Radiation effects on LDPE/EVA blends

Radiation effects of low‐density polyethylene/ethylene‐vinyl acetate copolymer (LDPE/EVA) blends were discussed. EVA content in the LDPE/EVA blends was an enhancement effect on radiation crosslinking of LDPE/EVA blends, and the highest radiation crosslinking was obtained when the EVA content was reached at 30% when irradiated by γ‐ray in air. The phenomenon was discussed with the compatibility, morphology, and thermal properties of LDPE/EVA blends and found that the enhanced radiation crosslinking of the LDPE/EVA blends was proportional to the good compatibility, the increasing degree of the amorphous region's content of the LDPE/EVA blends, and the vinyl acetate content of EVA. We also found that the vinyl acetate of EVA in the blends is easily oxidized by γ‐ray irradiation in air. The possible radiation crosslinking and degradation mechanism of LDPE/EVA blends was discussed quantitatively with a novel method “step‐analysis” process of irradiated LDPE/EVA blends in the thermal gravimetric analysis (TGA) technique. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1296–1302, 2002     

Radiation effects on HDPE/EVA blends

In this article, we discuss the radiation effects of high‐density polyethylene (HDPE)/ethylene–vinyl acetate (EVA) copolymer blends. In comparison with the low‐density polyethylene/EVA blends, the EVA content in the HDPE/EVA blends had a lower enhancement effect on radiation crosslinking by γ‐ray irradiation in air. The phenomenon is discussed with the compatibility, morphology, and thermal properties of HDPE/EVA blends. The HDPE/EVA blends were partly compatible in the amorphous region, and radiation crosslinking of the HDPE/EVA blend was less significant, although increasing the amorphous region's content of the HDPE/EVA blends and the vinyl acetate content of EVA were beneficial to radiation crosslinking. The good compatibility was a prerequisite for the enhancement effect of EVA on the radiation crosslinking of the polyethylene/EVA copolymer. The radiation crosslinking and the degradation mechanism of HDPE/EVA blends were examined quantitatively by a novel method, the step analysis process of irradiated HDPE/EVA blends with a thermal gravimetric analysis technique. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 553–558, 2002     

Melt grafting of poly(ethylene‐vinyl acetate) copolymer with maleic anhydride

Poly(ethylene‐vinyl acetate) (EVA) copolymer was melt grafted with maleic anhydride (MAH) in a twin screw extruder in the presence of peroxide. It is confirmed that MAH has been melt grafted on the backbone of EVA by FTIR using the method of hydrolysis. The NMR analysis suggests that the grafting reaction occurs on the tertiary carbon of main chain of EVA other than the methyl moiety of vinyl acetate (VA) group. The incorporation of VA groups onto the matrix shows a competitive effect on the grafting. The existence of VA groups promotes the extent of MAH graft onto EVA; nevertheless, it also weakens the crystallizability of main chain. When the content of peroxide initiator is 0.1 wt % based on the polymer matrix, the grafting degree increases with increasing the concentration of monomer. When the peroxide content is higher than 0.1 wt %, side reactions such as crosslinking or disproportionation will be introduced into this system. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 841–846, 2006     

Peroxide crosslinking of ethylene–vinyl acetate copolymer

The work reported here concerns the peroxide crosslinking of ethylene–vinyl acetate rubber. Calculated values for scission-to-crosslinking ratios are higher for EVA than for low-density polyethylene. In the temperature range from 150 to 200°C at a constant peroxide content, a rise in temperature results in a decrease in the obtained gel content. Some tensile and modulus–temperature results on crosslinked EVA samples are also reported on.     

Plastification of poly(vinyl chloride) by polymer blending

Blends of poly(vinyl chloride) (PVC) with different copolymers have been studied to obtain a plasticized PVC with improved properties and the absence of plasticizer migration. The copolymers used as plasticizers in the blends were acrylonitrile butadiene rubber, ethylene vinyl acetate (EVA), and ethylene-acrylic copolymer (E-Acry). Blends were studied with regard to their processing, miscibility, and mechanical properties, as a function of blend and copolymer composition. The results obtained were compared with those of equivalent compositions in the PVC/dioctyl phthalate (DOP) system. Better results than PVC/DOP were obtained for PVC/acrylonitrile butadiene rubber blends. The plasticizing effect on PVC of EVA and E-Acry copolymers was similar to that of DOP. It is shown that crosslinking PVC/E-Acry blends or increasing the vinyl acetate content in PVC/EVA blends, are alternatives that can increase the compatibility and mechanical properties of these blends. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1303–1312, 2000     

Thermodynamic interactions of EVA copolymer‐solvent systems by inverse gas chromatography measurements

The solubility parameter and the Flory–Huggins interaction parameter of two EVA (ethylene–vinyl acetate) copolymers, each one with different vinyl acetate content, are calculated by using inverse gas chromatography technique. The influence of the vinyl acetate percentage is analyzed and indicates that the polymer–solvent interactions are stronger in the case of the copolymer with the highest vinyl acetate percentage. The results also point to the fact that the most favorable solvents for the studied materials are the aromatic‐type ones. Finally, from the calculated values of the polymer solubility parameter (16.3 MPa^0.5 for EVA 460 and 15.1 MPa^0.5 for EVA410, at 50°C), it can be noticed that the solubility parameter of the EVA copolymer with the largest vinyl acetate content is the closest to the solubility parameter of pure vinyl acetate. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Radiation effects on poly(propylene) (PP)/ethylene–vinyl acetate copolymer (EVA) blends

Radiation effects on poly(propylene)/ethylene–vinyl acetate copolymer (PP/EVA) blends are discussed. Increasing the EVA content enhanced the crosslinking effect of radiation in PP/EVA blends. This effect was significant when the EVA content was ≥50% in PP/EVA blends that were exposed to γ‐ray irradiation in air. This phenomenon is discussed in relation to the compatibility, morphology, and thermal properties of PP/EVA blends. The results indicate that the effect is dependent on the compatibility, the increase in the amorphous region content, and the EVA content in PP/EVA blends. The possible mechanism of radiation crosslinking or degradation in irradiated PP/EVA blends was studied quantitatively by a novel method, a “step analysis” process, and thermal gravimetric analysis. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3420–3424, 2002     

Shape memory effect of ethylene–vinyl acetate copolymers

Crosslinked ethylene–vinyl acetate (EVA) copolymers with VA content of 28% by weight were prepared by a two‐step method by evenly dispersing the crosslinking agent (dicumyl peroxide) into the EVA matrix and then crosslinking at elevated temperatures. The crosslinking features of the samples were analyzed by Soxhlet extraction with xylene and dynamic mechanical measurements. All the samples were crystalline at room temperature, and the chemical crosslinks seemed to have little effect on the melting behavior of polyethylene segment crystals in the EVA copolymers. The shape recovery results indicated that only those specimens that had a sufficiently high crosslinking degree (gel content higher than about 30%) were able to show the typical shape memory effect, a large recoverable strain, and a high final recovery rate. The degree of crosslinking can be influenced by the amount of the peroxide and the time and temperature of the reaction. The response temperature of the recovery effect (about 61°C) was related to the melting point of the samples. The EVA shape memory polymer was characterized by its low recovery speed that resulted from the wide melting range of the polyethylene segment crystals. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1063–1070, 1999     

Melt functionalization of EVA copolymers with maleic anhydride

Ethylene vinyl acetate (EVA) copolymers with different amounts of vinyl acetate were melt‐functionalized with maleic anhydride. The effect of benzoyl peroxide, t‐butyl perbenzoate, and dicumyl peroxide (DCP) as free‐radical initiators on the functionalization performance was studied. The crosslinking reactions occur to a larger extent than in polyethylene, indicating that the vinyl acetate groups favor the formation of free radicals. From all the experiments performed in this study, the recommended initiation system to achieve the best values of the functionalization degree and the lower gel content involves the use of DCP in a concentration of about 0.3 wt % and a maleic anhydride concentration around 5.0 wt %. From FTIR and TGA analyses, it is suggested that the hydrogen abstraction in the EVA copolymers occurs both in the methyl group of the acetate moiety and in the tertiary C—H. The free radicals generated in the tertiary C—H react with maleic anhydride in a higher proportion. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1799–1806, 1999     

辐射交联LDPE/EVA混合体系泡沫片材性能的研究

辐射交联LDPE/EVA混合体系泡沫片材表观光滑、柔软,手感好,表观密度较小,材料具有优异的力学性能,较高的拉伸强度、断裂伸长率和撕裂强度。进一步研究了产生宏观性能差异的原因是辐射交联LDPE/EVA混合体系泡沫片材制备成型工艺的特殊性,体系的交联度对制品性能影响很大。通过凝胶分析知道交联度与辐照剂量、LDPE树脂的物理性能和EVA树脂在混合体系的含量有关。此外,LDPE树脂的物理性能和EVA在混合体系的含量对材料宏观性能也有影响。     

Effect of EVA copolymer on properties of different polyethylenes in silane crosslinking process

Abstract

The effect of molecular structure of polyethylene (PE) [low density PE (LDPE), linear LDPE and high density PE] and silane/peroxide concentration on the grafting level and gel content in silane crosslinking process has been studied. The effect of incorporation of ethylene vinyl acetate (EVA) copolymer on the rate of crosslinking and thermal properties of PEs has been reported. The order of gel content was LDPE>linear LDPE>high density PE. With the incorporation of EVA, the rate of crosslinking increased. The degree of crystallinity did not change with crosslinking significantly. However, the shape of melting and crystallisation peaks changed, and two regions due to gel and sol parts were formed. In EVA/PE blends, two melting points were observed for both crosslinked and uncrosslinked samples. The SEM images showed the droplet matrix morphology with the EVA as the dispersed phase, especially for EVA/LDPE blend. The EVA/PE blends failed in hot set test, while the origin of PEs passed the hot set test successfully.     

Investigation of flame retardancy in EVA

Strategies for fire retarding ethylene vinyl acetate copolymer (EVA) in electrical cable insulation by means of halogen‐free systems were explored. Attempts to increase char yield, promoting crosslinking of double bonds either created by deacetylation of vinyl acetate units or by dehydrogenation of ethylene sequences in EVA were carried out. Pd catalysed dehydrogenation was unsuccessful, whereas oxidative dehydrogenation seems promising as shown by using thermally decomposing KMnO₄. On the other hand organic peroxides failed to increase the rate of crosslinking of deacetylated units. Better results were obtained with the addition to EVA of an intumescent system which is a combination of melamine phosphate and phosphate‐phosphonate substituted trimethylamine. EVA was shown to play a substantial role in the intumescence phenomenon. Copyright © 2000 John Wiley & Sons Ltd.     

Thermal and mechanical properties of uncrosslinked and chemically crosslinked polyethylene/ethylene vinyl acetate copolymer blends

Uncrosslinked and chemically crosslinked binary blends of low‐ and high‐density polyethylene (PE), with ethylene vinyl acetate copolymer (EVA), were prepared by a melt‐mixing process using 0–3 wt % tert‐butyl cumyl peroxide (BCUP). The uncrosslinked blends revealed two distinct unchanged melting peaks corresponding to the individual components of the blends, but with a reduced overall degree of crystallinity. The crosslinking further reduced crystallinity, but enhanced compatibility between EVA and polyethylene, with LDPE being more compatible than HDPE. Blended with 20 wt % EVA, the EVA melting peak was almost disappeared after the addition of BCUP, and only the corresponding PE melting point was observed at a lowered temperature. But blended with 40% EVA, two peaks still existed with a slight shift toward lower temperatures. Changes of mechanical properties with blending ratio, crosslinking, and temperature had been dominated by the extent of crystallinity, crosslinking degree, and morphology of the blend. A good correlation was observed between elongation‐at‐break and morphological properties. The blends with higher level of compatibility showed less deviation from the additive rule of mixtures. The deviation became more pronounced for HDPE/EVA blends in the phase inversion region, while an opposite trend was observed for LDPE/EVA blends with co‐continuous morphology. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3261–3270, 2007     

Free‐radical grafting of trans‐ethylene‐1,2‐dicarboxylic acid onto molten ethylene‐vinyl acetate copolymer

Distinctive features of free‐radical grafting of trans‐ethylene‐1,2‐dicarboxylic acid (TEDA) onto macromolecules of molten ethylene‐vinyl acetate copolymer (EVA) in the course of reactive extrusion have been investigated along with structure, mechanical characteristics, and high‐elastic properties of molten functionalized products (EVA‐g‐TEDA). It is shown that EVA‐g‐TEDA yield depends on both the peroxide initiator concentration and content of vinyl acetate units in the copolymer molecular structure. At functionalization, acid grafting is accompanied by secondary reactions of macromolecular degradation and crosslinking. With a low‐peroxide initiator concentration (0.1 wt %), degradation prevails; with a higher (0.3 wt %) concentration, crosslinking of macromolecules prevails. It is reported that monomers being grafted attach mostly over secondary carbon atoms in the polymer chain. EVA‐g‐TEDA appears to have a less perfect crystal structure with a lower‐melting temperature and crystallinity as against the starting polymer. The functionalized products display enhanced rigidity and lower deformability in comparison with the initial copolymer. Variations in the swelling ratio and melt strength of EVA‐g‐TEDA depend on the course of competing secondary processes of macromolecular degradation and crosslinking. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

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

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

Preparation and characterization of ethylene vinyl acetate copolymer/montmorillonite nanocomposite

Ethylene vinyl acetate copolymer (EVA) and monmorillonite (MMT) nanocomposites have been investigated as a function of vinyl acetate content and molecular weight of EVA and types of substituted alkyl ammonium of MMT. It is found that vinyl acetate content and type of substituted alkyl ammonium are important factors for the intercalation behaviour of MMT in MMT/EVA nanocomposite. Maleic anhydride grafted high‐density polyethylene was used as a compatibilizer to improve the intercalation behaviour of MMT. X‐ray diffraction and transmission electron microscopy were used to characterize the intercalation/exfoliation behaviour, and mechanical properties were measured. © 2003 Society of Chemical Industry     

Tailoring viscoelastic and mechanical properties of the foamed blends of EVA and various ethylene‐styrene interpolymers

Foamed materials (EVA/ESI) have been prepared from blends of ethylene‐vinyl acetate copolymer (EVA) and ethylene‐styrene interpolymers (ESI) in the presence of various amounts of dicumyl peroxide (DCP). Four ESIs of different compositions were employed in this study; their styrene contents ranged from 30 to 73 wt% and their T_g ranged from −2 to 33°C. It has been found that microcellular morphology, degree of crosslinking and expansion ratio were strongly affected by the DCP concentration and the type of ESI employed. A minimum degree of crosslinking was required for making good foams and the same degree of crosslinking could be achieved by employing a smaller amount of DCP for an EVA/ESI blend having a higher styrene content. In contrast to other EVA blends, such as EVA/LDPE, these EVA/ESI blends exhibited no existence of any optimum DCP concentration, and the α glass transition temperatures of the foams varied with the ESI type, covering a wide span from 0°C to 37°C. Therefore, it was possible to tailor the T_g of an EVA/ESI blend by choosing an appropriate type of ESI. Furthermore, by correctly tailoring the T_g, the EVA/ESI foam could be made into a rubbery material with a custom‐designed damping factor. Tensile strength and modulus of the EVA/ESI foams increased generally with an increase in the styrene content, with the exception that ESIs with very low styrene content will confer on the blend a high modulus at small strain and a large elongation at break.     

Removal of sodium acetate in poly(vinyl alcohol) and its quantification by 1H NMR spectroscopy

A major impurity in poly (vinyl alcohol) (PVA) is sodium acetate which remains after its preparation by a base catalyzed hydrolysis of poly(vinyl acetate), and the amount of sodium acetate in commercial PVA samples may reach several percentages. To establish an optimal condition for the removal of sodium acetate, several washing parameters such as washing period, solvent polarity, and temperature were investigated in this study. Nuclear magnetic resonance (NMR) spectroscopy was successfully applied to determine the residual amounts of sodium acetate in the purified poly(vinyl alcohol). The relative integral value for the methyl peak of sodium acetate in PVA was converted to a relative mass value and finally to the sodium acetate content contained in PVA. The results showed that over 95% of sodium acetate in PVA was removed by a washing of PVA with distilled water within 2 h. When methanol was used as a washing solvent, a higher temperature than room temperature was required for an effective removal of sodium acetate. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Mechanical changes of electron beam irradiated ethylene–vinyl acetate copolymer (EVA) film (I)

Electron beam irradiation of ethylene-vinyl acetate copolymer (EVA) film results in a marked depression of sorption of flavour compounds. This effect is presumed to be brought about by radical reactions, following changes in the structure. The crosslinking density and gel fraction increased with irradiation dose, and the maximum percent gel reached 70% for 20 Mrad-50g kg^?1 EVA film, 35% for 20 Mrad-95g kg^?1 EVA film and 50% for 10 Mrad-150g kg^?1 EVA film. In calculating the ratio of scission to crosslinking events, it was found that EVA film is a polymer of the scission type. The degree of crystallinity, X_c decreased significantly with increasing irradiation dose in all irradiated films. For unirradiated films, X_c decreased with increase in vinyl acetate content, which suggests that crystalline regions of EVA film are primarily composed of ethylene units. Therefore, the scission reaction may predominantly take place in the crystalline region, resulting in the formation of methyl or end vinyl groups. This was supported by measuring the film density, peak melting temperature and stress at yield.     

Effects of compatibilizer on the layered silicate/ethylene vinyl acetate nanocomposite

Dispersion behavior of monmorillonite (MMT) is investigated in ethylene vinyl acetate (EVA)/MMT nanocomposite with various vinyl acetate content. Maleic anhydride (MAH) grafted polyethylenes with various MAH contents are used as a compatibilizer to enhance the dispersion of MMT. DMA and XRD studies indicate that an intercalated/exfoliated structure is obtained and vinyl acetate content and the concentration of PEMA play a critical role in EVA/MMT nanocomposite. Higher vinyl acetate content and concentration of grafted maleic anhydride result in better dispersion of MMT. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1057–1061, 2004