Mechanical behavior of lightly cross‐linked polyurethanes

Abstract

AbstractStress‐strain and stress‐relaxation behavior, ultimate properties and equilibrium swelling of polyurethane elastomers based on poly (ethylene adipate), poly (ethylene maleate), propylene glycol, and 4,4‐diphenyl methane diisocyanate (MDI) have been studied. The elastomers were crosslinked by an excess of MDI and by tetramethylthiuram disulfide (TMTD); the latter was supposed to form additional crosslinks on the unsaturated bonds. Although no true equilibrium was found during the stress relaxation experiments, samples crosslinked by MDI measured at 25, 50, and 80°C, and samples crosslinked with additional TMTD measured at 50°C gave very good Mooney‐Rivlin plots, from which the elastic parameters C1 and C2 could be determined. The E (10 sec) and E (100 sec) moduli from the stress‐relaxation experiments, the relaxation speed, C1 values, and equilibrium swelling degree v2 were used to estimate the effect of MDI and of additional crosslinks due to TMTD. It was found that if TMTD was added as a second crosslinking agent to MDI systems, the moduli first passed through a minimum. On the other hand, TMTD was found to have a negative effect on the tensile strength σb and strain‐at‐break εb values throughout the whole concentration range used. The results obtained were clarified on the basis of mutually influencing crosslinking reactions in the formation of the resulting networks.