Chlorinated polyethylene (CPE) is a chlorinated modification product of high-density polyethylene (HDPE). As a processing modifier for PVC, the chlorine content of CPE should be between 35-38%. Due to its excellent weather resistance, cold resistance, flame resistance, oil resistance, impact resistance (CPE is an elastomer), and chemical stability, as well as its good compatibility with PVC, CPE has become the most commonly used impact toughening modifier in PVC processing.
The performance of CPE is determined by two factors:
1. Molecular Configuration of HDPE
Due to the different process conditions during the polymerization reaction of PE, there are certain differences in the molecular configuration and properties of its polymer HDPE. The properties of CPE after chlorination of HDPE with different properties also vary. CPE manufacturers must choose suitable HDPE special powder resins in order to produce qualified CPE resins.
2. Chlorination conditions, i.e. chlorination process
CPE, as a PVC processing modifier, is usually formed by chlorination reaction using aqueous suspension chlorination method. The key conditions of this chlorination process are light energy, initiator dosage, reaction pressure, reaction temperature, reaction time, and neutralization reaction conditions. The principle of PE chlorination is relatively simple, but the chlorination mechanism is more complex.
Due to the relatively small investment in equipment for producing CPE, many rudimentary small CPE production plants are already scattered throughout China. This not only causes pollution to the ecological environment, but also is one of the important reasons for the instability of CPE quality.
At present, there are a large number of low-quality CPE on the market. Generally, there are two types of low-quality CPE. One is due to some production plants not having the technical conditions and outdated chlorination processes. Another method is to mix a certain amount of Calcium Carbonate or talc powder in CPE to engage in unfair competition.
For the first type of low-quality product, users only need to identify the manufacturer to prevent use, but for the second type of low-quality CPE, many people do not have enough understanding of it. As is well known, the prices of calcium carbonate and talc powder are relatively low, usually between 400-500 yuan/ton, while the price of CPE is generally between 8500-9500 yuan/ton. Some unscrupulous manufacturers mix low priced substances into CPE and sell them at slightly lower prices than qualified products to win market share. Even some manufacturers purchase cheap agglomerated CPE from CPE production plants, which are crushed and then mixed with a certain amount of calcium carbonate or talc powder. After repackaging, they sell it at a lower price (lower than the normal CPE price), engaging in unfair competition to seek improper benefits. Usually, the price of this type of CPE ranges from 7000 to 8000 yuan/ton, and even worse, it is sold at a price of 5000 to 6000 yuan/ton.
In the processing of PVC, these inferior CPE are used as modifiers for PVC processing. In order to achieve the purpose of impact resistance and toughening of PVC products, the amount of CPE will inevitably increase, which will lead to an increase in plasticization time, a decrease in equilibrium torque, and an increase in the time to achieve equilibrium torque. All of these will result in a decrease in the overall performance of the product and an increase in the scrap rate. Therefore, whether using cheap but low-quality CPE reduces or increases production costs is self-evident!
