The same plasticized PVC formulation can run consistently at one plant yet yellow prematurely, scorch or produce an inconsistent surface at another, even when the same stabilizer package is used. The cause often lies not in the quality of one additive, but in the interaction of the polymer resin, plasticizing component, stabilizer system, fillers and actual processing conditions.
PVC stabilizers and plasticizers perform different functions but operate as a single system. The plasticizing component provides material flexibility and affects processability, while the stabilizer package protects the polymer against thermal degradation. Changing the plasticizer type or dosage changes the behaviour of the whole compound, so its thermal stability and stabilizer-package performance must be reassessed.
Why the Polymer Requires a Heat Stabilizer
When polyvinyl chloride is heated, dehydrochlorination begins and hydrogen chloride is released. Conjugated double bonds form in the polymer chain, the material changes colour and its physical and mechanical properties gradually deteriorate. Released HCl accelerates further decomposition, so degradation progresses rapidly once it has begun.
A modern PVC heat-stabilizer package does more than bind HCl. Its components slow degradation, maintain initial colour and provide a thermal-stability reserve during mixing, extrusion or calendering.
Reapak and Revastab PVC Stabilizer Packages
The Revada Plastic range includes Reapak and Revastab stabilizer packages for various PVC processing technologies. The specific system is selected according to product type, plasticizer, filler loading, required colour, duration of thermal exposure and finished-material properties.
For lead-free formulations, calcium-zinc PVC stabilizers are used to achieve the required balance of initial colour, long-term thermal stability, processability and finished-product properties. Reapak and Revastab formulations are selected for the specific production process, not solely for the nominal component content of the compound.
How a Plasticizer Affects PVC Stabilizer Performance
Plasticizing components differ in polarity, plasticizing efficiency, volatility, heat resistance and compatibility with the polymer. They affect polymer-chain mobility, melt viscosity and the distribution of other components.
Replacing one plasticizing component with another while retaining the same heat-stabilizer dosage can change:
- initial colour;
- thermal-stability time;
- equipment load;
- surface quality;
- migration tendency;
- hardness and mechanical properties.
The structure and combination of plasticizers can affect heat-stabilizer compatibility with the polymer, its distribution in the compound, thermal stability and material transparency. Results obtained for one system cannot automatically be transferred to another formulation.
Epoxidized Soybean Oil: Edenol D81
Epoxidized soybean oil (ESBO) has a special role in plasticized polyvinyl chloride formulations. It complements the primary plasticizer system while also supporting the action of the heat stabilizer.
Epoxy groups bind HCl released when the polymer is heated, thereby slowing thermal degradation. Epoxidized soybean oil is therefore used as a secondary plasticizer and co-stabilizer.
For this purpose, the Revada Plastic range includes Edenol D81. The product complements the main stabilizer and plasticizer systems, helping achieve the required balance between processability, thermal stability and finished-material properties.
Edenol D81 does not replace the primary heat stabilizer. Its dosage is determined by the plasticizer-system composition, stabilizer-package type, product requirements and test results. An excessive level of secondary plasticizer can affect component compatibility and surface condition, so the entire formulation must be assessed.
Why the Same Formulation Can Produce Different Results
Even an identical list of components does not guarantee the same result on different equipment. The actual thermal history of the material is important, including:
- loading sequence;
- mixing intensity and duration;
- blend temperature;
- cooling efficiency;
- material residence time in the equipment;
- melt temperature and shear load;
- filler properties and moisture content.
Excessive heat load during mixing reduces the stability reserve required for subsequent processing. Insufficient distribution of the plasticizer or stabilizer can change equipment load and result in inconsistent colour.
A formulation should therefore not be transferred from one production site to another based only on its component list. It must be aligned with the equipment and actual processing conditions.
What to Check When Thermal Stability Declines
Premature yellowing of a compound does not mean that the stabilizer-package dosage should be increased immediately. First, check:
- Whether the grade or batch of polymer resin, plasticizer or filler has changed.
- Whether the loading sequence and mixing conditions are the same.
- Whether the liquid plasticizer is fully distributed.
- At which stage the colour change appears.
- How melt temperature, pressure and equipment load change.
- Whether migration, bloom or surface changes occur after ageing.
In comparative trials, change one significant variable per test. Replacing the stabilizer, plasticizer and filler at the same time does not allow the cause of the result to be determined.
How to Select a PVC Stabilizer and Plasticizer
Revada Plastic specialists select the stabilizer system with consideration for the plasticizing component, filler loading, equipment and finished-product requirements.
For comparative trials, Reapak and Revastab stabilizer packages and Edenol D81 epoxidized soybean oil can be proposed. The assessment compares initial colour, thermal stability, processability, surface quality, hardness, mechanical properties and migration tendency.
This approach makes it possible not merely to increase the dosage of one additive, but to identify the actual cause of instability and optimise the complete formulation.
For product selection and development of a test programme, you can provide Revada Plastic specialists with the current formulation, equipment description, processing conditions and finished-material requirements.
Frequently Asked Questions About Stabilizers and Plasticizers
Why does the material yellow during processing?
Yellowing is associated with the onset of polymer thermal degradation and the formation of polyene structures. It may be caused by insufficient stabilizer-system performance, material overheating, a change in plasticizer or filler, incorrect mixing conditions or increased material residence time in the equipment.
Can a plasticizer be replaced without changing the stabilizer?
After replacing a plasticizer, the stabilizer system must be reassessed. A different plasticizer changes viscosity, processing conditions, component compatibility and the heat load on the material. The existing stabilizer dosage may no longer be optimal.
Why is epoxidized soybean oil added to a formulation?
Epoxidized soybean oil is used as a secondary plasticizer and co-stabilizer. In a system with a stabilizer package, it produces a synergistic effect that improves the compound’s thermal stability.
