Optical spectra and images in the main optical emission lines were obtained for 21 type I planetary nebulae (PNe). IR images directed towards the detection of shocked molecular hydrogen were secured in 17 of these objects. No evidence of shocked H2 could be found in A 14 and Sh 2-71, and its existence needs to be confirmed in JnEr 1 and M 1-57. Bipolarity is obvious in most of these sources. A 24, JnEr 1 and M 3-5 may be bipolars seen nearly pole-on. The chemical composition of nearly half of these objects indicates that third dredge-up episodes may have occured in their progenitor star. The presence of shock waves in the ionized component is inferred in 9 PNe, where the temperature ratio T(O+2)/T(N+) is large and the Hα/[S II]6724 line ratio small, a typical combination in shock excited plasmas. A larger sample of type I PNe shows that small Hα/[S II]6724 line ratios are usually associated with large temperature ratios.