En este artículo nos hemos tomado el tiempo de platicar del comportamiento del espumante AZO, ó azodicarbonamida, donde presentamos algunos consejos a los fabricantes de cómo se comporta este aditivo, que si no se sabe manejar puede dar resultados indeseables en su producto terminado.
¿What is azodicarbonamide?
AZO is a foaming additive used in several industries including plastics, to reduce the weight of manufactured products and thus confer certain properties to the finished product. It is a yellow powder that, when it reaches a temperature between 200°C to 210°C, emits a large volume of gas consisting of carbon monoxide, nitrogen, and some small traces of ammonia. In the food industry, it has been replaced by other types of enzymatic foaming agents due to the minuscule presence of a compound called semicarbazide, although to date no direct health risks have been proven.
Among the properties that azodicarbonamide confers to plastic, we have a reduction in costs due to the low weight of finished parts, without sacrificing physical-mechanical properties, and being used as a thermal, impact, or sound insulator. The use of azodicarbonamide in polymers is recommended with a particle size between 3 – 7 microns to reduce the likelihood of cracking and to achieve uniform foaming, although more economical grades with particle sizes up to 18 microns are also managed.
¿How is it used?
Usually, adapting the use of azodicarbonamide s a process of trial and error that not all plant managers want to do because of the time and costs involved. The trick is to find a balance between the following variables: time (process speed), temperature, and melting. Usually, azodicarbonamide gives a yellow color to the finished product, giving an undesirable hue for customers, which is a sign that this material has not reacted completely. The base polymer and the viscosity it denotes are key to determining the speed and temperature at which it should be processed, as in extreme conditions the only thing that is caused is to collapse the foam, degrade it, and increase the density of the polymer.
Although azodicarbonamide has a reaction temperature of 200°C, it begins to foam from 160°C, and if the process is well controlled, the yellow color can be considerably reduced and even turned into white foam. It is important to have a less turbulent process, which generally opposes the productivity of a plant. Reducing temperatures and increasing exposure times will help improve the quality of our product. Adding a little white pigment, or titanium dioxide, will serve to disguise the yellowish tone a bit.
Many of our clients have concerns about the unpleasant odor emitted by azodicarbonamidewhich is why they are advised to let their finished product rest to reduce this property. By doing this, the unpleasant odor will be significantly reduced. Reducing the dose of AZO can also diminish the odor and yellowing, but it will be important to make adjustments in the process to find a new foaming balance.
On the other hand, adding azodicarbonamide in a previous process of high friction and temperature mixing is not advisable but should be added later at low temperatures and enough time to achieve good dispersion in the polymer. If added in pellets, as a finished product, liquid dispersants can be used to improve adherence to the plastic and improve dispersion throughout the batch.
Combinations with other additives in the plastic industry
Many clients mix azodicarbonamidewhich is an exothermic reaction agent, with other microspheres such as the hydrazide family and/or microspheres. Every benefit always has a sacrifice, these foaming agents that do not confer odor or color to the finished product, do not emit the same level of gas, so it is more difficult to maintain good foaming volume. The combination allows for better surface finish and with a closed foam cell, as opposed to using azodicarbonamide.
The azodicarbonamide can also have problems of origin, such as particle agglomeration that generate caverns in the process. Using a separating mesh is a good quality practice, to ensure that these agglomerations do not go into the process. Similarly, it is recommended to store in dry and low-temperature climates, since if exposed to a spark it can ignite and cause a fire.
Finally, the azodicarbonamide Finally, azodicarbonamide reacts with other additives that might be added in the process. For example, the use of metal salt complexes will serve as catalysts so that the reaction temperature is lower and this helps to improve the foam both in density and appearance. You can ask our specialists for a better recommendation according to our product portfolio; we also offer pre-activated azodicarbonamide grades to facilitate your mixing process. Visit our website www.chemicaladditives.com.mx to inquire about our additives or also at our sister company www.chemicalcompounds.com.mx where we offer PVC compound in pellet form.