White Frost on PVC Products? Heat Stabilizer May Be the Culprit! Here’s the Effective Solution

创建于01.06

Friends in PVC processing have probably encountered this frustrating issue: freshly produced products are smooth and transparent, but after a few days, a layer of white "frost" appears on the surface. Not only does it ruin the appearance, but in severe cases, it also affects touch and performance—leading to customer returns and lost orders.

Many people mistakenly blame impure raw materials or process issues, but in fact, such white frost is closely related to the improper selection or use of heat stabilizers! Today, we’ll clarify this connection and share a practical step-by-step plan from "quick diagnosis" to "permanent solution"—usable for both industry veterans and newcomers.

Ⅰ. First, Understand: Why Does Heat Stabilizer Cause White Frost on PVC?

Quick Fact: PVC tends to decompose and release HCl (hydrochloric acid) during processing. The core function of heat stabilizers is to "capture" HCl and prevent PVC degradation. The white frost we see is often a problem with the "by-products" of heat stabilizers after they work.

For example, common metal soap heat stabilizers (such as calcium stearate and zinc stearate)—if overused or improperly proportioned (calcium to zinc ratio)—will react with captured HCl to form water-soluble salts like calcium chloride and zinc chloride. These unstable salts gradually migrate from the interior of PVC to the surface, forming the visible white frost—a phenomenon known as "salting-out" in the industry.

You don’t need complex equipment to confirm this cause—just a simple test!

Ⅱ. 10-Minute Quick Diagnosis: 3-Step Solubility Test

Test Method (Materials Easily Available)

Gently scrape a small amount of white frost with a clean cotton swab. Prepare two liquids: one drop of water and one drop of organic solvent (e.g., acetone or ethanol). Place the frost in each liquid, stir gently, and observe solubility.

Result Interpretation: Identify Heat Stabilizer Issues at a Glance

Focus on "water solubility":

If the frost dissolves in water, it is most likely water-soluble salts from metal soap stabilizers, or excess internal lubricants/low-molecular-weight antioxidants (but heat stabilizers remain the primary suspect).

At this point, focus on inspecting the heat stabilizer in the formula: e.g., whether a single metal soap (especially calcium stearate) is overused, if the calcium/zinc ratio is reasonable, and if the total dosage or compounding scheme of the stabilizer is problematic.

Ⅲ. Targeted Solutions: Fix White Frost in 2 Steps (Starting with Heat Stabilizers)

Since the problem lies with heat stabilizers, the solution is clear—either optimize the existing stabilizer or adjust the formulation, with the core goal of improving compatibility and reducing salting-out.

Solution 1: Replace/Partially Replace the Heat Stabilizer

If a single metal soap stabilizer is confirmed as the cause, replace it directly! Recommended alternatives: high-efficiency composite organotin stabilizers or high-performance composite calcium-zinc stabilizers. These composite stabilizers offer distinct advantages:

· Better compatibility with PVC, preventing migration to the surface;

· Longer-lasting stability, fundamentally reducing salting-out.

Solution 2: Add Secondary Stabilizers to Reduce Primary Stabilizer Dosage

If you don’t want to drastically modify the primary stabilizer formula, use a "secondary + primary" combination. For example, add small amounts of secondary stabilizers (such as β-diketone, hydrotalcite, or phosphite) to the existing formula. They enhance overall thermal stability, allowing you to reduce the dosage of metal soap primary stabilizers and minimize salting-out risk at the source.

Critical Reminder: Always Conduct Lab-Scale Tests Before Replacement

Whether replacing stabilizers or adding secondary agents, adhere to this core principle: the new stabilizer must have better compatibility and long-term effectiveness. Additionally, replacement may affect the initial coloring (e.g., yellowing) and transparency of PVC products. Always conduct lab-scale tests first to confirm no issues before mass production—avoid blind adjustments that could lead to greater losses.

Ⅳ. Final Step: Verify + Prevent to Avoid Recurrence

Adjusting the formula isn’t the end—you need to verify results through testing and establish long-term control mechanisms to prevent future issues. This step includes three key stages: "short-term verification," "long-term confirmation," and "daily prevention."

1. Short-Term Verification: Small-Batch Trials to Screen Solutions

Based on the above adjustments, develop 2-3 optimized formulas for lab-scale tests. After producing samples:

· Store them in a standard laboratory environment (23±2℃, 50±10% humidity) for 48-72 hours, closely monitoring for white frost recurrence.

· Conduct an accelerated migration test: Place samples in an oven at 60-70℃ for 24-72 hours, cool, and observe. This method quickly predicts long-term storage migration risk—highly recommended.

2. Long-Term Stability Confirmation: Ensure Mass Production Safety

Samples passing short-term verification require longer-term room-temperature storage observation. For products used in special environments (e.g., outdoor or humid conditions), simulate real-world scenarios with tests like UV irradiation or thermal-humidity cycling to ensure no issues in actual use.

3. Daily Prevention: Source Control to Avoid Detours

To completely eliminate white frost, daily management is key. Implement these two practices:

· Establish incoming raw material inspection: Conduct compatibility tests for new batches of resin, fillers, plasticizers, and stabilizers to assess migration risk.

· Monitor key process parameters: Set SPC control points for processing temperature, cooling water temperature, etc., to avoid abnormal heat stabilizer reactions caused by process fluctuations.

Summary

White frost on PVC products is often linked to improper heat stabilizer use. Follow the steps above to diagnose, resolve, and prevent the issue effectively.

If you encounter specific problems in practice—such as choosing composite stabilizers or handling lab-scale test abnormalities—feel free to leave a comment for further discussion!

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