The conventional PVC identification methods are general […]
The conventional PVC identification methods are generally classified into the following three categories, namely:
(1) Identification of combustion method:
Softening or melting temperature range: 75~90 °C;
Combustion condition: self-extinguishing after ignition;
Burning flame state: there is smoke on the yellow and green; after the fire: off from the fire; smell: irritating sour.
This method is the easiest and straightforward and is generally preferred.
(2) Solvent treatment identification:
Solvent: tetrahydrofuran, cyclohexanone, ketone, dimethylformamide;
Non-solvent: methanol, acetone, heptane.
By adding suspected PVC plastic to the above solvent, observe the dissolution of the plastic to determine whether it is PVC. After the solvent is heated, the dissolution effect will be more pronounced.
(3) Specific gravity method:
The specific gravity of PVC is 1.35~1.45, which is generally around 1.38.
Polyvinyl chloride and other plastics can be distinguished by differences in specific gravity or by specific gravity.
However, because PVC can add plasticizers, modifiers and fillers, the PVC becomes very different in specific gravity, and the difference between soft and hard is great. At the same time, many properties of PVC plastics are changed due to the addition of some components, resulting in The commonly used identification method is not effective, and even the phenomenon changes, and it is impossible to make an accurate judgment. For example, in terms of density, plasticized polyvinyl chloride (about 40% plasticizer) is 1.19~1.35; while PVC hard products are increased to 1.38~1.50. In the case of highly filled PVC products, the density sometimes exceeds 2.
In addition, it can also be determined by measuring whether or not chlorine is contained in the material, but since vinyl chloride copolymer, neoprene, polyvinylidene chloride, chlorinated polyvinyl chloride, etc. all contain a relatively high proportion of chlorine, color development by pyridine is also required. Reaction to identify. Note that before the test, the sample must be extracted with diethyl ether to remove the plasticizer. Test method: Dissolve the sample taken with diethylbenzene in tetrahydrofuran, filter out the insoluble components, add methanol to precipitate, and extract the first 75 Dry below the degree. A small amount of dried sample was reacted with 1 ml of pyridine. After a few minutes, 2 to 5% sodium hydroxide in methanol (1 g of sodium hydroxide dissolved in 20 ml of methanol) was added, and the color was observed immediately, 5 min. And observe again after 1h. Different chlorine-containing plastics can be identified based on color.
