Introduction to Plasticizers for PVC
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In this article, we have taken the time to discuss PVC plasticizers, specifically DOP and DOTP, to understand why one might be used over the other.
To begin, it is important to understand that a PVC plasticizer is an additive that solvates this polymer, meaning it provides flexibility by altering its physical properties. The theory explains that the plasticizer positions itself between PVC particles to form a bridge that allows molecular mobility; the greater the amount of plasticizer, the higher the flexibility achieved.
This hardness is in turn controlled by a Shore A measurement scale (for flexible products) and a Shore D scale (for rigid products) using a durometer; the Shore A scale reaches a maximum of 95 points before we prefer to refer to a Shore D scale.
Due to their excellent polarity with the polyvinyl chloride (PVC) molecule, both DOTP and DOP can alter the softening temperature of PVC, which is normally around 86°C in a rigid product. As the amount of PVC plasticizer in a formulation is increased, the material transitions from rigid to semi-rigid, and eventually to fully flexible, significantly lowering the softening temperature of the PVC in question.
It is important to note that, as with any additive, PVC has a limit to the amount of plasticizer it can accept before issues such as exudation or processing problems arise.
Similarly, to achieve excellent processing results with plasticized PVC, the key is its addition during a high-speed mixing process that generates significant shear, thereby increasing the temperature of the resin. This allows the resin particles to expand, resembling a sponge, enabling them to absorb the PVC plasticizers and other additives the formulator wishes to include.
Failing to follow a gradual addition process, while controlling mixing temperatures and the order of PVC additives incorporation, can lead to agglomeration and encapsulation issues, which in turn result in surface defects in the final product. The molecular weight of the PVC resin used must also be considered, as higher values are typically employed and are directly related to the adsorption capacity of the resin.
The concept of solvation is very important when referring to polymer–plasticizer polarity. Depending on the type of PVC plasticizer used, a certain degree of compatibility is achieved, which determines the amount that must be added to a formulation to reach the desired hardness. For example, different quantities will be required to achieve a Shore A 65 hardness depending on the plasticizer used, whether DOP, DOTP, DINP, etc.
It is commonly believed that a PVC plasticizer only provides flexibility to the material, which is a misconception. PVC plasticizers can also affect chemical extraction resistance, low-temperature performance, electrical properties, lubrication during processing, and more. It is important to use the grade that best suits your final product and production process.
Plasticizer for PVC: DOTP vs DOP
There has been considerable controversy regarding the potential harms of using DOP plasticizer, which is why producers in the plastics market have opted to switch to DOTP. To date, studies have not conclusively shown that DOP causes any human illnesses due to the presence of phthalates, a chemical compound known to be toxic. The supporting tests were conducted on rodents at high doses over extended periods via intravenous exposure, which is hardly comparable to the use of a finished product by humans.
However, due to the industry's shift towards products with lower levels of toxicity, this is why DOTP It is the preferred term when discussing a product related to the medical and/or food industry.
Although the DOP plasticizer and DOTP have the same molecular weight, there is a difference in the arrangement of their molecular chains: DOP has an “ortho” position, whereas DOTP has a “meta” position. This difference is why the industry refers to DOTP as a terephthalate rather than a conventional phthalate.
From a commercial point of view, DOP It has been preferred, of course, when it is possible to use it, due to its greater compatibility with the PVC and therefore, faster absorption during the mixing process (better drying). Normally the DOP tends to be the PVC plasticizer more economical mainly due to the economies of scale achieved by this material, which result in a greater supply than the DOTP. In Plastisol the DOP It is preferred because it does not generate as many "mosquito bite" defects due to its different viscosity and preference for releasing gases trapped in the mixture, although care must be taken regarding the market to which it is directed.
Among the advantages of DOTP, We found the previously discussed issue of toxicity, which allows it to comply with regulations such as RoHS or California's Prop 65 List. Furthermore, the DOTP it's a plasticPVC fabric which provides excellent mechanical properties at low temperatures, which is an added value that many companies are willing to pay for.
In terms of color and appearance, both PVC plasticizers are transparent liquids that do not contain volatiles that could pose a concern to the user. They also have a very mild odor, which is generally pleasant for plant operators.
We hope you found this article helpful and enjoyed it. If you have any questions or comments, please don't hesitate to contact your technical support representative through our [link to support page/email/etc.]. social networks or through our website. Visit our section on PVC plasticizers.
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