Rheology, morphology and mechanical properties of polyethylene/ethylene vinyl acetate copolymer (PE/EVA) blends

Rheology, morphology and mechanical properties of binary PE and EVA blends together with their thermal behavior were studied. The results of rheological studies showed that, for given PE and EVA, the interfacial interaction in PE-rich blends is higher than EVA-rich blends, which in turn led to finer and well-distributed morphology in PE-rich blends. Using two different models, the phase inversion composition was predicted to be in 45 and 47 wt% of the PE phase. This was justified by morphological studies, where a clear co-continuous morphology for 50/50 blend was observed. The tensile strength for PE-rich blends showed positive deviation from mixing rule, whereas the 50/50 blend and EVA-rich blends displayed negative deviation. These results were in a good agreement with the results of viscoelastic behavior of the blends. The elongation at break was found to follow the same trend as tensile strength except for 90/10 PE/EVA blend. The latter was explained in terms of the effect of higher co-crystallization in 90/10 composition, which increased the tensile strength and decreased the elongation at break in this composition. The results of thermal behavior of the blends indicated that the melting temperatures of PE and EVA decrease and increase, respectively, due to the dilution effect of EVA on PE and nucleation effect of PE on EVA.     

Synergistic effect of combination of Irganox 1010 and zinc stearate on thermal stabilization of electron beam irradiated HDPE/EVA both in hot water and oven

Thermo-oxidative stability of HDPE/EVA blends can be considerably increased by combination of a high-molecular weight phenolic antioxidant and zinc stearate. In this work, the post-irradiation thermal stability of HDPE/EVA blends has been studied. High-density polyethylene and its blends with ethylene-vinylacetate copolymer in both pure form and mixed with Irganox 1010 and zinc stearate were exposed to electron beam radiation at doses between 80 and 150 kGy, at room temperature, in air. In order to evaluate the thermal stability of the samples, post-irradiation heat treatments were done in both hot water bath at 95 °C and in an oven at 140 °C. The mechanical properties and changes in the chemical structure were determined during thermal aging in hot water and oven. The gel content was enhanced by increasing EVA concentration in all applied doses. The stabilized blends have lower gel content than the unstabilized samples. From the results of heat aging treatments it was observed that the thermal stability of the unstabilized blend samples was lower than HDPE. Thermal stability of the samples has been improved by incorporation of Irganox 1010 and zinc stearate. Formation of hydroxyl group was insignificant for stabilized samples during heat aging in both conditions. Also, the changes in the value of oxidation induction time (OIT) for the stabilized samples were negligible after prolonged immersion in hot water.     

Photodegradation of polycaprolactone/poly(vinyl chloride) blend

The photodegradation of a 1:1 w/w blend of polycaprolactone and poly(vinyl chloride) has been studied by following carbon dioxide emission during UV exposure. Similar measurements were performed for polycaprolactone and poly(vinyl chloride) homopolymers which were prepared and irradiated in the same way. It was found that the blend gave lower CO₂ emission than either of the two homopolymers, indicating that the interaction of the two components in the blend provided a beneficial reduction of photodegradation. It is therefore deduced that the detailed morphological characteristics of the blend have a controlling influence over the photo-oxidation.     

UV aging behaviour of ethylene-vinyl acetate copolymers (EVA) with different vinyl acetate contents

The mild UV aging of ethylene-vinyl acetate copolymer (EVA) with two vinyl acetate (VAc) contents (14, 18 wt%) was performed in a xenon arc source chamber. The degradation mechanism was analyzed via attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), gel content and high temperature gel permeation chromatography (HTGPC). Photo-chemically induced deterioration was first initiated from vulnerable VAc units. Ketone formation preceded lactone generation, especially in EVA with high VAc content. Un-stable structures induced further degradation in the main chain. Competition between radiation induced cross-linking and chain scission in EVA was observed, and the later was confirmed to be dominant. Higher VAc content resulted in remarkable drop in molecular weight and growth in polydispersity. Apparent re-arrangement in crystallisation and consequent decrease in thermal stability are discussed through differential scanning calorimetry (DSC) and thermo-gravimetric analysis (TGA), which accorded well with the chain scission tendency. Interaction between photo-chemical degradation and physical annealing accounted for the first increasing then decreasing tendency in the mechanical properties of both EVAs.     

Characterization of poly(ethylene-co-vinyl acetate) (EVA) filled with low grade magnesium hydroxide

Low-grade magnesium hydroxide (LG-MH) is a solid by-product that undergoes an endothermic decomposition in the temperature range of 300-750 °C. Due to its thermal behaviour and its lower cost relative to pure Mg(OH)₂, it was studied as a non-halogenated flame retardant filler in a 28% vinyl acetate (VA) content poly(ethylene-co-vinyl acetate) matrix. The solid was characterized by XRF and the crystalline phases determined by XRD, composed predominantly of Mg(OH)₂ and calcium and magnesium carbonates. Particle size reduction was performed by both mechanical as well as air jet milling in order to optimize the particle size distribution.Composites with different filler concentrations were prepared to evaluate the mechanical properties and flame retardancy by means of limiting oxygen index tests. LOI was also determined in specimens filled with commercial flame-retardants to analyse the effectiveness of this solid.     

Investigation of the curing state of ethylene/vinyl acetate copolymer (EVA) for photovoltaic applications by gel content determination,rheology, DSC and FTIR

The cure behaviour of a specific ethylene vinyl acetate material as used for encapsulation of photovoltaic modules was analysed by rheometer, differential scanning calorimetry and Fourier transform infrared spectroscopy to test for a suitable replacement for the laborious determination of gel content.The results show that all applied methods are capable of describing the effects of the cross-linking process. Some provide results very similar to those yielded by analysis of the insoluble content, but the question remains as to whether indirect methods should be preferred over the direct measurement of physical properties, e.g. as performed by the curemeter.A material stored for one year was also tested to demonstrate the effect of extended storage on cure behaviour and how this is detected by different methods. This complements the other methods, which were clearly able to detect the different cure behaviour of the aged EVA, whereas determination of the gel content could not.     

Thermal stability and flammability characteristics of ethylene vinyl acetate (EVA) composites blended with a phenyl phosphonate-intercalated layered double hydroxide (LDH), melamine polyphosphate and/or boric acid

A phenyl phosphonate-intercalated MgAl-LDH (MgAl-PPh), melamine polyphosphate (MP), and boric acid (BA) were independently and concomitantly added to neat ethylene vinyl acetate (EVA) copolymer at loading fractions of 10% (w/w). The structural morphology of MgAl-PPh was established via powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM) while the presence of phenyl phosphonate in the galleries was confirmed by Fourier transform infrared (FTIR). Thermogravimetric analysis (TGA) and cone calorimetry were used to evaluate the thermal stability and flammability behavior of EVA and its composites. While time-to-ignition is greatly reduced for EVA composites compared to the virgin polymer, there are remarkable reductions in the peak heat release rate (PHRR) which relates to a reduction in flame intensity. Synergistic effects were observed in cone calorimetry for the formulation containing MgAl-PPh, MP, and BA.     

Nonisothermal crystallisation, melting behavior and wide angle X-ray scattering investigations on linear low density polyethylene (LLDPE)/ethylene vinyl acetate (EVA) blends: effects of compatibilisation and dynamic crosslinking

Crystallisation studies on LLDPE/EVA blends and the individual components were performed with wide angle X-ray scattering (WAXS) technique and differential scanning calorimetry (DSC) DSC was used to characterise the quiescent crystallisation behavior. The heat of fusion and crystallinity of the blends were reduced by the addition of EVA. The experimental and theoretical values of crystallinity of the blends were found to be mutually agreeing. Crystallisation of LLDPE remains impeded to some extent due to the presence of amorphous EVA. Compatibilisation does not affect crystallinity whereas crosslinking decreases crystallinity. Crosslinking and compatibilisation make no significant change in the melting temperature of the blends. X-ray diffraction studies were carried out on un-crosslinked and crosslinked LLDPE/EVA blends with a view to study the effect of blend composition and crosslinking on crystallinity and lattice distance. Studies revealed that LLDPE and EVA have orthorhombic unit cell. Blending with EVA did not affect the crystalline structure of LLDPE, but the crystallinity decreases with EVA content. At low concentrations of EVA the lattice parameters remain unchanged. Above 30% EVA content however, a linear increase has been observed. Dicumyl peroxide (DCP) crosslinked samples show considerable shift of (1 1 0), (2 0 0) and (0 2 0) crystalline peaks towards lower 2θ values indicating an increase of unit cell parameters of the orthorhombic unit cell of polyethylene. At lower EVA-concentrations (<50%) the crystalline structure remains unchanged. For EVA-contents of more than 70% however, increasing DCP-content reduces the crystallinity of the blends and increases the lattice distance. This indicates that DCP-crosslinking is more effective in EVA phase than in the LLDPE phase.     

Preparation of poly(ethylene terephthalate-co-isophthalate) by ester interchange reaction in the PET/PEI blend system

Optimum conditions for the synthesis of PEI of considerable molecular weight have been established. Poly(ethylene terephthalate-co-isophthalate) (PETI) has been prepared through the ester interchange reaction of a blend of poly(ethylene terephthalate) (PET) and poly(ethylene isophthalate) (PEI). NMR analysis has indicated that the PETI changes from a block-type copolymer to a random type copolymer as the ester interchange reaction proceeds. If the reaction is limited to 20 min, the resulting PETI is crystallizable. The effects of catalysts that have been used during the synthesis of PEI on the characteristics of PETI are also discussed. © 1997 John Wiley & Sons, Inc.     

Novel crosslinked chitosan/poly(vinylpyrrolidone) blend membranes for dehydrating tetrahydrofuran by the pervaporation technique

Pervaporation separation has been attempted for dehydrating tetrahydrofuran (THF) from its aqueous mixtures using the novel blend membranes of poly(vinylpyrrolidone) (PVP) and chitosan (CS). Membranes were physically blended and crosslinked with glutaraldehyde as well as with sulfuric acid in methanol/sulfuric acid mixture bath to enhance their selectivity and mechanical strength properties. Membranes were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TGA) and X-ray diffractometer (X-RD) to assess their intermolecular interactions, thermal stability and crystallinity. Sorption studies were carried out in pure as well as in different compositions of THF + water mixtures to assess polymer–liquid interactions. The membrane exhibited a high selectivity of 1025 with a reasonably high water flux value of 0.0995 kg/m² h at the azeotropic feed composition (94.31 wt.% of THF). Effect of operating parameters such as feed composition, membrane thickness and permeate pressure were evaluated.     

Sorption and diffusion of methyl substituted benzenes through cross-linked nitrile rubber/poly(ethylene co-vinyl acetate) blend membranes

The diffusion and sorption of methyl substituted benzenes through cross-linked nitrile rubber/poly(ethylene co-vinyl acetate) (NBR/EVA) blend membranes has been studied. The influence of blend composition, cross-linking systems, temperature and size of penetrants on the transport behaviour has been analysed. It was observed that as the EVA content increases in the blends, the solvent uptake decreases. An increase in the penetrant size also decreases the solvent uptake. The diffusion experiments were carried out in the temperature range 23–75 °C. As temperature increases the equilibrium uptake also increases. The transport coefficients namely diffusion coefficient, sorption coefficient and permeation coefficient have been calculated. The sorption data has been used to estimate the activation energies for permeation and diffusion. The van’t Hoff relationship was used to determine the thermodynamic parameters. The affine and phantom models for chemical cross-links were used to predict the nature of cross-links. Models for permeability were used and the theoretical values compared with the experimental results.     

Dynamically cured natural rubber/EVA blends: influence of NR‐g‐poly(dimethyl (methacryloyloxymethyl)phosphonate) compatibilizer

Graft copolymer of natural rubber and poly(dimethyl(methacryloyloxymethyl)phosphonate) (NR‐g‐PDMMMP) was prepared in latex medium via photopolymerization. It was then used to promote the blend compatibility of dynamically cured 40/60 natural rubber (NR)/ethylene vinylacetate copolymer (EVA) blends using various loading levels at 1, 3, 5, 7, 9, 12, and 15 wt%. It was found that the increasing loading levels of NR‐g‐PDMMMP in the blends caused the increasing elastic modulus and complex viscosity until reaching the maximum values at a loading level of 9 wt%. The properties thereafter decreased with the increasing loading levels of NR‐g‐PDMMMP higher than 9 wt%. The smallest vulcanized rubber particles dispersed in the EVA matrix with the lowest tan δ value was also observed at a loading level of 9 wt%. Furthermore, the highest tensile strength and elongation at break (i.e., 17.06 MPa and 660%) as well as the lowest tension set value (i.e., 27%) were also observed in the blend using this loading level of the compatibilizer. Addition of NR‐g‐PDMMMP in the dynamically cured NR/EVA blends also improved the thermal stability of the blend. That is, the decomposition temperature increased with the addition of the graft copolymer. However, the addition of NR‐g‐PDMMMP in the blends caused the decreasing degree of crystallinity of the EVA phase in the blend. However, the strength properties of the blend are still high because of the compatibilizing effect. Copyright © 2009 John Wiley & Sons, Ltd.     

Structure and compatibility of poly(vinyl alcohol)-silk fibroin (PVA/SA) blend films

The structure and compatibility of poly(vinyl alcohol)-silk fibroin (PVA/SF) blend films were analyzed by differential scanning calorimetry (DSC), thermomechanical (TMA) and thermogravimetric (TGA) analysis, x-ray diffractometry, and scanning (SEM) and transmission (TEM) electron microscopy. DSC curves of PVA/SF blend films showed a major endothermic peak at 220°C, along with a peak at 280°C. These endotherms were assigned to the thermal decomposition of the ordered PVA elements and to the thermal degradation of silk fibroin, respectively. The PVA/SF blends behaved in a manner intermediate to the pure components, as suggested by both contraction expansion and sample weight retention properties recorded by TMA and TGA measurements. The IR absorption spectra of the blends were identified as purely a composite of the absorption bands characteristic of both PVA and SF pure polymers. The X-ray diffraction patterns of PVA/SF blends showed overlapping spacing due to PVA and SF. A dispersed phase formed by spherical particles of 3–7 μm diameter was observed by SEM and TEM. All these findings suggest that PVA and SF are incompatible. © 1994 John Wiley & Sons, Inc.     

The effect of gamma irradiation on mechanical, and thermal properties of recycling polyethylene terephthalate and low density polyethylene (R-PET/LDPE) blend compatibilized by ethylene vinyl acetate (EVA)

A study has been made on the compatibility of recycled polyethylene terephthalate (R-PET) and low density polyethylene (LDPE) blend in the presence of ethylene vinyl acetate (EVA) as a compatibilizing agent prepared by extrusion hot stretching process. EVA content in the blend as a compatibilizing agent was an enhancement effect on radiation crosslinking of R-PET/EVA/LDPE blends and the highest radiation crosslinking was obtained when the EVA content was reached at 10 % EVA when irradiated by gamma irradiation. Blends containing different (EVA) ratios were irradiated to different doses of gamma irradiation 25, 50 and 100 kGy. The effect of the compatibilizer and radiation on mechanical, thermal properties of R-PET together with LDPE and morphology has been investigated. It was found that gamma irradiation together with the presence of compatibilizing agent (EVA) has positive effect on the mechanical and thermal properties of R-PET/LDPE blend. The structural properties of R-PET/LDPE modified by gamma irradiation and EVA as compatibilizing agent was examined by SEM. Also, it was found that the optimum concentration of EVA and gamma irradiation dose was found to be 10 % EVA and 100 kGy, respectively.     

Thermal,rheological, morphological and mechanical properties of high density polyethylene/ethylene vinyl acetate copolymer (HDPE/EVA) blends

Thermal, rheological, morphological and mechanical properties of binary HDPE and EVA blends were studied. The results of rheological studies showed that for given HDPE and EVA, the interfacial interaction in HDPE-rich blends is higher than EVA-rich blends. Using three different rheological criterions, the phase inversion composition was predicted to be in 30 wt% of the EVA phase. This showed good agreement with morphological studies. The tensile strength for HDPE-rich blends showed positive deviation from mixing rule, whereas the EVA-rich blends played negative deviation. These results were in a good agreement with the results of viscoelastic behavior of the blends. The thermal analysis revealed that high co-crystallizaiton in 90/10 composition, which increased the tensile strength and decreased the elongation at break in this composition. Furthermore, the results of thermal behavior of the blends indicated that the melting temperatures of HDPE decrease due to the dilution effect of EVA on HDPE.     

Properties stability and biodegradation behaviors of soy protein isolate/poly (vinyl alcohol) blend films

The objective of this work was to investigate the color, transparency, water sensitivity and mechanical properties stability in air under photo-oxidative degradation influencing consumer acceptance and biodegradation behaviors in soil of soy protein isolate (SPI)/poly (vinyl alcohol) (PVA) blend packaging films during 30 days. The results showed that PVA could dilute the yellow color and make the SPI-based films less darkness in application and the transparency of SPI/PVA films at various stages of degradation was improved. The addition of PVA decreased the ability of SPI protein molecules to absorb water and enhanced the mechanical properties of blend films comparing to pure SPI film in 30 days. Aerobic biodegradation of films in soil proved that the PVA compound interacting with protein imposed negative effects on biodegradation of blend films prolonging their decomposing time. The SPI/PVA blend films decomposed into small fragments of less complex molecules along with surface completely digested after 30 days.     

Dehydration of 1,4-dioxane through blend membranes of poly(vinyl alcohol) and chitosan by pervaporation

Blend membranes prepared from poly(vinyl alcohol) (PVA) and chitosan (CS) were crosslinked with glutaraldehyde and used in the pervaporation dehydration of 1,4-dioxane. Membranes were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and X-ray diffraction (X-RD) to assess, respectively, the intermolecular interactions, thermal stability and crystallinity. Equilibrium sorption studies were carried out in pure liquids and binary mixtures of different compositions of water + 1,4-dioxane mixtures to assess the polymer–liquid interactions. The crosslinked membrane showed a good potential in breaking the azeotrope of 82 wt.% aqueous 1,4-dioxane giving a selectivity of 117 with a reasonable water flux of 0.37 kg/m² h. The effect of operating parameters such as feed composition, membrane thickness and permeate pressure was evaluated.     

Pervaporation of alcohol-toluene mixtures through polymer blend membranes of poly(acrylic acid) and poly(vinyl alcohol)

Homogeneous membranes were prepared by blending poly(acrylic acid) with poly(vinyl alcohol). These blend membranes were evaluated for the selective separation of alcohols from toluene by pervaporation. The flux and selectivity of the membranes were determined both as a function of the blend composition and of the feed mixture composition. The results showed that a polymer blending method could be very useful to develop new membranes with improved permselectivity. The pervaporation properties could be optimized by adjusting the blend composition. All the blend membranes tested showed a decrease in flux with increasing poly(vinyl alcohol) content for both methanol—toluene and ethanol—toluene liquid mixtures. The alcohols permeated preferentially through all tested blend membranes, and the selectivity values increased with increasing poly(vinyl alcohol) content. The pervaporation characteristics of the blend membranes were also strongly influenced by the feed mixture composition. The fluxes increased exponentially with increasing alcohol concentration in the feed mixtures, whereas the selectivities decreased for both liquid mixtures.