GPC Analysis of Synthetic Resin Containers Composed Mainly of Polylactic Ac

Importance of the Topic

Gel permeation chromatography (GPC) is a cornerstone technique for characterizing the molecular weight distribution of synthetic and biodegradable polymers. Polylactic acid (PLA) is increasingly used in disposable packaging and medical devices due to its biodegradability and renewable origin. Understanding PLA’s molecular weight profile is critical for quality control, performance prediction, and ensuring consistent degradation behavior in practical applications.

Objectives and Study Overview

This application note describes the GPC analysis of a commercially available PLA cup using a mixed gel column to achieve a broad molecular weight coverage in a single run. The main goals are:

• Determine number and weight average molecular weights of the PLA sample.
• Demonstrate reduced analysis time and solvent consumption by employing a mixed gel column (Shodex GPC KF-805L).

Methodology and Instrumentation

The analysis was carried out on a Shimadzu Nexera GPC system equipped with a refractive index detector (RID-20A). Key conditions were:

• Column: Shodex GPC KF-805L (300 mm × 8.0 mm I.D.), shipped in THF and conditioned in chloroform following a gradual solvent exchange protocol.
• Mobile phase: Chloroform at 1.0 mL/min, column temperature 40 °C.
• Sample: 0.2 % PLA solution in chloroform, injection volume 50 µL.
• Detection: Refractive index detector at 40 °C.

Calibration was performed with polystyrene standards ranging from 580 to 3,730,000 Da, generating a linear log(MW) vs. retention time curve for data processing in LabSolutions GPC software.

Main Results and Discussion

The PLA cup exhibited a broad molecular weight distribution spanning approximately 2,000 to 2.3 million Daltons. Calculated polystyrene-equivalent values were:

• Number average molecular weight (Mn): 81,900 Da
• Weight average molecular weight (Mw): 179,600 Da
• Polydispersity index (Mw/Mn): 2.19

Use of the single mixed gel column eliminated the need for multiple columns in series, halving both run time and solvent consumption compared to conventional setups.

Benefits and Practical Applications

By covering a wide molecular weight range with one column, laboratories can:

• Increase sample throughput and reduce turnaround time for polymer QC.
• Lower solvent costs and waste generation, supporting green analytical practices.
• Simplify method development and maintenance efforts.

Future Trends and Opportunities

Emerging directions in polymer GPC analysis include:

• Integration of multi-detector configurations (e.g., light scattering, viscometry) for absolute molecular weight determination.
• Development of faster, higher-resolution mixed gel columns to further boost throughput.
• Automation and in-line sampling for real-time monitoring in manufacturing processes.
• Expansion of GPC methods to novel biodegradable and bio-based polymer systems.

Conclusion

GPC analysis of a PLA container using a Shodex mixed gel column on the Nexera system successfully provided comprehensive molecular weight data with reduced analysis time and solvent use. This streamlined approach meets the demands of modern polymer QC and sustainability goals.

Reference

Shimadzu Corporation. "High Performance Liquid Chromatograph Nexera™ GPC System: GPC Analysis of Synthetic Resin Containers Composed Mainly of Polylactic Acid." First Edition Jul. 2022.