The fusion bonding of neat polypropylene (PP) has been investigated under non-isothermal conditions with different initial adherend temperatures, and the results compared with results from bonds prepared under isothermal conditions with identical adherend temperatures. The mode I critical strain energy release rate of the bonds, Gc, was measured using a double cantilever beam geometry with a constant crack opening displacement. The effect of the adherend temperature and the hold time are summarized in time-temperature and fracture energy-temperature maps, a methodology that is easily applicable to other systems. Of immediate practical interest is the observation that for estimated interface temperatures just above the melting point, non-isothermal bonding gave bonds with Gc approaching that of the bulk resin after much shorter times than isothermal bonding.