Effect of the liquid–liquid phase separation on the crystallization behavior and mechanical properties of poly(ethylene‐ran‐vinyl acetate) and paraffin wax blend

The effect of liquid–liquid phase‐separation (LLPS) on the crystallization behavior and mechanical properties of poly(ethylene‐ran‐vinyl acetate) (EVA) with various amounts of vinyl acetate and paraffin wax blend was investigated. The blend of EVA‐H (9.5% vinyl acetate) and the wax became homogeneous at temperatures greater than its upper critical solution temperature (UCST) (98°C), and an LLPS was observed between UCST and the melting point of 88°C for EVA‐H in the blend. The existence of the LLPS is attributed to the relatively large amount of the hydrophilic component of vinyl acetate in EVA, although the molecular weight of the wax was just 560. However, LLPS did not occur for the EVA/wax blend when the content of vinyl acetate in EVA was less than 3%. This behavior was explained by using the Flory–Huggins lattice model with an effective interaction parameter. The degree of crystallinity of EVA‐H in the EVA‐H/wax blend, judged from a melting endothermic peak in differential scanning calorimeter (DSC) thermograms obtained during heating runs, decreased with increasing duration time in the LLPS region. The flexural modulus of the EVA/wax blend became maximum at certain blend composition (about 30 ∼ 40 wt % EVA depending upon the amount of vinyl acetate). This behavior can be explained by the fact that this blend composition has the largest relative degree of crystallinity of EVA measured by DSC and wide‐angle X‐ray scattering method. We found that the flexural modulus of the binder itself is directly related to that of a feedstock consisting of larger amounts of metal powder and the binder, which can help someone to develop a suitable binder system for a powder injection molding process. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1991–2005, 1999     

Effect of the liquid–liquid phase separation on the crystallization behavior of a poly(ethylene‐ran‐vinyl acetate) and paraffin wax blend

The effect of liquid–liquid phase separation (LLPS) on the crystallization behavior of poly(ethylene‐ran‐vinyl acetate) with a vinyl acetate content of 9.5 wt % (EVA‐H) in the critical composition of a 35/65 (wt/wt) EVA‐H/paraffin wax blend was investigated by small‐angle light and X‐ray scattering methods and rheometry. This blend exhibited an upper critical solution temperature (UCST) of 98°C, and an LLPS was observed between the UCST and the melting point of 88°C for the EVA‐H in the blend. As the duration time in the LLPS region increased before crystallization at 65°C, both the spherulite size and the crystallization rate of the EVA‐H increased, but the degree of the lamellar ordering in the spherulite and the degree of crystallinity of the EVA‐H in the blend decreased. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 707–715, 2000     

Toughening effect of ethylene‐vinyl acetate rubber on nylon 1010 compatibilized by maleated ethylene‐vinyl acetate copolymers

The toughening effect of ethylene‐vinyl acetate rubbers (EVM) with maleated ethylene‐vinyl acetate copolymers (EVA‐g‐MAH) on the nylon 1010 was investigated. The addition of 5 phr (per hundred nylon 1010) EVM increased the elongation at break of nylon 1010 to a great extent. The notched Izod impact strength of nylon/EVM blends increased with increasing EVM content. Scanning electron microscope showed that the EVM particle size was around 0.5 μm when the EVM content was 5 phr and increased with increasing EVM content. After the addition of EVA‐g‐MAH to nylon/EVM (100/20) blend, the average diameter of EVM particles decreased from more than 1 μm to 0.5–0.6 μm. EVA‐g‐MAH could improve the adhesion between nylon 1010 and EVM. A sharp brittle‐ductile transition (BDT) was observed when the interparticle distance was about 0.2 μm, independent of the addition of EVA‐g‐MAH. The notched Izod impact strength of nylon/EVM blends at low temperatures was measured and the BDT shifted toward low temperatures with increasing EVM or EVA‐g‐MAH content. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 434–444, 2009     

A comparative study of thermal ageing characteristics of poly(ethylene‐co‐vinyl acetate) and poly(ethylene‐co‐vinyl acetate)/carbon black mixture

In this comparative study, the effect of carbon black (CB) on the thermal ageing characteristics of poly(ethylene‐co‐vinyl acetate) (EVA) was investigated. EVA, containing 13% vinyl acetate (VA), and poly(ethylene‐co‐vinyl acetate)/carbon black mixture (EVA/CB) containing 13% VA and 1% CB were aged at 85°C in air up to 30 weeks. Sol‐gel analysis experiments were made to determine the percentage gelation of both virgin and aged samples. FT‐IR measurements were performed to follow the chemical changes which took place in the samples during ageing. Dynamic and isothermal thermogravimetric studies were performed for determination of the thermal stabilities of virgin and aged samples. Sol‐gel analysis results showed that EVA itself has a tendency to form a gel under thermal treatment, whereas EVA/CB never becomes a gel when being thermally aged under the same conditions. As a result of FT‐IR measurements, some oxidation products such as ketone, lactone and vinyl species were observed through thermal ageing of EVA. It is also clear that these kind of oxidation products did not appear to a considerable extent in EVA/CB. Thermal analysis experiments exhibit that thermal stability of EVA decreased through thermal ageing; whereas that of EVA/CB remained almost unchanged. Copyright © 2004 John Wiley & Sons, Ltd.     

Two‐way multi‐shape memory properties of peroxide crosslinked ethylene vinyl‐acetate copolymer (EVA)/polycaprolactone (PCL) blends

Rare studies have investigated on the 2‐way shape memory crosslinked blends with multiple shape memory behavior up to date. To consider the merit of commercial cost‐competitive crystalline polymers, ethylene vinyl‐acetate copolymer (EVA) / polycaprolactone (PCL) blends (60/40 and 30/70) were peroxide‐cured to form the 2‐way multi‐shape memory crosslinked blends using a melt‐blending method. Both resins were selected to have a similar controlled crosslinking degree, which allowed us to distinctly evaluate their actuation contributions from the cooling‐induced elongation (crystallization) and from the entropy‐driven elongation during cooling process, respectively. In the 2‐way process for the 60/40 system, 2 respective peaks contributed from the cooling‐induced crystallization of EVA and PCL in the cooling curves based on the strain derivate rates at various temperatures were observed. After the cooling process under the loading stress of 150 kPa, the 2‐step heating‐induced contraction process with increasing temperature started at 54.1°C above the melting temperature of PCL at 52.3°C and EVA at 78.3°C, demonstrating 2‐way multi‐shape memory behavior. The multi‐step behavior was more prominent at higher PCL composition and higher load for the 30/70 system. It was found that the entropy‐driven contribution to the overall actuation magnitude increased with increasing nominal loads due to the increased orientation of molecular networks in the blends. The current approach offers numerous possibilities in preparing 2‐way multi‐shape memory crosslinked blends.     

Kinetic Study of the Accelerating Effect of Coal-burning Additives on the Combustion of Graphite

The relationship between copolymer composition and transition temperatures was studied by means of differential scanning calorimetric analysis and dynamic mechanical spectroscopy. Six samples of ethylene vinyl acetate (EVA) copolymers containing from 5 to 40 mass per cent of vinyl acetate (VA) were studied. The differential scanning calorimetric analysis revealed that each EVA copolymer displays two endothermic peaks (T_m1 and T_m2 ) in the melting zone. Dynamic mechanical spectroscopy was used to determine the primary relaxation temperature (T_α ) for EVA copolymers. This latter characteristic is relatively insensitive to the level of vinyl acetate contained in the copolymer and is influenced by the pulsation frequency ω, also named the angular frequency. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis and characterization of organosoluble,thermoplastic elastomer/clay nanocomposites

We synthesized organosoluble, thermoplastic elastomer/clay nanocomposites by making a jelly like solution of ethylene vinyl acetate containing 28% vinyl acetate (EVA‐28) and blending it with organomodified montmorillonite. Sodium montmorillonite (Na⁺‐MMT) was made organophilic by the intercalation of dodecyl ammonium ions. X‐ray diffraction patterns of Na⁺‐MMT and its corresponding organomodified dodecyl ammonium ion intercalated montmorillonite (12Me‐MMT) showed an increase in the interlayer spacing from 11.94 to 15.78 Å. However, X‐ray diffraction patterns of the thermoplastic elastomer and its hybrids with organomodified clay contents up to 6 wt % exhibited the disappearance of basal reflection peaks within an angle range of 3–10°, supporting the formation of a delaminated configuration. A hybrid containing 8 wt % 12Me‐MMT revealed a small hump within an angle range of 5–6° because of the aggregation of silicate layers in the EVA‐28 matrix. A transmission electron microscopy image of the same hybrid showed 3–5‐nm 12Me‐MMT particles dispersed in the thermoplastic elastomer matrix; that is, it led to the formation of nanocomposites or molecular‐level composites with a delaminated configuration. The formation of nanocomposites was reflected through the unexpected improvement of thermal and mechanical properties; for example, the tensile strength of a nanocomposite containing only 4 wt % organophilic clay was doubled in comparison with that of pure EVA‐28, and the thermal stability of the same nanocomposite was higher by about 34 °C. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2065–2072, 2002     

Influence of Fe‐MMT on the fire retarding behavior and mechanical property of (ethylene‐vinyl acetate copolymer/magnesium hydroxide) composite

In this work, Fe‐montmorillonite (Fe‐MMT) is synthesized and used as a synergistic agent in ethylene vinyl acetate/magnesium hydroxide (EVA/MH) flame retardant formulations. The synergistic effect of Fe‐MMT with magnesium hydroxide (MH) as the halogen‐free flame retardant for ethylene vinyl acetate (EVA) is studied by thermogravimetric analysis (TGA), limiting the oxygen index (LOI), UL‐94, and cone calorimetry test. Compared with that of Na‐MMT, it indicates that the synergistic effects of Fe‐MMT enhance the LOI value of EVA/MH polymer and improve the thermal stability and reduce the heat release rate (HRR). The structure and morphology of nanocomposites are studied by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). The mechanical properties of the EVA composites have also been studied here, indicating that the use of Fe‐MMT reduces the amount of inorganic fillers. MH hence enhances the mechanical properties of the EVA composite while keeping the UL‐94 V‐0 rating. Copyright © 2008 John Wiley & Sons, Ltd.     

Thermodynamic properties of some concentrated polymer solutions

Solubilities of several solvents were measured in four molten polymers by using an isobaric vapor-pressure apparatus. Solvent concentration ranged from 0.5 to 15 wt-%. The systems polyisoprene–benzene and polyisobutylene–benzene were studied at 80.0°C; polyisobutylene–cyclohexane was studied at 100.0°C; ethylene–vinyl acetate copolymer (EVA)–cyclohexane, EVA–isooctane, and poly(vinyl acetate)–isooctane were studied at 110.0°C. Of six polymer–solvent systems studied, all except poly(vinyl acetate)–isooctane appear to exhibit hysteresis in a single sorption–desorption cycle starting with dry polymer. The desorption curves of solvent activity plotted versus solvent weight fraction show an inflection point, suggesting localized adsorption of solvent molecules. Experimental data were analyzed with a theory which takes into account adsorption of solvent by polymer in addition to differences in free volumes and intermolecular forces. The theory gives a semiquantitative representation of the experimental data.     

Nondoped Deep‐Blue Organic Light‐Emitting Diodes with Color Stability and Very Low Efficiency Roll‐Off: Solution‐Processable Small‐Molecule Fluorophores by Phosphine Oxide Linkage

A series of solution‐processable small molecules PO1 – PO4 were designed and synthesized by linking N‐phenylnaphthalen‐1‐amine groups to a phenyl phosphine oxide core through a π‐conjugated bridge, and their thermal, photophysical, and electrochemical properties were investigated. The phosphine oxide linkage can disrupt the conjugation and allows the molecular system to be extended to enable solution processability and high glass transition temperatures (159–181 °C) while preserving the deep‐blue emission. The noncoplanar molecular structures resulting from the trigonal‐pyramidal configuration of the phosphine oxide can suppress intermolecular interactions, and thus these compounds exhibit strong deep‐blue emission both in solution and the solid state with high photoluminescent quantum yield (PLQY) of 0.88–0.99 in dilute toluene solution. Solution‐processed nondoped organic light‐emitting diodes featuring PO4 as emitter achieve a maximum current efficiency of 2.36 cd A^?1 with CIE coordinates of (0.15, 0.11) that are very close to the NTSC blue standard. Noticeably, all devices based on these small‐molecular fluorescent emitters show striking deep‐blue electroluminescent color stability and extremely low efficiency roll‐off.     

Effect of EVM/EVA‐g‐MAH ratio on the structure and properties of nylon 1010 blends

The nylon 1010/ethylene‐vinyl acetate rubber (EVM)/maleated ethylene‐vinyl acetate copolymers (EVA‐g‐MAH) ternary blends were prepared. The effect of EVM/EVA‐g‐MAH ratio on the toughness of blends was examined. A super tough nylon 1010 blends were obtained by the incorporation of both EVM and EVA‐g‐MAH. Impact essential work of fracture (EWF) model was used to characterize the fracture behavior of the blends. The nylon/EVM/EVA‐g‐MAH (80/15/5) blend had the highest total fracture energy at a given ligament length (5 mm) and the highest dissipative energy density among all the studied blends. Scanning electron microscopy images showed the EVM and EVA‐g‐MAH existed as spherical particles in nylon 1010 matrix and their size decreased gradually with increasing EVA‐g‐MAH content. Large plastic deformation was observed on the impact fracture surface of the nylon/EVM/EVA‐g‐MAH (80/15/5) blend and related to its high impact strength. Then with increasing EVA‐g‐MAH proportion, the matrix shear yielding of nylon/EVM/EVA‐g‐MAH blends became less obvious. EVM and EVA‐g‐MAH greatly increased the apparent viscosity of nylon 1010, especially at low shear rates. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 877–887, 2009     

A comparative study of UV aging characteristics of poly(ethylene‐co‐vinyl acetate) and poly(ethylene‐co‐vinyl acetate)/carbon black mixture

In this comparative study, the effect of carbon black (CB) on the UV aging characteristics of poly(ethylene‐co‐vinyl acetate) (EVA) was investigated. EVA, containing 13% vinyl acetate (VA), and poly(ethylene‐co‐vinyl acetate)/carbon black mixture (EVA/CB), containing 13% VA and 1% CB, were aged by means of UV light with a wavelength in the vicinity of 259 nm, in air, up to 400 hr. Sol‐gel analyses were made to determine the percentage gelation of both virgin and aged samples. FT‐IR measurements were performed to follow the chemical changes which took place in the samples during aging. Dynamic and isothermal thermogravimetry studies were performed for determination of the thermal stabilities of virgin and aged samples. Sol‐gel analysis results showed that EVA itself has a tendency to form a gel under UV irradiation. EVA/CB, however, becomes a gel to a smaller extent, comparatively, under the same conditions. As a result of FT‐IR measurements, some oxidation products such as ketone, lactone and vinyl species were observed through UV ageing of EVA and EVA/CB. Thermal analysis experiments exhibited that the thermal stabilities of EVA and EVA/CB decreased, to a similar extent through UV aging. Copyright © 2004 John Wiley & Sons, Ltd.     

Preparation and Properties of Layered Silicate Nanocomposites Based on Ethylene Vinyl Acetate Copolymers

(Nano)composites based on ethylene vinyl acetate copolymers (EVA) and montmorillonite modified by various alkylammonium cations were processed by mechanical kneading. Polymer intercalation and filler exfoliation were evidenced by X‐ray diffraction and transmission electron microscopy, respectively. Nanocomposites tensile properties showed that Young's modulus increases significantly even at very low content of the organo‐modified filler while preserving high ultimate elongation and tensile stress. The matrix thermal stability in air was increased by 40°C and, interestingly, the obtained nanocomposites present flame retardant properties.     

On the wall slip of polymer blends

The slip flow of the polypropylene (PP)/poly[ethylene‐co‐(vinyl acetate)] (EVA) system was studied in a capillary rheometer for shear rates of 40–1000 s^?1 at four temperatures. Three dies made of aluminum with a length/diameter (L/D) ratio of 15 and diameters of 1.59, 1.19, and 0.79 mm provided the flow data. Calculations of the slip velocity by the Mooney method showed power‐law behavior with the stress. Blends were prepared at various proportions of PP and EVA for observation of the variation of the slip velocity for different compositions and temperatures. Direct microscopic observations of the slip layer on extruded samples showed domains of the dispersed phase unevenly distributed between the slip layer and the core and provided estimates of the thickness of the layer adjacent to the capillary wall. Results showed that the viscosity in the slip layer was 10–100 times lower than that in the bulk for the same value of the shear stress. In terms of the extrapolation length, the development of the slip layer was the result of different disentanglement dynamics of the molecules in the slip layer in comparison with those in the bulk. © 2002 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 303–316, 2002     

Properties of nitrocellulose‐coated and polyethylene‐laminated chitosan and whey films

Chitosan (chitosan acetic acid salt) and whey (65% protein) films were coated with a nitrocellulose lacquer or laminated with polyethylene to enhance their water resistance and gas barrier properties in humid environments. The barrier properties were measured by the Cobb₆₀ test and water‐vapor (100% relative humidity) transmission and oxygen (90% relative humidity) permeability tests. Mechanical properties were obtained with tensile tests. Packaging properties were studied with crease and folding tests. The Cobb₆₀ test revealed that the coated films were resistant to liquid water, at least for a short exposure time, if the coating thickness was at least 10–17 μm. Water‐vapor transmission rates comparable to those of polyethylene‐laminated films were obtained for coated chitosan at a coating thickness of 5–7 μm. The coated films possessed low oxygen permeability despite the high humidity. Coated films dried for 3 weeks showed oxygen permeabilities at 90% relative humidity that were similar to values for dry ethylene‐co‐vinyl alcohol at 0% relative humidity. The lacquer partly penetrated the whey films, and this led to excellent adhesion but poor lacquer toughness. The lacquer coating on chitosan was tougher, and it was possible to fold these films 90° without the coating fracturing if the coating thickness was small. The coated whey films were readily creasable. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 985–992, 2001     

Thermal conductivity of open‐cell polyolefin foams

The thermal conductivity and the cellular structure of novel open‐cell polyolefin foams produced by compression molding and based on blends of an ethylene‐vinyl acetate copolymer (EVA) and a low‐density polyethylene (LDPE) have been studied in the temperature range between 24 and 50 °C. The experimental results have shown that the cellular structure of the analyzed materials has interconnected cells because of the presence of large and small holes in the cell walls, this structure being clearly different to the typical structure of open‐cell polyurethane foams. It has been found that at low temperatures the materials have a slightly higher thermal conductivity than closed‐cell polyolefin foams of similar densities. The different mechanisms of heat flow, conduction, convection, and radiation have been analyzed by using experimental measurements and a theoretical model. It has been proved that, in spite of having an open‐cell structure, the convention mechanism is negligible, being the radiation mechanism the one which made different the conductivity of materials with varying cellular structures. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 212–221, 2008     

Reduced percolation thresholds of immiscible conductive blends

The DC conductivity of polymer blends composed of poly(ethylene‐co‐vinyl acetate) (EVA) and high density polyethylene (HDPE), where a conductive carbon black (CB) had been preferentially blended into the HDPE, were investigated to establish the percolation characteristics. The blends exhibited reduced percolation thresholds and enhanced conductivities above that of the individually carbon filled HDPE and EVA. The percolation threshold of the EVA/HDPE/CB composites was between 3.6 and 4.2 wt % carbon black, where the volume resistivity changed by 8 orders of magnitude. This threshold is at a significantly lower carbon content than the individually filled HDPE or EVA. At a carbon black loading of 4.8 wt %, the EVA/HDPE/CB composite exhibits a volume resistivity which is approximately 14 and 11 orders of magnitude lower than the HDPE/CB and EVA/CB systems, respectively, at the same level of incorporated carbon black. The dielectric response of the ternary composites, at a temperature of 23°C and frequency of 1 kHz, exhibited an abrupt increase of ca. 252% at a carbon concentration of 4.8 wt %, suggesting that the percolation threshold is somewhat higher than the range predicted from DC conductivity measurements. Percolating composites with increasing levels of carbon black exhibit significantly greater relative permittivity and dielectric loss factors, with the composite containing 6 wt % of carbon black having a value of ϵ′ ≈ 79 and ϵ″ ≈ 14. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1899–1910, 1999     

Synthesis and characterization of original alternated fluorinated copolymers bearing glycidyl carbonate side groups

A vinyl ether bearing a carbonate side group (2‐oxo‐1,3‐dioxolan‐4‐yl‐methyl vinyl ether, GCVE) was synthesized and copolymerized with various commercially available fluoroolefins [chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), and perfluoromethyl vinyl ether (PMVE)] by radical copolymerization initiated by tert‐butyl peroxypivalate. Although HFP, PMVE, and vinyl ether do not homopolymerize under radical conditions, they copolymerized easily yielding alternating poly(GCVE‐alt‐F‐alkene) copolymers. These alternating structures were confirmed by elemental analysis as well as ¹H, ¹⁹F, and ¹³C NMR spectroscopy. All copolymers were obtained in good yield (73–85%), with molecular weights ranging from 3900 to 4600 g mol^?1 and polydispersities below 2.0. Their thermogravimetric analyses under air showed decomposition temperatures at 10% weight loss (T_d,10%) in the 284–330°C range. The HFP‐based copolymer exhibited a better thermal stability than those based on CTFE and PMVE. The glass transition temperatures were in the 15–65°C range. These original copolymers may find potential interest as polymer electrolytes in lithium ions batteries. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Vinyl esters: Low cytotoxicity monomers for the fabrication of biocompatible 3D scaffolds by lithography based additive manufacturing

Lithography based additive manufacturing technologies (AMT) like stereolithography or digital light processing have become appealing methods for the fabrication of 3D cellular scaffolds for tissue engineering and regenerative medicine. To circumvent the use of (meth)acrylate‐based photopolymers, that suffer from skin irritation and sometimes cytotoxicity, new monomers based on vinyl esters were prepared. In vitro cytotoxicity studies with osteoblast‐like cells proofed that monomers based on vinyl esters are significantly less cytotoxic than (meth)acrylates. Photoreactivity was followed by photo‐differential scanning calorimetry and the mechanical properties of the photocured materials were screened by nanoindentation. Conversion rates and indentation moduli between those of acrylate and methacrylate references could be observed. Furthermore, osteoblast‐like cells were successfully seeded onto polymer specimens. Finally, we were able to print a 3D test structure out of a vinyl ester‐based formulation by μ‐SLA with a layer thickness of 50 μm. For in vivo testing of vinyl esters these 3D scaffolds were implanted into surgical defects of the distal femoral bone of adult New Zealand white rabbits. The obtained histological results approved the excellent biocompatibility of vinyl esters. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009     

Processability characteristics of chlorinated poly(vinyl chloride)

Chlorinated poly(vinyl chloride) (CPVC) is known to have a higher softening temperature than conventional poly(vinyl chloride) (PVC). Its processability characteristics are, however, different; it has been reported that CPVC is more difficult to process. However, only limited information on the processability characteristics is available. This paper describes some studies of the flow behavior of CPVC melts in a capillary rheometer. The true melt viscosity and activation energy were determined between 190° and 210°C for a number of samples, and they appear to be related to the cohesive energy density of the samples. It was observed that melt fracture, i.e., gross distortion of the extrudate, occurs even at low shear rates in samples having a high chlorine content. This has been attributed to the relatively high pressures that have to be used, the pronounced non-Newtonian nature of the melt, and melt elasticity. It is postulated that melt elasticity could result from crosslinking at the site of the double bond which is known to be formed by dehydrochlorination.