Meaning
Analytical measurement records the resistance and reactance of a material across a range of alternating current frequencies. Generating an electrical impedance spectrum for a polymer allows researchers to characterize its dielectric properties, which are sensitive to moisture content and the presence of fillers. This technique is often used to monitor the curing of thermosets or the degradation of thermoplastics during heat ageing.
Frequency Response
Variations in the electrical signal occur as the dipoles in the polymer chains attempt to align with the oscillating field. At low frequencies, the electrical impedance spectrum reveals information about ion mobility and interfacial polarization at the boundaries between the resin and additives. Higher frequencies probe the rotational movement of the polymer segments themselves.
Material Condition
Monitoring the moisture absorption in hygroscopic resins like nylon is a common application for this data. As the water content increases, the electrical impedance spectrum shifts, allowing for a non-destructive check of the material before it enters the injection moulder. This prevents defects like splaying or internal voiding caused by steam during the melting phase.
Laboratory testing uses this method to ensure that different batches of resin have consistent electrical signatures.
Process Characterization
Measurements taken during the moulding cycle can provide real-time feedback on the state of the polymer melt.
