Dynamic Vulcanization Process Research Articles

Morphological evolution and property changes of acrylate rubber/polyacetal thermoplastic vulcanizates during dynamic vulcanization process

AbstractA new type of thermoplastic vulcanizates (TPV) that is resistant to hot oil, high temperature, and aging was prepared using acrylate elastomer (ACM) and polyoxymethylene (POM) as raw materials. The phase transition process and micromorphology development of the blends with the change of dynamic vulcanization (DV) time, and to illustrate the effects of the phase transition and the degree of elastomer phase crosslinking on the macroscopic properties of TPV were investigated. It was shown that ACM crosslinking occurs continuously during 0–8 min of DV, whereas the phase inversion process occurs predominantly during 0–3 min. In contrast, the cross‐section of the blends after phase inversion is flat, The constant elongation stress under small deformation, hardness, and permanent deformation after break are reduced, and the elongation at break, nonrelaxable modulus, and aging resistance are improved. The increase in the degree of vulcanization of the ACM phase resulted in a significant increase in the modulus of the blends under large deformation, an increase in the nonrelaxable modulus and relaxable modulus, an increase in the aging resistance, and a decrease in the elongation at tear were observed.

The Effect of Polyamide 11 on the Thermal Stability and Light Transmittance of Silicone-Based Thermoplastic Vulcanizates.

The effect of polyamide 11 (PA11) on the thermal stability and light transmittance properties of silicone-based thermoplastic vulcanizates (TPVs) has been investigated. The blends were prepared through a dynamic vulcanization process by adding 15, 30, and 45 wt% PA11 to the silicon-based TPVs, respectively. The effect of PA11 on the dispersion of silicone rubber in the TPVs after dynamic vulcanization was characterized by a scanning electron microscope (SEM), the thermal stability of the compounds was evaluated through the changes in mechanical performance in the thermo-oxidative aging process, and the light transmittance of TPVs was measured by a haze meter. The results showed that adding PA11 to silicone-based TPVs caused a decrease in the size of the silicone rubber particles after dynamic vulcanization, resulting in improved dispersion. Due to this, by increasing the compatibility between the segments through silicone's effective dispersion, the amount of light absorption was reduced, and the amount of light transmittance was increased. Finally, according to the results of the thermal aging test, it was found that TPVs with 30 and 45 wt% PA11, respectively, showed outstanding thermal resistance after aging at 160 °C and 168 h and did not melt down.

Enhancing the Mechanical Properties of PBAT/Thermoplastic Starch (TPS) Biodegradable Composite Films through a Dynamic Vulcanization Process

Enhancing the Mechanical Properties of PBAT/Thermoplastic Starch (TPS) Biodegradable Composite Films through a Dynamic Vulcanization Process

Preparation of biodegradable PLA/PBAT blends with balanced toughness and strength by dynamic vulcanization process

Polylactic acid (PLA) has received significant attention in recent years as a commercially available biodegradable resin. However, its brittleness limits its broader adoption. Blending PLA with another biodegradable resin poly(butylene adipate-co-terephthalate) (PBAT) is a simple strategy to toughen PLA, however, the effect is limited and the tensile strength is generally harmed. In this work, PBAT, initiator BIBP and cross-linker TAIC were initially mixed and then extruded into pre-crosslinked PBAT pellets. Subsequently, the pre-crosslinked PBAT and PLA were melt-blended to create PLA/micro-crosslinked PBAT composites. The effects of different TAIC contents on the degree of PBAT gelation, properties and morphological structure of composites were explored. The results showed that TAIC could effectively improve the mechanical properties of PLA/PBAT, particularly the notched impact strength. When the TAIC content was 0.3 wt% of PBAT, the notched impact strength and elongation at break of PLA/PBAT (7/3) reached 42.26 kJ/m2 and 264.26 %, respectively, which are both far higher than those of the blend without cross-linking (9.37 kJ/m2 and 21.29 %). The composites still exhibited excellent tensile strength (46.23 MPa) and tensile modulus (1676.84 MPa), surpassing those of PLA/un-crosslinked PBAT composites. This enhanced toughening and tensile strength maintaining effect is attributed to the network structure in PBAT and the increased compatibility between PLA and PBAT caused by cross-linking within PBAT and at PLA/PBAT interface. The dynamic vulcanization strategy using an extruder provides a possibility for the large-scale preparation of stiff-tough PLA. Of course, further work, including pilot or industrial trials, is necessary to validate scalability.

Joining of PP/EPDM TPV to aluminium alloy 6061-T6 directly via generating sorbate in situ and adjusting the heat input of welding

At present, it is difficult to join the non-polar thermoplastic vulcanization based on Polypropylene (PP)/Ethylene-Propylene-Diene (EPDM) to aluminium alloy 6061-T6 (A6061) directly because of the great difference in physical and chemical properties between them. In this paper, zinc sorbate (ZDS) was introduced into the dynamic vulcanization process of PP/EPDM TPV to achieve high performance TPV interface modification. The results show that the polymerization of ZDS can enhance the interface compatibility, melt strength and surface energy of PP/EPDM/ZDS TPV while reducing the linear expansion coefficient of TPV. On this basis, the plate curing machine is used to simulate friction stir welding, and the heat input (temperature:180 °C, pressure:20 MPa, welding time:60 s) was optimized. PP/EPDM/ZDS TPV was directly connected to A6061, and the influencing factors of the joint strength were analyzed. The results show that the tensile shear strength of composite joints decreases with the static time and then keeps stable, reaching 3.53 MPa. The chemical bond (Al-C) is formed at the interface between A6061 and PP/EPDM/ZDS TPV, which plays a key role in improving the strength of the joint. The results of this work can expand the application range of PP/EPDM TPV, and provide basic data and theoretical support for the connection between TPV and metal.

Preparation of self-healing EPDM/ionomer thermoplastic vulcanizates with ionic network for automotive application: Effects of maleic anhydride grafted EPDM as compatibilizer

This work evaluates the effects of maleic anhydride grafted ethylene-propylene-diene rubber (EPDM-g-MAH) on the processing characteristics, compatibility and mechanical properties of EPDM/Ionomer blends. Dynamic vulcanization process was used to fabricate thermoplastic vulcanizates (TPVs) of different compositions using EPDM polymers and high acid (HA60D) or mid acid (MA60D) containing thermoplastic ionomers. The addition of EPDM-g-MAH in EPDM/Ionomer blends had a predominant role as a compatibilizing agent, which affected the processability and properties of the final material. The tensile properties showed significant improvement with increasing the content of compatibilizer in the vulcanizates. The microscopical analysis of fracture surfaces further supported the heterogeneous nature of the blends and compatibility of the polymer phases. The concept was based on a simple ionic crosslinking reaction between carboxyl groups present in the ionomer and zinc oxide (ZnO), where the formation of reversible Zn2+covalent crosslinks exhibits the self-healing behavior. The combination of blending and ionic cross-linking improved not only mechanical properties but also improved self-healing performance. The self-healing nature of the TPVs has been identified by scratch resistance test, where the ternary blends (EPDM/Ionomer/EPDM-g-MAH) showed 100% healing efficiency of the scratch surface at 89°C for 24 h.

Development of propylene butene copolymer/ethylene propylene diene monomer blend foam and the effect of network structure on its reprocessing properties

AbstractThermoplastic materials have received extensive attention for their excellent mechanical properties and reproducibility, and have been emerging in lightweight accessories. However, for the traditional thermoplastic vulcanized (TPV) rubber, the dynamic vulcanization process makes it difficult to achieve low density and good compression performance. Herein, lightweight propylene butene copolymer/ethylene propylene diene monomer (PPB/EPDM) blend foam was prepared by static vulcanization of PPB and EPDM blend and supercritical nitrogen (sc‐N2) foaming technology. The minimum density and compression set of the PPB/EPDM blend foam were 0.065 g/cm3 and 13.6% respectively, a significant improvement was obtained compared with TPV. In addition, the PPB/EPDM blends retained the mechanical properties after seven times reprocessing, and the blend foam had similar cell structures to that of dynamic vulcanized TPV foam because of the phase transition of PPB/EPDM blend during reprocessing. This work provided an idea for the preparation of high‐performance, lightweight, and recyclable thermoplastic materials.

Effect of dynamic vulcanization on the performance of high content rubber modified asphalt

AbstractHigh content rubber modified asphalt (HCRA) is usually prepared with devulcanized rubber (DR) in asphalt with good workability. However, the high‐temperature properties of HCRA deteriorate simultaneously. In this study, dynamic vulcanization approach was adopted to improve the high‐temperature properties of HCRA without mitigating the workability and low‐temperature performance of modified binder blends. The dynamic vulcanization process and mechanism were investigated based on the gel content, related chemical reactions, morphology, rheological behavior, and tensile properties of HCRA. The occurrence of dynamic vulcanization was confirmed by the increase in gel content. Fourier transform infrared spectroscopy reflected that CC bonds in trans‐olefins participated in dynamic vulcanization, followed by the reaction of those in conjugated olefins. Optical microscopy tests showed that dynamic vulcanization also improved the compatibility between the DR and asphalt. It was found that dynamic vulcanization of HCRA is the gradual stabilization process to form local cross‐linked networks in asphalt. With the addition of sulfur, degradation, aging, and dynamic vulcanization took place simultaneously in HCRA. Dynamic vulcanization increased the high‐temperature properties, fracture toughness, as well as storage stability of HCRA. Furthermore, dynamic vulcanization restricted rubber degradation and improved the aging behavior of HCRA.

Dynamically vulcanized poly (lactic acid)/polyurethane/MXene nanocomposites with balanced stiffness and toughness

When brittle poly (lactic acid) (PLA) toughened by elastomers, loss of strength and modulus are inevitable, how to avoid the strength and modulus loss for elastomer toughened PLA is an urgent problem to be solved. In this study, a one-step dynamic vulcanization strategy was reported to prepare PLA/polyurethane (PU)/MXene nanocomposites with balanced stiffness and toughness based on the reaction between polyethylene glycol (PEG) and isophorone diisocyanate trimer (IPDIT). The effect of MXene content on the morphology, mechanical properties, thermal transitions and rheological behavior were investigated in detail. The results show that the PU generated during the dynamic vulcanization process and PLA have very good compatibility, and MXene nanosheets can be well dispersed in PLA/PU polymer matrix after pre-intercalation with PEG molecular chains. This study provides a promising strategy for manufacturing high performance PLA with balanced stiffness and toughness at industrial level.

Preparation and characterization of peroxide‐based dynamically vulcanized thermoplastic elastomer of poly (lactic acid)/chloroprene rubber

AbstractThermoplastic vulcanizates (TPVs) composed of crosslinked rubber phase with high chemical and thermal resistance have received great attention in pharmaceutical and biological applications. In the present work, attempts have been made to prepare TPVs based on poly (lactic acid) (PLA) and chloroprene rubber (CR) via a melt mixing process in the presence of dicumyl peroxide (DCP) and a combination of magnesium oxide (MgO) and epoxidized soybean oil (ESBO) as hydrochloric acid (HCl) scavenger to minimize CR degradation by DCP. A honeycomb co‐continuous micromorphology was observed for the fabricated TPVs samples through scanning electron microscopy, significantly different from the classical “sea‐island” micromorphology. However, the PLA/CR vulcanizates prepared by only DCP did not show enhanced mechanical properties due to the CR thermal decomposition by the DCP radicals. Therefore, a novel formulation was designed to prevent thermal decomposition of the CR phase during dynamic vulcanization by the incorporation of a combination of ESBO and MgO as efficient HCl scavenger. The stabilized TPV samples exhibited an intense brittle‐ductile transition effect and improved tensile mechanical. The obtained results implied the effectiveness of ESBO and MgO in stabilizing CR phase during peroxide dynamic vulcanization process.

Enhancement of thermoelectric and mechanical properties of thermoplastic vulcanizates (TPVs) with hydroxylated graphene by dynamic vulcanization

Abstract In order to obtain higher thermoelectric and mechanical properties in nonpolar thermoplastic vulcanizates (TPVs), the butyl rubber/polypropylene (TPVs)/hydroxylated graphene (HGE) composites with nanosheet network were prepared through masterbatch technique and based on thermodynamic calculations, using polypropylene-graft-maleic anhydride (PP-MA) as a compatibilizer. The Fourier transform infrared (FTIR) and Raman spectra revealed the introduced maleic anhydride group on PP-MA can form strong interfacial interaction with hydroxyl-containing functional groups on HGE. Morphology study indicated the rubber particles in the composites occupied the most volume of the PP phase, as expected to hinder the aggregation of HGE and form the effective nanosheet network. The nanosheet network can be combined with the butyl rubber (IIR) cross-linked particles during the dynamic vulcanization process to improve the interface bonding between PP and IIR, thus increasing the tensile strength of TPVs. The prepared TPVs/HGE composites have significantly improved in mechanical properties, thermal properties and dielectric properties, which provides a guarantee for their potential application as multifunctional TPVs polymers.

Preparation of polyoxymethylene/methyl vinyl silicone rubber/thermoplastic polyurethane ternary thermoplastics vulcanizates with good toughness properties

Novel thermoplastic vulcanizates (TPVs) based on polyoxymethylene (POM) and methyl vinyl silicone rubber (MVQ) have been prepared by dynamic vulcanization process through a batch mixer. During the preparation of TPV blends, Di-(tert butyl peroxyisopropyl) benzene (BIBP) was used as the curing agent in order to make MVQ cross-linked and TPU was used to coat MVQ for improving the compatibility of MVQ and POM. In order to understand the influence of different compositions on TPV blends, five groups of experimental processes were described in detail. During these experiments, the amount of POM was reduced from 70phr to 30phr, that of MVQ was gradually increased from 18phr to 42 phr, and TPU was increased from 12phr to 28phr. In addition, the morphology and properties of TPVs were studied by DSC, FTIR, SEM, DMA and mechanical tests. The mechanical testing results showed that with the amount of POM decreasing and the total amount of MVQ and TPU increasing, the tensile strength of the TPV blends gradually was decreased, and the elongation at break was increased accordingly from 35.2 ± 6% of pure POM to 142.8 ± 11% of sample 5#.

Synergistic toughening of poly(lactic acid)/poly(ethylene vinyl acetate) (PLA/EVA) by dynamic vulcanization and presence of hydrophobic nanoparticles

AbstractThe presented research reports a successful preparation of a super toughened poly(lactic acid)/poly(ethylene vinyl acetate) (PLA/EVA) blend using simultaneous dicumyl peroxide (DCP)‐induced dynamic vulcanization and addition of hydrophobic spherical silica nanoparticles (NPs). The torque evolution during melt mixing of the samples was assessed to track the dynamic vulcanization process. NPs were localized mainly in the EVA droplets and at the interface where a layer of particles was formed with a small amount dispersed in the PLA matrix. The incorporation of NPs or DCP induced compatibilization, causing a drastic decline in the size of EVA droplets in addition to improving the interfacial adhesion. On the other hand, simultaneous dynamic vulcanization and NPs incorporation synergistically affected the compatibilization of EVA and PLA phases. Differential scanning calorimetry (DSC) was employed to analyze the thermal transition and crystallization behavior of the samples. Simultaneous incorporation of silica nanoparticles and DCP at an optimum content significantly improved the tensile toughness, elongation at break, and impact strength, giving rise to super toughened PLA/EVA blend. The elongation at break and impact strength of the dynamically vulcanized PLA/EVA blend containing 5% nanosilica showed an increase from 7% to 175% and 5.1 to more than 77 kJ/m2, respectively as compared to the neat sample. Based on SEM analysis of the fractured surface of the tensile samples, cavitation in combination with intensive shear yielding of the matrix were dominating toughening mechanisms. Finally, the effect of DCP and NPs on the microstructural properties of the sample was investigated through rheological evaluations.

A relative study of the effect of static and dynamic vulcanization upon shape memory nature of thermally actuated peroxide crosslinked polyolefinic blends

AbstractThermally actuated peroxide crosslinked shape memory polyolefinic blends of EOC and EPDM has been developed. Effect of static and dynamic vulcanization process on the shape memory character has been pursued in detail. Shape memory properties study at 60°C reveals that statically vulcanized blend and dynamically vulcanized blend are superior in terms of shape fixity character and shape recovery behavior, respectively. Breakage of lower percentage of crystalline structure gives higher percentage of shape fixity for the statically vulcanized blend. In a parallel way, statically vulcanized blend shows better stress–strain properties also. On the other hand, higher degree of crosslinked network structure results higher shape recovery percentage for the dynamically vulcanized blend. Similar to shape recovery characteristics, dynamically vulcanized blend shows better thermal stability and higher percentage of gel content.

Molecular evolution during dynamic vulcanization of polyolefin mixtures for lead‐free thermoplastic vulcanized

The preparation process and the final properties of new thermoplastic lead‐free medium voltage (MV) insulation compounds based on the thermoplastic vulcanized (TPV) technology are reported and discussed at molecular level. The TPV MV insulation compounds were prepared starting from a peroxide curable lead free MV insulation, which is the actual market benchmark. For this reason, they were extensively investigated in comparison to the standard lead free MV insulation. The results of the dynamic vulcanization process were evaluated and related to the formulation. Now in the present paper we are reporting a detailed analysis of the molecular changes induced by the vulcanization reaction with reference to the different polymers and low molecular weight additives present in the starting mixture. The results are analyzed with reference to the used polyolefins structure with the aim to provide insights helping to relate the formulation at molecular level to the behavior of the final complex materials thus offering an useful tool to a priori design of TPVs with the desired ultimate properties.

Effect of the geometry of cellulose nanocrystals on morphology and mechanical performance of dynamically vulcanized PLA/PU blend

Effects of the addition of single but geometrically different cellulose nanocrystals (CNCs) namely cylindrical CNCs (ultrasonic treated), spherical CNCs (chemically treated) and rod-like CNCs (commercial) on microstructural development and mechanical performance of the thermoplastic vulcanizates (TPVs) based on polylactic acid/polyurethane prepolymer (80/20) were studied. It was shown that a fraction of PLA molecules reacted with PU molecules during the dynamic crosslinking process. This was confirmed by the results of gel content measurements which showed an appreciable amount of additional gel content. This phenomenon together with the dynamic vulcanization process facilitated the development of a dual-continuous morphology in the TPV sample which was confirmed by the melt viscoelastic results and TEM micrographs. Interestingly, the addition of spherical CNCs to the TPV led to a remarkable enhancement in its toughness. A similar effect but to a lesser extent was observed in the TPV sample filled with cylindrical CNCs. These results could be explained in terms of a 3D percolated or interconnected network microstructure formed between finely dispersed CNCs localized in PLA and/or between CNCs and the PLA matrix. This fact was evidenced by observation of strong liquid–solid transition in the melt viscoelastic results, as well as TEM and AFM micrographs. On contrary to other counterparts, the rod-like CNCs had a weakening effect on toughness of the TPV which was attributed to their poor dispersion and/or formation of their aggregates which could act as stress concentrators. Moreover, DMTA results showed an almost similar reinforcing effect for the three CNCs on increasing the modulus of the TPV below Tg of the PU and partially compensated the PU reducing effect on modulus in the temperature range between the Tg of PU and PLA.

Morphology Evolution and Rheological Behaviors of PP/SR Thermoplastic Vulcanizate.

The thermoplastic vulcanizates (TPVs) of polypropylene (PP)/silicone rubber (SR) were prepared by dynamic vulcanization (DV) technology. The mixing torque, morphology, viscoelasticity, and creep response of PP/SR TPVs were investigated by torque rheometer, scanning electron microscope (SEM), transmission electron microscope (TEM), rotational rheometer, and dynamic mechanical analysis (DMA). A mixing-torque study showed that torque change and dynamic-vulcanization time increased with SR content increasing in the DV process, but DV rate was independent of SR content. TEM images indicated that the phase inversion of PP/SR-60 TPV from bicontinuous to a sea–island structure took place in the DV process, and a hot press would break the rubber aggregates and shrink a large SR phase. Dynamic-strain measurement demonstrated that PP/SR TPVs exhibit a distinct “Payne effect”, which can be attributed to the destruction and reconstruction of SR physical networks. Complex viscosity indicated that SR content did not affect the processability of PP/SR TPVs at high shear rates. Furthermore, the creep deformation and recovery of PP/SR TPVs at solid and melt states were studied, respectively.

The effect of dynamic vulcanization on the morphological and mechanical properties of the toughened poly (lactic acid)/epoxidized natural rubber

Poly (lactic acid)/epoxidized natural rubber (PLA/ENR) was prepared by using counter-rotating twin-screw extruder. For dynamic vulcanization process, ENR was compounded with 3 phr of N, N’-m-phenylenebismaleimide (HVA-2) as a crosslinking agent. The aim of this study is to determine the effect of unvulcanized and dynamically vulcanized of ENR on the properties of PLA/ENR blend. The blending of PLA with ENR was prepared with the various composition of ENR (0 wt% to 30 wt%). The morphology and mechanical properties of the blends were investigated by using scanning electron microscope (SEM), tensile test, and impact test. The unvulcanized blend produced a co-continuous morphology of PLA and ENR and the dynamically vulcanized blend shows the dispersed ENR rubber particles in PLA continuous matrix. For both systems, the tensile strength value was dropped with the increasing amount of ENR content. The impact strength of both systems shows the maximum value at 20 wt% of ENR content. However, dynamically vulcanized PLA/ENR blend shows a better tensile strength and impact strength value as compared with unvulcanized blend.

Effects of Rotor Speed on Peroxide/Bismaleimide Cured Polypropylene/Nitrile Rubber Thermoplastic Vulcanizates (TPVs)

Elastomer thermoplastics are a class of polymeric materials that received industry attention due to the possibility of joining the elastic of elastomers with the thermoplastics processability. The synergistic properties are linked to the appropriate processing. This study evaluated the effect of rotor speed during polymer mixing and the dynamic vulcanization process of polypropylene and nitrile rubber blends. Bismaleimide was employed as multipurpose agent (crosslinking coagent for peroxide and compatibilizer). Morphology, mechanical properties, compression set and oil resistance tests were evaluated for compositions containing 50 and 70 PHR of elastomer. The compatibilization of TPV was realized by infrared spectroscopy. It was shown a compatibilizer effect and better dispersion, achieving the inversion phase, only studying the effect of processing conditions (rotor speed, addition sequence, additives), without any extra interfacial agent. There is a tendency to obtain better performance with decrease speed at dynamic vulcanization or/and at torque stabilization, mainly for blends with 50 PHR of rubber.

Superior heat-resistant and oil-resistant blends based on dynamically vulcanized hydrogenated acrylonitrile butadiene rubber and polyamide 12

High-performance thermoplastic vulcanizates (TPVs) are the new generation of TPVs that provide superior heat and oil aging behavior. TPVs based on hydrogenated acrylonitrile butadiene rubber and polyamide 12 (PA12) have been first developed by the dynamic vulcanization process, in which selective cross-linking of the elastomer phase during melt mixing with the thermoplastic phase (PA12) was carried out simultaneously. In this present investigation, hydrogenated acrylonitrile butadiene rubber (HNBR)/PA12 and partially hydrogenated carboxylated acrylonitrile butadiene rubber (XHNBR)/PA12 with blend ratio of 50:50, 60:40, and 70:30 wt% were prepared at 185°C at a rotor speed of 80 rpm for 5 min. Di-(2-tert-butyl peroxy isopropyl) benzene was chosen as the suitable cross-linking peroxide to pursue the dynamic vulcanization. TPV based on 50:50 HNBR/PA12 and XHNBR/PA12 show better physico-mechanical properties, rheological behavior, thermal stability, dynamic mechanical analysis, and creep behavior among all the TPVs. Morphology study reveals that dispersed phase morphology has been formed with an average dimension of the rubber particles in the range of 0.8–1.5 µm. For aging test, TPVs were exposed to air and ASTM oil 3, respectively. Air aging tests were carried out in hot air oven for 72 hr at 125°C, while the oil aging tests were carried out after immersion of the samples into the oils in an aging oven. After aging, there is only slight deterioration in the physico-mechanical properties of the TPVs. In case of 50:50 blends of HNBR/PA12 and XHNBR/PA12, the retention of the properties upon after aging was found excellent. These TPVs are designed to find potential application in automotive sector especially for under-hood-application, where high-temperature resistance as well as high oil resistance is of prime importance. Copyright © 2016 John Wiley & Sons, Ltd.