Influence of Fillers and Ionic Liquids on the Crosslinking and Performance of Natural Rubber Biocomposites

Abstract

This work concerns the effect of fillers and ionic liquids on the cure characteristics of natural rubber (NR) compounds, as well as the mechanical and thermal properties of the vulcanizates. Three types of white filler were applied, such as cellulose, nanosized silica and hydrotalcite, to modify the performance of NR composites. Additionally, ionic liquids (ILs) with bromide anion and different cations, i.e., 1-butyl-3-methylimidazolium (Bmi) and 1-butyl-3-methylpyrrolidinium (Bmpyr), were used to improve the cure characteristics of NR compounds and functional properties of the vulcanizates. The type of filler and the structure of ILs were proved to affect the rheometric properties and cure characteristics of NR compounds as well as the performance of the NR vulcanizates. Owing to the adsorption of curatives onto the surface, silica reduced the activity of the crosslinking system, prolonging the optimal vulcanization time of NR compounds and reducing the crosslinking degree of the elastomer. However, silica-filled NR exhibited the highest thermal stability. Hydrotalcite increased the crosslink density and, consequently, the mechanical properties of the vulcanizates, but deteriorated their thermal stability. ILs beneficially influenced the cure characteristics of NR compounds, as well as the crosslink density and mechanical performance of the vulcanizates, particularly those filled with silica. Cellulose did not significantly affect the vulcanization of NR compounds and crosslink density of the vulcanizates compared to the unfilled elastomer, but deteriorated their tensile strength. On the other hand, cellulose improved the thermal stability and did not considerably alter the damping properties of the vulcanizates.

GTR/NBR/Silica Composites Performance Properties as a Function of Curing System: Sulfur versus Peroxides

“…Analyzing the data, it is obvious that the minimum torque, which is a numerical value that determines the processability of the material, for the sulfur cross-linked samples increases with the increasing amount of filler (10.5, 14.9, 24.0, and 45.6 dNm for 0, 5, 15, and 30 phr loadings of highly dispersive silica, respectively), which is in accordance with many independent studies about silica-filled elastomers [ 32 , 33 , 34 ]. The same trend is observed analyzing the maximal torque values (49.8, 52.0, 59.1, and 75.3 dNm for 0, 5, 15, and 30 phr loading of silica, respectively), indicating a drastic increase in the stiffness of the tested materials.…”

Influence of the Silica Specific Surface Area and Ionic Liquids on the Curing Characteristics and Performance of Styrene–Butadiene Rubber Composites

“…The least effect on the thermal stability of SBR vulcanizates was exhibited by BmiBr, which reduced T 5% by approximately 6-8 • C compared to the vulcanizates without ILs. On the other hand, BmpyrBr reduced T 5% by 26-28 • C. The same effect was achieved in our previous work for NR vulcanizates [17], and thus we confirmed that BmiBr-containing elastomers are characterized by a higher thermal stability than those with BmpyrBr, which is due to the higher thermal stability of pure BmiBr as compared with BmpyrBr.…”

“…Higher values of S min were associated with the size of the nanoparticles and the greater specific surface area of A380 silica, which limited the mobility of the elastomer molecular chains to a higher degree compared to VN3, and consequently significantly increased the viscosity of the uncrosslinked rubber compounds. The same effect of silica A380 on the S min and ∆S was observed in our previous work [17] for NR compounds as well as for NBR [45] and SBR [46] compounds. As expected, VN3 silica also increased the S min compared to unfilled SBR, but half as much as A380.…”

“…These properties lead to numerous difficulties when silica is used in rubber products. In order to overcome these inconveniences by reducing the ability of silica particles to agglomerate and their tendency to adsorb curatives, a wide range of additives has been applied, e.g., silanes, ionic liquids (ILs), and surfactants [ 13 , 17 , 18 , 19 , 20 , 21 , 22 ].…”

“…Currently, ILs are becoming more and more popular as additives improving the dispersion of fillers, including silica, in the elastomer matrix. In our previous work [ 17 ], the influence of silica and ILs on the crosslinking and performance of natural rubber (NR) bio-composites was established. Silica strongly affected the cure characteristics of NR composites by increasing the viscosity of the uncured rubber compounds, enhancing the torque increment during rheometric measurements and significantly extending the optimal vulcanization time as compared to the unfilled NR.…”