Study of synergistic effects during co-pyrolysis of cellulose and high-density polyethylene at various ratios

The mechanism of synergistic effects occurred during co-pyrolysis of cellulose (CE) and high-density polyethylene (HDPE), mixed at various mass ratios (3:1, 1:1, 1:3 w/w), was studied by thermogravimetric analysis coupled with mass spectrometry (TG-MS) and pyrolysis-gas chromatography coupled with mass spectrometry (Py-GC/MS). The TG analysis showed that the co-pyrolysis process was divided into two-stages: the first stage was the decomposition of CE (at 260 °C-410 °C), and the second stage between 410 °C and 527 °C was mainly the decomposition of HDPE. The experimental mass loss values of the mixtures were greater than the estimated values, which confirmed a synergistic effect in the co-pyrolysis of CE and HDPE. The results of MS and Py-GC/MS indicated that the effects of co-pyrolysis promoted the release of small-molecule volatile (H2O, CO/C2H4, CO2), and the promotion effect was strongest when the ratio was 1:3. Hydrogen transfer from the scission of HDPE could be provided for the decomposition of CE, and the oxygen-containing compounds from CE could promote the chain scission and cracking of HDPE. When the CE/HDPE ratio was less than 1:1, the production of carbohydrate, aldehyde, ketone, and furan groups assigned to CE pyrolysis was suppressed, and the production of alkane and alkene groups was promoted. The decomposition pathways in the co-pyrolysis process of CE and HDPE were proposed.