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     

Structure development and viscoelastic properties in silane‐crosslinked ethylene–octene copolymer

The development of structure and viscoelastic properties during silane crosslink reaction in metallocene ethylene–octene copolymer has been investigated. Using attenuated and transmission infrared spectroscopy, the concentrations of certain functional groups and change in sample thickness were monitored, giving the information on the progress of crosslink reaction. The evolution of crosslink content and viscoelastic properties was analyzed using a parallel‐plate rheometer. The results showed that crosslinking process started with the hydrolyzation of methoxy groups in the near‐surface layer, proceeding in a diffusion manner. At this stage no silanol groups could be detected, revealing that the condensation occurred promptly after hydrolyzation. The internal crosslink could not begin until there are sufficient water molecules in the surrounding. A water by‐product from the condensation reaction played an essential part in the center region. The rheological data showed a reduction in magnitude of creep compliance. As the reaction proceeded, more networks took place within an existing gel. The materials, then, acted more like elastic and exhibited an improvement in ability for recovery process. The immobilization of chain segments, due to the presence of tight network, disallowed conformations necessary for crosslink reaction and a certain amount of hydrolyzable groups and silanol groups remained after a long crosslinking process. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Crystallization behavior and mechanical properties of polypropylene random copolymer/poly(ethylene‐octene) blends

New polymer blends of polypropylene random copolymer (PP‐R) and poly(ethylene‐octene) (POE) were prepared by melt‐blending process using a corotating twin‐screw extruder. The POE content was varied up to 35%. The toughening efficiency of POE for PP‐R was evaluated by the mechanical properties of the resulted PP‐R/POE blends. The crystallization behavior and morphology of the blends were also studied. Results show that POE acts as nucleation agent to induce the crystallization of PP‐R matrix at higher crystallization temperature. Super‐toughened PP‐R/POE blends (Izod impact strength more than 500 J/m) can be readily achieved with only 10 wt % of POE. The high toughness of PP‐R/POE is attributed to cavitation and shear yielding of matrix PP‐R, as revealed by the morphology studies. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of octene content on peroxide crosslinking of ethylene–octene copolymers

Various ethylene–octene copolymers were crosslinked by dicumyl peroxide. Octene content was 16, 20, 30, 35 and 38 wt% and melt flow index was 1 or 3 g/10 min. The concentration of dicumyl peroxide was 0.3, 0.5 and 0.7 wt%. Crosslinking was analyzed by a rubber process analyzer in the temperature range 150–200 °C. Cross‐linkability was evaluated from the real part modulus s'_max versus peroxide level plots as the slope of the line. With decreasing octene content and increasing melt flow index the crosslinkability increased. This was confirmed also by tan δ analysis. The network density was measured by the gel content. A higher gel content was found for melt flow index 3 and low octene content. The melting points T_m and the crystallinities were evaluated by DSC. © 2012 Society of Chemical Industry     

Comparison in processability and mechanical and thermal properties of ethylene–octene copolymer crosslinked by different techniques

The crosslinking of metallocene ethylene–octene copolymer was investigated. The crosslinked polymers were prepared using two different techniques, i.e., peroxide crosslinking and silane–water crosslinking. In the former, the crosslinking reaction was conducted in a twin‐screw extruder, in the presence of dicumylperoxide. In the latter, the polymer was first grafted with vinyl trimethoxysilane in the extruder and subsequently crosslinked with water. The paper aims at investigation of the differences between these two techniques, in terms of processing and product mechanical and thermal properties. The results showed that the silane‐crosslinked polymers could be prepared with much higher gel contents than the peroxide‐crosslinked samples. The silane‐crosslinked polymers also retained the elastomeric characteristics of the pure polymer and showed remarkably higher extensibility, better thermal stability, and energy storage capacity. An explanation for the property differences between peroxide‐crosslinked and silane‐crosslinked polymers was proposed. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1179–1185, 2004     

Effect of heterogeneities on the physical properties of elastomers derived from butadiene cured with dicumyl peroxide

The scope of this paper is to continue our earlier study of the peroxide curing of elastomers derived from butadiene. Experimental evidence indicates that abstraction of allylic hydrogen and addition to the double bonds can act as a mechanism for cross‐linking. The addition reaction may give rise to a polymerization reaction between adjacent double bonds, thus generating a heterogeneous network, with negative effects on the physical properties of the vulcanizates. Copyright © 2004 Society of Chemical Industry     

Effect of the cross‐linking process on the electrical resistivity and shape‐memory behavior of cross‐linked carbon black filled ethylene‐octene copolymer

The electrical resistance of carbon black (CB) filled ethylene‐octene copolymer (EOC) was monitored during the compression molding step by means of conductivity sensors. It increases strongly during the cross‐linking process due to the de‐agglomeration of CB aggregates. After completion of cross‐linking reaction CB aggregates reagglomerate causing a decay of resistance. The electrically stimulated shape‐memory (SM) behavior was found to be strongly dependent on the extent of electrical resistivity and the rigidity of CB network, which is formed during compounding and subsequent cross‐linking process. The effect of amount of peroxide and cross‐linking conditions like time and temperature on resistivity and the related SM behavior was characterized. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Structure development in melt spinning of poly(ethylene‐co‐octene) filaments with various comonomer contents

An experimental study of the spinnability and the variation in crystallinity and orientation of melt spinning of poly(ethylene‐co‐octene) with different contents of comonomers was carried out. The spinning behavior of these polymers was investigated under different draw‐down ratios and temperatures and correlated to spinline stress. The melt‐spun filaments were characterized by wide‐angle X‐ray diffraction birefringence, and differential scanning calorimetry. S‐1 is a high‐density polyethylene and S‐2, S‐3, and S‐4 have 16, 22, and 38 wt % octene. An orthorhombic unit cell was found in all four polymers, but a dominant hexagonal structure (perhaps mesophase) was found for the highest octene level (S‐4). The orientation factors for the a‐, b‐, and c‐axis of the orthorhombic crystal structure and a‐axis of the hexagonal phase were then calculated. The crystalline orientation behavior of the lower octene copolymers (S‐1, S‐2, and S‐3) are similar and can be represented as a “row‐nucleated“ structure. However, the orientation behavior of S‐4 was different. The uniaxial mechanical properties were also measured. The Young's modulus and tensile strength generally increased with birefringence for all polymers. With increasing content of octene, the Young's modulus showed a decrease from semicrystalline thermoplastic toward an elastomer. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 9–22, 2004     

Study on the melt fracture of metallocene poly(ethylene‐octene) in capillary flow

Shear viscosity and melt fracture of a metallocene poly(ethylene‐octene) were studied using a capillary rheometer and dies with different lengths. The true wall shear stresses determined at zero die length showed a dip at high shear rates. The shear viscosity was derived from the true wall shear stress. With increasing shear rates, the extrudate staged from smooth to three types of melt fracture with regular patterns, and then turned into irregular shapes. Three types of regular melt fractures—sharkskin, helix, and spiral (in sequence)—were observed with an increase of the shear rates. The wavelength of the regular melt fracture was measured from extrudates, and the corresponding frequency was calculated. The frequency increased at elevated melt temperatures. Both shear viscosity and frequency at different temperatures correlated well by using the time–temperature Williams–Landel–Ferry (WLF) superposition. Additionally, it was found that the frequency decreased slightly for a longer die but it increased when the shear rate went up. Three frequency functions were associated with three melt fracture patterns, respectively. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 903–911, 2005     

Solvothermal process for grafting dibutylmaleate onto poly(ethylene‐co‐1‐octene)

Solvothermal process was successfully developed to graft dibutylmaleate (DBM) onto poly(ethylene‐co‐1‐octene) (POE) with dicumyl peroxide (DCP) as free radical‐initiator. FTIR spectra demonstrate that DBM is successfully grafted onto the backbone of POE by this novel method. The influences of DBM content, DCP concentration, POE concentration, reaction temperature and reaction time on the grafting copolymerization have been investigated in detail through grafting degree (GD). It is worthy to indicate that high grafting degree (above 15%) can be achieved through the one‐pot way when the graft reaction is carried out in 40 mL toluene at 150°C for 5 h with 1.6 g DBM, 6–8 g POE and 0.35 g DCP. This developed solvothermal process is becoming an effective way to prepare POE‐g‐DBM graft copolymers, and can be extended to other systems. In addition, TGA results show that the thermal properties of POE are enhanced after the grafting reaction. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Rheological and thermal properties of binary blends of polypropylene and poly(ethylene‐CO‐1‐octene)

Dynamic viscoelastic properties of binary blends consisting of an isotactic polypropylene (i‐PP) and ethylene‐1‐octene copolymer (PEE) were investigated to reveal the relation between miscibility in the molten state and the morphology in the solid state. In this study, PEE with 24 wt % of 1‐octene was employed. The PEE/PP blend with high PEE contents showed two separate glass‐relaxation processes associated with those of the pure components. These findings indicate that the blend presents a two‐phase morphology in the solid state as well as in the molten state. The PEE/PP blend with low PEE content showed a single glass‐relaxation process, indicating that PEE molecules were probably incorporated in the amorphous region of i‐PP in the solid state. The DMTA analysis showed that the blends with low PEE contents presented only one dispersion peak, indicating a certain degree of miscibility between the components of these blends. These results are in accordance with the results of the rheological analysis. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1634–1639, 2001     

Preparation of Poly(ethylene‐octene) Elastomer/Clay/Wood Flour Nanocomposites by a Melting Method

Summary: The new nanocomposites consisting of metallocene poly(ethylene‐octene) (POE), silicate clay and wood flour (WF) were prepared by means of a melt blending method. In addition, maleic anhydride grafted poly(ethylene‐octene) (POE‐g‐MAH) was studied as an alternative to POE. The samples were characterized by XRD, FT‐IR spectroscopy, DSC, TGA, SEM, and mechanical testing. Based on the consideration of thermal and mechanical properties, it was found that the clay content of 11 wt.‐% was optimal for the preparation of POE‐g‐MAH/clay nanocomposites. The POE‐g‐MAH/clay/WF hybrid could obviously improve the mechanical properties of POE‐g‐MAH/WF hybrid since the former had the smaller WF phase size (being always less than 1.5 µm), the Si? O? C bond and the nanoscale dispersion of silicate layers in the polymer matrix. The biodegradation studies showed that the mass of hybrids reduced by about the content of WF. The new POE‐g‐MAH/clay/WF nanocomposites produced from our laboratory can provide a plateau tensile strength at break when the WF content was up to 50 wt.‐%.

     

Effect of hot air aging on the properties of ethylene‐vinyl acetate copolymer and ethylene‐acrylic acid copolymer blends

The aim of this investigation is to evaluate the effect of hot air aging on properties of ethylene‐vinyl acetate copolymer (EVA, 14 wt % vinyl acetate units), ethylene‐acrylic acid copolymer (EAA, 8 wt % acrylic acid units), and their blends. Attenuated total reflection‐Fourier transform infrared spectroscopy, differential scanning calorimeter (DSC), wide angle X‐ray diffraction, and mechanical tests are employed to investigate the changes of copolymer blends' structures and properties. Increase of carbonyl index derived from ATR measurements with aging time suggests the incorporation of oxygen into the polymeric chain. By DSC measurements, the enthalpy at low temperature endothermic peak (T_m2) of EAA becomes less and disappears after 8 weeks aging, but enthalpy at T_m2 of EVA is not influenced by the hot air aging and remains stable despite of the aging time. For various proportions of EAA and EVA blends, enthalpy at T_m2 decreases as the EAA proportion increases when aging time is 8 weeks; after several weeks of hot air aging, the various blends appear a same new peak just over the aging temperature 70°C which is due to the completion of crystals which are not of thermodynamic equilibrium state. Mechanical tests show that increase of crystallinity and hot air aging deterioration both have influence on the hardness, tensile strength, and elongation at break. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Functionalization and cross‐linking of high‐density polyethylene in the presence of dicumyl peroxide—An FTIR study

High‐density polyethylene was thermolysed with short‐chain organic compounds (additives) with an ester functional group in the presence of free radical initiator such as dicumyl peroxide at 160°C. The experimental results inferred that an additive with a hydrogen donor containing a thiol group showed better efficiency toward functionalization and an additive with a methylene bridged group showed better efficiency toward cross‐linking. The FTIR spectral results indicated that the area of the carbonyl peak at 1730 cm^?1 increased with the increase in percentage grafting of additives with simultaneous increase of cross‐linking. The ester grafting was further confirmed by saponification reaction. The possibility of acid functionalization via intramolecular hydrogen transfer was also checked through acid hydrolysis of the saponified products. A suitable reaction mechanism was proposed in order to explain the experimental and spectral data obtained. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 766–774, 2005     

Cross‐Linking of Polyesters Based on Fatty Acids

This study aims at obtaining cross‐linked polymeric materials of biomass origin. For this purpose, one‐pot polyesterification of methyl ricinoleate and methyl 12‐hydroxystearate using titanium isopropoxide as a catalyst is performed leading to polyesters known as estolides. The obtained estolides are successfully cross‐linked using dicumyl peroxide or a sulfur vulcanization system. The so‐formed bio‐based elastomers appear to exhibit promising properties. The latter are analyzed by mechanical tensile tests and thermal techniques (TGA, DSC, DMA) and show high thermal stability (T_5% = 205–318 °C), tailored physico‐mechanical properties (low glass transition temperature in the range from ?69 to ?54 °C), and good tensile strength (0.11–0.40 MPa). Networks prepared from high molecular weight estolides appear to be promising bio‐based elastomers. Practical Applications: The vegetable oil‐based estolides described in this contribution are new fully bio‐based precursors for further elastomers synthesis. The resulting estolide networks (obtained by peroxide or sulfur cross‐linking) exhibit tailored thermo‐mechanical properties.     

Development of thin‐walled halogen‐free cable insulation and halogen‐free fire‐resistant low‐smoke cable‐sheathing compounds based on polyolefin elastomer and ethylene vinyl acetate blends

There is a growing interest in the use of polyolefins and their copolymer blends in cable industries. The present investigation deals with the development of thin‐walled halogen‐free cable insulation and thin‐walled halogen‐free fire‐resistant low‐smoke cable sheathing compounds based on polyolefin elastomer (Engage®) and ethylene vinyl acetate (EVA) blends. Blends of Engage (an ethylene octene copolymer) and EVA, varying in proportions, are prepared on a two‐roll mixing mill at an elevated temperature. Physicomechanical, electrical, and the most important flame‐retardant properties of the dicumyl peroxide/triallyl cyanurate cured blends have been basically studied. Properly compounded Engage‐EVA blends are found to be excellent materials in cable industry for insulation as well as for sheathing compounds. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

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.     

UV‐Induced Cross‐Linking of Poly(ethylene oxide) in Aqueous Solution

Summary: Hydrogels of high‐molecular‐weight poly(ethylene oxide) (PEO) have been obtained in situ by applying a very simple procedure that involves UV cross‐linking of PEO in aqueous solution. The efficiency of the photoactivated cross‐linking of thin layers of PEO in aqueous solution in the presence of (4‐benzoylbenzyl) trimethylammonium chloride as a photoinitiator has been determined at room temperature and in a frozen state (?25 °C). It was found that the efficiency varies with the concentration of PEO solution, the molecular weight of PEO, and especially with the temperature. When the UV cross‐linking was performed in the frozen state, porous hydrogels with very high yield of gel fraction (above 90%) and high cross‐linking density were obtained. After drying the hydrogels, films of 50–150 μm thickness were prepared. The films swell extremely fast in water and act as asymmetric membranes.

SEM of a dried PEO hydrogel obtained by UV cross‐linking of an aqueous solution at room temperature.     

Morphology and mechanical properties of binary blends of polypropylene with statistical and block ethylene‐octene copolymers

In the present work, statistical (EOCs) and block (OBCs) ethylene‐octene copolymers, with similar densities and crystallinities, were used as impact modifiers of isotactic polypropylene (iPP), and the toughening effects of these two types of elastomers were compared. The viscosity curves of EOCs were similar to those of OBCs with equivalent melt flow rate (MFR), enabling a comparison of the viscosity ratio and elastomer type as independent variables. No distinct differences on the crystal forms and crystal perfection of iPP matrix in various blends were observed by thermal analysis. Morphological examination showed that OBCs form smaller dispersed domains than EOCs with similar MFRs. The flexural modulus, yield stress, stress and strain at break showed the same variation tendency for all the investigated polypropylene/elastomer blends. However, the room temperature Izod impact toughness of iPP/OBC blend was higher than that of iPP/EOC blend containing elastomer with the similar MFRs. The experimental results indicated that the compatibility of iPP/OBCs was much higher than that of iPP/EOCs. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Cross‐linking of polybutadiene: correlation between solid‐state 1H NMR spectroscopy,thermoporosimetry, densimetry and crystallinity measurements

T₂ proton NMR relaxation times were used to follow the changes in the macromolecular chain mobility of a chemically (by dicumyl peroxide) cross‐linked polybutadiene matrix. The same phenomenon was also studied by an investigation of the ability of the polymer to crystallize using DSC measurements. The solubility of the elastomer depends on the size of its macromolecular chains. Cross‐linking, leading to an increase in the size of macromolecules, provokes an insolubility of the elastomer. By densimetry measurements, it was possible to follow the changes in the solubility of the polymer up to its gel‐point. Beyond the gel‐point, the swelling solvent, cyclohexane, was used as a textural probe. Using the shift of its solid‐solid thermal transition points, it was possible to calculate the distribution of the distances between the cross‐links as a function of the curing times by thermoporosimetry analysis. Copyright © 2003 Society of Chemical Industry