# Thermochemical upcycling of paper-mill waste into hydrocarbon-rich fuels and functional char for rubber reinforcement

## TL;DR

This study shows how paper-mill waste can be converted into valuable fuels and materials for rubber reinforcement through thermochemical processes.

## Contribution

The novel contribution is the use of co-pyrolysis to transform paper-mill waste into hydrocarbon-rich fuels and functional char suitable for rubber composites.

## Key findings

- Co-pyrolysis of paper-mill waste at 650°C yielded 48 wt% pyrolysis oil and 20 wt% char.
- Pyrolysis oil has a calorific value of 39–43 MJ kg−1, comparable to diesel, and contains hydrocarbons like toluene and xylene.
- Char from pyrolysis can reinforce rubber with acceptable mechanical properties and faster vulcanization.

## Abstract

This study investigates the thermochemical upcycling of paper-mill waste composed of mixed paper and residual plastics into high-value fuels and functional char for composite applications. Co-pyrolysis was conducted in a semi-pilot-scale rotary kiln reactor at 450–650 °C, producing maximal pyrolysis oil yields of 48 wt% and 20 wt% char at 650 °C. The pyrolysis oil was separated into heavy and light fractions, with calorific values of 39–43 MJ kg−1, demonstrating strong fuel potential comparable to that of petroleum diesel. GC-MS analysis revealed the presence of hydrocarbons, alcohols, and aromatic compounds, including toluene, styrene, and xylene, indicating synergistic degradation of cellulosic fibres and polyolefin plastics. Furthermore, vacuum distillation improved oil quality by enriching the C6–C18 hydrocarbon fractions and reducing the oxygenated species. The char exhibited a high carbon content (71.20%), a moderate ash content (30.30%), and an energy value of 16.5 MJ kg−1, along with a porous morphology and mineral traces, enabling its use as a composite filler and secondary fuel material. Rubber compounding trials using SBR-1502 demonstrated that replacing carbon black with pyrolytic char yielded acceptable performance: hardness (58 Shore A) and tensile strength (18 kg cm−2) were lower than the standard carbon-black compound (63–64 Shore A; 123 kg cm−2), yet significantly higher than the filler-free control. Notably, char-reinforced rubber displayed similar elongation (322%) and a reduced curing time (Tc90 = 9.1 min), highlighting faster vulcanisation due to catalytic ash components. These results confirm the potential of paper-mill waste pyrolysis for sustainable fuel production and the recovery of circular-economy materials.

This study investigates the thermochemical upcycling of paper-mill waste composed of mixed paper and residual plastics into high-value fuels and functional char for composite applications.