Dynamic Vulcanization Research Articles

Influence of melamine formaldehyde microsphere on the vulcanization kinetics and mechanical properties of nitrile butadiene rubber

The melamine formaldehyde (MF) microsphere/nitrile butadiene rubber (NBR) vulcanizates were prepared by adding MF into NBR through mechanical mixing, followed by a vulcanization process. The influences of MF on the vulcanization characteristics, vulcanization kinetics, and mechanical properties were investigated. The results showed that MF interacted with NBR through hydrogen bonds. In addition, parameter b calculated by the ratio of modulus and strains also demonstrated the strong interaction between MF and NBR. Adding MF into NBR would reduce the curing time of NBR compounds, and increase the curing rate, as well as the cross-linked density. The vulcanization kinetics of MF/NBR compounds could be simulated accurately by Ghoreishy’s model. The mechanical properties of MF/NBR increased with the incorporation of MF. The modulus at 100%, modulus at 300%, and tensile strength of NBR vulcanizates with 20 parts per hundred rubber MF had 155, 90, and 110% increment, respectively, compared with those of neat NBR. The MF also enhanced the tear strength of NBR by 80% with a rough tear-fractured surface of NBR recorded by scanning electron microscope.

Bio-Based PLA/NR-PMMA/NR Ternary Thermoplastic Vulcanizates with Balanced Stiffness and Toughness: “Soft–Hard” Core–Shell Continuous Rubber Phase, In Situ Compatibilization, and Properties

Stiffness and toughness are two mutually exclusive attributes of polymer materials that contribute to significant improvements in impact strength, usually accompanied by a reduction in tensile strength. In this study, ternary thermoplastic vulcanizates (TPVs) consisting of poly(lactic acid) (PLA), poly(methyl methacrylate)-grafted natural rubber (NR-PMMA), and natural rubber (NR) with balanced stiffness and toughness were successfully prepared via peroxide-induced dynamic vulcanization. With 10 wt% of NR and NR-PMMA, the PLA/NR-PMMA/NR ternary TPV displayed an enhanced yield stress of 41.7 MPa (only 38% loss compared to neat PLA) and a significantly higher impact strength of 91.30 kJ/m2 (nearly 32 times that of neat PLA). The in situ compatibilization between PLA and rubber phases was confirmed by Fourier transform infrared spectroscopy. Interfacial, rheological, and calorimetric measurements confirmed that the NR was encapsulated by NR-PMMA in the PLA phase. It was found that the flexibility of the “soft” NR core and outer “hard” NR-PMMA shell with excellent PLA/rubber interfacial adhesion are responsible for the super toughness and considerable tensile strength of the PLA/NR-PMMA/NR ternary TPVs.

Morphology, crystallization, and thermal and mechanical properties of dynamic vulcanization EPDM/PP thermoplastic elastomer

Dynamically vulcanized thermoplastic olefin based on polypropylene (PP)/ethylene–propylene–diene (EPDM) with different dicumyl peroxide (DCP) content was prepared by twin-screw extruder. The effect of DCP content on gel content, crystallinity, and morphological, thermal, and mechanical properties of dynamically vulcanized EPDM/PP blends with different DCP content was investigated. The scanning electron microscopy was performed to evaluate the structure, as well as to characterize the morphology formed during dynamic vulcanization. The regular cross-linked EPDM particle uniformly distributed in PP matrix when the DCP content was from 0.3% to 0.9%. The crystallization behavior analysis indicated that the cross-linked EPDM promoted the nucleation process of PP, but with increase in DCP content, the percentage of crystallinity of the dynamically vulcanized EPDM/PP blends decreased due to the PP degradation. The tensile strength and elongation at break first increase and then decrease with increase in DCP content. When the DCP content was 0.9%, the tensile strength and elongation at break of dynamically vulcanized EPDM/PP blends were the largest. The gel content of dynamically vulcanized EPDM/PP blends first increased and then decreased with increasing DCP content. When the DCP content was 1.2%, the gel content of dynamically vulcanized EPDM/PP blends was maximum. The proper content range of DCP was from 0.6% to 1.2%.

Effect of carbon nanofibers on mechanical and electrical behaviors of acrylonitrile‐butadiene rubber composites

Recently, carbon nanofibers have become an innovative reinforcing filler that has drawn increased attention from researchers. In this work, the reinforcement of acrylonitrile butadiene rubber (NBR) with carbon nanofibers (CNFs) was studied to determine the potential of carbon nanofibers as reinforcing filler in rubber technology. Furthermore, the performance of NBR compounds filled with carbon nanofibers was compared with the composites containing carbon black characterized by spherical particle type. Filler dispersion in elastomer matrix plays an essential role in polymer reinforcement, so we also analyzed the influence of dispersing agents on the performance of NBR composites. We applied several types of dispersing agents: anionic, cationic, nonionic, and ionic liquids. The fillers were characterized by dibutylphtalate absorption analysis, aggregate size, and rheological properties of filler suspensions. The vulcanization kinetics of rubber compounds, crosslink density, mechanical properties, hysteresis, and conductive properties of vulcanizates were also investigated. Moreover, scanning electron microscopy images were used to determine the filler dispersion in the elastomer matrix. The incorporation of the carbon nanofibers has a superior influence on the tensile strength of NBR compared with the samples containing carbon black. It was observed that addition of studied dispersing agents affected the performance of NBR/CNF and NBR/carbon black materials. Especially, the application of nonylphenyl poly(ethylene glycol) ether and 1‐butyl‐3‐methylimidazolium tetrafluoroborate contributed to enhanced mechanical properties and electrical conductivity of NBR/CNF composites.

Determination of thermophysical characteristics of vulcanizable rubber products by the mathematical modeling method

The studies of the vulcanization kinetics of elastomers were carried out using a Truck tyre tread rubber compound. The formal kinetic scheme of vulcanization of rubbers sulfur-accelerator curing system was used which generalizes the set of reactions occurring in the curing process. A mathematical model is developed for determining the thermal parameters vulcanizable mixture comprising algorithms for solving direct and inverse problems for system of equations of heat conduction and kinetics of the curing process. The performance of the model is confirmed by the results of numerical experiments on model examples.

Dynamically vulcanized high-density polyethylene/nitrile butadiene rubber blends compatibilized by chlorinated polyethylene

Thermoplastic vulcanizates (TPVs) based on high-density polyethylene (HDPE)/nitrile butadiene rubber (NBR) blends were prepared by dynamic vulcanization where chlorinated polyethylene (CPE) was used as a compatibilizer. The effects of CPE on mechanical properties, Mullins effect, dynamic mechanical properties, and morphology of the blends were investigated systematically. Experimental results indicated that CPE had an excellent compatibilization on the HDPE/NBR blends. Dynamic mechanical analysis studies showed that the glass transition temperature of NBR phase was slightly shifted toward higher temperature with the CPE incorporation, leading to the increasing interface compatibility. Mullins effect results showed that the compatibilized HDPE/NBR blend had relatively lower residual deformation and internal friction than that of HDPE/NBR blend, indicating the improvement of elasticity. Morphology studies showed that the size of the NBR particles was decreased with the existence of CPE; moreover, the fracture surface of HDPE/CPE/NBR TPV was relatively smoother than that of HDPE/NBR blend.

Relating Chemical Structure to Toughness via Morphology Control in Fully Sustainable Sebacic Acid Cured Epoxidized Soybean Oil Toughened Polylactide Blends

The use of soybean oil or its derivatives to toughen polylactide (PLA) usually leads to limited toughening efficiency, due to the incompatibility between toughening agents and parent PLA. Herein, we report a dynamic vulcanization method to toughen PLA using sebacic acid cured epoxidized soybean oil (VESO), a fully sustainable and biodegradable component. A series of sebacic acid cured epoxidized soybean oil precursors (SEPs) were prepared with different carboxyl/epoxy equivalent ratio (R), which consequently dictates the chemical structure and the morphology of PLA/VESO blends after the dynamic vulcanization. We demonstrated that the chemical structure of VESO plays a critical role in the compatibility, morphology, and toughness of the PLA/VESO blends. By optimizing the R-value, supertoughened PLA blends can be obtained, as evidenced by the significant improvement in the tensile toughness (up to 150.6 MJ/m3) and the impact strength (up to 542.3 J/m). The results of the toughening mechanism from the morpho...

Rheological characterization and modeling of vulcanization kinetics of natural rubber/starch blends

ABSTRACTVulcanization kinetics of natural rubber/starch (NR/ST) blends was investigated by oscillating disc rheometer. The scorch and cure times are significantly reduced with the loading of starch in all blends from 1.15 and 2.22 to 0.91 and 1.88 min, respectively, to improve curing rate. Meanwhile, the maximum torque values and the maximum vulcanization rate of NR/ST blend increase with the starch loading from 1.51 N m and 0.387 min−1 to 2.224 N m and 0.492 min−1 respectively. The results of vulcanization kinetics of NR and its blends revealed that it is controlled by two‐stages, chemical and diffusion. The experimental data of the vulcanization rate of NR/ST blends did not fit with autocatalytic kinetic model except the pure natural rubber. Therefore, the Criado method was used and it was observed that the reaction kinetic model of pure NR and its blends with starch is best described by the D diffusion model (D2). © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46347.

Novel fluorosilicone thermoplastic vulcanizates prepared via core‐shell dynamic vulcanization: Effect of fluororubber/silicone rubber ratio on morphology, crystallization behavior, and mechanical properties

Recently, we have reported a novel core‐shell dynamic vulcanization method to prepare poly(vinylidene fluoride) (PVDF)/fluororubber (FKM)/silicone rubber (SR) thermoplastic vulcanizates (TPVs) with cross‐linked rubber core‐shell particles. However, the shell thickness on the properties has not been studied in detail. Herein, these PVDF‐based TPVs different FKM‐shell thickness were prepared by changing FKM/SR ratios. The effect of FKM‐shell/SR‐core ratio on morphology, crystallization, and mechanical properties of the ternary TPVs was studied. The results showed that the FKM shell had more positive effect on interfacial‐induced crystallization behavior than the SR core due to its better compatibility with PVDF. When the FKM/SR ratio was <1, FKM was not enough to encapsulate SR completely, which resulted in the formation of imperfect core‐shell structure. However, when the FKM/SR ratio was >1, perfect core‐shell structure was formed. Therefore, the mechanical properties improved with increasing FKM content; especially, a remarkable improvement was observed when FKM/SR ratio was >1. This study could provide more information for the design of TPVs with core‐shell structure.

Nghiên cứu chế tạo blend giữa polypropylene (PP) và cao su butadiene acrylonitril (NBR) Phần 2. Qui hoạch hóa thực nghiệm quá trình chế tạo blend NBR/PP

AbstractBlend of polypropylene and nitril rubber was conducted via dynamic vulcanization in Brabender Plasticoder. MA‐g‐PP was used as coupling agent in this blend. The optimum of blending process was investgated using Design Expert software with three factor PP/NBR ratio, MA‐g‐PP concentration, mixing time and two levels 23 to evaluate the effects of these factors on the the tensile strength of blend. Analysis of variance ANOVA was showed the interaction of these factors. The recurrence equation was as following: TS = 8.6‐1.29A + 0.72C + 0.74D + 0.35 AC. According to the recurrence equation, the PP/NBR ratio had the showed the greatest influence on the tensile strength of blend.

Ionic liquids as coagents for sulfur vulcanization of butadiene\u2013styrene elastomer filled with carbon black

The aim of this work was to study the activity of several alkylimidazolium salts of bis(trifluoromethylsulfonyl)imides to obtain a very fast vulcanization of the butadiene–styrene (SBR) elastomer. Ionic liquids (ILs) such as alkylimidazolium salts with ethyl-, propyl-, butyl-, hexyl-, decyl-, dodecyl-, and hexadecyl chains in the cation together with nanosized zinc oxide are used to develop elastomer composites with very short vulcanization time and a reduced amount of vulcanization activator. In this article, we discuss the effect of the ILs with respect to the length of alkyl chain in their cation on the vulcanization kinetics of rubber compounds. The influence of ILs on the crosslink density as well as the mechanical properties of the vulcanizates and their resistance to thermo-oxidative and UV aging were also studied. ILs resulted in a shortened optimal vulcanization time and reduced the onset vulcanization temperature compared to zinc oxide containing rubber compound. This is very important from a technological point of view. A considerable increase in the crosslink density of vulcanizates was also observed.

Morphology Development via Static Crosslinking of (Polylactic Acid/Acrylic Rubber) as an Immiscible Polymer Blend

AbstractThe interrelation between crosslinking and morphology is investigated for an immiscible blend of polylactic acid (PLA) and acrylic rubber (ACM). The blends are prepared by solution mixing and static crosslinking is used to avoid the simultaneous effect of the flow field that occurs in dynamic vulcanization. It is carried out at different temperatures, times, and curing agent contents. Scanning force microscopy (SFM) and polarized optical microscopy are used to determine the morphology of the blends. The chemical interactions and viscoelastic properties of the blends after crosslinking are also studied using infrared spectroscopy and rheological tests, respectively. Before crosslinking, SFM shows matrix‐droplet morphology for the samples that it is retained after that for the blend with 30 wt% ACM; however, it is changed to cocontinuous one in the blend with 50 wt% ACM. Partially, grafting of PLA on the crosslinked ACM is confirmed by Fourier transform infrared spectroscopy. The rheological results show that the incorporation of ACM to the PLA slows down the chain relaxation and vulcanization intensifies this effect. A model is proposed to explain the morphology evolution during static crosslinking of an immiscible blend.

Nitrogen‐doped graphene as an alternative to ecotoxic zinc oxide in rubbers

ABSTRACTZinc oxide (ZnO) is an essential ingredient in industrial rubber production; it regulates the onset of vulcanization, accelerates the kinetics of vulcanization, and improves the mechanical properties of rubber. However, environmental pollution with ZnO is a concern because it is recognized to be significantly ecotoxic and might also have adverse effects on human health. One of the major sources of ZnO environmental pollution is rubber items, tires in particular. Nitrogen (N)‐doped graphene is a promising next‐generation catalyst. We show here that the replacement of 3 phr ZnO by just 0.1 phr N‐doped graphene in styrene–butadiene rubber reduced the vulcanization onset time by more than a factor of two while retaining the fast vulcanization kinetics and enhancing the tensile strength in comparison with rubber with just ZnO. A shorter vulcanization time implies energy savings, which, together with the nontoxicity of N‐graphene, should make the resulting rubbers substantially more environmentally friendly. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46116.

Effect of interface on the mechanical behavior of polybutadiene–silica composites: An experimental and simulation study

ABSTRACTThe effect of interface property on the mechanical behavior of silica–polybutadiene composites is systematically investigated via combined experimental and dynamics simulation. In experiment, the interface property is controlled by SiO2 particle size, silane coupling agents, and silane grafting density. The effects of these control parameters on the vulcanization kinetics, tensile strength, and dynamic mechanic properties are investigated and discussed. Both the experimental and simulation studies reveal the pivot role of filler–polymer interface on the mechanical reinforcement. Simulation study reveals that the constrained polymer layer (∼12 nm) surrounding the silica particles shows increased stress from 30 to 230 MPa, which is identified as the major reason for the overall enhancement of 100% modulus from 0.8 to 1.6 MPa. The molecular mechanics of interface from simulation is well correlated to the experimental results in this study, which provides a molecular level understanding of the relationship between interfacial interaction and mechanical reinforcement. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46089.

SMART THERMOPLASTIC ELASTOMERS WITH HIGH EXTENSIBILITY FROM POLY (VINYLIDENE FLUORIDE) AND HYDROGENATED NITRILE RUBBER: PROCESSING–STRUCTURE–PROPERTY RELATIONSHIP

ABSTRACT Novel smart thermoplastic elastomers (TPEs) with very high extensibility were prepared by blending polyvinylidene fluoride (PVDF) with hydrogenated nitrile rubber (HNBR) at an appropriate ratio, and their processing–structure–property relationship was investigated. Although the rubber phase was found to be dispersed in the matrix of PVDF for all compositions, morphology was shear sensitive and changed significantly after each processing step. Dropletlike structure was observed after the mixing in an internal mixer and compression molding, which changed to the lamellar structure after milling and injection molding. The compression molded sample exhibited very high extensibility (∼1600% elongation at break for 30/70 PVDF/HNBR blend) and a tensile strength of ∼6 MPa due to the formation of a strong interface. The elongation at break was much higher than any of the TPEs reported so far. Theoretical calculation of rubber particle size was also in agreement with the experimental observation. Dissipative particle dynamics simulation was run to capture the morphology, where HNBR chains were more sensitive to the shear force than the PVDF chains. The electromechanical sensitivity of the blend was 14.3 MPa−1, much better than the existing reported elastomeric actuator as well as pristine PVDF. Dynamic vulcanization gave further improvement in tensile strength and tension set properties.

AOTEMPO‐mediated dynamic vulcanization: Synthesis of impact‐modified polypropylene

New chemistry for controlling the dynamics and yields of radical‐mediated polyolefin modifications is adapted to prepare impact‐resistant thermoplastic vulcanizates. Dynamic vulcanization of polypropylene (PP) + poly(ethylene‐co‐octene) (EOC) blends using small amounts of acryloyloxy‐2,2,6,6‐tetramethylpiperidine‐N‐oxyl (AOTEMPO) overcomes the limitations of conventional peroxide formulations, giving products with fine EOC particle dispersions, high PP matrix viscosities, and superior mechanical toughness. Guidelines for selecting starting materials and reagent concentrations are developed before assessing the merits of an AOTEMPO‐derived products relative to benchmark blend materials. Measurements of dispersed‐phase size distributions and melt‐state oscillatory shear rheological properties are combined with solid‐state impact resistance, flexural, and tensile data to identify the strengths and limitations of AOTEMPO chemistry with respect to impact‐toughening applications. POLYM. ENG. SCI., 58:1999–2007, 2018. © 2017 Society of Plastics Engineers

Tailoring toughness of fully biobased poly(lactic acid)/natural rubber blends through dynamic vulcanization

Direct blending of poly(lactic acid) (PLA) with elastic natural rubber (NR) could not generate highly toughened blend, due to immiscibility between PLA and NR. In this study, we improved the compatibility of PLA/NR blend by dicumyl peroxide (DCP) initiated dynamic vulcanization and systemically investigated the effect DCP content on the morphology and mechanical properties of the resulting fully biobased PLA/NR blends. Both the pristine PLA/NR and dynamically vulcanized PLA/NR blends showed phase-separated morphology with dispersive NR particles dispersed in the PLA matrix. The particle size of NR decreased, the interfacial adhesion between the components increased, and the toughness of the sample first increased and then decreased with increase in the DCP content. When the DCP content was 3 wt%, the blend showed the highest toughening efficiency with impact strength and elongation at break of 220.2 J/m and 42.1%, respectively, which were 305% and 859% higher than those of pristine PLA/NR blend with the values of 72.1 J/m and 4.9%, respectively. The tensile strength and Young's modulus of the dynamically vulcanized samples were comparable to those of the pristine PLA/NR blend.

On the role of nano-silica in the kinetics of peroxide vulcanization of ethylene propylene diene rubber

This work discusses different roles of nano-silica in the kinetics of peroxide vulcanization of ethylene propylene diene (EPDM) rubber for the first time. Initially, it was shown that silica does not participate in the vulcanization mechanism by chemical bonding to other intermediates. Non-isothermal differential scanning calorimeter revealed that the enthalpy of vulcanization, proportional to the crosslinking reaction, goes through a minimum as silica loading increases. Therefore, silica has two roles affecting kinetics of peroxide vulcanization of EPDM: physical effect on the rate of crosslinking reaction through reduced dynamics of rubber chains and catalytic effect on the decomposition of peroxide. In the low-temperature isothermal vulcanization, the enthalpy of vulcanization decreased monotonically, indicating that the physical effect is dominant. The extent of physical effect was correlated to the immobilized bound rubber resulting from the filler-polymer and filler-filler interactions. However, at high-temperature isothermal or non-isothermal vulcanization, the catalytic effect surmounts the physical one.

New Antiozonants for Rubber Compounds Based on Oxyalkylated Derivatives of 4-Aminodiphenylamine

This paper sets out the properties and the results of the testing of new antiozonants 2PPD and 3PPD in place of standard and imported 6PPD and IPPD which are used in the production of mechanical rubber goods and tyres (in the sidewall, tread, and other elements). The proposed method for producing the new antiozonants makes it possible to organise their industrial production by low-cost technology, in contrast to 6PPD and IPPD production technology. The raw materials for the new antiozonants include ethylene and propylene glycols, available in Russia, and 4-aminodiphenylamine, imported for the production in Russia of antioxidant S789, which is widely used in the production of large-tonnage rubbers, in particular synthetic isoprene rubber SKI-3, over 70% of the volume of which is exported. A number of advantages of 3PPD over imported stabilisers have been established. These include a greater effectiveness in protecting rubber compounds against thermal oxidation and ozone cracking by comparison with the stabilisers it is replacing. The shortcomings of the new antiozonant (in terms of the form in which it is produced and in terms of its influence on the vulcanisation kinetics) are considered, and various ways to overcome these shortcomings are presented.

Theoretical and Experimental Insights into the Phase Transition of Rubber/Plastic Blends during Dynamic Vulcanization

While the phase inversion phenomena in thermoplastic vulcanizates have been extensively investigated, the mechanism underlying the evolution from the sea–island to island–sea phase transition is far from being understood. In this work, such transition of the polyolefin elastomer (POE)/polypropylene (PP) blend was studied simultaneously by density functional theory and experiments. Before vulcanization, the independent POE and PP phases were mixed into a homogeneous blend. After vulcanization, the microstructure of POE was altered, leading to a metastable state of the blend. Thereafter, the blend decomposed into two new phases. Accordingly, the interfacial density changed with the sea–island morphology transition. According to the nucleation thermodynamics, the predicted nanoparticle size of POE nuclei is in general agreement with our experimental measurement. Thus, this work provides a novel thermodynamic explanation regarding the phase inversion in thermoplastic vulcanizates.