Fast Discrimination of Industrial Polyamide Gears with Varying Regrind Material Content Using Advanced Polymer Chromatography for SEC/GPC

Importance of the Topic

In industrial polymer processing, incorporating recycled (regrind) material into polyamide (nylon) products requires reliable analytical techniques to ensure final properties match those of virgin materials. Monitoring molecular weight distribution and polydispersity is critical, as degradation during reprocessing can compromise mechanical performance and thermal stability.

Objectives and Study Overview

This study evaluates the performance of the Waters ACQUITY Advanced Polymer Chromatography (APC) System with hexafluoro-isopropanol (HFIP) as mobile phase for rapid size exclusion chromatography (SEC)/gel permeation chromatography (GPC) analysis of polyamide gears containing 0 to 100% recycled content. Key goals include reducing analysis time, solvent consumption, and hazardous waste compared to conventional high-temperature GPC.

Methodology and Instrumentation

Polyamide gear samples with varying percentages of regrind material were dissolved in HFIP (1 mg/mL) overnight. Chromatographic separations were performed on an APC system with an Isocratic Solvent Manager using HFIP containing 0.1% sodium trifluoroacetate. Separation utilized a bank of three ACQUITY APC XT columns (450 Å, 125 Å, 45 Å) at 50 °C with a 0.45 mL/min flow rate over a 15-minute run. Refractive index detection at 50 °C was employed, and data processing used Empower 3 CDS.

Main Results and Discussion

A PMMA calibration curve delivered an R2 of 0.9996 over the linear range for polyamide elution. Chromatographic overlays revealed systematic peak shifts to longer retention times, broader shapes, and lower heights as recycled content increased, indicating reduced molecular weight and broader distribution. Quantitatively, peak maximum molecular weight decreased from 127 kDa (0% regrind) to 97 kDa (100% regrind), a 24% drop. Corresponding changes in weight-average (Mw), number-average (Mn), z-average, and polydispersity index (Mw/Mn) suggest potential impacts on melt flow, strength, and flexibility.

Benefits and Practical Applications of the Method

• Analysis time reduced to 15 minutes per sample versus 45 minutes with traditional GPC
• Solvent consumption under 7 mL HFIP per injection compared to over 22 mL in conventional methods
• Six-fold reduction in hazardous waste generation
• Improved sample throughput and cost efficiency for quality control laboratories

Future Trends and Potential Applications

Advances may include coupling APC separations with thermal or rheological detectors for comprehensive polymer profiling, expanding HFIP-based methods to other engineering plastics, and integrating real-time process monitoring with inline sensors. Sustainable solvent approaches and high-pressure column developments will further enhance speed and environmental impact. Machine-learning models could predict performance based on chromatographic fingerprints.

Conclusion

The Waters APC system with HFIP mobile phase effectively differentiates industrial polyamide gears containing varied recycled content, delivering accurate molecular weight measurements in one-third the time and with significantly less solvent compared to high-temperature GPC. This method offers a rapid, sustainable, and robust alternative for polymer quality control.

References

• Palmer RJ. Polyamides, Plastics. In: Encyclopedia of Polymer Science and Technology. John Wiley & Sons; 2001.
• Beginners Guide to Size Exclusion Chromatography. Waters Corporation.
• Wudy K, Drummer D. Aging effects of Polyamide 12 in Selective Laser Sintering: Molecular Weight Distribution and Thermal Properties. Addit Manuf. 2018;25.
• Chen AL, Wei KL, Jeng RJ, Lin JJ, Dai S. Well-Defined Polyamide Synthesis from Diisocyanates and Diacids Involving Hindered Carbodiimide Intermediates. Macromolecules. 2010;44.
• APC System Chemical Compatibility Guide. Waters Corporation.
• Wold C, Uliyanchenko E. Ultra-High Size-Exclusion Separations of Engineering Plastics: Challenges and Opportunities. LCGC Europe.
• Trinite D. Waters Corporation Application Note, 2022.
• Browne J. TA Instruments Application of Polyamides Containing Recyclates. 2022.
• Mendelsohn R, Gough J. Fast, High-Resolution Analysis of Polydimethylsiloxanes in Toluene With Advanced Polymer Chromatography. Waters Application Note; 2022.