Why use Calcium Zinc thermal stabilizers?
PVC is a versatile plastic that requires additives to fulfill specific functions and acquire additional properties, as it has no practical use on its own. In this article, we will focus on Calcium Zinc thermal stabilizers, a type of additive whose function is to delay thermal degradation, which occurs when PVC is subjected to high temperatures and mechanical stress.
As with any organic compound, PVC tends to carbonize when exposed to high temperatures. The mechanism of thermal degradation essentially involves the release of hydrogen chloride, an irritant gas, which gradually causes yellowing of the plastic and loss of its mechanical properties. Since PVC must undergo a transformation process involving heat and mechanical stress, it is important to delay this decomposition as much as possible. This is where thermal stabilizers come into play, forming intermediate compounds to prolong the material’s stability. There are two main types of thermal stabilizers: tin-based and metal salt-based.
As PVC has evolved toward products that are more environmentally friendly and safer for human health, thermal stabilizers have also changed. Originally, Barium/Cadmium/Zinc (BaCdZn) stabilizers and tin-based stabilizers were pioneers in the industry. Although tin-based stabilizers remain widely used today, BaCdZn, which belongs to the metal salts group, has not had the same success due to increasing pressure to eliminate cadmium as a carcinogenic element.
All these changes and new developments led to Calcium Zinc thermal stabilizers (CaZn) emerging as a new solution in response to pressure from organizations to use non-toxic additives in PVC. Failing to do so could displace PVC from industries such as medical, food, and toys, which are constantly monitored by the FDA in the United States.
The first obstacle presented to the thermal stabilizers calcium zinc, The goal was to obtain a product with performance similar to accepted market grades at a competitive price. It's worth mentioning that the thermal stabilizers calcium zinc It can have different compositions. Firstly, there are derivatives of metallic salts in percentages that depend on the performance desired by the manufacturer in relation to its final application.
It is usually accompanied by antioxidants and "boosters" that work synergistically to improve product performance, and finally a vehicle that supports the dispersion of the additive in the matrix of the PVC. There are usually two types of thermal stabilizers calcium zinc, in powder or liquid form.
Depending on the process, application, and method of addition, the manufacturer can determine the most suitable option. Powdered materials have the advantage of not producing many volatiles, having low odor, and good demolding properties in the injection process; however, they can cause opacity at high concentrations and increase the viscosity of the formula. On the other hand, liquids offer good transparency and gloss, although they may produce more odor and volatiles.
The above is not the only important consideration when selecting the right thermal stabilizer for your PVC formulation. You may require certain light or weather resistance, initial color retention, long-term stability, and/or lubrication. These are important factors to determine when choosing a thermal stabilizer.
Nor can we forget the toxicity requirements established by organizations like California's Prop 65, which prohibits the use of certain high-performance antioxidants in stabilizers. This, in turn, forces them to be replaced by other, more expensive materials, making it more difficult to achieve the same performance. A prime example is Bisphenol A, a type of antioxidant that is being phased out in various medical, food, and toy applications.
Latest trends in calcium zinc thermal stabilizers
The latest developments in Calcium Zinc thermal stabilizers aim to enter markets where resistance still exists: rigid PVC. Currently, these materials are more commonly used in flexible, semi-rigid, and plastisol applications, primarily because high thermal stability is not required, as these formulations do not generate significant friction and torque during processing. This can be easily verified by measuring thermal stability in a rheometer.
These new developments in Calcium Zinc thermal stabilizers present an initial complexity: because they are lubricant-based packs, their mechanism relies on a properly balanced lubrication system in combination with the formulation to which they are applied. Excessive amounts can negatively affect the fusion of the product being manufactured. This is mainly because calcium and zinc chlorides are intermediate compounds that do not withstand heat for long periods, unlike other compounds in different thermal stabilizers. These grades are usually powders due to the negative effects liquids could have on the heat deflection temperature.For rigid PVC, a specific development must be carried out for each client, formula, and process, preventing a general-use grade from being marketed. Another relatively new application is Calcium Zinc thermal stabilizers for electrical cables, which partially replace lead-based thermal stabilizers that have been banned due to health concerns. These materials are formulated as packs whose ingredients provide hygroscopic properties and help maintain the volumetric resistivity of PVC-made cables.
Depending on the operating temperature of the cable being manufactured, there are different grades designed to protect the plastic and prevent it from losing its elongation and tensile properties over time. This is crucial for complying with market regulations.
At Chemical Additives, we offer PVC compounds and additives for your formulations.
You can visit our section on metal salt stabilizers HERE.
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