Detection of cross-linking in pre-cure stage polymeric materials by measuring their resistance

A method of monitoring extent of cross-linking of polymer in a B-staged material, comprising the steps of:

• a) selecting a B-staged material which has an uncertain extent of cross-linking or an unknown state of curing;
• and
• b) placing an insulated ground plane adjacent to the B-staged material in the pre-cure stage, substantially parallel to a sensor;
• c) applying a test signal through a sensor to the B-staged material in the pre-cure stage to determine a level of resistance and corresponding sample voltage representative of a degree of cross-linking within the material by shunting a reactive component of impedance of the ground plane;
• d) applying the test signal through the sensor to a reference resistance having a fixed resistance to determine a reference voltage;
• e) determining a voltage difference as the difference between the sample voltage and the reference voltage;
• f) correlating the voltage difference as a relative indicator of the extent of cross-linking which has occurred within the B-staged material, based on comparison of magnitude of the voltage difference with respect to a comparable potential range of resistance for the B-staged material from a low impedance stage at minimal cross-linking of the B-staged material to a high impedance stage at maximum impedance for total cross-linking of the B-staged material.

A device for testing extent of cross-linking of a polymer material in a pre-cure stage, said device comprising:

• a signal generator capable of generating a low frequency, low amplitude signal;
• a sensor coupled to the signal generator and adapted for receiving a coating of the pre-cure polymer material to be tested, said sensor having a known impedance;
• a ground plane parallel to the sensor but insulated from it by an insulating substrate;
• a reference resistance which has a resistivity approximately equal to the geometric mean of (i) the resistance of the sensor with polymer material in its lower-resistivity state, and (ii) the expected resistance of the polymer material when the polymer material has reached a high resistivity state upon full curing;
• voltage means for determining voltage difference between a signal detected through the sensor with polymer material in a pre-cure stage and a reference signal detected through the reference resistance by the voltage means;
• and
• converting means coupled to the voltage means for converting the voltage difference to a factor representing the extent of cross-linking which has occurred within the polymer material.

A method for monitoring extent of cross linking of polymer material, comprising the steps of:

• a) identifying polymer material in pre-cure stage;
• b) attaching a sensor in contact with the identified polymer as part of the material, which sensor enables intermittent or continuous reading of cure state of the polymer;
• c) placing an insulated ground plane adjacent to the polymer material and substantially parallel to the sensor;
• d) applying a test signal through the sensor to the polymer material in the pre-cure stage to determine a level of resistance and corresponding sample voltage representative of a degree of cross-linking within the material by shunting a reactive component of impedance to the ground plane;
• e) applying the same test signal through the sensor to a reference material having a fixed resistance to determine a reference voltage;
• f) determining a voltage difference between the test signal applied to the polymer at pre-cure stage and the test signal applied to the reference material as the reference voltage;
• g) correlating the voltage difference as a relative indicator of the extent of cross-linking which has occurred within the polymer material, based on comparison of magnitude of the voltage difference with respect to a comparable potential range of resistance for the polymer material from its lower impedance stage at minimal cross-linking to its high impedance stage at maximum impedance for total cross-linking;
• and
• h) maintaining the sensor in contact with the polymer throughout the pre-cure stage of the polymer as a means for determining extent of cure of the material to which the sensor is attached.

A method for monitoring extent of cross linking of polymer material, comprising the steps of:

• a) identifying a batch of polymer material in pre-cure stage;
• b) separating a sample of the polymer material from the batch;
• c) attaching a sensor in contact with the sample of the identified polymer material, which sensor enables intermittent or continuous reading of cure state of the polymer;
• d) placing an insulated ground plane adjacent to the polymer material and substantially parallel to the sensor;
• e) applying a test signal through the sensor to the polymer material in the pre-cure stage to determine a level of resistance and corresponding sample voltage representative of a degree of cross-linking within the material by shunting a reactive component of impedance to the ground plane;
• f) applying the same test signal through the sensor to a reference material having a fixed resistance to determine a reference voltage;
• g) determining a voltage difference between the test signal applied to the polymer at pre-cure stage and the test signal applied to the reference material as the reference voltage;
• h) correlating the voltage difference as a relative indicator of the extent of cross-linking which has occurred within the polymer material, based on comparison of magnitude of the voltage difference with respect to a comparable potential range of resistance for the polymer material from its lower impedance stage at minimal cross-linking to its high impedance stage at maximum impedance for total cross-linking;
• and
• i) maintaining the sensor and attached sample in contact with the batch of polymer material throughout the pre-cure stage of the polymer as a means for determining extent of cure of the material to which the sensor and sample are attached.