Thermosetting resins measurement techniques

The glass transition temperatures, specific for each thermosetting resin, are used to characterize cure kinetics. They can be measured by many techniques, of which the widely used are Differential Scanning Calorimetry (DSC) and Torsional Braid Analysis (TBA)... 

Differential Scanning Calorimetry (DSC) This is by far the widest utilized technique to obtain the degree and reaction rate of cure as well as the specific heat of thermosetting resins. It is based on the measurement of the differential voltage (converted into heat flow) necessary to obtain the thermal equilibrium between a sample (resin) and an inert reference, both placed into a calorimeter [143,144], As a result, a thermogram, as shown in Figure 2.7, is obtained [145]. In this curve, the area under the whole curve represents the total heat of reaction, AHR, and the shadowed area represents the enthalpy at a specific time. From Equations 2.5 and 2.6, the degree and rate of cure can be calculated. The DSC can operate under isothermal or non-isothermal conditions [146]. In the former mode, two different methods can be used [1] ... 

Testing procedures in the measurement of the chemorheology of thermosetting resins usually incorporate the following techniques ... 

Since the equipment to measure the temperature-induced dimension variation employs an LVDT displacement sensor, the requirement of a solid sample is mandatory. The effects of post-cure reaction on the measurement, instead, need much more detail and discussion. For a partially cured thermosetting resin, a post-cure reaction is expected when the actual temperature rises above the corresponding glass-transition temperature, Tg. Above this temperature, the volume variation due to post-cure reactions is superimposed upon thermal expansion (18). For this reason, TMA is a technique for measuring the CTE of the partially cured sample that is suitable only within the glassy region (T < Tg), while for a fiilly cured sample useful information can also be obtained for the CTE in the rubbery... 

The following experimental procedure can be used to measure the interfacial shear strength by means of the microbond technique for a thermosetting resin matrix. 

Shah, D.U., Schubel, P.J., 2010. Evaluation of cure shrinkage measurement techniques for thermosetting resins. Polymer Testing 29, 629—639. 

Frequency dependent complex impedance measurements made over many decades of frequency provide a sensitive and convenient means for monitoring the cure process in thermosets and thermoplastics [1-4]. They are of particular importance for quality control monitoring of cure in complex resin systems because the measurement of dielectric relaxation is one of only a few instrumental techniques available for studying molecular properties in both the liquid and solid states. Furthermore, It is one of the few experimental techniques available for studying the poljfmerization process of going from a monomeric liquid of varying viscosity to a crosslinked. Insoluble, high temperature solid. 

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