Why Calcium-Zinc is Replacing Lead in Modern PVC Stabilizer Applications？

Evolution of Thermal Protection in Polymer Processing

The PVC stabilizer plays a critical role in ensuring the long-term structural integrity of PVC during high-temperature processing. The PVC resin is inherently sensitive to heat and will begin to degrade significantly at temperatures of 120°C to 130°C. However, processing of PVC is typically carried out at temperatures ranging from 160°C to 220°C. Therefore, in the absence of an effective PVC stabilizer, the PVC resin will deteriorate rapidly due to degradation reactions such as dehydrochlorination. Upon dehydrochlorination, the hydrogen chloride (HCl) gas that is produced is extremely corrosive. This HCl gas, in turn, can cause the PVC to undergo an autocatalytic “zipper” reaction . The various forms of degradation described above can cause a number of critical failures:

Severe discoloration ranging from colorless to pale yellow, and eventually to complete blackening.A rapid decline in physical and mechanical properties, resulting in product brittleness.Corrosion of machinery and equipment due to the release of acidic fumes. The formation of conjugated polyene sequences compromises the aesthetic and structural value of the material.

The choice of a PVC stabilizer has to take into account the processing technology and the requirements placed on the end product. Inteam offers a wide range of products that intervene in the degradation cycles of PVC by neutralizing HCl as well as by removing unstable chlorine atoms.

Categorizing High-Performance Types of PVC Stabilizers

PVC stabilizers available on the global market are developed to best serve specific applications and at an optimal price. These systems consist of either single-additive, single-component types or of one-package, composite types.

Lead Salt Stabilizers: These are the most typical materials for thermal and electrical stabilization, due to their great thermal stability and excellent electrical insulation properties. Unfortunately, they are toxic.

Calcium zinc stabilizer: The non-toxic, eco-friendly alternative to other stabilizers that is increasingly mandated for use in food-contact applications as well as in medical applications.

Organotin Stabilizers: Highly efficient stabilization systems, clear appearance, high heat resistance, and hence suitable for high-end packaging applications.

Liquid Composite Systems: Our Liquid Composite Systems have the molecular-level dispersion and the best compatibility with resins compared to all of our solid powder forms.

Auxiliary Stabilizers: These are pure organic compounds that function as lubricating oil additives, such as phosphites, epoxy compounds, etc., to produce a synergistic effect with the primary metallic soaps.

Drivers Behind the Decline of PVC Lead Stabilizer Systems

While the PVC lead stabilizer has been the “industry standard” for many decades, its share of global usage has declined from approximately 60% in previous years to today. The phase-out is triggered by several technical and regulatory issues with the safety and performance of PVC lead stabilizer.

The operators and the environment are exposed to heavy metal toxicity when processing lead. Although several countries have established rules on the use of lead in products, such as EN-71-3 for toys, medical products, and food packaging, many of them have been banned completely already or will be banned in the future due to toxicity. The lead salts have low transparency and easily get contaminated with sulfides. This leads to an unwanted coloring of the end product. In production sites all over the world, the dust, which is released when using solid powder stabilizers, can cause heavy metal poisoning. Thus, dust-free alternatives are needed.
Inteam designs high-efficiency system components that have the same long-term thermal behavior as lead but are free from the health hazards associated with lead.

Advanced Stabilization Mechanisms in Calcium Zinc Stabilizer Technology

The latest developments in calcium zinc stabilizers for lubricating oils contain many layers of activity as described by the Frye-Horst mechanism, which significantly surpasses the action of single-component additives.

The metallic soap acts as a complex additive in several forms to protect polymer chains from decomposition.The primary function of the zinc soap is to replace the unstable allyl chloride atoms from the PVC chain, thus preventing early deterioration.The Calcium soap in the additive formula neutralizes the released HCl and reactivates the zinc soap with the metal chlorides in the used oil, thus preventing the creation of zinc chloride.The system prevents ‘zinc burning’ – a sudden, malignant failure caused by large amounts of accumulated zinc chloride, which acts as a very powerful catalyst.Auxiliary stabilizers such as β-diketones (e.g., Stearoylbenzoylmethane) are added in order to reduce early color and to improve heat stability at the end of life.

Research has shown that well-formulated calcium-zinc-based corrosion protection systems provide a suitable performance-to-price ratio for use on rigid pipes, sheets, and cable form.

Functional Superiority of Liquid Composite Systems

Liquid PVC stabilizers provide advantages to the processing of PVC products over traditional solid powders. Liquid PVC composite materials such as Inteam CZ-001 and CZ-002 offer higher stability and transparency due to the following factors.

The molecular dispersion in the resin itself prevents light from being deviated by interfacial refraction and provides uniform protection. The self-lubricating properties of these resins also prevent melt breakage and ensure good flowability in extrusion and calendering operations. In contrast to fillers, these resins do not cause dust poisoning and thus facilitate handling, precise measurement, and uniform mixing. Their high compatibility with plasticizers makes them suitable for hard, opaque articles as well as for soft, transparent products and plasticized pastes.

Within the team, we are paying particular attention to the high-viscosity stability of these new liquid formulations in order to prevent them from precipitating or ‘blooming’ on the surface of the end product.

Conclusión

Migrating from traditional lead-stabilized PVC to environmentally friendly calcium zinc stabilizer technology is a critical development tool for manufacturers wishing to remain competitive on the global market whilst producing the highest quality products. These PVC additives are available with innovative mechanisms such as Frye-Horst as well as in liquid composite forms to achieve high transparency, very high thermal and mechanical stability. Inteam, as a leading provider of PVC additives, is committed to assisting the global market of plastic materials to develop sustainably under the ISO9001:2015 Quality Management System.

Preguntas frecuentes

Q: What are the main types of PVC stabilizers used in food-grade packaging?

A: For applications with high hygiene requirements, non-toxic stabilizers from the group of calcium, zinc, or organotin compounds are used. These products are free of heavy metals and possess excellent transparency and color strength, and at the same time are harmless to man.

Q: How does a PVC stabilizer prevent the zipper reaction during processing?

A: A high-quality PVC stabilizer captures and neutralizes hydrogen chloride (HCl) gas immediately it is released as dehydrochlorination occurs. By removing from the reaction mixture the component that is acting as a catalyst for further degradation and by displacing the unsaturated chlorine atoms from the PVC chain, the stabilizer interferes with the so-called autocatalytic reaction mechanism and thus prevents discoloration and brittleness of PVC.

Q: Why is a liquid calcium zinc stabilizer preferred over solid powder for transparent films?

A: Liquid systems provide the best dispersion on a molecular level in the PVC resin. This results in the best transparency, due to the smallest amount of refraction of light, compared to solid powders. Also, Inteam’s liquid stabilizers, such as CZ-001, are easy to mix and do not cause dust poisoning, unlike the solid heavy metal salts.

Q: Can Inteam additives improve the mechanical properties of rigid PVC pipes?

A: Yes, Inteam provides integrated solutions where the PVC stabilizer is used in combination with toughening agents and with ACR processing aids. The combination of these components gives an increase of impact strength of 5 % points, and the thermal shrinkage in length is decreased from -1.8 % to -1.6 %. Thus, the dimensional stability is increased.

Q: Is the traditional PVC lead stabilizer still legal for all global construction projects?

A: Changing regulations are currently the subject of focus. Already in many countries around the world, the use of PVC with lead as a stabilizer is being banned for articles like building materials, toys, and medical devices, because of their toxicity. Most manufacturers now use lead-free types of stabilizers for PVC for environmental reasons worldwide. Thus, they fulfill the demands of the international standard EN-71-3 for safe toys.