Hydrogen (H2) applications have received extensive attention for the preparation of the energy transition. Thus, it is essential to understand the H2 gas transport properties in elastomers and degradation of elastomers under high pressure and high temperature. However, the effect of pressure on the gas sorption of H2 in fluoroelastomers (FKMs) as well as its relation to molecular properties of the gas remain unclear. In this work, hydrogen gas solubility in FKM as a function of pressure was carried out and a linear relationship was observed consistent with the Henry’s Law. A correlation between the solubility coefficient of H2 gas and critical temperature was quantitatively established. The temperature dependence of the solubility coefficient of H2 in FKM at 3000 kPa as well as the correlation between heat of sorption and molecular property of the gas were investigated. Furthermore, the diffusion coefficient and permeability coefficient of H2 gas in FKM were systematically studied and compared with those of N2 and CO2 systems. Similarly, degradation of the fluoroelastomer revealed that increasing aging temperature, aging pressure and aging time have deleterious effects on degradation of FKM materials in hydrogen, more than those in nitrogen. Spectroscopic analysis indicate abstraction of fluorine and crosslinking. Thus, this study enhances our current understanding of the H2 gas transport properties in FKM and degradation of FKM under high pressure and temperature, and will provide us an insight into elastomer performance under H2 environment to design superior formulations.Abstract
This study aimed to develop natural rubber/butadiene rubber (NR/BR) composites with low hardness, high abrasion resistance, and flame retardancy. Two flame-retardant plasticizers - triisopropyl phenyl phosphate with viscosities of 50 mm2 /s (IPPP-50) and 95 mm2/s (IPPP-95) - were incorporated into NR/BR matrices. We systematically compared the effects of IPPP-50 and IPPP-95 on the composite's compatibility, hardness, flame resistance, and abrasion resistance. The results demonstrated that IPPP-95 exhibited superior compatibility with the rubber matrix. The incorporation of IPPP-95 effectively reduced composite hardness while maintaining abrasion resistance and enhancing flame retardancy. However, when used as the sole additive, IPPP-95 provided insufficient flame retardancy for NR/BR composites. Subsequent formulation optimization combining IPPP-95 with aluminum diethylhypophosphite and aluminum hypophosphite synergistically achieved reduced hardness, improved flame resistance, and preserved abrasion resistance. Notably, IPPP-95 showed negligible impact on the tensile strength of NR/BR composites. This phenomenon can be attributed to two mechanisms: (1) enhanced molecular chain mobility and (2) increased strain-induced crystallinity, both of which indirectly contribute to maintaining abrasion resistance. Additionally, IPPP-95's lubricating effect further preserved the composite's wear resistance.Abstract
Under large-amplitude oscillatory shear, filled rubbers usually exhibit a rheological behavior characterized by a linear-nonlinear dichotomy. Specifically, while the amplitude of the stress deviates significantly from the linear dependence on strain, the time-dependent stress response remains linear and sinusoidal. This study seeks to unravel the origin of this complex rheological phenomenon, focusing on the evolution of the linear-nonlinear dichotomy under various dynamic and static strain conditions. Our results reveal that the linear-nonlinear dichotomy in rheological responses of filled rubbers is not due to a mismatch between filler network recovery time and dynamic perturbation time, as commonly believed. We have observed that even at extremely low frequencies (10-5 Hz), which far exceed the typical recovery time frame of the broken filler network in a polymer matrix, there is no sign of a transition in the stress response from sinusoidal to nonsinusoidal behavior. These results challenge the conventional understanding of the dichotomy in filled rubber rheology, suggesting that it is far more complex than previously thought.Abstract
The maturation process is an important means of industrially regulating natural rubber. It is of great significance to understand the change rule of properties in the maturation process for the production and processing of natural rubber. In this paper, the effects of maturation time on the non-rubber components, microstructure and macroscopic properties of natural rubber were studied. The test results of nitrogen content showed that the protein content of natural rubber decreased with the extension of maturation time. The results of the solid nuclear magnetic resonance and gel content test showed that the molecular chain entanglements of the rubber increased and the natural network structure increased during the maturation process. The test results of the vulcanisation curves showed that the scorching time of the rubber was significantly shortened with the prolongation of the maturation time; The test results of cross-linking density showed that the cross-linking density decreased with the extension of maturation time. The test results of compression heat build-up and Akron abrasion showed that the heat build-up of the rubber increased and the wear resistance deteriorated during the maturation process. In addition, when the maturation time was 2 days, the rubber had the highest molecular weight, highest storage modulus, smallest loss factor, best dispersion of carbon black, and best mechanical properties and aging resistance.Abstract
In order to further the design and use of flame retardants with a lower environmental impact, a large number of available, eco-friendly, bio-based and biocompatible flame retardants have begun to be used. This study explores the synthesis of a novel phosphorus-nitrogen synergistic flame retardant (PMO) using bio-sourced phytic acid (PA) and enteromorpha prolifera (EP), along with mineral-based modified sepiolite (OSEP) and melamine (MEL), to investigate its flame retardant and smoke suppression effects on ethylene-propylene-diene monomer rubber (EPDM). Experimental results demonstrate that compared to pure EPDM, EPDM with 50 phr PMO achieves a V-0 rating in UL-94 tests, with an increased Limiting Oxygen Index (LOI) to 31.1 %, Time to Ignition (TTI) extended from 6 s to 29 s, Peak Heat Release Rate (PHRR) reduced by 55.8 %, Total Heat Release (THR) decreased by 69.4 %, particularly Total Smoke Production (TSP) reduced by over 73 %, significantly enhancing the flame retardant performance of the rubber composite material. After loading with modified seafoam, the highly efficient PMO flame retardant was successfully prepared, which has a broad application prospect in general rubber materials.Abstract
Heterogeneity of microstructure is a key factor for dynamic-mechanical behavior of materials. For rubber, mostly development of domains consisting of different polymer types allow us to design high-tech materials. Such polymer blend systems can combine rubber-specific benefits of decisive significance for application performance. Generally, fillers like carbon black or silica are used to enhance ultimate properties, like tensile strength or wear resistance. In polymer blends, distribution of filler particles toward domains of various composition defines the quality of the material used. An already proven model for determining filler distribution based on experimental measurements was optimized and applied for the blend system made of natural rubber and styrene butadiene rubber, whose blend ratio, filler content, and type were varied systematically in fine steps. The model focuses on temperature function of loss modulus at glass transition, of which heterogeneous blend systems have two separated at different temperatures. The modulus contribution occurring in the temperature range between these was previously interpreted as a small layer between domains of different types called interphase, which is preferentially enriched with filler before other phases and therefore has very high filler loads. However, investigations using atomic force microscopy have shown no concentration of filler particles at phase boundaries but decreasing domain size in areas of high filler concentration. Fining of phase morphology due to filler particles indicates compatibility improvement of both polymers, so that the filler acts as a compatibilizer. The influence of the filler on miscibility is tremendous. In silica-filled blend systems, instead of two separate glass transitions with filler-enhanced interphase contribution between a single very wide plateaulike glass transition occurs at high filler loads.ABSTRACT
Heat-triggered shape memory polymers, consisting of plasticized polyvinyl chloride (PVC) and NBR, were prepared by dynamic vulcanization. A model describing the shape memory behavior of PVC/NBR thermoplastic vulcanizate (TPV) has been proposed. The favorable interfacial compatibility between PVC and NBR serves as the foundation for the noteworthy mechanical and shape memory properties of TPV. Field-emission scanning electron microscope images revealed the uniform distribution behavior of the coordination crosslinked NBR particles within the PVC matrix, forming a characteristic “sea-island” microstructure, whereas the NBR particle sizes ranged 1∼8 μm. The mechanical results indicate that the continuous PVC phase plays a primary role in determining the mechanical properties of the prepared TPV. A strong interfacial interaction between the two phases is crucial for maintaining the temporary shape and storing the recovery driving force. The shape memory behavior of PVC/NBR TPV was examined, demonstrating rapid recovery (<15 s) in various shapes. The mass ratio of PVC to NBR also influenced the shape memory properties obviously, with the best-integrated property achieved at the weight ratio of 80/20. Under optimal deformation temperature and recovery temperature, high shape-fixity (>90%) and shape-recovery (>90%) ratios could be achieved. This research provides the insight into the preparation and properties of PVC/NBR TPV as heat-triggered shape memory polymers.ABSTRACT
We present an in-depth exploration of the thermal conductivity of four commonly used rubbers in the tire industry: polyisoprene (PI), polybutadiene (PB), styrene-butadiene rubber (SBR), and butyl rubber (IIR), utilizing reverse nonequilibrium molecular dynamics (RNEMD) simulations. The thermal behavior of rubber materials holds significant importance across diverse industrial sectors, and understanding their thermal conductivity is crucial for optimizing their functionality. Our approach involves employing the atomic level details of the system to establish the factors governing heat transfer, thereby delving into the intricacies of thermal conductivity. By conducting RNEMD simulations under varying degrees of mechanical strain, we investigate the influence of strain on thermal conductivity. The simulations reveal essential insights into the anisotropic nature of thermal conductivity within rubber materials, elucidating how chain orientation and flexibility impact the directionality of heat propagation. Results from these simulations provide valuable insights into thermal conductivity profiles, mechanisms of heat transport, and the effects of strain and temperature on thermal properties. These findings enhance our understanding of atomic-scale dynamics dictating heat conduction in rubber polymers. Moreover, we emphasize the potential to tailor the thermal properties of rubber materials for specific applications by utilizing insights gathered from these simulations.ABSTRACT
The rubber industry is rife with problems associated with blooming of additives to the surface of rubber products; for sulfur blooms especially, this has led to the use of other forms of sulfur, particularly expensive insoluble sulfur. To tackle this issue, sulfur-encapsulated alginate beads were used in this study and the blooming characteristics in NR were compared with soluble and insoluble sulfur. At testing temperatures of 100 and 120 °C, sulfur-encapsulated beads yielded less sulfur blooming than soluble sulfur. The beads also showed relatively less blooming than insoluble sulfur at 120 °C, whereas the two were comparable at 100 °C. Statistically, the tensile strength of vulcanized rubber with the beads (mean ± SD, 18.9 ± 2.5 MPa) was not significantly different (p = 0.067) from that with insoluble sulfur (22.2 ± 2.5 MPa), although lower (p = 0.011) than that with soluble sulfur (23.3 ± 0.7 MPa). Altogether, the study results showed that the sulfur-encapsulated alginate beads could be used as a substitute for soluble sulfur and insoluble sulfur in rubber compounding.ABSTRACT
Although a series of studies have introduced noncovalent branched networks to enhance the properties of polyisoprene (PIP) based on a structural mimic of NR, it is still a challenge to reveal the relationship between properties of modified PIP and the aggregation behaviors of end groups. Herein, the two quadruple hydrogen bonding motifs 2-ureido-4-1[H]-pyrimidinones (UPy) and α-alanine tetrapeptide (4A) were introduced into the end of model PIP polymers. Branched networks of terminal groups were prepared by self-assembly of quadruple hydrogen bonding motifs, thereby elucidating the key role of the terminal structures in the PIP chain. Previous work has demonstrated that the branched network intensifies the entanglement between polymer chains, resulting in higher modulus and shear viscosity of the branched polymers than the linear polymers. Because of the stable aggregation of 4A, the mechanical properties of PIP-4A are superior to those of PIP-UPy. Rheological analysis and two-dimensional Fourier transform infrared spectroscopy collaboratively demonstrate that PIP-UPy and PIP-4A both exhibit two-step dissociation processes. These results expand our understanding of the role of the aggregation structures of PIP terminals and provide insight into the generic design of mechanically strong rubber.ABSTRACT
The experimental determination of the pure elastic response of filled rubbers remains a major challenge due to the very long times required for the viscoelastic effects to dissipate. Starting from an expedient proposed in 1930, we deal with an experimental procedure capable of dissipating viscoelastic effects in reasonably short times, to obtain a point-wise estimation of the intrinsic elastic response of the material.ABSTRACT
We introduce an innovative approach for predicting optimal vulcanization times in SBR-based rubber products to eliminate internal defects like blow holes and achieve a uniform structure. Unlike conventional rheological methods, which may overlook factors like product shape and thermal conductivity, our method visualizes the vulcanization process within a wedge-shaped sample to identify the equivalent vulcanization time [teq at blow point (BP)] required to prevent defects. Findings show that higher accelerator-to-sulfur (A/S) ratios and total content (A+S) accelerate vulcanization and reduce blow-related issues, with unique behavior in semiefficient vulcanization (s-EV, A/S ratio ∼ 1.1). The teq at BP emerges as a key indicator of vulcanization uniformity, potentially enhancing quality control beyond rheometer data alone. The blow-hole prevention area appears material dependent, indicating further study is needed to refine rubber formulations and vulcanization strategies. This approach complements traditional methods, offering enhanced precision in optimizing vulcanization for complex rubber products.ABSTRACT
The service life of rubber products lacks a comprehensive evaluation of the factors that influence rubber fatigue life and an accurate prediction of their fracture behavior. To address this gap, we developed a protocol to investigate the working conditions that affect the fatigue behavior of rubber and document changes in the fracture area during its fatigue life. We subjected natural rubber specimens to various fatigue tests under changing conditions, including temperature, deformation, aging, sample geometry and frequency. For each experimental setup, we conducted a detailed examination of the fracture area, recording the rate and direction of crack propagation. Our observations revealed that the applied load within a dynamic deformation range substantially impacted fatigue life, providing valuable insights into the effects of these factors on material behavior. Furthermore, our macromorphological analyses unveiled distinct characteristics of crack propagation rates and directions associated with each factor at different stages of the fatigue life of the rubber samples. Additionally, the surface temperature elevated as deformation levels increased, highlighting the need to consider this factor in conjunction with geometric, mechanical, and environmental influences on rubber fatigue life. The combined effect of these parameters has the potential to either extend or shorten the fatigue life of natural rubber.ABSTRACT
This effort focused on events taking place during the co-vulcanization of rubber compounds comprising ground rubber particles (GRPs) collected from end-of-life tires and assumed to be responsible for the commonly observed losses in key physical properties. Of greatest impact was the diffusion of cure ingredients (sulfur and cure accelerators) into the GRPs, causing additional crosslinking, low interfacial adhesion between the GRPs and the host matrix, and the formation of failure-promoting stiffness gradients. Their involvement and overall impact on failure properties were also assessed via finite element analysis. Based on this more detailed understanding, new methods were identified and tested in laboratory experiments that suggest successful novel GRP-based recycling pathways involving labyrinthine materials such as graphene oxide. These methods seem to offer promise compared with the merit of pyrolysis, which only recently is undergoing vigorous evaluations by the tire industry.ABSTRACT
This study explores the impact of carbon black on the structure-property relationships of natural rubber during thermo-oxidative ageing. Natural rubber samples containing 27% mass of carbon black were subjected to ageing in air at temperatures ranging from 70 °C to 115 °C for up to 270 days. The ageing process was monitored in terms of oxygen consumption, swelling, and tensile testing. Results revealed a substantial reduction in crosslink density, highlighting chain scission as the dominant process. Tensile properties were significantly affected, showing decreases in modulus, elongation at break, and stress at break. A comparison with previous studies on unfilled natural rubber shed light on the role of carbon black during oxidation. Our findings suggest that carbon black plays a minor role in macromolecular network modifications for similar exposure conditions. More specifically, we analyze the validity of structure–property relationships between the average crosslink density and mechanical properties during thermo-oxidative ageing regardless of whether the elastomer contains carbon black filler. These results illustrate a new strategy for studying the aging of filled elastomers.Abstract
I was honored by the award of the 2024 Charles Goodyear Medal 42 yr after I received my PhD in plant biology and thank Drs Judit Puskas and Adel Halasa for their nominations and support over several yr as well as the selection committee. As the second woman and first biologist to receive this recognition, I will describe some of the basic and applied research that led me to my admiration of plants and subsequent focus on the biological and geographical diversification of the global natural rubber (NR) supply. My focus across federal, industrial, and academic appointments has continuously been on making research meaningful, and my basic research has always been tethered to strongly applied research translation and goals. Achieving domestic rubber production means that the entire value chain from seed to product must be validated, and every part presented and still presents specific research and development challenges. Fortunately, core scientific and engineering principles are constant and readily adaptable to new areas. Many people were happy to advise me in areas in which I had no formal training. My innovative research has led to 10 start-up companies, about 36 issued or pending patents, many with student inventors, over 310 published papers, and an H-index of 51. Working in NR is not only very interesting but has left me with an unshakable belief that my research is meaningful. Failure is not an option because the consequences of relying on a single clonal tree species for this critical material could be unimaginably bad if the rubber tree crop collapses and no alternatives have previously been established at a rapidly scalable level.ABSTRACT
The development of palygorskite rubber filler meets the rubber industry’s demand for a low-cost green filler, but the high cost of mineral purification and modifiers limits its industrialization. In an effort to decrease such expenses, this study opted for eco-friendly l-(+)-cysteine as the modifier for organic grafting on the surface of low-grade palygorskite ore. l-(+)-Cysteine–modified low-grade palygorskite rubber reinforcing filler (CYS@PAL) was successfully prepared through ultrafine ball milling and modification. Under the conditions that the modifier dose is 1 wt% and the filling amount of modified powder is 90 phr, the 100 and 300% constant tensile stress, tensile strength, and elongation at break of reinforced EPDM composite reached 4.07 MPa, 7.66 MPa, 24.78 MPa, and 764.70%, respectively. In addition, after thermo-oxidative aging at 70 °C for 48 h, the aging coefficient of the composite rubber reached 0.873. This work provides a low-cost and environmentally friendly method to prepare a high-performance low-grade palygorskite reinforcing filler.ABSTRACT
Natural latex gloves are prone to allergies and adhesion during use. Corn starch and talc, while improving adhesion, do not solve the allergy problem. These powders even increase allergy transmission pathways as well as create safety hazards such as granulomas. Depositing polymethylmethacrylate (PMMA)-chitosan (CS) on glove surfaces improves surface adhesion and does not become airborne like powders. However, the physical stability of the film formed by PMMA-CS deposition leaves much to be desired, and azobisisobutyronitrile (AIBN) and hexadecane present safety hazards. To ameliorate these problems, PMMA-CS was prepared by replacing AIBN and hexadecane with tween-80 and β-cyclodextrin, and PMMA-TOFA was prepared by using methyl methacrylate (MMA) and tall oil fatty acid (TOFA). The sulfur-prevulcanized natural rubber (SPNR) films deposited with PMMA-CS and PMMA-TOFA (PMMA CS/PMMA-TOFA/SPNR) had fewer safety hazards, higher roughness and physical stability. It is expected that PMMA emulsion can be applied to the inner and outer surfaces of medical gloves to reduce the safety hazards that exist in medical gloves.ABSTRACT
Natural rubber is cross-linked with a tetrafunctional thiol using anhydrous cerium chloride as catalyst, at ambient temperature. The cured rubber is characterized by infrared spectroscopy, cross-polarization magic angle spinning solid-state nuclear magnetic resonance spectroscopy, thermogravimetric analysis and differential scanning calorimetry. The cross-linked rubber is observed to biodegrade in soil and partially breakdown when immersed in esterase buffer solution. This method involving thiol cross-linking of natural rubber could find application in developing coated rubber products using a variety of thiols, including natural thiols, from a solvent as well as in solid-state fabrication of molded rubber products.ABSTRACT
Fluorosilicone (FVMQ) rubber is commonly used in many military aircraft applications such as seals and gaskets due to its exceptional heat stability, low temperature flexibility and resistance to fuels and oil. In this investigation, a peroxide cured and silica filled FVMQ rubber compound was prepared and subsequently submitted to accelerated heat aging for up to 50 weeks at temperatures between 75 to 250°C. Heat aged samples were then tested for hardness, physical property characteristics and crosslink density by solvent swell and Double Quantum – Nuclear Magnetic Resonance (DQ NMR). The Arrhenius methodology was applied to the shifted experimental data assuming the principle of time-temperature superposition. The tensile strength and elongation at break both decrease upon thermal treatment. A small stiffness increase was observed by both the hardness and the tensile stress at 10% elongation test data. The characterization of the crosslink density by solvent swell testing was inconclusive. On the other hand, the DQ NMR testing clearly showed that the crosslink density decreases while the number of chain defects increases. The unaged crosslink distribution is heterogeneous in nature displaying much more heterogeneity than peroxide cured silicone. Non-linear Arrhenius behavior was observed between 75 to 250°C with a mechanism change at 175°C. The FVMQ crosslink distribution becomes more heterogeneous with aging. A significant loss of low molecular weight FVMQ due to depolymerization and backbiting reactions was observed at higher aging temperatures. Reactions with the silica surface also occurred with the creation of Si-O bonds. No direct evidence of thermo-oxidative and oxygenation reactions was observed. Reaction mechanisms have been proposed to explain the degradation of FVMQ due to heat aging.Abstract
Preparation and properties of the low hardness, high abrasion resistance and flame retardancy NR/BR composites with triisopropyl phenyl phosphate
INTERACTION OF HYDROGEN WITH FLUOROELASTOMER : SORPTION AND DEGRADATION
Exploring the Rheological Complexities of Filled Rubbers: Insights into the Linear-Nonlinear Dichotomy
Synthesis of the New P-N Flame Retardant Based on Sepiolite and the Flame Retardant and Smoke Suppression Study on EPDM
Effect of maturation time on the structure and properties of natural rubber
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