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, the PVC It tends to char when exposed to high temperatures. The thermal degradation mechanism consists of the dehydrochlorination of the polymer chain, with the release of hydrochloric acid (an irritant gas for the respiratory tract, mucous membranes, and eyes) and the formation of conjugated polyenes that cause the plastic to gradually yellow and lose its mechanical properties. Like plastic PVC It must undergo a transformation process where stress and temperature are applied; it is important to delay this decomposition mechanism as much as possible. This is where thermal stabilizers come in to form intermediate compounds and thus prolong this effect. There are two main classes of thermal stabilizers: tin-based and metallic salt-based.
As the evolution of PVC Towards products that are more environmentally friendly and safer for human health, thermal stabilizers have undergone changes. Originally, the pioneers of PVC thermal stabilization were lead stabilizers (lead silicate, lead stearate), used since the 1940s. Later, in the 1950s and 60s, barium/cadmium/zinc (BaCdZn) and tin stabilizers (thioglycolates and maleates) became available. Today, lead is banned in most markets due to its toxicity, and cadmium is being phased out for the same reason. Although tin-based stabilizers are still widely used today, BaCdZn, which belongs to the group of metallic salts, has not fared as well. This is due to increasing pressure to replace cadmium as a known carcinogen.
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 low volatiles, low odor, and good demolding properties during injection molding; however, they can cause opacity at high concentrations and increase the viscosity of the formula. Liquids, on the other hand, offer good transparency and gloss, although they may have a higher odor and more volatiles.
The above is not the only important factor when choosing the right thermal stabilizer for your formula. PVC. It may require a certain degree of light or weather resistance, a certain degree of initial color retention, a certain degree of long-term stability, and/or lubrication. These are important factors to consider when determining the use of a heat stabilizer.
Nor can we forget the toxicological requirements established by regulatory frameworks such as California's Prop 65, which lists substances with evidence of causing cancer, birth defects, or other reproductive harm. This has led to certain high-performing antioxidants in the PVC industry having to be replaced by other, more expensive materials that make it difficult to achieve the same performance. A prime example is Bisphenol A (BPA), an antioxidant widely used in PVC stabilizers—especially in plastic-coated electrical cable and in combination with heavy metal stabilizers—which is now being phased out in medical, food, and toy applications due to its toxicological classification as an endocrine disruptor.
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 the thermal stabilizers calcium zinc They have presented the first complexity: because they are lubricating packages, their mechanism depends on a correct balance between the lubrication system and the formula, avoiding excesses that could affect the product's melting. The additional complexity lies in the fact that the ZnCl₂ formed by the reaction of zinc stearate with HCl is a Lewis acid that catalyzes the dehydrochlorination of PVC itself (the 'zinc burn' phenomenon), which limits the thermal window for the process. Calcium stearate provides long-term stability by regenerating the zinc through ligand exchange. Powder grades are usually used because liquid grades contain carriers (plasticizers or solvents) that can exert an undesirable plasticizing effect on the rigid matrix, reducing the glass transition temperature (Tg) and the heat deflection temperature (HDT).That is why for the Rigid PVC, A specific development must be done for each client, for each formula and process, preventing the commercialization of a general-purpose grade. Another relatively new application is... thermal stabilizers calcium zinc For electrical cable, these materials partially replace lead-based thermal stabilizers, which have been banned due to their harmful effects on human health. These materials are packages whose ingredients provide anti-hygroscopic (hydrophobic) properties to help maintain the volumetric resistivity of the PVC cable, preventing moisture absorption that would degrade the electrical insulation.
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 additives and resins for your PVC formulations, and through our sister company, Chemical Compounds, we also provide finished PVC compounds in pellet form, ready for processing. Both companies work in close coordination to offer complete coverage from additive to final compound.
You can visit our section on metal salt stabilizers HERE.
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