Dynamic–Mechanical Properties of ModifiedPoly(ethylene-co-vinyl Acetate)

Ronilson V. Barbosa, Ricardo B. Neto, Raquel S. Mauler, Carlos J. Perez Gorga,Claudia G. Schneider, Adriane G. Simanke

Instituto de Quımica, Universidade Federal do Rio Grande do Sul, Departamento de Quımica Orga�nica, Avenida BentoGoncalves, 95000 Porto Alegre, Rio Grande do Sul, CEP 91501–970, Brazil

Received 26 April 2004; accepted 1 December 2004DOI 10.1002/app.21883Published online in Wiley InterScience (www.interscience.wiley.com).

ABSTRACT: To study the relationship among relaxationpeaks observed in dynamic mechanical experiments and thestructure of poly(ethylene-co-vinyl acetate) (EVA), EVA co-polymers with different substitution in the carbonyl groupwere synthesized. EVA was hydrolyzed to obtain poly (eth-ylene-co-vinyl alcohol) and was subsequently reacted withformic, hexanoic, and octanoic acids. The copolymers syn-thesized were characterized by infrared spectroscopy. Anal-ysis of the DMA spectra of the copolymers showed that their

relaxation behavior depends on the vinyl acetate concentra-tion. The �- and �-transitions were observed in EVA copol-ymers with 8 and 18 wt % of functional groups, and therelationship among relaxation process with the structure ofpolymer was investigated. © 2005 Wiley Periodicals, Inc. J ApplPolym Sci 97: 1371–1376, 2005

Key words: DMA; EVA; EVAL; relaxation process

INTRODUCTION

Semicrystalline polymers such as ethylene/vinyl ace-tate copolymers (EVA) have a complex morphologicalstructure that depends on the amount of side branchesand on the way they are distributed along the poly-meric chain. A three-phase model extensively used todescribe the morphological structure of semicrystal-line polymers comprises a crystalline phase, an inter-facial region, and an amorphous phase.1 In EVA co-polymers, the vinyl acetate groups are not included inthe crystals and their melting temperatures do notdepend directly on their composition but depend onthe sequence distribution of monomer units along thepolymeric chain.2 Therefore, the amount of vinyl ace-tate groups in the copolymer alters the relative com-position of the amorphous and interfacial regions.

Although the influence of the polymer structure andcomposition on the dynamic mechanical properties ofethylene copolymers has been the subject of manystudies,3–10 some aspects regarding the relation be-tween the segmental motions and the specific relax-ation observed are still neither well defined nor undergeneral agreement.

Similar to other ethylene copolymers, EVA exhibitsthree main relaxations called �-, �-, and �-transitions

in order of decreasing temperature.6,9 The �-transitionis related to the motions of chain units within thecrystals and their surrounding areas, and its intensitydecreases with the decrease of polymer crystallin-ity.6,10–12 Al though �-transition requires the presenceof a crystalline phase to occur, according to the liter-ature, both the amorphous and the crystalline phasescontribute to the �-relaxation process.12–14 The �-tran-sition temperature depends mainly on the crystallitethickness and on the method of crystallization andrecrystallization.

The �-transition is controversially discussed in theliterature. Some authors attribute �-transition to thesegmental chain motions that occur within the crystal–amorphous interfacial region,6,7,15 while others associ-ate it to the glass transition.10,14,16 An increment in thenumber of side chain branches increases the �-transi-tion intensity. The temperature of �-transition de-pends on the chemical nature and concentration of thecounit.1

The �-transition is attributed to a restricted motionof disordered chain segments in amorphous and crys-talline polymers, which requires at least three meth-ylenic units in succession9,10,17 and can be modeled interms of crankshaft mechanism.

Because of their interesting structures with flexibleester side groups, vinyl acetate polymers as well asmethyl acrylate polymers have been used as models tostudy the subglass relaxation processes associatedwith flexible side-group motions in polymers throughdielectric experiments.18,19 Thermal dynamic mechan-ical experiments have also been used to study the

Correspondence to: R. V. Barbosa (Ronilson@iq.ufrgs.br).Contract grant sponsor: CNPq; Contract grant sponsor:

FAPERGS; Contract grant sponsor: TECPOL.

Journal of Applied Polymer Science, Vol. 97, 1371–1376 (2005)© 2005 Wiley Periodicals, Inc.

phase transitions of vinyl acetate homopolymers andcopolymers and to evaluate the compatibility of theirblends with other polymers.20–24 The thermal dy-namic mechanical behavior of EVA copolymers incomparison with other ethylene copolymers, mainlyethylene/�-olefin copolymers, has been analyzed bysome authors.6,25

Yamaki et al.26 have studied the phase transitionsand relaxation processes of several random EVA co-polymers and their respective homopolymers (low-density polyethylene, LDPE, and poly(vinyl acetate))by fluorescence spectroscopy. The phase transitiontemperatures were assigned to the following:

(a) Tg: 27 to 37°C—glass transition of poly(vinylacetate);

(b) T�: �3 to 27°C—�-relaxation processes of theethylene units present in LDPE and EVA;

(c) Tg: �53 to �23°C—glass transition of the LDPEand EVA;

(d) T� or T�: �113 to �83°C—relaxation process ofinterfacial defects of methylenic chains of LDPE androtation of the acetate group of the poly(vinyl acetate)and EVA;

(e) T� : �183 to �143°C—relaxation processes ofsmall sequences of methylene units in LDPE and endgroups of poly(vinyl acetate).

The major difficulty in defining the dependence ofthe EVA relaxations on the vinyl acetate content seemsto be related to knowledge of the relative composi-tions of the amorphous phase and of the interfacebetween the crystalline and amorphous phases. It isnot clear whether the relaxation processes and thetemperature shown by Yamaki et al.26 are amorphousor crystalline contribution.

In the present work, a series of copolymers (EVA,EVF, EVH, EVO, and EVAL) with different counittypes and two counit contents (8 and 18 wt %) werestudied by DMA to evaluate the influence of thecounit type and content on the relaxation processes.

EXPERIMENTAL

EVA copolymers with 8 and 18 mol % of vinyl acetate(EVA-8 and EVA-18, respectively) were supplied byPetroquımica Triunfo SA. The copolymers were hy-drolyzed to obtain ethylene/vinyl alcohol copolymers(EVAL), with 8 mol % (EVAL-8) and 18 mol % (EVAL-18) of vinyl alcohol as described in previous works.11

The poly(ethylene-co-vinyl formic) (EVF), poly(ethyl-ene-co-vinyl hexanoic) (EVH), and poly(ethylene-co-vinyl octanoic) (EVO) copolymers, with 8 and 18 mol% of counits, were obtained through the esterificationof EVAL-8 and EVAL-18 with formic, hexanoic, andoctanoic acids in toluene and extraction of water dur-ing 48 h. The reaction was carried out in nitrogenatmosphere, and the polymers were purified throughprecipitation in ethanol. The esterification reaction

was followed by infrared spectrometry. Figure 1shows the schematic reaction of the copolymer syn-thesis.

Differential scanning calorimetry (DSC) measure-ments were performed by a Polymer LaboratoriesDSC instrument under nitrogen. The samples wereheated from 0 to 180°C, cooled down to 0°C at acooling rate of 10°C/min, and subsequently heated to180°C. The melting temperature (Tm) and the heat offusion (�Hf) values were taken from the second heat-ing curve.

For the DMA measurements, the samples were meltpressed at 180°C to obtain thin films and were allowedto cool at room temperature. Rectangular films aver-aging 5 mm wide, 12 mm long, and 0.2–0.3 mm thickwere used. The dynamic-mechanical experimentswere performed on a Polymer Laboratories DynamicMechanical Thermal Analyzer MK II Instrument in thetensile mode. The measurements were carried out at 1Hz. The temperature ranged from �125°C to next tothe melting point of each copolymer (100°C, depend-ing on the sample used), and the heating rate used was2°C/min.

Some samples were submitted to a thermal treat-ment before being analyzed in the DMA equipment.The samples were melt pressed at 180°C to obtain thinfilms and allowed to cool in liquid nitrogen for 15 min.Rectangular films averaging 5 mm wide, 12 mm long,and 0.2–0.3 mm thick were used.

RESULTS AND DISCUSSION

Figure 2a and b shows the loss tangent (tan �) versustemperature curves for EVA-8/EVAL-8 and EVA-18/EVAL-18, respectively. The EVA-8 presents the �-tran-sition with the maximum at 68°C and the �-transitionas a shoulder at �10°C. After the hydrolysis of theacetate group (EVAL-8), the �-peak maximumchanged to a higher temperature (80°C) and the�-peak decreased in intensity.

Figure 1 Scheme of the copolymers synthesis (PVF, PVH,and PVO).

1372 BARBOSA ET AL.

The same behavior is observed with EVA-18/EVAL-18. The �-transition is much more intense thanfor the EVA-8, indicating that the acetate group has ahigh contribution to this transition. When the acetategroup is changed to “–OH” the �-peak decreases con-siderably. The residual peak of both EVAL is probablydue to the alkyl branch formed during the radicalpolymerization of ethylene.

Observing the crystallization behavior of the copol-ymers (Table I) it is possible to visualize the differencein structure organization of EVA-8 and EVA-18. Theincrease in acetate groups decreases the crystallinityand the Tm. When the EVA was hydrolyzed, the Tm ofboth copolymers increases and they are the same.Also, observed an increase in the heat of fusion (�H) isobserved and this is more pronounced for the EVA-18,since the –OH may participate in the crystal structure.The format of the tan � curve shows a displacement ofthe peaks to high temperature. This transition is asso-ciated with the movements of chains within the crys-talline regions or in the crystal–amorphous interfaceand it is generally observed at temperatures 20–30°Clower than their melting temperatures.

The transition at �70 and �50°C for the EVAL-8and EVAL-18, respectively, can be associate with hy-drogen bonds of the hydroxyl groups in the main

chain. The high temperature to EVAL-18 is due to thehigh concentration of hydroxyl groups.

To verify the influence of acetate group in the�-transition of EVA-8 and EVA-18, a series of copoly-mers with different branches EVF-8/EVF-18 (formicgroup), EVH-8/EVH-18 (hexanoic group), and EVO-8/EVO-18 (octanoic group) was synthesized.

In Figure 3a and b, it is possible to observe the FTIRof these copolymers with 8 and 18 mol % of comono-mer, respectively. The FTIR shows that the EVA wascompletely hydrolyzed to EVAL. The carboxylic estergroup peak at 1780 cm�1 disappears and a hydroxylgroup band appears at 3200–3700 cm�1 in the EVAL-8and EVAL-18. The esterification reaction of EVALwith formic, hexanoic, and octanoic acid was com-plete, as observed in the FTIR with the disappearanceof the hydroxyl band at 3200–3700 cm�1 and the ap-pearance of the carboxylic peak at 1780 cm�1.

Figure 4 shows loss tangent (tan �) versus temper-ature obtained for EVA-8/EVF-8, EVA-8/EVH-8, andEVA-8/EVO-8 copolymers with 8 mol % of vinyl ac-etate, respectively. The EVF-8 and EVO-8 show similarbehavior and transitions with similar shapes and atthe same temperature range. However, the EVH-8shows a displacement of the �- and �-transition tolower temperatures.

When the acetic group in EVA-8 was substitutedby the formic group (EVF-8) a small shift of the�-transition to lower temperatures (�2°C) was ob-served. This copolymer also shows a sharp peak athigher temperature that can be associated with the�-transition.

Although a significant displacement of the transi-tion to lower temperature is observed with the changeto the hexanoic group, when the acetic group ischanged to the octanoic group, which is longer thanthe hexanoic group, the displacement to lower tem-perature is much smaller.

Figure 2 Tan � versus temperature curves of EVA-8 and EVAL-8 (a) and EVA-18 and EVAL-18 (b).

TABLE IDetermination of Tm and �H of Polymers by

Differential Scanning Calorimetry

Polymer

Tm (°C) �H (J/g)

8% 18% 8% 18%

EVA 98 88 80 64EVAL 110 110 89 110EVF 99 87 93 69EVH 98 81 47 50EVO 103 82 91 47

DYNAMIC–MECHANICAL PROPERTIES OF EVA 1373

The displacement toward lower temperature indi-cates an increase in the molecular (or chain) mobilitydue to a plastificant effect of the branch and the dif-ferences in behavior presented by EVOC-8 and EVH-8may be attributed to differences in mobility and crys-tallinity along the polymeric chain. The crystallinity ofthe EVOC-8 copolymer is higher than of the EVH-8 asshown in Table I. Also, since the octanoic group islonger than the hexanoic, interchain interactions mayoccur, restricting the movements and, by consequence,contributing to the increase in temperature.

In all three cases, the copolymers show transitionswith similar shapes and there is evidence of the de-velopment of a new peak at higher temperature(above 90°C), probably due to a small population ofmore organized crystalline structure.

Figure 5 shows loss tangent (tan �) versus temper-ature for EVA-18/EVF-18, EVA-18/EVH-18, and

EVA-18/EVO-18 with 18 mol % of vinyl acetate, re-spectively. Comparing these curves with the ones ob-tained for the copolymers with 8 mol % of comono-mer, it is possible to observe a pronounced displace-ment to lower temperatures. This displacement issimilar to the one observed for ethylene/�-olefin co-polymers,3 where there is a decrease in the tempera-ture of �- and �-transitions when the amount ofcomonomer (or branches) increases. The differences inthe shape of the peaks can also be related to the factthat these copolymers have a higher content ofcomonomer.

Copolymers with higher branch content are moreaffected by the size of the branch and the �- and�-transitions have almost the same intensity. The dif-ferences in the shapes of the curves when comparingwith the copolymers with 8 mol % is probably due toFigure 3 FTIR of EVA-8, EVF-8, EVH-8, and EVOc-8 (a)

and EVA-18, EVF-18, EVH-18, and EVOc-18 (b).

Figure 4 Tan � versus temperature curves of EVA-8,EVF-8, EVH-8, and EVOc-8.

Figure 5 Tan � versus temperature curves of EVA-18,EVF-18, EVH-18, and EVOc-18.

1374 BARBOSA ET AL.

the higher comonomer content where the groups in-teract with each other. Then, the intensity of the tran-sition at low temperature may be increased becausethe internal movement within the side group is af-fected by the presence of other side groups in a closeposition in the polymeric chain and perhaps may in-teract also with the side groups of the other chains.

The EVH-18 and EVOc-18 copolymers show a verywell-defined �-transition at �30°C (EVH-18) and�25°C (EVOc-18). All peaks including the �-transitionwere shifted to lower temperature region because ofthe plastificant effect of group in the polymer. Thecopolymer EVF-18 (Tm 93,7°C) had shifted to lowtemperature and the �- and �-transition is not wellseparated due to the small size of the branch. BothEVH-18 and EVOc-18 were capable of disorganizingthe crystalline structure and show the best definitionto the �-transition. The Tm and the crystallinity ofEVF-18 are quite similar to that of EVA-18 (Table I),but when the side group increases in size, both de-crease. So, the branching or pendant group affects the�-transition since the group is not kept inside thecrystal and is dependant on concentration of the vinylacetate. The concentration of the pendant group alsoaffects the lamellar thickness, decreasing the crystal-linity.3

EVAF-18, EVAH-18, and EVAOc-18 also present apeak at higher temperature at 104, 85, and 92°C, re-spectively. This peak seems to be more intense thanthat for EVAF-8, EVAH-8, and EVAOc-8.

In fact, the behavior of the DMA spectra is related tothe group introduced in the polymer chain, and thisrelationship is associated with the amorphous andcrystalline phase of the polymer structure. In EVA-8the peak from �25 to 95°C and in EVA-18 the peakfrom �25 to 95°C have contribution of both �- and�-transition. In EVA-8 the contribution of �-transitionis higher than the �-transition, because the ethylenegroup in the main chain controls the morphology ofthe polymer. In the case of EVA-18 the contribution of

crystalline phase is lower than in EVA-8; then bothtransitions are more evident.

Simanke at al.,3 working with ethylene/�-olefin,obtained a loss tangent (tan �) versus temperaturecurves of ethylene homopolymer and copolymer with2 mol % of 1-octadecene. The DMA spectra of thiscopolymer show a peak that starts from �50 to 110°C,like to the EVA-8 and EVAL-8 curve. They called thistransition an �-transition, associated with the crystal-line structure of polymer, which is in agreement withthe results shown. When the copolymers has 4.8 mol% of 1-octadecene, the curve showed two peaks andthe authors called that � and ��-transitions.

Lower temperature transition in the EVA and co-polymers with 18 mol % of comonomers has a rela-tionship with the moviment of the vinyl group andwith the �-transition. To confirm that the transitionsobserved in the EVA spectra are involved with �- and�-transitions, a sample after quenching to minimizethe crystallization effect was analyzed. The sampleswere melt pressed at 180°C to obtain thin films andallowed to cool in nitrogen liquid for 15 min. Figure 6aand b shows the spectra of tan � for the EVA-8/EVAOc-8 quenched and EVA-18/EVAOc-18 quenched,respectively. The contribution of the transition at highertemperature decreases with quenching of the polymer inboth polymers (EVA-8 and EVA-18), indicating that thistransition is associated with the crystallization behavioror the �-transition.

CONCLUSIONS

EVA-8 and the EVA-18 show two transitions in theDMA spectra; the �-transition, at high temperature, isassociated with the crystalline behavior and the�-transition, at low temperature, is associated with thecarboxylic branch. The �-transition is more affected bythe concentration of the vinyl acetate than bythe sizeof the pendant group, although the type of branchmay cause some displacement of this peak.

Figure 6 Tan � versus temperature curves of EVA-8/EVOc-8 (a) and EVA-18/EVOc-18 (b).

DYNAMIC–MECHANICAL PROPERTIES OF EVA 1375

References

1. Mandelkern, L.; Mark, J. E.; Eisenberg, A.; Graessley, W. W.;Samulski, E. T.; Koenig, J. L.; Wignall, G. D. (Eds.), PhysicalProperties of Polymers, American Chemical Society: 1993; pp145–200.

2. Alamo, R. G.; Madelkern, L. Thermochim Acta 1994, 238, 155.3. Simanke, A. G.; Galland, G. B.; Quijada, R.; Freitas, L.; Jornada,

J. A., Mauler, R. S. Polymer 1999, 40, 5489.4. Cerrada, M. L.; Benavente, R.; Pena, B.; Perez, E. Polymer 2000,

41, 5957.5. Nitta, K.-H.; Tanaka, A. Polymer 2001, 42, 1219.6. Popli, R.; Glotin, M.; Mandelkern, L.; Benson, R. S. J Polym Sci

Polym Phys Ed 1994, 22, 407.7. Clas, S.-D.; McFaddin, D. C.; Russell, K. E. J Polym Sci Polym

Phys Ed 1987, 24, 1057.8. Matthews, R. G.; Ward, I. M.; Capaccio, G. J Polym Sci Polym

Phys Ed 1999, 37, 51.9. McCrum, N. G.; Read, B. E.; Williams, G. Anelastic and Dielec-

tric Effects in Polymer Solids; Dover: New York, 1967.10. Khanna, Y. P.; Turi, E. A.; Taylor, T. J.; Vickroy, V. V.; Abott,

R. F. Macromolecules 1985, 18, 1302.

11. Barbosa, R. V.; Soares, B. G.; Gomes A. S. J Appl Polym Sci 1993,47, 1411.

12. Alberola, N.; Cavaille, J. Y., Perez, J. J Polym Sci Polym Phys Ed1990, 28, 569.

13. Perena, J. M.; Fatou, J. G.; Guzman, J. Makromol Chem 1980,181, 1349.

14. Boyd, R. H. Macromolecules 1984, 17, 903.15. Popli, R.; Mandelkern, L. Polym Bull 1983, 9, 260.16. Boyd, R. H. Macromolecules 1985, 26, 1123.17. Benavente, R.; Perena, J. M.; Bello, A.; Perez, E.; Aguilar, C.;

Martinez, M. C. J Mater Sci 1990, 25, 4162.18. Buerger, D. E.; Boyd, R. H. Macromolecules 1989, 22, 2694.19. Smith, G. D.; Boyd, R. H. Macromolecules 1991, 24, 2731.20. Lawrence, N. E. J Polym Sci 1960, XLII, 357.21. Smith, G. D.; Liu, F., Devereaux, R. W.; Boyd, R. H. Macromol-

ecules 1992, 25, 703.22. Ray, I.; Khastgir, D. Polymer 1993, 34, 2030.23. Koshy, A. T.; Kuriakose, B.; Thomas, S.; Varghese, S. Polymer

1993, 34, 3428.24. Jansen, P.; Soares, B. G. J Appl Polym Sci 2002, 84, 2335.25. Woo, L.; Ling, T. K.; Westphal, S. P. Thermochim Acta 1994, 243,

147.26. Yamaki, S. B.; Prado, E. A.; Atvars, T. D. Z. Eur Polym J 2002, 38, 1811.

1376 BARBOSA ET AL.