Molecular Weight Characterisation – The Use of GPC

By 4th November 2019Failure Analysis
molecular weight

One of the key characteristics of the polymers which eventually define the overall performance and end use is their molecular weight and molecular architecture. Effective molecular weight characterisation helps in the development of more efficient and advanced polymers, and at the same time can support quality control of the material before entering the market. The most important and accurate method for the characterisation of a polymer is the gel permeation chromatography (GPC) or size exclusion chromatography (SEC) with selected detectors.


What is Gel Permeation Chromatography?

Gel permeation chromatography (GPC) is a powerful analytical technique which enables the full characterisation of the molecular weight distribution of a polymer material. The basic principle of the GPC is the size categorisation of the polymeric molecules which are dissolved in an appropriate solvent.

During GPC analysis, the dissolved polymer is injected into a column with continually flowing stream of solvent.  As the test material passes through the column, it flows through millions of highly porous particles, which are packed together in a column. The particles vary in size depending on the tested polymer. GPC analysis is also included in international standards such as ISO 13885-1 or ISO 13885-2, ASTM D6474, ASTM D5296, ASTM D6579 etc.

GPC is widely used in the polymer manufacturing quality control, batch-to-batch variations, failure analysis and in the research and development. Impact Solutions is equipped with a state-of-the-art high temperature GPC machine from Agilent able to carry out molecular weight analysis on most polymers or plastic materials.

Recent applications include:-

  1. Assessment of polymer degradation – A polymer suspected of heavy degradation after ageing was compared to the original un-aged material.  The molecular weight distributions are compared in the accompanying figure and show extreme reduction in molecular weight.Screenshot 2020-01-17 at 10.07.02

  2. Application as part of a large a large-scale failure analysis project on polycarbonate (PC) parts, which were failing while in service. The failures occurred due a “bad” batch production and due to the lack of quality control processes. Although the problem in the production line was fixed, the identification of the “bad” batch in order to remove from the market would have been an impossible task without the GPC. Molecular weight tests have been carried out on products collected from around the world and compared with the reference data (Figure below). As a result, the faulty parts have been identified and removed from service in time and with the most efficient way.


molecular weight 2

Molecular weight distribution of various PC parts.

At Impact Solutions, as material experts, we are committed to providing the industry with testing, consulting and supporting solutions. We are known for the quality of our service combined with an impressive turn around the record. It is the combination of the advanced facilities and the high expertise of our technology team which makes us the number one choice for testing from the biggest “players” in the plastic/polymer industry in both product development and failure analysis of plastics.

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