Analysis of the isothermal crystallization of isotactic polypropylene nucleated with sorbitol derivatives

Development of a Measurement System Using Infrared Spectroscopy-Attenuated Total Reflectance, Principal Component Analysis and Artificial Intelligence for the Safe Quantification of the Nucleating Agent Sorbitol in Food Packaging

Sorbitol derivatives and other additives are commonly used in various products, such as packaging or food packaging, to improve their mechanical, physical, and optical properties. To accurately and precisely evaluate the efficacy of adding sorbitol-type nucleating agents to these articles, their quantitative determination is essential. This study systematically investigated the quantification of sorbitol-type nucleating agents in food packaging made from impact copolymers of polypropylene (PP) and polyethylene (PE) using attenuated total reflectance infrared spectroscopy (ATR-FTIR) together with analysis of principal components (PCA) and machine learning algorithms. The absorption spectra revealed characteristic bands corresponding to the C-O-C bond and hydroxyl groups attached to the cyclohexane ring of the molecular structure of sorbitol, providing crucial information for identifying and quantifying sorbitol derivatives. PCA analysis showed that with the selected FTIR spectrum range and only the first two components, 99.5% of the variance could be explained. The resulting score plot showed a clear pattern distinguishing different concentrations of the nucleating agent, affirming the predictability of concentrations based on an impact copolymer. The study then employed machine learning algorithms (NN, SVR) to establish prediction models, evaluating their quality using metrics such as RMSE, R2, and RMSECV. Hyperparameter optimization was performed, and SVR showed superior performance, achieving near-perfect predictions (R2 = 0.9999) with an RMSE of 0.100 for both calibration and prediction. The chosen SVR model features two hidden layers with 15 neurons each and uses the Adam algorithm, balanced precision, and computational efficiency. The innovative ATR-FTIR coupled SVR model presented a novel and rapid approach to accurately quantify sorbitol-type nucleating agents in polymer production processes for polymer research and in the analysis of nucleating agent derivatives. The analytical performance of this method surpassed traditional methods (PCR, NN).

Determination of nucleating agents in plastic materials by GC/MS after microwave-assisted extraction with in situ microwave-assisted derivatization

This work demonstrates the analysis of sorbitol-based nucleating and clarifying agents (NCAs) used as additives for polyolefin-based materials by gas chromatography/mass spectrometry (GC/MS), employing a highly reliable and efficient sample preparation methodology applying microwave irradiation. A derivatization by silylation of the analytes was done to improve the GC-suitability of the analytes. After successful optimization of the conditions for a microwave-assisted derivatization (MAD), the microwave-assisted extraction (MAE) of the analytes from polymer samples was investigated. Tetrahydrofuran (THF) turned out to be the best extraction solvent, as poorly soluble analytes show the highest solubility in this solvent and THF supports the silylation after extraction. This two-step approach and subsequent chromatographic determination resulted in reproducibilities from approximately 2% up to 6% and recoveries from 95.8% up to 104.2% in real samples. In order to reduce the number of sample preparation steps a one-step approach was investigated and optimized, in which MAE and MAD were carried out simultaneously. The developed procedure resulted in remarkably better repeatabilities ranging from 0.05% up to 4% and reproducibilities of up to 10%. The recoveries matched those obtained with the two-step process. Linearities could be achieved in both approaches with R(2) better than 0.99 for all selected analytes over two orders of magnitude. All data indicate the suitability of both presented methods for the reliable determination of sorbitol-based NCAs in polyolefin materials.