Internal Energy Contribution to the Elasticity of Natural Rubber

1970 ◽  
Vol 43 (2) ◽  
pp. 270-281 ◽  
Author(s):  
Mitchel Shen
Keyword(s):  
Natural Rubber ◽  
Elastic Stress ◽  
Tensile Elongation ◽  
Relative Energy ◽  
Rubber Elasticity ◽  
Energy Contribution ◽  
Constant Length ◽  
Shear Moduli ◽  
Energetic Stress ◽  
Apparent Strain

Abstract It has recently been noted by a number of workers that the relative energy contribution, fe/f, to the elastic stress of rubberlike materials appears to depend on the extension ratio at which thermoelastic measurements were carried out. This apparent strain dependence is in contradiction to the free energy additivity principle of the statistical theory of rubber elasticity. In this paper we resolve this problem by determining fe/f from the temperature coefficient of shear moduli. The shear moduli were not directly determined from measurements of shear, but calculated from tensile elongation data. This method circumvents the difficulty encountered in directly obtaining the relative energy contribution from stress—temperature data. Both constant length and constant stress thermoelastic measurements were used to obtain fe/f. A series of natural rubber samples, crosslinked in the presence of various amounts of n-hexadecane, were investigated. It is found that the relative energy contribution to the elasticity of natural rubber is 0.18. Changes in inter-molecular interactions, brought about by the incorporation of diluents, produce no variation in the value of fe/f. This observation supports the hypothesis that the energetic stress in rubber elasticity is wholly attributable to intrachain energies of the network chains.

Energy Contribution to Rubber Elasticity

1968 ◽  
Vol 39 (11) ◽  
pp. 4937-4943 ◽  
Author(s):  
Mitchel Shen ◽  
Paul J. Blatz
Keyword(s):  
Rubber Elasticity ◽  
Energy Contribution

scholarly journals Assessing the Effects of Acupuncture by Comparing Needling the Hegu Acupoint and Needling Nearby Nonacupoints by Spectral Analysis of Microcirculatory Laser Doppler Signals

2011 ◽  
Vol 2011 ◽  
pp. 1-9 ◽  
Author(s):  
Hsin Hsiu ◽  
Wei-Chen Hsu ◽  
Chia-Liang Hsu ◽  
Shih-Min Huang
Keyword(s):  
Blood Flow ◽  
Spectral Analysis ◽  
Relative Energy ◽  
Laser Doppler ◽  
Therapeutic Effects ◽  
Energy Contribution ◽  
Doppler Flowmetry ◽  
Vascular Activity ◽  
Doppler Signals ◽  
Present Design

We aimed to assess the effects of acupuncture by analyzing the frequency content of skin blood-flow signals simultaneously recorded at the Hegu acupoint and two nearby nonacupoints following acupuncture stimulation (AS). Laser Doppler flowmetry (LDF) signals were measured in male healthy volunteers in two groups of experiments: needling the Hegu acupoint (n= 13) and needling a nearby nonacupoint (control experiment;n= 10). Each experiment involved recording a 20 min baseline-data sequence and two sets of effects data recorded 0–20 and 50–70 min after stopping AS. Wavelet transform with Morlet mother wavelet was applied to the measured LDF signals. Needling the Hegu acupoint significantly increased the blood flow, significantly decreased the relative energy contribution at 0.02–0.06 Hz and significantly increased the relative energy contribution at 0.4–1.6 Hz at Hegu, but induced no significant changes at the nonacupoints. Also, needling a nearby nonacupoint had no effect in any band at any site. This is the first time that spectral analysis has been used to investigate the microcirculatory blood-flow responses induced by AS, and has revealed possible differences in sympathetic nerve activities between needling the Hegu acupoint and its nearby nonacupoint. One possible weakness of the present design is that different De-Qi feelings following AS could lead to nonblind experimental setup, which may bias the comparison between needling Hegu and its nearby nonacupoint. Our results suggest that the described noninvasive method can be used to evaluate sympathetic control of peripheral vascular activity, which might be useful for studying the therapeutic effects of AS.

Mechanical and Swelling Behavior of Double Networked Natural Rubber Cured Using a New Binary Accelerator System

2007 ◽  
Vol 80 (5) ◽  
pp. 809-819 ◽  
Author(s):  
C. V. Marykutty ◽  
G. Mathew ◽  
Sabu Thomas
Keyword(s):  
Mechanical Properties ◽  
Natural Rubber ◽  
Transverse Direction ◽  
Tensile Elongation ◽  
Longitudinal Direction ◽  
Chain Orientation ◽  
Swelling Studies ◽  
Natural Rubber Vulcanizates ◽  
Double Networks ◽  
Accelerator System

Abstract The concept of double networks, which impart chain orientation to elastomers, is a rather new idea. Double networks were induced in natural rubber vulcanizates cured with different accelerator systems. Double networked natural rubber with different extensions cured with N-cyclohexyl benzothiazyl sulphenamide (CBS) and 1-phenyl 5-ortho -tolyl 2,4 dithiobiuret was studied and the effect of extension on the mechanical properties and swelling was analyzed. The extent of chain orientation was analyzed through anisotropic swelling studies. The modulus, tensile strength and tear strength showed an increase with increased residual extension ratio. The effect was more predominant in the longitudinal direction than in the transverse direction. The ultimate tensile elongation showed a slight deterioration. It was revealed that the formation of double networks with higher residual extension ratios restricted the entry of the solvent. Based on the studies it was concluded that residual extension has a profound effect in determining the final properties of vulcanizates.

scholarly journals Mechanical Properties of Phormium Tenax Reinforced Natural Rubber Composites

Fibers ◽  
2021 ◽  
Vol 9 (2) ◽  
pp. 11
Author(s):  
Sivasubramanian Palanisamy ◽  
Kalimuthu Mayandi ◽  
Murugesan Palaniappan ◽  
Azeez Alavudeen ◽  
Nagarajan Rajini ◽  
...  
Keyword(s):  
Natural Rubber ◽  
Tensile Elongation ◽  
Natural Fibers ◽  
Rubber Composites ◽  
Elongation At Break ◽  
Roll Mill ◽  
Natural Rubber Composites ◽  
Mechanical Tensile ◽  
American Society ◽  
Tear Properties

The introduction of natural fibers as a filler in a natural rubber (NR) matrix can be of relevance for their eco-friendly and sustainable nature as the substitute for carbon-based fillers. In this work, short Phormium tenax fibers were introduced in random orientation into a NR matrix in different lengths (6, 10, and 14 mm) and various amounts (10, 20, and 30%, taking 100 as the NR weight). The composite was fabricated using a two-roll mill according to American Society for Testing and Materials (ASTM) D3184-11 standard. Several properties were determined, namely tensile and tear characteristics, hardness, and abrasion resistance. The results suggest that the shortest fiber length used, 6 mm, offered the best combination between loss of mechanical (tensile and tear) properties and hardness and the most acceptable resistance to abrasion, with the properties increasing with the amount of fibers present in NR. As a consequence, it is indicated that a higher amount of fibers could be possibly introduced, especially to achieve harder composites, though this would require a more controlled mixing process not excessively reducing tensile elongation at break.

scholarly journals Synergistic Mechanisms Underlie the Peroxide and Coagent Improvement of Natural-Rubber-Toughened Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) Mechanical Performance

Polymers ◽  
2019 ◽  
Vol 11 (3) ◽  
pp. 565 ◽  
Author(s):  
Xiaoying Zhao ◽  
Katrina Cornish ◽  
Yael Vodovotz
Keyword(s):  
Natural Rubber ◽  
Mechanical Performance ◽  
Tensile Elongation ◽  
Peroxy Radical ◽  
Reactive Extrusion ◽  
Organic Peroxide ◽  
Industrial Applications ◽  
Rubber Toughening ◽  
Wide Range ◽  
Rubber Toughened

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) is a promising bio-based and biodegradable thermoplastic with restricted industrial applications due to its brittleness and poor processability. Natural rubber (NR) has been used as a toughening agent, but further physical improvements are desired. In this study, rubber toughening efficiency was significantly improved through the synergistic use of a trifunctional acrylic coagent and an organic peroxide during reactive extrusion of PHBV and NR. The rheological, crystallization, thermal, morphological, and mechanical properties of PHBV/NR blends with 15% rubber loading were characterized. The peroxide and coagent synergistically crosslinked the rubber phase and grafted PHBV onto rubber backbones, leading to enhanced rubber modulus and cohesive strength as well as improved PHBV–rubber compatibility and blend homogeneity. Simultaneously, the peroxide–coagent treatment decreased PHBV crystallinity and crystal size and depressed peroxy-radical-caused PHBV degradation. The new PHBV/NR blends had a broader processing window, 75% better toughness (based on the notched impact strength data), and 100% better ductility (based on the tensile elongation data) than pristine PHBV. This new rubber-toughened PHBV material has balanced mechanical performance comparable to that of conventional thermoplastics and is suitable for a wide range of plastic applications.

Introductory remarks

1976 ◽  
Vol 351 (1666) ◽  
pp. 297-299
Keyword(s):  
Natural Rubber ◽  
Main Chain ◽  
Practical Interest ◽  
Rubber Elasticity ◽  
Elastic Behaviour ◽  
Essential Property ◽  
Present Position ◽  
Synthetic Rubber ◽  
Identical Material ◽  
The One

The purpose of this short conference is twofold. First to give the non-specialist a review of the present position in a subject of both theoretical and practical interest, and second to bring together workers whose methods of approach are different. The term rubber elasticity derives from the remarkable properties first observed in natural rubber ‒ a product obtained commercially from the tree Hevea brasiliensis , but also occurring widely in other plants and trees. This material is, chemically, cis -polyisoprene, and its main chain consists of several thousand carbon atoms. Once it was realized that these properties are due essentially to the long-chain molecular structure of the rubber, the way was, in principle, open for the synthesis either of an identical material or of substances having similar structures. Out of this has grown the large synthetic rubber industry which today offers a range of products broadly comparable with natural rubber, from which the manufacturer of rubber goods selects according to price and detailed properties. For the purpose of this conference we shall be content to group all these materials together under the general title of rubber, because we shall be concerned with the one essential property they share ‒ a type of elastic behaviour which we describe as ‘rubber elasticity’.

Method-Induced Differences of Energy Contributions in Women’s Kayaking

2018 ◽  
Vol 13 (1) ◽  
pp. 9-13
Author(s):  
Yongming Li ◽  
Margot Niessen ◽  
Xiaoping Chen ◽  
Ulrich Hartmann
Keyword(s):  
Relative Energy ◽  
Oxygen Deficit ◽  
Energy Calculation ◽  
Longitudinal Assessment ◽  
Energy Contribution ◽  
Training Experience ◽  
Incremental Exercise Test ◽  
Accumulated Oxygen Deficit ◽  
Anaerobic Energy ◽  
Gas Metabolism

Context: Different relative aerobic energy contribution (WAER%) has been reported for the 2 women’s Olympic kayaking disciplines (ie, 200 and 500 m). Purpose: To investigate whether the adopted method of energy calculation influences the value of WAER% during kayaking time trials. Methods: Eleven adolescent female kayakers (age 14 ± 1 y, height 172 ± 4 cm, body mass 65.4 ± 4.2 kg, VO2peak 42.6 ± 4.9 mL·min−1·kg−1, training experience 1.5 ± 0.3 y) volunteered to participate in 1 incremental exercise test and 2 time trials (40 and 120 s) on the kayak ergometer. A portable spirometric system was used to measure gas metabolism. Capillary blood was taken from the ear lobe during and after the tests and analyzed for lactate afterward. The method of modified maximal accumulated oxygen deficit (m-MAOD) and the method based on the fast component of oxygen-uptake off-kinetics (PCr-La-O2) were used to calculate the energy contributions. Results: The anaerobic energy portions from m-MAOD were lower than those from PCr-La-O2 in the 40-s (41.9 ± 8.8 vs 52.8 ± 4.0 kJ, P > .05) and 120-s (64.1 ± 27.9 vs 68.2 ± 10.0 kJ, P > .05) time trials, which induced differences of WAER% between m-MAOD and PCr-La-O2 (36.0% vs 30.0% in 40 s, P > .05; 60.9% vs 57.5% in 120 s, P > .05). Conclusions: The reported different WAER% in women’s Olympic kayaking could be partly attributed to the adopted method of energy calculation (ie, m-MAOD vs PCr-La-O2). A fixed method of energy calculation is recommended during the longitudinal assessment on the relative energy contribution in women’s Olympic kayaking.

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