Effects of quasi‐nanogel particles on the rheological and mechanical properties of natural rubber: A new insight

Abstract

The influence of sulfur-crosslinked, quasinanosized gels on the rheological and mechanical properties of raw natural rubber (NR) was investigated. Latex gels with different crosslink densities were prepared through the variation of the sulfur-to-accelerator ratio. These gels were characterized by dynamic light scattering, solvent swelling, and mechanical properties. The gels were mixed with raw NR latex at concentrations of 2, 4, 8, and 16 phr, and their effect on the rheological properties of NR was studied by Monsanto processability tester. The presence of gel in raw NR reduced the apparent shear viscosity and die swell considerably. Initially, the viscosity decreased up to a 8 phr gel loading and then increased with an increase in the gel loading. However, the change in the viscosity was related to the crosslink density of the gels. A new empirical equation relating the viscosity, volume fraction of the gels, and crosslink density was proposed. The die swell of gel-filled raw NR was at least 10% lower than that of unfilled raw NR and decreased with an increase in the gel loading. The effect of the gels on the die swell properties was explained through the calculation of the principal normal stress difference of gel-filled NR systems. Scanning electron photomicrographs of the extrudates revealed much better surface smoothness for the gel-filled virgin rubber systems than for the unfilled rubber. The addition of the gels to raw NR increased the modulus and tensile strength, whereas the elongation at break decreased. The effect of the gels on the dynamic mechanical properties of NR was also investigated.

Description of Extrudate Swell for Polymer Nanocomposites

“…NR latex gel were then mixed into raw NR forming the filled natural rubber. The rheological tests were similar to those in reference [29]. …”

“…To verify the above swell theory in nanocomposites, experimental die swell data for organo-bentonite-filled polypropylene nanocomposites [34], calcium carbonate nanoparticle-filled isotactic polypropylene [35], clay filled fluoroelastomer nanocomposites [36], quasi-nanogel particles filled natural rubber [29] and electron beam-cross-linked gels filled natural rubber [37] are chosen The experimental details can be found in the corresponding publications. The different key points with regards to rheometry are summarized as follows.…”

“…For quasi-nanogel particles filled natural rubber [29], natural rubber (NR) latex was vulcanized by sulfur in the presence of zinc diethyl dithiocarbamate (ZDC) as an accelerator and zinc oxide (ZnO) as an accelerator activator. The sulfur-to-accelerator ratios were kept at 3, 2, 1, 0.5, and 0.33 leading to the final gel percentages of 97, 96, 94, 88, 86 and crosslingk density of 0.27, 0.36, 0.75, 10.0, 1.11 respectively.…”

“…This is almost true for extrusion in long capillaries, but for short capillaries, the entry effect figures prominently and entrance effects are relatively numerous and complicated in short-tube flow of polymer melts [1,3,9,11,28,29]. For the case of a short capillary, Liang [11] obtained some semi-empirical quantitative relationships of the swell ratio with material characteristics and operational parameters [30].…”

Rheological Behavior of Raw Natural Rubber Coagulated by Microorganisms

“…The rheological properties of the liquid rubbers consist of linear chains of low molecular weight depend mainly on the composition of the main chain were investigated by G. N. Petrov et al [13] . Mitra et al [14,15] observed that the influence of quasi-nanosized gels on the rheological and mechanical properties of raw NR and styrene-butadiene rubber (SBR) was investigated. It has been found that the rheological properties of these cross-linked gelfilled polymers depend on several factors such as gel concentration, size, distribution, and crosslink density.…”