A proven PVC formulation can lose stability after only one component is replaced. A new stabilizer may perform well in the laboratory, yet equipment load increases on the production line. Another filler may reduce cost but impair the surface. An additional lubricant may eliminate sticking but slow plastication.
In such cases, the issue is not necessarily related to the quality of the new additive. More often, the balance of the entire compound has changed.
Unlike many commodity polymers, PVC processing and properties depend particularly strongly on the interaction of the stabilizer, lubricants, filler, modifiers, plasticizers and processing conditions. A meaningful comparison therefore cannot be reduced to replacing one product in an otherwise unchanged formulation and evaluating a single parameter.
A Stabilizer Changes More Than Thermal Stability
A stabilizer package is not a single active substance, but a system of components. In addition to the heat-stabilising component, it may include lubricants, co-stabilizers, antioxidants and processing additives.
Replacing a stabilizer can therefore change:
- polymer-chain structure during processing;
- system viscosity;
- plastication time;
- torque and pressure;
- initial colour;
- material behaviour during prolonged processing;
- surface quality;
- the tendency to form deposits.
If a new stabilizer package contains a different lubricant package, retaining the previous dosage of external lubricants may disrupt the overall balance. The resulting problem may appear to be insufficient stabilizer performance, whereas the actual cause is a change in plastication or in melt interaction with the equipment.
This is why Reapak and Revastab stabilizers should be evaluated together with the existing lubricant system, rather than solely by static thermal-stability results.
An Additional Lubricant Can Solve One Problem and Create Another
When sticking or increased equipment load occurs, increasing the lubricant dosage may seem like the natural solution. However, this step does not always address the underlying cause.
Insufficient external lubrication can indeed result in sticking, overheating and deposits. Excessive lubrication can slow plastication, impair melt homogeneity and affect the mechanical properties of the product.
In addition, the distinction between internal and external lubricants is conditional. Many products show mixed behaviour that changes with temperature, dosage and compound composition.
Revalube lubricants should therefore be selected based on measurable parameters: plastication time, torque, pressure, melt temperature, surface condition and deposit formation.
A Filler Is Not a Neutral Component
Two calcium carbonate grades at the same dosage can affect processing differently. Particle size and distribution, specific surface area, treatment, moisture content and the tendency to agglomerate all matter.
Replacing a filler can change:
- the compound’s lubricant requirement;
- plastication rate;
- viscosity and equipment load;
- impact strength;
- product surface quality;
- the distribution of pigments and functional additives;
- thermal stability.
After changing a filler grade, it is therefore not always correct to adjust only the modifier or stabilizer level. First, it is necessary to determine which parameter has changed: plastication, dispersion, interfacial interaction or the actual filler loading.
A Modifier Works Only Within a Properly Balanced Compound
Impact modifiers and processing aids perform different functions.
The former improve resistance to failure, including at low temperatures. The latter affect plastication, melt homogeneity and strength, surface quality and process stability.
However, the effect of any modifier depends on:
- the PVC grade and K-value;
- the modifier structure and molecular weight;
- the amount and type of filler;
- the stabilizer system;
- lubricant balance;
- processing conditions.
Increasing the modifier dosage does not always lead to a proportional improvement in the property. If the compound is insufficiently plasticated or the filler is poorly dispersed, an additional modifier may not produce the expected result.
Revamod products should be selected not for the general purpose of “improving processability” or “increasing impact strength,” but according to the specific cause of the production issue.
A Plasticizer Affects the Entire Flexible PVC System
In plasticized PVC, the plasticizer determines more than hardness and elasticity. It affects viscosity, component compatibility, processing, migration, low-temperature flexibility and material behaviour during thermal ageing.
Replacing a plasticizer can therefore change stabilizer performance and the distribution conditions of other additives. A formulation adjusted for one plasticizer will not necessarily retain its previous balance after switching to another product with similar stated efficiency.
Edenol D81 is used as a secondary plasticizer and co-stabilizer. Its epoxy groups interact with HCl released during PVC thermal degradation and support the primary stabilizer system.
However, the result is determined not by the mere presence of epoxidized soybean oil, but by its combination with the primary plasticizer, stabilizer and finished-product requirements.
A Flame-Retardant System Cannot Be Evaluated Only by Active-Component Content
When selecting a flame retardant, the price per kilogram and active-substance content are often compared. For a complex system, this approach can lead to an incorrect conclusion.
Revaguard RG69P is a flame-retardant masterbatch for PVC containing up to 70% ATO and additional components that influence smoke generation. It is not a damped form of pure antimony trioxide or its mechanically diluted equivalent.
RG69P should therefore be compared with standard ATO not only by the content of the antimony component. Testing should assess:
- flame spread;
- oxygen index, if used for preliminary evaluation;
- smoke generation;
- colour and surface quality;
- mechanical properties;
- processability;
- the cost of the formulation that passes the target tests.
The same dosage of RG69P and ATO can be used as a starting point for a trial, but it is not a universal replacement ratio.
Why One Formulation Performs Differently on Different Lines
Even an identical composition does not guarantee the same result. Processing is affected by the loading sequence, mixing intensity, dry-blend temperature, cooling efficiency, residence time in the equipment, actual melt temperature, shear load and the condition of the forming tool.
Transferring a formulation to another line may therefore require changes to the lubricant balance, stabilizer or processing conditions.
What works is not the formulation on its own, but the combination of three elements: compound composition, equipment and processing conditions.
How to Compare Two Formulations Correctly
When testing a new component, all other significant parameters should initially remain unchanged. Replacing the stabilizer, lubricant and filler at the same time does not make it possible to identify the cause of the result.
The minimum control set usually includes:
- plastication time and torque;
- melt pressure, current and temperature;
- initial colour and thermal stability;
- surface quality and deposit formation;
- target mechanical properties;
- line throughput;
- finished-compound cost.
For flexible PVC, hardness, migration and properties after ageing are also evaluated. For rigid PVC, impact strength and degree of plastication are checked. For flame-retardant materials, testing is carried out according to the requirements of the specific product.
The Revada Plastic Approach
Revada Plastic offers not a universal additive for every formulation, but integrated solutions for PVC stabilisation, plasticisation, lubrication, modification and flame retardancy.
The portfolio includes Reapak and Revastab stabilizers, Revalube lubricants, Revamod modifiers, Edenol D81 epoxidized soybean oil, Revaguard flame-retardant solutions and Revatiox titanium dioxide.
To start a comparative project, it is necessary to determine:
- Which property needs to be changed.
- At which stage the problem occurs.
- Which formulation components have been changed.
- How current, pressure and temperature behave.
- Which finished-product indicators are mandatory.
Based on this information, a product can be selected and a test sequence developed that makes it clear which change actually produced the result.
