Heterogeneities in polybutadiene network structures formed during high pressure and peroxide vulcanisation

High Pressure Vulcanisation (HPV) is referred to as crosslinking of rubber materials merely by treatment at high temperature and elevated pressure, th us without any vulcanisation agents. The reaction mechanisms in crosslinkin g of polybutadiene by HPV have been penetrated and compared with the crossl inking at different pressures when peroxide is present. The effect of press ure on the reactions has been investigated in terms of molecular mobility, and the heterogeneity of the network has been examined. It was found that t he two vulcanisation processes are very similar and that they both proceed mainly by addition to vinyl unsaturations. They are, however, different wit h regard to the initiation step, and this is shown to lead to a more homoge neous network in the purely HPV-crosslinked polybutadienes. The crosslinkin g efficiency of peroxide vulcanisation at 170 degrees C was calculated to v ary between 8 and 12 as the pressure increased from 26 to 293 MPa which is the pressure range that has been investigated.