The DOTPor by its chemical name di(2-ethylhexyl phthalate), is a general-purpose primary plasticizer that has been gaining ground compared to DOP. The reason for this is that although its molecular weight is equal to DOP (390.50 g/mol), it has a “Para” positioning in the branching of its molecular structure, making it considered less toxic. Consequently DOTP is deemed to be a terephthalate in order to differentiate it in this respect.
When using a plasticizer, one must consider its polarity with the PVC matrix, solvation capacity, behavior at high and low temperatures, volatility, yellowing index, among other factors. Normally, DOP is used as a benchmark to determine the substitution factor when seeking to achieve a desired hardness in PVC using another plasticizer, with DOTP having an approximate factor of 1.03. This means that DOTP solvates less and a greater quantity must be added during the mixing process. Additionally, this translates into a longer process time to obtain a dry mix, allowing the resin time to properly absorb this and other additives.
The DOTP s preferred for applications where good performance at low temperatures is required without the product becoming brittle or breaking, and it has a low level of volatiles. Its permanence is limited at high temperatures and it can migrate if there is not a correct balance in its formula. It is a material that does not have an odor and tends to be crystalline, sometimes presenting slight yellowing depending on the alcohol used by the manufacturer, which can have negative effects on the finished product.
In cases where a very flexible material is required, preheating is recommended to improve its absorption by the PVC resin, preferably being of high molecular weight and with a high degree of porosity. In the case of Plastisol, it tends to have a different impact on the viscosity of the mixture, so one cannot expect the same behavior when substituting DOP for DOTPRegardless of the application, the producer must always keep in mind that the fusion and gelation of PVC changes when the plasticizer is changed. This demands slight adjustments in process conditions in terms of speed, residence time, and temperatures used.
When aiming for international markets, it is highly recommended to remove DOP, where organizations like the FDA and REACH have banned its use and have looked favorably upon other alternatives depending on the final application, such as DOTP and DIDP.
It is important to mention that DOTP reduces the softening temperature of PVC, so it is not recommended as a lubricant in rigid applications. Essentially, what it does is create bridges between PVC molecules and facilitate mobility in their chains, thus providing different and additional properties such as an increase in the elongation of the finished base PVC product.
It is also interesting that DOTP akes about 48 hours to be completely absorbed by the suspension PVC particle, so it is recommended to allow rest and cooling time to be able to measure the real hardness based on the chosen dosage. This is a common and advisable practice in process control and quality processes.
Another important feature is that, although its volatility is minimal, there is some loss of material in contact with high temperatures. Also, being careful in its addition is very important because not respecting the order of addition during mixing can cause other additives, such as mineral fillers, to absorb and reduce the efficiency of the added DOTP often requiring the addition of more than normal to achieve the desired hardness.
Although DOTP usually has good compatibility with PVC compared to other plasticizers, it has a low resistance to chemical attack with certain substances such as palm oil, gasoline, and transmission oils as they tend to extract it, causing hardness loss in the short term in finished products. The use of other plasticizers that meet market requirements is recommended.
If you require technical assistance or are interested in our DOTPplasticizer, please do not hesitate to contact us on our website at Chemical Additives from Mexico.