Simultaneous Measurement of Polymerization Shrinkage and Elastic Modulus Development

Objective:  Polymer-based materials can exhibit shrinkage of monomers during the polymerization process. The development of polymerization shrinkage (or polymerization kinetics) is an important parameter for processing and developing polymer-based products.  In addition, elastic modulus development during network reaction is a key measure of polymerization completion level and the materials’ ability to transfer stress to their surrounding constraints.  The objective of the study is to expand the capability of a cantilever beam-based instrument, such that the polymerization shrinkage kinetics and stress, as well as the elastic modulus development, can be simultaneously obtained in real time.

Method:  Using the tensometer, composite (or resin) specimens are mechanically attached to a cantilever beam via a quartz rod adhesively in contact with the specimen, and the specimen is also adhesively attached to a fixed lower rod. Upon polymerization, the composite shrinkage stress induces a deflection in a calibrated cantilever beam, and the beam deflection is measured using a linear variable differential transformer. The polymerization stress is calculated through a beam formula according to the measured deflection. The proposed approach is to conduct two independent tensometer experiments using samples of the same size but at different locations on the cantilever beam.  The resulting two sets of polymerization stress data obtained will be used to deduce the rate of shrinkage and modulus development.

Results:  Our results show rates of polymerization shrinkage and modulus development, which previously have to be obtained in separate experiments, are simultaneously obtained using the same instrument for the stress measurement.

Conclusion: We have identified elegant and simple procedures to simultaneously measure key polymerization properties. The proposed concept can also be applied to measure thermal and swelling expansion of polymeric and non-polymeric materials.

Acknowledgements: Interagency Agreement between the National Institute of Dental and Craniofacial Research and the National Institute of Standards and Technology [Y1-DE-7005-01].