What are PVC lubricants and how do they work?
Probably most of PVC experts can agree that this is one of the most complex topics in the world of PVC. This group of additives cover different grades and each one of them serves a specific purpose.
As we have mentioned in other articles, PVC needs from other additives in order to transform into a functional end-product. Among these plasticizers, thermal stabilizers and PVC lubricants highlight as the most relevant.
When we talk about PVC lubricants let's not forget that we refer to how we will affect the rheology of a no-newtonian fluid.
During processing, most commonly in extrusion, factors such torque, compression, temperature and melt viscosity, play a great role in the fusion of PVC. The term fusion in PVC refers to a material that has completely transformed into a smooth surface product and with good physical properties. Not achieving a proper fusion can translate into a product out of specifications.
Basic concepts related to PVC lubricants
Fusion is not something easy to get as formulators need to adapt the lubricating system to the corresponding process. It will never be the same to formulate a rigid PVC formula designed, for example, to make PVC pipes than to produce semi rigid injected caps.
Another important factor is melt flow, which operators might want to check in order to measure productivity and proper process control with minimum idle times. A highly lubricated formula will have a high melt flow but, on the other hand, could show fusion problems. Opposed to the latter, a low lubricating system can provoke mass sticking to the equipment and eventually PVC degradation. This can considerably increase scrap from your processing line.
PVC lubricants can be divided in three groups according to their PVC polarity. They are the internal, internal/external and external PVC lubricants. Those considered internal serve mainly to promote fusion, without the need to increase process temperature, to reduce mass friction and to improve melt flow. On the other hand, external lubricants delay fusion time but serve to avoid mass stickiness with the internal wall of the equipment. Some of these are also useful in improving surface glow. Last but not least, the intermediate internal/external PVC lubricants have mix of the previous effects.
A lubricant polarity needs to be seen as its compatibility with the PVC matrix according to their molecular structure and their capacity to absorbed. Usually internal PVC lubricants are composed of short carbon chains and some examples include fatty acids and glicerin. For this reason they are great at providing transparency. Those externals are usually high molecular weight hydrocarbon waxes that, because of their low polarity, only cover the PVC molecule and delay fusion. Other PVC lubricants are stearates, stearic acid, amides, paraffin wax, to name a few others.
The formulator cannot forget that the secret of having the right lubricating system for a certain process resides not only on choosing the right additives but on understanding the interaction among them. Let's not oversight that PVC additives such as thermal stabilizers and plasticizers have great impact on lubrication.
The are some PVC lubricants that aside from having an effect during fusion process, they also prove useful afterwards. Some are good release agents, antiblocking agents or antistatic.
PVC lubricant appearance vary depending on customer needs and preferences. Most common presentations are flakes, prills, powder or liquid.
If you need technical assistance, our PVC experts will happily help you in making the decision that best fits your needs. If you don't want to formulate and you prefer PVC compound you can visit Chemical Compounds.
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