Lambient Technologies studied room temperature cures of a polyurethane
resin with three different catalysts. An LT-451 Dielectric Cure Monitor made
measurements during each test at excitation frequencies from 0.1 Hz to 100 kHz
for 24 to 36 hours.
How to use the start triggers and digital outputs.
The Lambient Technologies LT-451 Dielectric Cure Monitor is designed for dielectric
measurements of polymeric materials during the curing process, and a typical LCR
(Inductance-Capacitance-Resistance) meter, such as the QuadTech 1920, is designed for
high speed measurements of the electrical parameters of electronic components.
Lambient Technologies tested samples of a commercially available two-part acrylic
structural adhesive with the LT-451 Dielectric Cure Monitor.
Lambient Technologies tested the base gel for a nail polish system that
requires near-ultraviolet light to cure.
Lambient Technologies conducted several tests to measure noise with a
Mini-Varicon sensor when used with the LT-451 Dielectric Cure Monitor, and
demonstrated that electrical interference may be reduced effectively with
grounded shields around the sensor.
This application note will examine the effect of a textured sample surface similar to that
of a fabric. The resulting measurement of permittivity is less than the true permittivity
of the material and results from the contribution of air pockets created by the textured surface.
This application note will model the effect of these air pockets to develop an understanding of the measurement error.
CureView has an option to facilitate ASTM D150
standard measurements with the LT-4203 Parallel Plate Test Fixture. This option allows the user to
calibrate the LT-4203 for accurate measurements, make multiple measurements with calculation of
average and standard deviation, and automatically calculate dielectric constant and dissipation
for the contacting electrode method of measurement.
Raw gain-phase data measured by CureView and the LT-451 or LTF-631 Dielectric Cure Monitors is
converted to the dielectric properties of permittivity (ε') and loss factor (ε"). Loss factor, however, has two components...
Dielectric sensors connect directly to the instrument with a three-terminal Dielectric Sensor
Connector or with an extension cable. To reduce noise in the response signal, the signal leads from
the sensor should be shielded.
Clean sensors with acetone, alcohol or other solvent to remove oils and
contaminants. Solvent or water adsorbed onto the surface of the sensor normally
will not interfere with cure monitoring because it is released at elevated
temperatures and would not be present at typical process temperatures.
Occasionally it may be necessary for a user to test either the LT-451 Dielectric Cure Monitor
or the LTF-631 High Speed Dielectric Cure Monitor for proper operation. It is important to investigate
the various parts of the system to establish that a component is working as expected, or to determine
that a component is faulty.
Large composite structures such as an airplane wing are processed in
autoclaves or molds that apply pressure to form the part until it has cured. The
need to maximize use of this equipment may require cycling material through it
as quickly as possible, and often a part is removed as soon as it has hardened
enough to retain its shape. Afterwards, it may undergo post-cure in an oven for
several hours to several days. During this time cure continues at elevated
temperature until the composite material has hardened further or achieved other
Samples from a single batch of carbon fiber reinforced prepreg (CFRP)
were tested for repeatability and effect of temperature on cure rate. The data
from dielectric cure monitoring clearly show that:
(1) Critical Points identify characteristic features of the cure such as minimum ion viscosity, maximum slope of log(ion viscosity) and the time to a chosen end of cure and,
(2) Cure time decreases as cure temperature increases, as expected for a reaction that is thermally driven.
The curing behavior of Sheet Molding Compound (SMC) was observed
using the LT-451 Dielectric Cure Monitor. Bulk Molding Compound (BMC) is the
generally the same material as SMC but in bulk form, so the analysis of results
apply to BMC as well.