重新導向訊息
詢價

硅橡胶质量控制

AN-NIR-084

2020-06

zh

Fast determination of vinyl content without chemicals

硅橡胶中乙烯基含量的测定是一个漫长而具有挑战性的过程。首先，乙烯基必须通过与酸反应转化为乙烯，然后用气相色谱法（GC）测定生成的乙烯。本应用说明表明，可见近红外光谱法为测定硅橡胶中的乙烯基含量提供了一种经济、快速的解决方案。使用 DS2500 近红外固体分析仪，无需样品制备或任何化学试剂，一分钟内即可获得结果。

Determination of the vinyl content of silicone rubber is a lengthy and challenging process. First, the vinyl groups must be converted to ethylene by reacting with an acid, followed by the determination of the produced ethylene with gas chromatography (GC).

This application note demonstrates that Vis-NIR (visible near-infrared) spectroscopy provides a cost-efficient and fast solution for the determination of vinyl content in silicone rubber. With the DS2500 Solid Analyzer it is possible to obtain results in less than a minute without sample preparation or any chemical reagents. The standard GC method requires one hour to perform, along with highly trained analysts. In contrast to the primary method, Vis-NIR spectroscopy, is a cost-efficient and fast analytical solution for the determination of vinyl content in silicone rubber.

Figure 1. DS2500 Solid Analyzer with silicone rubber sample present in DS2500 Slurry Cup.

Silicone samples were measured with a DS2500 Solid Analyzer in transflection mode over the full wavelength range (400–2500 nm). A DS2500 Slurry Cup was employed, which simplifies the positioning of the sample and cleaning of the sample vessel. The 1 mm gold diffuse reflector defines the same path length for all measurements to guarantee reproducible results. As displayed in Figure 1, samples were measured without any preparation step. The Metrohm software package Vision Air Complete was used for all data acquisition and prediction model development.

Table 1. Hardware and software equipment overview
Equipment Metrohm number
DS2500 Analyzer 2.922.0010
DS2500 Slurry Cup 6.7490.430
Gold Diffuse Reflector 1 mm 6.7420.000
Vision Air 2.0 Complete 6.6072.208

The obtained Vis-NIR spectra (Figure 2) were used to create prediction models for quantification of vinyl content in silicone rubber. The quality of the prediction models was evaluated using correlation diagrams, which display the correlation between Vis-NIR prediction and primary method values. The respective figures of merit (FOM) display the expected precision of a prediction during routine analysis.

Figure 2. Selection of silicone rubber Vis-NIR spectra obtained using a DS2500 Analyzer and a rotating DS2500 Slurry Cup.
Figure 3. Correlation diagram and the respective figures of merit for the prediction of the vinyl content in silicone rubber using a DS2500 Solid Analyzer. The vinyl content lab value was evaluated using gas chromatography.
Table 2. Figures of merit for the prediction of the vinyl content in silicone rubber using a DS2500 Solid Analyzer.
Figures of merit Value
R2 0.989
Standard error of calibration 0.0076%
Standard error of cross-validation 0.0089%

This application note demonstrates the feasibility of NIR spectroscopy for the analysis of vinyl content in silicone rubber. In comparison to gas chromatography methods (Table 3), the time to result is a major advantage of NIR spectroscopy, since a single measurement is performed in less than a minute.

Table 3. Time to result overview for the parameter vinyl content.
Parameter Method Time to result
Vinyl content Gas chromatography ∼10 min (preparation) + ∼50 min (GC)
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Internal reference: AW NIR CN-0016-082019