The Chain End Distributions and Crosslink Characteristics in Black-Filled Rubbers

1998 ◽  
Vol 71 (5) ◽  
pp. 975-987 ◽  
Author(s):  
Asahiro Ahagon
Keyword(s):  
Average Molecular Weight ◽  
Chain Scission ◽  
Polymer Phase ◽  
Chain Mobility ◽  
Filled Rubber ◽  
Bound Rubber ◽  
Filled Rubbers ◽  
Carbon Gel ◽  
Two Phases ◽  
Chain Slippage

Abstract A black-filled rubber compound consists of two phases: the free polymer phase, where no particle exists, and the carbon black agglomerate phase, where highly concentrated particles are bound by a small amount of the polymer—so called bound rubber. The Charlesby—Pinner virtual linear number-average molecular weight Mn1 of the polymer in each phase is determined for black-filled compounds to obtain information about the chain end distribution in the compounds. The nominal crosslink density of the bound rubber is also measured by means of the swelling measurement of the “carbon gel” to characterize the crosslink variation in the vulcanizates. The results indicate that the chain end density is much higher in the agglomerate phase than in the free polymer phase due to enhanced chain scission during mixing. The enhancement of scission is considered due to the free radical crosslinking which imposes restriction to chain slippage in the flow field. This together with the previous findings suggests the features of the phase construction in the filled vulcanizates: tightly crosslinked free polymer phase with fewer chain ends, and loosely crosslinked agglomerate phase with more chain ends but, with rather suppressed chain mobility due to the dense nano-scale particles. The features match well with the energy dissipating and the toughened nature of the filled vulcanizates.

STUDY ON NANOMORPHOLOGY OF HIGH-STRUCTURE CARBON BLACK AND ITS BOUND RUBBER BY AFM

2012 ◽  
Vol 19 (01) ◽  
pp. 1250003
Author(s):  
JIAN CHEN ◽  
YONGZHONG JIN ◽  
JINGYU ZHANG ◽  
YAFENG WU ◽  
CHUNCAI MENG
Keyword(s):  
Carbon Black ◽  
Cluster Structure ◽  
Chemical Activity ◽  
Styrene Butadiene Rubber ◽  
Butadiene Rubber ◽  
Atomic Force ◽  
Filled Rubber ◽  
Bound Rubber ◽  
Styrene Butadiene ◽  
High Structure

Bound rubber in carbon black (CB) filled rubber (natural rubber (NR) and styrene–butadiene rubber (SBS)) was prepared by the solvent method. The nanomorphology of CB and rubber/CB soluble rubber was observed by atomic force microscope. The results show that high-structure CB DZ13 has a "grape cluster" structure which consists of many original particles with the grain size of about 30–50 nm. Graphitizing process of CB decreases the amount of bound rubber. The NR/DZ13 soluble rubber with island–rim structure has been obtained, where the islands are DZ13 particles and the rims around the islands are occupied by NR film. But when the graphitized DZ13 particles were used as fillers of rubber, we have only observed that some graphitized DZ13 particles were deposited on the surface of the globular-like NR molecular chains, instead of the spreading of NR molecular chains along the surface of DZ13 particles, indicating that graphitized DZ13 has lower chemical activity than ungraphitized DZ13. Especially, we have already observed an interesting unusual bound rubber phenomenon, the blocked "bracelet" structure with the diameter of about 600 nm in which CB particles were blocked in ring-shaped SBS monomer.

MODIFIED GUTH–GOLD EQUATION FOR CARBON BLACK–FILLED RUBBERS

2013 ◽  
Vol 86 (2) ◽  
pp. 218-232 ◽  
Author(s):  
Y. Fukahori ◽  
A. A. Hon ◽  
V. Jha ◽  
J. J. C. Busfield
Keyword(s):  
Carbon Black ◽  
Volume Fraction ◽  
Solid Particles ◽  
Carbon Particles ◽  
Filler Volume Fraction ◽  
Rigid Filler ◽  
Bound Rubber ◽  
Small Volume Fraction ◽  
Filled Rubbers ◽  
Good Agreement

ABSTRACT The modulus increase in rubbers filled with solid particles is investigated in detail here using an approach known widely as the Guth–Gold equation. The Guth–Gold equation for the modulus increase at small strains was reexamined using six different species of carbon black (Printex, super abrasion furnace, intermediate SAF, high abrasion furnace, fine thermal, and medium thermal carbon blacks) together with model experiments using steel rods and carbon nanotubes. The Guth–Gold equation is only applicable to such systems where the mutual interaction between particles is very weak and thus they behave independently of each other. In real carbon black–filled rubbers, however, carbon particles or aggregates are connected to each other to form network structures, which can even conduct electricity when the filler volume fraction exceeds the percolation threshold. In the real systems, the modulus increase due to the rigid filler deviates from the Guth–Gold equation even at a small volume fraction of the filler of 0.05–0.1, the deviation being significantly greater at higher volume fractions. The authors propose a modified Guth–Gold equation for carbon black–filled rubbers by adding a third power of the volume fraction of the blacks to the equation, which shows a good agreement with the experimental modulus increase (G/G0) for six species of carbon black–filled rubbers, where G and G0 are the modulus of the filled and unfilled rubbers, respectively; ϕeff is the effective volume fraction; and S is the Brunauer, Emmett, Teller surface area of the blacks. The modified Guth–Gold equation indicates that the specific surface volume ()3 closely relates to the bound rubber surrounding the carbon particles, and therefore this governs the reinforcing structures and the level of the reinforcement in carbon black–filled rubbers.

Flocculation in Silica Reinforced Rubber Compounds

2009 ◽  
Vol 82 (5) ◽  
pp. 524-540 ◽  
Author(s):  
S. Mihara ◽  
R. N. Datta ◽  
J. W. M. Noordermeer
Keyword(s):  
Activation Energy ◽  
Coupling Agent ◽  
Physical Phenomenon ◽  
Interfacial Interaction ◽  
Shielding Effect ◽  
Interaction Layer ◽  
Filled Rubber ◽  
Rubber Compounds ◽  
Bound Rubber ◽  
Flocculation Rate

Abstract Flocculation plays an important role in reinforcement of silica filled rubber compounds, even if coupling agents are applied. It is well known that silica tends to flocculate during the early stages of vulcanization, when no dense rubber network has been formed yet. In the present study, flocculation was monitored by following the change in storage modulus at low strain, the so-called Payne effect, using a RPA2000 dynamic mechanical tester. The kinetic parameters: the rate constant and the activation energy of the silica flocculation were calculated according to the well-known Arrhenius equation. On basis of the value of the activation energy obtained for flocculation, it can be concluded that the silica flocculation is a purely physical phenomenon. Bound rubber measurements were also done in order to estimate the interfacial interaction layer between silica and polymer resulting from the coupling agent. The silica flocculation rate decreases with increasing interfacial interaction layer on the silica surface. This indicates that the decrease of the flocculation rate is due to the shielding effect of the coupling agent. It is argued that the attractive flux from forces related to polarity differences between the silica and the rubber is the determining factor for silica flocculation.

Tack and Related Properties of Isopropyl Azodicarboxylate Modified Polybutadiene

1984 ◽  
Vol 57 (1) ◽  
pp. 227-242 ◽  
Author(s):  
G. R. Hamed ◽  
C-H. Shieh
Keyword(s):  
Initial Increase ◽  
Infrared Analysis ◽  
Additional Contribution ◽  
Great Loss ◽  
Entanglement Density ◽  
Green Strength ◽  
Chain Mobility ◽  
Modified Polymers ◽  
Slow Rise ◽  
Two Phases

Abstract Polybutadiene has been modified by reaction with isopropyl azodicarboxylate (IAD). The reaction is quite efficient, resulting in a structure in which there are pendant hydrazoester groups dangling from the BR backbone. The Tg's of the modified polymers increase with IAD content. Eventually, at high levels of modification, two Tg's are observed, indicating the presence of two phases. Infrared analysis indicates the presence of H-bonding within the modified polymers. The green strength of these polymers increases with IAD content, whereas, tack passes through a maximum with increasing IAD level. At low IAD levels, the increase in green strength is attributed to increased polar interactions between chains, whereas, at higher IAD levels, there appears to be an additional contribution from strain-induced phase separation (see Reference 1). This type of behavior is favorable for high tack. The initial increase in tack as IAD is incorporated is due, in part, to the enhanced green strength. A more important feature is that the green strength is enhanced without great loss of the molecular mobility needed to form a tack bond. This occurs because of 1) the slow rise in Tg and 2) a lowering of the entanglement density with modification. Blocky additions of the IAD contributes to the former effect as does the presence of the alkyl group (isopropyl) in the polar IAD moiety. Additionally, it is inferred that the IAD-BR molecules do not have to interdiffuse as far across the interface to develop a strong tack bond as do purely hydrocarbon BR chains. Evidence for this is the rapid initial increase in relative tack for the IAD modified elastomers. Finally, the loss of tack at high IAD levels is due to a severe decrease in chain mobility, thereby prohibiting the formation of an extensive tack bond.

scholarly journals Anisotropic Hydrolysis Susceptibility in Deformed Polydimethylsiloxanes

2019 ◽  
Author(s):  
Matthew Kroonblawd ◽  
Nir Goldman ◽  
James Lewicki
Keyword(s):  
Density Functional ◽  
Degrees Of Freedom ◽  
Tight Binding ◽  
Hydrolytic Degradation ◽  
Chain Scission ◽  
Functional Theory ◽  
Chain Mobility ◽  
Mechanical Deformations ◽  
Macro Scale ◽  
Backbone Atoms

<div>Chemical reactions involving the polydimethylsiloxane (PDMS) backbone can induce significant network rearrangements and ultimately degrade macro-scale mechanical properties of silicone components. Using two levels of quantum chemical theory, we identify a possible electronic driver for chemical susceptibility in strained PDMS chains and explore the complicated interplay between hydrolytic chain scissioning reactions, mechanical deformations of the backbone, water attack vector, and chain mobility. Density functional theory (DFT) calculations reveal that susceptibility to hydrolysis varies significantly with the vector for water attacks on silicon backbone atoms, which matches strain-induced anisotropic changes in the backbone electronic structure. Efficient semiempirical density functional tight binding (DFTB) calculations are shown to reproduce DFT predictions for select reaction pathways and facilitate more exhaustive explorations of configuration space. We show that concerted strains of the backbone must occur over at least few monomer units to significantly increase hydrolysis susceptibility. In addition, we observe that sustaining tension across multiple monomer lengths by constraining molecular degrees of freedom further enhances hydrolysis susceptibility, leading to barrierless scission reactions for less substantial backbone deformations than otherwise. We then compute chain scission probabilities as functions of the backbone degrees of freedom, revealing complicated configurational inter-dependencies that impact the likelihood for hydrolytic degradation. The trends identified in our study suggest simple physical descriptions for the synergistic coupling between local mechanical deformation and environmental moisture in hydrolytic degradation of silicones.</div>

scholarly journals Multiphysics Coupling In Aging Process of Filled-Rubber

2019 ◽  
Vol 8 (6) ◽  
pp. 4010-4013
Keyword(s):  
Aging Process ◽  
Internal Variables ◽  
Plastic Behavior ◽  
Element Formulation ◽  
Filled Rubber ◽  
Multiphysics Coupling ◽  
Filled Rubbers ◽  
Aging Phenomenon ◽  
Mechanical Dissipation ◽  
Fully Coupled

Filled rubbers are used popularly in damping parts which can be found in automobile sector or in building sector. However, the mechanical properties of material depend sensitively on temperature, chemical composition and environment conditions. In fact, the mechanical dissipation due to damping process leads to the increase of temperature considerably. Aging process can be activated sequentially by the heat which result in the change of damping properties during usage time. This paper presents a new behavior model that considers the simultaneous effects of temperature, mechanical loads on the behavior of materials along with the aging of materials. With the assumption of internal variables related to aging phenomenon and visco-plastic behavior, the model is built in the thermodynamical framework. A fully coupled finite element formulation is proposed to solve simultaneously thermo, chemical and mechanical phenomenon appeared in this material. An example illustrates the number of applicability of the model to predict the behavior of materials under the effect of cyclic loads in extremely working conditions

COMPARISON OF STRESS–SOFTENINGS IN CARBON-BLACK FILLED NATURAL RUBBER AND STYRENE–BUTADIENE RUBBER

2013 ◽  
Vol 86 (4) ◽  
pp. 572-578 ◽  
Author(s):  
Julie Diani ◽  
Yannick Merckel ◽  
Mathias Brieu ◽  
Julien Caillard
Keyword(s):  
Carbon Black ◽  
Natural Rubber ◽  
Cyclic Softening ◽  
Styrene Butadiene Rubber ◽  
Amplitude Dependence ◽  
Butadiene Rubber ◽  
Fatigue Lifetime ◽  
Filled Rubber ◽  
Filled Rubbers ◽  
Styrene Butadiene

ABSTRACT The authors compared the mechanical behavior and, more precisely, the Mullins and the cyclic (post-Mullins) softenings of two filled rubbers. A crystallizing natural rubber and a noncrystallizing styrene–butadiene rubber of similar compositions resulting in similar cross-link densities and filled with 40 phr of N347 carbon-black fillers were tested in cyclic uniaxial tension at room temperature and at 85 °C. Crystallization in filled rubbers is known to increase stress at high stretch, stretch at break, cycle hysteresis, and fatigue lifetime and to reduce crack propagation. In this study, it is shown that crystallization also seems to enhance the Mullins softening (softening at the first cycle) and to favor the apparent cyclic softening. Results reveal that natural rubber shows an amplitude dependence on the cyclic softening, whereas the styrene–butadiene rubber does not. Finally, results demonstrate that studying filled rubber softening cannot help predict lifetime.

Continuous Ultrasonic Treatment of Uncured and Sulfur Cured SBR: Effect of Styrene Content

2005 ◽  
Vol 78 (4) ◽  
pp. 606-619 ◽  
Author(s):  
A. I. Isayev ◽  
S. H. Kim ◽  
Wenlai Feng
Keyword(s):  
Molecular Weight ◽  
Ultrasonic Treatment ◽  
Crosslink Density ◽  
Main Chain ◽  
Structural Characteristics ◽  
Average Molecular Weight ◽  
Chain Scission ◽  
Gel Fraction ◽  
Styrene Content ◽  
Good Agreement

Abstract Unvulcanized and vulcanized SBR samples with styrene content of 18 and 23.5% were used to investigate the effect of ultrasound treatment on their structural characteristics. Gel fraction and crosslink density of gel are measured. Molecular weight and molecular weight distribution of sol are studied to determine the level of degradation of the macromolecular chain in ultrasonically treated unvulcanized and vulcanized rubbers. It is shown that the weight and number average molecular weight of sol in devulcanized SBR is, respectively, lower and higher in the samples having higher styrene content. Ultrasonic treatment of virgin unvulcanized SBR causes generation of gel along with its main chain modification due to the competition between chain scission and crosslinking. The competitive reactions taking place during this treatment are discussed. It was found that the intermolecular bonds in SBR vulcanizates containing higher styrene content are easier to break. The structural characteristics of devulcanized SBR rubber were simulated using the Dobson-Gordon theory of rubber network statistics. A fairly good agreement between experimental data and theoretical prediction on normalized gel fraction vs. normalized crosslink density was achieved. The simulation of devulcanized SBR rubber indicated that the rate of crosslink rupture is much higher than that of main chain. The styrene content in SBR rubber does not affect kp/kα substantially.

Bound rubber morphology and loss tangent properties of carbon-black-filled rubber compounds

2015 ◽  
Vol 294 (3) ◽  
pp. 501-511 ◽  
Author(s):  
Dina Gabriel ◽  
Alexander Karbach ◽  
Doris Drechsler ◽  
Jochen Gutmann ◽  
Karlheinz Graf ◽  
...  
Keyword(s):  
Carbon Black ◽  
Loss Tangent ◽  
Filled Rubber ◽  
Rubber Compounds ◽  
Bound Rubber

Low Strain Dynamic Properties of Filled Rubbers

1971 ◽  
Vol 44 (2) ◽  
pp. 440-478 ◽  
Author(s):  
A. R. Payne ◽  
R. E. Whittaker
Keyword(s):  
Carbon Black ◽  
Dynamic Properties ◽  
Fatigue Behavior ◽  
Van Der Waals ◽  
Three Dimensional ◽  
Solid Particles ◽  
Spherical Particles ◽  
Filled Rubber ◽  
Secondary Network ◽  
Filled Rubbers

Abstract Carbon black does not exist as single spherical particles but forms itself into a rodlike primary structure. These rodlike structures then form into an aggregated secondary network. This secondary network is believed to be held together by Van der Waals-London attraction forces. The decrease in shear modulus of filled rubber vulcanizates with strain is due almost certainly to these secondary forces. Special mixing techniques such as attrition of the carbon black, increased time of mixing, or the addition of chemical promoters which aim at dispersing the carbon black within the mix better are shown to decrease the value of G′0−G′∞. The absence of any modulus change with strain for unfilled vulcanizates and secondly the little change observed in values of G′0−G′∞ with increasing vulcanization of the rubber when containing the same amount of carbon black confirms that the decrease in modulus with strain amplitude is in no way associated with the gum phase of the filled vulcanizate. The similarity in behavior of carbon black filled rubbers with clay/water and clay/rubber systems indicates that the decrease in modulus with amplitude is due to the breakdown of the three dimensional filler aggregates. A number of rheological studies on clay systems has confirmed that clay particles form into rigid three dimensional structures when dispersed in a medium. Evidence for the aggregated filler structure to be held together by Van der Waals-London attraction forces comes from the reasonable agreement between the experimental values for the forces required to breakdown the carbon black aggregates in paraffin oil and the forces calculated from Van den Tempel's model for flocculated solid particles in a liquid. The successful application of a domain model to the hysteretical behavior exhibited by carbon black filled vulcanizates at low strains indicates that the carbon black structure breaks down under stress but reforms to the original state when the stress is removed. This conclusion is also supported by the similarity in behavior between filled rubbers and a dendritic crystal structure of PBNA in rubber. Under the optical microscope the PBNA is seen to break down and reform under a stress-strain cycle. The breakdown and reformation of this secondary aggregated carbon black structure increases the hysteresis in filled rubber vulcanizates. Other sources of hysteresis include viscoelasticity of the polymer, crystallization, stress-softening, and changes in network structure (e.g., breakage of weak crosslinks). These mechanisms have been discussed in depth in previous publications. Recent work has shown, however, that the strength of a rubber is dependent on the combined effect of the different hysteretical mechanisms. The breakdown and reformation of the carbon black structure at low strains in filler reinforced rubbers therefore not only affects the heat build up, transmissibility, and fatigue behavior but also influences the failure properties of the filled vulcanizate.

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