Pergamon

Eur. Polym. J. Vol. 33, No. 10-12, 9~. 1651-1658, 1997 0 1997 Elwier Science Ltd. All rights -cd

Printed in Great Britain PII: s0014-3057(!vpoo47-5 OOM-3057197 s17.00 + 0.00

MISCIBILITY OF PVC/EVA HYDROLYSED BLENDS BY VISCOSIMETRIC, MICROSCOPIC AND THERMAL

ANALYSIS

ELISANGELA CORRADINI, ADLEY FORT1 RUBIRA and EDVANI CURT1 MUNIZ*t

Departamento de Quimica, Universidade Estadual de Maring& CEP 87020-900. Maring& Paran&, Brazil

(Received 23 July 1996; accepted in final form 30 October 1996)

Ahstraet-The miscibility of PVC and hydrolysed EVA was investigated by viscosimetric, microscopic and thermal analysis. EVA with 20 and 40% molar acetate groups were submitted to alkaline hydrolysis. Partially hydrolysed products with different properties were obtained, when the hydrolysis degree was varied. The crystallinity and the melting point of hydrolysed products depend on the hydrolysis degree. Our results have led us to conclude that, when the hydrolysed product has a molar ratio of 1:l in acetate: hydroxyl groups, their blends with PVC are miscible. The miscibility, observed by three different techniques, was explained as a result of synergistic effect, due to the presence of hydroxyl and acetate groups in a molar ratio of 1: 1. Under this condition, we proposed that repulsive interactions of -OH and -AC groups are stabilised by chlorine atoms of PVC polymer. 0 1997 Elsevier Science Ltd

INTRODUCIION

Several works on polymer-polymer miscibility have been developed in the last twenty years [l-4]. For such investigations, the techniques most used are electronic microscopy [5], spectroscopy [6], thermal analysis [7j and inverse gas chromatography [8]. These techniques have been very powerful for such applications, but, for most of them, they become very expensive. Consequently, other methods for poly- mer-polymer miscibility investigation were proposed, either using alternatives properties [9] or low cost equipment [lo]. Viscometry, in this way, is a very promising technique. Some important contributions on polymer-polymer miscibility have been published [ll-141, based on viscosity measurements of dilute polymer solutions. It is a non-expensive technique and has also been used in polymer science to determine the molecular weight and distribution [ 151, and branching degree [ 16, 17. It is also very sensitive for the evaluation of interactions in polymer solutions [ll-13, 181.

Plots of the intrinsic viscosity, [q], against blend composition or plots of specific viscosity divided by solution concentration, Q&, against solution com- position, C, have been used as a criterium for polymer-polymer compatibility [ 111. The presence of a sharp crossover in s,/C vs C curves or of non-linearity of [s] vs blend composition indicates incompatibility between its constituents. This cri- terion, used to analyse the compatibility of PVC/ABS blends, gave results that match very well with literature results, but it does not seem to have been used much for other polymer-polymer systems. Later on, Chee [ 121 developed a novel approach, the p

*To whom all correspondence should he. addressed. te-mail: ecmuniz@uem.br

parameter, to determine polymer-polymer miscibility by viscosity measurements. The method is based on the classical Huggins equation and uses an additivity law for the viscosity [15]. Also, based on the arguments of Chee, Sun et al. [13] proposed another criterion for polymer-polymer miscibility, the tl parameter. This parameter contains hydrodynamic attraction or repulsion terms and it may be determined by viscosity measurements.

Blends of poly(viny1 chloride) and poly(ethylene- co-vinyl acetate), PVC/EVA, are often studied [19,20]. It is known that PVC is miscible with EVA only when the content of vinyl acetate groups, VA, on EVA ranges between 45 and 75% molar fl9]. McGrath and Matmer [21] verified that when EVA20 (having 20% molar of VA) is completely hydrolysed, their blends with PVC are almost miscible. Despite this important result, few works were found treating the influences of hydrolysis degree of EVA copolymer on miscibility of PVC/EVA blends.

In this work we have investigated the miscibility of hydrolysed EVA/PVC blends using several criteria based on viscosity measurements and compare them with thermal and microscopic analysis. The hydroly- sis degree of EVA and the vinyl acetate contents of original EVA were varied.

EXPERIMENTAL

Hydrolysis of poly(ethylene-co-vinyl acetate), EVA

PVC, having A& (kg mol-I) = 117.0, was supplied by Solvay do Bra&, S.A. EVA copolymers, with 20 and 40% molar in VA, were supplied by PolioleBnas S.A. So Paulo Brazil. EVA were &ssolvei in toluene at 50°C and hydrolysed using sodium hydroxide methanolic solutions at 50°C. Three different concentrations of hydroxide were used to give three different hydrolysis degrees. The hydrolysed products were washed with distilled water until neutral pH. The precipitated materials were separated by filtration and

1651

1652 E. Corradini et al.

were dried at 70°C for 24 hr at low pressure. The followina hydrolysed materials: EVAHZO, EViH2010, EVAH40 ad EVAH4020 with 77.5. 46.0. 92.3 and 47.3% degrees of hydrolysis, respectively, were obtained. The h&olysis degree was determined from a calibration curve, obtained according to Takeuchi and Mori [22], and it will be briefly described in the results section.

Dilure solution viscosimetry measurements

Solutions, having 8 g/100 mL, of each polymer in tetrahydrofuran (THF) were prepared. The calculated volume of the solutions were mixed to give the proportions: O/100, 25/75, SO/SO, 75/25 and O/100 of EVAH/PVC, in mass, and the respective mass fractions of PVC, WPVC: 0, 0.25, 0.50, 0.75 and 1.0, when only polymeric species are considered. The viscosity measurements of each blend composition were performed in a suspended-level Ubbelo- hde capillary viscometer, Cannon (50/F576), at a controlled temperature. The following temperatures were utilised: 3O.O”C to EVAH402O/PVC and EVAH4O/PVC systems and 4O.o”C to EVAHZOjPVC and EVAH2010/PVC systems. At 30°C. EVAHZO and EVAH2010 are not soluble enough to perfo’rm viscosimetric measurements. Flowtimes of ckach blend composition were determined by the serial dilution technique. At least five dilutions were made for each blend composition. From the flowtime measurements, made for each blend composition, the specific, gsp, and reduced, qrcdr viscosities at different concentrations were calculated. Finally, the intrinsic viscosity, [q], was determined plotting the qsp/C and +d/C against the solution concentration, C, for each blend composition, according the equations [15]:

%ed = [q]c + &[~]2c2

where & and KK are the Huggins and Kraemer constants, respectively.

Differential scanning calorimerric analysis

The polymeric samples used in thermal analyses were in an even tilm form. They were prepared by solution casting from THF at ambient temperature. To remove the residual solvent, the films were dried at 50°C and at reduced pressure for three days, at least. Films having PVC molar fraction, Wpvc. of 0. 0.25. 0.50. 0.75 and 1.0 were DreDared. Calorimetric. measurements were made using a Shimadzu differential scanning calorimeter, TA-50 model, at a heating rate ZO”C/min, in a nitrogen atmosphere flowing at 20ml/min. The thermograms were obtained after a pre-heating to 200°C. At this temperature, phase separation was not observed. Thermogravimetric analysis showed no degradation under these conditions.

X-Ray scattering analysis

The degree of crystallinity of EVAH films were evaluated using a Shimadzu wide-angle X-ray diffraction (WAXD), XE3A model. It was operated at 35 kV and 25 mA, using CuK. as radiation source. The scans were obtained with a Z”/min step program with a collection time of 10 sec. per step.

8

‘i Ratio of absorption of acetate (at 1760 cm-‘) and C-H groups

9 Q 2- z g b 3: $1 0 II

u A -

I I I I 0 10 20 30 40

Vinyl acetate content (% molar)

Fig. I. Calibration curve utilised to determine the residual acetate group content in EVAH.

Microscopic analysis

The morphology structures of pure components and their blends were investigated using a Olympus Optical Microscope, CBA model, having a polarised light accessory. The analyses were carried out at ambient temperature. The morphology and structure of casting films of pure components and their blends were also analysed utilising a scanning electron microscope, SEM Philips, model 100505.

RESULTS AND DISCUSSION

Determination of hydrolysis degree

The degree of hydrolysis of EVAH samples were determined using a calibration curve obtained from IR measurements of EVAs. From the IR spectra of EVA having VA contents varying from 0 to 40%, the ratios of absorption of carbonyl groups (at 1760cm-‘) and C-H groups (at 1410cm-I), Abs ,,60cm-‘/Abs,4,0crn-i, were determined. The cali- bration curve is presented in Fig. 1. The ratio Abs 1760cm-~/Abs1410cm-~ was also determined in each EVAH and the hydrolysis degree was determined by interpolation of the calibration curve. Table 1 shows the hydrolysis degree and the respective molar ratio of OH and residual acetate groups obtained for each hydrolysed product.

As will be described in the next section, the hydrolysis of EVA causes changes in some properties like the melting point and degree of crystallinity, as compared with those of the original EVA. The changes depend on the extent of hydrolysis, being more intense for higher hydrolysis degrees.

Thermal analysis

The melting point, TM, of EVAH was determined in pure components and their blends. TM values were determined through the inflection point of the DSC curve, using the first derivative. DSC curves for pure EVAH20, EVAH2010, EVAH40 and EVAH4020

Table 1. Hydrolysis degree and the molar relation of hydroxyl and acetate groups, OH/AC, obtained in hydrolyaed products

Hydrolysed Droduct Hydrolysis degree

(%) Molar relation in OH AC

Rl,OUW

EVAHZO 77.5 3:l EVAH2010 46.0 1:l EVAH40 92.3 12:l EVAH4020 41.6 I:1

Miscibility of PVC/EVA hydrolysed blends 1653

-6 -

-8 -

0

a

EVAH2010

I I I I

50 100 150 200 Temperature (“C)

-8 I I I I

0 50 100 150 200 Temperature (“C)

Fig. 2. DSC curves obtained for (a) EVAHZO and EVAH2010; (b) EVAH40 and EVAH4020.

copolymers are presented in Fig. 2. TM for pure hydrolysed EVAs and their blends with PVC are presented in Table 2. Note that TM for EVAHZO is ca 13°C higher than for EVAH2010, showing that hydrolysis degree influences the TM. The same behaviour was observed for the EVAH40 and EVAH4020 copolymers. In this case, the difference in TM is cu 40°C.

The dependence of TM with the hydrolysis degree for EVA20 copolymer is presented in Fig. 3. Original EVA20 has a TM near 80°C and the melting point in the hydrolysed product showed an almost linear increase when the hydrolysis degree was increased.

DSC curves for pure EVAH2010, EVAH4020 and its blends with PVC are presented in Fig. 4. Analogous curves were obtained for EVAH20/PVC and EVAH4O/PVC systems. From these curves, TM values for the blends were determined.

From data presented in Table 2, decreases in the melting point for the EVAH2010 and EVAH4020

” EVAHZO,

EVAH2010

751 I I I I 0 20 40 60 80

Hydrolysis degree (%)

Fig. 3. Dependence of melting point temperature on hydrolysis degree for EVA20 copolymer.

systems may be observed when the PVC content is raised. However, in EVAH20 and EVAH40 systems the TM does not depend on the PVC content. The decrease in TM was more properly evaluated by plotting the difference l/T& - l/T& against the square of volume fraction of PVC in the blend, &,c, as presented in the Fig. 5. T; and Ti are the melting point of pure hydrolysed EVA and the melting point of the blends. It may observed that the decrease, l/T& - l/T;, is linear with &.vc. As will be discussed later, the decrease in TM of a blend composed of a semi-crystalline polymer A and amorphous polymer B with the composition of B is directly related to the dispersion of the polymer A into B, at the molecular level.

The degree of crystallinity

The crystallinity degree of hydrolysed EVA was qualitatively evaluated by X-ray diffraction and determination of the area of fusion peaks presented in Fig. 6. WAXD patterns were obtained from EVAH40, EVAH4020, EVAH20 and EVAH2010 films. Sharp peaks in diffractometers from EVAH2010 and EVAH4020 were observed. EVAH20 showed broader peaks, suggesting a lower crystallinity degree than those of EVAH2010, EVAH40 and EVAH4020.

Viscosity measurements

The linear and angular coefficients were calculated by a linear regression procedure from the q,/C vs C curves, giving, respectively, the intrinsic viscosity, [q], and b. In this case, b = d(qJC)/dC or more properly, b = &[q]*. In Table 3 the values of [q] and b for pure components and their blends are shown. Viscosity measurements of EVAHIIO/PVC could not be used to evaluate the miscibility because pure EVAH40 gives very high [q] and b values, suggesting a self association.

Table 2. TM values obtained for pure components and their blends

TM, “C Composition WPVC EVAHZO/PVC EVAH2010/PVC EVAH40/PVC EVAH4020/PVC

0 101.4 88.8 104.7 65.3 0.25 101.9 87.4 104.9 65.1 0.50 100.2 85.5 104.6 63.5 0.75 101.8 84.3 104.9 57.0 1.00

1654 E. Corradini et al.

25%

EVA2010 content

Blends of EVA2010/PVC I I I I

50 100 150 200

Temperature (“C)

O-B

c -1 - 2 .s 3 -2- 2 z 0 -3- X

-4 - “Blends of EVAH4020IPVC

I I I I 1 0 50 100 150 200

Temperature (“C)

Fig. 4. (a) DSC curves for EVAH2010 and its blends having 25, 50 and 75% mass of EVAH2010. (b) DSC curves for EVAH4020 and its blends having 25, 50 and 75% mass of

EVAH4020.

Curves of [q] us PVC composition. Plots of [n] against the PVC content in the blends, Wp~c, are presented in Fig. 7. Curves of [q] vs WWc are linear for the EVAH2010/PVC and EVAH402O/PVC systems, and non-linear for the EVAHZO/PVC system. The linearity of the [q] vs WW, curves was utilised to evaluate the miscibility of binary blends. Linear curves are common for compatible blends, whereas for incompatible systems, non-linear or S-type curves are obtained [Ill. From this criterium,

2 EVAHZOK’VC 1

EVAH4020iPVC

0 0.1 0.2 0.3 0.4 0.5 0.6 Volume fraction of PVC on the bend (Wwc)

Fig. 5. The difference l/ML + l/T: plotted against the square of PVC volume fraction, qY, for EVAH2010,

EVAHZO, EVAH40 and EVAH4020 systems.

L

-1ooJ ’ ’ ’ ’ . ’ . ’ 10 20 30 40 50 60

28

Fig. 6. WAXD patterns obtained from EVAH40, EVAH4020, EVAH20 and EVAH2010 films.

the blends of EVAHZO may be considered immiscible and the other two systems are shown to be miscible.

Curves of the p parameter us PVC composition. The p parameter was calculated from the viscosimetric data shown in Table 3, using Chee’s equation (3), which may be applied only when [)llpyc # [q]avAH.

p =

J - bwc bw,w - bwc

[rtl - [rtlrwc - [rllwa” - [ttkc 1 x {2+h’A” - b/l)}-’ (3)

where b is given by the expression

J = H’hrbwc + W’iv,,bwaH + 2 B’w, Wwmbmm

(4)

and beLEND is the slope of the &C vs C curve for the blend. The term [q] is the mean viscosity and is calculated by the expression [12]

hl = WPVCbllPVC + WEvAH[qlEvAH

Results obtained are given in Table 3. According to the Chee theory [12], the value of the

p parameter depends on the presence of interactions of polymer components and may be used to evaluate the miscibility in polymer blends. For miscible blends p > 0, while immiscible blends have negative values of p. Curves of n vs W,C are presented in Fig. 8 for EVAH20 and EVAH4020 systems. Blends of EVAH20/PVC showed negative p values while positive values were obtained for the EVAH4020/ PVC blends. The p parameter for EVAH2010/PVC system could not be calculated because [tr]~~ = [~]EVAHU)IO. According to the p parameter, EVAHZO/PVC blends may be considered immiscible, whereas blends of EVAH402O/PVC are miscible for all PVC compositions.

Curves of a parameter vs PVC composition. As published by Sun [13], the a parameter has been used to evaluate the miscibility of blends, from viscosimet- ric data. In this work, blends of EVAH/PVC were also investigated applying this criterium, using the equation

a= KBLEND - KI (6)

Miscibility of PVC/EVA hydrolysed blends 1655

Table 3. Viscosimetric data: [q] and b, and the respective p and IX parameters for pure components and binary blends of EVAH20, EVAH2010, EVAH40 and PVC

EVAH402O/PVC EVAHZO/PVC EVAHZOIO/PVC

WPVC In1 b a ll bll b t( P hl b OL

8.25 0.552 0.708 0.137 0.201 -&03 0 0.356 0.469 0.855 0.429 0.253 -:.795 -0.330 0 0.920 0.907 0.479 0.428 0 0.039 0.50 0.826 0.281 -0.008 0.464 1.112 0.191 -0.912 -0.721 0.894 0.498 0.174 0.75 0.927 0.369 -0.019 0.364 1.035 0.311 -0.233 -0.343 0.907 0.423 0.095 1.00 1.034 0.431 0 0 1.034 0.431 0 0 1.034 0.431 0

Units: [q] = dL/g; b = (dL/g)2.

where KBLENo is the Huggins constant obtained for blend. K, is calculated using the equation

(7)

where Ki is the Huggins constant and [qli is the intrinsic viscosities of the ith pure polymeric component. As proposed by Sun [13], if a 2 0 attraction forces between polymers occurs, resulting in miscibility. If a < 0 repulsion forces prevail and immiscibility is expected.

Curves of the a parameter against PVC compo- sition are shown in Fig. 9. It can be verified that EVAHZO/PVC blends show negative TV values. On the other hand, values of the a parameter for blends of EVAH2010/PVC, EVAH4020/PVC are either posi- tive or zero. Then, from this point of view, EVAHZO/PVC blends are immiscible, whereas blends of EVAH40/PVC and EVAH4020/PVC are miscible over the whole range of compositions.

Microscopic analysis. The miscibility of a polymer blend may be evaluated by the analysis of the surface morphology. In a mixture of amorphous with semi-crystalline polymer, dispersion may be observed by optical microscopy using a polarised light accessory. Through this technique, a good dispersion of crystalline EVAH2010 and EVAH4020 in a PVC amorphous phase was observed. When the content of PVC is increased, a decreasing of the crystal dimensions occurs, but the dispersion seems almost homogeneous. On the other hand, in EVAH20/PVC and EVAH4O/PVC blends, characteristics of phase separated structures were observed. In these immis- cible blends the major phase is surrounded by the minor phase and the dimension of the crystals does

not seem to depend on the PVC content. Using scanning electron microscopy, SEM, the same results were observed. In Fig. 10, the micrography of EVAH20/PVC and EVAH201 O/PVC blends, having Wp, equal to 0.5, are shown.

Influence of hydrolysis degree on the miscibility of EVAHIPVC blenok

The EVA used in this work is a random copolymer. Then hydrolysed products have a simultaneous presence of hydroxyl and acetate groups beyond ethylenic segments in a randomised sequence. As described in Table 1, the ratio of vinyl acet- ate:hydroxyl groups is near 1: 1 in EVAH2010 and EVAH4020, 1:3 in EVAH20 and 1: 12 in EVAH40. This difference leads to different behaviours of the miscibility in the respective blends with PVC. When the ratio is 1: 1, the blends are shown to be miscible. At the molecular level, the ratio of vinyl acet- ate:hydroxyl groups is used to explain the level of miscibility in EVAH/PVC blends.

The presence of hydroxyl on the macromolecule chain induces a self organisation in the solid state and is reflected by an increasing value of TM. The lower volume of the -OH groups and their interactions may be used to explain the increase of TM with hydrolysis degree, as observed in Fig. 3. Under this condition, crystallisation is favoured. On the other hand, the presence of acetate side groups as in original EVA,

1.1 - EVAHZOlO/PVC

EVAH402OlPVC

03 I I I I I 0 0.2 0.4 0.6 0.8 1.0

Mass fraction of PVC on the blend

Fig. 7. Intrinsic viscosity as a function of PVC content in: EVAHZO/PVC, EVAHZOlO/PVC and EVAH402O/PVC.

0.5 - I

EVAH4020iPVC

-I.OL I I I 1 0 0.25 0.50 0.75 1.00

Mass fraction of PVC on the blend

Fig. 8. Curves of the p parameter against IV.&, for the EVAHZO, and EVAH4020 systems.

1656 E. Corradini er af

o’31 EVAH40201PyC ,

EVAH2010/PVC

EVAH20/PVC

-0.91 I I I I 0 0.25 0.50 0.75 1.00

Mass fraction of PVC on the bend

Fig. 9. Curves of the o! parameter against PVC composition for the EVAHZO/PVC, EVAH2010/PVC and EVAH4020/

PVC blends.

inhibits the self organisation. Therefore, no crystalli- sation is observed [23] at high VA content. When EVA20 is totally hydrolysed, the resultant product has a TM near 1 lO”C, as observed by us and also by Alamo et al. [24].

Blends of hydrolysed EVA with PVC have different behaviours around the melting temperature, as the ratio -AC:-OH in EVAH is varied. When this ratio is 1: 1, as in EVAH2010 and EVAH4020, the melting temperature of respective blends is dependent on the PVC content, as shown in Fig. 5. There is a direct relation between miscibility and the depression of TM. According to the theory proposed by Nishi and Wang [25], a binary miscible blend constituted by semi-crystalline and amorphous polymers exhibit a decreasing in the melting point when the amorphous polymer content increases. The decrease in TM is described by the equation [25].

where p&,, is the molar volume of EVAH in the mixture having volume fraction &.K and u indicates that the value of the parameter is given per repeating unit of the polymer. B is the free energy density and is related to the interaction parameter 1 by the equation

B = xRTU%AH (9)

The use of the equation (9) to obtain x values for polymer mixtures has been critically reviewed [26]. Rigorously, the melting point temperatures used should be equilibrium temperatures; however Nishi and Wang [25] concluded that the absence of equilibrium had little influence on the melting point depression. Consequently a plot of the left-hand side of equation (8), as a function of & , should be linear with a zero intercept, from which a value of B, and hence 1, can be extracted from the slope.

We have plotted the l/PM - l/T; against $& in the blend, as shown in Fig. 5. For EVAH2010/PVC and EVAH402O/PVC blends, a straight line was obtained for the depression of TM, and the lines intercept of zero, in accordance with the Nishi and Wang theory. By analysis of the slope of l/TL - l/ Tk vs c#&, a negative interaction parameter would be expected for EVAH2010/PVC and EVAH4020/

PVC blends. However, for EVAH20/PVC and EVAH4O/PVC blends no changes in TM were observed. When a dispersion occurs, at the molecular level, of semi-crystalline EVAH chains and amor- phous PVC chains, the crystal dimensions become lower and then, the TM of the blend is reduced.

The plots of [q] against Wevc are shown in Fig. 7. A linear increase of [q] as a function of Wp,, for EVAH2010/PVC and EVAH402O/PVC blends was observed. Sharma [ 1 l] predicted that miscible blends tend to obey the law of additivity for the viscosity, that is given, for a binary system, by equation (5).

As shown in Fig. 7, a large departure of linearity was observed for the EVAHZO/PVC blends. These blends showed a viscosity higher than the one calculated by equation (7) and may, therefore, be considered immiscible.

The Huggins constant for a polymer blend, KBLEND described in equation (l), depends on the overlapping of several kinds of interactions, which are thermo- dynamic and hydrodynamic contributions [ 131. Thermodynamic contributions are not present at the 0 temperature, but hydrodynamic contributions are always present. According to Sun [ 131, there are three factors that may influence the hydrodynamic contributions: (i) long range hydrodynamic inter- actions, K,; (ii) aggregate formation from intra-mol- ecular interactions, K2 and (iii) attraction or repulsion by unlike segments of macromolecules, a. When these factors are joined, the Huggins constant for a polymer blend may be described by the following equation

KBLEND = K, + KI + u (10)

where K, is calculated by equation (7). At dilute conditions, aggregate formation may be neglected, then K,,LEND = K, + tl and the tl parameter is calculated using t( = KsL~~D - k.

On the other hand, if repulsive interactions prevail, it gives a < 0. If a > 0, attractive interactions prevail, or KeLENo > K,. As such, the determination of a

values have been used to evaluate the interactions in dilute solution of polymeric blends.

Blends of EVAH2010/PVC and EVAH402O/PVC showed positive values of the a parameter. Blends of EVAHZO/PVC showed negative values of the a parameter. The viscosimetric results are consistent with thermal and microscopic analyses, which lead us to conclude that blends of EVAHZO/PVC are immiscible. In contrast, EVAH2010 or EVAH4020, when mixed with PVC, gives miscible blends.

Electrostatic interactions have been considered to explain miscibilities in polymer blends [27]. For example, in some miscible blends involving PVC, hydrogen atoms of PVC interact with electronegative atoms of another polymer, such as oxygen, nitrogen, or others. This consideration could not be utilised to explain the miscibility of partially hydrolysed EVA with PVC, because it leads us to conclude that EVAHZO should also be miscible with PVC. Our results suggest that there is a synergistic effect due to the presence of acetate and hydroxyl groups in a I:1 molar relation. When this relation is different, as in EVAH20 or EVAH40, the synergistic effect may not be present.

Miscibility of PVC/EVA hydrolysed blends 1657

The synergistic effect may have originated in several systems involving homopolymer/copolymer, possible repulsive interactions between acetate and in which there is a miscibility “window”. hydroxyl groups. These repulsions could be stabilised Blends of PVAc/PVC or PVC with poly(viny1 by chlorine atoms of PVC and miscibility is alcohol), PVOH, are immiscible. A possible miscibil- promoted. The theory of repulsion proposed by Paul ity of PVC with partially hydrolysed PVAc could be [28] has been utilised to explain the miscibility in utilised to reinforce the synergistic effect idea to

Fig. 10. SEM micrography obtained for EVAH2010/PVC and EVAHZO/PVC having 50% PVC mass. Magnification of 4000 x was obtained for each one.

1658 E. Corradini et al.

Table 4. CL parameter for PVAcH/PVC blends in DMSO

WPVC a parameter

0 0 0.25 -0.012 0.50 -0.027 0.75 0.089 1.00 0

explain the miscibility of EVAH/PVC blends. Viscosity measurements of 50% hydrolysed WAC, PVAcH, with PVC in DMSO were carried out and the corresponding a parameter determined. In Table 4 the a parameter obtained for PVAcH/PVC blends in DMSO is shown.

The blend of PVAcH/PVC with Wpvc = 0.75 showed a positive value of the a parameter, suggesting miscibility. This suggests that the simul- taneous presence of hydroxyl and acetate groups in a 1: 1 molar ratio in hydrolysed PVAc induces the appearance of miscibility between the polymeric constituents when compared with PVAc/PVC blends.

CONCLUSIONS

For 20 and 40% molar EVA in acetate groups, partially hydrolysed products, EVAHs, with different properties were obtained, when the degree of hydrolysis was varied. The crystallinity and the melting point of the hydrolysed products were seen to depend on the hydrolysis degree. The miscibility of blends of partially hydrolysed EVA and PVC were analysed by thermal, microscopic and viscosimetric techniques. Our results have led us to conclude that, when the hydrolysed product has a 1: 1 molar relation in acetate/hydroxyl groups, their blends with PVC are miscible. The miscibility, observed by three different techniques, was explained as a result of a synergistic effect, due to the presence of hydroxyl and acetate groups in a 1: 1 molar relation. Under this condition, we proposed that the repulsive interactions of -OH and -AC groups are stab&d by the chlorine atoms of the PVC polymer.

Acktrowlc&emenrs-The authors are grateful for support from CNPq, Proc. no. 520308/94-8, and also to C&a Regina Cavichiolo France and to the Centro de Microscopia Eletrikka da UFPr-Curitiba-Pr. for the ektron n&xoscopies. E.C. is grateful to UEM-CNPq for a fellowship.

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