Why Does a Retort Pouch Delaminate After 121°C Sterilization?
7/1/20262 min read
I. What Do You See?
Figure 1: Schematic Diagram of Delamination Phenomenon
After retorting, some pouches may exhibit surface whitening, delamination, and a "separated" feeling when pressed. In severe cases, it looks like the layers can be peeled apart one by one. Simply put: the bag isn't broken, but the inside has come apart.
II. What Should It Look Like Normally?
Figure 2: Cross-Sectional Diagram of Retort Pouch Structure
A retort pouch is made by laminating multiple layers of materials together — for example, the outer layer is PET, the middle layer is aluminum foil or a barrier layer, and the inner layer is CPP — all bonded into one structure with adhesive.
III. Why Does Delamination Occur After 121°C Sterilization?
Figure 3: Three-Stage Change Diagram (Normal → Blistering → Delamination)
It can be simply understood as three things happening together:
① The adhesive weakens.
At high temperatures, the adhesive layer softens → it no longer bonds firmly.
② Moisture gets in.
Steam seeps into microscopic gaps → forms bubbles → pushes the structure apart.
③ Materials "pull against each other."
Different materials shrink at different rates → creates stress.
End result: Weak adhesive + moisture ingress + material = delamination.
IV. How Serious Is This Problem?
Severity depends on the extent of delamination. Minor delamination mainly affects appearance and may still be acceptable. Significant delamination compromises seal strength and poses a leak risk. In severe cases, the bag's integrity is destroyed, and the product should not be used. Immediate inspection of the same batch is required.
V. Solutions
Improvements should focus on three areas:
Use high-temperature-resistant adhesive (rated for 121°C)
Optimize the production process (to ensure stronger bonding)
Optimize material combinations (to reduce differences in thermal expansion/contraction)
Therefore, retort pouch delamination is essentially caused by the combined effects of high temperature, moisture, and material mismatch, which together lead to adhesive failure.
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