Meaning
International standards for molecular weight determination define the parameters for evaluating polymer chains in solution. The document designated iso 13885-1 describes the test method using tetrahydrofuran as the eluent for gel permeation chromatography. It establishes the baseline conditions for column temperature, flow rates and detector response.
Chromatographic Separation
Separation occurs as the dissolved polymer passes through a column packed with porous gel particles. Large molecules cannot enter the pores and elute quickly, while smaller chains penetrate the gel and take longer to emerge. Following the iso 13885-1 procedure allows analysts to generate a complete molecular weight distribution curve.
This curve indicates the polydispersity of the resin, which is a major factor in melt strength.
Process Prediction
Processors use molecular weight data to predict how a resin will behave under shear in the extruder. A polymer tested under iso 13885-1 that shows a broad distribution will process differently than one with a narrow distribution. High molecular weight fractions improve melt strength, while low molecular weight fractions act as internal lubricants.
Calibration Standard
Accurate results require calibrating the chromatograph with polymer standards of known molecular weight. These standards must be compatible with tetrahydrofuran and cover the entire expected size range. Adherence to the iso 13885-1 guidelines ensures that measurements from different laboratories are directly comparable.
