Lubrication of Calcium stearate in PVC formulation

Calcium stearate was initially used as an auxiliary stabilizer in PVC, mainly to absorb chloride ions generated by PVC degradation; At the same time, we should also find that Calcium stearate is also widely used in polyolefin formulations. Maybe not many people know the purpose of using Calcium stearate in polyolefin formulations in the initial design. In fact, Calcium stearate was originally used in polyolefin formulations to absorb some halogen ingredients added during polyolefin polymerization, so it is called halogen absorbent. 

So why is it also called a lubricant?

As we all know, many types of additives need to be added in formula design. Even if lubricants are not specifically added to polyolefins, the dispersant they add is also a lubricant, equivalent to adding lubricants in a disguised form. In practice, it is found that when Calcium stearate exists in the blend system, the lubrication performance will change significantly. Therefore, Calcium stearate is a lubricant and has become the research object of experts and scholars, with considerable achievements.

In fact, research has found that Calcium stearate can act as a "rivet" in the presence of other lubricants to enhance the adhesion effect of other lubricants, thus enhancing the lubrication effect. That is to say, Calcium stearate just plays a synergistic effect. If you don't believe it, in the formula system, except for Calcium stearate, other additives that can play a role in lubrication are not added. You can see how much lubrication effect Calcium stearate has? Of course, the high solid Calcium stearate specially compounded for lubrication is excluded.

In other words, it is of little significance to talk about the lubrication of Calcium stearate without other additives that play a role in lubrication. The reason why it is Calcium stearate instead of barium stearate, Zinc stearate and others is that the stearate family is still large enough. In fact, the reason is very simple. The Li Ming experiment at Shanghai Jiaotong University confirmed that Calcium stearate in this family has the smallest impact on the mechanical properties of the matrix. That is to say, it is the crystallization of generations of technicians that has created Calcium stearate.

At the end of the article, we briefly introduce the precautions for the use of Calcium stearate:

1. The amount of Calcium stearate added in PVC transparent products cannot be more than 0.5 phr, otherwise the transparency of PVC transparent products will be affected.

2. The addition amount of Calcium stearate in the lead salt composite stabilizer should be strictly controlled. Excessive addition will lead to the appearance of over plasticized corners and the decline of mechanical strength.

3. In the calcium zinc composite heat stabilizer system, too low proportion of Calcium stearate will lead to poor initial heat stability of PVC products, and too high proportion will lead to yellowing color and poor weather resistance;

4. The decomposition temperature of AC foaming agent after adding Calcium stearate will be reduced from 211 ℃ to 162 ℃, so pay attention to properly increasing the amount of stabilizer when using.

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