Abstract
Natural rubber (NR) latex was modified with unmodified boehmite alumina (BA) nanoparticles, added in NR up to 15 parts per hundred rubber (phr) amounts. Dispersion of the BA nanofillers was inspected in scanning electron microscopy (SEM). The tensile and fracture mechanical (J-integral approach) properties of the NR/BA nanocomposites were determined. Information on the rubber-BA and possible BA-BA interactions were deduced from dynamic mechanical analysis (DMA) and differential scanning calorimetric (DSC) tests. It was found that BA particles, through agglomerated, were well dispersed in the NR/BA nanocomposites up to a given threshold (7.5 phr). Improvements in the tensile (strength) and fracture mechanical properties (crack initiation- and propagation-related data) were found until this threshold BA content. DMA results confirmed enhanced stiffness and Payne-effect with increasing BA content both in the glassy and rubbery states and in the rubbery state, respectively. The amount of the bound NR fraction on the BA surface was rather small according to DSC results. It was thus concluded that unmodified BA acts as a semi-active nanofiller in NR.
Highlights
Nanocomposites can be produced using polymer latices and water swellable, water dispersible nanofillers
The latex precompounded natural rubber (NR)/boehmite alumina (BA) samples were mixed with sulfur, zinc oxide (ZnO), SA, DM, CBS, TMQ according to the recipe in Table 1 on a laboratory two roll mill (Toyoseiki, Tokyo, Japan) at room temperature for 15 min
Differential scanning calorimetry (DSC) served to investigate the glass transition region of the neat and BA-containing NR systems. 3-5 mg samples were heated from -90 oC to room temperature at a rate of 5°C/min under nitrogen flushing in a Q2000 device of TA Instruments (New Castle, DE, USA)
Summary
Nanocomposites can be produced using polymer latices and water swellable, water dispersible nanofillers. The basic reason of the successful preparation of thermoplastic nanocomposites with clays and BAs through water-mediated melt compounding is that the concentration of these nanofillers in their aqueous dispersions may be as high as 10 wt% This is a surprising fact because many properties of BAs are in favour of application in rubbers These features are: high specific surface (comparable to traditional fillers, such as carbon black and silica), different shapes (aspect ratios), surface basicity (unlike acidity, it does not influence the vulcanization substantially), versatile surface modification (to tailor the interfacial adhesion) and nanoscale dispersion in aqueous media (the possibility of using latex (pre)compounding). Differential scanning calorimetry served to estimate the bound ( termed to immobilized) NR fraction
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