PEROXIDE CROSS-LINKING OF EPDM USING MOVING DIE RHEOMETER MEASUREMENTS. I: EFFECTS OF THE THIRD MONOMER CONCENTRATION AND PEROXIDE CONTENT

2015 ◽  
Vol 88 (1) ◽  
pp. 40-52 ◽  
Author(s):  
He Wang ◽  
Ying Ding ◽  
Shugao Zhao ◽  
Claus Wrana
Keyword(s):  
Network Structure ◽  
Monomer Concentration ◽  
Cross Linking ◽  
Cross Link ◽  
Peroxide Content ◽  
Entanglement Density ◽  
The Third ◽  
Link Density ◽  
Cross Links ◽  
Cross Link Density

ABSTRACT The influence of the third monomer 5-ethylene-2-norbornene (ENB) and peroxide content on cure behavior and network structure of peroxide-cured EPDM were investigated by moving die rheometer, NMR relaxation, and dynamic mechanical thermal spectroscopy. According to the rubber elasticity theory, the torque measurement results showed the network structure of peroxide-cured EPDM contained chemical cross-links via combination reaction (Ccom), chemical cross-links via addition reaction (Cadd), and the contribution of entanglement density and network defects to the total cross-link density (CEN). The total cross-link density (Ctot) increased linearly with the peroxide content. The increase of ENB concentration was beneficial for the improvement of cross-linking efficiency of peroxide, but it made the diene conversion of EPDM decrease. CEN was dependent on the third monomer content, which also provided the dominant contribution to the Ctot at low peroxide contents. Furthermore, Ccom and Cadd were dependent on peroxide content linearly, and the latter also was governed by the ENB level.

PEROXIDE CROSS-LINKING OF EPDM USING MOVING DIE RHEOMETER MEASUREMENTS. II: EFFECTS OF THE PROCESS OILS

2018 ◽  
Vol 91 (3) ◽  
pp. 561-576 ◽  
Author(s):  
He Wang ◽  
Tao Zhuang ◽  
Xinyan Shi ◽  
Martin Van Duin ◽  
Shugao Zhao
Keyword(s):  
Dilution Effect ◽  
Gel Permeation Chromatography ◽  
Chemical Effect ◽  
Cross Linking ◽  
Cross Link ◽  
Entanglement Density ◽  
Link Density ◽  
Oil Concentration ◽  
Cross Link Density ◽  
The Cross

ABSTRACT A series of compounds based on peroxide-cured ethylene–propylene–diene monomer rubber (EPDM) was prepared with varying amounts of paraffinic process oil, such as Sunpar 2280, squalane, and dodecane. The cross-linked network composition of EPDM vulcanizates, which correlated directly with the structure and the concentration of process oils, was successfully carried out by either an exponential or a linear fitting procedure. It was found that an increase in process oil concentration caused a decrease in total cross-link density, which could be quantitatively divided into the effect of dilution and chemical effect of oil, represented as a linear and an exponential function of process oil concentration, respectively. Experimental results indicated that whether dilution effect or chemical effect, the addition of Sunpar 2280 affected the decrease of cross-link densities of EPDM vulcanizates most obviously, followed by squalane, and then dodecane, which was the weakest. On the other hand, at lower squalane loading, the chemical effect of squalane dominated the decrease of cross-link density of peroxide-cured EPDMs compared with the dilution effect of oils. Gel permeation chromatography spectra confirmed squalane could consume the free radicals derived from peroxide, forming dimers and trimers, and the variation of squalane content did not affect the activation energy of the cross-linking reaction calculated based on the Kissinger method. The cross-linking efficiency of peroxide and physical entanglement density both linearly decreased with the increase of squalane content.

Mechanical and structural consequences of associative dynamic cross-linking in acrylic diblock copolymers

2021 ◽  
Author(s):  
Jacob Ishibashi ◽  
Ian Pierce ◽  
Alice Chang ◽  
Aristotelis Zografos ◽  
Bassil El-Zaatari ◽  
...  
Keyword(s):  
Viscoelastic Properties ◽  
Diblock Copolymers ◽  
Microphase Separation ◽  
Network Connectivity ◽  
Ethyl Acrylate ◽  
Cross Linking ◽  
Cross Link ◽  
Block Polymers ◽  
Link Density ◽  
Cross Link Density

<p>The composition of low-T<sub>g</sub> <i>n</i>-butylacrylate-<i>block</i>-(acetoxyaceto)ethyl acrylate block polymers is investigated as a strategy to tune the properties of dynamically cross-linked vinylogous urethane vitrimers. As the proportion of the cross-linkable block is increased, the thermorheological properties, structure, and stress relaxation evolve in ways that cannot be explained by increasing cross-link density alone. Evidence is presented that network connectivity defects such as loops and dangling ends are increased by microphase separation. The thermomechanical and viscoelastic properties of block copolymer-derived vitrimers arise from the subtle interplay of microphase separation and network defects.</p><div><br></div><p></p>

scholarly journals Magnetic composites based on NR and strontium ferrite

2019 ◽  
Vol 12 (1) ◽  
pp. 63-69
Author(s):  
Ján Kruželák ◽  
Andrea Kvasničáková ◽  
Rastislav Dosoudil ◽  
Ivan Hudec
Keyword(s):  
Carbon Black ◽  
Strontium Ferrite ◽  
Rubber Matrix ◽  
Cross Link ◽  
Magnetic Composites ◽  
Link Density ◽  
Cross Links ◽  
Cross Link Density ◽  
The Cross ◽  
Thermo Physical Properties

Abstract Two types of composites based on natural rubber (NR) and strontium ferrite were tested in this study. Composites of the first type were prepared by incorporation of strontium ferrite in the concentration range ranging from 0 to 100 phr (parts per hundred rubber) into pure NR based rubber matrix, while with those of the second type, strontium ferrite was dosed in the same concentration level into NR based rubber batch with constant amount of carbon black — 25 phr. For rubber matrices cross-linking, a standard sulfur based curing system was used. This work is focused on the effect of magnetic filler content on physico-mechanical, magnetic and thermo-physical properties of composite materials. Subsequently, the cross-link density and the structure of the formed sulfidic cross-links were examined. The results showed that the cross-link density of both types of composites increased with the increasing content of magnetic filler, while the structure of the sulfidic cross-links was almost not influenced by the amount of strontium ferrite. Tensile strength of rubber composites with pure rubber matrix was slightly improved by the incorporation of ferrite, while in case of composites based on a carbon black batch, the incorporation of magnetic filler resulted in the decrease of this characteristic. The presence of magnetic filler in both types of composites leads to a significant increase of the remanent magnetic induction.

PEG Cross-Linked Alginate Hydrogels with Controlled Mechanical Properties

1998 ◽  
Vol 530 ◽  
Author(s):  
Petra Eiselt ◽  
Jon A. Rowley ◽  
David J. Mooney
Keyword(s):  
Mechanical Properties ◽  
Tissue Engineering ◽  
Molecular Weight ◽  
Elastic Modulus ◽  
Cell Transplantation ◽  
Cross Linking ◽  
Cross Link ◽  
Link Density ◽  
A Cell ◽  
Cross Link Density

AbstractReconstruction of tissues and organs utilizing cell transplantation offers an attractive approach for the treatment of patients suffering from organ failure or loss. Highly porous synthetic materials are often used to mimic the function of the extracellular matrix (ECM) in tissue engineering, and serve as a cell delivery vehicle for the formation of tissues in vivo. Alginate, a linear copolysaccharide composed of D-mannuronic acid (M) and L-guluronic acid (G) units is widely used as a cell transplantation matrix. Alginate is considered to be biocompatible, and hydrogels are formed in the presence of divalent cations such as Ca2+, Ba2+ and Sr2+. However, ionically cross-linked alginate gels continuously lose their mechanical properties over time with uncontrollable degradation behavior. We have modified alginate via covalent coupling of cross-linking molecules to expand and stabilize the mechanical property ranges of these gels. Several diamino PEG molecules of varying molecular weight (200, 400, 1000, 3400) were synthesized utilizing carbodiimide chemistry. Sodium alginate was covalently cross-linked with these cross-linking molecules, and mechanical properties of the resulting hydrogels were determined. The elastic modulus of the cross-linked alginates depended on the molecular weight of the cross-linking molecules, and ranged from 10-110 kPa. The theoretical cross-link density in the hydrogels was also varied from 3 to 47% (relative to the carboxylic groups in the alginate) and the mechanical properties were measured. The elastic modulus increased gradually and reached a maximum at a cross-link density of 15%. In summary, covalently coupled hydrogels can be synthesized which exhibit a wide range of mechanical properties, and these materials may be useful in a number of tissue engineering applications.

scholarly journals Application of Peroxide Curing Systems in Cross-Linking of Rubber Magnets Based on NBR and Barium Ferrite

2019 ◽  
Vol 2019 ◽  
pp. 1-10
Author(s):  
Ján Kruželák ◽  
Andrea Kvasničáková ◽  
Elena Medlenová ◽  
Rastislav Dosoudil ◽  
Ivan Hudec
Keyword(s):  
Mechanical Properties ◽  
Barium Ferrite ◽  
Cross Linking ◽  
Butadiene Rubber ◽  
Cross Link ◽  
System Composition ◽  
Peroxide Curing ◽  
Link Density ◽  
Cross Link Density ◽  
Curing Systems

Rubber magnetic composites were prepared by incorporation of barium ferrite in constant amount—50 phr into acrylonitrile-butadiene rubber. Dicumyl peroxide as the curing agent was used for cross-linking of rubber magnets alone, or in combination with four different types of co-agents. The main aim was to examine the influence of curing system composition on magnetic and physical-mechanical properties of composites. The cross-link density and the structure of the formed cross-links were investigated too. The results demonstrated that the type and amount of the co-agent had significant influence on cross-link density, which was reflected in typical change of physical-mechanical properties. The tensile strength increased with increasing amount of co-agents, which can be attributed to the improvement of adhesion and compatibility on the interphase filler-rubber due to the presence of co-agents. Magnetic characteristics were found not to be influenced by the curing system composition. The application of peroxide curing systems consisting of organic peroxide and co-agents leads to the preparation of rubber magnets with not only good magnetic properties but also with improved physical-mechanical properties, which could broaden the sphere of their application uses.

Elongation at Break as a Measure of Cross-Link Density in Vulcanized Elastomers

1966 ◽  
Vol 39 (3) ◽  
pp. 726-739 ◽  
Author(s):  
E. DiGiulio ◽  
G. Bellini ◽  
G. V. Giandinoto
Keyword(s):  
Crosslink Density ◽  
Cross Linking ◽  
Total Degree ◽  
Cross Link ◽  
Elongation Ratio ◽  
Elongation At Break ◽  
Ethylene Propylene ◽  
First Approximation ◽  
Link Density ◽  
Cross Link Density

Abstract After recalling the reaction mechanism suggested for the crosslinking of ethylene propylene copolymers with organic peroxides, the authors consider the relation between concentration of curing agent and crosslink density. It is experimentally found that, as a first approximation, the elongation ratio at break of vulcanizates (unfilled or filled with small quantities of carbon black) is a function of molar concentration of peroxide only: αR=K/P1/2 This relation can be theoretically justified on the basis of the extensibility of polymer chain segments and of the criterion for rupture originally put forward by Taylor and Darin. By applying the above relation to ethylene propylene copolymers it is possible to evaluate the influence of the chain-splitting reaction during cross-linking. The reciprocal of the square of elongation ratio at break (1/αR2) measures the total degree of crosslinking.

scholarly journals Influence of the chemical structure of cross-linking agents on properties of thermally reversible networks

2016 ◽  
Vol 88 (12) ◽  
pp. 1103-1116 ◽  
Author(s):  
Lorenzo Massimo Polgar ◽  
Robin R.J. Cerpentier ◽  
Gijs H. Vermeij ◽  
Francesco Picchioni ◽  
Martin van Duin
Keyword(s):  
Chemical Structure ◽  
Chemical Conversion ◽  
Rubber Matrix ◽  
Cross Linking ◽  
Cross Link ◽  
Molar Amount ◽  
Link Density ◽  
Cross Link Density ◽  
Cross Linker ◽  
The Cross

Abstract It is well-known that the properties of cross-linked rubbers are strongly affected by the cross-link density. In this work it is shown that for thermoreversibly cross-linked elastomers, the type and length of the cross-linker also have a significant effect. A homologous series of diamine and bismaleimide cross-linkers was used to cross-link maleic-anhydride-grafted EPM irreversibly and furan-modified EPM thermoreversibly, respectively. Bismaleimide cross-linkers with a polarity close to that of EPM and a relatively low melting point have a better solubility in the rubber matrix, which results in higher chemical conversion and, thus, higher cross-link densities at the same molar amount of cross-linker. Samples cross-linked with different spacers (aromatic and aliphatic spacers of different lengths) were compared at the same cross-link density to interpret the effects on the material properties. The rigid character of the short aliphatic and the aromatic cross-linkers accounts for the observed increase in hardness, Young´s modulus and tensile strength with respect to the longer, more flexible aliphatic cross-linkers. In conclusion, the structure of the cross-linking agent can be considered as an alternative variable in tuning the rubber properties, especially for thermoreversibly cross-linked rubber.

Network Structure in Acrylate Systems: Effect of Junction Topology on Cross-Link Density and Macroscopic Gel Properties

2016 ◽  
Vol 49 (17) ◽  
pp. 6531-6540 ◽  
Author(s):  
Bing Wu ◽  
Walter Chassé ◽  
Ron Peters ◽  
Ton Brooijmans ◽  
Aylvin A. Dias ◽  
...  
Keyword(s):  
Network Structure ◽  
Cross Link ◽  
Gel Properties ◽  
Link Density ◽  
Cross Link Density
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