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Recycling flexible polyurethane foam (F-PUF) scraps is difficult due to the material's high cross-linking structure. In this work, a wedge-block-reinforced extruder with a considerable enhanced shear extrusion and stretching area between the rotating screw and the stationary wedge blocks was utilized to recycle F-PUF scraps into powder containing surface-active hydroxyl groups. The powder was then utilized for the quantitative replacement of polyol in the foaming process. Characterizations showed that the continuous shear extrusion and stretching during the extrusion process reduced the volume mean diameter (VMD) of the F-PUF powder obtained by extruding it three times at room temperature to reach 54 μm. The -OH number (OHN) of the powder prepared by extruding it three times reached 19.51 mgKOH/g due to the mechanochemical effect of the powdering method. The F-PUF containing recycled powder used to quantitively replace 10 wt.% polyol was similar in microstructure and chemical structure to the original F-PUF, with a compression set of 2%, indentation load deflection of 21.3 lbf, resilience of 43.4%, air permeability of 815.7 L/m 2 ·s, tensile strength of 73.0 Kpa, and tear strength of 2.3 N/cm, indicating that the recycling method has potential for industrial applications.

Low-temperature mechanical chemical devulcanization is a process that can produce reclaimed rubber with exceptional mechanical properties. However, the inadequacy and low efficiency of the devulcanization have significantly restricted its application. To address the issues, alcoholic amines, including hydroxyethyl ethylenediamine (AEEA), ethanolamine (ETA), and diethanol amine (DEA), are utilized as devulcanizing agents to promote the devulcanization process. Careful characterizations are conducted to reveal the devulcanizing mechanism and to depict the performances of reclaimed rubbers. Results show that the amine groups in the devulcanizing agents can react with sulfur after the crosslink bonds are broken by mechanical shear force, thus blocking the activity of sulfur and introducing hydroxyl groups into the rubber chains. The incorporation of alcoholic amines can enhance the devulcanizing degree and devulcanizing efficiency, reduce the Mooney viscosity, and improve the mechanical and anti-aging performance. When using DEA as the devulcanizing agent, the sol content of reclaimed rubber increases from 13.1% to 22.4%, the devulcanization ratio increases from 82.1% to 89.0%, the Mooney viscosity decreases from 135.5 to 83.6, the tensile strength improves from 14.7 MPa to 16.3 MPa, the retention rate of tensile strength raises from 55.2% to 82.6% after aging for 72 h, while the devulcanization time is shortened from 21 min to 9.5 min, compared with that without using alcoholic amines. Therefore, alcoholic amines exhibit remarkable advantages in the devulcanization of waste rubber, thus indicating a promising direction for the advancement of research in the area of waste rubber reclamation.

Carbon nanotube (CNT), as reinforcing agents in natural rubber (NR), has gained a large amount of consideration due to their excellent properties. Uniform dispersion of CNT is the key to obtaining high-performance NR nanocomposites. In this contribution, a novel ultrasonic grinding dispersion method of CNT with waterjet-produced rubber powder (WPRP) as a carrier is proposed. Microscopic morphologies show that a Xanthium-like structure with WPRP as the core and CNTs as the spikes is formed, which significantly improves the dispersion of CNT in the NR matrix and simultaneously strengthens the bonding of the WPRP and NR matrix. With the increase in the WPRP loading, the Payne effect of CNT/WPRP/NR composites decreases, indicating the effectiveness of the dispersion method. The vulcanization MH and ML value and crosslinking density increase with the increase in the WPRP loading, whereas the scorch time and cure time exhibit a decreasing trend when the WPRP loading is less than 15 phr. It is found that the CNT/WPRP/NR composites filled with 5 phr WPRP have a 4% increase in 300% modulus, a 3% increase in tensile strength, while a 5% decrease in Akron abrasion loss, compared to CNT/NR composites.