In this article, we have taken the time to discuss the behavior of the blowing agent AZO, or azodicarbonamide, providing some guidance to manufacturers on how this additive behaves. If not handled properly, it can lead to undesirable results in the finished product.
What is azodicarbonamide?
AZO is a foaming agent used in various industries, including plastics, to reduce the weight of manufactured products and thus impart certain properties to the finished product. It is a yellow powder that, when heated to between 200°C and 210°C, emits a large volume of gas consisting of carbon monoxide, nitrogen, and trace amounts of ammonia. In the food industry, it has been gradually replaced by other types of enzymatic foaming agents due to the minute presence of a compound called semicarbazide, although to date, no direct risks to human health have been proven.
Among the properties that azodicarbonamide imparts to plastics are cost reduction due to the lower weight of finished parts without sacrificing physical or mechanical properties, as well as its use as a thermal, impact, or sound insulator. The use of azodicarbonamide in polymers is recommended with a particle size between 3–7 microns to minimize the likelihood of cracking and to ensure uniform foaming, although more economical grades with particle sizes up to 18 microns are also available.
How is it used?
Adapting the use of azodicarbonamide is usually a trial-and-error process that not all plant managers are willing to undertake due to the time and costs involved. The key is to find a balance among the following variables: time (process speed), temperature, and fusion. Typically, azodicarbonamide imparts a yellow color to the finished product, resulting in an undesirable hue for customers, which indicates that the material has not fully reacted. The base polymer and its resulting viscosity are critical for determining the processing speed and temperature, as extreme conditions can collapse the foam, degrade it, and increase the polymer density.
Although azodicarbonamide has a reaction temperature of 200°C, it begins to foam at around 160°C. If the process is carefully controlled, the yellow coloration can be significantly reduced, and the foam can even become white. It is important to maintain a low-turbulence process, which generally conflicts with plant productivity. Lowering temperatures and increasing exposure times will help improve product quality. Adding a small amount of white pigment, such as titanium dioxide, can help mask the yellowish hue.
Many of our customers are concerned about the unpleasant odor emitted by azodicarbonamide. It is recommended to let the finished product rest, which will significantly reduce this odor. Lowering the AZO dosage can also decrease both odor and yellowing; however, it is important to adjust the process to reestablish a balanced foaming point.
On the other hand, adding the azodicarbonamide In a pre-mixing process involving high friction and temperature, it is not recommended to add it; instead, it should be added later at low temperatures and for a sufficient time to achieve good dispersion within the polymer. If added in pellet form as a finished product, liquid dispersants can be used to improve adhesion to the plastic and enhance dispersion throughout the batch.
Combinations with other additives in the plastics industry
Many customers blend azodicarbonamide, an exothermic reaction agent, with other microspheres such as hydrazide-based families and/or other microbeads. Every benefit comes with a trade-off: these blowing agents, which do not impart odor or color to the finished product, release less gas, making it more difficult to maintain good foam volume. The combination allows for a better surface finish and a closed-cell foam structure, unlike using azodicarbonamide alone.
Azodicarbonamide can also have inherent issues, such as particle agglomeration, which can create voids during processing. Using a separating mesh is a good quality practice to ensure these agglomerates do not enter the process. It is also recommended to store it in dry, low-temperature conditions, as exposure to a spark could ignite it and cause a fire.
Finally, the azodicarbonamide It reacts with other additives you might add to your process. For example, using metal salt complexes will act as catalysts, lowering the reaction temperature and improving the foam's density and appearance. You can ask our specialists for a more personalized recommendation based on our product portfolio; we also offer pre-activated grades of azodicarbonamide to simplify 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.