Peroxide-induced Dynamic Vulcanization Research Articles

Study on Shape Memory Behavior of Ternary Poly(Lactic Acid)/Poly(Methyl Methacrylate)-grafted Natural Rubber/Natural Rubber Thermoplastic Vulcanizates

ABSTRACT Here, poly(lactic acid) (PLA)/poly(methyl methacrylate)-grafted natural rubber (NR-PMMA)/natural rubber (NR) ternary blends with co-continuous phase structure were prepared via peroxide-induced dynamic vulcanization. The good compatibility between NR-PMMA with PLA and NR and the interfacial grafting reaction during the preparation process ameliorated the interfacial compatibility between the phases. Therefore, the energy stored in the rubber phases could be effectively transferred to PLA, thus achieving an excellent shape-memory effect even under-repeated shape-memory cycles. Furthermore, by adding 10 wt% NR-PMMA, the TPVs exhibited improved impact strength and tensile strength up to 98.05 kJ/m2 and 45.2 MPa, respectively.

Toward strong and super-toughened PLA via incorporating a novel fully bio-based copolyester containing cyclic sugar

Blending polylactide (PLA) with flexible polymers is usually capable of reducing its inherent brittleness, which, however, is accompanied with a substantial decrease in tensile strength. Here, considering the integration of flexibility and rigidity, 1,4-butanediol and dodecanedioic acid with flexible alkyl chains as well as isosorbide with a rigid cyclic sugar structure is used to synthesize a new bio-based copolyester. By virtue of interfacial compatibilization between PLA and the copolyester via dicumyl peroxide-induced dynamic vulcanization, well balanced mechanical properties are achieved for resulting blends, that is, elongation at break and notched impact strength are increased to 298.4% and 578.0 J/m that represent 37- and 24-fold increases, while tensile strength maintains at 59.5 MPa that decreases by only ~15% compared with that of neat PLA. Massive shear yielding of PLA matrix triggered by internal micro-voids accounts for the toughening mechanism. Given the high mechanical strength and supertoughness, the PLA-based materials have potential applications in different areas.

Magnesium acrylate induced interfacial compatibilization of EPDM/PP thermoplastic vulcanizate and shape memory behavior

The effect of magnesium acrylate (MgMA) on the interfacial compatibility and shape memory behavior of ethylene propylene diene monomer (EPDM)/polypropylene (PP) thermoplastic vulcanizates (TPVs) prepared through peroxide-induced dynamic vulcanization was investigated in this paper. MgMA could react with both PP and EPDM at their phase interface, which improved the EPDM/PP interfacial compatibilization. The PP continuous phase fixed the temporary shape and the crosslinked EPDM particles provided driving force for shape recovery. The improved phase interface played a significant role in the stress transmission between PP and EPDM phases. It is found that the shape fixity ratio (Rf) and the shape recovery ratio (Rr) of TPVs exceeded ∼90% and ∼92.5%, respectively. With the increase of MgMA content, the Rf of TPVs increased firstly and then decreased, while the Rr and recovery rate enhanced in the whole process. Furthermore, the mechanical properties of TPVs were also improved with the increasing MgMA content.

Dynamically vulcanized PP/EPDM blends with balanced stiffness and toughness via in-situ compatibilization of MAA and excess ZnO nanoparticles: Preparation, structure and properties

It is a challenge to simultaneously improve the stiffness and toughness of polymer blends due to that the stiffness and toughness are two mutually exclusive attributes. In this paper, we successfully prepared dynamically vulcanized polypropylene/ethylene-propylene-diene rubber (PP/EPDM) blends with balanced stiffness and toughness through in-situ compatibilization of in-situ formed zinc dimethacrylate (i-ZDMA). The i-ZDMA came from the neutralization of methacrylic acid (MAA) and excess zinc oxide (ZnO) nanoparticles. With i-ZDMA, strong PP/EPDM interface and size reduction of EPDM particles were achieved during peroxide-induced dynamic vulcanization. The average size of EPDM particles was reduced to 260–280 nm, which significantly enlarged PP/EPDM interfacial surfaces. At the same time, the residual excess ZnO nanoparticles migrated into PP phase and served as nucleating agents to increase the crystallinity of PP phase. When the MAA/ZnO reached 2/1.3, the Izod impact strength was increased to 80.1 kJ/m2, nearly 1.6 times that of the blend without i-ZDMA and 22 times that of neat PP, while the Young's modulus and yield stress were increased to 373 MPa and 14.8 MPa, respectively, showing an improved rigidness of blend.

Model construction of particle size in dynamic vulcanization of PVDF/SR blends—matching degree between crosslinking and shearing rates

Abstract Peroxide-induced dynamic vulcanization of poly (vinylidene fluoride)/silicone rubber (PVDF/SR) blends was studied in this paper. We controlled the size of rubber particles by changing the rotor speed, and discussed the influence of shearing on the particle diameter and the particle diameter polydispersity (dp). The size of SR particle was confirmed to be decreased with increasing the rotor speed. However, a good matching degree of shearing and crosslinking rate helped the SR phase to achieve a uniform crosslinking, as well as a narrow dp. In this particular PVDF/SR system, the suitable rotor speed was found to be 90 rpm, at which the dp reached a minimum of 1.1981 and 1.1614 for the P9S1 and the P7S3, respectively. At last, we discussed the influences of the macroscopic breaking energy (Edk) and the coalescence (P) on the number-average particle diameter (Dn) of the SR. This work is thus devoted to construct a model for predicting the particle size in dynamic vulcanization of PVDF/SR blends.

Investigation of the Behavior of Organo-Metallic Compound and Its Influence on Polyurethane

Abstract HZMMA is a zinc salt of unsaturated carboxylic acids with a single hydroxyl group. The chemical behavior and morphological changes of the HZMMA were investigated by Fourier Transformed Infra Red spectroscopy (FTIR), thermal gravimetry (TGA), Scanning electron microscopy (SEM) and X-ray diffractometry (XRD). The experimental results showed that it was possible for HZMMA to be used as a reactive enhancer to prepare ionic polymers/polyurethane composites. A series of ionic polymer/polyurethane were prepared by poly (tetramethylene glycol) (PTMG), toluene diisocyanate (TDI) and self-made chain extenders which consisted of Dimethylthio toluene diamine (DMTDA), Dicumyl Peroxide (DCP) and HZMMA by prepolymerization. The effect of the content of HZMMA on the structure and properties of the composites were studied by DMA, TGA, XRD. The results indicated that HZMMA had formed poly-HZMMA particles by peroxide-induced dynamic vulcanization and the degree of micro phase separation of polyurethane were improved when the content of HZMMA was suitable. The poly-HZMMA particles improved the maximum decomposition temperature of the soft segment and the storage modulus of polyurethane. When the mass fraction of HZMMA and DCP were at 2 ‰, the maximum in the mechanical properties of the ionic polymers/polyether polyurethane composites was achieved.

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.

Bio-based polylactide/epoxidized natural rubber thermoplastic vulcanizates with a co-continuous phase structure

A bio-based thermoplastic vulcanizate (TPV) composed of polylactide (PLA) and epoxidized natural rubber (ENR) was fabricated through dicumyl peroxide-induced dynamic vulcanization. It was found that the crosslinked ENR phase had a specific continuous structure, hence forming a bi-continuous structure in the TPV. We designed cyclic stress-strain, stress-soften and stress-relaxation tests and SEM observation to reveal the relationship between the PLA continuous phase and crosslinked ENR continuous phase. It was found that the PLA phase generated crazes to adapt the elongation of the ENR continuous phase during stretching. At the same time, the enhanced interface between PLA and ENR kept the stress transferring between the two phases. The ENR with more epoxy groups showed better compatibility with PLA, which resulted in better mechanical properties.

The effect of lanthanum trimethacrylate on the mechanical properties and flame retardancy of dynamically vulcanized PP/EPDM thermoplastic vulcanizates

A new kind of polypropylene/ethylene–propylene–diene monomer (PP/EPDM) thermoplastic elastomer (TPE) with good mechanical properties and flame retardancy was prepared via in situ peroxide-induced dynamic vulcanization using lanthanum trimethacrylate (LaTMA) as a reinforcing agent. The morphology, structure, and mechanical properties and reinforcement mechanism of PP/EPDM/LaTMA TPE were investigated by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, rubber process analyzer, cross-link density test, and so on. The flame retardancy was investigated by limiting oxygen index (LOI) test. The results showed that when the amount of lanthanum oxide was 4.96 phr and methyl methacrylate was 7.85 phr, the compatibility between EPDM and PP was greatly improved. Besides, the tensile strength, tear strength, elongation at break, and hardness (shore A) of PP/EPDM/LaTMA TPE were increased from 6.2 MPa, 41.7 kN m−1, 148%, and 81 up to 11.1 MPa, 77.3 kN m−1, 365%, and 89, respectively. And the LOI of PP/EPDM/LaTMA TPE was increased to 19.0%. The SEM images, the higher G′, and the ionic cross-link suggested that a strong filler–filler network was formed by the polymerization and the grafted of LaTMA in the PP and EPDM phase which enhanced the compatibility between PP and EPDM. The DSC and FTIR results further proved that during the processing.

Morphology and non-isothermal crystallization of dynamically vulcanized PP/EPDM blends in situ compatibilized via magnesium dimethacrylate

Polypropylene/ethylene-propylene-diene rubber (PP/EPDM) blends in situ compatibilized by magnesium dimethacrylate (MDMA) were fabricated via peroxide-induced dynamic vulcanization. Scanning electron microscope observation indicated that the size of cross-linked EPDM particles decreased with incorporation of MDMA. Polarizing Optical Microscope (POM) analysis suggested that the spherulite size of PP phase decreased sharply with incorporation of MDMA during dynamic vulcanization. The Pseudo-Avrami, Ozawa and Mo's models were applied to analyze the non-isothermal crystallization kinetics of the composites. The analyzed data indicated that the crosslinked EPDM particles and homopolymerized MDMA acted as heterogeneous nucleating agents, which enhanced the crystallizability and decreased the spherulite size of the PP phase. In addition, the non-isothermal crystallization activation energy (ΔE) was calculated through the Kissinger and Friedman methods, and the ΔE value was found increase with incorporation of MDMA.

Morphology and properties of super-toughened bio-based poly(lactic acid)/poly(ethylene-co-vinyl acetate) blends by peroxide-induced dynamic vulcanization and interfacial compatibilization

Super-toughened poly(lactic acid) (PLA)/poly(ethylene-co-vinyl acetate) (EVA) blends were prepared via 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (AD) induced dynamic vulcanization and in situ interfacial compatibilization. The effects of AD on the morphology and properties of PLA/EVA blends were studied using a Brabender torque rheometer, gel content test, scanning electron microscopy (SEM), differential scanning calorimetry (DSC) thermogravimetric analysis (TGA) and mechanical properties test. The torque and gel content demonstrated that EVA and PLA was successfully vulcanized in the presence of free radicals obtained by the decomposition of the 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (AD). Additionally, the gel content results indicated that, compared with PLA, EVA is more aggressive with free radicals. The SEM revealed that a relatively uniform phase morphology and good interfacial compatibilization were achieved in the dynamically vulcanized PLA/EVA/AD blends. The interfacial reaction and compatibilization between the component polymers resulted in the formation of super-toughened PLA/EVA blended materials.

Fully Biobased Shape Memory Material Based on Novel Cocontinuous Structure in Poly(Lactic Acid)/Natural Rubber TPVs Fabricated via Peroxide-Induced Dynamic Vulcanization and in Situ Interfacial Compatibilization

Shape memory polymers (SMPs) based on fully biobased poly(lactide) (PLA)/natural rubber (NR) thermoplastic vulcanizates (TPVs) were fabricated via peroxide-induced dynamic vulcanization. Simultaneously, in situ reactive compatibilization was achieved by PLA molecule grafting onto NR chains. Differing from the general concept of spherical rubber particles being formed after dynamic vulcanization, the cross-linked NR was found to be a “netlike” continuous phase in the PLA matrix. This novel structure explained the surprising shape memory property of PLA/NR TPVs well (shape fixities ∼ 100%, shape recoveries > 95%, and fast recovery speed < 15 s at the switching temperature, ∼60 °C): the cross-linked NR continuous phase offers strong resilience and the PLA phase serves as the heat-control switch. We envision that the “green” raw materials and excellent shape memory properties of the dynamically vulcanized PLA/NR SMPs will open up a wide range of potential applications in intelligent medical devices.

Biobased Heat-Triggered Shape-Memory Polymers Based on Polylactide/Epoxidized Natural Rubber Blend System Fabricated via Peroxide-Induced Dynamic Vulcanization: Co-continuous Phase Structure, Shape Memory Behavior, and Interfacial Compatibilization

A biobased heat-triggered shape-memory polymer (HSMP) consisting of polylactide (PLA) and epoxidized natural rubber (ENR) was fabricated by peroxide-induced dynamic vulcanization. The cross-linked ENR phase exhibits a continuous net-like structure embedded in the PLA phase, which is different from a conventional plastic/rubber system having the typical “sea–island” morphology in which vulcanized rubber particles were dispersed in plastic matrix. In situ interfacial compatibilization was confirmed by FTIR analysis. The shape-recovery ratios of the PLA/ENR HSMPs were significantly improved over 90%, compared to that (60–70%) of PLA. The shape fixing and memorizing capability of PLA/ENR HSMPs was realized by the glass transition of the PLA phase: cross-linked ENR continuous phase at rubbery state offered strong recovery driving force, improved interface provided effective stress-transferring during shape recovery, and PLA continuous phase served as a “control-switch” for recovery. The biobased PLA/ENR HSMP c...

Fully biobased and supertough polylactide-based thermoplastic vulcanizates fabricated by peroxide-induced dynamic vulcanization and interfacial compatibilization.

A fully biobased and supertough thermoplastic vulcanizate (TPV) consisting of polylactide (PLA) and a biobased vulcanized unsaturated aliphatic polyester elastomer (UPE) was fabricated via peroxide-induced dynamic vulcanization. Interfacial compatibilization between PLA and UPE took place during dynamic vulcanization, which was confirmed by gel measurement and NMR analysis. After vulcanization, the TPV exhibited a quasi cocontinuous morphology with vulcanized UPE compactly dispersed in PLA matrix, which was different from the pristine PLA/UPE blend, exhibiting typically phase-separated morphology with unvulcanized UPE droplets discretely dispersed in matrix. The TPV showed significantly improved tensile and impact toughness with values up to about 99.3 MJ/m(3) and 586.6 J/m, respectively, compared to those of 3.2 MJ/m(3) and 16.8 J/m for neat PLA, respectively. The toughening mechanisms under tensile and impact tests were investigated and deduced as massive shear yielding of the PLA matrix triggered by internal cavitation of VUPE. The fully biobased supertough PLA vulcanizate could serve as a promising alternative to traditional commodity plastics.

Crosslinked bicontinuous biobased polylactide/natural rubber materials: Super toughness, “net-like”-structure of NR phase and excellent interfacial adhesion

Polylactide (PLA) and natural rubber (NR) are two major renewable resources in the polymer materials field. However, their blend has not yet met engineering needs, largely because of a lack of interfacial adhesion between the continuous PLA phase and dispersed NR droplets. To address this issue, we have designed a novel super toughened biobased PLA/NR blend prepared by peroxide-induced dynamic vulcanization, in which the cross-linked NR phase has a specific continuous “net-like” structure. A sharp brittle-ductile transition occurred in the blend with 35 wt% NR, showing impact strength of 58.3 kJ/m2, approximately 21 times that of the neat PLA. The peroxide initiated reactive compatibilization at the interface between PLA and NR. The toughening mechanism and deformation of the crosslinked “net-like” NR phase during stretching are discussed. Our results provide evidence of a continuous “net-like” NR located in the PLA matrix with good interfacial adhesion, which potentially enhances the mechanical properties of the material.

Highly toughened poly(vinylidene fluoride)/nitrile butadiene rubber blends prepared via peroxide-induced dynamic vulcanization

Nitrile butadiene rubber (NBR) toughened poly(vinylidene fluoride) (PVDF) blends were prepared via dynamic vulcanization in the presence of dicumyl peroxide (DCP). A super toughened PVDF/NBR blend was achieved with 28 wt% NBR, showing Izod impact strength of 77.5 kJ/m2, which was 6–7 times higher than the pure PVDF. The effects of the NBR incorporation on morphology and properties of the blends were investigated. Good interfacial interaction was found between the PVDF continuous phase and crosslinked spherical NBR particles with diameter of 1–3 μm. The complex viscosity and storage modulus of the blends increased significantly with increasing NBR content. The incorporation of the NBR component decreased the thermal stability of the PVDF/NBR blends, while the mass of residual char of the blends was much higher than that of pure PVDF and NBR.

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.

Highly toughened polypropylene/ethylene–propylene-diene monomer/zinc dimethacrylate ternary blends prepared via peroxide-induced dynamic vulcanization

Polypropylene (PP)/ethylene–propylene-diene monomer (EPDM)/zinc dimethacrylate (ZDMA) blends with remarkable toughness and extensibility were successfully prepared via peroxide dynamical vulcanization. A unique structure with the EPDM particles surrounded by a transition zone containing numerous polymerized ZDMA (PZDMA) nano-particles was observed for the first time by using transmission electron microscopy (TEM) examination, which contributed to the dramatically increase of Izod impact strength. Dynamic mechanical analysis (DMA) confirmed that the possible PZDMA graft products resulted from peroxide dynamical vulcanization improved the compatibility between EPDM and PP phases. The specific morphology of the PP/EPDM/ZDMA blends indicated that ZDMA can lead to size reduction and good distribution uniformity of the crosslinked rubber particles and the increase of adhesion between PP matrix and EPDM phases during deformation. The synergic effect of the increase in the effective volume of the EPDM phase, the improved compatibility and adhesion between EPDM and PP phases and the deformation of those fine rubber particles is believed to result in the remarkable high toughness and extensibility of the PP/EPDM/ZDMA blends. Particularly for the PP/EPDM ratio of 70/30, the PP/EPDM/ZDMA (70/30/9, w/w/w) ternary blends with the Izod impact strength nearly 2 times higher than PP/EPDM (70/30, w/w) binary blends and 15–20 times higher than PP are achieved; besides, the elongation at break of PP/EPDM/ZDMA ternary blends is 4–5 times higher than that of PP/EPDM binary blends.