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• Time of issue:2022-02-24
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(Summary description)Polyethylene and polypropylene are the most commonly used olefin plastics. Polybutene-1 and poly-4-methylpentene-1 are also used. Some copolymers of ethylene ethylene and polyisobutylene used for gaskets are also important polyolefin plastics. The easiest way to identify these plastics is by infrared spectroscopy. But some information can also be obtained from the melting temperature range

The host said: Polyethylene (related to density) 105~130℃ Polypropylene 160~170℃ Polybutene 120~135℃ Poly-4-methylpentene-1 more than 240℃

The reactions of the pyrolysis gases of these plastics and mercury oxide are different from each other. Therefore, first soak the filter paper with a sulfuric acid solution containing 0.5 g of yellow mercury oxide (1.5 ml of concentrated sulfuric acid added to 8 ml of water), and then put a small amount of dry sample into the cracking tube, cover the mouth of the tube with the above filter paper, and heat. If the steam causes golden spots on the filter paper, this indicates that these plastics may contain polyisobutylene, butyl rubber, and polypropylene (in small amounts it may take a few minutes for the color to develop). Polyethylene does not react. Natural rubber, nitrile rubber and polybutadiene can produce brown spots. Polyethylene and polypropylene produce waxy products during pyrolysis. Polyethylene has a paraffin-like odor, while polypropylene has a slightly aromatic odor.

Simple identification method of common plastics (2): polystyrene

The identification method of polystyrene and most styrene-containing copolymers is as follows: put a small amount of sample in a small test tube, add four drops of fuming nitric acid, and acid vapor will be released without destroying the polymer. The residue is heated on a flame for about 1 minute, the test tube is positioned so that the open end is slightly downward, and the mouth of the tube is covered with a piece of filter paper. The filter paper was treated by soaking with 2,4-dibromoquinoneimine in ether and drying in air. If you add a drop of ammonia on the filter paper, the filter paper turns blue indicating styrene.

If the sample still contains some free nitric acid, the test is completely affected and the filter paper turns brown to mask the blue color. This identification reaction is also useful for styrene-butadiene copolymers and abs (acrylonitrile-butadiene-styrene copolymers). The presence of acrylonitrile can be verified by assaying for ammonia.

Simple identification method of common plastics (3): chlorine-containing polymers

In addition to polyvinyl chloride (pvc), chlorinated polymers and various copolymers of vinyl chloride are: polyvinylidene chloride, chlorinated rubber, hydrochlorinated rubber, chlorinated polyolefin, polychloroprene and polytriene Chlorofluoroethylene. In addition to using the Bolstein test to detect chlorine, these polymers can also be identified by their color reaction with pyridine (see table).

First, the sample must be extracted with ether to remove the plasticizer. The sample can also be dissolved in tetrahydrofuran. Filter to remove possible insoluble components, add methanol to re-precipitate, after suction filtration, dry at below 75°C, and react with 1 ml of pyridine with a small amount of sample. Let stand for a few minutes, then add 2~5 drops of 5% sodium hydroxide solution in methanol. (1 g of sodium hydroxide dissolved in 20 ml of methanol). Note the color change just after adding the reagent, 5 minutes and 1 hour later

A further test was to boil a small amount of plasticizer-removed specimen with 1 ml of pyridine for one minute, then divide the solution into 2 portions, reheat to boiling, and immediately add 2 drops of 5% sodium hydroxide in methanol To one part of the solution, the other part is cooled first, then add 2 drops of sodium hydroxide methanol solution, observe the color and observe the color change after 5 minutes.