Permeability of Elastic Polymers to Hydrogen

1941 ◽  
Vol 14 (2) ◽  
pp. 444-448
Author(s):  
Theron P. Sager
Keyword(s):  
Molecular Structure ◽  
Natural Rubber ◽  
Activation Energies ◽  
Energy Requirements ◽  
Synthetic Materials ◽  
Lower Permeability ◽  
Increasing Temperature

Abstract The permeabilities to hydrogen of natural rubber, Perbunan, Neoprene G, Vistanex, Thiokol DX, and Pliofilm diminished in the order mentioned. The increase in rate of permeation with increasing temperature was exponential in all cases. Values for the activation energies or permeability for hydrogen were found to be 6,800 calories per mole for natural rubber and 8,400 to 9,500 calories per mole for the synthetic materials. The greater magnitude of the energy requirements of the latter indicates that their lower permeability may be attributed to differences in their molecular structure.

scholarly journals Detailed Study on the Mechanical Properties and Activation Energy of Natural Rubber/Chloroprene Rubber Blends during Aging Processes

2020 ◽  
Vol 2020 ◽  
pp. 1-7
Author(s):  
Quang Nguyen Trong ◽  
Hung Dang Viet ◽  
Linh Nguyen Pham Duy ◽  
Chuong Bui ◽  
Duong Duc La
Keyword(s):  
Mechanical Properties ◽  
Natural Rubber ◽  
Dynamic Loading ◽  
Dynamic Properties ◽  
Activation Energies ◽  
Rubber Matrix ◽  
Static Properties ◽  
Rubber Blends ◽  
Aging Conditions ◽  
Mechanical Aging

Selection of a suitable thermal aging process could render desirable mechanical properties of the rubbers or blended rubbers. In this work, the effect of the aging processes on the mechanical properties and activation energies of natural rubbers (NR) and NR/chloroprene rubbers (CR) blends with low CR contents (5–10%) was investigated. Three aging processes including heat aging (at 110°C for 22 hours), mechanical aging (under dynamic loading to 140% strain for 16000 cycles), and complex aging (heat and mechanical aging) were studied. The results revealed that the compatibility of CR in natural rubber matrix had a significant effect on the dynamic properties of the blended rubber and negligible effect on the static properties. The changes in activation energies of the blended rubber during aging processes were calculated using Arrhenius relation. The calculated changes (ΔUc, ΔUd, and ΔUT) in activation energies were consistent with the results of mechanical properties of the blended rubber. Interestingly, the change in activation energies using complex aging conditions (ΔUc) was mostly equal to the total changes in activation energies calculated separately from heat aging (ΔUT) and mechanical aging (ΔUd) conditions. This indicates that, in complex aging conditions, the heat and dynamic loading factors act independently on the properties of the blended rubber.

Relaxation Processes in Vulcanized Rubber. II. Secondary Relaxation Due to Network Breakdown

1963 ◽  
Vol 36 (2) ◽  
pp. 389-398 ◽  
Author(s):  
A. N. Gent
Keyword(s):  
Molecular Structure ◽  
Experimental Study ◽  
Natural Rubber ◽  
Relaxation Process ◽  
Relaxation Processes ◽  
Secondary Relaxation ◽  
Oxidative Deterioration ◽  
Vulcanized Rubber ◽  
Oxidation Inhibitors ◽  
Natural Rubber Vulcanizates

Abstract An experimental study is described of a “secondary” relaxation process in stretched vulcanizates, which becomes dominant after long periods at normal temperatures. It is shown to be affected markedly by the temperature, the atmosphere in which the test is conducted, and the presence of oxidation inhibitors. It is therefore attributed to oxidative deterioration of the molecular structure. In some vulcanizates, however, a similar or even greater relaxation is found to occur in vacuo, and this is attributed to the failure of specific crosslink structures. The extent of recovery on releasing the extended testpieces has also been investigated for a number of natural rubber vulcanizates.

Radiation-Sensitized Thermal Cracking of n-Butane. II. Ionic Reactions

1975 ◽  
Vol 53 (1) ◽  
pp. 92-97 ◽  
Author(s):  
Shingo Matsuoka ◽  
Takaaki Tamura ◽  
Keichi Oshima ◽  
Yunosuke Oshima
Keyword(s):  
Room Temperature ◽  
Material Balance ◽  
Thermal Cracking ◽  
Activation Energies ◽  
Chain Reactions ◽  
Ionic Reactions ◽  
Cracking Mechanism ◽  
High Yields ◽  
Increasing Temperature ◽  
First Time

Ionic reactions in the radiolysis of n-butane were studied at temperatures ranging from 17 to 548 °C. Ionic chain reactions were found for the first time to take part in the radiation-sensitized thermal cracking mechanism of hydrocarbon system.The isobutane and isobutene yields increased with increasing temperature and at 548 °C their G-values reached 31.2 and 12.1, respectively, though they were not formed by the thermal cracking of n-butane. The formation was completely suppressed by the addition of 0.15 mol% ammonia. They were produced with high yields irrespective of the kind of wall of the irradiation cells. It was concluded from these results that isobutane and isobutene were formed by homogeneous ionic chain reactions with activation energies. Part of the propane product was also found to have been formed by ionic chain reactions. From the effect of adding n-pentane on the yields of the ionic products, C4H9+ ion was inferred as the carrier ion.In the vicinity of room temperature, formation by ionic reactions of polymers with more than 14 carbon atoms was inferred from the material balance of the products from H2 to C14.

Rheological Behavior Characterization of Natural Rubber Containing Different Gel

2014 ◽  
Vol 970 ◽  
pp. 320-323 ◽  
Author(s):  
Saengchao Thongseenuch ◽  
Wirach Taweepreda ◽  
Krisda Suchiva
Keyword(s):  
Molecular Structure ◽  
Natural Rubber ◽  
Rheological Behavior ◽  
Loss Modulus ◽  
Natural Rubber Latex ◽  
Gel Structure ◽  
Gel Content ◽  
Molecular Weights ◽  
Branching Points

This research, natural rubber containing different gel contents were prepared by deproteinization and saponification treatment from high ammonium natural rubber latex. Deproteinization natural rubber was further treated as acetone extraction and then transesterification. It was founded that gel content and molecular weights of treated natural rubber were decreased and almost absented for transesterification treatment. Rheological respond on small amplitude oscillating shear (SAOS) and large amplitude oscillating shear (LAOS) deformation of treated natural rubber were captured by using rubber process analyzer (RPA 2000). Firs harmonic rheological properties, storage modulus, G and loss modulus, G decreased as gel content and molecular weight decreased. It was believed that gels, explicitly branching points, were destroyed after the natural rubber was deproteinized, transesterification, or saponification according to the molecular structure of natural rubber presumed by Tanaka et al, which functional groups contain protein and fatty acid are participated in branching to forming gel structure. It was concluded that gel content as the same as molecular structure of natural rubber could be characterized as rheological behavior.

scholarly journals Studies on the Transport of Aromatic Solvents through Filled Natural Rubber

2012 ◽  
Vol 2012 ◽  
pp. 1-11 ◽  
Author(s):  
Isaac O. Igwe ◽  
Obumneme E. Ezeani
Keyword(s):  
Particle Size ◽  
Weight Gain ◽  
Natural Rubber ◽  
Activation Energies ◽  
Free Energies ◽  
Snail Shell ◽  
Aromatic Solvents ◽  
Benzene Toluene ◽  
Powder Content ◽  
Shell Powder

The transport of three aromatic solvents (benzene, toluene and xylene) through snail shell powder filled natural rubber was studied at 313, 333, and 353 K by conventional weight-gain experiments. The effects of snail shell powder content, particle size, nature of solvent, and temperature on the transport characteristics of natural rubber were determined. The estimated Arrhenius activation energies for the processes of sorption, diffusion, and permeation showed that the activation energies were highest in xylene at all the filler contents investigated. The calculated enthalpies, and entropies of sorption were all positive for the solvents investigated. Similarly, the change in the estimated free energies of sorption were all positive; an indication of the non-spontaneity of the solubility of snail shell powder filled natural rubber in the aromatic solvents at 313 k.

scholarly journals Microstructure and Lamellae Phase of Raw Natural Rubber via Spontaneous Coagulation Assisted by Sugars

Polymers ◽  
2021 ◽  
Vol 13 (24) ◽  
pp. 4306
Author(s):  
Wanna Bai ◽  
Jie Guan ◽  
Huan Liu ◽  
Shihong Cheng ◽  
Fuchun Zhao ◽  
...  
Keyword(s):  
Molecular Structure ◽  
Molecular Weight ◽  
Biological Activity ◽  
Natural Rubber ◽  
Excellent Performance ◽  
Brown Sugar ◽  
Degree Of Crystallization ◽  
Traditional Process ◽  
Acid Coagulation ◽  
Environmental Challenge

Natural rubber (NR) as a renewable biopolymer is often produced by acid coagulation of fresh natural latex collected from Hevea brasiliensis. However, this traditional process is facing a huge economic and environmental challenge. Compared with the acid coagulation, spontaneous or microorganism coagulation is an ecofriendly way to obtain NR with excellent performance. To clarify the influence of different sugars on NR quality, several sugars were used to assist the coagulation process. Influence of different sugars on microstructure and cold crystallization were examined by 1H NMR, DSC, etc. The results indicated that sugars exhibit different biological activity on terminal components of fresh field latex and can influence the resultant molecular structure and basic properties. Brown sugar exhibits higher metabolic activity and is inclined to decompose the protein and phospholipids crosslinking compared with other sugars. The larger molecular weight of sugar molecule is beneficial for the formation of the stable α lamellae phase and higher overall degree of crystallization.

X-Ray Analysis of the Molecular Structure of Rubbers. X-Ray Diffraction of Amorphous Rubber

1952 ◽  
Vol 25 (2) ◽  
pp. 258-264 ◽  
Author(s):  
V. I. Kasatochkin ◽  
B. V. Lukin
Keyword(s):  
Molecular Structure ◽  
Natural Rubber ◽  
Crystalline Phase ◽  
X Ray Diffraction ◽  
Amorphous Halo ◽  
Crystallization Property ◽  
X Ray ◽  
Synthetic Rubber ◽  
Continuous Background ◽  
Diffraction Patterns

Abstract The potentialities of x-ray analysis of the molecular structure of rubbers can be widely extended by measuring the intensities of the amorphous halo and continuous background of scattering in the diffraction patterns of unstretched test-specimens. This method can be applied to the study of the effect of repeated stretching of rubbers. Questions pertaining to the fatigue of rubbers have immense importance now in the performance of rubber products. The methods of determining the crystallization of natural rubber and of measuring the intensity of the amorphous halo for synthetic rubber were employed for investigating the changes of the molecular structure of rubber due to repeated stretching. The crystallization of raw smoked-sheet rubber decreased as a result of fatigue; a similar phenomenon was observed for its vulcanizates. The vulcanizates which were stretched less than 300 per cent lost their crystallization property altogether after fatigue, and, at greater elongations, the content of the crystalline phase greatly decreased (see Figure 1).

Crystallization of Cis-Polyisoprenes in a Capillary Rheometer. II. The Effects of Experimental Parameters and Molecular Structure

1971 ◽  
Vol 44 (1) ◽  
pp. 12-28 ◽  
Author(s):  
V. L. Folt
Keyword(s):  
Molecular Structure ◽  
Molecular Weight ◽  
Natural Rubber ◽  
Crystallization Process ◽  
Complex Function ◽  
Capillary Rheometer ◽  
Optimum Conditions ◽  
Experimental Parameters ◽  
Static Conditions

Abstract Cis-polyisoprenes are readily crystallized under the pressure and orientation forces existing in a capillary rheometer. The ease at which crystallization can be effected is a complex function of the interrelationships existing among the temperature, the molecular weight, stereoregularity, and the dimensions of the capillary. For a given cis-polyisoprene and capillary, crystallization occurs more readily as the molecular weight is increased. Decreasing the diameter of the capillary and/or increasing the length of the capillary enhances the ease at which a given cis-polyisoprene can be crystallized. Using the optimum conditions presently available, natural rubber has been crystallized at 146° C. The ease at which crystallization is effected decreases drastically as the cis-1,4 content of the polyisoprene is reduced. Trans-1,4 and 3,4 are similarly effective in retarding the crystallization process and their effects are proportional to their concentrations in the molecular chains. However, polyisoprenes which will not crystallize under static conditions at −20° C are readily crystallized in the capillary rheometer at much higher temperatures.

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