Abstract The rubber-producing species Scorzonera tau-saghyz (mountain gum) was used as a significant source of natural rubber between 1930 and 1950 by the U.S.S.R because this perennial species can accumulate up to 40% rubber in its roots on a dry weight basis. Wild stands were harvested, and plants were tested in nursery and field trials in multiple locations. Most of the data are lost but a few, rare, early reports have been discovered and translated by our co-authors in Kazakhstan. In this paper, these early data from different sites have been plotted and analyzed to guide modern cultivation efforts in both Kazakhstan and the United States. The use of an NPK complex fertilizer appeared most effective in increasing overall yield, promoting growth, and enhancing the content of rubber, resin, and carbohydrates in the plants. The highest rubber and the lowest resin concentrations were observed in September-October. The greatest yields of root biomass and rubber were obtained on relatively acidic, magnesium-rich soils (pH 5.35–7.45) with a mild climate (Krasnograd, Ukraine). However, S. tau-saghyz was able to perform quite well even when winter temperatures dropped to -20 °C (Poltavka, Russia). Good plant performance on the Poltavka, Krasnograd and irrigated Almaty (Kazakhstan) sites suggests that adequate water is needed for good yield. Lack of water and higher pH both appeared to be detrimental to yield in Balashov (Russia), and non-irrigated Almaty.

Abstract Autonomously repairing tire sealants are critical for vehicle safety; however, conventional self-healing formulations frequently fail under prolonged high-speed tire operation due to excessive flowability, resulting in compromised sealing performance and dynamic imbalance. Here, we have designed a dual-crosslinked butyl rubber-based interpenetrating network (IPN) incorporating dynamic hydrogen bonds and imine bonds, which collectively ensure excellent self-healing capability, reprocessability, and high-temperature structural integrity. The fabricated IPNs exhibit an ultimate stress of 1.4–3.1 MPa and a breaking strain of 1450–2600%. The imine-crosslinked network ensures structural integrity at elevated temperatures, while the hydrogen-bonded network significantly enhances strength and toughness via reversible hydrogen bond breakage and reformation, facilitating efficient energy dissipation. Moreover, the designed IPNs achieve a high healing efficiency of ~85% after 4 h at 80 °C. Such a healing efficiency stems from the synergistic interaction between imine bond exchange reactions and hydrogen bond dissociation/reformation dynamics. The IPNs architecture harnesses the rapid reversibility of hydrogen bonds and the robust exchangeability of imine bonds, while the imine-bond crosslinked network preserves the material's structural integrity. This design effectively mitigates the flow behavior observed in conventional self-healing sealants during high-speed operation, providing a versatile platform for developing high-temperature-resistant, healable tire sealants with tunable mechanical properties.

Abstract Fatigue crack growth (FCG) tests were performed on eleven styrene-butadiene rubber (SBR) vulcanizates using pure-shear specimens at a frequency of 5 Hz and a strain ratio of 0.1, in air at room temperature. The vulcanizates were either unfilled, carbon black (CB)-filled, or silica (SC)-filled, with filler contents ranging from 5 to 25 vol.%. While the FCG data for all vulcanizates could be fitted using power-law equations, deviations from the fitted curves were observed in the high tearing energy regime when the filler content exceeded 15 vol.%. This deviation is attributed to a transition in the crack growth mechanism from cycle-dependent to time-dependent behavior. For both CB- and SC filled vulcanizates, the threshold tearing energy increased and the power-law exponent decreased with increasing filler content; however, both values tended to plateau beyond 15 vol.%. Notably, at equivalent filler contents, SC-filled vulcanizates exhibited threshold tearing energy values approximately three times higher than those of CB-filled compounds, despite comparable hysteresis ratios. This unique threshold behavior was interpreted in terms of crack tip deformation, as evaluated by crack opening displacement, and the underlying fracture mechanisms, namely chain scission and interfacial delamination.

Abstract Vulcanized rubber, due to unique characteristics, saw main uses in automobiles, mostly as tires. Even with the latest shifts in the industry towards electrical drives, vehicles still ride on tires. Today, tires reported in the public domain, consist of about 19% natural rubber and 24% synthetic rubbers, while plastics, metal, fillers, and additives make up the rest. Globally, the Rubber Industry claims to produce over 1.6 billion tires annually and waste managers report returning billion waste tires; the rest remains with the users, breaks down in service, or illegally pills in dumpsters. Tires of extensive designs and complex manufacturing withstand the harshness of service life. Consequently, their disposal creates monumental technical and industrial challenges. Current disposal strategies to retiring tires, consisting of incineration, crumb rubber generation, and landfilling, show clear shortcomings. Waste tire rubber recovery and regeneration are preferred for rubber sustainability and rubber product circular economy. Multiple devulcanization processes introduced selective cleavages of vulcanizate’s crosslinks while retaining polymeric networks. This paper reviews devulcanization methods explored, such as chemical, mechanical, biological, and their combinations. The paper presents additional steps necessary to turn post-consumer goods based on rubbers (like end-of-life tires) into engineering materials and products. The paper offers a new perspective on sustainable waste rubber recovery and reuse. A follow-up paper will discuss the steps to put post-industrial rubbers and rubber products back in production, towards zero waste rubber and rubber product manufacturing.

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 non-sinusoidal 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 NR. It is of great significance to understand the change rule of properties in the maturation process for the production and processing of NR. In this study, the effects of maturation time on the nonrubber components, microstructure, and macroscopic properties of NR were examined. The test results of nitrogen content showed that the protein content of NR decreased with the extension of maturation time. The results of the solid NMR and gel content test showed that the molecular chain entanglements of the rubber increased and that the natural network structure increased during the maturation process. The test results of the vulcanization curves showed that the scorching time of the rubber was significantly shortened with the prolongation of the maturation time; The test results of crosslinking density showed that the crosslinking 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 that 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 To further the design and use of flame retardants with lower environmental impacts, many available, ecofriendly, biobased, and biocompatible flame retardants have begun to be used. This study explores the synthesis of a novel phosphorus-nitrogen synergistic flame retardant (PMO) by using biosourced phytic acid and enteromorpha prolifera, along with mineral-based modified sepiolite and melamine, to investigate its flame retardant and smoke suppression effects on EPDM. Experimental results demonstrate that compared with pure EPDM, EPDM with 50 parts per hundred of rubber PMO achieves a V-0 rating in UL-94 tests, with an increased limiting oxygen index to 31.1%, time to ignition extended from 6 to 29 s, peak heat release rate reduced by 55.8%, and total heat release decreased by 69.4% (particularly total smoke production reduced by >73%), thereby significantly enhancing the flame retardant performance of the rubber composite material. After loading with modified seafoam, a highly efficient PMO flame retardant was successfully prepared that has a broad application prospect in general rubber materials.

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 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 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.