Simple identification of common plastics

Most plastics need to be sorted before they can be reused in various plastic recycling methods. Due to the complexity and complexity of plastic consumption channels, some post-consumer plastics are difficult to distinguish by appearance. Therefore, it is better to mark the variety of materials on plastic products. China has formulated the GB/T16288-1996 "Recycling Marks for Plastic Packaging Products" with reference to the type of materials proposed and implemented by the American Plastics Association (SPE). Although the above marking methods can be used to facilitate sorting, there are still many unmarked products in China. Plastic products, to bring difficulties to sorting, in order to separate different types of plastic, in order to separate and recycle, first of all to master the knowledge of different plastics, the following describes the plastic simple identification method:

1. Appearance identification of plastic

By observing the appearance of the plastic, it is possible to initially identify the major categories of plastic products: thermoplastics, thermosetting plastics or elastomers. Typical thermoplastics are crystalline and amorphous. Crystalline plastics appear semi-transparent, opaque or opaque, and only transparent in the film state, the hardness from soft to horny. Amorphous is generally colorless, and is completely transparent when no additives are added, and hardness is harder than that of keratin rubber (additives such as plasticizer are often added at this time). Thermosetting plastics usually contain fillers and are impervious to transparency, and are transparent when they do not contain fillers. The elastomer has a rubbery feel and has a certain stretch rate.

2. Identification of plastic heating

The heating characteristics of the above three types of plastics are also different and can be identified by heating. Thermoplastics soften when heated, melt easily, and become transparent when melted, often pulling the filaments from the melt, and are often susceptible to heat sealing. The thermosetting plastic is heated until the material is chemically decomposed, and its original hardness is not softened, the size is relatively stable, and the decomposition temperature is charred. When the elastomer is heated, no flow occurs until the chemical decomposition temperature, and the material decomposes and carbonizes to the decomposition temperature.

Commonly used thermoplastic softening or melting temperature range see table

Variety of plastic softening or melting range / °C Variety of plastic softening or melting range / oc

Polyacetate 35~85 Polyoxymethylene 165~185

Polystyrene 70~115 Polypropylene 160~170

PVC 75~90 Nylon 12 170~180

Polyethylene

Density 0.92/cm3 110 Nylon 11 180~190

Density 0.94/cm3 About 120 Polychlorotrifluoroethylene 200~220

Density 0.96/cm3 About 130 Nylon 610 210~ 220

Poly-1-butene 125~135 nylon 6 215~225

Polyvinylidene chloride 115 to 140 (softened) Polycarbonate 220 to 230

Plexiglass 126~160 Poly-4-methylpentene-1 240

Cellulose acetate 125~175 nylon 66 250~260

Polyacrylonitrile 130~150 (Softening) Polyethylene Terephthalate 250~260

3. Identification of plastic solvents

Thermoplastics swell in solvents but are generally insoluble in cold solvents. In hot solvents, some thermoplastics dissolve. For example, polyethylene dissolves in xylene. Thermosetting plastics are insoluble in solvents. They generally do not swell or swell slightly. Elastomers do not dissolve in solvents, but they usually swell.

4. Density identification of plastics

Different types of plastics have different densities. Plastics can be used to determine the density; however, foaming products should be separated at this time because the density of the foam is not the true density of the material. In the actual industry, there is also the use of different plastic density to sort plastics. The density of commonly used plastics is shown in the table below: Density/(g/cm3) Material Density/(g/cm3) Materials

0.80 silicone rubber cavity (filled with silica to 1.25) 1.19~1.35 plasticized polyvinyl chloride (approx. 40% plasticizer)

0.83 Polymethylpentene 1.20~1.22 Polycarbonate (Bisphenol A Type)

0.85~0.91 Polypropylene 1.20~1.26 Crosslinked Polyurethane

0.89~0.93 High Pressure (Low Density) Polyethylene 1.26~1.28 Phenol Formaldehyde Resin (Unfilled)

0.91~0.92 1-polybutene 1.26~1.31 PVA

0.9~0.93 Polyisobutylene 1.25~1.35 Cellulose Acetate

0.92~1.00 Natural Rubber 1.30~1.41 Phenol Formaldehyde Resin (filled organic material: paper, fabric)

0.92~0.98 Low pressure (high density) polyethylene 1.30~1.40 Polyvinyl fluoride

1.01~1.04 Nylon 12 1.34~1.40 Celluloid

1.03~1.05 Nylon 11 1.38~1.41 Polyethylene Terephthalate

1.04~1.06 Acrylonitrile Butadiene Styrene (ABS) 1.38~1.50 Rigid PVC

1.04~1.08 Polystyrene 1.41~1.43 Polyoxymethylene (polyoxymethylene)

1.05~1.07 Polyphenylene ether 1.47~1.52 Urea-melamine resin (with organic filler added)

1.06~1.10 Styrene-acrylonitrile copolymer 1.47~1.55 Chlorinated polyvinyl chloride

1.07~1.09 Nylon 610 1.50~2.00 Bakelite and aminoplast (with inorganic filler)

1.12~1.15 Nylon 6 1.70~1.80 Polyvinylidene fluoride

1.13~1.16 Nylon 66 1.80~2.30 Polyester and Epoxy (with glass fiber added)

1.10~1.40 epoxy resin, unsaturated polyester resin 1.86~1.88 polyvinylidene chloride

1.14~1.17 Polyacrylonitrile 2.10~2.20 Polytrifluoro-vinyl chloride

1.15~1.25 Cellulose Acetate 2.10~2.30 PTFE

1.161.20 Polymethyl methacrylate

1.17~1.20 polyvinyl acetate

1.18~1.24 cellulose propionate

Commonly used solution for density identification of plastics

Solution type density (25oc)/(g/cm3) Preparation method Plastic (product) type

Floating solution sinks into solution

Water 1 Polyethylene, Polypropylene Polyvinyl Chloride, Polystyrene

Saturated salt solution 1.19 74ml water and 26g salt polystyrene, ABS PVC

58-4% alcohol solution 0.91 100ml water and 140ml 95% alcohol polypropylene polyethylene

55-4 alcohol solution 0.925 100ml water and 124ml 95% alcohol high pressure polyethylene low pressure polyethylene

Calcium Chloride Aqueous Solution 1.27 100g Calcium Chloride (Industrial) and 150ml Water Polystyrene, Perspex, ABS Polyvinyl Chloride, Phenolic

5. Identification of plastic pyrolysis test

The pyrolysis test discriminating method is to heat the plastic to the pyrolysis temperature in the pyrolysis tube, and then use the litmus test paper or pH test paper to test the pH of the evolved gas to identify the method. Commonly used plastic pyrolysis products litmus and pH test paper test results

Litmus paper

Red is basically colorless blue

pH test paper

0.5~4.0 5.0~5.5 8.0~9.5

Halogen-containing polymer Polyvinyl ester Cellulose ester Polyethylene terephthalate Phenolic resin Polyurethane elastomer Unsaturated polyester resin Fluoropolymer Hard fiber board Polythioether polyolefin Polyvinyl alcohol Polyvinyl formal Polyethylene ether Styrene Polymer (Including: Styrene-Acrylonitrile Copolymer) 2 Polymethacrylate Polyoxymethylene Methacrylate Polycarbonate Linear Polyurethane Phenolic Resin Epoxy Resin Crosslinked Polyurethane Polyamide ABS Polymer Polyacrylonitrile Phenol and Cresol Resin Amino Resins (Aniline-Melamine-Urea-Formaldehyde Resins)

1 Heat the pyrolysis tube slowly 2 Some samples show a weak alkaline

6. Identification of plastic combustion test

The combustion test discriminating method uses a small fire to burn a plastic sample to observe the combustibility of the plastic in the fire and outside the fire, and at the same time pays attention to the method of identifying the type of plastic by dropping the drop form and odor of the molten plastic after the flameout.

Combustion properties Flame state Vapors Odor materials

Non-flammable - Irritant (HF, HF) Silicone Polytetrafluoroethylene, Polychlorotrifluoroethylene Polyimide

Flame-retardant, extinguished after leaving the flame, with bright yellow smoke, green edge of flame, shiny, black smoke yellow, gray smoke, orange, blue smoke phenol, formaldehyde ammonia, amines, formaldehyde formaldehyde - - Charred animal keratin resin amino resin chlorinated rubber, polyvinyl chloride, polyvinylidene chloride (no flammable plasticizer) Polycarbonate silicone rubber polyamide

Burn in the flame, leave the flame then slowly extinguish or still burn yellow, shiny, material decomposition, orange, orange, black smoke, yellow, blue, yellow, blue phenol, charred paper Irritant, damaged, burned rubber Fresh aromatic aromas Irritating (isocyanate) Paraffin wax Phenolic resin Polyvinyl alcohol Polychloroprene Polyethylene terephthalate Polyurethane Polyethylene, Polypropylene

It is flammable. After leaving the flame, it will continue burning and shining. It will have black smoke and yellow sparkles. It will have black smoke, deep yellow, a little black smoke, deep yellow, sparkling black smoke, and the center emits blue sparks. It has a strong pungent phenolic aroma. , Day and then Acetic Acid Charred Rubber Aromatic, Fruit Fragrance Formaldehyde Polyester Resin (Glass Fibre Reinforced) Epoxy Resin (Glass Fibre Reinforced) Polystyrene Polyvinyl Acetate Polymethyl Methacrylate Polyoxymethylene

Easily ignited, continue to burn after leaving the flame Deep yellowish spark Sparkling greenish, giving off sparks Bright orange and strong Acetic acid and butyric acetic acid Charred paper Nitrogen oxides Butyl acetate Cellulose Acetate Cellulose Nitrocellulose

7. Identification of color reaction in plastics

Some plastics can be identified by different indicators. A few milligrams of sample are dissolved or suspended in 2 ml of hot acetic anhydride. After cooling, 3 drops of 50% sulfuric acid (made up of equal volumes of water and concentrated sulfuric acid) are added and immediately observed. Color reaction, observe the color of the sample after placing the sample for 10 minutes, then heat the sample to 100 degrees in the water bath, observe the color of the sample. Use this method to identify the plastic in the table below. This color reaction is called Liebermann-Storch-Morawski reaction

Liebermann-Storch-Morawski color reaction of several plastics

Immediately after the material is colored for 10 minutes, the color is heated to 100 degrees.

Phenolic Resin Light Red Violet - Pink Brown Brown - Red

Polyvinyl Alcohol Colorless - Light Yellow Colorless - Light Yellow Brown - Black

Polyvinyl acetate colorless - light yellow blue gray brown - black

Chlorinated rubber yellow brown yellow brown light red - yellow brown

Epoxy Resin Colorless to Yellow Colorless to Yellow Colorless - Yellow

Polyurethane Lemon Yellow Lemon Yellow Brown - Green Fluorescent

Chlorinated plastics include polyvinyl chloride, chlorinated polyvinyl chloride, chlorinated rubber, polychloroprene, polyvinylidene chloride, polyvinyl chloride, etc. They can be identified by pyridine color reaction. See the chart below. Note that prior to the test, the sample must be extracted with ether to remove the plasticizer. Test method: The sample taken from ethyl ether benzene is dissolved in tetrahydrofuran, and the insoluble components are filtered off. Methanol is added to precipitate the sample. Degrees of dryness below. A small amount of the dried sample was reacted with less than 1 ml of pyridine. After a few minutes, 2 drops of 5% sodium hydroxide in methanol (1 g of sodium hydroxide dissolved in 20 ml of methanol) were added and the color was observed immediately. 5 min. Observe them once and again after 1 h. According to the color, different chlorine-containing plastics can be identified.