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Comparison of Accuracy of Curing Degree Testing Methods for Silicone Pressure-Sensitive Adhesives (Solvent Extraction Method, DSC Method and FTIR Method)
Views: 0 Author: Site Editor Publish Time: 2026-07-24 Origin: Site
I. Measurement Principles and Essential Differences
1. Solvent Extraction Method
This method measures gel content. Samples are repeatedly extracted with good solvent; uncrosslinked molecules dissolve out. The dried residue is weighed to calculate the mass fraction of insoluble substances, reflecting the proportion of macro insoluble network structure.
2. DSC Method
This method measures residual reaction heat. The total heat release of uncured samples (ΔHtotal) and residual heat release of test samples (ΔHresidual) are measured respectively. Curing degree: α=1−ΔHresidual/ΔHtotal It characterizes the proportion of residual reactive functional groups.
3. FTIR Spectroscopy Method
This method monitors the consumption of characteristic functional groups. For hydrosilylation systems, peak area variations of Si-H (≈2160 cm⁻⊃1;) or Si-Vi (≈1595 cm⁻⊃1;) are tracked. An internal standard peak (e.g., Si-CH₃ at ≈1260 cm⁻⊃1;) is adopted for normalization, directly yielding the conversion rate of specific chemical bonds.
II. Accuracy Comparison and Major Errors
1. Solvent Extraction Method
Unreacted chain segments trapped by physical entanglement and topological locking are mistakenly identified as “crosslinked structure”, leading to systematic overestimation of chemical curing degree. Besides, test results are affected by dissolution efficiency, microgel loss and fluctuation of operating conditions, with precision of only ±2–5%.
2. DSC Method
It delivers relatively high accuracy at low-to-medium conversion rates. However, at high curing degrees, residual functional groups cannot fully react due to diffusion limitation, resulting in lower measured heat release and significant overestimation of curing degree. Additional errors originate from baseline selection, side reactions and determination of ΔHtotal. Its repeatability is favorable (<±2%).
3. FTIR Method
It directly observes chemical bond evolution and boasts the highest consistency with actual chemical conversion. Main errors stem from peak overlap (e.g., water vapor interference on Si-H signals). The ATR mode only detects surface layers; test data will be distorted if curing uniformity differs between surface and interior. Measurement complies with the Lambert-Beer Law and relies on uncured reference samples. It features high precision of approximately ±1–3%.
III. Comprehensive Accuracy Ranking
Judged by the actual conversion degree of chemical bonds, the accuracy sequence is: FTIR Method > DSC Method (low-to-medium conversion range) > Solvent Extraction Method
Solvent Extraction Method Lowest accuracy. Test values are elevated due to physical contributions and show the poorest correlation with chemical crosslinking status. Nevertheless, its results are closest to practical service performance in industrial applications.
DSC Method Reliable and accurate under low-to-medium conversion rates. It may generate falsely high curing degree readings within diffusion-controlled regions, so it shall not be independently applied to evaluate highly cured systems.
FTIR Method Highest accuracy, capable of finely distinguishing chemical conversion, especially suitable for differentiation under medium-to-high conversion rates.
IV. Practical Application Recommendations
Solvent Extraction Method Suitable for quality inspection to rapidly verify whether gel content meets service requirements. Its readings shall not be directly equated to chemical crosslink density.
DSC Method Applicable for reaction kinetics research and process monitoring. Attention shall be paid to measurement deviation at high conversion stages. Joint testing with FTIR Method is recommended.
FTIR Method Preferred calibration method for R&D by Jiangsu PTFE high-temperature fabric manufacturers. It can directly establish criteria for chemical conversion rates for formula development and process optimization. Combined with DSC testing, it provides complementary information on curing progression.
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