REINFORCEMENT OF RUBBER USING REACTIVE OLIGO(β-ALANINE) SUPRAMOLECULAR FILLERS

Abstract

ABSTRACT Oligo(β-alanine)–based supramolecular fillers that possess an 11-mercaptoundecanoyl oleophilic moiety and an oligo(β-alanine) oleophobic moiety of varied lengths (SA1, SA2, and SA3, having a β-alanine unimer, dimer, and trimer moiety, respectively) have been systematically investigated for reinforcement of SBR. An analog of SA2 with 11-mercapto-undecanoyl being replaced by 3-mercaptopropanoyl, SA2′, was also studied for comparison. Fourier transform infrared evidence has confirmed that all supramolecular fillers exist exclusively as hydrogen-bonded β-sheets in the rubber composites. Differential scanning calorimetry studies have revealed that SA2, SA2′, and SA3 form crystalline domains in the SBR phase at all filler loadings, while SA1 only forms crystalline domains at >15 phr, indicating that microphase separation from the SBR phase is weaker for SA1 than for its higher congeners. Transmission electron microscopy investigations have shown that the filler crystalline domains are dispersed uniformly as short fibers in a continuous SBR phase. The widths of the fibers are below 10 nm, and the lengths range from a few tens to a couple of hundreds of nanometers. The oligo(β-alanine)–based supramolecular fillers exhibit diverse reinforcing characteristics among themselves and in comparison with carbon black. SA1 gives comparatively high extensibility and low tensile strength, while SA2 and SA3 give relatively low extensibility, high stiffness, and high strength. SA2′ behaves similarly to SA1 at low filler loadings but significantly compromises the extensibility at relatively high loadings. Cyclic tensile testing shows that SA1 gives high hysteresis and high set, while SA2 and SA3 give low hysteresis at low elongation and high hysteresis at high elongation in comparison with carbon black. Dynamic mechanical study at 2% strain shows that SA1, SA2, and SA3 result in markedly lower tan δ at 60 °C than carbon black. In addition, abrasion study shows that SA1 and SA2 result in lower weight loss than carbon black at 30 phr of filler loading.