Effects of molecular weight of hydroxyl telechelic natural rubber on novel cationic waterborne polyurethane: A new approach to water-based adhesives for leather applications

Renewable resource based cationic waterborne polyurethanes (cWPUs) have been prepared from hydroxyl telechelic natural rubber (HTNR) with a range of number average molecular weights (Mn) (2820, 1800, and 950 g mol−1), toluene-2,4-diisocyanate (TDI), N-methyl diethanolamine (NMDEA), and ethylene glycol (EG). The chemical structure of the cWPUs was confirmed by FT-IR and 1H NMR. Particle size and zeta potential of prepared cWPUs were also characterized by ZS nanosizer. By varying the levels of Mn of HTNR, the obtained cWPUs were stable with a milky blue appearance, forming yellowish films. The smallest particle sizes of 76.4 nm were achieved using Mn of HTNR of 2820 g mol−1 while zeta potential value ranges from 67 to 71 mV were observed with increasing Mn of HTNR. Lap shear testing of these WPUs indicates their potential in real cow leather adhesive applications, with the best adhesive result coming from cWPU based on an HTNR molecular weight of 1800 g mol−1. The results show the potential of natural rubber as a green adhesive material in suitable aqueous environments.