Calibration of cyclohexane solid–solid phase transition thermoporosimetry and application to the study of crosslinking of elastomers upon aging

Abstract Photo-aging of elastomers results in two competitive processes: chain- scissions and crosslinking. The solid-to-solid cyclohexane phase transition was used to investigate the crosslinking extent in photo-oxidised ethylene propylene diene monomer (EPDM) samples by thermoporosimetry technique. Before apply this technique to EPDM, texturally well-known silica gel samples were used to calibrate the method. By contrast to the case of liquid-to-solid heptane transition, no linear relationship was obtained between the solid-to-solid point depression (ΔT) and the pore radius (Rp). The following correlation was obtained: R p ( A )=16.93+125.43 exp − 1/ Δ T+0.0756 0.0205 with 0> Δ T>−55 ° C . Pore size distributions (PSD), calculated by thermoporosimetry using the solid-to-solid transition, were in a good agreement with those obtained by gas sorption method (BJH). Elastomeric gels were assumed to be similar to a porous medium where the pore notion is replaced by the mesh notion. Using the same relations which were used to calculate the PSD, the mesh size distributions (MSD) were calculated for various EPDM samples crosslinked under irradiation. The width and the maximum of these MSD are related to the extent of crosslinking.