GPC/SEC Analysis of Polymer Branching

Abstract

In this application note, four PVC samples of known differences in glossiness were measured with both multi-detector GPC and rotational rheometry. The results both explain the differences in glossiness and the likely cause of those differences.

Introduction

Polyvinyl chloride (PVC) is a common polymer used in countless applications from pipes, to flooring, and electrical insulation. As one of the world’s most widely produced polymers, it is very much a commodity polymer where tight margins mean little room for detailed analysis. However, even in this case, high level analytical tools can be used to characterize the polymer for appropriate grading. For example, the glossiness of a PVC sample has a significant effect on its finish and grade, and for which applications it can be used. Applying appropriate characterization tools can help grade different PVC batches, assigning them to appropriate applications to maximize the value of high quality batches, saving lower grades for others.

Gel-permeation chromatography (GPC) and rotational rheology are two common and highly complementary tools used in polymer characterization. GPC is primarily used to measure the molecular weight and molecular weight distribution of polymers. Historically, GPC generated a ‘relative’ molecular weight against calibration standards such as polystyrene, however light scattering detectors enable the measurement of absolute molecular weight. The addition of a viscometer further enables analysis of structural aspects such as branching and cross-linking to be performed. As a molecular characterization tool, GPC can be used to predict the properties of polymeric materials. It can therefore be used as a quality control tool to predict product performance prior to spending time and energy on manufacturing. Rotational rheometry is a bulk characterization tool for measuring the viscoelastic properties of polymers and polymeric formulations. A benefit of rotational rheometry is that it can simulate ‘real-world’ situations to indicate how finished products and complex formulations might behave after manufacturing. In this application note, four PVC samples of known differences in glossiness were measured with both multi-detector GPC and rotational rheometry. The results both explain the differences in glossiness and the likely cause of those differences.

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