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We study the chemical abundances of a wide sample of 142 Galactic planetarynebulae (PNe) with good quality observations, for which the abundances havebeen derived more or less homogeneously, thus allowing a reasonable comparisonwith stellar models. The goal is the determination of mass, chemicalcomposition and formation epoch of their progenitors, through comparison of thedata with results from AGB evolution. The dust properties of PNe, whenavailable, were also used to further support our interpretation.  We find that the majority ($\sim60\%$) of the Galactic PNe studied has nearlysolar chemical composition, while $\sim40\%$ of the sources investigated havesub-solar metallicities. About half of the PNe have carbon star progenitors, inthe $1.5~M_{\odot} < M < 3~M_{\odot}$ mass range, which have formed between 300Myr and 2 Gyr ago. The remaining PNe are almost equally distributed among PNeenriched in nitrogen, which we interpret as the progeny of $M > 3.5~M_{\odot}$stars, younger than 250 Myr, and a group of oxygen-rich PNe, descending fromold ($> 2$ Gyr) low-mass ($M < 1.5~M_{\odot}$) stars that never became C-stars.  This analysis confirms the existence of an upper limit to the amount ofcarbon which can be accumulated at the surface of carbon stars, probably due tothe acceleration of mass loss in the late AGB phases. The chemical compositionof the present sample suggests that in massive AGB stars of solar (or slightlysub-solar) metallicity, the effects of third dredge up combine with hot bottomburning, resulting in nitrogen-rich - but not severely carbon depleted -gaseous material to be ejected.

The evolution of Galactic planetary nebula progenitors through the comparison of their nebular abundances with AGB yields