Meaning
Analytical technique used to separate a polymer into its soluble and insoluble fractions based on its molecular structure. Xylene crystallization is a standard method for measuring the isotactic content of polypropylene. The process involves dissolving the resin in hot xylene and then cooling it to allow the crystalline portion to precipitate.
Fractionation Method
Portion of the polymer that remains in the liquid at room temperature is known as the xylene soluble fraction. This soluble part represents the amorphous or less-ordered chains in the material. Xylene crystallization provides a clear picture of the tacticity and the distribution of the polymer chains.
Mechanical Correlation
Higher percentage of insoluble material usually correlates with greater stiffness and higher melting points. Moulders use the results of xylene crystallization to predict how a resin will behave in the press. If the soluble fraction is too high, the part may be too flexible or have poor impact resistance.
Quality Control
Testing for xylene solubles is a routine part of checking the consistency of a resin supply. Xylene crystallization helps identify shifts in the reactor conditions at the polymer plant. Maintaining a stable fraction is essential for ensuring that the shrinkage and warpage of the moulded parts remain constant.
This laboratory test is a fundamental tool for material qualification.
