Strain-induced crystallization in rubber: A new measurement technique

The crystallinity of stretched crystallizable rubbers is classically investigated using X-ray diffraction. In this study, we propose a new method based on temperature measurement and quantitative calorimetry to determine rubber crystallinity during mechanical tests. For that purpose, heat power density are first determined from temperature variation measurements and the heat diffusion equation. The increase in temperature due to strain-induced crystallization is then deduced from the heat power density by subtracting the part due to elastic couplings. The heat capacity, the density, and the enthalpy of fusion are finally used to calculate the crystallinity from the temperature variations due to strain-induced crystallization. The characterization of the stress-strain relationship and the non-entropic contributions to rubber elasticity is not required. This alternative crystallinity measurement method is therefore a user-friendly measurement technique, which is well adapted in most of the mechanical tests carried out with conventional testing machines. It opens numerous perspectives in terms of high speed and full crystallinity field measurements.