The hottest research support project of Guangzhou

2022-10-14
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Guangzhou Social Science Foundation research support project

I. separation technology of plastic packaging waste

Plastic packaging waste can be separated from other garbage manually or mechanically (gravity method), and then adopt visual identification, combustion identification, specific weight identification, solvent separation, wind screening, electrostatic separation, low-temperature crushing and other methods

1. Visual identification and sorting technology

for small batches of waste plastics, the following methods can be adopted for classification: first, remove metal, glass, rope and other debris and seriously polluted waste plastics; The second is to classify agricultural film, packaging film, foam plastic and plastic bottle boxes; Third, the products are classified according to the color depth; Fourth, the commonly used PVC, polystyrene, polyethylene, polypropylene and other plastics are classified by simple methods such as visual inspection, hand feeling, specific gravity, combustion and so on

2. Density sorting technology

all kinds of plastics have different densities. Put different kinds of plastics in a specific solution, and classify and identify plastics according to their buoyancy in the solution. Because the plastic is non wetting, it needs surfactant for pretreatment, wetting it, and then sorting. Commonly used plastic solutions include water, saturated salt solution, alcohol solution and calcium chloride solution

3. Solution separation technology

the separation of waste plastics is realized by using different solubility of various plastics in organic solutions. The method is to add waste plastic fragments into specific solvents, control different temperatures, and selectively dissolve and sort various plastics. This technology has less solvent loss, and the recovered polymer can be reused after heating and granulation, with good performance

4. Wind screening technology

when there is a large amount of waste and sundries, wind screening technology can be used. In this method, the crushed waste plastic is put from the top in the re screening room, and the air is sprayed laterally. The self weight of the plastic and the different air resistance are used for screening

5. Electrostatic separation technology

electrostatic separation technology originates from the dry separation method, which is characterized by the separation of granular substances with a diameter of less than 8mm independent of density. Its size and shape do not affect the separation, low energy consumption and large processing capacity

II. Recycling of plastic packaging waste

Plastic packaging waste is extremely harmful to the environment and society, so its recycling is particularly important. Generally, the following ways can be adopted: manufacturing building materials, manufacturing daily necessities, manufacturing chemical products, cracking gas, oil and units, burning together with other garbage, and heat recovery (steam, hot gas and power generation)

1. Recycling of waste PVC

PVC accounts for more than 30% of plastic products in China. The recycling of waste PVC is mainly to directly recycle or supplement appropriate new materials and re produce various products. When these recycled materials are too dirty to make other products, they can still be used for infrastructure and water conservancy products (pipes, grooves, belts, plates, etc.)

① directly compounding and reusing the recycled products of waste PVC, corresponding additives should be added according to different varieties to meet the use requirements. The formula is shown in the table below. Waste PVC recycling material formula

materials soft hard soft foam waste PVC plastic

dibutyl phthalate

alkylbenzene sulfonate

tribasic lead sulfate

barium stearate

stearic acid or paraffin

Azodicarbonamide 100.0

10.0

5.0

1.0

0.8

0.2

-- 100.0

--

--

1.5

1.0

0.2

-- 100.0

5.0

5.0

0.5

1.0

0.2

6.0

PVC has a complex composition. In addition to resin, there are a certain amount of plasticizers, stabilizers, lubricants, pigments and other auxiliary materials. These additives will volatilize and lose in varying degrees due to the action of light and heat in the process of use. In the process of reproduction, an appropriate amount of addition must be carried out in order to maintain good physical mechanism performance after the replication of PVC waste plastics

② make asphalt felt and plastic ointment

waste polyethylene plastic is reacted with coal tar in a reactor. In the presence of catalyst, naphthalene anthracene and other components with a small degree of aggregation in coal tar are easy to react with chain PVC molecules to form cross-linking, forming a two-dimensional structure, so as to improve the softening point of modified tar pitch. Its performance is better than general petroleum asphalt felt and tar asphalt felt, especially good low temperature resistance, especially suitable for construction in northern areas. The specific operation: add asphalt into the enamel reaction kettle, stir it electrically at 150 ~ 200r/min, heat it up to 150 ~ 170 ℃ and react for 3h, then add filler, and stir it for a moment to obtain electrically modified tar asphalt

basic formula: Tar 100, waste PVC plastic 12 ~ 15, plasticizer 29 ~ 32, filler 30 ~ 50

2. Utilization of waste polystyrene

polystyrene is mainly used in the form of foamed plastic as shockproof packaging materials for household appliances such as televisions, refrigerators, washing machines, precision instruments and handicrafts. It is also used in food packaging such as fast food lunch boxes, and can also be used as thermal insulation materials. Most of these packaging materials are disposable and become waste after use

① reprocessing and reuse

there are two molding methods for polystyrene foam: one is direct foaming method, and the other is expandable bead method. These two methods are physical processes, which do not destroy the structure of polystyrene polymer and keep its original properties. Therefore, it can be recycled. Take the waste fast-food box as an example, its process flow is:

waste fast-food box → washing → drying → crushing → forced feeding → pre plasticization → extrusion plasticization (machine head with quick change filter) → molding → cooling → granulation → bagging

the granulation conditions are not high, so fls-75 extruder can be used

② making building cement products

the surface density of waste polystyrene foam is 20 ~ 25kg/m3, and the wet density of concrete after processing and mixing is 220 ~ 270kg/m3, which is basically equivalent to expanded pebble. The density after drying can be greatly reduced, and there are no special requirements for the cement mixed with it

there are many manufacturing methods for using waste polystyrene foam as light building materials. For example, use polystyrene foam particles, cement as binder, broken wood as filler, add water to mix, and then mold into various lightweight cement partitions. Plant fibers and Portland cement can also be compounded into thin plates, and the middle of the two layers of thin plates can be filled with the mixture of foam polystyrene and cement to make light solid wallboards, which are especially suitable for non bearing walls inside and outside buildings

③ preparation of paint

polystyrene has a transparency of about 90% and a refractive index of 1.59 ~ 1.60. It can be used as a vacuum coating primer on polypropylene and ABS as a new nano material with the thinnest, highest strength and strongest conductivity and heat conductivity found at present, which can improve the height of the light coating film of plastic parts. Of course, it can also be used to produce general antirust paint and furniture paint. Available: chloroform, banana water, xylene, dibutyl phthalate, glycerol, rosin modified phenolic resin, rosin, methylcellulose, aluminum stearate and pigments. Operation steps: cleaning. Clean, decontaminate, degrease and dry the collected waste polystyrene plastic (PS). Remove the residual water from the cleaned waste plastics (PS) and dry them, or dry them or dry them for preparation. After the above washed and dried waste plastics are properly broken, they are put into the reactor with stirrer without surgical removal. Phenolic resin, methylcellulose, rosin and mixed solvents (chloroform, banana water, xylene) with appropriate proportion are added and soaked for 1 day. After soaking, stir for more than 3H to dissolve and modify it into a uniform colloidal solution, and stick the extracted colloidal solution with a stick to form a linear drop and filter. Filter the above colloidal solution with 80 mesh copper sieve to obtain qualified modified plastic glue, which can be used to manufacture various paint pastes. Select the pigment, add appropriate solvent, grind it to the required fineness with a ball mill, and then filter it with a 100 ~ 200 mesh copper sieve to obtain the color paste

3. Utilization of polyolefin waste plastics

polyolefin refers to polyethylene and polypropylene. They are mainly used to produce films, hollow products and plastic textile bags

① recycling of waste polypropylene plastic woven bags

the collected waste polypropylene plastic woven bags are washed, dried, crushed, mixed into new polypropylene, and then mixed with about 10% low-pressure polyethylene. According to the quality requirements of woven bags, the mixing amount can be 20 ~ 70%. When using recycled materials, a small amount of titanium dioxide and yellow pigment must be added to adjust the color. Compared with polypropylene plastic woven bags made of brand-new materials with the same specification and weight, there is a slight difference in strength, but it has little impact on the use quality

② manufacturing calcium plastic

in waste plastics such as polyethylene, polypropylene and polyvinyl chloride, a large number of inorganic fillers can be added to make calcium plastic materials. This kind of waste plastic with high filling capacity has similar properties to wood, but its rigidity, wear resistance and heat resistance are better than wood. Calcium plastic can be processed by plastic molding. Due to the large increase of inorganic fillers in waste plastics, the influence of impurities mixed in waste plastics cannot be changed accordingly. The advantage of this product is its low price, but its strength and chromaticity are far less than those of products processed from new materials. It can only process black or brownish red products with little stress. The inorganic materials filled should have fine particle size, good dispersion, low water content and low price. Commonly used are light calcium carbonate, talc powder, two fly powder or four fly powder (natural calcium carbonate) and waste generated during the production of sulfuric acid (mainly containing iron oxide), etc

4. Recycling of waste polyester containers

plastic bottles as packaging supplies have developed very rapidly, among which pet bottles are used in food packaging on a large scale. The material is a plastic saturated polyester, non-toxic and tasteless, suitable for food packaging

① direct recycling, cleaning and use

pet bottles can be recycled and "melted" for reuse like metal cans and paper packaging, and can also be recycled and reused like glass bottles. In 1989, it took the lead in launching the new technology of reusable PET bottles in the Dutch market and gradually entered the world market. At present, there are equipment specially designed for reusable PET bottles. First of all, it is required that PET bottles should be temperature resistant, because the cleaning method of recycled PET bottles is the same as that of glass, and the caustic soda concentration is required to be 2 ~ 3%, and the temperature is 40 ~ 68 ℃

② crushing and recycling

the waste broken polyester packaging containers and broken granulated packaging containers after re blowing and stretching processing can only be used for non food packaging. The reason is that some molecules of recycled polyester decompose to acetaldehyde under high temperature blowing and stretching, Acetaldehyde has "with the completion of the acquisition, it can only be used in non food packaging.

because some pet bottles include polyester (PET) bottle body, high-pressure polyethylene (HDPE) bottom support, aluminum cap, and ethylene vinyl acetate copolymer (EVA) Cover liner, paper label and glue, etc. If it is impossible to separate by hand, the crushed fragments can be washed by blower and water to separate EVA, paper, pet, HDPE and Al with their density differences. That is, HDPE is removed by water suspension, and then pet and aluminum are separated by suspension of salt solution with a density of 1.4g. The main equipment is: crusher, air separator, flotation device and

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