Nitrile Elastomer/LDH Composites with Varying Mg/Al Ratio, Curing, Nanoparticles Dispersion and Mechanical Properties

Abstract

Layered double hydroxides (LDHs) tend to be a promising material in the field of polymer nanocomposites because it possesses unique chemical and structural properties. The novelty of layered double hydroxides (LDHs) comparing to other conventional fillers is connected with possibility of surface functionalization by introduction of various organic species into an interlayer area. Organic modifiers could act not only as intercalation promoters but also have additional functions such as UV stabilizers, anti-aging substances, pigments, antimicrobial, and antifungal activity. Additionally, in the case of nitrile elastomers, layered double hydroxides (LDHs) could play role as curing substances, reinforcing fillers, and improve mechanical, barrier and thermal properties of rubber products. The purpose of our experimental work was to examine the effect of Mg-Al-LDHs on the crosslink density and properties of nitrile rubber. Various LDHs containing, respectively, 30, 63, 70 wt% of magnesium were applied as a curing system for carboxylated acrylonitrile-butadiene rubber (XNBR) composites prepared by melt compounding methods. The influence of ionic liquids containing saccharinate, acesulfamate ions on the curing reactions and properties of rubber was investigated.

Curing kinetics and ionic interactions in layered double hydroxides–nitrile rubber Mg–Al-LDHs–XNBR composites

“…This fact is attributed to a stronger filler-filler interactions and larger surface area of both MG5 and MG30 fillers. According to our previous studies [14], the surface area of MG63 and MG70 (Mg-rich fillers) was much lower (MG63 −200 m 2 ˑg −1 , MG70 −196 m 2 ˑg −1 ) than MG5 and MG30 (MG5 250 m 2 ˑg −1 , MG30 276 m 2 ˑg), as measured after activation (calcination) at 550 °C for 3 h. Others studies showed [30] that also before calcination MG63 and MG70 fillers exhibited lower surface area comparing to MG30. The increase in this parameter resulted in the enhancement of the interphase contact between the solid surface and elastomer and thus had impact on the flow behavior at whole range of shear rate.…”

“…The increment of elastic torque ΔS ′ defined as ΔS ′ = S ′ max -S ′ min , where S ′ max -maximum elastic torque, S ′ min -minimum elastic torque, was calculated based on the curing curves. The range of temperatures studied and vulcanization parameters were chosen based on our previous studies [14] and based on the DSC measurements indicating the range of curing temperatures for every type of Mg-Al-LDHs-XNBR formulas. From rheometric RPA experimental data, the cure rate α at time t was calculated using Eq.…”

“…The carboxylic salts can be formed between carboxylic groups and metal oxides (e.g., ZnO, MgO, CaO) leading to the ionomers with the thermoplastic nature and the enhanced mechanical properties [10][11][12][13]. Many authors [6,14] reported that ionomer salts can associate to form two principal types of ionic phase: multiplets, statistically dispersed in polymer matrix, which do not form any separate phase, and aggregated clusters containing a higher amount of ion pairs as well as nonionic hydrocarbon content. Therefore, the properties of elastomers cured in such way strongly depend on the type of formed ionic phase.…”

“…These ionic interactions were responsible for the formation of an inorganic-organic gellike structure. Previously, it was reported [14,28,30] that the Mg-Al-LDHs can be used as an alternative to conventional curing systems. This way the production of mechanically strong and transparent elastomer composites without any supplementary additives is enabled.…”

“…This way the production of mechanically strong and transparent elastomer composites without any supplementary additives is enabled. It is huge ecological and economical benefit for layered double hydroxides (LDHs) to serve multifunctional suitability in XNBR, such as cross-linking substance, UV screener, thermal, mechanical and barrier property enhancer [14,28,30].…”