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One of the puzzling findings in the study of the chemical evolution of(post-)AGB stars is why very similar stars (in terms of metallicity, spectraltype, infrared properties, etc...) show a very different photosphericcomposition. We aim at extending the still limited sample of s-process enrichedpost-AGB stars, in order to obtain a statistically large enough sample thatallows us to formulate conclusions concerning the 3rd dredge-up occurrence. Weselected two post-AGB stars on the basis of IR colours indicative of a pasthistory of heavy mass loss: IRAS08281-4850 and IRAS14325-6428. They are coolsources in the locus of the Planetary Nebulae (PNe) in the IRAS colour-colourdiagram. Abundances of both objects were derived for the first time on thebasis of high-quality UVES and EMMI spectra, using a critically compiled linelist with accurate log(gf) values, together with the latest Kurucz modelatmospheres. Both objects have very similar spectroscopically defined effectivetemperatures of 7750-8000K. They are strongly carbon and s-process enriched,with a C/O ratio of 1.9 and 1.6, and an [ls/Fe] of +1.7 and +1.2, for IRAS08281and IRAS14325 resp. Moreover, the spectral energy distributions (SEDs) point toheavy mass-loss during the preceding AGB phase. IRAS08281 and IRAS14325 areprototypical post-AGB objects in the sense that they show strong post 3rddredge-up chemical enrichments. The neutron irradiation has been extremelyefficient, despite the only mild sub-solar metallicity. This is not conformwith the recent chemical models. The existence of very similar post-AGB starswithout any enrichment emphasizes our poor knowledge of the details of the AGBnucleosynthesis and dredge-up phenomena. We call for a very systematic chemicalstudy of all cool sources in the PN region of the IRAS colour-colour diagram.

IRAS08281-4850 and IRAS14325-6428: two A-type post-AGB stars with s-process enrichment