Rapid Quality Control in Polyamide Production: Viscosity, Functional Group and Moisture Analyses in Under 1 Minute with Vis-NIRS

Introduction Plastics have become an integral part of modern lifestyles today. These substances, which fundamentally possess a synthetic organic polymer structure, can be found in a wide range of products spanning from food packaging to small household appliances, automotive parts, decorative items and textiles (and indeed many other components vital to sustaining our lives). The properties of plastic materials can be easily adapted according to the intended use, and—unlike many natural materials—can be produced at relatively low costs. The increasingly widespread use of synthetic polymers in daily life, on one hand, has contributed to the emergence of many new application areas (e.g., conductive polymers), while on the other hand, it has brought to the fore growing awareness of vital issues such as impacts on human health, waste management, and environmental pollution, as well as significant research and development efforts within this framework (e.g., bioplastics). Effective quality control in plastic production is an important process that extends from raw material input through reaction management, intermediate product optimization, final product quality, and even energy consumption, recycling and sustainability. Given the importance of consumption rate and product quality, the implementation of quality control analyses with precision, accuracy, speed and low cost is of paramount importance for manufacturers. Various standard analytical techniques and methodologies are used to monitor parameters in polymer quality control processes; volumetric or coulometric Karl Fischer (KF) titrations for moisture content measurements, potentiometric titration and/or FTIR for functional group determination, viscometric measurements for relative viscosity, and UV-VIS detection for color determination are among the most prominent of these. Besides the fact that some of these techniques require lengthy and demanding sample preparation stages, potential errors that may occur in such processes can result in significant delays during production stages and, due to faulty production, financial losses reaching up to 30% on a total revenue basis. Within the scope of this review article, we aim to examine the analyses performed in polyamide production quality control and to present detailed information particularly on the advantages that Near-Infrared Spectroscopy (NIRS) techniques can provide to such processes.

Near-Infrared Spectroscopy (NIRS)

Near-infrared spectroscopy (NIRS) is a methodology built upon a system infrastructure based on molecule-light interaction; it provides significant contributions to practical, rapid and precise monitoring of measurement parameters in quality control analyses. The NIRS technique, being a non-destructive method and requiring no sample pre-preparation, enables you to perform faster, more environmentally friendly and more economical analyses compared to wet chemistry methods. In the quality control processes of polyamides, we observe that parameters determined particularly within the framework of ASTM D789 (relative viscosity and functional groups) and moisture content analysis stand out.   With Metrohm's new Polymer Analyzer system, which combines visible (Vis) and near-infrared (NIR) regions, it is possible to measure various chemical and physical quality control parameters in less than one minute without any sample preparation, non-destructively, without chemicals and without the need for consumables. Within the scope of our experimental content and workflow investigation, repeated measurements were performed on polyamide pellets using a Metrohm Polymer Analyzer across the entire Vis-NIR wavelength range (400-2500 nm) in reflection mode. Polyamide pellets were placed in a DS2500 Large Sample Cup rotatable sample holder, thus eliminating potential factors related to particle size or chemical component irregularities and ensuring repeatable spectrum scanning through fully automated measurements from different points. As can be seen in Figure 2, all measurements were performed without any sample pre-preparation.

Method Development

The Vision Air Complete software package was used for data collection, model building and quantification method development processes. Thanks to this triple package software that takes the user interface experience to an entirely new level, all instrument management, including the assignment of operation procedures, is carried out from the office with the aid of Vision Air Manager Network, while all actual measurements are performed with the Vision Air Routine interface in the quality control laboratory. The obtained spectra are automatically uploaded to the database and made available for direct access for method development. Quantitative method development was performed using Vision Chemometrics Software.

Analysis Results

The obtained Vis-NIR spectra (see Figure 3) were used to create prediction models for quantitative determination of relative viscosity, amine end groups, carboxyl end groups and moisture content parameters in polyamides. The quality of the prediction models was evaluated through correlation graphs showing the relationship between values obtained from primary methods of titration, viscometry and KF titration and Vis-NIR data (See Figures 4, 5, 6 and 7). Reliability data (FOM) related to the expected data accuracy during routine analysis are also shown in these figures. [caption id="attachment_103448" align="aligncenter"] Figure 4: Vis-NIR correlation graph and reliability values for relative viscosity in polyamides (relative viscosity laboratory values were evaluated using a viscometer).[/caption]

Conclusion

This review demonstrates that typical key quality control parameter analyses in polyamides can be performed using Near-Infrared Spectroscopy (NIRS) technique. Compared to wet chemistry methods, rapid access to analysis results represents the most striking advantage of NIRS technique. The ability to determine all parameters (both physical and chemical) in less than one minute within a single measurement enables superior time and cost savings to be achieved particularly in the polymer industry. As Metrohm, in addition to being the global industry leader in primary methodologies (potentiometric titration & Karl Fischer titration) underpinning NIRS analytical techniques in the polymer sector, we directly present to you fully integrated, rapid, precise and reliable solutions under the same roof with our Vis-NIRS system solutions and software compatible with international standards.

References

1. Metrohm Application Note AN-NIR-060 Quality Control of Polyamides 2. Metrohm Application MI-2019-1-AP-2 It's all made of plastic! Analysis in the polymer industry     Pelin Kömürcü Spectroscopy Applications Chemist Metrohm Turkey