The Dependence of Dielectric Properties on Crosslink Density of Rubbers

1978 ◽  
Vol 51 (1) ◽  
pp. 72-80 ◽  
Author(s):  
R. Bakule ◽  
A. Havránek
Keyword(s):  
Dielectric Properties ◽  
Natural Rubber ◽  
Crosslink Density ◽  
Unit Volume ◽  
Volume Distribution ◽  
Dicumyl Peroxide ◽  
Frequency Range ◽  
Polar Groups ◽  
Main Transition ◽  
Macroscopic Parameters

Abstract The dielectric properties of natural rubber, synthetic polyisoprene, andpolybutadiene samples crosslinked with sulfur and of natural rubber samplescrosslinked simultaneously with sulfur and dicumyl peroxide were studied. Inthe investigated systems, the number of polar groups in unit volume and thecrosslink density may be changed independently over relatively wide ranges.The measurements were performed in the frequency range from 101 to 105 Hzat various temperatures, and macroscopic parameters describing the dielectricproperties of the samples were evaluated. The position and intensity of thedielectric dispersion peak in the main transition zone is only slightly dependenton the crosslink density of the samples. These two values are mainly influencedby the amount of combined sulfur, or more generally, by the number and thedipole moments of polar groups in the sample. The influence of crosslink densityon the width of the absorption curve is very strong; the width increases withincreasing crosslink density. The possibility of explaining this effect in termsof the dependence of the free volume distribution function on crosslink densityis discussed.

Dielectric Studies of Admicelled Natural Rubber with Poly(3-Trimethoxysilylpropyl Methacrylate)

2013 ◽  
Vol 844 ◽  
pp. 373-376
Author(s):  
Suparat Nooma ◽  
Rathanawan Magaraphan
Keyword(s):  
Dielectric Constant ◽  
Composite Materials ◽  
Dielectric Properties ◽  
Chemical Modification ◽  
Natural Rubber ◽  
Microwave Frequency ◽  
Dielectric Studies ◽  
Frequency Range ◽  
Admicellar Polymerization ◽  
Methoxy Groups

In this work, 3-trimethoxysilylpropyl methacrylate (MPS) was used as a substrate for coating on natural rubber (NR) particles by admicellar polymerization. The incorporation of MPS monomer, consisting of silicon element and 3 reactive methoxy groups (R-Si(OCH3)), is expected to increase dielectric properties of NR. Under the admicellar polymerization, the R-Si(OCH3) groups can be hydrolyzed and condensed into polysiloxane existed on NR particles. This method aims to prepare composite materials from NR and MPS with various amounts of MPS. The effects of microwave frequency and chemical modification by admicellar polymerization were studied. The dielectric properties of admicelled natural rubber (adNR) with PMPS were investigated at 20 °C in a frequency range extended from MHz to GHz. The results showed that the dielectric constant of adNR increased with PMPS contents. To study the effect of crosslinking on the dielectric properties of adNR, the dielectric spectroscopy measurements were performed on prevulcanized and non-prevulcanized adNR. The investigation showed that the dielectric constant of non-prevulcanized adNR was less than prevulcanized adNR.

Structure and Properties of Loaded Rubber Mditures. XII. Dielectric Properties of Natural Rubber-Carbon Black Mditures

1955 ◽  
Vol 28 (1) ◽  
pp. 84-91
Author(s):  
A. I. Lukomskaya ◽  
B. A. Dogadkin
Keyword(s):  
Dielectric Properties ◽  
Carbon Black ◽  
Natural Rubber ◽  
Dielectric Losses ◽  
Structure And Properties ◽  
Frequency Range ◽  
Carbon Black Content ◽  
Vulcanized Rubber ◽  
Direct Current Conductivity ◽  
Frequency Curves

Abstract 1. The temperature and frequency curves of dielectric constant ε′ and coefficient of dielectric loss ε″ of unvulcanized natural rubber and simple rubber-carbon black mixtures, and also vulcanizates of natural rubber containing various proportions of thermal black or channel black, were studied in the frequency range from 50 to 2.5×107 cycles per second at 20° C, and in the temperature range from −75° to 152° C at frequencies of 103 to 4×104 cycles per second. 2. As in the case of sodium-butadiene mixtures, the addition of carbon black to the rubber leads to three kinds of dielectric losses, viz., a loss due to the nonuniformity of the dielectric, a loss due to the passage of a direct current (conductivity), and a loss due to structure formation. Vulcanization of rubber leads to the appearance of dipolar dielectric losses, which can be explained by the orientation of the sulfur dipoles in the electric field. Loading of vulcanizates causes a change of the dipolar dielectric properties, which depend both on the content and type of filler and on the type of vulcanized rubber. 3. For all the types of vulcanizates, the dependence of the dielectric properties (a measure of the orientation processes in the rubber phase) on the form factor ( a measure of the structure-forming capacity of the carbon black) corresponds to the dependence of the physical-mechanical properties on the carbon black content.

Effect of Bromination on the Properties of Ethylene-Propylene-Diene Rubber in the Presence of Divinylbenzene

1995 ◽  
Vol 68 (5) ◽  
pp. 824-835 ◽  
Author(s):  
J. R. Yoon ◽  
Y. Ikeda ◽  
A. S. Hashim ◽  
S. Kohjiya
Keyword(s):  
Natural Rubber ◽  
Tensile Properties ◽  
Crosslink Density ◽  
Die Swell ◽  
Dicumyl Peroxide ◽  
Peroxide Curing ◽  
Ethylene Propylene Diene Rubber ◽  
Lower Torque ◽  
And Storage ◽  
Diene Rubber

Abstract The curing behavior and vulcanizate properties of EPDM and brominated EPDM (BEPDM) were compared using a dicumyl peroxide curing system. The BEPDM displayed lower torque and crosslink density, but better tensile properties than the EPDM. In the presence of divinylbenzene (DVB) coagent, all vulcanizates, i.e., EPDM, BEPDM, and their blends with natural rubber, had improved tensile properties. At low DVB concentration, the filler effect of DVB on the modulus enhancement was noticed. At high and comparable DVB concentration, both the BEPDM and NR/BEPDM blend showed significantly higher modulus (M100) and tensile strength than their EPDM counterparts. The BEPDM was also found to have higher crosslink density and storage modulus (E′) than the EPDM. This observation could be attributed to the better dispersion of DVB in the BEPDM and NR/BEPDM vulcanizates, as supported by TEM measurements. The TEM data is also consistent with the properties observed on the uncured mixes, in which the NK/BEPDM + DVB mix has favorable viscosity and die swell properties due to the more homogeneous DVB dispersion in the rubber phases. Thus, the bromination of EPDM has resulted in better processing and vulcanizate properties of the rubber and its blend with natural rubber.

Vulcanization of natural rubber by dicumyl peroxide in the presence of sulphur

1973 ◽  
Vol 38 (2) ◽  
pp. 408-416 ◽  
Author(s):  
B. Bakule ◽  
J. Honskus ◽  
J. Nedbal ◽  
P. Zinburg
Keyword(s):  
Natural Rubber ◽  
Dicumyl Peroxide

INFLUENCE OF La2O3 ADDITIONS ON CHEMICAL DURABILITY AND DIELECTRIC PROPERTIES OF BOROALUMINOSILICATE GLASSES

2012 ◽  
Vol 19 (06) ◽  
pp. 1250062 ◽  
Author(s):  
X. H. ZHANG ◽  
Y. L. YUE ◽  
H. T. WU
Keyword(s):  
Dielectric Properties ◽  
Chemical Durability ◽  
Tangent Loss ◽  
Frequency Range ◽  
Scanning Calorimetry ◽  
Glass Transition Temperatures ◽  
Weight Losses ◽  
Quenching Method ◽  
Scanning Electron

Boroaluminosilicate glasses containing La2O3 were prepared by the normal quenching method. The glass transition temperatures (Tg) were measured by differential scanning calorimetry (DSC). The structural role of RO was investigated by nuclear magnetic resonance (NMR). Chemical durability was evaluated by weight losses of glass samples after immersion in HC1 solution. High resolution scanning electron microscopy (HR-SEM) was used to examine the surface micrographs of corroded glass samples. The dielectric constant and tangent loss were measured in the frequency range 10–106 Hz. The results revealed that chemical durability and dielectric properties increased with increasing La2O3 content.

Aging of Natural Rubber Vulcanizates in the Presence of Dithiocarbamates

1959 ◽  
Vol 32 (3) ◽  
pp. 739-747 ◽  
Author(s):  
J. R. Dunn ◽  
J. Scanlan
Keyword(s):  
Stress Relaxation ◽  
Natural Rubber ◽  
Protective Action ◽  
Dicumyl Peroxide ◽  
Vulcanized Rubber ◽  
Aging Properties ◽  
Photochemical Aging ◽  
Natural Rubber Vulcanizates

Abstract The thermal and photochemical aging of extracted dicumyl peroxide-, TMTD (sulfurless)- and santocure-vulcanized rubber, in presence of a number of metal and alkylammonium dithiocarbamates, has been investigated by measurements of stress relaxation. The dithiocarbamates have a considerable protective action upon the degradation of peroxide- and TMTD-vulcanizates, but they accelerate stress decay in santocure-accelerated vulcanizates. The reasons for this behavior are discussed. It is suggested that the excellent aging properties of unextracted TMTD vulcanizates are due to the presence of zinc dimethyldithiocarbamate formed during vulcanization.

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