Characterization of crosslinking of random polymer network by rheological and equilibrium swelling data

The transesterification reaction in the molten state of ester groups of ethylene vinyl acetate (EVA) copolymers and ethylene acrylic ester (EMA) copolymers has been used to crosslink the chains of this polymeric system. The relative EVA copolymers (or EMA copolymers) concentration dependence of the network formation by co-crosslinking of EVA/EMA miscible blends has been assessed. EVA/EMA networks were characterized by swelling experiments, rheological measurements, and determination of the extent of the reaction through a chromatographic technique. All results can be compared in a master curve. The influence of the polydispersity and the microstructure of EVA and EMA samples was put in evidence. On the other hand, a scaling law (v2～M_c^?3/5) was observed in agreement with predictions of the Flory-Rhener expression. © 1994 John Wiley & Sons, Inc.     

Influences of three different ethylene copolymers on the toughness and other properties of polylactide

The aim of this study was to investigate influences of three different ethylene copolymers on the toughness and other properties of very brittle biopolymer PLA (polylactide). For this aim, PLA was melt blended by twin-screw extruder with various amounts of ethylene vinyl acetate (EVA), ethylene-methyl-acrylate (EMA) and ethylene-n-butyl acrylate-glycidyl-methacrylate (EBA-GMA). SEM and DSC analyses indicated that these ethylene copolymers were thermodynamically immiscible with phase separation in the form of 1–5?µm sized round domains in the PLA matrix. Rubber toughening mechanisms of EVA, EMA and EBA-GMA were very effective to improve ductility and toughness of PLA significantly. Depending on the type and content of the ethylene copolymers, the highest increases in % elongation at break, Charpy impact toughness and G_IC fracture toughness values of PLA were as much as 160, 320 and 158%, respectively. Although there were no detrimental effects of using EVA, EMA and EBA-GMA on the thermal properties of PLA, they resulted in certain level of reductions in stiffness, strength and hardness values.     

Property of ethylene vinyl acetate copolymer in melting processing

The study is focused on the processing behavior of poly(ethylene‐co vinyl acetate) (EVA) in high temperature, such as 200°C. The specimens are characterized using HAAKE minilab, dynamic mechanical analysis (DMA), and positron annihilation lifetime spectroscopy (PALS) to understand the rheological behavior and microstructure of EVA. It was concluded that in high processing temperature, the viscosity declined first and then increased. The PALS results showed that the free volume of EVA became large at the beginning, and became small afterwards. The glass transition temperature measured with DMA got lower at first and then nearly unchanged with increasing handling time. The results can be explained that the degradation of EVA prevailed, and then degradation was not dominant. A good correlation has been found between the processing time and temperature of the transition point in the viscosity curve. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2022–2026, 2006     

Modelling of reversible poly(ethylene terephthalate) reactors

The second stage of batch poly(ethylene terephthalate) (PET) reactor with bis(2-hydroxyethyl) terephthalate (BHET) as the feed has been simulated. In this stage, the overall polymerization is not diffusion limited and is known to be a complex reaction. In this work it has been assumed to consist of polycondensation, reaction with monofunctional compounds (cetyl alcohol), redistribution, and cyclization reactions. The forward and reverse steps of each of these have been modelled in terms of the rate constants involving functional groups and the reacted bonds. The equations for the calculation of the molecular weight distribution (MWD) in batch reactors have been written and solved numerically. The MWD reported in this work is assumed to include the monofunctional products only, and, for the case where ethylene glycol is not removed from the reaction mass, it was found to be unaffected by the choice of the redistribution rate constant (k_r). Since the removal of ethylene glycol is not mass transfer controlled, its concentration in the reaction mass is assumed be given by the vapor–liquid equilibrium existing at the pressure applied on the reactor. In this work, the level of ethylene glycol concentration, y_g (?[G]/[P₁]₀), has been taken as a parameter, and, on application of vacuum, the MWD results were found to vary with k_r with the sensitivity increasing with y_g. It was then shown that the importance of the redistribution reaction is enhanced when the cyclization reaction also occurs. The effect of vacuum on the performance of the reactor has been studied by varying y_g. For y_g less than 0.01, the change in the MWD of the polymer becomes very small. The effects of polymerization temperature and initial concentration of monofunctional compounds on MWD were found to be small.     

Highly selective homogeneous ethylene epoxidation in gas (ethylene)‐expanded liquid: Transport and kinetic studies

Recently a homogeneous liquid‐phase ethylene oxide (EO) process with nearly total EO selectivity, catalyzed by methyltrioxorhenium with H₂O₂ as an oxidant, was reported. Fundamental mass transfer and kinetic studies of this reaction are reported in the present work. Volumetric expansion studies revealed that the liquid reaction phase (methanol + H₂O₂/H₂O) is expanded by up to 12% by compressed ethylene in the 20–40^°C range and up to 50 bars. This represents an increase in ethylene solubility by approximately one‐order of magnitude, attributed to the unique exploitation of near‐critical ethylene (P_c = 50.76 bar; T_c = 9.5^°C). Interphase mass‐transfer coefficients for ethylene dissolution into the liquid phase were obtained experimentally. Operating at conditions that enhanced the ethylene solubility and eliminated interphase mass‐transfer limitations maximized the EO productivity (1.61–4.97 g EO/h/g cat), rendering it comparable to the conventional process. Intrinsic kinetic parameters, estimated from fixed‐time semibatch reactor studies, disclosed the moderate activation energy (57 ± 2 kJ/mol). © 2012 American Institute of Chemical Engineers AIChE J, 59: 180–187, 2013     

Synthesis of ethylene carbonate from urea and ethylene glycol over zinc/iron oxide catalyst

BACKGROUND: Ethylene carbonate (EC) was synthesised via urea and ethylene glycol (EG) over zinc/iron oxide catalyst. By so doing, the by‐product, EG, generated in the process of producing dimethyl carbonate by the transesterification route was converted back to the raw material, EC. The reaction mechanism of EC synthesis was also investigated by means of gas chromatography/mass spectrometry and in situ Fourier transform infrared/attenuated total reflection spectroscopy. RESULTS: Suitable conditions for the preparation of zinc/iron oxide catalyst were as follows: zinc acetate and iron nitrate as precursors, Zn/Fe molar ratio 8:1, calcination temperature 350 °C and calcination time 4 h. Characterisation by X‐ray diffraction revealed two different crystal phases: ZnO and ZnFe₂O₄. The highest yield of EC (66.1%) was obtained under the following conditions: reaction temperature 150 °C, reaction time 2.5 h, catalyst weight percentage 1.5% and urea/EG molar ratio 1:8. The study of the reaction mechanism revealed that the reaction for the synthesis of EC proceeded in two steps. CONCLUSION: The synergistic effect of ZnO and ZnFe₂O₄ promoted the catalytic performance of zinc/iron oxide. Copyright © 2008 Society of Chemical Industry     

Morphology,resistivity, and thermal behavior of EVOH/carbon black and EVOH/graphite composites prepared by simple saponification method

Poly(ethylene‐co‐vinyl alcohol) (EVOH)/carbon black (CB) and EVOH/graphite (GP) electro‐conductive composites were prepared by saponification of poly(ethylene‐co‐vinyl acetate) (EVA)/CB and EVA/GP composites in ethanol/KOH solution. The electrical resistivity change and positive temperature coefficient (PTC) behavior of these composites were investigated. The volume resistivity of EVA/CB and EVA/GP composites was decreased with saponification time. It can be observed that EVA/CB10 and EVA/GP05 composites showed a significant reduction in resistivity after saponification for 1 h. With the increase in saponification time, PTC peak temperature of both composites was shifted at a higher temperature. Tensile properties, morphology, and thermal behavior of the prepared composites have been also evaluated using universal test machine, scanning electron microscopy, and differential scanning calorimetry, respectively. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Preparation of expandable graphite with silicate assistant intercalation and its effect on flame retardancy of ethylene vinyl acetate composite

A halogen‐free intumescent flame retardant expandable graphite composite (EG), with an initial expansion temperature of 202°C and expansion volume of 517 mL g⁻¹, was successfully prepared via a facile two‐step intercalation method, i.e. using KMnO₄ as oxidant and H₂SO₄, Na₂SiO₃·9H₂O as intercalators. The prepared EG flame retardant was characterized by field emission scanning electron microscope, X‐ray diffraction spectroscopy, energy dispersive spectroscopy and Fourier transform infrared spectroscopy. Furthermore, flame retardancy and thermal property of various ethylene vinyl acetate copolymer (EVA) composites, including EVA/EG and EVA/EG/APP (ammonium polyphosphate) specimens, were studied through limiting oxygen index instrument (LOI), vertical combustion UL‐94 rating, thermal gravimetric and differential thermal analysis. The results indicate that the EVA/EG and EVA/EG/APP composites exhibit a better flame retardancy. Addition of EG at a mass fraction of 30% leads LOI of 70EVA/30EG composite improved to 28.7%. Even more, the synergistic effect between EG and APP improves the LOI of 70EVA/10APP /20EG composite to 30.7%. This synergistic efficiency is attributed to the formation of compact and stable layer‐structure, and the prepared EG can make EVA composite reach the UL‐94 level of V‐0. POLYM. COMPOS., 36:1407–1416, 2015. © 2014 Society of Plastics Engineers     

Morphology,Resistivity, and PTC behavior of EVOH/CB composites prepared by solvent‐casting saponification and precipitation saponification

Poly(ethylene‐co‐vinyl alcohol)/carbon black (EVOH/CB) composites were prepared by a solvent‐casting saponification (‐D) and precipitation saponification (‐P) methods with a poly(ethylene‐co‐vinyl acetate)/CB (EVA/CB) toluene suspension. The effects of the CB content and saponification time on the morphology, electrical resistivity, thermal, and mechanical properties of EVA/CB composites were examined. The volume resistivity (ρ _v) of the EVA/CB‐D and EVA/CB‐P samples decreased significantly with increasing CB content and the percolation threshold of such composites was determined about 10 wt%. At 10 wt% of CB content, the ρ _v of EVA/CB‐D composite decreased significantly with the saponification time, whereas ρ _v of EVA/CB‐P composites did not change. As the saponification time increased, EVA/CB25wt% composites form cavity structure which CB is usually located in oval cavities larger than the particles themselves. This oval cavity structure almost resembles extruded high‐density polyethylene (HDPE)/CB composites. The morphology and PTC behavior of prepared composites were compared with those of HDPE/CB and the mechanism of PTC and NTC effects was discussed. POLYM. COMPOS., 38:1462–1473, 2017. © 2015 Society of Plastics Engineers     

Viscoelastic,thermal, and morphological analysis of HDPE/EVA/CaCO<Subscript>3</Subscript> ternary blends

High density polyethylene (HDPE), calcium carbonate (CaCO₃), and ethylene vinyl acetate (EVA) ternary reinforced blends were prepared by melt blend technique using a twin screw extruder. The thermal properties of these prepared ternary blends were investigated by differential scanning calorimetry. The effect of EVA loading on the melting temperature (T _m) and the crystallization temperature (T _C) was evaluated. It was found that the expected heterogeneous nucleating effect of CaCO₃ was hindered due to the presence of EVA. The melt viscosities of the ternary reinforced blends were affected by the % loading of CaCO₃, EVA, and vinyl acetate content. Viscoelastic analysis showed that there is a reduction of the storage modulus (G′) with increasing of EVA loading as compared to neat HDPE resin or to HDPE/CACO₃ blends only. The morphology of the composites was characterized by scanning electron microscopy (SEM). The dispersion and interfacial interaction between CaCO₃ with EVA and HDPE matrix were also investigated by SEM. We observed two main types of phase structures; encapsulation of the CaCO₃ by EVA and separate dispersion of the phases. Other properties of ternary HDPE/CaCO₃/EVA reinforced blends were investigated as well using thermal, rheological, and viscoelastic techniques.     

Microstructure and crystallization of melt‐mixed poly(ethylene terephthalate)/poly(ethylene isophthalate) blends

Physical blends of poly(ethylene terephthalate) (PET) and poly(ethylene isophthalate) (PEI), abbreviated PET/PEI (80/20) blends, and of PET and a random poly(ethylene terephthalate‐co‐isophthalate) copolymer containing 40% ethylene isophthalate (PET₆₀I₄₀), abbreviated PET/PET₆₀I₄₀ (50/50) blends, were melt‐mixed at 270°C for different reactive blending times to give a series of copolymers containing 20 mol % of ethylene isophthalic units with different degrees of randomness. ¹³C‐NMR spectroscopy precisely determined the microstructure of the blends. The thermal and mechanical properties of the blends were evaluated by DSC and tensile assays, and the obtained results were compared with those obtained for PET and a statistically random PETI copolymer with the same composition. The microstructure of the blends gradually changed from a physical blend into a block copolymer, and finally into a random copolymer with the advance of transreaction time. The melting temperature and enthalpy of the blends decreased with the progress of melt‐mixing. Isothermal crystallization studies carried out on molten samples revealed the same trend for the crystallization rate. The effect of reaction time on crystallizability was more pronounced in the case of the PET/PET₆₀I₄₀ (50/50) blends. The Young's modulus of the melt‐mixed blends was comparable to that of PET, whereas the maximum tensile stress decreased with respect to that of PET. All blend samples showed a noticeable brittleness. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3076–3086, 2003     

Study of glycolysis of poly(ethylene terephthalate) recycled from postconsumer soft‐drink bottles. III. Further investigation

A modified glycolysis reaction of recycled poly(ethylene terephthalate) (PET) bottles by ethylene glycol (EG) was investigated. Influences of the glycolysis temperature, the glycolysis time, and the amount of catalysts (per kg of recycled PET) were illustrated in this study. The manganese acetate was used as a glycolysis catalyst in this study. Bis‐2‐hydroxyethyl terephthalate (BHET) and its dimer were predominately glycolysis products. It was found the optimum glycolysis temperature is 190°C. And the best glycolysis condition is 190°C of glycolysis temperature, 1.5 h of glycolysis time, and 0.025 moles of manganese acetate based on per kg of recycled PET. If the best glycolysis condition is conducted, the glycolysis conversion may be as high as 100%. For a given reaction time (1.0 h), the ln(% glycolysis conversion) is linear to 1/T (K^?1) and the activation energy (E) of glycolysis reaction is around 92.175 kJ/(g mole). The glycolysis conversion rate increases significantly with increasing the glycolysis temperature, the glycolysis time, or the amount of manganese acetate (glycolysis catalyst). Thermal analyses of glycolysis products were examined by a differential scanning calorimetry (DSC) and a thermogravimetric analysis (TGA). According to the definition of a 2³ factorial experimental design, the sequence of the main effects on the glycolysis conversion of the recycled PET, in ascending order, is the glycolysis time (0.18) < the amount of catalyst per kg of the recycled PET (0.34) < the glycolysis temperature (0.40). Meanwhile, the prediction equation of glycolysis conversion from the result of a 2³ factorial experimental design is ? = 0.259+0.20X₁+0.09X₂+0.17X₃+0.06X₁ X₂+0.145X₁X₃+0.05X₂X₃+0.035X₁X₂X₃. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2004–2010, 2003     

Crosslinking and grafting ethylene vinyl acetate copolymer with accelerated electrons in the presence of polyfunctional monomers

In this study, we have studied the effects of polyfunctional monomers (PFMs) on physical properties of ethylene vinyl acetate (EVA) copolymer crosslinked with electron beam (EB) or peroxides. The PFMs used were triallylcyanurate, triallylisocyanurate, trimethylolpropane trimethacrylate, zinc diacrylate, and ethylene glycol dimethacrylate. Using PFMs has led to (1) optimum cure time t ₉₀ decrease from 19′25″ to 17′30″–18′45″, (2) scorch time increase from 2′ to maximum 3′45″, (3) increasing the crosslink density of peroxide or EB-cured systems by increasing the efficiency of productive radical reactions. The most efficient PFM for EVA copolymer blends has been triallylisocyanurate. Tensile strength and tear strength of samples crosslinked with EB for all irradiation doses are significantly better than those obtained for samples crosslinked with peroxides (differences up to 190%). The results show that EB irradiation gave the best results     

Study of heat shrinkability of crosslinked low‐density polyethylene/poly(ethylene vinyl acetate) blends

In this study, the heat‐shrinkage property in polymer was induced by first compounding low‐density polyethylene/poly(ethylene vinyl acetate) (LDPE/EVA) blends with various amounts of peroxide in a twin‐screw extruder at about 130°C. The resulting granules were molded to shape and chemically crosslinked by compression molding. A process of heating–stretching–cooling was then performed on the samples while on a tensile machine. Shrinkability and effective parameters were also investigated using thermal mechanical analysis. The results showed that the gel fraction was higher for the sample of higher EVA content with the same amount of dicumyl peroxide (DCP). A decrease in the melting point and heat of fusion (ΔH_f), as determined from DSC, was observed with an increase in the DCP content. Studies on the heat shrinkability of the samples showed that samples stretched above the melting point had a higher shrinkage temperature than those stretched around the crystal transition temperature. The results showed that by increasing the peroxide content, the shrinkage temperature was decreased. These could be attributed to the formation of new spherulites as well as changes in the amount and the size of crystals. Furthermore, in samples elongated at 120°C (above the melting point), the rate of stretching had no effect on the shrinkage temperature. The results showed that the extent of strain had no effect on the temperature of shrinkage, but rather on the ultimate shrinkage value. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1389–1395, 2004     

Mechanical and barrier properties of thermoplastic whey protein isolate/ethylene vinyl acetate blends

Crude oil is becoming scarcer and more expensive, resulting in alternative biobased or partially biobased materials gaining importance in the field of plastic packaging and encouraging the development of naturally derived, protein‐based plastics (Endres, 2009; Jones and McClements, Compreh. Rev. Food Sci. Food Safety 2010, 9, 374; Khwaldia et al., Compreh. Rev. Food Sci. Food Safety 2010, 9, 374). A strategy to improve extrusion processing behavior of proteins is the blending with other polymers. In this study ethylene vinyl acetate (EVA) was used for such purpose. The aim of this study was to determine the properties of blends of thermoplastic whey protein (TPP) and ethylene vinyl acetate (EVA). Mechanical and barrier properties were tested. Blends of differing TPP/EVA ratio were produced and extruded into flat films. Morphological analysis of the blends shows immiscibility of the TPP and EVA, greatly influencing the mechanical properties. Young's modulus measurements shows the values approached that of pure EVA with increasing EVA ratios. At values of about 21 MPa, corresponding to EVA ratios of 30% (w/w) and above, continuous extrusion including material take‐off was possible. At higher whey protein ratios in the blends the water vapor transmission rate increased, i.e., the higher water vapor transmission rate of whey protein compared with EVA dominated this property. This study showed that whey proteins can be utilized for extrusion by blending with EVA. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41172.     

Kinetics of ethylene polymerization at high temperature with Ziegler–Natta catalysts

A kinetic technique is developed for the study of ethylene polymerization reaction at high temperature with Ziegler–Natta catalysts. The technique is based on the calculation of polymerization rate parameters from the data on ethylene consumption vs. time. It takes into account increase of reaction temperature at the beginning of the reaction. Kinetic data in coordinates “polymerization rate–time” are presented for several pseudohomogeneous catalysts (TiCl₄? AlEt₂Cl, Ti(OiC₃H₇)₄? AlEt₂Cl), heterogeneous catalysts (δ-TiCl₃? AlEt₃, δ-TiCl₃? AlEt₂Cl, TiCl₄/MgCl₂? AlEt₃, TiCl₄/MgCl₂? AlEt₂Cl) and solubilized catalysts (δ-TiCl₃? poly-1-hexene? AlEt₂Cl) at 180°C and reaction pressure 14.6 atm for first 10 min of the reaction. These data are useful for the selection of Ziegler–Natta catalysts for testing in ethylene polymerization reaction in continuous high pressure reactors at short residence times.     

Morphological,transport, and adsorption properties of ethylene vinyl acetate/polyurethane/bentonite clay composites

The effect of polyurethane (PU) foam on the morphological and transport properties of ethylene vinyl acetate (EVA) with 9% vinyl acetate and the potential application of 3%bentonite/28.5% PU/68.5% EVA composites fabricated via the melt‐blending method in heavy‐metal extraction from water systems were investigated. EVA did not swell in water, whereas the PU/EVA blend attained a maximum percentage of deionized water uptake of 2.158 mol %. A 3% bentonite/28.5% PU/68.5% EVA composite blend successfully removed 90% of Pb²⁺ from an aqueous solution with an initial concentration of 30 mg/L, whereas 3% bentonite/97% EVA could only extract 7.323% of Pb²⁺ ions. Pb²⁺ adsorption was found to obey the Langmuir adsorption isotherm and pseudo‐second‐order kinetic model. Thermodynamic studies demonstrated that the adsorption was favorable at room temperature and the uptake of Pb²⁺ was mostly by physical adsorption, as also indicated by the value n = 2.449 (where n is an empirical parameter indicating transport mode) from the Freundlich adsorption isotherm. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Miscibility and adhesive properties of ethylene vinyl acetate copolymer (EVA)‐based hot‐melt adhesives. I. Adhesive tensile strength

A series of ethylene vinyl acetate copolymers (EVA) were blended with some tackifier resins that are made from wood extracts, and possible relations between their miscibility and properties as hot‐melt adhesives (HMA) were investigated. From our previous report on miscibility of various EVA‐based HMAs, we chose some blends that represent some of typical miscibility types and measured their adhesive tensile strengths. When the blends were miscible at testing temperatures, the temperature at which the maximum value of adhesive tensile strength was recorded tended to move toward higher temperature as tackifier content of blends increased. This result corresponds to the glass transition temperature (T_g) of the blends that became higher as tackifier content of blends increased when blend components were miscible. In terms of HMA performances, we suggest that factors other than miscibility affect absolute values of adhesive tensile strength more directly than miscibility; this idea has to be investigated further in a future study. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 719–725, 2002     

Transesterification reaction kinetics of poly(ethylene terephthalate/poly(ethylene 2,6‐naphthalate) blends

The transesterification reaction of poly(ethylene terephthalate)/poly(ethylene 2,6‐naphthalate) blends during melt‐mixing was studied as a function of blending temperature, blending time, blend composition, processing equipment, and different grades of poly(ethylene terephthalate) and poly(ethylene 2,6‐naphthalate). Results show that the major factors controlling the reaction are the temperature and time of blending. Efficiency of mixing also plays an important role in transesterification. The reaction kinetics can be modeled using a second‐order direct ester–ester interchange reaction. The rate constant (k) was found to have a minimum value at an intermediate PEN content and the activation energy of the rate constant was calculated to be 140 kJ/mol. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2422–2436, 2001