One of the most evident synergic pyrolysis behaviours has been demonstrated by Brebu et al. [16]. By co-feeding pine cones with waste polyolefin, they showed that it was possible to significantly decrease the overall char yield and increase the amount of volatile produced. For binary blends of pine cones and polyethylene (PE), polypropylene (PP) or polystyrene (PS), the char yield decreased (by over 6 % units for PE) compared to the calculated value by linear combination, hence revealing synergic behaviour. When a blend of pine cones and the three polymers (PE/PP/PS) was pyrolyzed in the ratio 3:4:2:1, the synergy was even more significant. The reported char yield was lower than the average calculated value by 10 % units and the liquid product yield increased by over 11 % units. However, while these types of synergies are desired, they have been rarely observed. One typical example is the co­pyrolysis of biomass with coal. Weiland et al. [46] explored the possible synergetic interactions between coal and biomass in pyrolysis. Unfortunately, the interaction was almost nonexistent. Linear combination explained most of the variations with the various blends of coal/biomass.