ECF/TCF

ECF

(Elemental Chlorine Free) when a paper is declared as ECF, the paper concerned is bleached by using chlorine dioxide instead of using the environmentally less acceptable
chlorine gas method of bleaching.
 
TCF

(Totally Chlorine Free) when paper is declared as TCF, the paper concerned is bleached by using hydrogen peroxide instead of chlorine.
This is the most environmentally acceptable method of bleaching.