Glass Transition Temperature Of Rubber Research Articles

Impact of Sacrificial Hydrogen Bonds on the Structure and Properties of Rubber Materials: Insights from All-Atom Molecular Dynamics Simulations.

The inclusion of sacrificial hydrogen bonds is crucial for advancing high-performance rubber materials. However, the molecular mechanisms governing the impact of these bonds on material properties remain unclear, hindering progress in advanced rubber material research. This study employed all-atom molecular dynamics simulations to thoroughly investigate how hydrogen bonds affect the structure, dynamics, mechanics, and linear viscoelasticity of rubber materials. As the modified repeating unit ratio (β) increased, both interchain and intrachain hydrogen bond content rose, with interchain bonds playing a predominant role. This physical cross-linking network formed through interchain hydrogen bonds restricts molecular chain movement and relaxation and raises the glass transition temperature of rubber. Within a certain content of hydrogen bonds, the mechanical strength increases with increasing β. However, further increasing β leads to a subsequent decrease in the mechanical performance. Optimal mechanical properties were observed at β = 6%. On the other hand, a higher β value yields an elevated stress relaxation modulus and an extended stress relaxation plateau, signifying a more complex hydrogen-bond cross-linking network. Additionally, higher β increases the storage modulus, loss modulus, and complex viscosity while reducing the loss factor. In summary, this study successfully established the relationship between the structure and properties of natural rubber containing hydrogen bonds, providing a scientific foundation for the design of high-performance rubber materials.

Influence of environmentally friendly Phytonorman oils on the adhesive properties of frost-resistant rubbers based on nitrile butadiene rubber

The use of plasticizers based on esters of various acids most effectively improves the processing of rubber compounds and the frost resistance of NBR-based rubbers. In this work, as a plasticizer, products based on vegetable raw materials were tested - Phytonorman oils produced by the Biochemical Holding ORGKHIM, which are di- and triglycerides containing fatty acids of tall oil. Model rubber compounds based on BNKS-18AMN contained 10, 20, 30 wt. including eco-oils of the Phytonorman 212 and Phytonorman 213 brands, a mixture without oil and with 10 wt. including dibutyl phthalate (DBPh). To assess the effect of the type and dosage of eco-oils on the properties of rubbers and rubber compounds, methods for studying technological, physical-mechanical and adhesive properties were used. Determination of frost resistance, a comparison was made of methods for determining the glass transition temperature: differential scanning calorimetry (DSC) and thermomechanical analysis (TMA, Fourier). When using vegetable oils Phytonorman -212 and Phytonorman -213, the technological properties of rubber compounds are significantly improved compared to the mixture without oil and are on the same level with DBPH traditionally used in nitrile rubbers. It has been established that the introduction of Phytonorman 213 eco-oil into the formulations of rubber compounds based on BNKS 18AMN up to 10 wt. hours allows you to improve the technological parameters, as well as lower the glass transition temperature of rubber. At the same time, the physical and mechanical parameters and adhesive properties of vulcanizates are reduced by an average of 10%. It is also worth noting that rubbers with Phytonorman 213 oil are not inferior to nitrile rubbers with DBPh in terms of basic characteristics, and they are superior in adhesive properties by 27%.

ADHESION AND HYSTERETIC FRICTION OF TIRE TREAD RUBBERS HAVING PROCESS OILS WITH DIFFERENT AROMATIC CONTENT

ABSTRACT The extent of modification of wet grip of tire tread rubber by safe aromatic process oils has been the subject of controversy, as this property has conventionally been judged by indirect methods such as the loss factor at 0 °C. The present work aims to directly measure the dry and wet frictional behavior of rubbers containing various loadings of distillate aromatic extract (DAE) or treated distillate aromatic extract (TDAE) and to elucidate the contributions resulting from the adhesion and the hysteretic terms of friction. Physico-mechanical tests including rubber hardness, rubber–substrate work of adhesion, rubber–oil compatibility, hysteretic properties, and the rubber glass transition temperature were evaluated to disclose the underlying friction mechanisms. Interestingly, TDAE-containing rubbers presented a comparable or even better hysteretic friction not only at low oil loadings but also at high oil levels. As the loss factor properties of DAE and TDAE are very close to each other and there is the possibility of a crossover point within the frictional zone, care must be exercised not to merely rely on the values of tanδ at 0 °C in judging the preference of DAE or TDAE with regard to the wet grip performance.

Time Temperature Superposition Evaluation and Modeling for Container Closure System's Seal Performance at Low Temperatures.

There has been a growing interest in the assessment of container closure systems (CCS) for cold storage and shipment. Prior publications have lacked systematic considerations for the impact of dynamic time temperature transition on sealing performance associated with the viscoelastic characteristics of rubber stoppers used in container closure systems (CCSs). This paper demonstrates that sealing performance changes inherently and is fundamentally both time- and temperature-dependent. Our research results display this critical time temperature transition impact on CCS sealing performance by applying compression stress relaxation (CSR) on a rubber stopper for experimental data collection and modeling evaluation. The experimental results agree with modeling evaluation following Maxwell-Wiechert theory and the time temperature superposition based on the Arrhenius and Williams-Landel-Ferry methods. Both testing and modeling data show good consistency, demonstrating that the sealing force inevitably changes over time together with temperature transition because of the viscoelastic nature of the rubber stoppers. Our results show that compression seal force decreases quickly as temperature decreases. The significant loss of rubber stopper sealing force at lower temperature transitions could contribute significant risk to CCI at low storage and transport temperatures. Modeling evaluation, with a powerful capability to handle actual testing data, can be employed as a predictive tool to evaluate the time- and temperature-dependent sealing force throughout the entire sealed drug product life span. The present study is only applicable before reaching the rubber glass transition temperature Tg - a critical transition phase that can not be skipped/separated from real time temperature transition, and it will further determine the CCS sealing performance while approaching cryogenic temperature. The present work provides a new, integrated methodology framework and some fresh insights to the parenteral packaging industry for practically and proactively considering, designing, setting up, controlling, and managing stopper sealing performance throughout the entire sealed drug product life span.

Rolling friction of elastomers: role of strain softening.

We study the temperature and velocity dependency of rolling friction. Steel and PMMA cylinders are rolled on sheets of nitrile butadiene rubber (NBR), with and without filler, and fluoroelastomer (FKM) with filler. Measurements of the rolling friction are performed for temperatures between -40 °C and 20 °C, and for velocities between 5 μm s-1 and 0.5 cm s-1. For the unfilled NBR, a smooth rolling friction master curve is obtained using the bulk viscoelastic frequency-temperature shift factor aT. For the filled rubber compounds, a small deviation from the bulk viscoelastic shift factor is observed at low temperatures. The experimental data are analyzed using an analytical theory of rolling friction. For the filled compounds, good agreement with theory is obtained when strain softening is included, which increases the rolling friction by a factor ∼2 for the filled FKM and ∼3 for the filled NBR compounds. For the unfilled NBR, the maximum of the rolling friction occurs at higher sliding speeds than predicted by the theory. We discuss the role of the adhesive (crack-opening) contribution to the rolling friction, and the role of frozen-in elastic deformations as the rubber is cooled down below the rubber glass transition temperature.

Effect of interface on bulk polymer: control of glass transition temperature of rubber

In current paper, we demonstrated that molecular dynamics and glass transition of rubber can be controlled by constructing attractive interface between rubber matrix and fillers. Based on a combination of experiments and molecular simulations, it was revealed that interfacial segmental mobility was reduced and glass transition temperatures (Tgs) of epoxidized natural rubber (ENR) were significantly improved due to in situ polymerization of zinc dimethacrylate (ZDMA). During curing, ZDMA polymerizes in rubber matrix, resulting in the appearance of nanodispersion phases of poly-ZDMA (PZDMA). It was demonstrated that coordination interaction exists between epoxy groups and PZDMA in interfacial regions. Furthermore, using dynamic Monte Carlo simulations, it was observed that the interfacial regions that have highest content of epoxy groups exhibit lowest segmental mobility. Then, the increase of ZDMA content leads to the rise of the fraction of absorbed interfacial segments, and thus the Tgs of filled rubbers are improved.

Rubber friction: The contribution from the area of real contact.

There are two contributions to the friction force when a rubber block is sliding on a hard and rough substrate surface, namely, a contribution Fad = τf A from the area of real contact A and a viscoelastic contribution Fvisc from the pulsating forces exerted by the substrate asperities on the rubber block. Here we present experimental results obtained at different sliding speeds and temperatures, and we show that the temperature dependency of the shear stress τf, for temperatures above the rubber glass transition temperature Tg, is weaker than that of the bulk viscoelastic modulus. The physical origin of τf for T > Tg is discussed, and we propose that its temperature dependency is determined by the rubber molecule segment mobility at the sliding interface, which is higher than in the bulk because of increased free-volume effect due to the short-wavelength surface roughness. This is consistent with the often observed reduction in the glass transition temperature in nanometer-thick surface layers of glassy polymers. For temperatures T < Tg, the shear stress τf is nearly velocity independent and of similar magnitude as observed for glassy polymers such as PMMA or polyethylene. In this case, the rubber undergoes plastic deformations in the asperity contact regions and the contact area is determined by the rubber penetration hardness. For this case, we propose that the frictional shear stress is due to slip at the interface between the rubber and a transfer film adsorbed on the concrete surface.

Surface migration of carboxylic acid in styrene–butadiene rubber and its tribological consequences

AbstractSurface migration of the carboxylic acids (C10H21COOH, C11H23COOH, C12H25COOH, C15H31COOH, C16H33COOH, and C17H35COOH) in styrene–butadiene rubber (SBR) matrix was investigated together with its influence on tribological properties of the vulcanisates. Macro‐ and microtribological properties were correlated with properties that come from carboxylic acid addition to the samples. A plastifying effect was characterized by a decrease of the rubber glass transition temperature measured by the DSC method. Thickness of an acid bloom was directly determined from an indentation experiment and estimated from the DSC curve as well as from FTIR reflection spectra. Morphology of the bloom was studied using an AFM technique to characterize topography as well as microroughness of the bloom surface. Macrofriction was studied using block‐on‐ring tribometer. Microfriction was examined with a Nano Test apparatus, applying ball‐on‐plate contact. Despite correlation found between plastification, morphology, and bloom thickness on the one hand, and tribologic properties of the rubber on the other hand, influence of the chain length of carboxylic acids on properties of the samples still needs further qualitative investigation. Tribological properties of SBR modified with carboxylic acids are the result of balance of two opposite effects: plastification of rubber—leading to an increase of friction and lubrication—which causes a decrease of friction of the rubber. Apart from plastifying and lubrication effects microroughness also plays an important role in friction. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3368–3376, 2002

Tire Treadwear—The Joint Influence of Compound Properties and Environmental Factors

Abstract The wear rate of tire tread compounds depends jointly on the properties of the compound and on certain tire use or environmental factors. A previous publication clearly demonstrated the influence of rubber glass transition temperature (Tg) and carbon black (reinforcement) level under varying seasonal conditions (summer vs. winter testing) for several test courses with varying levels of pavement microtexture or abrasiveness. The variations in treadwear performance were interpreted in terms of two mechanisms of wear: (1) a highly elastic rupture deformation mechanism, rubber element vs. pavement asperity, called E-wear and (2) a highly viscous or plastic deformation mechanism (abrasive wear), called P-wear. The work of the previous publication has been extended by the use of the compound loss modulus (at 0 °C) as a single property to characterize tread compounds, that is superior to other typical properties (hardness, fatigue flex life, rupture energy). The varied dependence of wear on loss modulus (negative, zero, positive dependence) is explained on the basis of the two mechanisms. Thus an increase in loss modulus may have beneficial or detrimental effects on wear rate depending on the loss modulus level and certain environmental factors. The loss modulus is dependent on Tg, the carbon black level and morphology, the process oil content, as well as certain polymer microstructure properties such as cis/trans ratio and block (polymer) characteristics. The measured loss modulus is capable of being expressed in terms of components attributable to the above properties. The use of these components opens up the possibility of accurately characterizing tread compounds for their treadwear performance under selected environmental conditions and thus improve on the largely trial and error process of tread compound development.

A Review of Important Factors Affecting Treadwear

Abstract For any specific tire use condition, treadwear performance is influenced by three main factor categories: (1), tire construction; (2), tread materials; and (3), environmental and vehicle use conditions. Tire construction factors are—generic type (bias, belted-bias, radial), tread pattern groove void level, and geometric shape, i.e., aspect ratio. The relative importance of nominal variations in each of these factors for treadwear performance is 100, 46, and 39, respectively. Performance improves for a change from bias to radial; high to low groove void; and high to low aspect ratio. The combined influence of generic type, aspect ratio, and other internal construction features (e.g., belt stiffness) can be described by one parameter, the ratio of the treadband edgewise bending stiffness, KBo and the carcass (spring) stiffness, Kc. Treadlife is a direct linear function of this ratio. Treadwear compound or material performance is a function of the rubber glass-transition temperature (weighted avg. for blends), and the degree of reinforcement which is dictated by the carbon-black structure, surface area, and surface chemistry, in addition to the amount of black in the compound. The effect of each of these is a complex function of (i), the severity of tire use (e.g., cornering intensities) and (ii), the long term (seasonal) and short term (daily) environmental factors of pavement microtexture (0.01 mm scale) and ambient temperature. Precipitation directly influences microtexture level through a chemical etching of the pavement aggregate particles. Increased Tg and carbon-black reinforcement can improve or degrade treadwear performance depending on the external factors of pavement microtexture and ambient temperature and also on the general severity of tire use. Treadwear performance is also influenced by the degradation characteristics of the tread compound. Degradation propensity is influenced by crosslink structure and general susceptibility to oxidation. High wear rates are encountered for compounds cured with high-sulfur cure systems (high crosslink polysulfide content) and with low levels of antioxidant. Substantial evidence exists to support a “two-mechanism” theory of rubber abrasion. Mechanism 1 is predominant when the rubber tread element experiences highly elastic surface deformations induced by frictional contact with the pavement asperities. Rubber particles are removed by a tear-tensile rupture process. Mechanism 2 is predominant when the rubber experiences a plastic or rigid body type of contact with the pavement asperities. This contact exists on a smaller scale (reduced deformation domain) and particles are removed by an abrasive-cutting action. Mechanism 1 is called “E-Wear”; Mechanism 2 is called “P-Wear”. E-wear is favored by high temperatures, low microtexture pavements, soft (low Tg) compounds with low reinforcement levels. P-wear is favored by high microtexture, low ambient temperatures, hard (high Tg) compounds with high levels of reinforcement. The confusing treadwear performance frequently encountered for compounds—when tested at different locations, at different times, with substantial treadwear index changes, and outright reversals—can be rationally explained on the basis of a shift of the predominant mechanism. These shifts are due to changes in the environmental factors and tire-use severity as tires are tested at different locations over varying seasonal periods. Microtexture follows a seasonal cyclic pattern; high in winter and low in summer. Ambient temperature follows an opposite cyclic pattern. Short term changes (daily ) in both microtexture and temperature occur within the long-term seasonal periods. These changes have to be accommodated in interpreting treadwear performance.