Reutilization of polyurethane-based shoe sole scrap as a reinforcing filler in natural rubber for the development of high-performance composites

Abstract

Reutilization of industrial waste is one of the emerging strategies to combat solid waste disposal for the protection of our environment. The present work describes a novel and economic approach to reutilize finely ground shoe sole scrap, a thermoset polyurethane-based waste (PUW) material generated during shoe sole production in footwear industries as an efficient reinforcing filler in natural rubber (NR). Shoe sole scrap was ground to fine powder and characterized by various analytical techniques. NR-PUW composites were prepared using 0–20 phr (parts per hundred of rubber) of PUW. The cure characteristics, mechanical, thermal, and morphological properties of prepared composites were studied. Composite with 5 phr PUW showed a remarkable improvement in tensile strength by 10% and modulus at 300% elongation increased by 9% compared to that of neat sample. A considerable increase in abrasion resistance and tear strength was also observed in 5 phr PUW loaded composites. Other mechanical properties like hardness, heat build-up and compression set showed a regular increase with further filler loading. To estimate the level of interfacial adhesion between the filler and the matrix, the experimental values of tensile strength were compared with Nicolais–Narkis (N–N), Lu, and Turcsányi–Pukànszky–Tüdõs (T–P–T) models and elastic modulus values with Einstein and Guth and Smallwood models. The tensile strength values are in agreement with T-P-T model (B = 4), up to 5 phr PUW proving the better adhesion between NR and PUW at lower filler loadings. At higher PUW loading, the experimental results are approaching Lu and N–N models indicating that this adhesion is collapsed. The incorporation of PUW as a filler in NR does not adversely impact the thermal stability of prepared composites. The results obtained are not only promising from a circular economy perspective, but also is contributive in production of high-performance, low-cost NR composites for various industrial applications.

Evaluation of composites based on virgin rubber/devulcanized rubber reinforced with chemically and radiation activated polyurethane scrap for possible applications

“…The XRD curve for WPU is primarily characterized by a diffraction peak at around 20°, which indicates that the structure is semicrystalline, 22 the others peaks at 2 θ of 29°, 35.4°, 38.9°, 42.9°, 47°, 48°, 57.4°, and 65° indication the CaCO 3 powder that filled WPU is crystalline 5 . The acrylate polyfunctional monomer and gamma radiation treatment of the WPU resulted in a decrease in peak intensity, indicating increased crystallinity and the interaction of the WPU with TMPTMA.…”

“…The free NH stretching band is observed at $3420 cm À1 for PU and is also related to the hydroxyl of CaCO 3 , which may be used as a filler for PU. 5,16 ( CH 2 ) stretching peaks at 2920 cm À1 , while ( CH 3 ) stretching peaks at 2850 cm À1 . 5 The band at 2513 cm À1 for calcite.…”

“…5,16 ( CH 2 ) stretching peaks at 2920 cm À1 , while ( CH 3 ) stretching peaks at 2850 cm À1 . 5 The band at 2513 cm À1 for calcite. 16,17 The unreacted isocyanate groups in the PU may be the cause of the band at 2335 cm À1 .…”

“…It involves converting solid waste into flakes, granules, or powder. Bashpa et al 5 used WPU with size of 50–100 μm, to reinforce NR for producing a low cost composite. Various percentages of WPU (2.5, 5, 10, 20 phr) of WPU were used, where it was found that, the highest tensile strength, hardness, tear strength, and the lowest abrasion loss were obtained at 5 phr of WPU.…”

Recycling waste polyurethane from the refrigeration industry as filler in SBR/NR composites for industrial applications

“…Currently, polyurethane waste has been used as additives for prefabricated mortar panels, 24 to sorption of oils, 25,26 as filler in gypsum matrix 27 or geopolymers 28 decreasing in thermal conductivity and into natural rubber (NR) matrix. 29 Natural rubber has outstanding qualities (e.g., tensile strength, tear resistance, and good abrasion resistance) to produce tires, conveyor belts, fluid transfer systems, body sealing, car suspension, seals, adhesives, coatings, and body parts. 30 Deformation-induced crystallization in NR improves its mechanical properties, especially when wide strain amplitudes are used.…”