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Polyvinyl chloride (PVC) identification method

2019-07-10 11:40:47
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Conventional PVC identification methods are generally summarized into the following three categories, namely:


(1) Identification of combustion method:


Softening or melting temperature range: 75~90°C;


Burning situation: self-extinguishing after ignition;


Burning flame status: yellow up and green with smoke; after leaving the fire: extinguished after leaving the fire; smell: pungent sour.


This method is the easiest and most direct, generally as a direct choice.


(2) Identification of solvent treatment:


Solvent: tetrahydrofuran, cyclohexanone, methyl ketone, dimethylformamide;


Non-solvents: methanol, acetone, heptane.


By adding the suspected PVC plastic to the above solvents, observe the dissolution of the plastic to determine whether it is PVC. After the solvent is heated, the dissolving effect will be more obvious.


(3) Proportion method:


The specific gravity of PVC is 1.35~1.45, generally around 1.38.


The difference in specific gravity or the method of determining specific gravity can be used to distinguish PVC from other plastics.


But because PVC can add plasticizers, modifiers and fillers to make the PVC become very different in specific gravity, the difference in softness and hardness is very large, and at the same time, due to the addition of some components, many properties of the PVC plastic will change, resulting in Our commonly used identification methods are not effective, and even the phenomenon has changed, making it impossible to make accurate judgments. For example, in terms of density, plasticized polyvinyl chloride (containing about 40% plasticizer) is 1.19~1.35; while PVC hard products have increased to 1.38~1.50. If it is a highly filled PVC product, the density sometimes exceeds 2.


In addition, it can also be determined by measuring whether the material contains chlorine, but because vinyl chloride copolymers, neoprene rubber, polyvinylidene chloride, chlorinated polyvinyl chloride, etc. all contain a relatively high proportion of chlorine, they must be colored by pyridine Reaction to identify. Note that before the test, the sample must be extracted with ether to remove the plasticizer. Test method: Dissolve the sample taken from ether with benzene in tetrahydrofuran, filter out the insoluble components, and add methanol to precipitate it. After extraction, the first 75 Below the degree of dryness. Do not need 1ml of pyridine to react with a small amount of dried sample. After a few minutes, add 2 drops of methanol solution of 5% sodium hydroxide (1g sodium hydroxide dissolved in 20ml methanol), and observe the color immediately, 5min Observe again after and 1h. Different chlorinated plastics can be identified based on the color.


In daily life, PVC and PE plastic film (bag) need to be distinguished from more contact. Simple method:


⑴Touch method


It feels lubricious to the touch, and the surface looks like a layer of wax (chemically called wax feel). This is a non-toxic polyethylene film bag, while the PVC film feels a little sticky.


⑵ Shake method When shaking with hands, the sound is crisp, and the thing that floats easily is a polyethylene film bag. The low sound of shaking with hands is a polyvinyl chloride film bag.


⑶ Combustion method


In case of fire, it is flammable, the flame is yellow, and there is paraffin-like oil dripping when burning, and there is gas from candle burning. It is a non-toxic polyethylene film bag. If it is not easy to burn, it will be extinguished after leaving the fire, and the flame will be green and it is a polyvinyl chloride film bag.


⑷ Immersion method


The plastic bag is immersed in water and pressed into the water with your hand. Polyethylene that can rise to the surface and polyvinyl chloride that sinks to the bottom is polyvinyl chloride (polyethylene has a density less than water, and polyvinyl chloride has a density greater than water; at room temperature, they are about 0.92g/cm3 and 1.4g/cm3).


You can also take a piece of copper wire and burn it into red in the fire. Then, the copper wire is brought into contact with the test plastic film to produce a chemical change, and then the copper wire dipped in the plastic component is put back into the flame. At this time, you need to observe carefully. If there is a colorful and dazzling green flame, it means that this plastic material contains chlorine and belongs to the polyvinyl chloride material.


      Yangzhou Sanxing Plastic Co., Ltd. mainly involves PET sheet, PET transparent sheet, PET coil, PET anti-fog sheet, PET antistatic sheet, PET sheet, PET plastic sheet, PET clothing template, PVC sheet, PVC transparent sheet, PVC roll Materials, PVC sheets, PVC profiles, PVC membranes, GAG sheets, RPET sheets, PET plastic folding box sheets, PVC plastic folding box sheets, APETG sheets, APETG plastic folding boxes and other products.

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