Improved resistance to crack growth of natural rubber by the inclusion of nanoclay

The effect of nanoclay on the fatigue crack growth behavior was investigated. Fatigue tests were carried out on edge notched specimens under cyclic tension loadings. A power–law dependency between crack growth rate and tearing energy was obtained. Natural rubber (NR) filled with 5 phr organically modified montmorillonite (OMMT) possessed the lowest value of the exponent, b, and the smallest crack growth rate at a given tearing energy, denoting the strongest resistance to crack growth. Strain‐induced crystallization was probed by synchrotron WAXD experiments, showing earliest occurrence and strongest ability of crystallization in NR with 5 phr OMMT due to the better exfoliation and orientation of clay layers. The study on the viscoelastic property by dynamic mechanical analysis indicated that NR filled with 10 phr OMMT had the largest contribution to tearing energy attributed to the viscoelastic dissipation in the viscoelastic region in front of the crack tip. This revealed that the strain‐induced crystallization played a more important role in the crack growth resistance than the viscoelastic dissipation for clay filled rubber. Copyright © 2010 John Wiley & Sons, Ltd.     

A finite element method based comparative fracture assessment of carbon black and silica filled elastomers: Reinforcing efficacy of carbonaceous fillers in flexible composites

This study is focused on numerical investigation on fracture behaviors of carbon black (CB) and silica filled elastomeric composites. Finite element analysis (FEA) in compliance with multi-specimen method is used to calculate J-integral and geometry factor of the rubber composites up to a displacement of 20 mm for single edge notch in tension (SENT) and double edge notch in tension (DENT) specimens. An empirical relationship between crack tip opening displacement (CTOD) and crack advancement is established depending on notch to width ratio (NWR). The stress contours across the notches for SENT and DENT specimens is discussed briefly. It is found that fracture propagation resistance of CB filled elastomer is 125% more than that of silica filled elastomer. Although, Silica filled elastomer have good tensile strength and crosslink density but it fails to replace carbon black in terms of fracture properties. The critical J-integral for CB filled elastomer is 18.7% and 32.2% more than silica filled elastomer for SENT and DENT specimens respectively. The effect of specimen type on various fracture properties is also explored. The factor of safety is found to be significantly more in case of CB filled elastomers making them less vulnerable to crack propagation and catastrophic failure.     

Preparation and properties of natural rubber composites reinforced with pretreated carbon nanotubes

In order to achieve dramatic improvements in the performance of rubber materials, the development of carbon nanotube (CNT)‐reinforced rubber composites was attempted. The CNT/natural rubber (NR) nanocomposite was prepared through solvent mixing on the basis of pretreatment of CNTs. Thermal properties, vulcanization characteristics, and physical and mechanical properties of the CNT/NR nanocomposites were characterized in contrast to the carbon black (CB)/NR composite. Through the addition of the CNTs treated using acid bath followed by ball milling with HRH (hydrated silica, resorcinol, and hexamethylene tetramine) bonding systems, the crystallization melting peak in differential scanning calorimetry (DSC) curves of NR weakened and the curing rate of NR slightly decreased. Meanwhile, the over‐curing reversion of CNT/NR nanocomposites was alleviated. The dispersion of the treated CNTs in the rubber matrix and interfacial bonding between them were rather good. The mechanical properties of the CNT‐reinforced NR showed a considerable increase compared to the neat NR and traditional CB/NR composite. At the same time, the CNT/NR nanocomposites exhibited better rebound resilience and dynamic compression properties. The storage modulus of the CNT/NR nanocomposites greatly exceeds that of neat NR and CB/NR composites under all temperature regions. The thermal stability of NR was also obviously improved with the addition of the treated CNTs. Copyright © 2008 John Wiley & Sons, Ltd.     

Cut growth and abrasion behaviour,and morphology of natural rubber filled with MWCNT and MWCNT/carbon black

Various amounts of predispersed multi-wall carbon nanotubes (MWCNT) were mixed with natural rubber (NR), with and without carbon black (CB), for preparing MWCNT-filled NR (NC) and MWCNT/CB-filled NR (NH) vulcanizates. All NH vulcanizates contained 30 phr CB and the amount of MWCNT for both NC and NH was varied from 0 to 8 phr. Helium ion microscopy (HIM) and FE-SEM images showed that MWCNT in the NH was dispersed much better than in the NC. Additionally, the well dispersed CB and MWCNT in the NH functioned synergistically in promoting an increase in longitudinal crack growth, leading to enhancement of edge-cut tensile strength (CTS) with increasing MWCNT loading. In contrast, all NC specimens ruptured in a simple lateral direction relating to their lower CTS. Results also revealed that abrasion resistance of the NH was not significantly changed with increasing MWCNT, whereas that of the NC increased. Nevertheless, abrasion resistance of both vulcanizates showed good correlation with the average value of ridge spacing on their abraded surfaces. It was also found that tensile strength of the NH was almost unchanged when the MWCNT loading was increased because the reinforcement by CB predominates over the MWCNT. However, 100% modulus and hardness of both NC and NH increased with increasing MWCNT content.     

Comparison of the mechanical properties at similar hardness level of natural rubber filled with various reinforcing-fillers

Commercially, the alteration of a rubber formulation is usually made in such a way as to keep the hardness of the rubber product constant. This is because a specific hardness of the rubber product sets the limit to its practical applications. Therefore, in this paper, natural rubber (NR) vulcanizates containing various fillers were prepared to have the same hardness level, and their mechanical properties were compared and related to the degree of filler dispersion. The results show that higher amounts of carbon black (CB) and silica are needed for CB- and silica-filled natural rubber vulcanizates to achieve the same hardness value as a NR vulcanizate containing 6 phr of montmorillonite clay. At equal loading of fillers, clay-filled vulcanizate exhibits higher modulus, hardness, tensile strength and compression set, but lower heat build-up resistance and crack growth resistance than those of the vulcanizates containing conventional fillers. For the vulcanizate having the same hardness value, CB-filled vulcanizate gives the better overall mechanical properties followed by the clay-filled and silica-filled vulcanizates, respectively. The explanation is given as the better dispersion of carbon black, as can be seen in the SEM micrograph.     

原位接枝炭黑/天然橡胶复合材料的制备及性能

采用原位固相接枝方法,使在高温和强剪切作用下降解的天然橡胶接枝到炭黑表面.通过对接枝前后炭黑填充天然橡胶的性能对比发现,原位接枝炭黑不但能提高天然橡胶的硫化速度,还能提高拉伸强度,定伸应力和撕裂强度等;动态力学性能的测试结果表明接枝炭黑填充的天然橡胶中接枝炭黑网络化程度较低,这些结果主要归因于接枝炭黑在橡胶基体中分散性的改善及炭黑与橡胶之间作用力的增加.     

Strain‐induced crystallization and mechanical properties of functionalized graphene sheet‐filled natural rubber

The effects of functionalized graphene sheets (FGSs) on the mechanical properties and strain‐induced crystallization of natural rubber (NR) are investigated. FGSs are predominantly single sheets of graphene with a lateral size of several hundreds of nanometers and a thickness of 1.5 nm. The effect of FGS and that of carbon black (CB) on the strain‐induced crystallization of NR is compared by coupled tensile tests and X‐ray diffraction experiments. Synchrotron X‐ray scattering enables simultaneous measurements of stress and crystallization of NR in real time during sample stretching. The onset of crystallization occurs at significantly lower strains for FGS‐filled NR samples compared with CB‐filled NR, even at low loadings. Neat‐NR exhibits strain‐induced crystallization around a strain of 2.25, while incorporation of 1 and 4 wt % FGS shifts the crystallization to strains of 1.25 and 0.75, respectively. In contrast, loadings of 16 wt % CB do not significantly shift the critical strain for crystallization. Two‐dimensional (2D) wide angle X‐ray scattering patterns show minor polymer chain alignment during stretching, in accord with previous results for NR. Small angle X‐ray scattering shows that FGS is aligned in the stretching direction, whereas CB does not show alignment or anisotropy. The mechanical properties of filled NR samples are investigated using cyclic tensile and dynamic mechanical measurements above and below the glass transition of NR. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Structure and properties of styrene-butadiene rubber (SBR) with pyrolytic and industrial carbon black

To evaluate the performance of pyrolytic carbon black (pCB), we filled styrene-butadiene rubber (SBR) with pCB and N330 industrial carbon black (CB). We used two ratios of pCB and N330: 1/9 and 1/1. N330 was selected because its specific surface area was close to that of pCB. The overall CB content in the mixes was 0, 30, 45 and 60 part per hundred rubber (phr). We studied the effects of types and amounts of CB on the dispersion, cure behavior, dynamic mechanical thermal behavior, tensile mechanical and fracture mechanical properties of the filled rubbers. Dispersion of pCB was poorer than that of N330 CB. With respect to tensile mechanical properties – except tear strength – N330 outperformed pCB. The tear strength and fracture mechanics characteristics (J-integral at crack tip opening, and trouser tear strength) of SBR were higher with pCB than with N330. This can be attributed to the broader dispersion of pCB than N330. The combined use of N330 and pCB resulted in intermediate values, reflecting the actual N330/pCB ratio for all measured parameters. We wanted to correlate the mechanical performance with the apparent molecular weight between crosslinks (M_c), and found reasonable correlations for the Payne effect, tensile strength and critical J-integral. On the other hand, we only found a tendency for tear characteristics; this was ascribed to additional effects of (p)CB dispersion.     

Super Strong and Tough Elastomers Enabled by Sacrificial Segregated Network

The integration of high strength and toughness concurrently is a vital requirement for elastomers from the perspective of long-term durability and reliability. Unfortunately, these properties are generally conflicting in artificial materials. In the present work, we propose a facile strategy to simultaneously toughen and strengthen elastomers by constructing 3 D segregated filler network via a simple latex mixing method.The as-fabricated elastomers are featured by a microscopic 3 D interconnected segregated network of rigid graphene oxide(GO) nanosheets and a continuous soft matrix of sulfur vulcanized natural rubber(NR). We demonstrate that the interconnected segregated filler network ruptures preferentially upon deformation, and thus is more efficient in energy dissipation than the dispersed filler network. Therefore, the segregated filler network exhibits better reinforcing effects for the rubber matrix. Moreover, the excellent energy dissipating ability also contributes to the outstanding crack growth resistance through the release of concentrated stress at the crack tip. As a result, the strength, toughness and fatigue resistance of the nanocomposites are concurrently enhanced. The methodology in this work is facile and universally applicable, which may provide new insights into the design of elastomers with both extraordinary static and dynamic mechanical performance for practical applications.     

Compounding,mechanical and morphological properties of carbon-black-filled natural rubber/recycled ethylene-propylene-diene-monomer (NR/R-EPDM) blends

Blends of natural rubber/virgin ethylene-propylene-diene-monomer (NR/EPDM) and natural rubber/recycled ethylene-propylene-diene-monomer (NR/R-EPDM) were prepared. A fixed amount of carbon black (30 phr) was also incorporated. The effect of the blend ratio (90/10, 80/20, 70/30, 60/40 and 50/50 (phr/phr)) on the compounding, mechanical and morphological properties of carbon-black-filled NR/EPDM and NR/R-EPDM blends was studied. The results indicated that both the carbon-black-filled NR/EPDM and NR/R-EPDM blends exhibited a decrease in tensile strength and elongation at break for increasing weight ratio of EPDM or R-EPDM. The maximum torque (S′M_H), minimum torque (S′M_L), torque difference (S′M_H?M_L), scorch time (ts₂) and cure time (tc₉₀) of carbon-black-filled NR/EPDM or NR/R-EPDM blends increased with increasing weight ratio of virgin EPDM or R-EPDM in the blend. SEM micrographs proved that, for low weight ratios of virgin EPDM or R-EPDM, the blends exhibited high surface roughness and matrix tearing lines. The blends also showed a reduction in crack path with increasing virgin EPDM or R-EPDM content over 30 phr. This reduction in crack path could lead to less resistance to crack propagation and, therefore, low tensile strength.     

Nanocavitation around a crack tip in a soft nanocomposite: A scanning microbeam small angle X‐ray scattering study

We explore nanocavitation around the crack tip region in a styrene‐butadiene random copolymer filled with typical carbon black (CB) particles used in the rubber industry for toughening the rubber. Using quasistatic loading conditions and a highly collimated X‐ray microbeam scanned around the crack tip, we demonstrate the existence of a damage zone consisting of nanovoids in a filled elastomer matrix. The existence of voids near the crack tip is demonstrated by a significant increase of the scattering invariant Q/Q₀ in front of both fatigued and fresh cracks. The size of the zone where cavities are present critically depends on the macroscopic strain ε_m, the loading history, and the maximum energy release rate G applied to accommodate the crack. Our findings show that nanovoiding occurs before fracture in typical CB‐filled elastomers and that realistic crack propagation models for such elastomers should take into account a certain level of compressibility near the crack tip. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 422–429     

纳米微晶纤维素对炭黑补强天然橡胶力学性能和动态性能的影响

采用酸水解工业微晶纤维素(MCC)制备纳米微晶纤维素(NCC),将其与天然胶乳共凝沉,混炼时加入炭黑(CB),制备了天然橡胶(NR)/NCC/CB复合材料,研究了NR/NCC/CB和NR/NCC/CB/RH(间苯二酚-六亚甲基四胺络合物)复合材料的力学性能和动态性能,并与NR/CB体系的性能进行对比.结果表明NCC可以均匀分散在天然橡胶基体中,且依拉伸方向取向,随着NCC替代炭黑的份数增加,Payne效应减弱,说明NCC本身并不构成强的填料网络,NR/NCC/CB与NR/CB比较,前者整体的网络化程度减弱,体系的损耗因子变化不大,NCC的加入改善了NR/CB的力学性能和抗屈挠龟裂性能,降低压缩疲劳温升和压缩永久形变,当NCC取代5～20 phr CB后,仍然保持高耐磨炭黑补强天然橡胶的耐磨耗性能.动态力学性能显示NR/NCC/CB的玻璃化转变温度较NR/CB变化不大,0℃的tanδ略有下降的同时60℃的tanδ明显降低.NR/NCC/CB/RH体系的Payne效应较NR/NCC/CB明显减弱,力学性能、抗屈挠龟裂性能和耐磨耗性能进一步改善,体系的压缩疲劳温升和压缩永久形变更小.     

Experimental test and curve fitting of creep recovery characteristics of modified graphene oxide natural rubber and its relationship with temperature

The creep recovery properties of different graphene-doped rubber and the effect of temperature on them were studied. Doping graphene, especially with the surface functional group or surface microstructure, can significantly improve the creep resistance of natural rubber (NR). The permanent creep of each composite tested under the same conditions for 20 min. Graphene oxide, hydrazine hydrate reduced graphene oxide, and 3-aminopropyltriethoxysilane (APTS) grafted graphene oxide was 33%, 16%, and 51% lower than those filled with carbon black respectively. Four parameter model and Weibull distribution function used to analyze and evaluate the creep and recovery test results of composite rubber. These curve fitting results can adequately describe the influence of different types of nanofillers on the creep and recovery properties of composite rubber. The long-term creep of composites forecasted by the time-temperature superposition principle (TTSP). The results show that graphene doping can improve the creep resistance of the rubber. Besides, graphene oxide and surface-modified graphene oxide had better creep resistance than reduced graphene oxide filled natural rubber. It can see that the interfacial properties between the graphene sheet and the natural rubber matrix play an essential role in the creep and recovery properties of graphene/natural rubber composites.     

Influence of Carbon Black and Silica Filler on the Rheological and Mechanical Properties of Natural Rubber Compound

Rubber compounds are reinforced with fillers such as carbon black and silica. In general, filled rubber compounds shows smooth rheological behavior and mechanical properties. Variation in rheological behavior and mechanical properties was studied in terms of the filler composition using natural rubber compounds filled with both carbon black and silica CB/Si = 0/60, 20/40, 30/30, 40/20 and 60/0 phr (parts per hundred rubber is parts of any non-rubbery material per hundred parts of raw gum elastomer (rubbery material)). The rheological behaviour can be showed in measurement of Mooney viscosity and cure time. The Mooney viscosity of rubber compounds increase with the increasing the carbon black in the compounds. The compound filled with CB/Si of 30/30 and 60/0 showed abnormal rheological behaviour in which the cure time decreased suddenly and the increased at certain ratio during the measurement. The mechanical properties such as hardness, abrasion resistance and tensile stress at 300% elongation were studied. In the hardness and abrasion resistance measurement, the higher ratio CB/Si decrease contribution of silica, which resulting smaller of hardness value. Ratio CB/Si 40/20 gives an optimum filler blended. It is also clearly understood that higher abrasion resistance mainly due to the lower hardness value under the same condition. The tensile stress at 300% elongation of rubber compound increased with the increasing carbon black filler.     

Development of an O-ring from NR/EPDM filled silica/CB hybrid filler for use in a solid oxide fuel cell testing system

This research presents the effects of oxygen pressure and ambient temperatures on the crack behavior of O-rings from a semi-EV of NR/EPDM rubber with silica/CB filler, exposed to the inlet flow and outflow oxygen pressure in a Solid Oxide Fuel Cell (SOFC) environment. Blends of NR/EPDM were prepared with various ratios of silica/CB filler at 00/60, 10/50, 20/40, 30/30, 40/20, 50/10, and 60/00 phr. The fabricated O-ring complied with the standard for O-rings (TIS 2728-2559), with a minimum hardness of 65–75 Shore A, minimum tensile strength of 9 MPa, minimum elongation at break of 200%, and a minimum 100% modulus of 2.7 MPa. The mechanical properties of the compounds were tested, and the appropriate compound was chosen to make the O-rings to test in SOFC. The crack morphology of the fabricated O-rings was investigated and compared with a commercial O-ring after testing in the SOFC. As a result, the compound with silica/CB of 40:20 ratio provided the optimum mechanical properties, and passed the criteria standard of TIS 2728-2559. The mechanical properties of the prepared and commercial O-rings were similar (P-value of commercial with 60/00 = 0.273, 50/10 = 0.273, 40/20 = 0.144, 30/30 = 0.465, 20/40 = 0.465, 10/50 = 1.000 and 00/60 = 0.273; all > 0.05) and and both could still be continued to be used in SOFC despite some inner cracks after 24 h. The price of the prepared O-ring is cheaper than the commercial O-rings due to the low price of NR used in its formulation. Therefore, a prepared O-ring can be used in a SOFC, or other applications due to their mechanical properties and their reasonable price.     

Relationship among mechanical properties,heat ageing resistance,cut growth behaviour and morphology in natural rubber: Partial replacement of clay with various types of carbon black at similar hardness level

In this experiment, various types of carbon black (CB) were employed to partially substitute the calcined clay for preparing natural rubber (NR) compounds of similar hardness. At similar hardness, the compounds containing both clay and CB give the better tensile strength, edge-cut tensile strength, tear strength and thermal ageing resistance compared to the control, but the control had better gas barrier property. In addition, the cracking behaviour of the vulcanizate has a transition from simple lateral growth to oblique crack with partial substitution of the clay with CB, and the vulcanizate containing N330 exhibits the greatest longitudinal cracking corresponding to its highest edge-cut tensile strength. This means the presence of N330 causes the greater orientation of the NR chains along the applied force. Furthermore, the vulcanizate containing N330 yields the highest tensile and tear strength, and lowest resilience, although it has the lowest volume fraction of filler. The explanation is given as the higher reinforcing efficiency of N330 and the better filler dispersion shown in SEM micrographs.     

Crack initiation and evolution in vulcanized natural rubber under high temperature fatigue

The nanoscaled crack initiation and evolution of natural rubber under high temperature (85 °C) and small strain amplitude (strain maximum α = 1) fatigue condition were investigated. It was shown by scanning electron microscopy (SEM) images that cracks and cavities with dimensions in nanoscale in the NR matrix appear during the high temperature fatigue. FTIR study indicated that thermal oxidation effect leads to the crosslinking structure destruction. According to the combined analysis of SEM, energy-dispersive X-ray (EDX) spectrometer and small angle X-ray scattering investigations, it was deduced that the destruction of crosslinking structure mainly locates in the vicinity of the ZnS particles with a diameter of 20.2 nm. The ZnS particles are generated as a byproduct in the vulcanization process. Further, the real-time SAXS analysis revealed that the cracks are primarily initiated at relative higher strains (0.7<α < 1) in the region of ZnS aggregations and larger cavities are derived from the enlargement of the cracks.     

Structure and properties of star‐shaped solution‐polymerized styrene‐butadiene rubber and its co‐coagulated rubber filled with silica/carbon black‐I: morphological structure and mechanical properties

The morphological structure and mechanical properties of the star‐shaped solution‐polymerized styrene‐butadiene rubber (SSBR) and organically modified nanosilica powder/star‐shaped SSBR co‐coagulated rubber (N‐SSBR) both filled with silica/carbon black (CB) were studied. The results showed that, compared with SSBR, silica powder could be mixed into N‐SSBR much more rapidly, and N‐SSBR/SiO₂ nanocomposite had better filler‐dispersion and processability. N‐SSBR/SiO₂/CB vulcanizates displayed higher glass‐transition temperature and lower peak value of internal friction loss than SSBR/SiO₂/CB vulcanizates. In the N‐SSBR/SiO₂/CB vulcanizates, filler was dispersed in nano‐scale resulting in good mechanical properties. Composites filled with silica/CB doped filler exhibited more excellent mechanical properties than those filled with a single filler because of the better filler‐dispersion and stronger interfacial interaction with macromolecular chains. N‐SSBR/SiO₂/CB vulcanizates exhibited preferable performance in abrasion resistance and higher bound rubber content as the blending ratio of silica to CB was 20:30. Copyright © 2008 John Wiley & Sons, Ltd.     

Structural evolution during uniaxial deformation of natural rubber reinforced with nano‐alumina

The mechanical properties of natural rubber (NR) were enhanced by the inclusion of nano‐alumina. In order to gain further insights into the reinforcement mechanism, synchrotron wide‐angle X‐ray diffraction (WAXD) was used to monitor the evolution of the molecular structure during stretching in real time, and the tube model theory was applied to study the effect of nanoparticles on rubber network. For the filled rubber, the onset strain of crystallization shifted to much lower value compared with that of the unfilled, indicating the presence of special strain amplification effect, which can be revealed by the reduction of configurational entropy. In addition, the crystallinity increased and the lateral crystallite size decreased after the addition of the nanofiller. During deformation, the crystallites of the filled rubber showed lower orientational fluctuations differing from that of NR reinforced by carbon black. Copyright © 2010 John Wiley & Sons, Ltd.     

Toughening of Epoxy Nanocomposites: Nano and Hybrid Effects

In this paper, we review recent progress made in the field of epoxy-based binary and ternary nanocomposites containing three-, two-, and one-dimensional (i.e., 3D-, 2D-, and 1D) nano-size fillers with a special focus on their fracture behaviors. Despite investigations conducted so far to evaluate the crack-resistance of epoxy nanocomposites and attempts made to clarify the controlling toughening mechanisms of these materials, some questions remain unsolved. It is shown that silica nanoparticles can be as effective as rubber particles in improving the fracture toughness/energy; but incorporation of carbon nanotubes (CNTs) or clay platelets in epoxy matrices delays crack growth only modestly. The “nano” effects of silica (<25 vol.%) and rubber (>10 wt.%) nanoparticles in toughening epoxy resin are confirmed by comparison with silica and rubber micro-particles of the same loading. There is clear evidence of both synergistic and additive toughening effects in the silica/rubber/epoxy ternary nanocomposites. In addition, positive hybrid toughening effect has been observed in the nano-rubber/CNT/epoxy composites; however, a negative hybrid effect is predominant in nano-clay/nano-rubber/epoxy ternary nano-composites. Future research directions for epoxy-based nanocomposites towards multi-functional applications are discussed.