The amount of addition varies depending on the system used, generally 1%-5% of the total amount, and can be added at any stage of production.
The preliminary results of the study show that ammonium perfluorooctanoate may decompose to form carcinogens at high temperatures. Therefore, some large companies in the world are committed to the development of fluorocarbon surfactant substitutes. A more promising idea is to replace the long carbon chain perfluoroalkyl group with a relatively short perfluoroalkyl group (Ca). (C: or above), but the final results in this regard need to be further studied.
Film forming aids
The paint film of latex paint is usually thermoplastic, in order to ensure its performance, it should not be too soft. In fact, it is desirable that the glass transition temperature of the emulsion polymer be as high as possible, so that the performance of the coating film, especially the hardness and stain resistance, is better. But things are always two-fold. While the performance is good, the minimum film-forming temperature (MFT) of latex paint is also relatively high, which brings problems to the construction and film-forming at lower temperatures. Therefore, it is often necessary to add film-forming additives to reduce MFT and achieve a balance between high performance and low construction temperature.
Mechanism of film-forming aids
The film-forming mechanism of the film-forming aid is closely related to the free volume. Therefore, the free volume is briefly introduced first.
The volume of an amorphous material consists of two parts: one part is the volume occupied by molecules, called the occupied volume; the other part is the volume not occupied by molecules, called amide wax cas no the free volume. Plot the specific volume (volume per unit mass) against temperature, and the slanted part is the free volume.
When the polymer cools, the free volume begins to decrease gradually, and when it reaches the glass transition temperature T, the free volume reaches the minimum value, which is 2.5%, at which time the polymer enters the glass state. However, the value of T obtained by rapid cooling is lower than the value of T obtained by slow cooling. In the glass state, the free volume is frozen, and the movement of the molecular chain that maintains a constant value is also frozen. At this time, there is not enough space for molecular chain diffusion and conformation adjustment. Therefore, the glass state of the polymer can be regarded as an equal free volume state.
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