Covulcanization of LLDPE/EMA blends using dicumyl peroxide

The effect of dicumyl peroxide (DCP) content on the gel fraction, mechanical, dynamic mechanical, and thermal properties of linear low‐density polyethylene (LLDPE)/ethylene‐co‐methyl acrylate (EMA) blends were studied. Gel content of the blends increases with increasing DCP content, and EMA is more prone to crosslinking than LLDPE. Wide‐angle X‐ray diffraction (WAXD) and differential scanning calorimetry (DSC) were used to study the effect of DCP crosslinking on percent crystallinity and crystalline structure of the blends and individual components. At lower level of DCP loading, crosslinking process does not have significant effect on the crystalline structure of the LLDPE, which was confirmed from the percent crystallinity and lattice distance value. However, at higher DCP content, percent crystallinity decreases significantly. At lower EMA concentration (<50%), percent crystallinity and lattice distance remain unchanged up to 2 wt % of DCP. For EMA contents of more than 50 wt %, increasing DCP content reduces the crystallinity of the blends and increases the lattice distance. The highest level of mechanical and dynamic mechanical properties was observed for 60/40 LLDPE/EMA blends at 2 wt % DCP. Addition of LLDPE‐g‐MA (3 wt %) as a compatibilizer enhances the properties of the vulcanizates. Blends crosslinked with DCP up to 0.3 wt % can easily be reprocessed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

The Effect of Dicumyl Peroxide Vulcanization on the Properties & Morphology of Polypropylene/Ethylene-Propylene Diene Terpolymer/Natural Rubber Blends

ABSTRACT

This article discusses some properties such as tensile properties, chemical and oil resistance, gel content, crystallinity, and morphology of polypropylene (PP)/ethylene-propylene diene terpolymer (EPDM)/natural rubber (NR) blends. Dicumyl peroxide (DCP) was applied as a crosslinking agent. In terms of tensile properties, peroxide vulcanized blend shows higher tensile strength and tensile modulus (stress at 100% elongation, M₁₀₀) as compared with the unvulcanized blend. The elongation at break of the peroxide vulcanized blend is higher for the blend with NR rich content compared with the EPDM rich content. The improvements in chemical and oil resistance as well as gel content of peroxide vulcanized blends have also proved the formation of crosslinks in the rubber phase. Scanning electron microscopy (SEM) micrographs from the surface extraction of the blends support that the crosslinks have occurred during dynamic vulcanization. Dynamical vulcanization with DCP has decreased the percent crystallinity of blends that can be attributed to the formation of crosslinks in the rubber.     

Dynamically vulcanized polypropylene/styrene–butadiene rubber blends: The effect of a peroxide/bismaleimide curing system and composition

Polypropylene (PP)/styrene–butadiene rubber blends were studied with special attention given to the effects of the blend ratio and dynamic vulcanization. Dicumyl peroxide (DCP) was used as the curing agent in combination with N,N′‐m‐phenylene bismaleimide (BMI) as the coagent for the curing process. Outstanding mechanical performance, especially with regard to the elongation at break, and better resistance to compression set were achieved with the dynamic vulcanization; this indicated that the DCP/BMI system also acted as a compatibilizing agent. This phenomenon was also confirmed by Fourier transform infrared spectroscopy of the insoluble material, the crystallinity degree of the PP phase (as investigated by X‐ray diffractometry), and scanning electron microscopy. The dynamic mechanical properties of the nonvulcanized and vulcanized blends were also investigated. The aging resistance of the blends was also evaluated. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Influence of static and dynamic crosslinking techniques on the transport properties of ethylene propylene diene monomer rubber/poly (ethylene-co-vinyl acetate) blends

The transport characteristics of dynamically and statically cross-linked Ethylene Propylene Diene Monomer/poly (ethylene-co-vinyl acetate) (EPDM/EVA) blends have been examined in the temperature interval of 28–58 °C using benzene, toluene and xylene as probe molecules. The dynamically vulcanized blends exhibited enhanced properties on the sorption and diffusion features compared to the corresponding statically vulcanized blends. In both the cases, as the EVA content increased in the blends, the solvent uptake decreased. The experimental observations have been correlated with the phase morphology of the blends, using scanning electron micrographs. The crystallinity of the blends was studied using X-ray diffraction patterns. Among the three vulcanising systems, viz, sulphur, dicumyl peroxide (DCP), and a mixture consisting of sulphur and peroxide, employed for the matrix, the DCP cross linked system exhibited the lowest solvent uptake. The molar mass between cross links and the diffusion coefficients have been computed to complement the observed sorption behaviour.     

Blends of polyamide 6 and epichlorohydrin elastomers. II. Thermal,dynamic mechanical,and mechanical properties

The mechanical blending of polyamide 6 and epichlorohydrin elastomers, polyepichlorohydrin, PEPI, and poly(epichlorohydrin‐co‐ethylene oxide), ECO, is accompanied by grafting copolymerization. In this work the influence of the graft copolymer on the thermal and mechanical properties of the blends is investigated. The blends are immiscible and the crystallinity degree normalized to the polyamide 6 contents in the blends is higher than expected. The X‐ray diffraction results show that the grafting copolymer is also crystalline; hence, the presence of crystalline phase of copolymer can be responsible for the apparent enhancement of crystallinity. The DMA analysis reveals the presence of a shoulder in the peak corresponding to the PA 6 glass transition, as observed by loss modulus curves, which was assigned to relaxations of the grafting copolymer. Tensile tests show that the blends are more fragile than the PA 6, despite the graft copolymer. These results were attributed to the mechanical fragile interface constituted by a network type structure of the graft copolymer. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1835–1841, 1999     

Effect of crosslinking on polyamide 11/butadiene-acrylonitrile copolymer blends

The effect of crosslinking of polyamide 11 and butadiene-acrylonitrile copolymer (nitrile rubber) was studied. The effect of static and dynamic crosslinking on blending are described. Static and dynamic crosslinking do not significantly improve impact strength of low-rubber-content PA11/NBR blends. For blends with dynamic crosslinking and high rubber contents, mechanical properties including impact strength improve. Thermal behavior of crosslinked PA11/NBR blends were studied by DSC and DMA. SEM was used for investigation of the effect of crosslinking on particle size and particle size distribution, phase morphology, and fracture surface morphology. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1605–1611, 1997     

Tailoring viscoelastic and mechanical properties of the foamed blends of EVA and various ethylene‐styrene interpolymers

Foamed materials (EVA/ESI) have been prepared from blends of ethylene‐vinyl acetate copolymer (EVA) and ethylene‐styrene interpolymers (ESI) in the presence of various amounts of dicumyl peroxide (DCP). Four ESIs of different compositions were employed in this study; their styrene contents ranged from 30 to 73 wt% and their T_g ranged from −2 to 33°C. It has been found that microcellular morphology, degree of crosslinking and expansion ratio were strongly affected by the DCP concentration and the type of ESI employed. A minimum degree of crosslinking was required for making good foams and the same degree of crosslinking could be achieved by employing a smaller amount of DCP for an EVA/ESI blend having a higher styrene content. In contrast to other EVA blends, such as EVA/LDPE, these EVA/ESI blends exhibited no existence of any optimum DCP concentration, and the α glass transition temperatures of the foams varied with the ESI type, covering a wide span from 0°C to 37°C. Therefore, it was possible to tailor the T_g of an EVA/ESI blend by choosing an appropriate type of ESI. Furthermore, by correctly tailoring the T_g, the EVA/ESI foam could be made into a rubbery material with a custom‐designed damping factor. Tensile strength and modulus of the EVA/ESI foams increased generally with an increase in the styrene content, with the exception that ESIs with very low styrene content will confer on the blend a high modulus at small strain and a large elongation at break.     

Structure–property correlations of heat‐shrinkable polymer blends based on ethylene vinyl acetate/carboxylated nitrile rubber in the presence of different curatives

Elastic memory was introduced into heat‐shrinkable polymer blends in the form of an elastomeric phase and through subsequent crosslinking. Blends of ethylene vinyl acetate and carboxylated nitrile rubber with different curative systems were studied with respect to their shrinkability. With an increase in the cure time (the crosslinking density, or memory point), shrinkage increased for the blends with all the curative systems except dicumyl peroxide (DCP). Increasing the elastomer content increased shrinkability because of the increasing driving retraction force of the oriented elastomer phase. A sample stretched at a high temperature (HT) showed greater shrinkage than a sample stretched at room temperature (RT) because of the greater concentration and degree of orientation of the extended chains. Generally, the crystallinity of the stretched (RT and HT) samples was higher than that of ordinary unstretched and shrunk samples, and this increased the effectiveness of intermolecular interactions in the former. For all systems except DCP, RT‐stretched samples showed higher crystallinity than corresponding HT‐stretched samples. With RT stretching, rapid extension and subsequent recrystallization occurred in samples molten at high local values of the stored elastic energy. An increase in the crosslinking density and orientation of the blends increased the thermal stability because of the formation of strong networks and compact structures. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1414–1420, 2003     

Thermal and mechanical properties of uncrosslinked and chemically crosslinked polyethylene/ethylene vinyl acetate copolymer blends

Uncrosslinked and chemically crosslinked binary blends of low‐ and high‐density polyethylene (PE), with ethylene vinyl acetate copolymer (EVA), were prepared by a melt‐mixing process using 0–3 wt % tert‐butyl cumyl peroxide (BCUP). The uncrosslinked blends revealed two distinct unchanged melting peaks corresponding to the individual components of the blends, but with a reduced overall degree of crystallinity. The crosslinking further reduced crystallinity, but enhanced compatibility between EVA and polyethylene, with LDPE being more compatible than HDPE. Blended with 20 wt % EVA, the EVA melting peak was almost disappeared after the addition of BCUP, and only the corresponding PE melting point was observed at a lowered temperature. But blended with 40% EVA, two peaks still existed with a slight shift toward lower temperatures. Changes of mechanical properties with blending ratio, crosslinking, and temperature had been dominated by the extent of crystallinity, crosslinking degree, and morphology of the blend. A good correlation was observed between elongation‐at‐break and morphological properties. The blends with higher level of compatibility showed less deviation from the additive rule of mixtures. The deviation became more pronounced for HDPE/EVA blends in the phase inversion region, while an opposite trend was observed for LDPE/EVA blends with co‐continuous morphology. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3261–3270, 2007     

Tailoring morphology to improve the gas‐barrier properties of thermoplastic polyurethane/ethylene‐vinyl alcohol blends

The morphology and helium‐barrier properties of thermoplastic polyurethane (TPU)/ethylene‐vinyl alcohol (EVOH) blends with and without dicumyl peroxide (DCP) were investigated by melting blending. A lamellar dispersion of EVOH with good helium‐barrier properties was observed in the TPU matrix with DCP. The evolution of the morphology of the blends is mainly related to the variation of the viscosity ratio between the dispersed phase and the matrix phase. Compared with pure TPU, lamellar morphology increased the helium‐barrier properties of the TPU/EVOH (60/40) blend by as much as 10‐fold. We also explored the effects of composition, DCP content, and blending sequence on the morphology and helium‐barrier properties of the TPU/EVOH blends. The morphology of the blends ranged from a droplet‐matrix to a lamellar structure. We determined the optimum amount of DCP to improve the helium barrier of the blends. The helium‐barrier properties of the blends prepared by direct blending were superior to those of the blends prepared by two‐segment blending, and the blends prepared by direct blending exhibited a well‐developed lamellar morphology. We compared the permeability of the samples with the theoretical results to explain the relationship between morphology and helium‐barrier properties. POLYM. ENG. SCI., 56:922–931, 2016. © 2016 Society of Plastics Engineers     

Dynamically vulcanized blends of polypropylene and ethylene‐octene copolymer: Comparison of different peroxides on mechanical,thermal, and morphological characteristics

Thermoplastic vulcanizates (TPVs) are prepared by the dynamic vulcanization process, where crosslinking of an elastomer takes place during its melt mixing with a thermoplastic polymer under high shear. TPVs based on polypropylene (PP) with different grades of ethylene‐octene copolymers (EOC) were prepared with a coagent assisted peroxide crosslinking system. The effect of dynamic vulcanization and influence of various types and concentrations of peroxide were mainly studied on the basis of the mechanical, thermal, and morphological characteristics. Three structurally different peroxides, namely dicumyl peroxide (DCP), tert‐butyl cumyl peroxide (TBCP), and di‐tert‐butyl peroxy isopropyl benzene (DTBPIB) were investigated. The mechanical properties of the TPVs are primarily determined by the extent of crosslinking in the EOC and the degree of degradation in the PP phase. Among all peroxides used DCP gives best overall properties with low‐molecular‐weight EOC, whereas TBCP shows best property level with high‐molecular‐weight EOC‐based TPVs. These can be explained on the basis of the molecular characteristics of EOC and the nature of the peroxide used. Differential scanning calorimetery (DSC) and morphological analysis reveal that PP and EOC are a thermodynamically immiscible system. The melting endotherm was studied to determine the influence of various peroxides on crystallinity of the PP phase. Tensile fracture patterns were also analyzed to study the failure mechanism of the samples. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermoplastic elastomers based on high‐density polyethylene,ethylene–propylene–diene terpolymer,and ground tire rubber dynamically vulcanized with dicumyl peroxide

Thermoplastic vulcanizates (TPVs) based on high‐density polyethylene (HDPE), ethylene–propylene–diene terpolymer (EPDM), and ground tire rubber (GTR) were dynamically vulcanized with dicumyl peroxide (DCP). The polymer blend was composed of 40% HDPE, 30% EPDM, and 30% GTR, and the concentration of DCP was varied from 0.3 to 3.6 parts per hundred rubber (phr). The properties of the TPVs were determined by evaluation of the gel fraction content and the mechanical properties. In addition, IR spectroscopy and differential scanning calorimetry analysis were performed as a function of the DCP content. Decreases in the Young's modulus of the blends and the crystallinity of HDPE were observed when the content of DCP was greater than 1.8 phr. The results regarding the gel content indicate that the presence of DCP promoted the crosslinking of the thermoplastic matrix, and optimal properties were obtained with 1.5% DCP. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39901.     

Morphology and mechanical properties of ethylene‐vinyl acetate rubber/polyamide thermoplastic elastomers

High performance thermoplastic elastomers based on ethylene‐vinyl acetate rubber (EVM) and ternary polyamide copolymer (tPA) were prepared through a dynamic vulcanization process in the presence of dicumyl peroxide (DCP). The morphology, crystallization, and mechanical properties of the EVM/tPA blends were studied. A phase transition of EVM/tPA blend was observed at a weight ratio of 60/40. The presence of EVM increased the melting enthalpy at the high temperature of tPA, ascribing to the heterogeneous nucleating effect of EVM. The tensile strength of EVM/tPA (70/30) blends was increased up to 20.5 MPa as the DCP concentration increased to 3.5 phr, whereas the elongation at break of the blends kept decreasing as the DCP concentration increased. The addition of ethylene‐acrylic acid copolymer (EAA) or maleic anhydride‐grafted EVM (EVM‐g‐MAH) to the EVM/tPA blends both induced finer dispersion of the EVM particles in the tPA phase and improvement in the tensile strength and elongation at break of the blends, which were ascribed to the compatibilization of EAA or EVM‐g‐MAH. Finally, a high performance EVM/tPA (70/30) thermoplastic elastomer with Shore A hardness of 75, tensile strength of 24 MPa, elongation at break of 361%, and set at break of 20% was obtained by adding 5 wt % of EVM‐g‐MAH and 3.5 phr DCP. It has great potential in automotive and oil pipeline applications. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Toughening modification of PLLA/PBS blends via in situ compatibilization

Biodegradable polymer blends consisting of poly(L ‐lactic acid) (PLLA) and poly(butylene succinate) (PBS) were prepared in the presence of dicumyl peroxide (DCP). The effects of DCP content on the mechanical properties, thermal and rheological behavior, phase morphology as well as the toughening mechanism of the blends were investigated. The notched Izod impact strength of PLLA/PBS (80/20) blend significantly increased after the addition of 0.05–0.2 phr DCP, but the strength and modulus monotonically decreased with increasing DCP content. PBS acted as a nucleating agent at the environmental temperature below its melting temperature and accelerated the crystallization rate of PLLA but had little effect on its final degree of crystallinity. The degree of crystallinity of PBS and the cold crystallization ability of PLLA gradually reduced with increasing DCP content. The addition of DCP induced an increase in viscosity of the blends at low frequencies as well as finer dispersion of PBS particles and better interfacial adhesion between PLLA and PBS, indicating the in situ compatibilization occurred between the two components. The optical clarity of PLLA/PBS blends was significantly improved after the addition of DCP, which was in accordance with the crystallization behavior and phase structure of the blends. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers     

Dynamic mechanical properties of polypropylene‐g‐maleic anhydride and ethylene–propylene–diene terpolymer blends: Effect of blend preparation methods

In this work, we attempted two different ways of processing to improve interfacial adhesion of polypropylene (PP) and ethylene–propylene–diene terpolymer (EPDM) by introducing maleic anhydride (MAH); In one way, the in situ grafting and dynamic vulcanization (ISGV) were performed simultaneously from PP and EPDM with MAH in the presence of dicumyl peroxide (DCP) in an intensive mixer. In another way, PP was first grafted with MAH and then the PP‐g‐MAH was blended with EPDM in the intensive mixer in the presence of DCP by the dynamic vulcanization (DV). It was found that the glass transition temperatures (T_gs) of both PP and EPDM phases were shifted to higher temperature as the EPDM content increased for the blends prepared by both IGSV and DV methods, mainly due to the crosslinking of EPDM. The higher T_gs and larger storage moduli were observed for the blends prepared by the ISGV method than those prepared by the DV method, while the morphology showed that the size reduction of dispersed particles in latter blends was larger than that of the former blends. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2777–2784, 2000     

Reactive processing of ethylene-vinyl acetate rubber/polyamide blends via a dynamic transesterification reaction

Dynamic vulcanization process of ethylene-vinyl acetate rubber (EVM) and ternary polyamide copolymer (tPA) blends in the presence of tetraethyloxysilane (TEOS) was investigated. The morphology, crosslink density and mechanical properties of the resultant EVM/tPA thermoplastic elastomers (TPEs) were characterized. The dynamically crosslinked EVM phase was distributed homogeneously in the continuous tPA phase for the EVM/tPA (70/30) TPE, and the phase size of EVM decreased further as the TEOS content increased. The crosslink density reached 3.17 × 10^?5 mol cm^?3, and the tensile strength and the elongation at break were up to 10.6 MPa and 296 %, respectively, when the TEOS content was increased to 8 phr, and the heat oil resistance was accordingly enhanced. As compared to dicumyl peroxide-initiated crosslinking reaction of EVM, the crosslinking reaction of EVM through the transesterification reaction between EVM and TEOS presented lower crosslinking rate constant and activation energy, indicating that the transesterification reaction is more suitable for high temperature dynamic vulcanization processing. The optimized dynamic vulcanization process of EVM/tPA TPEs is useful for developing high-performance TPEs for automotive applications.     

Selective crosslinking reaction in polymer blends. III. The effects of the crosslinking of dispersed EPDM particles on the impact behavior of PP/EPDM blends

The selective dynamic crosslinking reaction by means of the N,N'-m-phenylene–bismaleimide/poly-(2,2,4-trimethyl-1,2-dihydroquinoline) system was carried out on PP/EPDM blends and its effect on the Izod impact strength (IIS) was investigated. Three series of PP/EPDM combinations were adopted to establish different morphologies. In each series, the EPDM wt % varied from 5 to 30 at 5 wt % intervals. The system crosslinked the EPDM particles selectively without PP degradation and change of morphology. Following the crosslinking, the IIS at 23, ?10, and ?30°C increased in all blends, and the critical EPDM wt % at 23°C necessary to cause the dramatic IIS increase was lowered. The increase in interfacial adhesion is considered to be the most important factor necessary for the improvement. The nucleation effect of the crosslinked particles and the decrease of crystallinity of the EPDM were also considered to contribute to the improvement in the IIS. Impact fracture energy absorption can thus be changed by adjusting the magnitude of the interfacial adhesion by the dynamic crosslinking even at essentially the same morphology. © 1995 John Wiley & Sons, Inc.     

The Effects of Dynamic Vulcanization by Dicumyl Peroxide (DCP) and N,N-m-Phenylene Bismaleimide (HVA-2) on the Properties of Polypropylene (PP)/Ethylene-Propylene Diene Terpolymer (EPDM)/Natural Rubber (NR) Blends

ABSTRACT

This paper discusses some properties of the polypropylene (PP)/ethylene-propylene diene terpolymer (EPDM)/natural rubber (NR) blends, such as tensile properties, heat resistance, gel content, and morphology. Dicumyl peroxide (DCP) and N,N-m-phenylene bismaleimide (HVA-2) and their combination were applied in PP/EPDM/NR blends as cross-link agents. In terms of tensile properties, the combination of DCP with HVA-2 shows the highest tensile strength and elongation at break in all PP/EPDM/NR blend ratios compared to similar blends, except with DCP or HVA-2 alone. The addition of HVA-2 produced blends with good heat resistance, while the combination of DCP with HVA-2 shows the highest gel content dealing with the cross-links formation. SEM micrographs from the surfaces extraction of the blends support that the cross-links have occurred during dynamic vulcanization process.     

A comparative study of poly(l‐lactide)‐block‐poly(ϵ‐caprolactone) six‐armed star diblock copolymers and polylactide/poly(ϵ‐caprolactone) blends

This paper deals with the synthesis of a series of six‐armed star diblock copolymers based on poly(l ‐lactide) (PLLA) and poly(?‐caprolactone) (PCL) by ring‐opening polymerization using stannous octoate as catalyst and the preparation of polylactide (PLA)/PCL linear blends using a solution blending technique, while keeping the PLA‐to‐PCL ratio comparable in both systems. The thermal, rheological and mechanical properties of the copolymers and the blends were comparatively studied. The melting point and the degree of crystallinity were found to be lower for the copolymers than the blends due to poor folding property of star copolymers. Dynamic rheology revealed that the star polymers have lower elastic modulus, storage modulus and viscosity as compared to the corresponding blends with similar composition. The blends show two‐phase dispersed morphology whereas the copolymers exhibited microphase separated morphology with elongated (worm‐like) microdomains. The crystalline structures of the copolymers were characterized by larger crystallites than their blend counterparts, as estimated using Sherrer's equation based on wide‐angle X‐ray diffraction data. © 2016 Society of Chemical Industry     

DCP用量对动态硫化POE/PP热塑性弹性体性能的影响

研究了过氧化二异丙苯(DCP)用量对动态硫化乙烯一辛烯共聚物聚丙烯(POE/PP)体系的物理性能以及PP结晶形态和POE相态结构的影响。结果表明:随DCP用量的增加,POE/PP体系的交联密度增大,而断裂伸长率、永久变形和拉伸强度下降。过量DCP的加人会导致PP降解,使体系的熔体流动速率随DCP用量的增加呈上升趋势。DSC分析表明,随着DCP用量的增加,POE/PP体系结晶度下降。微观分析得出,DCP对POE/PP体系相态结构影响显著,当DCP用量为1份时交联POE以较小的颗粒均匀分布于PP连续相中。