New Technique to Quantitatively Characterize Crosslink Density in IR and Brominated Poly(Isobutylene-CO-Paramethyl Styrene) Blends

1997 ◽  
Vol 70 (4) ◽  
pp. 663-670 ◽  
Author(s):  
Yu F. Wang ◽  
Hsien C. Wang
Keyword(s):  
Molecular Weight ◽  
Network Structure ◽  
Crosslink Density ◽  
Volume Fraction ◽  
Processing Condition ◽  
Product Attributes ◽  
Rubber Blends ◽  
Individual Phase ◽  
Condition Optimization ◽  
The Individual

Abstract The physical properties and application performance of rubber blends are highly dependent on the curing behavior of blend components, morphology, and network structure. Crosslink density or molecular weight between crosslinks characterizes the network structure. It is desirable to develop correlations between product attributes, such as flex, ozone resistance, and permeability with crosslink density of the individual phase in the blend. This will aid developing high performance rubber blends via curative systems, elastomer components and concentration, bromine composition distribution, and processing condition optimization. One major road block is to quantitatively and unambiguously measure the individual phase crosslink density in the blend. A method has been developed and verified with solvent freezing point depression technique. The method can quantitatively determine the individual phase crosslink density in polyisoprene (IR)/Brominated Poly-(isobutylene-co-paramethyl styrene) (BIMS) blends. The method is based on the principle that the molecular weight between crosslinks does not change in different solvents. This is coupled with mass balance equations to determine rubber volume fraction of each phase in the swollen blends. The crosslink density of each phase is then calculated by the Flory-Rehner equation. The method can evaluate the effect of curative distribution, processing conditions, and curative systems on GPR/BIMS blend performance. IR and BIMS blends were cured with zinc oxide and sulfur in this study. It was found that the IR and BIMS phase crosslink density reaches a plateau when the amount of the curing agent is greater or equal to 1.25 phr. The IR phase has a greater crosslinking density than the BIMS phase in the blends. These are valuable information to optimize the curative systems and enhance product attributes.

Effect and Detection of Loose Chain Ends in Crosslinked Polyurethane Elastomers

1971 ◽  
Vol 44 (1) ◽  
pp. 152-165 ◽  
Author(s):  
A. E. Oberth
Keyword(s):  
Crosslink Density ◽  
Volume Fraction ◽  
Present Theory ◽  
Swelling Ratio ◽  
Polyurethane Elastomers ◽  
Equilibrium Volume ◽  
Equilibrium Swelling ◽  
Volume Swelling

Abstract The effect of loose chain ends on tensile properties and equilibrium swelling of crosslinked polyurethane rubbers is studied. As in plasticized elastomers, tensile strength and elastic modulus are reduced approximately by a factor (1−νE,P)2, where νE,P is the volume fraction of loose chain ends, plasticizer, or both. This effect is much larger than predicted by present theory. Also the equilibrium volume swelling ratio, V0/V, of rubbers having terminal chains or an equal volume of plasticizer is the same, provided they do not differ in crosslink density. However, the volume fraction of “network rubber” in the equilibrium swollen specimen, ν2, differs owing to the non-extractability of terminal chains. On this basis a method is proposed which allows experimental determination of the volume fraction of loose ends. Elastomers abounding in loose chain ends show markedly less long term stress relaxation. This effect is not clearly understood but is useful to detect the presence of non load-bearing network.

scholarly journals Effects of Molecular Weight of Functionalized Liquid Butadiene Rubber as a Processing Aid on the Properties of SSBR/Silica Compounds

Polymers ◽  
2021 ◽  
Vol 13 (6) ◽  
pp. 850
Author(s):  
Donghyuk Kim ◽  
Byungkyu Ahn ◽  
Kihyun Kim ◽  
JongYeop Lee ◽  
Il Jin Kim ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Anionic Polymerization ◽  
High Performance ◽  
Crosslink Density ◽  
Functional Group ◽  
Vital Role ◽  
Butadiene Rubber ◽  
Molecular Weights ◽  
Mooney Viscosity ◽  
Silica Dispersion

Liquid butadiene rubber (LqBR) which used as a processing aid play a vital role in the manufacturing of high-performance tire tread compounds. However, the studies on the effect of molecular weight, microstructure, and functionalization of LqBR on the properties of compounds are still insufficient. In this study, non-functionalized and center-functionalized liquid butadiene rubbers (N-LqBR and C-LqBR modified with ethoxysilyl group, respectively) were synthesized with low vinyl content and different molecular weights using anionic polymerization. In addition, LqBR was added to the silica-filled SSBR compounds as an alternative to treated distillate aromatic extract (TDAE) oil, and the effect of molecular weight and functionalization on the properties of the silica-filled SSBR compound was examined. C-LqBR showed a low Payne effect and Mooney viscosity because of improved silica dispersion due to the ethoxysilyl functional group. Furthermore, C-LqBR showed an increased crosslink density, improved mechanical properties, and reduced organic matter extraction compared to the N-LqBR compound. LqBR reduced the glass transition temperature (Tg) of the compound significantly, thereby improving snow traction and abrasion resistance compared to TDAE oil. Furthermore, the energy loss characteristics revealed that the hysteresis loss attributable to the free chain ends of LqBR was dominant.

Effects of accelerator type on stress relaxation behavior and network structure of aged natural rubber/chloroprene rubber vulcanizates

2016 ◽  
Vol 49 (5) ◽  
pp. 381-396 ◽  
Author(s):  
Farzad A Nobari Azar ◽  
Murat Şen
Keyword(s):  
Stress Relaxation ◽  
Natural Rubber ◽  
Network Structure ◽  
Structural Changes ◽  
Relaxation Behavior ◽  
Stress Relaxation Behavior ◽  
Rubber Blends ◽  
Chloroprene Rubber ◽  
Weather Changes ◽  
Behavior Network

Natural rubber/chloroprene rubber (NR/CR) blends are among the commonly used rubber blends in industry and continuously are exposed to severe weather changes. To investigate the effects of accelerator type on the network structure and stress relaxation of unaged and aged NR/CE vulcanizates, tetramethyl thiuram disulfide, 2-mercaptobenzothiazole, and diphenyl guanidine accelerators have been chosen to represent fast, moderate, and slow accelerator groups, respectively. Three batches have been prepared with exactly the same components and mixing conditions differing only in accelerator type. Temperatures scanning stress relaxation and pulse nuclear magnetic resonance techniques have been used to reveal the structural changes of differently accelerated rubber blends before and after weathering. Nonoxidative thermal decomposition analyses have been carried out using a thermogravimetric analyzer. Results indicate that there is a strong interdependence between accelerator type and stress relaxation behavior, network structure, cross-linking density, and aging behavior of the blends. Accelerator type also affects decomposition energy of the blends.

scholarly journals Extracting interface correlations from the pair distribution function of composite materials

Nanoscale ◽  
2021 ◽  
Author(s):  
Harry Geddes ◽  
Henry Hutchinson ◽  
Alex R Ha ◽  
Nicholas P Funnell ◽  
Andrew Goodwin
Keyword(s):  
Distribution Function ◽  
Composite Materials ◽  
Pair Distribution Function ◽  
Complex Mixtures ◽  
Individual Phase ◽  
The Individual ◽  
Matrix Factorisation

Using a non-negative matrix factorisation (NMF) approach, we show how the pair distribution function (PDF) of complex mixtures can be deconvolved into the contributions from the individual phase components and...

scholarly journals Shape and Temperature Expansion of Free Volume Holes in Some Cured Polybutadiene-Polyisoprene Rubber Blends

2021 ◽  
Vol 22 (3) ◽  
pp. 1436
Author(s):  
Giovanni Consolati ◽  
Eros Mossini ◽  
Dario Nichetti ◽  
Fiorenza Quasso ◽  
Giuseppe Maria Viola ◽  
...  
Keyword(s):  
Free Volume ◽  
Radial Direction ◽  
Volume Fraction ◽  
Spherical Shape ◽  
Suitable Model ◽  
Positron Annihilation Lifetime ◽  
Rubber Blends ◽  
Free Volume Fraction ◽  
Hole Model ◽  
Best Fit

The free volume fraction of a macromolecular structure can be assessed theoretically by using a suitable model; however, it can also be evaluated from experimental data obtained from dilatometry and positron annihilation lifetime spectra. In this second case, a regular geometry of the sub-nanometric cavities forming the free volume has to be assumed, although in fact they are irregularly shaped. The most popular approach is to guess spherical holes, which implies an isotropic growth of these last with temperature. In this work, we compared the free volume fraction, as obtained from experiments in a set of polybutadiene and polyisoprene cured rubbers and their blends, with the analogous quantity expected by using the lattice-hole model. The results allowed us to obtain insights on the approximate shape of the holes. Indeed, a cylindrical flattened geometry of the cavities produced a better agreement with the theory than the spherical shape. Furthermore, the best fit was obtained for holes that expanded preferentially in the radial direction, with a consequent decrease of the aspect ratio with temperature.

Novel modification of styrene butadiene rubber/acrylic rubber blends to improve mechanical, dynamic mechanical, and swelling behavior for oil sealing applications

2021 ◽  
pp. 096739112110313
Author(s):  
Ahmed Abdel-Hakim ◽  
Soma A el-Mogy ◽  
Ahmed I Abou-Kandil
Keyword(s):  
Mechanical Properties ◽  
Crosslink Density ◽  
Physical And Mechanical Properties ◽  
Dynamic Mechanical Properties ◽  
Styrene Butadiene Rubber ◽  
Butadiene Rubber ◽  
Rubber Blends ◽  
Dynamic Mechanical ◽  
Oil Resistance ◽  
Styrene Butadiene

Blending of rubber is an important route to modify properties of individual elastomeric components in order to obtain optimum chemical, physical, and mechanical properties. In this study, a novel modification of styrene butadiene rubber (SBR) is made by employing acrylic rubber (ACM) to obtain blends of outstanding mechanical, dynamic, and oil resistance properties. In order to achieve those properties, we used a unique vulcanizing system that improves the crosslink density between both polymers and enhances the dynamic mechanical properties as well as its resistance to both motor and break oils. Static mechanical measurements, tensile strength, elongation at break, and hardness are improved together with dynamic mechanical properties investigated using dynamic mechanical analyses. We also proposed a mechanism for the improvement of crosslink density and consequently oil resistance properties. This opens new opportunities for using SBR/ACM blends in oil sealing applications that requires rigorous mechanical and dynamic mechanical properties.

Molecular weight determines the frequency of delayed type hypersensitivity reactions to heparin and synthetic oligosaccharides

2005 ◽  
Vol 94 (12) ◽  
pp. 1265-1269 ◽  
Author(s):  
Susanne Alban ◽  
Roland Kaufmann ◽  
Edelgard Lindhoff-Last ◽  
Wolf-Henning Boehncke ◽  
Ralf J. Ludwig ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Heparin Therapy ◽  
Delayed Type Hypersensitivity ◽  
Published Data ◽  
Low Molecular Weight ◽  
Hypersensitivity Reactions ◽  
Type Iv ◽  
Total Data ◽  
The Individual

SummaryEczematous lesions, resulting from type IV sensitizations are well-known and relatively frequent cutaneous adverse effects of s.c. heparin therapy. If anticoagulation is further required intravenous heparin, heparinoids or lepirudin may be used as a substitute. However, these alternatives are not optimal in terms of practicability and/or safety-profiles. As molecular weight of different heparin preparations has repetitively been implied to determine the frequency of sensitization, we hypothesized, that due to its low molecular weight the pentasaccharide fondaparinux may provide a practicable and safe anticoagulant therapy in patients with delayed type hypersensitivity reactions (DTH) to heparin and other oligosaccharides. To test this concept, patients referred for diagnosis of cutaneous reactions after s.c. anticoagulant treatment underwent a series of in vivo skin allergyand challenge-tests with unfractionated heparin, a series of low molecular weight heparins (nadroparin, dalteparin, tinzaparin, enoxaparin and certoparin), the heparinoid danaparoid and the synthetic pentasaccharide fondaparinux. In total, data from twelve patients was evaluated. In accordance with previously published data, we report a high crossreactivity among heparins and heparinoids. In contrast – and in support of our initial hypothesis – sensitization towards the synthetic pentasaccharide fondaparinux was rarely observed. Plotting the cumulative incidence against the determined molecular weight of the individual anticoagulant preparations, shows that molecular weight generally is a key determinant of sensitization towards heparins and other oligosaccharides (r2=0.842, p=0.009). Hence, fondaparinux may be used as a therapeutic alternative in patients with cutaneous DTH relations towards heparin and other polysaccharides.

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