Photoinitiated crosslinking of ethylene‐vinyl acetate copolymers and characterization of related properties

Photoinitiated crosslinking of EVA in the presence of benzophenone (BP) as photoinitiator and triallyl isocyanurate (TAIC) as crosslinker and characterization of the related properties have been studied by gel determination, heat extension, DSC, DMTA, TGA, and mechanical measurements. The photoinitiated crosslinking efficiency of the EVA‐BP‐TAIC system and various factors affecting the crosslinking process, such as photoinitiator and crosslinker and their concentrations, irradiation temperature, and irradiation atmosphere were studied in detail and optimized by comparison of gel contents. The results show that the EVA samples with a thickness of 1 mm are readily crosslinked to a gel content of above 80% with 5 s UV‐irradiation under optimum conditions. The data from the heat extension and DSC show that the crosslinking density of photocrosslinked EVA increase and their crystallinities decrease with increasing the UV‐irradiation time. At the same time, photocrosslinking of EVA leads to a lowering of the melt temperature and a decrease of heat of fusion. The DMTA results show that photocrosslinking increases the amorphous phase and storage modulus of the crosslinked EVA, but does not change the glass transition temperature. The data from TGA and mechanical tests give evidence that the thermal stability and mechanical properties of photocrosslinked EVA samples are much better than those of the uncrosslinked EVA. POLYM. ENG. SCI., 47:1761–1767, 2007. © 2007 Society of Plastics Engineers     

Photocrosslinking of halogen‐free flame‐retarded ethylene‐vinyl acetate copolymer by phosphorous‐nitrogen compound NP28

The photoinitiated crosslinking of halogen‐free flame‐retarded ethylene‐vinyl acetate copolymer (EVA) by the phosphorous‐nitrogen compound NP28 in the presence of photoinitiator and crosslinker and characterization of the related properties have been investigated by gel determination, heat extension test, thermogravimetric analysis (TGA), mechanical measurement, and thermal aging test. The photocrosslinking efficiency of EVA/NP28 blend and various factors affecting the crosslinking process, such as photoinitiator, crosslinker, NP28 content, and irradiation temperature, were studied in detail and optimized by comparison of gel content. The results show that the EVA/NP28 blend filled with 28.2 wt % NP28 with a thickness of 1.6 mm is homogeneously photocrosslinked to a gel content of above 80 wt % with 4.8 s UV‐irradiation under optimum conditions. The data from TGA, mechanical measurement, and thermal aging test give evidence that the thermal stability and mechanical properties of photocrosslinked EVA/NP28 blend are much better than those of the unphotocrosslinked one.© 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Mechanical properties,morphological structure,and thermal behavior of dynamically photocrosslinked PP/EPDM blends

A dynamically photocrosslinked polypropylene (PP)/ethylene–propylene–diene (EPDM) rubber thermoplastic elastomer was prepared by simultaneously exposing the elastomer to UV light while melt‐mixing in the presence of a photoinitiator as well as a crosslinking agent. The effects of dynamic photocrosslinking and blend composition on the mechanical properties, morphological structure, and thermal behavior of PP/EPDM blends were investigated. The results showed that after photocrosslinking, tensile strength, modulus of elasticity, and elongation at break were improved greatly. Moreover, the notched Izod impact strength was obviously enhanced compared with corresponding uncrosslinked blend. Scanning electron microscopy (SEM) morphological analysis showed that for uncrosslinked PP/EPDM blends, the cavitation of EPDM particles was the main toughening mechanism; whereas for dynamically photocrosslinked blends, shear yielding of matrix became the main energy absorption mechanism. The DSC curves showed that for each dynamically photocrosslinked PP/EPDM blend, there was a new smaller melting peak at about 152°C together with a main melting peak at about 166°C. Dynamic mechanical thermal analysis (DMTA) indicated that the compatibility between EPDM and PP was improved by dynamic photocrosslinking. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3371–3380, 2004     

Study of the Photocrosslinking of Ethylene Propylene Diene Monomer Terpolymer Under UV Irradiation

The photocrosslinking of thick samples of 5-ethylidene-2-norbornene–ethylene propylene diene monomer (ENB-EPDM) under air at room temperature was investigated. First, a model study was carried out on low-molecular weight oligomers: squalene, 1,2-polybutadiene, and 1,4-polybutadiene. Several crosslinking agents (meth(acrylics), bismaleimide, and thiol) combined with various photoinitiators were tested to improve the reactivity of these oligomers under UV irradiation. Gel contents, crosslinking densities, viscosities, and viscoelastic properties were measured in order to characterize the extent of crosslinking. Acrylate-based crosslinking agents appeared to be the most reactive species and these results were then applied to a low-molecular weight EPDM. Several photoinitiators were tested and benzophenone turned out to be the most efficient photoinitiator when combined with trimethylolpropane triacrylate. Finally, a commercial EPDM was subsequently photocrosslinked and high gel content and crosslinking density were obtained after only 2 min of irradiation. POLYM. ENG. SCI., 60:95–103, 2020. © 2019 Society of Plastics Engineers     

Vinyl acetate content and electron beam irradiation directed alteration of structure,morphology, and associated properties of EVA/EPDM blends

A series of ethylene vinyl acetate/ethylene–propylene diene elastomer (EVA/EPDM) blends with four types of EVAs with various vinyl acetate (VA) content, are prepared without and with crosslinker, trimethylol propane triacrylate (TMPTA). These are irradiated by electron beam (EB). As the VA content increases, the gel content, i.e., degree of crosslinking of EVA/EPDM blends, is increased. With increase in VA content, the modulus and tensile strength are decreased but elongation at break is increased due to increase in amorphousness. On EB irradiation, modulus and tensile strengths are increased but at the cost of elongation at break. Crystallinities of all blends are decreased with increase in VA and EB crosslinking. The thermal stability of EVA/EPDM blend is decreased with increase in VA content but increased after EB irradiation. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) show that with increase in VA content the miscibility of two polymers keeps on increasing, which even become more after EB irradiation. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43468.     

Structure–property relationship of electron‐beam‐modified EPDM rubber

Electron‐beam‐initiated grafting of trimethylolpropane triacrylate (TMPTA) onto the bulk ethylene propylene diene monomer (EPDM) was carried out with varying concentrations of TMPTA at a constant irradiation dose of 100 kGy and over a wide range of irradiation doses (0–500 kGy) at a fixed concentration (10%) of TMPTA. The rubber was also modified in the bulk by tripropylene glycol diacrylate (TPGDA, 10%) and tetramethylol methane tetraacrylate (TMMT, 10%) at an irradiation dose of 100 kGy. The modified rubbers were characterized by IR spectroscopy, crosslinking density measurements, and mechanical, dynamic mechanical, and electrical properties. The IR studies indicated increased peak absorbances at 1730, 1260, and 1019 cm⁻¹ due to increased 〉CO and C O C concentrations up to certain levels of TMPTA and irradiation dose. These are accompanied by an increase in the crosslinking density. The tensile strength of the samples increases gradually with increasing both the concentration of the monomer and radiation dose up to a certain level. The values of the modulus also increase at the expense of the elongation at break. An increase in the number of double bonds from two in the case of the diacrylate to four in the case of the tetraacrylate also brings about an increase in the tensile strength and moduli values. The elongation at break, however, decreases. The DMTA measurements indicate changes in the glass transition temperature, T_g, and tan δ_max on modification. The T_g shifts to a higher temperature with a simultaneous lowering of the tan δ_max values as the TMPTA level is increased. A similar trend is observed when the irradiation dose is increased and the nature of the monomer changes from di‐ to tetraacrylate. The dielectric loss tangent registers an increase on modification by irradiation of TMPTA while the permittivity is decreased. All the results could be explained on the basis of the structural modification and crosslinking density. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 323–337, 2000     

Preparation and characterization of vinyltrimethoxysilane and dicumyl peroxide–cured (ethylene propylene diene monomer)/polypropylene thermoplastic vulcanizates

The present investigation deals with understanding the influence of vinyltrimethoxysilane (VTMS) concentration on the mechanical, thermal, thermomechanical, rheological, morphological, gel content, crosslinking density, and compression set properties of dynamically vulcanized ethylene propylene diene monomer (EPDM)/polypropylene (PP) (60/40, w/w) ‐based thermoplastic vulcanizates. It was determined that the values of crosslinking density, gel content, tensile strength, Young's modulus, elongation at break, and viscosity increased; whereas that of compression set, melting temperature, enthalpy of melting, crystallinity, and damping factor decreased with increased addition of VTMS in the EPDM/PP‐based thermoplastic vulcanizate. This is attributed to the physical crosslinking caused because of VTMS grafting on EPDM and chemical crosslinking induced by VTMS between PP and EPDM. This has been confirmed by Fourier‐transform infrared spectroscopy spectra, whereas the thermomechanical and scanning electron microscopy analysis confirmed increased compatibility between EPDM and PP on the addition of VTMS. J. VINYL ADDIT. TECHNOL., 23:312–320, 2017. © 2015 Society of Plastics Engineers     

Electron‐beam irradiation of poly(vinyl chloride)/epoxidized natural rubber blends in presence of trimethylolpropane triacrylate

Electron‐beam initiated crosslinking of poly(vinyl chloride)/epoxidized natural rubber blends, which contained trimethylolpropane triacrylate (TMPTA), was carried out over a range of irradiation doses (20–200 kGy) and concentrations of TMPTA (1–5 phr). The gel content increased with the irradiation dose and the TMPTA level, although the increase was marginal at higher doses and higher TMPTA levels. Blends containing 3–4 phr TMPTA achieved optimum crosslinking, which in effect caused the maximum tensile strength (TS) at a dose of 70 kGy. A further addition of TMPTA caused a decline in the TS above 40 kGy that was due to embrittlement, which is a consequence of excessive crosslinking and the breakdown of the network structure. The possible formation of a more open network as a result of the breakdown of the network structure was further confirmed by the modulus results. Dynamic mechanical analysis (tan δ curve) and scanning electron microscopy studies on samples irradiated at 0 and 200 kGy were undertaken in order to gain further evidence on the irradiation‐induced crosslinking. The plasticizing effect of TMPTA prior to irradiation and the formation of microgels upon irradiation were also discussed. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1926–1935, 2001     

Gelation and crosslinking characteristics of photopolymerized poly(ethylene glycol) hydrogels

The gelation and crosslinking features of poly(ethylene glycol) (PEG) hydrogels were scrutinized through the UV polymerization processes of poly(ethylene glycol) methacrylate (PEGMA) and poly(ethylene glycol) dimethacrylate (PEGDMA) mixtures. The real‐time evolutions of the elastic moduli of the prepolymerized mixtures with different crosslinking ratios of PEGMA and PEGDMA and the photoinitiator concentrations were measured during photopolymerization. The rheological properties were compared with other properties of the PEG hydrogels, including the relative changes in the C?C amounts in the mixtures before and after UV irradiation, water swelling ratio, gel fraction, mesh size, and mechanical hardness. As the portion of PEGDMA as a crosslinker increased, the final elastic modulus and gel fraction increased, whereas the swelling ratio and scratch penetration depth at the hydrogel film surface decreased because of the formation of compact networks inside the hydrogels. These results indicate that there was a good correlation between the rheological analysis for predicting the crosslinking transition during photopolymerization and the macroscopic properties of the crosslinked hydrogels. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41939.     

Irradiation effects on the relaxation behaviour of EPDM elastomers

γ‐irradiation of ethylene–propylene diene monomer (EPDM) elastomers under oxidant atmosphere was carried out in order to change their mechanical and dielectric behaviour. Three different formulations of EPDM (70 wt% ethylene, 28 wt% propylene; diene monomer: 2 wt% norbornene) were studied: a non‐crosslinked EPDM terpolymer, a crosslinked EPDM and a crosslinked EPDM stabilized with an antioxidant. Dielectric and mechanical relaxation show a β‐sub‐glass relaxation at about ?120 °C (1 Hz) and an α‐relaxation at ?15 °C (1 Hz) associated with the glass transition but influenced by the effects of irradiation. The local mobility associated with the β‐relaxation is only weakly influenced by γ‐irradiation up to 450 kGy. The α‐process is shifted to higher temperatures as a result of crosslinking and changes in the semicrystalline structure. The amplitude of the dielectric α‐process increases as a result of the formation of oxidized species during irradiation under oxygen. In contrast, the mechanical α‐relaxation amplitude decreases as a result of physical and chemical cross‐linking. It was shown that the main factors that determine the crosslinking/chain scission balance are (1) the presence of oxygen together with the irradiation dose, (2) the dose rate and (3) the initial crosslink density of the EPDM material. As a result, the individual contribution of crosslinking and crystallization, and therefore the understanding and prediction of the properties after γ‐irradiation can only be deduced after comparison of the polymer behaviour below and above its melting temperature. Copyright © 2004 Society of Chemical Industry     

Preparation and relaxation dynamics of ethylene–propylene–diene rubber/clay nanocomposites with crosslinking interfacial design

Ethylene–propylene–diene rubber (EPDM)/clay nanocomposites with crosslinking bonding at the interface were fabricated through the intercalation method involving double‐bond functional groups. For comparison, an organoclay modified with an intercalation agent without double bonds was also prepared. X‐ray diffraction indicated that the EPDM intercalated into the galleries of the nanoclay due to crosslinking with the organic intercalation reagent containing double bonds. According to the dielectric relaxation spectra, the segmental relaxation of EPDM was greatly confined, due to the strong filler/polymer interfacial interaction. And a new relaxation appeared at higher temperature and lower frequency than segmental relaxation when the content of clay with double bonds reached 10 phr; the new relaxation is attributed to interfacial relaxation. Whereas the new relaxation did not appear by adding ordinary organoclay, the dynamic mechanical analysis loss peak of EPDM, corresponding to the glass transition, moved to a higher temperature due to covulcanization. The presence of crosslinking in the EPDM/clay nanocomposites can play a significant role in improving their mechanical properties. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45553.     

Study on the properties of crosslinking of poly(ethylene oxide) and hydroxyapatite–poly(ethylene oxide) composite

This study covers the crosslinking of poly(ethylene oxide) (PEO) and its composite with calcium hydroxyapatite (HA), their mechanical and swelling properties, and morphology. Sheets of the composites of PEO (two different grades with M_v: 5 × 10⁶ and 2 × 10⁵) and HA and neat PEO were prepared by compression molding. The prepared composite and PEO (0.1‐mm‐thick) sheets were crosslinked with exposure of UV‐irradiation in the presence of a photoinitiator, acetophenone (AP). This simple method for crosslinking, induced by UV‐irradiation in the presence of AP, yielded PEO with gel content up to 90%. Gel content, equilibrium swelling ratio, and mechanical and morphological properties of the low molecular weight polyethylene oxide (LMPEO)–HA crosslinked and uncrosslinked composites were evaluated. Although the inclusion of HA into LMPEO inhibits the extent of crosslinking, the LMPEO–HA composite with 20% HA by weight shows the highest gel content, with appreciable equilibrium swelling and mechanical strength. The growth of HA in simulated body fluid solutions on fractured surfaces of LMPEO and also LMPEO–HA was found to be very favorable within short times. The dimensional stability of these samples was found to be satisfactory after swelling and deposition experiments. The good compatibility between the filler hydroxyapatite and poly(ethylene oxide) makes this composite a useful tissue‐adhesive material. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 488–496, 2003     

Tensile,flexural and morphological properties of electron beam-crosslinked LDPE–EPDM blends

The effect of electron beam (EB) irradiation on the tensile, flexural and morphological properties of low-density polyethylene (LDPE)/ethylene-propylene diene elastomer (EPDM) blends had been studied in the absence and presence of crosslink promoters, such as trimethylolpropane triacrylate (TMPTA) and triallyl cyanurate (TAC). Blends were prepared by melt mixing of LDPE and EPDM followed by EB irradiation at various doses. The gel fraction (%) of irradiated blends was increased with an increase in EPDM content as well as EB irradiation dose and consequently the tensile and flexural properties of the blends increased. The incorporation of crosslinking promoters accelerated the gel formation and improved the properties upon irradiation more efficiently. The phase morphology of fractured surface displayed immiscibility with a rough appearance before irradiation. But after irradiation, the surface became fine, smooth and uniform, which went on increasing upon irradiation, supporting the steady increase in mechanical properties. Surface appeared even smoother in the presence of TMPTA and TAC.     

Effect of ultrasound on extrusion of PP/EPDM blends: Structure and mechanical properties

The effects of ultrasonic irradiation on the mechanical properties, morphology, and crystal structure of polypropylene (PP)/ethylene‐propylene‐diene terpolymer (EPDM) blends were examined. Results show that appropriate irradiation intensity can noticeably increase the toughness of the PP/EPDM blends without reducing rigidity. Scanning electron microscopic (SEM) observation shows that with ultrasonic irradiation, the morphology of a well‐dispersed EPDM phase is formed in the PP/EPDM blend. The glass transition temperatures of PP and EPDM phase approach each other as a result of ultrasonic irradiation. Differential Scanning Calorimetric (DSC) analysis indicates that the crystallinities of the PP and EPDM phases increase with ultrasonic irradiation, and β crystals of PP form in the PP/EPDM blend with ultrasonic irradiation, which is proven by wide angle X‐ray diffraction (WAXD) analysis. Polym. Eng. Sci. 44:1509–1513, 2004. © 2004 Society of Plastics Engineers.     

Dynamic vulcanization of recycled milk pouches (LDPE–LLDPE) and EPDM blends using dicumyl peroxide

The viability of thermomechanical recycling of post‐consumer milk pouches (blend of low‐density polyethylene (LDPE) and linear low‐density polyethylene (LLDPE)) and its scope for suitable engineering applications were investigated. The effects of blending with ethylene‐propylene‐diene monomer (EPDM) rubber and subsequent curing using dicumyl peroxide (DCP) on the macromolecular structure and properties of recycled polyethylene (PE) blends were studied. The crosslinking efficiency of recycled PE/EPDM blends and possible thermooxidative degradation of recycled polymer upon peroxide curing was assessed using torque and gel content measurements along with infrared spectroscopic analysis. Both the torque and gel content of the blends varied with DCP crosslinking reactions and also were affected by oxidative degradation. In view of the electrical application area of this recycled blend material, the dielectric breakdown strength and volume resistivity were measured. The mechanical performance and thermal stability of recycled PE/EPDM blends improved with progressive crosslinking by DCP but deteriorated somewhat at higher DCP dose. Scanning electron microscopy showed good interface bonding between recycled polymer and dispersed EPDM phase in the cured blends compared to the non‐cured blends. Copyright © 2007 Society of Chemical Industry     

Effect of ultrasound on extrusion of polypropylene/ethylene–propylene–diene terpolymer blend: Processing and mechanical properties

The effects of ultrasonic irradiation on extrusion processing and mechanical properties of polypropylene (PP)/ethylene–propylene–diene terpolymer (EPDM) blends are examined. Results show that appropriate irradiation intensity can prominently decrease die pressure and apparent viscosity of the melt, increase output, as well as increase toughness of PP/EPDM blends without harming rigidity. In case the blends are extruded with ultrasonic irradiation twice, the impact strength of the blend rises sharply at 50–100 W ultrasonic intensity, and amounts to more than 900 J/m, 1.5 times as high as that of blend without ultrasonic irradiation. Scanning electron microscopy observation shows that with ultrasonic irradiation, morphology of uniform dispersed EPDM phase and good adhesion between EPDM and PP matrix was formed in PP/EPDM blend. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3519–3525, 2003     

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.     

Dynamic mechanical analysis of ethylene–propylene–diene monomer rubber and styrene–butadiene rubber blends

The effects of blend ratio, crosslinking systems, and fillers on the viscoelastic response of ethylene–propylene–diene monomer (EPDM)/styrene–butadiene rubber (SBR) blends were studied as functions of frequency, temperature, and cure systems. The storage modulus decreased with increasing SBR content. The loss modulus and loss tangent results showed that the EPDM/SBR blend vulcanizate containing 80 wt % EPDM had the highest compatibility. Among the different cure systems studied, the dicumyl peroxide cured blends exhibited the highest storage modulus. The reinforcing fillers were found to reduce the loss tangent peak height. The blend containing 40 wt % EPDM showed partial miscibility. The dispersed EPDM phase suppressed the glass‐transition temperature of the matrix phase. The dynamic mechanical response of rubbery region was dominated by SBR in the EPDM–SBR blend. The morphology of the blend was studied by means of scanning electron microscopy. The blend containing 80 wt % EPDM had small domains of SBR particles dispersed uniformly throughout the EPDM matrix, which helped to toughen the matrix and prevent crack propagation; this led to enhanced blend compatibility. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Influence of the clay modification and compatibilizer on the structure and mechanical properties of ethylene–propylene–diene rubber/montmorillonite composites

Ethylene–propylene–diene rubber (EPDM)/montmorillonite (MMT) composites were prepared through a melt process, and three kinds of surfactants with different ammonium cations were used to modify MMT and affect the morphology of the composites. The morphology of the composites depended on the alkyl ammonium salt length, that is, the hydrophobicity of the organic surfactants. Organophilic montmorillonite (OMMT), modified by octadecyltrimethyl ammonium salt and distearyldimethyl ammonium salt, was intercalated and partially exfoliated in the EPDM matrix, whereas OMMT modified by hexadecyltrimethyl ammonium chloride exhibited a morphology in which OMMT existed as a common filler. Ethylene–propylene–diene rubber grafted with maleic anhydride (MAH‐g‐EPDM) was used as a compatibilizer and greatly affected the dispersion of OMMT. When OMMTs were modified by octadecyltrimethyl ammonium chloride and distearydimethyl ammonium chloride, the EPDM/OMMT/MAH‐g‐EPDM composites (100/15/5) had an exfoliated structure, and they showed good mechanical properties and high dynamic moduli. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 638–646, 2004     

Analysis of organic solvent–insoluble portions included in ethylene–propylene–diene terpolymer

Organic solvent–insoluble portions included in the varying type of ethylene–propylene–diene terpolymers (EPDM) were analyzed by the solubility test, differential scanning calorimetry, x-ray diffraction, infrared spectrometry and the electron microscope. It was found that insoluble portions are resolved into microcrystalline gel owing to association of the long ethylene linkage and the crosslinking gel based on the presence of the third component by the variety of EPDM. The differences in the analytical results of the microcrystalline gel was ascribed to the differences in the monomer sequence distribution along the polymer chain.