Polyblends of Polyvinyl Chloride with Ethylene-Vinyl Acetate

20

Downloaded by EAST CAROLINA UNIV on October 27, 2014 | http://pubs.acs.org Publication Date: May 5, 1989 | doi: 10.1021/ba-1989-0222.ch020

Polyblends of Polyvinyl Chloride with Ethylene-Vinyl Acetate Copolymers Miscibility and Practical Properties Rudolph D. Deanin, Sujal S. Rawal, Nikhil A. Shah, and Jan-Chan Huang Plastics Engineering Department, University of Lowell, Lowell, MA 01854

In polyblends of polyvinyl chloride (PVC) withethylene-vinylacetate (EVA) copolymers, plots of properties versus the PVC/EVA ratio generally indicated two-phase behavior, growing softer with increasing EVA content in the blends and with increasing vinyl acetate (VA) content in the copolymers. Differential scanning calorimetry indicated that increasing the VA content in the copolymer lowered crystallinity, and that amorphous PVC plus amorphous EVA formed a new phase that behaved like plasticized PVC.

M ISCIBLE BLENDS ACT AS POLYMERIC PLASTICLZERS

when a rubber is added to a rigid polymer. However, semicompatible blends can produce dramatic synergistic improvement of the impact strength of the rigid plastic (1-4). Conversely, when a rigid plastic is added to a rubber, it can produce useful increases in modulus and strength. These effects depend on the degree of molecular miscibility and practical compatibility. Rigid polyvinyl chloride (PVC) is a fairly tough material, but for many applications it is toughened further by addition of 5-25% of rubbery "impact modifiers". Typically, these modifiers are graft copolymers of acrylonitrile, methyl methacrylate, and styrene on a backbone of butadiene rubber (5, 6). A particularly interesting family of impact modifiers comes from copolymers of ethylene with vinyl acetate (EVA). Increasing VA content in the E V A gradually converts them from crystalline, nonpolar, rigid materials into amor phous, polar, rubbery materials. In blends of P V C with E V A , there may be separate phases for crystalline P V C , amorphous P V C , crystalline polyeth-

0065-2393/89/0222-0403$06.00/0 © 1989 American Chemical Society

In Rubber-Toughened Plastics; Riew, C.; Advances in Chemistry; American Chemical Society: Washington, DC, 1989.

404

R U B B E R - T O U G H E N E D PLASTICS


ylene (PE) blocks, amorphous E V A , and one or two phases for molecular blends of amorphous P V C with amorphous E V A . Early studies indicated that E V A of 45-75% VA content produced maximum miscibility with P V C (7-10). When P V C was blended with 0-25% E V A as impact modifiers, syner gistic peak improvement occurred at 5-15% E V A (Figures 1 and 2). At higher VA content in the E V A , the peaks tended to move toward higher E V A content and become broader (11). Electron microscopy showed that increasing E V A content produced increasing E V A domain size, until phase inversion made E V A the continuous matrix phase and its properties inverted from a rigid high-impact plastic to a thermoplastic elastomer (12). The present study was undertaken to explore the entire range of P V C / E V A ratios from 100:0 to 0:100, using EVAs of equal molecular weight and VA contents from 0 to 51% of the E V A . These were evaluated for mechanical and thermal mechanical properties and calorimetric characterization.

Figure 1. Impact strength versus EVA content in PVC; 28-45% VA in EVA.



20.

DEANIN ET AL.

Miscibility of Polyvinyl Chloride Blends

EVA

%

in

405

PVC

Figure 2. Impact strength versus EVA content in PVC; 45-60% VA in EVA.

Experimental Details Medium-molecular-weight P V C (Goodrich Geon 30) was stabilized by 2 phr of organotin mercaptide ( M & T Thermolite 31) and lubricated by 0.5 phr of stearic acid. It was blended with each of five EVAs (percent V A in parentheses): • N A - 1 7 1 (0) • U E - 6 3 7 (9) • U E - 6 2 1 (18) • U E - 6 4 5 (28) • U E - 9 0 4 - 2 5 (51) in ratios of P V C / E V A of 100:0, 75:25, 50:50, 25:75, and 0:100, by mixing 5 min at 168 °C (335 °F) on a 6- X 12-in. (15.25- X 30.50-cm) differential-speed two-roll m i l l


406


Milled sheets were pressed 0.125 in. (3.17 mm) thick for 3 min at 177 °C (350 °F) and cut into test specimens. The specimens were tested for tensile properties ac cording to ASTM D 638 Type IV at 5.08 cm/min (2 in./min) and for Clash-Berg torsional modulus versus temperature according to ASTM D 1043. Thermal analysis was carried out on a differential scanning calorimeter (Perkin-Elmer DSC-2C) at 20 °C/min.


Mechanical and Thermal-Mechanical Properties Modulus versus P V C / E V A ratio (Figure 3) gave S-shaped curves typical of two-phase polyblend systems. Increasing VA content in the E V A gave pro gressively softer curves. This configuration suggested that random copolymerization decreased the regularity and crystallinity of the E V A .

9

U

r

1

'«

100/0

50/50

PVC/EVA

Ratio

Figure 3. Modulus versus PVC/EVA ratio.


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DEANIN ET AL.


407

Ultimate tensile strength versus P V C / E V A ratio (Figure 4) gave sharply U-shaped curves typical of very sensitive properties in incompatible systems, where any heterogeneity can act as a stress concentrator to initiate premature failure.


Ultimate elongation increased with E V A content in the blends (Figure 5). The major factor was inversion to an E V A continuous matrix phase, with decreasing content of rigid P V C . Elongation also increased with VA content in the E V A because of increasing miscibility with P V C . This miscibility reduced the heterogeneities that could cause premature failure. Clash-Berg torsional modulus versus temperature gave typical curves for the leathery region. For quantitative comparison, the temperature T when torsional modulus approached 6035 psi was chosen as a measure of the leathery-rubbery transition. This value was read from the curves of all the blends (Figure 6). Transition temperature versus P V C / E V A ratio gave S-shaped curves typical of two-phase polyblend systems. Increasing VA con tent in the E V A gave progressively softer curves. This change suggested that l r

Figure 4. Tensile strength versus PVC/EVA ratio.



408


100/0

50/50 PVC/EVA R a t i o

0/100

Figure 5. Ultimate elongation versus PVC/EVA ratio. random copolymerization decreased the regularity and crystallinity of the E V A . The P V C plateau disappeared at 51% VA in the E V A . Apparently the E V A was miscible enough in the P V C matrix to act as a polymeric plasticizer.

Thermal Analysis Differential scanning calorimetry suffered from overlap of the P V C glass transition versus the broad E V A melting range (Figures 7-11), but still yielded useful information. The crystalline melting point of low-density poly ethylene ( L D P E ) at 108 °C (13) was lowered progressively by copolymeri zation with increasing amounts of VA (Table I). However, it was not further affected by blending with P V C . This stability indicated that the crystalline regions of P E blocks did not blend with the P V C . The enthalpy of melting was approximately proportional to the percent of E V A in the polyblends



20.

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409

EH

... 100/0

1 50/50 PVC/EVA R a t i o

0/100

Figure 6. Leathery-rubbery transition temperature versus PVC/EVA ratio. 1 . 5 0 ί-

Ο.00 330

350 370 Temperature °K Figure 7. DSC of PVC.


390



410

ν 2 50

300 Temperature

Figure 9. DSC of 75:25 PVC/EVA;

C

K

350

18% VA.


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DEANIN ET AL.

411



2.00

o.oo j

I 230

j

~

2 50 Temperature °K

i— 270

Figure 10. DSC of EVA; 51% VA.

1.00,

2 50

300 3 50 Temperature °K

Figure 11. DSC of 75:25 PVC I EVA; 51% VA.


400

412


(Table II), a result that confirmed that the crystalline P E regions did not blend with the P V C . Glass-transition temperatures (T ) were more complex and sometimes too faint for the sensitivity of the instrument (Table III). Pure P V C was observed at 88 °C, denoting the maximum-use temperature of unmodified rigid vinyl plastics. High-VA-content EVAs were rubbery; their T values (-27 and - 3 3 °C) represented the molecular flexibility of the random E V A copolymer molecule. In P V C - E V A blends, intermediate T s of - 4 to - 1 0 °C also appeared. These values reflect a new phase composed of a homo geneous blend of amorphous P V C with amorphous E V A copolymer. Thus the separate T values for P V C and for E V A would correspond to the plateaus in the property versus P V C / E V A ratio curves. Similarly, the T of the mis cible polyblend phase would correspond to the more gradual linear property transitions. g

g


g

g

g

In rigid vinyl plastics and thermoplastic E V A elastomers, the P V C and E V A plateaus would be of primary importance, and the miscible phase would serve mainly to provide interfacial adhesion. In highly miscible blends, the E V A would serve primarily as a polymeric plasticizer for flexible vinyl plastics and elastoplastics.

Table I. Effect of Copolymerization on Melting Points (° C) of P V C - E V A Blends VA in EVA (%) 18 28 51

75:25

50:50

25:75

0:100

85 40-83 none

84 39-84 none

85 47-87 none

87 49-90 none

Table II. Effect of EVA Concentration in P V C - E V A Blends on Enthalpy of Melting (cal/g) VA in EVA (%) 18 28

75:25

50:50

25:75

0:100

2.4 1.6

6.3 4.0

9.3 5.0

11.8 6.4

Table III. Effect of Concentration on Glass-Transition Temperatures (° C) of P V C - E V A Blends VA in EVA (%) 0 18 28 51

100:0

75:25

50:50

25:75

0:100

-8 -10 - 8 , 85

-7 -5 -25, - 4 , 86

-8 -9 -26, - 9 , 85

-33 -27

88


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413

Conclusions


Increasing VA content in E V A increases polarity closer to that of P V C , first producing stronger interfacial bonding between phases and later increasing miscibility of the two polymers to form one or more blended phases. Si multaneously, increasing VA content in E V A decreases polyethylene crys tallinity, making the polymer more soft and flexible. These two effects together determine the efficiency of E V A as an impact modifier in rigid P V C , and also as a polymeric plasticizer in flexible P V C . Overall, this makes the E V A family a very versatile modifier for P V C .

References 1. Deanin, R. D. Encycl. Polym. Sci. Technol. Suppl. 1977, 2, 458. 2. Manson, J. Α.; Sperling, L . H. Polymer Blends and Composites; Plenum: New York, 1976. 3. Paul, D . R.; Newman, S. Polymer Blends; Academic: New York, 1978. 4. Deanin, R. D . Polym. Mater. Sci. Eng. 1987, 56, 35; Seymour, R. B . ; Mark,

H . F. Applications of Polymers; Plenum: New York, 1988;p53. 5. Ryan, C . F . ; Jalbert, F . L. In Encyclopedia of PVC; Nass, L . I., Ed., Dekker: New York, 1977; Vol. 2, Chapter 12, pp 609-632.

6. Deegan, C . C . Mod. Plast. Encycl. 1985, 62, 154. 7. Hammer, C . F. Macromolecules 1971, 4, 69. 8. Marcincin, K . ; Ramonov, Α . ; Pollak, V. J. Appl. Polym. Sci. 1972, 16, 2239. 9. Feldman, D.; Rusu, M . Eur. Polym. J. 1974, 10, 41.

10. Shur, Y. J.; Ranby, B.J.Appl. Polym. Sci. 1975, 19, 1337. 11. Deanin, R. D.; Shah, N . A . Org. Coat. Plast. Chem. 1981, 45, 290. 12. Deanin, R. D.; Shah, N . A .J.Vinyl Technol. 1983, 4, 167. 13.

Brydson, J. A . Plastics Materials; Butterworth, London, 1982; p 199.

RECEIVED 7, 1988.

for review February 11, 1988.

ACCEPTED

revised manuscript September


Polyblends of Polyvinyl Chloride with Ethylene-Vinyl Acetate

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