Testing to ensure gloves are silicone-free

SATRA can use infrared spectroscopy to determine whether silicone – a troublesome contaminant – is present on the surface of gloves.

Silicones are polymers made of silicon, carbon and oxygen, and they have very desirable properties for uses in industrial lubricants, mould-release agents and greases – especially those that can resist high temperatures. However, some of those same attractive properties can be very undesirable in other applications, such as during the application of painted or dipped coatings, or when adhesives are applied.

Silicone inhibits coating adhesion and often prevents a strong bond being formed between the substrates. It is therefore undesirable in some situations. The high degree of chemical inertness, thermal stability and resistance to oxidation of silicones can also be a problem, as silicone can be difficult to remove. Industrial applications that require workers to wear protective gloves while carrying out processes where silicone can cause major problems often require confirmation that this substance is not present on their gloves. Such applications include clean room working and paint spraying.

Testing for the presence of silicone in gloves

Silicone contamination could arise from many different stages in the glove manufacturing process. This includes from lubricants in machinery used to knit supported gloves, from machinery utilised in the dipping process for dipped gloves, or from contamination at the final glove-packing stage. In order to determine whether silicone is present on the surface of gloves, SATRA has developed a new test method – SATRA TM458:2020 – ‘Qualitative analysis for silicone content’. The approach taken at SATRA is to extract a specimen from the palm area of the gloves with petroleum ether (a volatile organic solvent) in an ultrasonic bath. The solvent is separated from the gloving material and concentrated to dryness at room temperature in a fume cabinet. The dried residue is then dissolved in a small volume of petroleum ether, and the liquid is analysed by Fourier Transform Infrared spectroscopy (FTIR).

FTIR spectroscopy

This analytical instrument exposes the liquid specimen to infrared radiation, and different wavelengths in the infrared spectra are absorbed by various chemical bonds in the dried residue. The wavelengths absorbed by the residue from this radiation relates to the energy required to vibrate and rotate the variety of chemical bonds present. Different chemical bonds will vibrate at slightly different wavelengths, measured in cm^-1.

For example, a carbon to hydrogen bond (C-H) vibrates at a wavelength of around 3,000cm^-1, while a carbon to oxygen double bond (C=O) vibrates at around 1,740cm^-1. When the amount of infrared radiation transmitted through the specimen is plotted against the wavelengths, a characteristic infrared spectrum is obtained. The principle of FTIR is that the analysed residue is situated between the radiation source and the detector. If there is silicone present in the liquid extract, the signal that reaches the detector will have a lower response at approximately 800, 1,020, 1,090 and 1,260cm^-1 (see figure 1). These specific wavelengths correspond to the energy absorbed by the silicon to oxygen and silicone to carbon bonds.

Qualitative analysis

This analysis to determine whether silicone is present on the surface of gloves is a qualitative determination – that is, it will not define the concentration of silicone. The size of the inverted peaks at approximately the four wavelengths previously mentioned does provide an indication of the amount of silicone present, as trace amounts will only give very small inverted peaks.

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