A Model Study of the Influence of the Natural Rubber (NR)- Endogenous Gel Fraction on the Rheological Performance of NR Using Synthetic Polyisoprene Rubber (IR) Blends with Different Ratios of Gel

Nonrubber components (NRCs) contribute to the natural networks and endow natural rubber (NR) with exceptional qualities. It is known that the previously proposed NR microstructure has two types of terminal groups, the ω-terminal, which binds to proteins by intermolecular hydrogen bonds, and the α-terminal, which is linked with phospholipids. These connections are believed to be the basis for the formation of naturally occurring networks or gels, which is attributable to the distinctive properties of NR. Using a model of synthetic polyisoprene rubber (IR), the contribution of the gel structure was scrutinized by removing the endogenous gel component derived from NR and adding it in varying quantities to the IR. Through the use of Fourier transform infrared spectroscopy (FT-IR), gel permeation chromatography (GPC), and super-resolution laser scanning confocal microscopy (SR-LSCM), the microstructure of the prepared materials was analyzed. The SR-LSCM analysis revealed that phospholipids exclusively dominated the structure of the sol fraction, whereas both of proteins and phospholipids made up the majority of the gel fraction in NR. The gel microstructure was verified by the GPC analysis, which revealed that short NR chains were networked together. The viscoelastic and mechanical properties of rubber were assessed using an oscillatory shear measurements and tensile testing. The viscoelastic and mechanical performance of the mixed IR with the NR-endogenous gel fraction were strengthened when a substantial proportion of the gel or branch points was incorporated.