Recycling waste polyethylene terephthalate (PET) fibers is critical for both environmental and resource protection. However, the PET fiber possesses good chemical stability and high crystallinity, resulting in the conversion of PET. Herein, we developed a strategy of stepwise feeding process to recycle PET fibers and recover the potential monomer by adding it to the glycolysis agent diethylene glycol after it had been warmed up to reaction temperature. The results show a significant increase in the PET fiber conversion (92.5%) and yield of water-soluble products (70.4%) in 90 min as compared to a one-step feeding process of 28 and 14.4%, respectively. These water-soluble products are monomers and dimers which are confirmed by Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, mass spectroscopy, and high-performance liquid chromatography. It is also obviously found that the conversion of PET and yields of fibers are lower than those of bottle flakes and particles. In addition, a 'column shrinkage model' is proposed to describe the glycolysis process of the fibers. The apparent reaction activation energy of fibers was derived as 27.19 kJ/mol, which is somewhat higher than those of PET bottle flakes and particles.

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A major challenge in waste rubber (WR) industry is achieving a high sol fraction and high molecular weight of recycled rubber at the same time. Herein, the WR from the shoe industry was thermo-mechanically ground via the torque rheometer. The effect of grinding temperature and filling rate were systematically investigated. The particle size distribution, structure evolution, and morphology of the recycled rubber were explored by laser particle size analyzer, Fourier transform infrared spectroscopy (FTIR), sol fraction analysis, gel permeation chromatography (GPC), differential scanning calorimeter (DSC), and scanning electron microscope (SEM). The results indicate that the thermo-mechanical method could reduce the particle size of WR. Moreover, the particle size distribution of WR after being ground can be described by Rosin’s equation. The oxidation reaction occurs during thermal-mechanical grinding. With the increase of the grinding temperature and filling rate, the sol fraction of the recycled WR increases. It is also found that a high sol fraction (43.7%) and high molecular weight (35,284 g/mol) of reclaimed rubber could be achieved at 80 °C with a filling rate of 85%. Moreover, the obtained recycled rubber compound with SBR show a similar vulcanization characteristics to pure SBR. Our selective decomposition of waste rubber strategy opens up a new way for upgrading WR in shoe industry.

High-temperature vulcanized silicone rubber (HTV SIR) possesses great chemical resistance and high thermal stability, but these excellent performances also impede its recycling. In this respect, the waste HTV SIR from retired composite insulators with/without the KOH catalyst was ground by solid-state shear milling (S 3 M). The morphology and structure of silicone rubber powder were analyzed, and the pyrolysis behaviors of the obtained silicone rubber powders were revealed by thermogravimetry (TG) and pyrolysis gas-phase/mass spectrometry (Py-GC/MS). The results show that the mechanochemical milling via S 3 M could significantly reduce the particle size of silicone rubber and destroy the cross-linking structure of the waste HTV SIR, thus leading to an obvious improvement in the sol fraction. The maximum weight loss rate temperature of waste HTV SIR with the KOH catalyst assisted by mechanochemical milling was 150 °C lower than those without milling. Moreover, a greatly reduced catalytic pyrolysis duration along with more concentrated pyrolysis products at 400 °C was achieved after grinding three times. At last, the pyrolysis mechanism of the waste HTV SIR assisted by mechanochemical milling is proposed. These obtained results provide a great potential for large-scale recycling of waste silicone rubber with stable structure and complex components.