There are six major categories of commonly used plastics, polyester (PET polyethylene terephthalate), high-density polyethylene (HDPE), low-density polyethylene (LDPE), polypropylene (PP), polyvinyl chloride ( PVC), polystyrene (PS).
But, do you know how to identify these plastics? How to develop your own "fiery eyes"? I will teach you some practical methods, it is not difficult to know the commonly used plastics in seconds!
There are roughly the following methods for identifying plastics: appearance identification, combustion identification, density identification, melt identification, solvent identification, etc.
The first two methods are simple and easy to use, and they can also identify these types of plastics very well. The density identification method can classify plastics and is often used in production practice. Therefore, here we mainly introduce three of them.
Each plastic has its own characteristics, with different colors, gloss, transparency, hardness, etc. Appearance identification is to distinguish different varieties based on the appearance characteristics of plastics.
The following table shows the appearance characteristics of several common plastics. Experienced sorting workers can accurately distinguish the types of plastics based on these appearance characteristics.
Appearance identification of several commonly used plastics
1. Polyethylene PE
Properties: When not colored, it is milky white, translucent, and waxy; the product feels smooth when touched by hand, soft and tough, and slightly elongated. Generally, low-density polyethylene is softer and has better transparency, while high-density polyethylene is harder.
Common products: plastic film, handbags, water pipes, oil drums, beverage bottles (calcium milk bottles), daily necessities, etc.
2. Polypropylene PP
Properties: It is white, translucent and waxy when not colored; lighter than polyethylene. The transparency is also better than polyethylene and harder than polyethylene. Excellent heat resistance, good breathability, heat resistance up to 167°C.
Common products: boxes, barrels, films, furniture, woven bags, bottle caps, car bumpers, etc.
3. Polystyrene PS
Properties: Transparent when not colored. The product will make a metallic sound when it is dropped or struck. It has good gloss and transparency, similar to glass. It is brittle and easy to break. You can scratch the surface of the product with your fingernails. Modified polystyrene is opaque.
Common products: stationery, cups, food containers, home appliance casings, electrical accessories, etc.
4. Polyvinyl chloride PVC
Properties: The original color is slightly yellow, translucent and shiny. The transparency is better than polyethylene and polypropylene, but worse than polystyrene. Depending on the amount of additives used, it is divided into soft and hard PVC. Soft products are flexible and tough, and feel sticky. Hard products have a hardness higher than low-density polyethylene but lower than polypropylene, and whitening will occur at the bends. It can only withstand heat up to 81°C.
Common products: shoe soles, toys, wire sheaths, doors and windows, stationery, packaging containers, etc.
5. Polyethylene terephthalate PET
Properties: Very good transparency, better strength and toughness than polystyrene and polyvinyl chloride, not easily broken, smooth and shiny surface. Resistant to acid and alkali, not resistant to high temperatures, easy to deform (can only withstand temperatures below 69°C).
Common products: often bottle products: Coke bottles, mineral water bottles, etc.
in addition
The six commonly used categories of plastics can also be identified by recycling marks. The recycling mark is usually at the bottom of the container. The Chinese mark is a two-digit number with a "0" in front. The foreign mark is a single digit without a "0". The following numbers represent the same type of plastic. Products from regular manufacturers have this mark. Through the recycling mark, the type of plastic can be accurately identified.
For ordinary plastic varieties, the combustion method can be used to identify them more accurately. Generally, you need to be proficient in selecting and have a master to guide you for a period of time, or you can find various plastics and conduct combustion experiments by yourself, and you can master them by comparing and memorizing them repeatedly. There is no shortcut. Searching. The color and smell of the flame during burning and the state after leaving the fire can be used as the basis for identification.
If the type of plastic cannot be confirmed from the combustion phenomenon, samples of known plastic types can be selected for comparison and identification for better results.
Plastics have different densities, and their sinking and floating phenomena in water and other solutions are also different. Different solutions can be used to distinguish different varieties. The densities of several commonly used plastics and the densities of commonly used liquids are shown in the table below. Different liquids can be selected according to the types of separation.
PP and PE can be rinsed out from PET with water, and PP, PE, PS, PA, and ABS can be rinsed out with saturated brine.
PP, PE, PS, PA, ABS, and PC can be floated out with saturated calcium chloride aqueous solution. Only PVC has the same density as PET and cannot be separated from PET by floating method.
Post time: Nov-30-2023