DOTP, or by its chemical name di(2-ethylhexyl phthalate), is a general-purpose primary plasticizer that has gained ground compared to DOP. Although its molecular weight is the same as DOP (390.50 g/mol), it has a “para” position in the branching of its molecular structure, making it less toxic. For this reason, DOTP is considered a terephthalate to differentiate it in this regard.
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. DOP is typically used as a reference to determine the substitution factor when aiming to achieve a desired PVC hardness with another plasticizer. DOTP has an approximate factor of 1.03, meaning it solvates less and a higher quantity must be added during the mixing process. This also translates to longer processing times to achieve a dry blend, allowing the resin to properly absorb this and other additives.
DOTP is preferred for applications requiring good low-temperature performance without making the product brittle or prone to breakage. It also exhibits low volatility. Its stability is limited at high temperatures and it may migrate if the formulation is not properly balanced. This material is odorless and tends to be crystalline, occasionally showing 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, it is recommended to preheat to improve its absorption by the PVC resin, preferably one with a high molecular weight and a high degree of porosity. In the case of plastisol, it usually has a different impact on the viscosity of the mixture, so the same behavior cannot be expected when substituting DOP with DOTP. In any case, the producer must always keep in mind that PVC fusion and gelation change when the plasticizer is changed. This requires making slight adjustments to processing conditions, including speed, residence time, and temperatures used.
When targeting international markets, it is highly recommended to remove DOP, as organizations such as the FDA and REACH have banned its use and have favored other alternatives depending on the final application, such as DOTP and DIDP.
It is important to note that DOTP lowers the softening temperature of PVC, so it is not recommended as a lubricant in rigid applications. Essentially, it creates bridges between PVC molecules, facilitating chain mobility and providing different and additional properties, such as increased elongation in the finished PVC product.
It is also noteworthy that DOTP takes approximately 48 hours to be fully absorbed by suspension PVC particles. Therefore, it is recommended to allow resting and cooling time to accurately measure the actual hardness based on the chosen dosage. This is a common and recommended practice in process and quality control procedures.
Another important characteristic is that, although its volatility is minimal, some material loss can occur when exposed to high temperatures. Careful addition is also crucial, as failing to follow the correct order of incorporation during mixing may result in other additives, such as mineral fillers, absorbing the DOTP and reducing its efficiency, often requiring higher-than-normal amounts to achieve the desired hardness.
Although DOTP generally has good compatibility with PVC compared to other plasticizers, it has low chemical resistance to certain substances such as palm oil, gasoline, and transmission oils, which tend to extract it, causing a short-term loss of hardness in the finished products. The use of other plasticizers that meet market requirements is recommended.
If you require technical assistance or are interested in our DOTP plasticizer, do not hesitate to contact us through our website at Chemical Additives Mexico.