Re: identifying plastics

    jorge my old friend!
the polyolefin family has three main subgroups..... PE,PP,PMP.
       methylpentene (rare but cool properties)
the nice thing about these is that the specific gravity is .9 to .95 or so
which makes the old "float" test the first to try. only these three float
of all of the (non foamed) thermoplastics
ther are many PE Mol. wts. lldpe,ldpe,mdpe,hdpe,vhmw,uhmw
in general as the mol. wt. goes up so do the physical properties.
(and to a certain degree the electrical)
if it sinks,then time use the "burn" test. burn carefully(!!!!!!!!!) smell some
of the fumes....... 
PE is a translucent white/clear
PP   same or slightly yellowish tint
avoid colors especially black as many times this is done with carbon.
natural white is the best 
let me know and i can give you some more tests that can be done in the
kitchen to ID almost  any plastics and even  a fair number of plastic alloys
oregon city