Just burn a small piece of it on a bit of tin foil. Snuff out the flames after it has burned a bit. Cellulosic fibers, like Jute, Hemp, Cootn and linen will leave behind only a papery ash and soft charcoal.  Rayon burns similarly, but smells like vinegar.  Synthetic fibers tend to leave behind a hard black plasticy residue.  Wool and silk leave behind a hard cinder like residue that can be easily crushed between the fingers, These usually smell like burning hair.
I would be more worried about pesticide residues in the Burlap than synthetic fibers. Pesticide residues can wipe out a whole hive, from what  I hear.
Syntheic baggig is usually easily identified as such- it has the texture of a blue tarp.
I have not encountered blended fiber contents in sacking.
Ellen
 Milt Lathan <[log in to unmask]> wrote:Didn't I see a test here for determining whether burlap has plastic in it?
A coffee processor just moved into my neighborhood and they just throw them
away.


---------------------------------
Do you Yahoo!?
Yahoo! Mail Plus - Powerful. Affordable. Sign up now