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    Home > Coatings News > Paints and Coatings Market > A brief review of chromatography for determining free TDI in polyurethane coatings

    A brief review of chromatography for determining free TDI in polyurethane coatings

    • Last Update: 2020-12-04
    • Source: Internet
    • Author: User
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    1 Foreword
    The presence of reactive toluene diocyanate (i.e. free TDI) in polyurethane coatings, when the coating is applied, the free TDI will slowly evaporate into the air to cause harm to the human body. TDI is a highly toxic inhalable poison, in the human body has a build-up and latent nature of its chemical activity is very high, very easy to air moisture reaction and become non-volatile substances. In today's world countries on environmental protection requirements are increasingly strict situation, the free monomer content in the preconjudent must be controlled at less than 0.5%, some have reached less than 0.1%, which requires the use of trace or even trace analysis to detect TDI
    China
    . The literature is mostly gas chromatography and high-efficiency liquid chromatography. China's original chemical standard HG/T2425-93, German standard DIN55956 (1981), Canadian standard 1-GP-180M, ISO10283 (1977, 1,8) are the use of gas chromatography within the standard legal quantity.2 Factors that affect the accuracy of gas chromatography
    When determining the content of free TDI in polyurethane coatings by gas chromatography, for the technical personnel involved in this method for the first time, they can not grasp the control factors such as column, internal marker, moisture and sample port temperature, so it is difficult to determine the content of TDI easily and quickly, of course, accuracy and precision will be serious problems.
    2.1 chromatography column
    now the gas chromatography method to measure TDI are selected capillary column, the column is more kinds, However, especially SE-30 bars commonly used, separation effect is also better, with 8% SE-30, 10% SE-30 and 25% SE-30 bars as columns, after numerous real room proof, only 25% SE-30 bars, can make separation, peak shape to achieve a good effect, and has a higher sensitivity and its columns have different degrees of separation, peak shape and sensitivity problems.
    2.2 the choice of the internal object
    the gas chromatography method to determine TDI should be within the statutory amount, so the choice of the internal label is also the key point of the law, in terms of tropobenzene and positive xyluane two internal objects, the former peak position is obviously on the tail of the solvent peak, very easy to lead to an increase in analytical errors, and positive xylene peak just after TDI, there is no such problem.
    effect of 2.3 inset temperature on sample analysis
    according to literature, TDI prejudes heating is easy to decompose. When the temperature of the infringing port is high, the decomposition of the polyurethane coating produces TDI, affecting the test results, and the testing experiments of the polyurethane paint curing agent at the in-in-inkou temperature of 150 degrees and 250 degrees show that: 250 degrees significantly increases the TDI peak (208.6min). , other than, when the gasification chamber temperature is below 130 degrees, TDI can not be fully vaporized, which will cause the test results to be low, so the temperature of the infested port should be well controlled.3 When establishing a gas chromatography-mass spectrometry analysis method
    3.1 TDI gas chromatography-mass spectrometry analysis
    using phase gas chromatography-mass spectrometry to analyze the free TDI content in polyurethane, Through comparative experiments, it is found that it has advantages over gas chromatography in solvent, choice of chromatography conditions and quantitative results of parts, while chromatography-mass spectrometography has the characteristics of qualitative accuracy, simplicity and speed, which is more suitable for free TDI detection in construction environment.
    3.2 Solid-phase micro-extraction (SPME) gas chromatography - mass spectrometry analysis method
    In the pretreatment of polyurethane coating determination, the traditional methods are: liquid-liquid extraction, distillation extraction, top empty sample, supercritical extraction, etc., but these pretreatment methods have common shortcomings; The solid-phase micro-extraction technology developed in the 1990s is a new and efficient pre-treatment technology. With the maturity of solid-phase micro-extraction gas chromatography technology to determine benzene products in coatings, promoting the application of solid-phase micro-extraction rich TDI, there are already literature reports that solid-phase micro-extraction (SPME) gas chromatography-mass spectrometry analysis method is suitable for the determination of TDI in polyurethane coatings, and this method has a strong advantage in regression equation linearity, detection limits, precision and so on.
    3.3 lysate gas chromatography - mass spectrometry
    polyurethane coatings, due to the variety of polycyanate and alcohol, it is necessary to find out its specific chemical structure. When composed of lysation gas chromatography (PGC) laboratory lysation products, more structural information can be obtained, but the chromatography quality ability is poor. The lysative gas chromatography-mass spectrometry (PGC-MS) combines the advantages of PGC and MS, and is of great significance for the rapid separation, qualitative analysis and non-sample pre-treatment of lysing products.4 Summary
    Although the standard method of free TDI in China's detection coatings provides for the use of gas chromatography, but in view of the trend of strict international control of TDI content, the change of its analytical method is also imperative, gas chromatography - mass spectrometrography analysis of the widespread use of TDI will be the only way.
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