The rheological properties of vinyl chloride–vinyl acetate copolymers

Copolymers of vinyl chloride–vinyl acetate have been prepared with different vinyl acetate contents and molecular weights and under different polymerization conditions. A rheological study of these copolymers indicates that they behave in some ways like externally plasticized PVC. For instance, as the vinyl acetate content increases, the melt viscosity decreases, the flow activation energy decreases, and the copolymer becomes more Newtonian. However, the critical shear rate for melt fracture increases, resembling the addition of elastic polymers to PVC. An increase in copolymer molecular weight has a similar effect on the rheological behavior as in PVC, except that the flow activation energy is observed to increase rather than decrease. Decreasing the polymerization temperature affects the flow properties of the copolymer, probably due to changes in degree of branching and crystallinity. A copolymer made by the delayed addition of vinyl chloride, having a more random structure than one made by the conventional batch method, exhibited quite different flow behavior. It had a lower melt viscosity, higher critical shear rate, and lower flow activation energy.     

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     

Achieving compatibility in blends of low‐density polyethylene/polyamide‐6 with addition of ethylene vinyl acetate

Polymer alloys and blends, whose major advantage is the potential of achieving a range of physical and mechanical properties, have continued to be a subject of interest over recent years. Addition of a block or graft copolymer, with chemically similar segments to those involved in the polymer blend considered, led to a variety of desirable properties. The copolymer added to the blend functioned to promote a homogeneous dispersion of the constituent phases and to enhance their mutual adhesion. Such agents that enable better dispersion in polymer blends are known as compatibilizers. In this study an attempt has been made to improve the compatibility in a polymer blend composed of two normally incompatible constituents, LDPE and PA₆, by addition of a compatibilizer. The compatibilizer agent, ethylene vinyl acetate (EVA), was added to the polymer blend in ratios of 1, 5, and 10% by using a twin‐screw extruder. The effect of EVA on the crystallization of the polymer constituents was observed through DSC examinations. Furthermore, the control sample and all three blends of LDPE/PA₆/EVA were subjected to examinations to obtain their yield and tensile strengths, elasticity modulus, percentage elongation, izod impact strength, hardness, and melt flow index. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1748–1754, 2001     

LDPE／EVA共混物挤出工艺与拉伸性能研究

研究了5种EVA添加量、VA含量和MFR对挤出LDPE/EVA共混物的挤出机各段温度、挤出机螺杆扭矩及拉伸性能的影响。     

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     

Evaluation of mechanical properties and physical interactions of a ternary blend of poly(ethylene‐co‐octene)/poly(ethylene‐co‐vinyl acetate)/poly(vinyl chloride) in the molten state

In this work, ethylene‐co‐vinyl acetate (EVA), poly(ethylene‐co‐octene) (POE), and poly(vinyl chloride) (PVC) blends were processed in a molten state process using a corotating twin‐screw extruder to assess both the balance of mechanical properties and physical interactions in the melt state. Tensile measurements, scanning electron microscopy, and oscillatory rheometry were performed. By means of flow curves, the parameters of the power law as well as the distribution of relaxation times were assessed with the aid of a nonlinear regularization method. The mechanical properties for the EVA‐POE blend approximated the values for POE, while inclusion of PVC shifted the modulus values to those of neat EVA. The rise in modulus was corroborated by the PVC phase dispersion as solid particles that act as a reinforcement for the ternary blend. The rheological properties in the molten state show that the POE does not present molecular entanglement effects and so tends both to diminish the EVA mechanical properties and increase the fluidity of the blend. However, the addition of PVC both restored the EVA typical pseudoplastic feature and promoted the increase in the viscosity and the mechanical properties of the ternary blend. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Improving viscoelasticity and rebound resilience of crosslinked low‐density polyethylene foam by blending with ethylene vinyl acetate and polyethylene‐octene elastomer

To obtain high‐rebound resilience of crosslinking low‐density polyethylene (LDPE) foam and decrease the foam density at the same content of foaming agent, the melt viscoelasticity of LDPE with different compositions (ethylene vinyl acetate [EVA], polyethylene‐octene elastomer, and crosslinking agent) was investigated by dynamic rheology test. Then, LDPE/EVA/(polyethylene‐octene elastomer) foams with different composition ratios were produced by a continuous foaming process and investigated by the rebound resilience test. The results show that the melt viscoelasticity behavior of LDPE and its blends in the molten state possessed more melt elasticity behavior after the crosslinking was introduced. Meanwhile, the rebound resilience of LDPE foam was increased 54% at the lower foam density (0.031 g/cm³). It could meet the requirements of sports mats for high‐rebound resilience (>50%) and decrease the material cost when EVA was introduced into the foaming system. J. VINYL ADDIT. TECHNOL., 22:61–71, 2016. © 2014 Society of Plastics Engineers     

Melt-rheological properties of PP/EVA blend

This paper describes a study of melt-rheological properties of the binary blend of isotactic polypropylene (PP) and ethylene–vinyl acetate copolymer (EVA) at varying blending ratios (from 0 to 40 wt % EVA content) and using three samples of EVA containing different vinyl acetate contents (VA %), viz. 9, 12, and 19%. Measurements made on a capillary rheometer at three different temperatures (210, 220, and 230°C) in a shear stress range of 10⁴–10⁶ Pa (shear rate 10¹–10⁴ s^?1) are presented and discussed for the effects of blend composition and shear stress on the flow curves, melt viscosity and melt elasticity. Morphology of the blend studied through scanning electron microscopy revealed distinct differences in size and number density of dispersed EVA droplets, which are discussed in terms of the variation of average size and number density of the dispersed EVA droplets as a function of blend composition and shear stress. Melt-rheological properties and morphology of dispersion are correlated and found quite consistent.     

Influence of polarity of polymer on inorganic particle dispersion in dielectric particle/polymer composite systems

The influence of the polarity of polymers on the degree of dispersion of BaTiO₃ particles in BaTiO₃/polymer composite systems was investigated. The BaTiO₃ polymer composite systems were prepared from BaTiO₃ particles and low-density polyethylene (LDPE) or ethylene vinyl acetate copolymer (EVA) with 7 and 15 wt % vinyl acetate. Scanning electron microscopy observation showed that BaTiO₃ particles aggregated in the polymer matrices and dispersed more readily into the EVA matrix than into LDPE. The shift of the β-peak temperature by ca. +5°C in the temperature dispersion of the loss modulus was observed for EVA–BaTiO₃ composite systems in dynamic mechanical property measurement. On the other hand, the β-peak temperature of the polymers filled with graphite particles, which have hydrophobic surfaces, was almost constant in a volume fraction region of 0–0.3. The ellipsoidal axes' ratios given by comparison of experimental dielectric constant values and theoretical ones using the Maxwell equation were 4.2, 3.6, and 3.1 for LDPE/BaTiO₃, EVA(7%)/BaTiO₃, and EVA(15%)/BaTiO₃ composite systems, respectively. The axes' ratio decreased by the introduction of polar vinyl acetate groups into nonpolar LDPE. The results confirmed that the polarity of the polymers was one of the key factors governing the dispersibility of BaTiO₃ particles in the polymer matrix. © 1995 John Wiley & Sons, Inc.     

Strategies for improving graft degree of urethane derivative of 2‐hydroxymethyl methacrylate grafted onto LDPE

A novel monomer, 2‐methyl‐acrylic acid 2‐(3‐isocyanato‐2‐methyl‐phenyl carbamoyloxy)‐ethyl ester (HT), was synthesized by the reaction of 2‐hydroxymethyl methacrylate with toluene diisocyanate. The influences of solvents, temperature and catalyst, dibutyl tin dilaurate on the total yield of HT were investigated and theoptimum synthesis conditions were obtained. The obtained monomer was then used to modify low density polyethylene (LDPE) in the Haake Rheomix 600P via melt grafting copolymerization. The modified LDPE was characterized by Fourier transform infrared. During the grafting process, single‐step and two‐step procedures were compared and the results showed that the two‐step procedure was more favorable. In a two‐step procedure, the influences of melting temperatures, monomer amount, and ethylene vinyl acetate copolymer (EVA, M_n = 800–1200) on the graft degree were also investigated. The investigation confirmed that EVA acting as a dispersant could enhance the dispersion of the monomer and improve graft degree significantly, and net value of increased graft degree was about 1.5%. The better dispersion of HT in the matrix of LDPE was confirmed via scanning electron microscope after adding EVA to the system. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Viscoelastic and adhesion properties of EVA/tackifier/wax ternary blend systems as hot-melt adhesives

Two types of wax were added to a ethylene vinyl acetate (EVA) copolymer/aromatic hydrocarbon resin (tackifier) blend in the molten state and the miscibility, viscoelastic and adhesion properties of ternary blends as hot-melt adhesives (HMAs) were investigated. Miscibility and viscoelastic properties were studied using differential scanning calorimetry (DSC), Brookfield viscometry and dynamic mechanical thermal analysis (DMTA), and their adhesion strength was determined in terms of single lap shear strength. DSC thermograms of both types of waxes showed their melting peaks in a similar region to that of EVA/tackfier blend. It was difficult to evaluate the miscibility of ternary blends using DSC because the melting peaks of the waxes overlapped with those of the EVA/tackifier blend, although the glass transition temperature (T _g) of the ternary blend systems slightly increased with increasing wax concentration. However, their storage modulus (E′) increased slightly and loss tangent (tan δ) showed different peaks when two types of wax were added to the EVA/tackifier blend. Therefore, the miscibility of EVA/tackifier blend altered with addition of waxes. In addition, their melt viscosity decreased with increasing wax concentration. Furthermore, the adhesion strength of the ternary blends decreased with increasing wax concentration, despite the increment of storage modulus. These results suggested that the ternary blends of EVA/tackifier/wax were heterogeneous.     

Toughening effects of ethylene–vinyl acetate copolymers with different vinyl acetate content and viscosity on nylon 1010 blends

Nylon 1010 blends with ethylene–vinyl acetate copolymer (EVA) and maleated ethylene–vinyl acetate (EVA‐g‐MAH) were prepared through melt blending. The vinyl acetate (VA) content and viscosity of EVA significantly affected the notched impact strength of nylon/EVA/EVA‐g‐MAH (80/15/5) blends. The nylon/EVA/EVA‐g‐MAH blends with high notched impact strength (over 60 kJ/m²) were obtained when the VA content in EVA ranged from 28 to 60 wt%. The effect of VA content on the notched impact strength of blends was related to the glass transition temperature for EVA with high VA content and crystallinity for EVA with low VA content. For nylon blends with EVA with the same VA content, low viscosity of EVA led to high notched impact strength. Fracture morphology of nylon/EVA/EVA‐g‐MAH (80/15/5) blends showed that blends with ductile fracture behavior usually had large matrix plastic deformation, which was the main energy dissipation mechanism. A relationship between the notched impact strength and the morphology of nylon/EVA/EVA‐g‐MAH (80/15/5) blends was well correlated by the interparticle distance model. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

木质素填充LDPE、EVA对复合物性能的影响

以木质素为填充剂分别与低密度聚乙烯(LDPE)、乙烯-乙酸乙烯酯共聚物(EVA)共混,经双螺杆造粒机共混挤出造粒,再经吹塑成膜。研究了木质素/LDPE、木质素/EVA共混物薄膜的表面形貌、力学性能、热性能和红外光谱。热分析表明木质素与EVA共混物的热稳定性比木质素与LDPE的共混物热稳定性好;红外光谱分析表明木质素与EVA分子间产生了强烈的相互作用,扫描电镜分析表明木质素与EVA共混的相容性较好,力学性能分析表明低于30%的木质素与LDPE、EVA共混力学性能较好。     

Real-time analysis of ethylene vinyl acetate random copolymers using near infrared spectroscopy during extrusion

Poly(ethylene vinyl acetate) (EVA) is a very common polymer used in hot melt adhesives. The rheological and thermal-mechanical properties of these adhesives are strongly related to the content of vinyl acetate (VA) incorporated into this random copolymer during polymerization. Results of in-line monitoring of VA content in flowing molten EVA polymers, using fiberoptic near infrared spectroscopy, shall be discussed in detail. In-line monitoring is not only desired for its numerous advantages (such as high quality products, lower waste, lower developmental cycle time, and lower costs) but also because it eliminates the sample handling concerns associated with molten polymers.     

Mechanical properties of recycled LDPE/EVA/ground tyre rubber blends: Effects of EVA content and postirradiation

Thermoplastic elastomers were prepared from recycled low density polyethylene [rLDPE] and virgin low density polyethylene (LDPE), respectively, ground tyre rubber (GTR), and ethylene vinyl acetate (EVA) copolymer. The amounts of the rLDPE and GTR were fixed at 40 and 30 wt %, respectively, in the formulations, whereas the LDPE and EVA contents varied each between 0 and 30 wt %. The fresh LDPE served for reduction of the melt viscosity and EVA was used for improving the elastomeric properties. Blends of different compositions (by varying the LDPE/EVA ratio) were produced by twin-screw extrusion and pelletized. Specimens were produced by injection molding and subjected to tensile and instrumented falling weight impact (IFWI) tests. To improve the mechanical performance of the blends, the injection molded specimens were electron beam irradiated at 150 kGy absorbed dose. Static tensile and hysteresis, IFWI and dynamic mechanical thermal analysis tests were performed on the specimens and the fracture surface was inspected with a scanning electron microscope. The results indicated that better rubber-like properties were achieved with increasing EVA content. Moreover, postirradiation proved to be very beneficial, especially for blends containing relative high amounts of EVA. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Melt rheology and elasticity of natural rubber—ethylene–vinyl acetate copolymer blends

The melt rheology of blends of natural rubber (NR) and ethylene–vinyl acetate copolymer (EVA) has been studied with reference to the effects of blend ratio, cross-linking systems, shear stress, and temperature. When EVA formed the dispersed phase, the viscosity of the blends was found to be a nonadditive function of the viscosities of the component polymers at lower shear region, i.e., a positive deviation was observed. This behavior has been explained based on structural buildup of dispersed EVA domains in the continuous NR matrix. The effect of the addition of silica filler on the flow characteristics of the blends has been investigated. The melt elasticity parameters such as die swell, principal normal stress difference, recoverable shear strain, and elastic shear modulus of NR–EVA blends were also evaluated. © 1993 John Wiley & Sons, Inc.     

Effect of electron beam irradiation and vinyl acetate content on the physicochemical properties of LDPE/EVA blends

The radiation‐induced crosslinking, compatibility, and surface modification of low density polyethylene/ethylene vinyl acetate blends (LDPE/EVA) were investigated. The structural and physical properties were characterized in terms of gel content, hot set, mechanical properties, contact angle, and surface free energy. The highest crosslink density was obtained at 20 wt % of EVA. Gel content of LDPE/EVA blends was increased with increasing irradiation dose, vinyl acetate (VA), and EVA contents. The hot set results are consistent with the gel content data. Mechanical testing showed that the tensile strength of samples increased with increasing irradiation dose up to 180 kGy, whereas the elongation at break was decreased with increasing irradiation dose. Contact angle measurements showed that the surface hydrophillicity of LDPE blend was increased with increasing irradiation dose and contents of both VA and EVA. The surface free energy was greatly dependent on irradiation dose and content of both VA and EVA. The total surface free energies of different LDPE formulations were in the range 17.25–32.51 mN/m, in which the polar (^pσ) and disperse (^dσ_s) values were within the range 16.52–26.6 and 0.9–5.91 mN/m, respectively. In conclusion, electron beam irradiation and blending LDPE with EVA improved the wettability or adhesion properties of LDPE/EVA blends. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Effect of maleated EVA on compatibility and toughness of PETG/EVA blend

Maleic anhydride (MAH) grafted onto ethylene vinyl acetate copolymer (EVA), mEVA (modified EVA) was blended with poly(ethylene glycol‐co‐cyclohexane‐1,4‐dimethanol terephthalate) (PETG) with various mEVA and EVA (unmodified) content in the internal mixer. The effect of reactive compatibilizer to decrease the dispersed particle diameter was observed. The brittle–ductile transition was found at about d_n: 0.37 µm and d_v: 0.55 µm of particle diameter, a critical particle diameter, regardless of EVA content, and the blend was also toughened at above the critical particle diameter regardless of dispersed EVA content and compatibility. The toughening mechanism and the effect of the particle diameter on the impact strength of the blend were investigated by morphological observation, and it was found that the toughening of the PETG/EVA blend system resulted from the shear deformation, induced by cavitation of dispersed EVA particles. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Hybrid silicate nanofillers: Impact on morphology and performance of EVA copolymer upon in vitro physiological fluid exposure

Ethyl vinyl acetate (EVA) copolymers are recyclable plastics with exceptional biocompatibility, thus they are potent candidate materials for biomedical applications. In this study, improvement in the EVA biostability was aimed by the incorporation of hybrid nanofillers. EVA copolymer incorporating 3 wt % organically modified montmorillonite/bentonite (OMMT/Bent) hybrid nanofillers in different ratios (3:0, 2.75:0.25, 2.5:0.5, 2.25:0.75, 2:1 and 0:3 in wt %) were prepared by melt compounding process and then analyzed for their biostability upon in vitro physiological fluid exposure. Results indicated that the addition of OMMT_2.75/Bent_0.25 hybrid nanofillers can reduce the degradation of the EVA copolymer under physiological fluid environment through hydrophilic bentonite–vinyl acetate interactions. The obtained nanocomposite material achieved the best retention in tensile and thermal properties upon 4 weeks exposure in the in vitro physiological fluid. The findings indicate the potential of using the hybrid OMMT/Bent nanofillers for biostability enhancement of the EVA while reducing the nanocomposite production costs through the addition of cheaper natural bentonite as co‐nanofiller with the OMMT. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44640.     

A rheological method for the study of crosslinking of ethylene acetate and ethylene acrylic ester copolymer in a polypropylene matrix

Transesterification may be used to crosslink a copolymer such as ethylene vinyl acetate with poly(ethylene acrylate-co-propylene) in the presence of dibutyltin oxide as a catalyst. A rheological study of the mechanism of this exchange reaction has been made: The kinetics of the crosslinking reaction was determined by studying the time and temperature dependence of the dynamic storage modulus G′(t, T)_ω. Kinetic curves obtained for different reactive blends (EVA, PP/EVA, and PPf/EVA) allowed for the evaluation of the activation energy of the reaction and, thus, specified the appropriate parameters (temperature and time) for carrying out this reaction in a molten state.