Application of Differential Scanning Calorimeter (DSC) in Pesticide Industry

Differential Scanning Calorimeter (DSC) analyzes the phase transition behavior of materials by measuring the changes in heat flux during programmed temperature control. For pesticides, physical or chemical changes such as melting, crystallization, decomposition, oxidation, etc. occur during the heating or cooling process, which are accompanied by the absorption or release of heat. Differential scanning calorimetry can accurately measure these heat flux changes and obtain relevant thermal performance parameters of pesticides.

The thermal performance parameters of pesticides, such as melting point, glass transition temperature, thermal decomposition temperature, etc., are important indicators for characterizing their thermal stability, purity, crystallization performance, etc. For example, the melting point can reflect the purity of pesticides, and pesticides with higher purity usually have sharper melting point peaks; The glass transition temperature is closely related to the storage stability and processing performance of pesticides; The thermal decomposition temperature can be used to evaluate the stability of pesticides in different temperature environments, providing reference for their storage, transportation, and use.

1. Measuring instruments

Instrument model: DZ-DSC300 differential scanning calorimeter

Instrument brand: Nanjing DaZhan Testing Instrument

2. Sample preparation

1. Sampling requirements: Take approximately 5-20mg of pesticide sample to ensure uniformity and no contamination. For solid pesticide samples, they should be ground into fine powder as much as possible to ensure uniform heat conduction; For liquid pesticide samples, it is necessary to use well sealed containers to prevent volatilization.

2. Pre treatment: If pesticide samples contain moisture or volatile solvents, they can be dried at low temperatures to eliminate their impact on experimental results. For certain pesticide samples that require elimination of thermal history, a heating cooling cycle can be performed, such as raising the temperature to a certain level at 10 ° C/min and then cooling it down.

3. Instrument calibration

1. Calibrate the temperature and heat flux signals of DSC using standard substances such as indium and tin. The melting point and enthalpy value of the standard substance are known. By measuring the DSC curve of the standard substance, the temperature and heat flux of the instrument can be calibrated to ensure the accuracy of the measurement results.

Ensure nitrogen or inert gas protection (flow rate 50-100mL/min) to prevent oxidation reactions of pesticide samples during the testing process, which may affect the experimental results.

4. Experimental parameter settings

Temperature range: 30-350 ° C

Set an appropriate heating range based on the properties of pesticide samples and the expected thermal transition temperature. Generally speaking, the starting temperature should be lower than the expected thermal transition temperature of pesticides, and the ending temperature should be higher than their thermal decomposition temperature.

Heating rate: 10 ° C/min

Excessive heating rate can lead to peak temperature shift and reduced resolution; If the heating rate is too low, the experimental time will be too long. Therefore, it is necessary to choose an appropriate heating rate based on the specific situation.

Nitrogen protection (50mL/min)

Repeated testing: Each group of samples should undergo at least 2 to 3 parallel experiments to verify the repeatability and reliability of the data.

5. Measurement spectrum and analysis

The melting peak temperature is 132 ° C, indicating that the pesticide begins to melt at this temperature.

The thermal decomposition temperature is 142 ° C, indicating that the pesticide has good thermal stability below 250 ° C.

Through analysis of the DSC curve, it was also found that the pesticide has a glass transition temperature, providing a basis for further research on its physical state and performance changes.

6. Graph data analysis

1. Melting peak identification

Analyze the DSC curve through software to locate the endothermic peak (melting peak). Determine the following characteristic temperatures:

Starting point: The starting point at which the baseline of the curve deviates, usually indicating the temperature at which the pesticide sample begins to melt.

Peak: The peak temperature of the endothermic peak, corresponding to the melting point of the pesticide sample.

Termination point: The end point of the melting process, marking the completion of the pesticide sample melting.

2. Thermal decomposition analysis

Observe the exothermic peak in the DSC curve and analyze the thermal decomposition behavior of pesticide samples.

The position and area of the exothermic peak can reflect information such as the starting temperature, decomposition rate, and decomposition heat of thermal decomposition. By analyzing the thermal decomposition curve, the stability of pesticides at high temperatures can be evaluated, providing safety guidance for their storage and use.

3. Analysis of Glass Transition Temperature

The glass transition shows a step like change in the baseline on the DSC curve. By determining the starting, middle, and ending points of the steps, the glass transition temperature range of pesticide samples can be obtained. The glass transition temperature is of great significance for understanding the physical state and performance changes of pesticides. For example, during storage, when the temperature is lower than the glass transition temperature, the pesticide sample is in a glass state and has good stability; When the temperature is higher than the glass transition temperature, the flowability of the material increases, which may affect its performance and quality.

7. Common problems and solutions

1. Baseline drift or high noise

Reason: Excessive sample size and unstable gas flow rate.

Solution: Reduce the sample size to an appropriate range, usually 5-10mg; calibrate the gas flow rate to ensure it remains stable at the set value.

2. The test results have a large deviation from the literature values

Reason:

1. Differences in pesticide batches, additives (such as adjuvants, solvents), or blending modification effects.

2. Inaccurate calibration or abnormal instrument status.

Solution:

1. Compare literature data of samples from the same source to confirm the consistency of material composition.

2. Re calibrate the instrument, check the sensitivity of the sensor and the sealing of the furnace body.

3. Thermal decomposition of the sample interferes with the melting peak

Reason: Some pesticide samples degrade before melting.

Solution:

1. Using inert gas (such as nitrogen) protection to reduce the risk of oxidative degradation.

2. Use rapid heating (such as 20 ° C/min) to shorten the high-temperature residence time.

Differential scanning calorimetry provides an efficient and sensitive method for characterizing the thermal properties of pesticide samples. By standardizing the sample preparation process, optimizing testing parameters, and analyzing data reasonably, key thermodynamic parameters of pesticide samples can be accurately obtained, providing theoretical support for the research and development, production, storage, and use of pesticides. In the field of pesticides, differential scanning calorimetry technology has broad application prospects, which can help researchers better understand the properties and behaviors of pesticides and promote the development of the pesticide industry. More product inquiries:.