Identification Methods for PVC
One, Ignition Method Identification
Softening or melting temperature range: 75~90°C;
Burning Condition: Self-extinguishing after ignition.
Burning flame state: Upper yellow, lower green with smoke; After being removed from the flame: Extinguishes upon removal; Odor:刺激性酸味 (Stimulating acidic smell)
This method is straightforward and convenient, usually the first choice.
Section II: Solvent Treatment Identification
Solvents: Tetrahydrofuran, cyclohexanone, dimethylformamide
Non-solvent: Methanol, acetone, heptane.
By adding suspected PVC plastic to the above solvent and observing the plastic's dissolution to determine if it's PVC, the solvent's heating will enhance the dissolution effect.
Section 3: Weight Ratio Method
The density of PVC ranges from 1.35 to 1.45, typically around 1.38. The difference in density or the method of measuring it can distinguish polyvinyl chloride from other plastics. However, due to the ability of PVC to be modified with plasticizers, modifiers, and fillers, resulting in significant variations in density and hardness, and changes in many properties due to the addition of certain components, our common identification methods are often ineffective, sometimes even showing altered phenomena, making accurate judgments impossible. For instance, the density of plasticized PVC (containing about 40% plasticizer) is 1.19 to 1.35; whereas the density of rigid PVC products is increased to 1.38 to 1.50. For high-filled PVC products, the density can sometimes exceed 2.
Additionally, the presence of chlorine in the material can be determined, but due to the high chlorine content in chlorinated polyvinyl chloride, chlorobutyl rubber, polyvinylidene chloride, and chlorinated polyvinyl chloride, a pyridine color reaction is required for identification. Note that before the test, the sample must be extracted with ether to remove plasticizers. The testing method involves dissolving the ether-extracted sample in tetrahydrofuran, filtering out the insoluble components, adding methanol to precipitate, and then drying at below 75 degrees. A small amount of the dried sample is reacted with no more than 1 mL of pyridine, and after a few minutes, 2 to 3 drops of a 5% sodium hydroxide methanol solution (1g sodium hydroxide dissolved in 20 mL methanol) are added. Observe the color immediately, and then again after 5 minutes and 1 hour. The color change can be used to differentiate between various chlorinated plastics.
In daily life, the most commonly encountered plastics that require distinction are PVC and PE film (bags). Simple method:
1. Touch method
The texture feels slippery, with a surface resembling wax (chemically known as waxy feel), this is a non-toxic polyethylene film bag, whereas polyvinyl chloride film feels slightly sticky.
2. Vibration Method
The film bags that rattle with a crisp sound and are lightweight and easily float are polyethylene bags. Those that rattle with a low, dull sound are polyvinyl chloride film bags.
3. Combustion Method
Flammable when exposed to fire, with yellow flames and droplets of paraffin-like oil falling during combustion, emitting gas similar to that from candle burning—it is a non-toxic polyethylene film bag. If it does not ignite easily and extinguishes upon removal from the flame, with green flames, it is a polyvinyl chloride film bag.
4. Immersion Method
Submerge the plastic bag in water, press it under with your hand, and if it floats to the surface, it's polyethylene; if it sinks to the bottom, it's polyvinyl chloride (polyethylene has a density less than water, while polyvinyl chloride has a density greater than water; at room temperature, their densities are approximately 0.92g/cm³ and 1.4g/cm³, respectively).
Also, take a copper wire, heat it until it turns red in the fire, then, touch the copper wire to the test plastic film, causing a chemical change. Next, re-introduce the copper wire coated with the plastic's components back into the flame. Carefully observe; if a colorful, dazzling green flame appears, it indicates that the plastic material contains chlorine, and is classified as a polyvinyl chloride material.
