Dynamic Vulcanization Research Articles

Novel natural rubber-g-N-(4-hydroxyphenyl)maleimide: synthesis and its preliminary blending products with polypropylene

Graft copolymer of natural rubber and N-(4-hydroxyphenyl)maleimide (i.e., NR-g-HPM) was synthesized. It was found that the grafting yield increased upon increasing the grafting temperature and the highest grafted HPM content was obtained at 200 °C. Furthermore, increases in concentration of HPM led to drop in grafted HPM. Therefore, an optimum grafting temperature and dose of HPM were found to be 200 °C and 2 phr, respectively. Dynamically cured 60/40 NR-g-HPM/PP blends with various loading levels of HPM in graft copolymerization were then achieved by dynamic vulcanization. It was found that the blend with 2 phr of HPM exhibited the highest tensile strength, elongation-at-break, mixing torque during dynamic vulcanization, storage modulus and complex viscosity and the lowest tension set (i.e., the highest elasticity). This was attributed to the highest grafted HPM which created greater possibility to form linkage between NR-g-HPM and the phenolic modified PP compatibilizer molecules which promoted easier interactions between the blend components. TGA analysis found that the NR-g-HPM/PP blends exhibited two stages of weight loss while the pure PP exhibited a single stage. Furthermore, the NR-g-HPM/PP blend exhibited higher degradation temperature than that of the unmodified NR/PP blend which was the confirmation of higher heat resistance of NR-g-HPM.

Morphology and properties of poly(vinylidene fluoride)/silicone rubber blends

ABSTRACTBlends of poly(vinylidene fluoride) (PVDF) and silicone rubber (SR) were prepared through melt mixing. The morphology, rheology, crystallization behavior, mechanical properties, dynamic mechanical properties and thermal properties of the PVDF/SR blends were investigated. The blend with 9 wt % of SR showed spherical shape of disperse phase whereas the blend with 27 wt % of SR resulted in irregular shape of rubber phase. The rheology showed that the complex viscosity and storage modulus of the blends decreased with increasing the SR content. The mechanical properties of the blends were decreased with increasing the SR content but that were significantly improved after dynamical vulcanization. The crystallization temperature of PVDF phase in PVDF/SR blends was increased. The incorporation of SR improved the thermal stability of PVDF/SR blends, and the temperature at 10% mass loss of the blends increased to about 489°C compared with 478°C of the pure PVDF. The mass of residual char in experiment of the blends was lower than that obtained in theory. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39945.

Effects of partial replacement of silicone rubber with flurorubber on properties of dynamically cured poly(vinylidene fluoride)/silicone rubber/flurorubber ternary blends

Blends of poly(vinylidene fluoride) (PVDF), silicone rubber (SR) and flurorubber (FKM) were prepared via peroxide dynamic vulcanization. The effect of FKM loading on the morphology, mechanical properties, crystallization behavior, rheology and dynamic mechanical properties of the PVDF/SR/FKM ternary blends was investigated. A “network” was observed in the PVDF/SR binary blends, which disappeared in the ternary blends, but a core-shell-like structure was formed. The mechanical properties were significantly improved. The Izod impact strength of PVDF/SR/FKM blend with 19 wt% FKM was 18.3 kJ/m2, which was 3–4 times higher than the PVDF/SR binary blend. The complex viscosity and storage modulus of the PVDF/SR/FKM blends decreased with increasing FKM content, hence the processability was improved. The increase of FKM content seemed to show a favorable effect on the crystallization of the PVDF component. It promoted the nucleation process of PVDF, leading to increased polymer crystallization rate and higher crystallization temperature. The glass-rubber transition temperature of the PVDF phase moved to a lower temperature.

Influence of cross-linked system on morphology and properties of thermoplastic vulcanizates based on isotactic polypropylene and ethylene propylene diene monomer

Thermoplastic vulcanizates (TPVs) based on isotactic polypropylene (iPP) and oil-free/oil-extended ethylene propylene diene monomer (EPDM) rubber were prepared by dynamic vulcanization. Their rheological and tensile properties as well as morphological peculiarities were examined and compared with those of uncured blends. Vulcanization was performed using two types of cross-linking agents: phenolic resin and sulfur-accelerating systems. Dynamic vulcanization was shown to change the melt viscosity of oil-free and oil-extended iPP/EPDM blends. These changes were found to depend on both rubber content and type of vulcanizing agent. For identical composition, the melt viscosity of TPVs cured by sulfur system was higher than that of blends cured by phenolic resin system (PRS). Dynamic vulcanization by PRS decreased tensile properties of TPVs in comparison with sulfur vulcanization. Morphology of iPP/EPDM blends studied by atomic force microscope was found to be dependent on the ratio of components, type of elastomer, and nature of vulcanizing system.

Effect of additives on the morphology evolution of EPDM/PP TPVs during dynamic vulcanization in a twin-screw extruder

Ethylene-Propylene-Diene Monomer/Polypropylene thermoplastic vulcanizates (EPDM/PP TPVs) have been widely used as a kind of typical “green” elastomer because of their excellent mechanical properties and recyclability. The industrial TPVs always contain various types of additives, which influence the viscosity ratio of EPDM and PP and the morphology of TPVs. This work studied the morphology evolution of EPDM/PP TPVs with various amounts of curing agents, fillers, and plasticizer during dynamic vulcanization in a twin-screw extruder, which provides much more complicated dynamic vulcanization process than haaker rheometer. The results show that the increased curing agents content leads to the faster morphology evolution of TPV because it enhances the cross-linking speed and the viscosity of EPDM. The increased fillers content leads to the later breakup of EPDM and the bigger size of the rubber aggregation because it enhanced the modulus of EPDM and weakens the interfacial interaction between EPDM and PP. In addition, the increase in the plasticizer content leads to the earlier breakup of EPDM and the larger size of the rubber phase in TPV. Our work firstly demonstrates the morphology evolution of industrial EPDM/PP TPV, and thus can provide a guidence for the industrial production of high-performance EPDM/PP TPVs.

Mechanical properties, Payne effect, and Mullins effect of thermoplastic vulcanizates based on high-impact polystyrene and styrene–butadiene rubber compatibilized by styrene–butadiene–styrene block copolymer

Thermoplastic vulcanizates (TPVs) based on high-impact polystyrene (HIPS)/styrene–butadiene rubber (SBR) blends were prepared by dynamic vulcanization technique, and the TPVs were compatibilized by styrene–butadiene–styrene block copolymer (SBS). Experimental results indicate that SBS had a good compatibilization effect on the HIPS/SBR TPVs. A rubber process analyzer reveals that elastic modulus increased with increasing frequency and increasing SBR content in the TPVs led to obvious decrease in elastic modulus. A softening phenomenon could be observed in the stress–stretch curves of HIPS/SBR and HIPS/SBS/SBR TPVs during the uniaxial loading–unloading cycles. Compatibilized HIPS/SBR TPV had the relatively lower stress and internal friction loss.

The Effects of Dynamic Vulcanization in Virgin Polyethylene (vPE)/Recycled Polyethylene (rPE)/Ethylene Propylene Diene Terpolymer (EPDM) Blends: Thermal Properties and Swelling Behaviour

The effects of dynamic vulcanization on the thermal properties and swelling behaviour of vPE/rPE/EPDM blends were studied. The discarded polyethylene used in the study was obtained from local wire insulation industry. The thermal properties and swelling behaviour of the blends were analyzed. Results show that increasing of sulfur loading had improved the thermal stability of the blends. The swelling percentage and swelling index of vPE/rPE/EPDM blends also decreased, inversely proportional to the increasing of sulfur loading. Thus, the increased incorporation of sulfur loading had improved the chemical and oil resistance of the blends.

In Situ Reactive Compatibilization of Polypropylene/Ethylene–Propylene–Diene Monomer Thermoplastic Vulcanizate by Zinc Dimethacrylate via Peroxide-Induced Dynamic Vulcanization

This work demonstrates an approach of in situ reactive compatibilization between polypropylene (PP) and ethylene-propylene-diene monomer (EPDM) by using zinc dimethacrylate (ZDMA) as a compatibilizer and, simultaneously, as a very strong reinforcing agent. With the incorporation of 7phr ZDMA in the PP/EPDM (30/70, w/w) thermoplastic vulcanizate (TPV), the tensile strength, tear strength, elongation at break, and hardness of PP/EPDM/ZDMA TPV were increased from 5.3 MPa, 31.3 kN/m, 222%, and 78 up to 11.2 MPa, 64.2 kN/m, 396%, and 83, respectively. This tremendous reinforcing as well as the compatibilization effect of the ZDMA was understood by polymerization of ZDMA and ZDMA reacted with EPDM and PP during peroxide-induced dynamic vulcanization. A peculiar phase structure that rubber particles were surrounded and "bonded" by a thick transition zone that contained numerous of nanoparticles with dimensions of about 20-30 nm was observed from transmission electron microscopy. Scanning electron microscopy results confirmed that incorporation of ZDMA reduced the size of the cross-linked EPDM particles. Moreover, we found that the compatibilized TPV showed a higher tan δ peak temperature for EPDM phase and a lower tan δ peak temperature for PP phase. The suggested method for in situ reactive compatibilization of PP and EPDM offers routes to the design of new TPV-based technical products for diversified applications.

Partially Dynamically Vulcanized Thermoplastic Elastomer Based on Natural Rubber-Polypropylene-Clay Nanocomposites

Thermoplastic vulcanizate (TPV) nanocomposites based on 60/40 (%wt) natural rubber (NR)/polypropylene (PP) blends were prepared by dynamic vulcanization. Sodium montmorillonite (Na-MMT) was use as a filler to improve TPV properties. The addition effect of Na-MMT on the TPV properties was examined. The results indicated that the blend exhibited a co-continuous phase structure. The presence of clay in the NR phase decreased crosslinking level of NR, but improved mixing of NR and PP during dynamic vulcanization. The addition of clay marginally enhanced the 100% modulus and tensile strength, but decreased elongation at break due to more homogeneous blend morphology. The optimal level of tensile strength improvement was obtained when loading of clay was 5 phr. The permanent set of the blends did not changed significantly with the clay dispersion. The storage modulus and resistance to oil and heat improved with incorporation of clay, proportional to clay loading.

Nanocomposites based on thermoplastic polyurethane, millable polyurethane and organoclay: Effect of matrix composition and dynamic vulcanization

ABSTRACTDynamically vulcanized thermoplastic polyurethane (TPU)/millable polyurethane (MPU) blend nanocomposites, simple TPU/MPU blend nanocomposite, and TPU nanocomposite with 3 parts per hundred (phr) of organoclay were melt compounded in an internal mixer. Interfacial interactions between the organoclay and polyurethanes were examined by Fourier transform infrared spectroscopy, X‐ray diffraction, and transmission electron microscope analysis, which revealed that the dispersion of organoclays significantly improved with increasing TPU content in the TPU/MPU blends and dynamic vulcanization process. Tensile test and dynamic mechanical analysis showed that the mechanical properties are improved with the TPU content in the TPU/MPU blends and dynamic vulcanization process. Both hardness and tension set of the samples decreased with increasing MPU content in the TPU/MPU blends. Thermal stability determined by thermo‐gravimetric analysis revealed that it increased with increase in TPU concentration in the samples. Differential scanning calorimetry study showed that the glass transition temperature (Tg), melting temperature (Tm), and melt crystallization temperature (Tc) of the samples were significantly affected by the blend composition and dynamic vulcanization. Dynamic melt rheology of the nanocomposite samples in the molten state revealed a pseudo solid‐like behavior as well as an enhanced shear thinning behavior, and the variation of the rheological properties are well correlated with blend compositions and morphology of the nanocomposites. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4014–4023, 2013

In situ reactive compatibilization and reinforcement of peroxide dynamically vulcanized polypropylene/ethylene‐propylene‐diene monomer tpv by zinc dimethacrylate

This work demonstrates an approach of in situ reactive compatibilization between polypropylene (PP) and ethylene‐propylene‐diene monomer (EPDM) by using ZDMA as a compatibilizer and, simultaneously, as a very strong reinforcing agent. With 7phr ZDMA in the PP/EPDM (30/70, w/w) thermoplastic vulcanizate (TPV), the tensile strength and elongation at break were increased from 5.3 MPa and 222% up to 11.2 MPa and 396%, respectively. Increasing the PP concentration further improved mechanical properties of the TPVs with ZDMA. This tremendous reinforcing as well as the compatibilization effect of the ZDMA was understood by polymerization of ZDMA and ZDMA reacting with EPDM and PP during peroxide induced dynamic vulcanization. A peculiar nano‐composite structure that the crosslinked rubber particles were “bonded” by a transition zone which containing numerous of nano‐particles with dimensions of about 20–30 nm was observed from transmission electron microscopy (TEM). Scanning electron microscopy (SEM) results showed that increase of PP/EPDM ratio reduced the size of crosslinked EPDM particles. Moreover, we found that the ZDMA reinforced EPDM particles resulted in a higher tan δ peak temperature for EPDM phase and built “filler‐filler”‐like networking in the PP melt. POLYM. COMPOS. 34:1357–1366, 2013. © 2013 Society of Plastics Engineers

Preparation and properties of dynamically cured poly(vinylidene fluoride)/silicone rubber blends

Blends of poly(vinylidene fluoride) (PVDF) and silicone rubber (SR) were prepared through dynamic vulcanization. The effects of SR content on crystallization behavior, rheology, dynamic mechanical properties and morphology of the blends were investigated. Morphology characterization shows that the crosslinked spherical SR particles with an average diameter of 2-4 μm form a “network” in the PVDF continuous phase. The dynamic mechanical properties indicate the interface adhesion between PVDF and rubber phase is improved by the dynamic vulcanization. The rheology study shows that with the increase of rubber content the blends pseudoplastic nature is retained, while the viscosity increases, and hence the processability is less good. The incorporation of SR phase promotes the nucleation process of PVDF, leading to increased polymer crystallization rate and crystallization temperature. However, a higher content of SR seems to show a negative effect on the crystallinity of the PVDF component.

Morphology Study of Peroxide-Induced Dynamically Vulcanized Polypropylene/Ethylene-Propylene-Diene Monomer/Zinc Dimethacrylate Blends during Tensile Deformation

Polypropylene (PP)/ethylene-propylene-diene monomer (EPDM)/zinc dimethacrylate (ZDMA) blend (EPDM/PP ratio of 30/70) with remarkable extensibility was successfully prepared via peroxide dynamic vulcanization. The uniaxial tensile properties, crystallization behavior, structure, and morphology during stretching were investigated. The tensile process study showed that the PP/EPDM/ZDMA blend exhibited the rubbery-like behavior with an elongation beyond 600%. The ZDMA graft-product domain increased the compatibility and interfacial adhesion between rubber and PP phases, while it reduced the crystallinity of the PP phase. On the basis of TEM and SEM analyses, we found that the cross-linked rubber particles could be elongated and oriented along the tensile direction, whereas the ZDMA graft-product domain "encapsulated" rubber phase together, acting as a "bridge" between elongated rubber phases and the PP phase during uniaxial stretching. The stress could be effectively transferred from the PP phase to the numerous elongated rubber phases due to the excellent compatibility and interfacial adhesion between rubber and PP phases, resulting in the rubbery-like behavior.

Novel Ionic Liquids as Accelerators for the Sulfur Vulcanization of Butadiene–Styrene Elastomer Composites

The aim of this work was to study the activity of novel benzalkonium and ammonium ionic liquids with 2-mercaptobenzothiazolate as accelerators in the sulfur vulcanization of butadiene–styrene elastomer (SBR). In this Article, the effect of the ionic liquids on the vulcanization kinetics of the rubber compounds, the cross-link density, and the mechanical properties of the vulcanizates, as well as their resistance to thermal and UV aging, was studied. The application of novel ionic liquids allowed for the elimination of N-cyclohexyl-2-benzothiazolesulfenamide from SBR compounds and for the considerable reduction of the amount of 2-mercaptobenzothiazole present in rubber products. Synthesized salts seem to be good substitutes for standard accelerators in the sulfur vulcanization of SBR rubber, without the observation of any detrimental effects on the vulcanization process, the physical properties, or the thermal stability of the obtained vulcanizates.

Mechanistic modeling of reversion phenomenon in sulphur cured natural rubber vulcanization kinetics

A novel kinetic model of natural rubber sulphur vulcanization is proposed. The modeling approach takes into account current knowledge on the different polysulfidic structures present during vulcanization, and the associated individual reactions. A simplified scheme is proposed, giving a mechanistic view of the reversion phenomenon, which results in a decrease of the elastic modulus (related to the sulphur crosslink density) for long vulcanization times at high temperature. The resulting set of differential equations is solved by an appropriate numerical method to predict the evolution of the degree of vulcanization for isothermal cure conditions.The vulcanization kinetics of a model natural rubber compound was characterized experimentally by rheological measurements, in order to test the proposed kinetic model. A remarkable agreement between model predictions and experimental data is observed. The identified kinetic parameters corresponding to the individual reactions taken into account by the mechanistic model are consistent with those of an existing, less refined, pseudo-mechanistic model. The proposed model thus allows bridging the gap between the prediction of macroscopic variations of the elastic modulus and the evolution of molecular scale structure during vulcanization when the reversion phenomenon is present.

Zinc Dimethacrylate-Reinforced Thermoplastic Vulcanizates Based on Ethylene-Vinyl Acetate Copolymer/Chlorinated Polyethylene Rubber/Nitrile Butadiene Rubber Blends

Thermoplastic vulcanizates (TPVs) based on ethylene-vinyl acetate copolymer (EVA)/chlorinated polyethylene rubber (CPE)/nitrile butadiene rubber (NBR) blends were prepared by dynamic vulcanization, with the TPVs being reinforced by zinc dimethacrylate (ZDMA). Experimental results indicated that mechanical properties of dynamically vulcanized EVA/CPE/NBR blends were enhanced remarkably by the incorporation of ZDMA. There were some ZDMA particles dispersed on the etched surface of EVA/CPE/NBR/ZDMA blends with diameters of about 10 µm. A rubber process analyzer revealed that the storage modulus decreased significantly with increasing strain when the strain was 2% above and the incorporation of ZDMA in the TPVs enhanced the Payne effect.

Vulcanization Kinetics of Natural Rubber Based On Free Sulfur Determination

The determination of free sulfur in the rubber vulcanizates provided significant representation of vulcanization reaction. In this research, the effects of vulcanization temperature, the mixing method of carbon black into rubber, the ingredients mixing sequence and the type of carbon black were studied on masticated and milled natural rubber in which the reaction was observed by un-reacted sulfur determination. The results showed that higher vulcanization temperature provided faster vulcanization reaction and greater reaction rate constant. Similarly, the mixing sequence of ingredient and carbon black into rubber influenced the rate of vulcanization reaction. The subsequent ingredients mixing sequence, in this case, resulted in higher vulcanization rate compared to that of the simultaneous one. However, the mixing method of carbon black into rubber brought small effect on the rate of vulcanization reaction. The type of carbon black applied was observed to influence the reaction rate of vulcanization. Smaller particle sizes of carbon black gave larger reaction rate constant. In this case, the type of carbon black N 330 gave faster vulcanization rate than that of N 660.

Microstructure and properties of solvent-resistant fluorine-contained thermoplastic vulcanizates prepared through dynamic vulcanization

Authors believe that two aspects of this manuscript will make it interesting to general readers of the journal “Materials & Design”. First, in this manuscript we report for the first time that a new fluorine-contained thermoplastic vulcanizate (TPV) was successfully prepared through dynamic vulcanization. Our results indicated that the dispersion of FKM particles in PVDF matrix and the mechanical properties of TPVs were significantly improved after dynamic vulcanization. The tensile strength of PVDF/FKM (50/50) blends increased from 16.2 to 33.5MPa, by about 107%; while elongation at break increased from 125.6% to 468.9%, by 2.7 times after dynamic vulcanization. Second, it was found that the solvent resistant properties of the prepared TPVs are better than the traditional compression molded FKM vulcanizates. The approach proposed here provides a viable technological alternative for the cost-effective preparation of fluorine-contained TPVs with superior properties to substitute present FKM vulcanizates which are difficult to recycle.

Vulcanization Kinetics of Starch Xanthate /Natural Rubber Composite

The starch xanthate/natural rubber (SX/NR) composite was prepared by directly mixing and co-coagulating NR latex and the modified starch paste with carbon bisulfide. The vulcanization kinetics of NR and SX/NR composite were investigated by using a rubber process analysis (RPA). The mechanism of SX/NR composite vulcanization was similar to that of pure NR. The values t0and tdisof XS/NR composite were shorter than that of NR, and the activation energy E1for the induction period was smaller. The activation energies E2and E3for the curing period were smaller than that of NR.

Vulcanization kinetics of graphene/natural rubber nanocomposites

In the present work, the influence of graphene (GE) on the vulcanization kinetics of natural rubber (NR) with sulfur curing system was investigated in detail for the first time. It is found that on adding graphene the induction period of the vulcanization process is remarkably depressed, whereas the vulcanization rate is enhanced at low graphene loading and then suppressed. As a result, the optimum cure time decreases dramatically at first and subsequently shows a slight increase with increasing graphene loading. At the same time, the crosslinking density of NR increases monotonically, because graphene takes part in the vulcanization process. The exothermal peak of the vulcanization reactions is split into two peaks on adding ≥0.5 phr graphene. It is interpreted in terms of two reaction stages, i.e., chemical reaction controlling stage and diffusion controlling stage. The activation energy of the former stage decreases with increasing graphene loading, while that of the latter stage is higher than the former one and increases with graphene loading. A possible mechanism was proposed to interpret the accelerating effect of graphene and the enhanced crosslinking density of NR.