Abstract:This work highlights the relationship of crosslink density, entanglement points and various sulfide crosslinks with the thermogenesis properties of natural rubber (NR). The impact of cross‐link and entanglement on thermogenesis properties was evaluated by heat build‐up test, swelling behavior, statistical thermodynamic calculation, and classic viscoelastic theory. It was found that cross‐link and entanglement points have “pinning” effect to the rubber chain, thus remarkably restricting the motion of the rubber… Show more
“…The thermodynamic statistical method is used to calculate the entropy and creep of the samples under dynamic load. The specific calculation process is as follows [ 51 ]: where N is the average number of chain segments between two adjacent cross-linking points, M s is the molar mass of a single chain segment in NR, M s = 105 g/mol, d 0 is the fluctuation range of the chain segment, l s is the Kuhn segment (generally take 0.76 nm in NR), n s is the number density of NR segments, n s = 5.46 nm −3 ; n e is the number of segments between two adjacent entanglement points [ 52 , 53 ].…”
Section: Resultsmentioning
confidence: 99%
“…This results in the molecular chain moving more easily in its internal structure, thus generating more energy during dynamic loading process. As for TSR 10CV, its dynamic mechanical properties have been significantly improved, which indicates that the cross-linked points can restrict the motion of rubber chains, and have the impeding and “pinning” effect during the deformation process of the rubber chain [ 51 ]. Tubular model theory also proves this.…”
It well-known that the superior performance of natural rubber (NR) compared to its synthetic counterpart mainly derives from nonisoprene components and naturally occurring network, which varies during the progress of the maturation and thereby results in technically graded rubber with different properties. However, identifying the roles of these two factors in the forming of excellent performance of NR is still a challenge as they change simultaneously during the maturation process. Here, influences of naturally occurring networking and nonisoprene degradation on the components, structures and properties of NR were systematically investigated by tailored treatments of maturation. It was found that the maturation-induced formation of natural network structure contributes to the increase in initial plastic value, Mooney viscosity and gel content for un-crosslinked NR, while the decomposition of nonisoprene components plays a dominant role in improving the mechanical properties of vulcanized NR. Stress-strain curve and Mooney-Rivlin analysis demonstrate that the biodegradation of the nonisoprene components significantly boost the vulcanization process, which significantly increases the number of chemical cross-link networks and effective cross-link density of the material, greatly improving the mechanical properties of NR vulcanizates. This resulted in the tensile strength of TSR 10CV being able to reach 22.6 MPa, which is significantly improved compared to 15.8 MPa of TSR 3CV. Evidenced by tubular model fitting, the increase in chemical cross-linking points effectively reduces the movable radius of the molecular chain under dynamic loading, making the molecular chain more difficult to move, which suppresses the entropy change under dynamic loading and consequently endows NR excellent dynamic mechanical properties. This resulted in a significant decrease in the temperature rising of TSR 10CV to 3.3 °C, while the temperature rising of TSR 3CV was still as high as 14.5 °C. As a minor factor, the naturally occurring network improves the mechanical properties of vulcanizates in the form of sacrificial bonds.
“…The thermodynamic statistical method is used to calculate the entropy and creep of the samples under dynamic load. The specific calculation process is as follows [ 51 ]: where N is the average number of chain segments between two adjacent cross-linking points, M s is the molar mass of a single chain segment in NR, M s = 105 g/mol, d 0 is the fluctuation range of the chain segment, l s is the Kuhn segment (generally take 0.76 nm in NR), n s is the number density of NR segments, n s = 5.46 nm −3 ; n e is the number of segments between two adjacent entanglement points [ 52 , 53 ].…”
Section: Resultsmentioning
confidence: 99%
“…This results in the molecular chain moving more easily in its internal structure, thus generating more energy during dynamic loading process. As for TSR 10CV, its dynamic mechanical properties have been significantly improved, which indicates that the cross-linked points can restrict the motion of rubber chains, and have the impeding and “pinning” effect during the deformation process of the rubber chain [ 51 ]. Tubular model theory also proves this.…”
It well-known that the superior performance of natural rubber (NR) compared to its synthetic counterpart mainly derives from nonisoprene components and naturally occurring network, which varies during the progress of the maturation and thereby results in technically graded rubber with different properties. However, identifying the roles of these two factors in the forming of excellent performance of NR is still a challenge as they change simultaneously during the maturation process. Here, influences of naturally occurring networking and nonisoprene degradation on the components, structures and properties of NR were systematically investigated by tailored treatments of maturation. It was found that the maturation-induced formation of natural network structure contributes to the increase in initial plastic value, Mooney viscosity and gel content for un-crosslinked NR, while the decomposition of nonisoprene components plays a dominant role in improving the mechanical properties of vulcanized NR. Stress-strain curve and Mooney-Rivlin analysis demonstrate that the biodegradation of the nonisoprene components significantly boost the vulcanization process, which significantly increases the number of chemical cross-link networks and effective cross-link density of the material, greatly improving the mechanical properties of NR vulcanizates. This resulted in the tensile strength of TSR 10CV being able to reach 22.6 MPa, which is significantly improved compared to 15.8 MPa of TSR 3CV. Evidenced by tubular model fitting, the increase in chemical cross-linking points effectively reduces the movable radius of the molecular chain under dynamic loading, making the molecular chain more difficult to move, which suppresses the entropy change under dynamic loading and consequently endows NR excellent dynamic mechanical properties. This resulted in a significant decrease in the temperature rising of TSR 10CV to 3.3 °C, while the temperature rising of TSR 3CV was still as high as 14.5 °C. As a minor factor, the naturally occurring network improves the mechanical properties of vulcanizates in the form of sacrificial bonds.
“…This is due to the fact that the protein in the natural latex is decomposed into amino acids after enzymatic hydrolysis, which is removed in layers after high-speed centrifugation 30 . The loss of protein will affect the vulcanization kinetics 31 , 32 , resulting in a weakening of the interaction force between the molecular chains 33 , an increase in the curl up-extension between the molecular chains and in heat dissipation. Figure 1 Temperature rise curve of FNR, CNR-1, CNR-2 and CNR-3.…”
Under high-speed strain, the thermogenesis performance of natural rubber products is unstable, leading to aging and early failure of the material. The quality of rubber latex and eventually that of the final products depends among others on the protein content. We found that when the protein is almost removed, the heat generated by the vulcanized rubber increases rapidly. After adding soy protein isolate to the secondary purification rubber, the heat generation of the vulcanized rubber is reduced, and the heat generation is the lowest when the added amount is 2.5–3.0 phr, which on account of protein promotes the construction of a vulcanization network and increases the rigidity of the rubber chain, resulting in a decrease in the potential frictional behavior of the rubber chain during the curl up-extension process.
“…The good dispersion and interfacial interaction between the nanosprings and the polymer chains can significantly decrease the hysteresis loss of composites [38]. The relationship of crosslink density and entanglement points with the thermogenesis properties of NR was proposed by Yue-Hua Zhan [39]. They found that the crosslink and entanglement points can hold the rubber chain to restrict the movement of the polymer chain and reduce heat generation.…”
Rubber composites are extensively used in industrial applications for their exceptional elasticity. The fatigue temperature rise occurs during operation, resulting in a serious decline in performance. Reducing heat generation of the composites during cyclic loading will help to avoid substantial overheating that most likely results in the degradation of materials. Herein, we discuss the two main reasons for heat generation, including viscoelasticity and friction. Influencing factors of heat generation are highlighted, including the Payne effect, Mullins effect, interface interaction, crosslink density, bond rubber content, and fillers. Besides, theoretical models to predict the temperature rise are also analyzed. This work provides a promising way to achieve advanced rubber composites with high performance in the future.
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