Synergistic effect between graphene nanoplatelets and carbon black to improve the thermal and mechanical properties of natural rubber nanocomposites

In this study, the hybrid effect of nanocellulose/carbon nanotube (NCC/CNT) reinforcement on natural rubber (NR) nanocomposites was investigated. To this end, three series of NR nanocomposites were prepared: NCC/NR, CNT/NR and NCC/CNT/NR. First, the nanocomposites morphology and the filler–rubber interactions were studied using scanning electron microscopy (SEM) and the swelling behavior in toluene, respectively. The results showed that the presence of NCC improved the NCC/CNT hybrid filler dispersion forming a 3D network, while the presence of CNT increased the filler–matrix interaction. The curing results also confirmed that the degree of crosslinking increased when hybrid fillers were used, but the curing time was not modified. In addition, it was observed that using a NCC/CNT hybrid system led to superior mechanical properties, dynamic mechanical properties and thermal conductivity than each material used separately. When 10 phr hybrid filler (with a filler ratio of 1) was added to NR, the tensile strength, modulus at 300% elongation (M300), storage modulus at 10% strain and thermal conductivity were all increased by 57%, 137%, 120%, and 30%, respectively. The results also showed that the NR nanocomposites properties can be controlled by tuning the NCC/CNT filler ratio.

Natural rubber (NR) nanocomposite containing different types of filler, i.e., nanoclay (clay) and cellulose nanofiber (CNF) were prepared in this study. The masterbatches of NR with 5 parts per hundred parts of rubber of nanofiller were firstly prepared by using the latex mixing method, followed by compounding on two roll mill and compression molding to obtain NR nanocomposite specimens. The unfilled NR sample was also prepared for comparison. Morphological properties of NR nanocomposites were investigated by using transmission electron microscopy, while the mechanical and dynamic properties were studied by using a universal tensile testing machine and dynamic mechanical analyzer (DMA). It was found that the clay with platelet morphology was uniformLy dispersed, while the long and flexible CNFs were aggregated and poorly dispersed. The greater improvement of modulus at various strains was achieved from CNF filled NR nanocomposites, while the highest tensile strength was obtained from the clay filled nanocomposite. As compared to the clay containing nanocomposite, the addition of CNF markedly decreased the tensile strength and elongation at break of the NR due to poor dispersion of CNF. However, a significant improvement in mechanical properties at low strain was obtained when the CNF was used as filler due to high degree of fiber entanglement, as suggested by DMA observation.

Natural rubber (NR) nanocomposites were prepared by incorporating carbon nanotubes (CNTs), CNT/silver nanoparticles (AgNP) hybrid fillers, and CNT-AgNP in the presence of varying loadings of ionic liquid (IL). SEM micrographs confirmed the successful decoration of AgNP on CNT surfaces and the formation of filler networks, facilitated by connecting end-to-end CNT bundles with AgNP. The incorporation of CNTs into NR resulted in superior mechanical strength, initial modulus, torque difference, crosslink density, vulcanization rate, and electrical properties in contrast to the gum NR vulcanizate. The decoration of CNT surfaces with AgNP and their end-to-end connection further elevated these properties. Additionally, the introduction of IL to form NR/CNT-AgNP/IL nanocomposites accelerated the curing properties, evidenced by an increased cure rate index and reduced scorch and cure times. Incorporating 1 to 3 phr of IL significantly enhances mechanical, thermo-mechanical, torque difference, crosslink density, and associated properties. However, exceeding 3 phr leads to property deterioration due to notable formation of filler agglomerations and IL pools in the NR/CNT-AgNP/IL nanocomposites containing 5 and 7 phr of IL. In contrast, electrical conductivity continues to increase beyond the 3 phr IL threshold, attributed to the emergence of IL pools serving as a highly conductive electrolyte. Graphical abstract.

This work presents the effect of carbon black (CB)/multiwall carbon nanotubes (MWCNT) hybrid filler system on the mechanical properties and thermal conductivity of natural rubber (NR) based nanocomposites. A 30 phr (parts per hundred of rubber) of CB nanocomposite was used as a reference for which various amounts (0.5, 1, 2 and 5 phr) of MWCNT were incorporated as a CB replacement. Scanning electron microscopy (SEM) was used to investigate the state of dispersion of the CB/MWCNT fillers inside the NR matrix, while dynamic mechanical analysis (DMA) was performed to characterize their storage and loss moduli, Payne effect and loss factor (tan δ). The scorch time (t10) and optimum curing time (t90) gradually increased with increasing MWCNT content due to the shape difference between CB and MWCNT, as well as the adsorption of curatives onto the MWCNT. Finally, due to the intrinsic properties of MWCNT and its synergy with CB, substantial improvements in thermal conductivity and mechanical properties were achieved by the substitution of 5 phr CB with MWCNT. For example, a thermal conductivity of 0.602 W/m.K was achieved, which corresponds to a 80% increase compared to the reference sample. Furthermore, a 72% and 54% increase of the modulus at 100% and 300% strain (M100 and M300) was respectively achieved, while the elongation at break decreased by only 20%.

The interlayer basal spacing of organoclay (OC) could be increased with stearic acid (SA) added, thus OC changed into expanded organoclay by SA (OCSA). The effect of various loadings of OCSA on the curing, mechanical and swelling properties of natural rubber (NR) nanocomposites were studied. The natural rubber/expanded organoclay (NR/OCSA) nanocomposites were prepared by melt intercalation using a laboratory open mill. The curing characteristics of NR compounds were determined using a Moving Die Rheometer (MDR). The X-ray Diffraction (XRD), Attenuated Total Reflectance Infrared (ATR-IR) Spectroscopy and Field Emission Scanning Electron Microscopy (FESEM) were used to study the dispersion of OCSA in the NR matrix. The mechanical properties of NR/OCSA nanocomposites such as tensile strength, elongation at break and hardness were determined using ISO standard and swelling of NR/OCSA nanocomposites in toluene were determined using ISO 1817. The results showed that the SA intercalated into the gallery of OC and reacted with the hydroxyl groups in OC. It was indicated with the shifting of the negative peak 1,700 to 1,723 cm-1 in the ATR-IR spectrum and increase the d-spacing of OC. The adding of various loadings of OCSA into NR could increase the torque and accelerate the curing of nanocomposites and it also could increase the mechanical and swelling properties of nanocomposites. The change in modulus at 100% elongation significantly increased with increasing the OCSA load until maximum loading at 10 phr. This trend was same with the hardness and modulus at 300% elongation. Meanwhile, the improvement of tensile strength and elongation at break was higher at 4 phr OCSA compared with the other loading. The increase of mechanical and swelling properties of NR/OCSA nanocomposites was due to intercalation/exfoliation of OCSA in NR matrix. It was revealed by appearing of the out-of-plane Si-O-(Al) stretch with peak value 1080 cm-1 in the ATR-IR spectrum and the peaks of OCSA in the XRD pattern was disappeared until the loading of OCSA 8 phr and the thickness of morphology of OCSA below 100 nm.

This study investigates the effect of nanoclay modification on the properties of natural rubber (NR) nanocomposites using zinc stearate (ZS) and di(hydrogenated tallow) dimethylammonium chloride (DHDT). The aim is to enhance the compatibility of modified nanoclay (NC) and NR molecules for determining cure characteristics, mechanical properties, and morphologies. The effect of unmodified and modified NC as the secondary filler was studied using the 10 phr NC regarding the received properties of the silica-based composites. Results indicated that the NR composites with modified NC exhibited a significant improvement of 32.06% estimated crosslink density, 16.6% tensile strength, 30.1% Payne effect together with the production time of 3.9 min relative to the composites with unmodified NC. This related to the dispersion and distribution degree of the NC and it suggests that the modification of nanoclay with ZS and DHDT can positively impact to the NR nanocomposites, enhancing their mechanical performance and processing characteristics. Keywords: Modified nanoclay, Natural rubber, Nanocomposites

The structural and mechanical properties of natural rubber (NR) nanocomposites filled with starch nanocrystals (SNC) extracted from four different starch sources are investigated. The aim of this work is to explore the influence of botanic sources on final properties of nanocomposites and SNC reinforcing capability. A general trend seems to be that the higher the amylose content of native starch granules used for preparing SNC, the lower the water uptake and reinforcing effect (except for potato starch). It is postulated that SNC prepared from higher amylose content starch might release loosely bonded amylose chains during preparation and/or soaking in water and thus prevent SNC to participate in the formation of a reinforcing network.magnified image

In order to achieve improvements in the performance of rubber materials, the development of carbon nanotube (CNT)-reinforced rubber composites was attempted. The CNT/epoxidised natural rubber (ENR) nanocomposite was prepared through latex technology. Physical and mechanical properties of the CNT/ENR nanocomposites were characterized in contrast to the carbon black (CB)/ENR composite. The dispersion of the CNTs in the rubber matrix and interfacial bonding between them were rather good; monitored transmission electron microscopy and scanning electron microscopy. The mechanical properties of the CNT-reinforced ENR showed a considerable increase compared to the neat ENR and traditional CB/ENR composite. The storage modulus of the CNT/ENR nanocomposites greatly exceeds that of neat ENR and CB/ENR composites and a maximum conductivity of about 1 S m-1 can be achieved. The approach presented can be adapted to other CNT/polymer latex systems.

Research was undertaken on natural rubber (NR) nanocomposites with organoclays. A double-network (DN) structure is formed when a partially cross-linked elastomer is further cross-linked during a state of strain. Two methods were used in the preparation of NR/organoclay nanocomposites: the ordinary method (single-network NR nanocomposite) and double-networked NR (DN-NR) nanocomposites. The single-networked NR nanocomposites were used for comparison. The effects of organoclay (5 phr) with a different extension ratio on curing characteristics, mechanical properties, hardness, swelling behavior, and morphology of single- and double-networked NR nanocomposites were studied. The results showed that double-networked NR nanocomposites exhibited higher physical and mechanical properties. The tensile strength of DN-NR nanocomposites increased up to 33 MPa (more than four times greater than that of pure NR) and then decreased with an increasing extension ratio. Modulus and hardness continuously increased with an increased extension ratio. The microstructure of the NR/organoclay systems was studied by X-ray diffraction and field emission scanning electron microscopy. The effects of different extension ratios on the dispersion of organoclay layers in the nanocomposites were investigated. Generally, results showed that the optimized extension ratio in DN nanocomposites was equal (or about or around) to α= 2.

A comprehensive study on the thermal and electrical conductivity of EPDM composites with hybrid carbon fillers

In this study, multiwalled carbon nanotubes (MWCNTs) and silica were used as hybrid fillers in natural rubber (NR) nanocomposites. The addition of MWCNTs and silica to NR was varied with the total filler loading fixed at 30 phr. The curing characteristics and mechanical, thermal, and morphological properties were investigated in this study. The results show that the scorch and curing time decreased as the MWCNT loading increased in the silica/MWCNT hybrid, but the maximum torque was increased by about 35%. The highest tensile strength was achieved at a loading ratio of 29 phr silica/1 phr MWCNTs. As the MWCNT loading increased in the silica/MWCNT hybrid, the tensile strength, elongation at break, and fatigue life decreased. However, the tensile modulus and rubber filler interaction increased. The scanning electron microscopy results show a good dispersion and better interaction between silica and the MWCNTs with the NR matrix at a 29/1 silica/MWCNT loading ratio. As the MWCNT loading ratio increased, the agglomeration of the MWCNTs became dominant and reduced the reinforcing effect of the MWCNTs. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

The preparations of natural rubber composites and nanocomposites are mainly outlined in this chapter according to classification of reinforcing agents. Up to present, the reinforcing agents have been mainly divided into four different types of nano-fillers, namely, conventional fillers, natural fillers, inorganic metal or metallic compound fillers and hybrid fillers. The natural rubber composites and nanocomposites are generally prepared by three main methods, namely, mechanical blending, solution mixing and melting blending. The thermal and mechanical properties of natural rubber composites and nanocomposites were summarized. The advantages and disadvantages of each method were discussed in detail with emphasis on the classification of reinforcing fillers.

Effects of organoclay loading (organophilic modified montmorillonite with octadecylamine) in comparison to silica loading on the curing characteristics, tensile properties, thermal stability, and morphology of natural rubber (NR) nanocomposites were studied. Organoclay loading from 2 to 10 phr and silica with 10 and 30 phr loading were used as fillers in this study. The NR/organoclay nanocomposites were compounded using two roll mills and cured at 150°C. The results indicate that the tensile strength and tensile modulus reach maximum at 8 phr of organoclay but elongation at break and thermal stability increase with increasing organoclay loading. Tensile strength, tensile modulus, and elongation at break increase with increasing amount of silica from 10 to 30 phr. Overall results show that organoclay filled NR nanocomposites exhibit shorter processing time and higher tensile properties than silica filled NR nanocomposites. The enhanced properties are due to the homogenous dispersion of individual silicate layers in NR matrix, which is evidenced from the X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) results.

In this study, natural rubber (NR) nanocomposites based on carbon black (CB) and two poly(ethylene glycol) (PEG)‐modified clay hybrid filler were fabricated. The morphology and mechanical properties were studied. The dynamic properties of NR vulcanizates were investigated over a range of strain amplitude at two temperatures. It was found that NR with hybrid filler exhibits superior mechanical properties over that with CB as single phase filler. The hybrid filler causes a significant alteration in the dynamic properties of rubber. The Payne effect becomes more pronounced in rubber with modified clay. A decrease in loss factor (tanδ) was observed for rubber with hybrid filler also. The results revealed that the inclusion of nanoclay (NC) could induce a stronger and more developed filler network. Because of the anisotropy of the nanolayers, NC would depress the reconstruction of filler network, or lower the reformation rates when broken down under deformation, giving rise to lower tanδ value at broad temperature range as well as strain amplitude. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Natural rubber (NR) nanocomposites reinforced with five parts per hundred rubber (phr) of two different nano-fillers, i.e., nanoclay (abbrev. NC) and cellulose nanofiber (abbrev. CNF), were prepared by using latex mixing approach, followed by mill-compounding and molding. The morphology, stress–strain behavior, strain-induced crystallization, and bound rubber of the NR nanocomposites were systematically compared through TEM, tensile test, WAXS, DMA, and bound rubber measurement. The aggregated CNFs were observed in the NR matrix, while the dispersed nanosized clay tactoids were detected across the NR phase. The reinforcement effects of NC and CNF were clearly distinct in the NR nanocomposites. At the same nano-filler content, the addition of NC and CNF effectively accelerated strain-induced crystallization of NR. The high tensile strength obtained in the NC-filled NR nanocomposite was attributed to strain-induced crystallization of NR accelerated by well-dispersed NC. However, the larger tensile modulus and low strain for the CNF-filled NR were related to the formation of immobilized NR at the interface between CNF aggregate and NR. The immobilization effect of NR at the CNF surface offered by a mutual entanglement of CNF aggregate and NR chain led to local stress concentration and accelerated strain-induced crystallization of CNF/NR nanocomposite. From the present study, the NR nanocomposites combined with 5 phr CNF shows high-tensile modulus and acceptable breaking tensile stress and strain, suggesting the application of CNF/NR based nanocomposite in automotive and stretchable sensors for next-generation electronic devices.