PA polyamide
PET polyethylene terephthalate.
PE Polyethylene.
PVC Polyvinyl chloride.
PP is polypropylene.
ABS is a ****polymer of acrylonitrile, butadiene and styrene.
①Polyvinyl chloride (PVC) It is one of the most used plastics in construction. Rigid polyvinyl chloride density of 1.38 ~ 1.43g/cm3, high mechanical strength, good chemical stability ② polyethylene (PE) ③ polypropylene (PP) Polypropylene density in all plastics is the smallest, about 0.90 or so. Polypropylene is commonly used to produce pipes, sanitary ware and other building products. Polystyrene (PS) Polystyrene is a colorless and transparent glass-like plastic. ⑤ ABS plastic ABS plastic is a modified polystyrene plastic, acrylic eye (A), butadiene (B) and styrene (S) based on the composition of the three components.
PS: Polystyrene
is a colorless and transparent plastic material. It has a glass transition temperature higher than 100 degrees Celsius, so it is often used to make a variety of disposable containers that need to withstand the temperature of boiling water, as well as disposable foam lunch boxes.
PP: Polypropylene
is a semi-crystalline thermoplastic. It has high impact resistance, strong mechanical properties, and is resistant to a variety of organic solvents and acid and alkali corrosion. It has a wide range of applications in industry and is one of the usual common polymer materials. Australia's coins also use polypropylene production.
PE: polyethylene
is one of the most commonly used polymer materials in daily life, a large number of products used in the manufacture of plastic bags, plastic film, milk pails.
Polyethylene is resistant to a wide range of organic solvents and to corrosion by many acids and bases, but it is not resistant to oxidizing acids, such as nitric acid. Polyethylene is oxidized in oxidizing environments.
Polyethylene can be considered transparent in the thin film state, but when present in bulk form is opaque due to the presence of a large number of crystals within it, which undergo strong light scattering. The degree of crystallization of polyethylene is affected by the number of branched chains; the more branched chains there are, the more difficult it is to crystallize. The melting temperature of polyethylene crystals is also affected by the number of branch chains and ranges from 90 degrees Celsius to 130 degrees Celsius, with the more branch chains the lower the melting temperature. Polyethylene single crystals can usually be prepared by dissolving high-density polyethylene in xylene at temperatures above 130 degrees Celsius.
Structural formula: - CH2 - CH2 - CH2 - CH2 - CH2 - CH2 - CH2 - CH2
ABS: a synthetic plastic of acrylonitrile, butadiene, styrene
Acrylonitrile, butadiene, styrene, three monomers of the grafting of the *** polymerization product, take the first letter of their English names. It is a high strength, good toughness, excellent overall performance of the resin, a wide range of uses, commonly used as engineering plastics. Industry to polybutadiene latex or styrene content of low styrene rubber main chain, and acrylonitrile, styrene two monomer mixture of graft **** polymerization. In fact, it is often a mixture of butadiene-containing graft polymers and acrylonitrile-styrene **** polymer SAN (or AS). In recent years, there are also first styrene, acrylonitrile two monomers *** polymerization, and then with the graft *** polymerization of ABS resin to different proportions of the mixture, in order to produce to adapt to the different uses of a variety of ABS resins. the mid-20th century 50's has begun in the United States industrialized production.
Industrial production methods can be divided into two main categories: one is the polybutadiene or styrene-butadiene rubber and SAN resin in the roller for mechanical **** mixing, or two kinds of latex **** mixing, and then **** polymerization; the other is in the polybutadiene or styrene content of low-butadiene latex to add styrene and acrylonitrile monomers for the emulsion grafting **** polymerization, or then mixed with the SAN resin in different proportions.
Structure, Properties and Applications In ABS resin, the rubber particles are in a dispersed phase, dispersed in the continuous phase of SAN resin. When impacted, the cross-linked rubber particles withstand and absorb this energy, dispersing the stress and thus preventing the development of cracks, thereby improving tear resistance.
The purpose of graft*** polymerization is to improve the compatibility and adhesion of the rubber granule surface to the resin phase. This is related to the amount of free SAN resin and the composition of the SAN resin grafted onto the rubber main chain. The difference between the acrylonitrile content of these two resins should not be too large, otherwise the compatibility is not good, which will lead to cracking at the interface between the rubber and the resin.
ABS resin can be used in injection molding, extrusion, vacuum, blow molding and roller pressing molding methods such as processing for plastic, can also be used mechanically, bonding, coating, vacuum evaporation and other methods for secondary processing. Because of its excellent overall performance, a wide range of uses, mainly used as engineering materials, can also be used for household appliances. Because of its oil resistance and resistance to acids, alkalis, salts and chemical reagents, such as good performance, and can be plated, plated with a metal layer has a good luster, light weight, low price and other advantages, can be used to replace some of the metal. Can also synthesize self-extinguishing and heat-resistant type and many other varieties to adapt to a variety of uses.
PET: polyethylene terephthalate
Polymer of terephthalic acid and ethylene glycol. Abbreviated PET, it is mainly used in the manufacture of polyethylene terephthalate fibers (Chinese trade name polyester). This fiber has high strength, its fabric wearing performance is good, is currently the highest yield of synthetic fibers in a variety of world production in 1980 about 5.1 million tons, accounting for 49% of the world's total output of synthetic fibers
Properties of molecular structure of the high degree of symmetry and rigidity of the chain of the phenylene, so that the polymer has a high degree of crystallinity, high melting temperature and insoluble in organic solvents in general, the melt temperature is 257 ~ 265 ℃; the polymer is mainly used to manufacture polyethylene terephthalate fiber (Chinese commercial name of polyester). is 257～265℃; its density increases with the increase of crystallinity, the density of amorphous state is 1.33 g/cm^3, after stretching due to the increase of crystallinity, the density of fibers is 1.38～1.41 g/cm^3, from the X-ray study, the density of the complete crystalline was calculated to be 1.463 g/cm^3. The glass transition temperature of the amorphous polymer is 67℃; the density of the crystalline polymer is 81°C. The polymer has a heat of fusion of 113-122 J/g, a specific heat capacity of 1.1-1.4 J/(g. K), and a dielectric constant of 1.1-1.4 J/(g. K). The specific heat capacity is 1.1-1.4 J/(g. K), the dielectric constant is 3.0-3.8, and the specific resistance is 10^11 10^14 ohm. cm. PET is not soluble in common solvents, only in some more corrosive organic solvents such as phenol, o-chlorophenol, m-cresol, trifluoroacetic acid mixture of solvents, PET fibers are stable to weak acids, weak bases.
Applications Mainly used as raw materials for synthetic fibers. Staple fibers can be blended with cotton, wool, hemp, made of textiles for clothing or upholstery; filaments can be used for clothing or industrial filaments, such as filter cloth, tire cord, parachutes, conveyor belts, seat belts and so on. The film can be used as the base for photographic film and cassette tape. Injection molded parts can be used as packaging containers.
PVC: Polyvinyl Chloride
It is a polymer material that uses a chlorine atom to replace a hydrogen atom in polyethylene.
The most important characteristic of polyvinyl chloride is that it is flame retardant, so it is widely used in fireproofing applications. However, polyvinyl chloride releases hydrochloric acid and other toxic gases during combustion.
Structural formula: - CH2 - CHCl - CH2 - CHCl - CH2 - CHCl -
POM: Polyoxymethylene
Scientific name is polyoxymethylene, a thermoplastic crystalline polymer. Abbreviation for POM. structural formula for CH - O, 1942 years ago, formaldehyde polymerization is mostly polymerization is not high, easy to heat depolymerization of polyoxymethylene glycol HO CH O H, of which = 8 ~ 100 for the polyformaldehyde; more than 100 for the - polyformaldehyde, around 1955, the U.S. DuPont polymerization of formaldehyde from formaldehyde homopolymer, that is, homopolymer, the trade name of the polyoxymethylene. The U.S. Celanese company by the start of the triple formaldehyde, with a small amount of dioxin pentacyclic or ethylene oxide **** polymer, that is, **** polyformaldehyde, trade name Celcon.
Properties polyformaldehyde is easy to crystallize, the degree of crystallinity of 70%; through high-temperature annealing, the degree of crystallinity can be increased. The melting temperature of paraformaldehyde is 181°C, and its density is 1.425 g/cm . *** The melting point of paraformaldehyde is about 170℃. The glass transition temperature of homopolyformaldehyde is -60℃. Phenolic compounds are the best solvents for paraformaldehyde. It is known from the study of melt index that the molecular weight distribution of homopolyformaldehyde is narrow. Except for strong acids, oxidizing agents and phenols, ***Polyformaldehyde is stable to other chemicals, while homopolyformaldehyde is also unstable to concentrated ammonia. Stabilized paraformaldehyde can be heated to 230°C without significant decomposition. Polyformaldehyde can be used in compression, injection, extrusion, blow molding and other methods of molding, processing temperature of 170 ~ 200 ℃; can also be processed by machine tools, can also be welded. Products are light, hard, rigid and elastic, dimensionally stable, small coefficient of friction, low water absorption, good insulation properties, and resistance to organic solvents; can be used in a wide range of temperatures (-50 ~ 105 ℃) and humidity range; in a variety of
Technical Department; Feng Zhenxing
April 2, 2010
Plastic awareness
ABS is the company's most common type of plastic. The company's most common type of plastic this plastic raw material for the original color of beige; the most common products are the front frame of the TV; fixed picture tube corner of the four corners of the corner, etc. '; the characteristics of this plastic for the flexibility; rigidity is very good; the biggest characteristic of this material is that it can be plated.
Identification methods first; the naked eye to identify the method to look at the inner side of the product is beige if it is then can be concluded that the ABS material ABS material appearance is relatively smooth
Identification methods second; physical testing method in similar colors and products to identify the ABS to be more than the other similar material to be harder than the other similar material to be higher flexibility than the other similar material especially fragile may not be the ABS material Why do you say that may; because some products are years old; rigidity is very good; the biggest characteristic of this material is that can be plated. Said may; because some products after a long period of time weathering can be attenuated products of organic matter; in more than 10 years of products this approach is not good judgment.
Identification method three; fire identification method ABS in the burning smoke is very thick fire red part of the burned off for the state of coke
Waste plastics recycling is a systematic project, to distinguish between a variety of waste plastics, I'm afraid that you have to go to the purchase of some polymer materials books! Yazhijiang here for some simple introduction to see if you help. The specific classification of many plastics, polymer materials, I'm afraid that is not a couple of words can be included, but in terms of plastics, from the following classifications: thermosetting plastics and thermoplastic plastics thermosetting plastics definition: polymer resins through the heating of plasticization or the introduction of additives to plasticization, curing and shaping by cooling can not be re-formed through the thermoplastic molding material, such as phenolic plastics, urea-formaldehyde plastics, 191 resin toughening Plastic, etc. That is, thermosetting plastics can not be recycled and granulated again. Definition of thermoplastic plastic: polymer resin through the heating of plasticization, through the cooling of the stereotypes, can again according to the needs of the second heating plasticization molding, week after week. Plastic recycling granulation refers to this type of plastic. Further classification of thermoplastics can be divided into conventional thermoplastics through the use of plastics and engineering plastics, commonly used thermoplastic general-purpose plastics are polyethylene (PE) polypropylene (PP) polyvinyl chloride (PVC) polystyrene (PS), etc., engineering plastics are acrylene acrylene-butadiene-styrene (ABS) high impact polystyrene (AS) or (HIPS). Simple identification of plastics, available in the following ways: intuitive identification method refers to the human sense to experience some intuitive characteristics of plastic. Appearance: Transparent? Translucent? Opaque? How about the color (when not dyed)? Put into the water, floating? Sinking? Smell with the nose: does it smell? What kind of odor? Touch: smooth or rough? Does it feel cold or hot? Scratch it with your fingernail: are there any marks? Stretch it with your hand, is it hard or soft? Is there any toughness and elasticity? Plastic will fall a fall, listen to its sound, loud? Crisp? Or low? Fragile? Or tough? Through these sensory checks, you can identify which kind of plastic it is. (PE) Polyethylene The raw material of LDPE is white wax, transparent; HDPE is white powder or white translucent granular resin. Floating in the water, odorless and tasteless, with a wax-like smooth feeling, traces after scratching, the film is soft and can be stretched.LDPE is soft, extensible, bendable, but easy to break; MDPE, HDPE is harder, better rigidity and toughness, the tone is low
(PP) polypropylene raw materials are white waxy, semi-transparent, floating in the water, odorless and tasteless, smooth to the touch, no trace after scratching, can be bent, can be bent. Not easy to break, tensile strength and rigidity is good, sound loud (PS) polystyrene standard glass-like transparent; impact resistance, no luster, sinking in water, odorless, tasteless, smooth to the touch, brittle, easy to break the fingernail playing metal sound, commonly known as "ringing glue"
ABS milky white or beige, amorphous, opaque, no luster, sinking in water, no trace after scratching, can be bent, can be bent, can be bent, can be bent, can be bent, can be bent, can be bent, can be bent, can be bent. No luster, sinking in water, odorless, tasteless, tough material, hard, rigid and good. Not easy to break, sound crisp
(PVC) polyvinyl chloride products depending on the plasticizer and filler, some opaque. Sinking in the water, varying with the variety of hard products when heated to 50 ℃ is soft, and can be bent; soft products will sag, and some have elasticity, hard products such as windows and doors, sewer pipes, etc.
PA-6
PA-66 polyamide (nylon) raw materials milky white color, such as gelatin. When heated to more than 250 ℃ into a water syrup. Sinking in water Odorless and tasteless Surface is hard and hot, will not break when gently hammered, low tone
PMMA polymethyl methacrylate (plexiglass), glassy and transparent, beautiful appearance. Sinking in water, odorless and tasteless, can be freely bent when heated to 120 ℃, can be manually processed, hard, not fragile with a finger playing a blunt heavy sound
PTEE white wax-like, low transparency, smooth, non-combustible, non-absorbent, excellent weather resistance. Sinking in the water, odorless and tasteless, lubrication, low tone
PU has five forms of foam, elastomers, coatings, synthetic leather and adhesives, etc., with different forms, some sinking in the water, some floating. Odorless and tasteless, with different forms, the sound low (PC) polycarbonate raw materials for white crystalline powder, light yellow to amber, transparent solid, products close to colorless. For advanced insulation materials, odorless, tasteless, metallic, hard, bending resistance, impact resistance, toughness, sound louder combustion identification method can be cut a small piece of plastic specimen, clamped with tweezers, placed on the ignition of the alcohol lamp or lighter to burn, carefully observe the ease of combustion, leave the source of ignition is to continue to burn or immediately extinguished, the color of the flame, the situation of the smoke, the combustion of plastic in the combustion and combustion have What state changes, what odor when burning. According to the burning characteristics of plastics, to determine its type. Thermoplastic plastics become soft and melt when burning, and even burn; thermosetting plastics become brittle and burn when burning, but do not soften. Containing chlorine, phosphorus, fluorine and silicon elements of the plastic is not easy to burn and self-extinguishing, containing sulfur and nitro plastics are very easy to burn, some plastics burn black smoke, some plastics will decompose when burning and produce a special smell ...... These phenomena of combustion can be used as a basis for identifying plastics, distinguishing between varieties. Plastic name Burning difficulty After leaving the fire Flame characteristics Plastic state change Odor
PE can burn Continue to burn Bright, bottom blue, upper end yellow Molten droplets continue to burn, smokeless Molten droplets Candle blowing out Odor
PP Upper end yellow, bottom blue, a small amount of black smoke Softening, foaming Petroleum Odor Pungent odor
PS easy to combust Bright, orange, thick black smoke, soot Molten, foaming, soot, black smoke. Soot Melting, blistering, slightly charred Aromatic odor (styrene monomer odor)
ABS Yellow flame, bright, black smoke Softening, melting, scorching, no dripping Rubbery odor
PA Slow burning Slow extinguishing Yellow-orange, blue at edges Melting, dripping, blistering Burning wool, fingernails Special odor
PC Yellow, bright, soot Softening, melting, blistering, charring Fruit and peanuts. Softens, melts, blisters, scorches Fruity odor
PVC Refractory Extinguishes on release Yellow-orange, green edges, white smoke, light green and yellow flames Softens, draws, irritating HCl odor
UF Self-extinguishing Yellow, light blue at tip Swells, cracks, turns white, caramelizes Formaldehyde odor, ammonia odor
MF Pale yellow, whitish at edges Swells, cracks, turns white, scorches Formaldehyde odor, light fishy odor
PF Glowing, yellow sparks Cracking, turning darker Phenol and formaldehyde odor
PF (wood flour) Slow burning Yellow, black smoke Expansion, cracking Wood and phenol odor
CP is an amorphous, odorless, ※-free, highly transparent colorless or slightly yellow thermoplastic engineering plastics, with excellent physical and mechanical properties, especially impact resistance Excellent, high tensile strength, bending strength, compression strength; small creep, dimensional stability; good heat resistance and low temperature resistance, stable mechanical properties in a wide range of temperatures, dimensional stability, electrical properties and flame retardant, can be used for a long time at -60 ~ 120 ℃; no significant melting point, 220-230 ℃ is a melt; due to the rigidity of the molecular chain, the viscosity of the resin melt is large; Small water absorption, small shrinkage, high dimensional accuracy, good dimensional stability, film permeability is small; is a self-extinguishing material; light stable, but not UV resistance, good weather resistance; oil resistance, acid resistance, not resistant to strong alkali, oxidizing acids and amines, ketones, soluble in chlorinated hydrocarbons and aromatic solvents, long-term hydrolysis in the water easily caused by hydrolysis and cracking, the disadvantage of fatigue strength due to poor, easy to produce stress cracks, solvent resistance is poor, abrasion resistance is not good. PC can be injection molding, extrusion, molding, blow molding, thermoforming, printing, bonding, coating and machining, the most important processing method is injection molding. Before molding must be pre-dried, moisture content should be less than 0.02%, trace moisture in the processing of high temperature will make the products produce white color, silver wire and bubbles, PC at room temperature has a considerable forced high elastic deformation capacity. The impact toughness is high, so it can be cold pressed, cold drawn, cold rolled and other cold molding process. Extrusion with PC molecular weight should be greater than 30,000, to use gradual compression screw, L/D ratio 1:18~24, compression ratio 1:2.5, can be used for extrusion blow molding, injection - blowing, injection - pulling - blowing method of molding high-quality, high-transparent bottles.PC alloys a wide range of types of alloys, to improve the PC melt viscosity (processability) and the products are prone to stress cracking and other defects, PC and different polymers to form alloys or **** blends, to Improve material properties. Specifically PC / ABS alloys, PC / ASA alloys, PC / PBT alloys, PC / PET alloys, PC / PET / elastomer **** blend, PC / MBS **** blend, PC / PTFE alloys, PC / PA alloys, etc., Lee has two material performance advantages, and reduce costs, such as PC / ABS alloys, PC mainly contributes to high heat resistance, better toughness and impact strength, high strength, flame retardant, ABS can improve moldability, apparent quality, reduce density.PC's three major applications are the glass assembly industry, the automotive industry and the electronics, electrical appliances industry, followed by industrial machinery parts, CD-ROMs, packaging, computers, and other office equipment, medical and health care, film, recreation, and protective equipment.PC can be used as glass for windows and doors, and PC laminates are widely used in Protective windows in banks, embassies, detention centers and public **** places, used in aircraft cabin covers, lighting equipment, industrial safety stalls and bulletproof glass. PC boards can be used for various signs, such as gasoline pump dials, automobile instrument panels, cargo and open-air commercial signs, point sliding indicators, PC resin used in automobile camera systems, dashboard systems and interior decorative systems, used as headlamp covers, front and rear automobile gear boards with reinforcing ribbing, reflective mirror frames, door frames, operating rod sheathing, flow blocking boards, PC is used as a junction box, sockets, plugs and bushings, spacers, TV conversion devices, telephone line brackets under the communication cables, PC is applied as a junction box, receptacles, plugs and sleeves, gaskets, television conversion PC is used as junction boxes, sockets, plugs and bushings, gaskets, TV converters, connectors for communication cables under telephone line brackets, electric switch boxes, telephone switchboards, switchboard components, relay housings, PC can be used as low load parts for household appliance motors, vacuum cleaners, shampooers, coffee makers, toasters, handles for power tools, various gears, worm gears, bushings, guide gauges, shelves in refrigerators, etc. PC is an ideal material for optical disc storage media. PC bottles (containers) are lightweight, good impact resistance, and resistant to certain high temperatures and corrosive solution washing, as recyclable bottles (containers).
Waste plastics are usually disposed of in landfills or incinerated. Incineration will produce a large number of toxic gases causing secondary pollution. Landfill will occupy a large space; natural degradation of plastics requires more than a hundred years; precipitation additives to pollute the soil and groundwater and so on. Therefore, the development trend of waste plastics treatment technology is recycling, but at present the recycling and regeneration of waste plastics has a low utilization rate. The reason for this is that there are problems in management, policy and recycling, but more importantly, the recycling technology is still not perfect.
Waste plastics recycling technology is diverse, there can be recycled a variety of plastics technology, there are also specialized in the recovery of a single resin technology. In recent years, plastic recycling technology has made many welcome progress, this article mainly for the more general technology to do a summary.
1 Separation and sorting technology
One of the key links in the recycling of waste plastics is the collection and pretreatment of waste plastics. Especially in China, the important reason for the low recycling rate is the low degree of waste classification and collection. As the melting point and softening point of different resins differ greatly, in order to make better recycling of waste plastics, it is best to classify and treat single varieties of resins, so separation and screening is an important part of waste plastics recycling. For small quantities of waste plastics, artificial sorting method can be used, but the artificial sorting efficiency is low, will make the recovery cost increase. Foreign countries have developed a variety of separation and sorting methods.
1.1 Instrument identification and separation technology
Italy's Govoni company first used X-ray detectors and automatic classification system to separate PVC from mixed plastics [1]. The U.S. Plastics Recycling Technology Research Center developed an X-ray fluorescence spectrometer, which can be highly automated to separate PVC containers from rigid containers. Refrakt in Germany, on the other hand, utilizes heat source identification technology to separate molten PVC from mixed plastics at lower temperatures by heating [1].
Near-infrared light has the function of recognizing organic materials, and the speed of recognizing plastics by the light filter using near-infrared technology [1] can reach more than 2,000 times/second, and the common plastics (PE, PP, PS, PVC, PET) can be clearly differentiated, and when the mixed plastics pass through the near-infrared spectral analyzer, the device can automatically sort out the five common plastics, and the speed can be as fast as 20-30 pieces/min.
1.4 Flotation separation method
A Japanese materials research institute used common infiltrating agents, such as sodium lignosulfonate, tannic acid, Aerosol OT and saponin, to successfully separate the plastic mixtures of PVC, PC (polycarbonate), POM (polyoxymethylene formaldehyde), and PPE (polyphenylene ether), etc.[4].
1.5 Electrical separation technology [5]
The separation of mixed plastics (e.g., PAN,, PE, PVC, and PA) by friction-generated electricity. The principle is that two different non-conductive materials friction, they gained through the electron gain or loss of the opposite charge, in which the material with a high dielectric constant with a positive charge, the material with a low dielectric constant with a negative charge. Plastic recycling mixed materials in the rotating pot frequent contact and generate charges, and then be sent as another surface charged pot and be separated.
2 incineration recovery energy
Polyethylene and polystyrene combustion heat up to 46000kJ/kg, more than the average fuel oil value of 44000 kJ/kg, PVC calorific value is also as high as 18800 kJ/kg. Waste plastics combustion speed, low ash, foreign countries to use it instead of coal or oil used in the blast furnace blowing or rotary kiln cement. As PVC combustion will produce hydrogen chloride, corrosion of boilers and pipelines, and the exhaust gas contains furans, dioxins and so on. The U.S. has developed RDF technology (Refuse Solid Fuel), which mixes waste plastics with waste paper, wood chips, fruit shells, etc., which not only dilutes the chlorine-containing components, but also facilitates storage and transportation. For those technically impossible to recover (such as a variety of composite materials or alloy mixing products) and difficult to regenerate waste plastics can be incinerated to recover heat energy. The advantages are large treatment quantities, low cost and high efficiency. The disadvantage is the production of harmful gases, the need for specialized incinerators, equipment investment, loss, maintenance, running costs are high.
3 Molten regeneration technology
Molten regeneration is to heat and melt the waste plastics and then re-plasticize. According to the nature of the raw material, can be divided into simple regeneration and composite regeneration of two kinds. Simple regeneration mainly recycles the marginal waste of resin and plastic product factories and those disposable consumer products that are easy to pick and clean, such as polyester beverage bottles and food packaging bags. After recycling, its performance is similar to that of new materials.
The raw materials for composite recycling, on the other hand, are collected from different channels of waste plastics, which are characterized by many impurities, complex varieties, diverse forms, and dirt, etc. Therefore, the recycling processing procedures are more complicated, and the separation technology and screening workload is large. Generally speaking, the nature of composite recycled plastics is unstable, easy to become brittle, often used to prepare lower grade products. Such as construction filler, garbage bags, microporous sandals, raincoats and packaging materials for instruments.
4 Cracking for Recovery of Fuels and Chemicals
4.1 Thermal Cracking and Catalytic Cracking Technology
Due to the increasing theoretical research on cracking reactions [6-11], many advances have been made in the development of cracking technology both at home and abroad. Cracking technology is divided into two kinds depending on the end products: one is to recover chemical raw materials (such as ethylene, propylene, styrene, etc.) [12], and the other is to get fuels (gasoline, diesel, tar, etc.). Although both convert waste plastics into low molecular substances, the process routes are different. The production of chemical materials is to heat the waste plastics in a reaction tower and reach the decomposition temperature (600-900°C) in a boiling bed, which generally does not produce secondary pollution, but the technical requirements are high and the cost is also high. Cracking olefinization technology, on the other hand, usually have two kinds of thermal cracking and catalytic cracking.
Japan's Fuji Cycle's waste plastics into gasoline, kerosene and diesel technology, the use of ZSM-5 catalysts, through two reactors for the conversion reaction will be cracked plastic into fuel. Each kilogram of plastic can generate 0.5L gasoline, 0.5L kerosene and diesel. Amoco (USA) has developed a new process to convert waste plastics into basic chemicals in a refinery. Pretreated waste plastics are dissolved in hot refinery oil and decomposed into light products under the action of high temperature FCC catalyst. LPG and aliphatic fuels are recovered from PE; aliphatic fuels are recovered from PP, and aromatic fuels can be obtained from PS.Yoshio Uemichi et al [13] developed a composite catalytic system for the degradation of polyethylene, with the catalysts being silica/alumina and HZSM-5 zeolite. Experiments showed that this catalyst is more effective for selective production of high-quality gasoline, the resulting gasoline yield of 58.8%, octane number 94.
Domestic Li Mei et al [14] reported that waste plastics at a reaction temperature of 350-420 ℃, reaction time of 2-4s, can be obtained MON73 gasoline and SP-10 diesel fuel, can be produced in continuous production of the process. Li Jianhong et al [3] carried out a study of catalysts for the degradation process of waste plastics. The ideal catalyst for the catalytic cracking process with PE, PS and PP as raw materials is a molecular sieve type catalyst with acidic surface, an operating temperature of 360°C, a liquid yield of more than 90%, and a gasoline octane rating of more than 80. Liu Gongzhao [15] researched and developed a pilot plant for the catalytic cracking of waste plastics into gasoline and diesel fuel at one time, which can produce gasoline and diesel fuel of 2t per day, and is capable of realizing gasoline and diesel fuel The cracking reactor is characterized by good heat transfer and large production capacity. With the catalyst addition of 1-3% and the reaction temperature of 350-380℃, the total yield of gasoline and diesel can reach 70%, the octane number of gasoline produced from waste polyethylene, polypropylene and polystyrene is 72, 77 and 86 respectively, and the freezing point of diesel is 3, -11, -22℃, the process is safe to operate and there is no emission of three wastes. Yuan Xingzhong [16] studied the technology of catalytic cracking of waste plastics in fluidized moving bed reactor for the problems of slag removal from the bottom of the kettle and pipe gumming. It lays the foundation for realizing safe, stable, long cycle continuous production, reducing energy consumption and cost, and improving yield and product quality.
Cracking waste materials to produce chemical raw materials and fuels is an important way to recover resources and avoid secondary pollution. Germany, the United States, Japan and other large-scale factories, our country in Beijing, Xi'an, Guangzhou, also built a small-scale waste plastic olefinization plant, but there are still many problems to be solved. Due to the poor thermal conductivity of waste plastics, the plastic is heated to produce high viscosity melt, not conducive to transport; waste plastics containing PVC leads to HCl, corrosion of equipment at the same time make the catalyst activity is reduced; carbon residue adhering to the reactor wall, not easy to remove, affecting the continuous operation; catalyst service life and low activity, so that the high cost of production; production of oil residue produced by the current no better way of dealing with it, and so on. There are still many domestic reports on pyrolysis oleochemical[43-54], but how to absorb the existing results and overcome the technical difficulties is what we urgently need to do.
4.2 Supercritical oiling method
The critical temperature of water is 374.3 ℃, the critical pressure is 22.05Mpa. critical water has the performance of organic solution in the normal state, can dissolve organic matter and can not dissolve inorganic substances, and can be completely miscible with air, oxygen, nitrogen, carbon dioxide and other gases. Japanese patents useful supercritical water for waste plastics (PE, PP, PS, etc.) for recycling report, the reaction temperature of 400 ~ 600 ℃, reaction pressure of 25Mpa, reaction time of 10min or less, you can get more than 90% of the oleochemical yield. The advantages of using supercritical water for the degradation of waste plastics are obvious: water as a medium is inexpensive; carbonization during pyrolysis can be avoided; the reaction is carried out in a closed system, which does not bring new pollution to the environment; the reaction is fast, and the production efficiency is high. Qiu Ting et al [17] summarized the progress of supercritical technology in the recycling of waste plastics.
4.3 Gasification Technology
Gasification has the advantage of being able to mix municipal waste without separating the plastics, but the operation requires higher temperatures than pyrolysis (typically around 900°C). Germany Espag's Schwaize Pumpe refinery can process 1,700t of waste plastics into municipal gas per year. rWE plans to gasify 220,000t of lignite, 100,000t of plastic waste and petroleum sludge produced by town oil processing plants each year. Germany Hoechst company uses high-temperature Winkler process to gasify mixed plastics, and then converted into water gas as a raw material for synthetic alcohols.
4.4 Hydrogenation cracking technology
Germany Vebaeol company set up a hydrogenation cracking device, so that the waste plastic particles in the 15 ~ 30Mpa, 470 ℃ hydrogenation, to produce a synthetic oil, of which 60% of the chain alkanes, 30% of the cycloalkanes, aromatics for 1%. The effective utilization rate of energy of this processing method is 88%, and the effective rate of material conversion is 80%.
5 Other use of technology
Waste plastics have a wide range of uses. Texas State University used yellow sand, stone, liquid PET and curing agent as raw materials to make concrete, and Bitlgosz [18] used waste plastics as raw materials for cement. Xie Liping et al [19] used waste plastics with wood and paper to prepare mesoporous activated carbon, Lei Yanying et al [20 reported the application of waste polystyrene to make paint, and Li Lingling [21] reported that plastics can be turned into wood. Song Wenxiang [22] describes the production of high-strength plastic sleepers from abroad using HDPE as raw material by a special method to make glass fibers of different lengths in the mold in the same direction along the axial direction of material flow. Pu Tingfang [23] and others used waste polyethylene to make high value-added polyethylene wax. Li Chunsheng et al [24] reported that polystyrene, compared with other thermoplastics, is characterized by low melt viscosity and high fluidity, so that after melting, it can be well infiltrated with the surfaces contacted to play a good adhesive role. Zhang Qiangqi et al [25] modified asphalt with waste plastics, one or more plastics in a certain proportion of uniformly dissolved in asphalt, so that the road performance of asphalt has been improved, so as to improve the quality of asphalt pavement and extend the life of the pavement.
Conclusion
The control of white pollution is a huge systematic project, need various departments, industries *** with efforts, need the whole society in thought and action *** with participation and support, depends on the whole people's awareness of science and technology, environmental protection awareness of the improvement. Government departments in the formulation of regulations to strengthen the management at the same time, the development of environmental protection technology and environmental protection industry as an important channel to stimulate the economy and expand employment, so that the collection of waste plastics, processing and recycling industrialization. At present, China's recycling and processing enterprises are scattered, small-scale .