Analysis And Solutions For The Reasons Why Rotomolded Products Become Soft

Rotomolded products become soft usually due to improper material selection, poor process control or mismatched use environment**. The following is a detailed analysis of the reasons and solutions:

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I. The main reasons for the softening of rotomolded products

1. Material problems (core factors)
- Wrong resin selection:
- When using low-density polyethylene (LDPE) or linear low-density polyethylene (LLDPE), it is inherently soft and more easily deformed at high temperatures.
- No reinforcing fillers (such as calcium carbonate, glass fiber) are added, resulting in insufficient rigidity.
- Material degradation:
- Excessive heating (>280℃) causes molecular chains to break, and the material becomes brittle or soft.
- The proportion of recycled materials is too high (>30%), which reduces material performance.
2. Improper process control
- Heating time is too long or temperature is too high:
- The resin is over-melted, the molecular structure is destroyed, and the hardness decreases.
- Cooling speed is too slow:
- Slow cooling leads to reduced crystallinity and softening of the product.
- Uneven wall thickness:
- Too thin area (<3mm) is not rigid enough and easy to deform.

3. Influence of use environment
- High temperature environment (>60℃):
- PE material will soften at high temperature (HDPE has better temperature resistance than LLDPE).
- Chemical corrosion:
- Contact with organic solvents (such as gasoline, grease) causes the material to swell and soften.
- Long-term load:
- Continuous force (such as stacking storage) causes creep deformation.

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Structural design optimization
- Add reinforcement ribs (applicable to large flat products):
- Rib height = wall thickness × 1.5 times, spacing ≤150mm.
- Optimize wall thickness distribution:
- Thicken the key stress area (such as edge ≥5mm).

4. Adaptation to the use environment
- High temperature environment: use heat-resistant materials (such as PP, PA6).
- Chemical contact: choose solvent-resistant materials (such as PTFE coating).
- Long-term load: Add support structure or use anti-creep formula.

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II. Emergency remedial measures (softening of produced products)

1. Local heating correction (applicable to slight deformation):

- Use a hot air gun (200-230℃) to heat and reshape.

2. Epoxy resin reinforcement (applicable to stress-bearing parts):

- Apply epoxy resin + fiberglass cloth to the soft area.

3. Add external support (such as metal frame):

- Applicable to large containers or tanks.

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III. Preventive measures (long-term solution)

✅ Material testing: Melt index (MFI) and density are tested for each batch.

✅ Process monitoring: Infrared thermal imager monitors mold temperature uniformity.

✅ Accelerated aging test: Simulate the use environment (high temperature + load) to verify product life.

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Summary
The main reasons for the softening of rotomolded products are improper material selection, poor process control or mismatch of use environment. The best solution is:
1. Use high-rigidity resin (HDPE/PP) and add fillers;
2. Optimize heating and cooling processes;
3. Add reinforcement or adjust wall thickness;
4. Adapt to the use environment (temperature resistance/chemical corrosion resistance).

Through system optimization, the hardness of the product can be significantly improved and deformation problems can be avoided.