PVC Stabilisers

One important application of zeolite 4A is in the production of PVC materials. In addition to the standard ZP-4A zeolite for the application in the production of PVC thermal stabilizers, Silkem has developed a zeolite free from coarse particles and impurities, which is particularly suitable for use in the production of thermal stabilizers for advanced PVC products without unwanted visible surface imperfections.

Polyvinyl chloride (PVC) is one of the most widely used thermoplastic materials due to its low cost and its outstanding mechanical properties, which make it suitable for a very wide range of applications. The properties of PVC can be modified by using different additives during the manufacturing process.

As PVC has low thermal stability but is molded at high temperatures, thermal stabilizers are an important additive in its production. Exposure to thermal stress accelerates the degradation of PVC, with breakage of the polymer chains leading to deterioration of the material’s properties. This unwanted process affects the mechanical resistance, color, appearance and other characteristics of PVC products. To limit degradation, thermal stabilizers, including zeolite, are used in PVC production.

Zeolites in PVC stabilizers

In recent decades, zeolites have thus become an indispensable additive in the production of PVC materials, primarily due to their role as thermal stabilizers. Thanks to its unique structure and properties, this aluminosilicate mineral effectively prevents PVC from degrading at high temperatures, thereby extending the lifetime and improving the mechanical properties of products.

Zeolites have replaced lead in calcium- and zinc-salt-based thermal stabilizers. By using zeolites in PVC stabilizers, the European Stabiliser Producers Association (ESPA) has successfully met its commitments from the Vinyl Plus program.

Due to their uniform size distribution (d50 = 3–5 µm), zeolite crystals can be homogeneously mixed into different formulations. High whiteness and the absence of any visual impurities are the main properties of the ultra-pure zeolite ZP-4A-TSR. This is particularly important in the production of PVC window profiles, pipes, insulation and other PVC products with smooth surfaces.

Functions of zeolites

The main functions of zeolite used as a thermal stabilizer are to:

prevent degradation during production

by receiving and emitting heat and acting as a thermal compensator

capture metal ions

which are thermal degradation catalysts, due to its excellent ion exchange properties

neutralize the acidic by-products (HCl)

produced when PVC materials are processed or used.

Characteristics of zeolites

Zeolites are aluminosilicates with the general formula 𝐌₂/𝑛𝐎 ∙ 𝐀𝐥₂𝐎₃ ∙ 𝑦𝐒𝐢𝐎₂ ∙ 𝑤𝐇₂𝐎, where M is an alkali metal cation. The presence of these cations makes zeolites alkaline. They also have a microporous structure, making them excellent ion exchangers. The effectiveness of their use in the production of PVC stabilizers is determined by various factors.

Alkaline nature of zeolites:

One of the reasons zeolites are used as thermal stabilizers is their alkaline nature.

The alkalinity strength of zeolites depends on their three-dimensional structure.

In a typical zeolite three-dimensional tetrahedral structure,

one oxygen atom connects two tetrahedra.

If all tetrahedra contained only silicon, the whole structure would be neutral.

The presence of aluminum causes an imbalance in the crystal lattice’s charge, which requires relatively large amounts of cations to be neutralized.

Therefore, the structure’s resistance to acids and consequently its thermal stability increase with increasing aluminum content.

Presence of crystallization water:

When the HCl molecule is released during the processing of PVC materials, the hydroxide groups in the zeolite structure react with chloride ions.

Microporous structure:

Zeolite’s highly porous structure enables HCl removal and neutralization in a number of ways.

The pores enable HCl adsorption on the zeolite’s large surface area, and at the same time allow for high mobility of hydroxyl groups within the crystal structure, resulting in high ion exchange capacity.

Zeolites have thus become essential to the PVC industry, enabling the production of high-quality, sustainable and safe PVC products.

Their ability to neutralize acids, adsorb impurities and improve the workability of PVC makes them one of the most useful additives in this industry.

We can expect further development and optimization of zeolite use to lead to many more innovations in PVC materials. As environmental requirements increase and pressure mounts to develop more sustainable materials, the use of zeolites in the PVC industry is expected to continue to grow.

Product	Applications	Effect
Zeolites	PVC thermal co-stabilizers for smooth-surface PVC products	HCl adsorption and neutralization