, its growth rate far exceeded the region's average GDP growth rate. China's Tenth Five-Year Plan made it clear that the focus of development in the field of plastics for the electronics, communications and other industries supporting the use of plastic materials or products, planning to pay special attention to plastic modification technology, the use of plastic alloys and other modified plastics and general engineering plastics with unique properties and special engineering plastics. In the future, with the progress of research, development and specialization of engineering plastics, its application areas will continue to expand, the market outlook is very broad.
Four. Recycling
In order to adapt to the need to protect the Earth's environment, the world's plastics processing industry has studied many new technologies for environmental protection. In terms of saving resources, mainly to improve product resistance to aging performance, extended life, multifunctionality, product appropriate amount of design; in terms of resource reuse, mainly research on efficient sorting of plastic waste, separation technology, high efficiency melt recycling technology, chemical recycling technology, completely biodegradable materials, water-soluble materials, edible film; in terms of reduction technology, mainly research on the waste of plastics compression and reduction technology, film bagging container technology, and the plastic recycling technology, the plastic recycling technology, the plastic recycling technology, the plastic recycling technology, the plastic recycling technology, the plastic recycling technology, the plastic recycling technology. Technology, film bagging container technology, under the premise of ensuring the application of performance, as far as possible, thin products technology; in the development of CFC substitutes, mainly research on carbon dioxide foaming technology; in the study of substitutes, mainly the development of PVC and PVDC substitutes.
In the municipal plastic solid waste disposal, the current main use of landfills, incineration and recycling three methods. Because of different national conditions, countries are different, the United States to landfill-based, Europe, Japan to incineration-based. The use of landfill disposal, because plastic products are large and light, and not easy to rot, will lead to landfill sites become soft foundation, it is difficult to utilize in the future. The use of incineration, because the heat generated by the plastic is large, easy to damage the furnace, plus incineration of the gas will contribute to the warming of the earth, some plastics in the incineration of harmful gases will also be released and pollute the atmosphere. The method of recycling, due to labor consumption, high recycling costs, and the lack of appropriate recycling channels, the world's recycling accounted for only about 15% of the total plastic consumption. However, since the world's oil resources are limited, from the perspective of saving the earth's resources, the recycling of plastics is of great significance. For this reason, countries all over the world have invested a lot of manpower and material resources to develop various key technologies for recycling waste plastics, and are committed to reducing the cost of recycling plastics and developing their suitable application areas.
One, the recovery of thermal energy method
Most of the plastics to petroleum as raw materials, the main components are hydrocarbons, can be burned, such as polystyrene combustion heat than the dye oil is still high. Some experts believe that the plastic waste into the incinerator burning, can provide heating or power generation of heat, because 86% of the oil dyes are directly burned, of which only 4% made of plastic products, plastic used up and then sent when the heat is burned is very normal, the use of heat is one of the last methods of plastics recycling, not to be taken lightly. However, many environmental groups are against incineration of plastics, they believe that incineration method to the mess of chemicals all centralized combustion, will produce toxic gases. For example, half of the composition of PVC is chlorine, burning chlorine gas released has a strong erosion destructive force, and is the culprit causing the evil Ying.
Currently, Germany has 200,000 tons of PVC waste each year, 30% of which is burned in the incinerator, burned to panic, the law had to formulate countermeasures. The German Federal Environment Agency has stipulated that all incinerators must comply with the value of less than 0.1ng (ng) per cubic meter of exhaust gas limit. Germany's incinerator air pollution standards, although already belong to the world's high standards, but still do not dare to say that the combustion method will not release harmful substances due to mechanical failure, so it can be predicted that the countries of the environmental protection groups will continue to vigorously oppose the incineration method of heat recovery.
Two, classification and recycling method
As plastic recycling, the most important thing is to be classified. Common plastics are polystyrene, polypropylene, low-density polyethylene, high-density polyethylene, polycarbonate, polyvinyl chloride, polyamide, polyurethane and so on, the difference between these plastics is generally very difficult to distinguish. Nowadays, most of the work of plastic classification is done manually. Recently, machine classification has new research progress, a German chemical technology association invented to infrared light to identify the category, both rapid and accurate, just sorting costs are higher.
Three, chemical reduction
Researchers are beginning to find ways to extract the chemical components of plastics for reuse. The process used is to cut off the long chains of polymers to restore their original properties, cracking out the raw materials can be used to make new plastics. In some cases, chemical elements are added to induce chemical cracking of the combined carbon atoms, or energy is added to facilitate thermal cracking.
Bayer in Germany has developed a hydrolytic chemical reduction method to crack PUC foam pads. Tests have shown that the chemical reduction method is technically feasible, but it can only be used to deal with clean plastics, such as powdered edges and other plastic waste from the manufacturing process. Plastics used in the home that are stained with other dirt are difficult to treat with the chemical reduction method. The application of this reduction method will not make significant use of hydrolysis to treat waste until the 21st century. Some new chemical decomposition methods are still in the research process, the United States Ford Motor Company is currently applying the ester decomposition method for the treatment of automotive waste plastic parts.
Air Pollution Overview
Even when the skies are clear, the atmosphere around us is not as clear as it seems. The air is full of invisible solids, liquids and gases in different forms: pollen, bacteria, soot, moisture and so on. By air pollution, we mean the presence of one or more pollutants in the air, the amount, nature and duration of which can harm human, plant and animal life, damage property, or interfere with a comfortable living environment, such as the presence of foul odors. In other words, as long as a substance exists in sufficient quantity, nature and duration to affect human beings or other living creatures or property, we can call it an air pollutant; and the phenomenon caused by its presence is air pollution. Before understanding what kind of substances enter the air to cause pollution, we need to first understand the composition of clean air. The composition of clean air is shown in Table 1: Usually we call "air pollutants" such as nitrogen dioxide, ozone, sulfur dioxide, carbon monoxide and other substances. Sulphur dioxide, carbon monoxide and other substances are present in very small amounts in clean air; however, when polluted, some of these specific substances can increase in large quantities. In other words, an abnormal increase in the amount of certain substances in the air creates an air pollution situation.
Types of air pollutants
There are many types of air pollutants, which may be in the form of solid particles, droplets or gases, or a mixture of these. What are the types of air pollutants that are currently defined in our country's laws and regulations? According to the Air Pollution Prevention and Control Act and related regulations, air pollutants can be divided into four major items, namely, gaseous pollutants (including sulfur oxides, carbon monoxide, nitrogen oxides, hydrocarbons, chlorine, hydrogen gas, fluoride, chlorinated hydrocarbons, etc.), particulate pollutants (including suspended particles, gold bureau soot, black smoke, acid mist, fallout, etc.), and secondary pollutants (refers to the pollution generated by pollutants in the air through photochemical reactions, including photochemical reactions). secondary pollutants (pollutants in the air through photochemical reactions, including photochemical fog, photochemical high oxides, etc.) and malodorous substances (including chlorine, hydrogen sulfide, methyl sulfide, mercaptans, methyl amines) and so on. The more common air pollutants include suspended particulates, carbon monoxide, sulphur oxides, nitrogen oxides and hydrocarbons, etc., most of which are generated by human factors. Most of the air pollutants generated by human factors (e.g., chimney emissions, vehicle emissions, etc.) are regulated by "emission standards" in our laws and regulations.
Three, air pollution indicators
Air pollution indicators (Pollutant Standard Index, referred to as PSI) for reference to the U.S. Environmental Protection Agency and other organizations to study the decision of the index, to 0 to 500 values to indicate the degree of air pollution. The relationship between this index and health effects is categorized into the following five levels:
Indicator Value 0-50
51-100
101-199
200-299
300-350
Health Effects Good
(Good)
Moderate
(Moderate)
(Moderate)
Bad
(Unhealthy)
Very Unhealthy
(Very Unhealthy)
Hazardous
http://ies.dyu.edu.tw/es _25.htm
Air pollutants include smoke, vapors, charred paper, dust, soot, grime, carbon fumes, gases, mist, odors, particulate matter, radioactivity, and other pollutants. ), RadioactiveMaterials, NoxiousChemicals, or other outdoor airborne substances.
Prevention and Control of Air Pollution
Prevention and Control of Air Pollution is a huge systematic project, which requires individual, collective, national, and even global efforts of all countries **** the same efforts, the following measures can be considered:
1. Reduce the emission of pollutants. Reform of the energy structure, the use of non-polluting energy (such as solar, wind, hydropower) and low-polluting energy (such as natural gas), pre-treatment of fuels (such as desulfurization of coal before burning), improve combustion technology can reduce emissions. In addition, before the pollutants enter the atmosphere, the use of dust removal and smoke elimination technology, condensation technology, liquid absorption technology, recycling and treatment technology to eliminate some of the pollutants in the exhaust gas can reduce the amount of pollutants entering the atmosphere.
2, control emissions and make full use of the atmosphere's self-purifying ability. Different meteorological conditions, the capacity of the atmosphere for pollutants will be different, discharged into the same amount of pollutants, resulting in different concentrations of pollutants. For windy, well-ventilated, turbulent, convective areas and time, the atmosphere has a strong diffusion and dilution capacity, and can accept more activities of factories and mining enterprises. In areas and times of inversion, the atmospheric diffusion and dilution capacity is weak, so it can not accept more pollutants, otherwise it will cause serious air pollution. Therefore, should be different areas, different times for effective control of emissions.
3, plant site selection, chimney design, urban and industrial planning should be reasonable, do not emit a large number of transitional concentration, do not cause repeated iterative pollution, the formation of local serious pollution events.
4, greening and afforestation, so that there are more plants to absorb pollutants, reduce the degree of air pollution.