1, Two batches of rubber compounds (Sample A and Sample B) with identical formulations were tested for curing characteristics using a rotorless rheometer. Results were extremely similar, and both batches would normally be qualified, indicating consistent quality of cured products.
2, Notably, Sample A had a slightly longer TC90 value than Sample B, suggesting better processing safety in theory. However, during actual extrusion, Sample B exhibited a smooth surface while unexpected scorching occurred with Sample A.
Test Conditions
T = 177℃, F = 1.67Hz, S = ±7%, t = 15 min
Test Data
| Sample | ML (dNm) | MH (dNm) | ts1 (min) | ts2 (min) | TC50 (min) | TC90 (min) |
|---|---|---|---|---|---|---|
| Sample A | 2.37 | 20.55 | 1.67 | 2.33 | 4.20 | 7.67 |
| Sample B | 2.37 | 22.41 | 1.63 | 2.17 | 3.91 | 7.17 |
3, The three-point frequency sweep test shows that the overall tanD value of Sample A is lower than that of Sample B at various shear rates, indicating that Sample A has higher elasticity than Sample B. The higher elasticity can be attributed to the higher molecular weight or the presence of long-chain branches.
4, Filler interaction analysis via the Payne effect shows that the storage modulus G’ of Sample A is higher than that of Sample B at high strain (high shear rate), indicating stronger elasticity and higher heat generation under high shear force in Sample A.
- Cause: Dynamic tests reveal that Sample A has high elasticity and long-chain branches, leading to local heat buildup at high shear rates and resulting in scorching.
- Conclusion: Traditional curing tests at low shear rates are insufficient to identify the intrinsic differences in rubber compounds.
- Solution: Process adjustment – properly reduce the extrusion speed and temperature for Sample A.