Mass balance closure with and without catalyst The effect of different kinds of plastics in the initial feedstock on the two-stage reaction system with and without catalyst is discussed in this section. The selected plastics were PP, HDPE, PS and a mixture of real world plastics (RP). In all the experiments to study this influence, a biomass/plastic ratio of 80/20 was used. Table 3, shows that in the uncatalyzed reaction, gas yield was the highest at 18.6 wt.% when HDPE was used as the copyrolysis raw material, which is probably because the aliphatic molecular structure allows the production of lighterinter mediate radicals