The testing specimens of all injected polypropylene sample were subjected to heat treatment for 30 min at various temperatures around its melting peak

and then the treated samples were characterized by DSC．It was found that there existed an temperature window at which the resulting melting temperature and crystallinity of the treated sample increased obviously．For heat treated specimens under static conditions the temperature window occured only below the peak melting temperature．For heat treated specimens under vibration in a dynamic mechanical analyzer with definite amplitude and frequency

this temperature window covered the whole melting range．Heat treating the PP sample under vibration in a temperature range of 5℃ above its melting peak．the resulting specimen possessed a maximum melting temperature．