Organoclay–natural rubber nanocomposites synthesized by mechanical and solution mixing methods

A comprehensive review on the recent advancements in natural rubber nanocomposites

Natural rubber (NR) is an eminent sustainable material and is the only agricultural product among various rubbers. Use of nanofillers in NR matrix as a reinforcing agent has gained huge attention because they offer excellent matrix-filler interaction upon forming a good dispersion in the NR matrix. Nanoscale dispersion of fillers lead to greater interfacial interactions between NR and fillers compared to microfillers, which in turn lead to a conspicuous reinforcing effect. Addition of various nanofillers into NR matrix improves not only the mechanical properties but also the electrical, thermal and antimicrobial properties to an extreme level. The current review describes the reinforcing ability of various nanofillers such as clay, graphene, carbon nanotube (CNT), titanium dioxide (TiO₂), chitin, cellulose, barium titanate (BaTiO₃) and lignin in NR matrix. Moreover, reinforcement of various hybrid nanofillers in NR is also discussed in a comprehensive manner. The review also includes the historical trajectory of rubber nanocomposites and a comprehensive account on the factors affecting the properties of the NR nanocomposites.

Study on the Use of CTAB-Treated Illite as an Alternative Filler for Natural Rubber

Fillers are indispensable for rubber composites. Carbon black as an efficient reinforcing filler is most widely used in the rubber industry. However, the utilization of nonrenewable feedstock, energy consumption, and footprint for making carbon black lead to the seeking of alternative substitutes for carbon black, which is of great significance. Here in this work, the possibility of illite, a most common mineral in sedimentary rocks, as an alternative filler for natural rubber (NR) is determined. It is found that pristine illite slows the curing rate and decreases the cross-linking density of NR, which results in the inferior performance of NR. This is associated with the weak filler-rubber interaction, which is a vital factor in deciding the performance of rubber composites. Therefore, illite has been modified using hexadecyl trimethyl ammonium bromide (CTAB), a commonly used cation surfactant, for improving the filler-rubber interaction. The thus obtained C-illite is confirmed to be efficient for (i) enhancing the illite-NR interaction, (ii) improving the dispersion of illite in the NR matrix, and (iii) accelerating the curing process of NR with increased cross-linking density. All of these lead to significantly improved mechanical properties and wear resistance of the C-illite/NR composites, e.g., a 71.88% increase of the modulus at 300% strain compared to the pure NR and a 23.79% reduction of the DIN abrasion volume compared to the NR filled with 40 phr pristine illite. This illustrates the high possibility of CTAB-modified illite with an optimal particle size as a promising alternative filler of carbon black for reinforcing rubbers.

IMPROVEMENT OF SILICA-REINFORCED NATURAL RUBBER TIRE TREAD COMPOUNDS BY JOINT HYBRIDIZATION WITH SMALL AMOUNTS OF SECONDARY FILLERS AND POLYMERS

To improve the properties of silica-reinforced truck tire tread compounds, especially abrasion resistance, the effect of vinyl contents in butadiene rubber (BR) or solution styrene–butadiene rubber (SSBR) as secondary polymers in silica-filled natural rubber (NR) compounds at a ratio of 80/20 phr is investigated in the first part of this study. By increasing the levels of vinyl contents in BR in combination with NR, a better Payne effect, 300% modulus, reinforcement index, and tan delta at −20 and 0 ° C are obtained, whereas the tensile strength, elongation at break, and DIN abrasion resistance index decrease with increasing vinyl contents. Higher vinyl contents in SSBR result in improvements in Payne effect, 300% modulus, tan delta at −20 and 0 °C but only a small improvement in DIN abrasion resistance index. Combinations of secondary fillers and polymers in silica-filled NR are covered in the second part of present study. Silica/carbon black–filled NR/BR and NR/SSBR, respectively, and silica/organoclay–filled NR/BR and NR/SSBR show positive effects on scorch time and optimum cure time, with only slight changes in Payne effect, tensile properties, tan delta at −20 and 0 ° C and DIN abrasion resistance as compared with compounds with carbon black N134. The use of organoclay results in an enhanced Payne effect and tan delta at 60 °C, indicative of reduced filler–filler networking and consequently a lower rolling resistance of tire tread compounds as compared with the compound without organoclay. The specific combination of a small amount of organoclay replacing the same amount of silica, together with some of the NR replaced by high-vinyl BR, promises a substantial overall boost in wet and ice traction, abrasion, and wear resistance as compared with straight NR/silica tire treads. This new observation helps to overcome one of the main shortcomings of NR/silica compounds: their generally low wear resistance.

Enhancement of mechanical properties of natural rubber–clay nanocomposites through incorporation of silanated organoclay into natural rubber latex

In this study, cetyl trimethyl ammonium bromide (CTAB) modified montmorillonite (MMT) which is called as organoclay (OMMT) was mixed with natural rubber, and masterbatches were produced using the acid-free co-coagulation (AFCC) method in the presence of a combined gelling agent, a mixture of CTAB and sodium dodecyl sulfate. The OMMT was further modified by grafting of bis(triethoxysilylpropyl)tetrasulfide as to reduce the surface energy in silanated organoclay (OMMT-S). As expected, the nanocomposites prepared with OMMT-S compared to those with OMMT exhibited greater mechanical properties due to the development of rubber–clay interactions and due to proper dispersion of small clay layers in the rubber matrix combined with the gelling agent. The improvement of elongation at break, hardness and tear strength of the nanocomposites with OMMT/OMMT-S was an added advantage when the nanocomposites are prepared using the AFCC method without having any adverse effect from the combined gelling agent.

ENHANCING PERFORMANCE OF SILICA-REINFORCED NATURAL RUBBER TIRE TREAD COMPOUNDS BY APPLYING ORGANOCLAY AS SECONDARY FILLER

Silica-reinforced natural rubber (NR) tire tread compounds are investigated using organoclay (OC) as secondary filler. By varying mixer temperature settings at a silica/OC ratio of 45/10 phr, dump temperatures are reached of approximately 120, 140, 150, and 160 °C. The increased dump temperature leads to a better silanization reaction resulting in lower mixing torque, Mooney viscosity, and Payne effect. The optimum mixing dump temperature was found to be around 150 °C. By varying the loadings of OC in the silica-filled NR compounds from 0 to 36 wt% relative to total filler amount, the increased OC loadings decreased the Payne effect and compound viscosities, significantly shortened scorch and cure times, and raised the tan delta at −20 and 0 °C as indications for ice traction and wet skid resistance of tire treads made therefrom. The optimum loading of OC of 9 wt% relative to total filler content shows better Payne effect, cure rate index, tan delta at −20 and 60 °C indicative for rolling resistance, and DIN (German Institute of Standardization) abrasion resistance index. The results indicate that the use of this hybrid filler may provide tires with better wet traction and lower rolling resistance and wear resistance compared with the pure silica-filled system.

A Review of the Synthesis and Applications of Polymer–Nanoclay Composites

Recent advancements in material technologies have promoted the development of various preparation strategies and applications of novel polymer–nanoclay composites. Innovative synthesis pathways have resulted in novel polymer–nanoclay composites with improved properties, which have been successfully incorporated in diverse fields such as aerospace, automobile, construction, petroleum, biomedical and wastewater treatment. These composites are recognized as promising advanced materials due to their superior properties, such as enhanced density, strength, relatively large surface areas, high elastic modulus, flame retardancy, and thermomechanical/optoelectronic/magnetic properties. The primary focus of this review is to deliver an up-to-date overview of polymer–nanoclay composites along with their synthesis routes and applications. The discussion highlights potential future directions for this emerging field of research.

Natural Rubber/Dendrimer Modified Montmorillonite Nanocomposites: Mechanical and Flame-Retardant Properties

A series of flame-retardant nanocomposites were established based on compounding of natural rubber (NR) and dendrimer modified flame-retardant organic montmorillonite (FR-DOMt). The merits of these nanocomposites were focused on their better mechanical and flame-retardant properties. X-ray diffractometer (XRD) together with scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis revealed that exfoliation, intercalation, or aggregation status in the NRmatrix can be achieved by addition of different amounts of FR-DOMt. The sound effects of blend ratio of FR-DOMt on mechanical, thermal stability, and flame-retardant (FR) properties of NR were studied. The NR/FR-DOMt-20 composite possessed the highest tensile strength, and this resulted from complicated interactions between layered silicates and elastomers. In addition, with loading of 20 phr of FR-DOMt, the flammability parameters of NR, such as heat release rate (HRR), smoke evolution area (SEA), and carbon monoxide (CO) concentration, were obviously reduced from cone calorimeter analysis.

Elastomer Nanocomposites Based on NR/EPDM/Organoclay: Morphology and Properties

Natural rubber/Ethylene Propylene Diene Monomer (NR/EPDM) blends of five different compositions (0/100), (25/75), (50/50), (75/25) and (100/0) with 1, 3, 5 and 7 phr organo-modified nanoclay (Cloisite 15A) were prepared by two-roll mill. The effect of organo-modified layered nanosilicates and composition on the cure characteristics, microstructure, mechanical, and rheological properties of the nanocomposites were studied. Results suggested the intercalation of polymer chains into the silicate layers which was evidenced by d-spacing results of X-ray diffraction patterns. TEM micrographs also directly confirmed XRD results. Mechanical properties of the nanocomposites depicted a nearly 40% percents increase respectively in the tensile modulus of 75NR/25EPDM containing 7 wt.% nanoclay.

NATURAL RUBBER HYBRID NANOCOMPOSITES REINFORCED WITH SWELLED ORGANOCLAY AND NANO-CALCIUM CARBONATE

Two natural rubber (NR) nanocomposites have been prepared with organoclay(MMT) and swelled organoclay (SMMT) using melt intercalation method. The effect of these two MMTss on the morphology, rheometery, and mechanical behaviors of NR has been evaluated. Scorch times for the MMT-filled compounds were very short compared to unfilled compounds. A more pronounced effect was achieved by using SMMT as reinforcing agent. The obtained results reveal that nanocomposites reinforced by SMMT have more adequate morphology, rheometery, and mechanical behaviors as well as swelling resistance. The microstructure of the NR/MMT systems was studied by x-ray diffraction and field emission scanning electron microscopy. Following, the effect of different content of nano-calcium carbonate on dispersion of MMT layers in NR/SMMT nanocomposites was investigated. The results show that the optimized value of filler in dual fillers-based nanocomposite systems was equal to 10 phr nano-calcium carbonate. NR based hybrid nanocomposites containing SMMT and nano-calcium carbonate was showed 445% increase in tensile strength, 144% stress improvement at 100% strain, and only 3% increase in elongation at break compared to pure NR.