Should EVA be dissolved in xylene to prepare the solution? If so, what ratio and operational conditions are recommended?

Yes, xylene is a commonly used solvent to dissolve Ethylene Vinyl Acetate (EVA) when preparing solutions for use in lubricant formulations or as a pour point depressant (PPD). Xylene is a good choice because it is a hydrophobic solvent that can dissolve a variety of non-polar and semi-polar polymers like EVA while offering the necessary volatility and evaporation properties once the solution is incorporated into the oil.

Dissolving EVA in Xylene: Key Considerations

1. Solubility of EVA in Xylene:
   • EVA has a low polarity, which makes it soluble in non-polar or slightly polar solvents like xylene.
   • The solubility of EVA in xylene depends on the vinyl acetate content of the EVA. EVA with higher vinyl acetate content tends to be more amorphous and more readily soluble in solvents like xylene.
2. Typical Solvent Ratios:
   • A common ratio for dissolving EVA in xylene is 1 part EVA to 3 to 5 parts xylene by weight (20-25% EVA concentration). This ensures that the EVA is adequately dissolved and forms a homogenous solution.
   • You may adjust the concentration depending on the intended application, but this range allows for a manageable solution viscosity while maintaining sufficient polymer concentration to provide effective PPD performance.
3. Operational Conditions for Dissolution:
   • Temperature: EVA generally requires moderate heat for dissolution. Heating to 60-80°C (140-176°F) can speed up the dissolution process. Ensure that the temperature does not exceed 100°C (212°F) to avoid evaporation of the solvent or degradation of EVA.
   • Stirring: Continuous stirring is important to ensure uniform dissolution. Mechanical stirring or agitators at moderate speeds (e.g., 500-1000 rpm) can help achieve a homogeneous solution.
   • Solvent Addition: Add the xylene to the EVA in small portions while stirring to avoid clumping or incomplete dissolution.
4. Mixing Time:
   • The dissolution process may take from 1 to 3 hours, depending on the concentration of EVA, the type of EVA (its molecular weight and vinyl acetate content), and the temperature. The goal is to ensure that no visible particles or undissolved EVA are present.
5. Solvent Removal:
   • Once EVA is dissolved in xylene, the solution can be incorporated into the lubricant formulation. The xylene will typically evaporate during the blending or processing of the final oil product.
   • The evaporation of xylene can be facilitated by mild heating during the blending process (for example, at temperatures 60-80°C), or by letting the solution air dry, depending on your formulation needs.
6. Final Concentration:
   • After dissolving, the concentration of EVA in the final lubricant formulation will depend on the desired PPD effectiveness and the total volume of lubricant. Typically, you’d add this EVA-xylene solution to the base oil, aiming for a final EVA concentration of 0.1% to 1.0% by weight in the total lubricant.
7. Safety Considerations:
   • Ventilation: Xylene is a volatile solvent with potential health hazards, so ensure adequate ventilation when working with it.
   • Personal Protective Equipment (PPE): Wear gloves, goggles, and appropriate protective clothing to avoid direct contact with xylene.
   • Flammability: Xylene is flammable, so take appropriate precautions, such as using non-sparking equipment and keeping away from open flames or heat sources.

Summary: Recommended Process for Dissolving EVA in Xylene

1. Ratio: Use a 1:3 to 1:5 ratio of EVA to xylene by weight (20-25% EVA concentration).
2. Temperature: Heat the solution to 60-80°C.
3. Stirring: Stir the solution continuously at moderate speed (500-1000 rpm) to promote dissolution.
4. Evaporation: Once dissolved, evaporate the xylene at 60-80°C during blending, or allow it to air dry in the final product.
5. Final Concentration: Incorporate the solution into the lubricant at a final EVA concentration of 0.1% to 1.0% by weight.

By following these guidelines, you can prepare an effective EVA-based PPD solution that can help improve the low-temperature properties of lubricants.

A solution of 20% EVA by weight in xylene was prepared, but upon cooling, the solution became completely solid. Therefore, this ratio is very high. However, at 0.02%, a viscous solution was obtained upon cooling. How can I ensure that the material remains a viscous fluid and does not become solid upon cooling?

It sounds like the concentration of EVA in your 20% solution is too high for it to remain in a fluid state at room temperature. When the concentration is high, the polymer chains tend to aggregate or crystallize as the solvent evaporates or cools, causing the solution to become solid. This is especially true if you’re using a high molecular weight EVA, which tends to form a more rigid network when concentrated.

Here are a few ways to ensure that the solution remains viscous and doesn’t turn solid:

1. Lower the EVA Concentration:

• The concentration of 20% EVA is too high for a fluid solution. A lower concentration of 5-10% by weight (or even lower, depending on the molecular weight of the EVA) will likely yield a more stable, viscous fluid after cooling. If you were seeing success at 0.02% EVA, that suggests you might need an even lower concentration for a liquid, non-solidified solution.

2. Adjust the Molecular Weight of EVA:

• If you’re using a high molecular weight EVA, it will form a more solid network when concentrated. Try using lower molecular weight EVA, which can help maintain the fluidity of the solution.
• Lower molecular weight EVA will also help achieve the desired viscosity without solidification.

3. Use a Plasticizer or Softener:

• If you want to keep the EVA at a higher concentration but prevent it from becoming solid, you can incorporate a plasticizer (such as dioctyl phthalate (DOP), tricresyl phosphate (TCP), or toluene). The plasticizer can reduce the rigidity of the EVA, keeping the solution more fluid.
• A typical starting point is adding 5-10% plasticizer by weight relative to the EVA. You may need to experiment with ratios to prevent the solidification while maintaining the desired viscosity.

4. Improve Solvent Use and Ratio:

• The xylene-to-EVA ratio also plays a key role. Since you’re using xylene as a solvent, try increasing the amount of xylene to EVA to ensure the solution stays fluid at higher concentrations of EVA. However, be careful not to use excessive solvent, as it may negatively impact the effectiveness of the PPD in your final formulation.
• A solvent-to-EVA ratio of around 5:1 or 10:1 might keep the solution more fluid.

5. Incorporate a Viscosity Modifier:

• You can try using a viscosity modifier such as a polymeric dispersant to maintain the viscosity of the solution. This can also improve the dispersion of EVA when it is mixed into base oils, ensuring that the final lubricant formulation remains homogenous.

Experimentation:

• Since you’re seeing good results at 0.02% EVA, it may be worth experimenting with gradually increasing the concentration in small increments (e.g., 0.1%, 0.5%, 1%) while monitoring the behavior of the solution upon cooling. This way, you can find the optimal concentration where the solution remains fluid but still provides sufficient PPD performance.

Summary of Recommendations:

• Try reducing the EVA concentration to 5-10% or lower.
• If you want to keep a higher concentration, consider adding a plasticizer (5-10% by weight).
• Use a lower molecular weight EVA for better fluidity.
• Increase the xylene ratio (use more solvent to dilute the EVA) to prevent solidification.

A solution of 20% EVA by weight in xylene was prepared, but upon cooling, the solution became completely solid. Therefore, this ratio is very high. However, at 0.02%, a viscous solution was obtained upon cooling. How can I ensure that the material remains a viscous fluid and does not become solid upon cooling?

To prevent your 20% by weight EVA (Ethylene Vinyl Acetate) solution in xylene from solidifying after cooling and to maintain a viscous fluid state, you need to adjust a few key parameters. When the concentration of EVA is too high, the polymer tends to form a network or crystalline structure as the solvent (xylene) evaporates or as the solution cools, leading to solidification. Based on your observation that a 0.02% solution works well, here are some strategies to maintain viscosity without turning solid:

1. Lower the EVA Concentration:

• The 20% concentration is indeed too high for the solution to remain viscous but fluid at room temperature. When you dilute it, the solution remains a viscous fluid, which means reducing the concentration is the most straightforward solution.
• Try reducing the EVA concentration to 5-10% by weight. You can experiment with these concentrations to find the balance between good viscosity and stability.
• A concentration of 0.1% to 1% is typically ideal for PPDs in lubricant formulations, depending on the desired performance.

2. Use a Lower Molecular Weight EVA:

• Higher molecular weight EVA polymers have larger, more rigid polymer chains, which can easily lead to solidification at higher concentrations. If you are using high molecular weight EVA, it may be worth considering a lower molecular weight EVA.
• Lower molecular weight EVA will have less tendency to form solid networks and is more likely to maintain a viscous state at lower concentrations.

3. Adjust the Solvent-to-EVA Ratio:

• The solvent-to-EVA ratio directly impacts the final viscosity. With 20% EVA, the ratio is too low for adequate solubility and stability. Increasing the amount of xylene (or using a higher solvent-to-EVA ratio) can help.
• Consider using a 5:1 or 10:1 ratio of xylene to EVA (by weight). This will result in a more diluted solution that should remain viscous without solidifying upon cooling. If you need a higher concentration of EVA for performance reasons, the additional solvent will help maintain a fluid state.

4. Add Plasticizers:

• If you still want to keep the EVA concentration higher than what is typically used, consider adding a plasticizer to reduce the rigidity of the polymer chains and prevent solidification. Common plasticizers include:
  • Dioctyl phthalate (DOP)
  • Tricresyl phosphate (TCP)
  • Toluene
• Start by adding 5-10% plasticizer by weight relative to the EVA. This will make the EVA more flexible and prevent it from forming a solid matrix.

5. Consider Using a Surfactant or Dispersant:

• If you’re dealing with a high molecular weight EVA and need to maintain the viscosity while ensuring the solution stays in liquid form, you might want to incorporate a dispersing agent or surfactant. These help maintain the uniform dispersion of EVA in xylene, preventing aggregation or crystallization.
  • Examples include polyisobutylene succinimide (PIBSI) or polyetheramine dispersants.

6. Test at Lower Concentrations:

• Since you’ve seen success at 0.02% EVA, it suggests that this concentration is low enough to keep the solution viscous. You might want to gradually increase the concentration, step-by-step (e.g., 0.05%, 0.1%, 0.5%), while monitoring the cooling behavior to find the highest concentration that remains a viscous fluid.

Summary of Key Steps:

1. Lower the EVA concentration to a range of 5-10% by weight or even less for better fluidity.
2. Consider using a lower molecular weight EVA to prevent solidification.
3. Increase the xylene-to-EVA ratio (e.g., 5:1 or 10:1) to ensure the solution stays diluted and doesn’t solidify.
4. Add a plasticizer to soften the polymer and prevent rigidity, starting with 5-10% plasticizer.
5. Use surfactants or dispersants if needed to maintain stability and dispersion.
6. Gradually experiment with higher concentrations while monitoring the cooling behavior.