Migration of PVC plasticizers into alcohols

Migration of PVC plasticizers into alcohols Emmanuel M. Kampouris, F. Regas, S. Rokotas, S. Polychronakis and M. Pantazoglou Laboratory of Special Chemical Technology, National Technical University of Athens, Athens 147, Greece (Received 14 April 1975,"revised4 July 1975) The use of labelled plasticizers and radioactivity measurements in conjunction with weight loss, can give quantitative information on the amount of migrated plasticizer, and on the amount of the liquid medium that diffuses into the polymer during the migration process. In the case of PVC plasticized with dibutyl phthalate and dioctyl phthalate and immersed in alcohols, the specimens soon become heterogeneous due to loss in compatibility between the polymer and the mixtures of plasticizer-alcohol high in alcohol. These mixtures are formed in the polymer as a result of continuous migration and diffusion processes. The following factors affecting the migration process were examined: nature of alcohol, nature of phthalate plasticizer, amount of plasticizer, molecular weight of polymer, thickness of specimens, presence of epoxy plasticizers, plasticization process, presence of stabilizers, temperature, and time.

INTRODUCTION The problem of plasticizer migration is of special interest in the case of polymers modified with considerable amounts of plasticizers. Of the common polymers PVC is the one used in the largest volume as flexible or plasticized PVC. Therefore any study on the plasticization and migration processes may be of practical importance for the PVC industry. In all applications a plasticized polymer is in contact with some kind of surrounding medium. Under these conditions the plasticizer must stay in place during the useful life of the formed plastic item, otherwise it migrates with the result that (a) the polymer, because of loss of plasticizer, stiffens and becomes less desirable, and (b) the surrounding medium is contaminated by the plasticizer. Thus there arises the need for a thorough study of factors affecting the migration process, and for a simple and accurate method of measuring amounts of plasticizer which may be present in a given medium. The possible factors which can affect the migration process can be classified in relation to: (a) the polymer, i.e. nature, molecular weight, crystallinity; (b) the plasticizer, i.e. ~ature, amount, possible interactions (especially in the case of mixed plasticization systems); (c) the other components usually present in the plasticized polymer, i.e. stabilizers, lubricants, fillers; (d) the plasticization process and conditions, and therefore the homogeneity of the system; (e) the surrounding medium, i.e. nature, compatibility with the plasticizer, effect on polymer; (f) the conditions of the test, i.e. time, temperature, type of contact. The plasticizer that migrates can be estimated as: the amount leaving the polymer, or the amount entering into the liquid. In the first case the amount can be measured by weight 1 or radioactivity2 loss. In the second case the amount of plasticizer can be measured by chromatography3,4, spectrometry s, impulse-polarography6, and radioactivity7,8. This paper presents the results, obtained by radiometric and weight loss methods, of a study of the effect of the

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following factors upon the migration of phthalate plasticizers from plasticized PVC into alcohols: nature of alcohol, molecular weight of the polymer, nature of plasticizer, amount of plasticizer, presence of epoxy plasticizers, presence of stabilizers, plasticization process, thickness of specimens, temperature, and time..

EXPERIMENTAL

Synthesis of labelled dibutyl phthalate (DBP) 5 mg of labelled n-butahol (1-14C; 0.25 mCi) were diluted with n-butanol(28 ml) and added to a four-necked flask containing powdered phthalic anhydride (49 g). The flask was equipped with stirrer, thermometer, N 2 inlet tube, and a side condenser. The mixture was heated at 100°C for 1 h, then n-butanol (95 ml) and concentrated sulphuric acid (0.4 ml) were added, and the mixture was heated at 130°C for 3 h. During this period a slow stream ofN 2 was passed and n-butanol was periodically added to make up for that distilling. After cooling, the reaction product was diluted with ether (500 ml) and the ethereal solution was washed with 10% aqueous sodium carbonate solution, then with water, and finally evaporated to remove ether and unreacted n-butanol. The diester was purified by vacuum distillation (yield 82 g of labelled DBP of radioactivity 4.8 x 103 counts/mg/min). Products with lower radioactivities were obtained by dilution with pure unlabelled DBP.

Synthesis of labelled d&ctyl phthalate (DOP) The product was synthesized according to the literature method s from labelled phthalic anhydride (7-14C) and 2ethylhexanol.

Preparation of specimens Suspension polymerized PVC was blended at 80°C with the calculated amounts of plasticizers and stabilizers. No

Migration o f PVC plasticizers into alcohols: Eo /14. Kampouris et aL Table I

Effect of the nature of alcohol upon the migration (mg) of plasticizers from plasticized PVC

Methanol

Ethanol

n-Propanol

Isopropanol

n-Butanol

2-Ethylhexanol

Isobutanol

Time (days)

DBP

DOP

DBP

DOP

DBP

DOP

DBP

DOP

DBP

DOP

DBP

DOP

DBP

DOP

1 2 4 6 10 15 20 25 30

152 255 344 399 452 484 506 521 528

57 82 110 140 187 228 254 272 282

101 152 265 338 422 470 491 506 514

163 209 274 319 396 464 516 551 575

73 110 175 230 322 401 444 475 497

241 340 450 527 616 627 718 742 751

51 87 147 189 256 308 349 376 392

82 119 153 181 230 275 307 332 354

74 110 181 239 324 387 433 464 485

260 399 518 588 663 705 736 754 762

47 81 138 174 217 252 280 308 332

84 125 163 194 242 288 329 350 371

26 37 54 69 78 115 133 147 161

94 135 178 224 274 325 361 390 412

lubricant was used. For stabilization Ba-Cd (1.5 phr) and alkyl aryl phosphite (0.5 phr) type stabilizers were used. The dry blend was then plasticized by hot working for 7 min in the mixing head of a Brabender Plasticorder at 160°C and 30 rev/min. The plasticized mass was then formed by hot rolling to a sheet from which specimens of 20 x 50 mm were cut. Immersion Each of the specimens was immersed in 250 ml of the liquid medium contained in a 300 ml glass-stoppered Erlenmeyer flask. The following alcohols were used as liquids: methanol, ethanol, 96% ethyl alcohol, n-propanol, isopropanol, n-butanol, isobutanol, and 2-ethylhexanol. All tests were made in duplicate, the flasks were kept at temperatures maintained to -+2°C, and the specimens were selected with weight differences not exceeding 100 mg.

Table 2 Effect of the nature of alcohol upon the migration (mg) of DBP and DOP from plasticized PVC: comparison of the results after 30 days of immersion DBP

DOP

Alcohol

I

II

III

IV

I

II

III

IV

Methanol Ethanol n-Propanol Isopropanol n-Butanol Isobutanol 2-Ethylhexanol

545 538 507 417 493 312

528 514 497 392 485 332

289 227 192 164 202 145

239 287 305 228 283 187

275 582 731 372 745 378

282 575 751 354 762 371

124 317 428 126 420 133

158 258 323 228 342 238

145

161

57

104

396

412

160

252

I = Migrated plasticizer, by radioactivity loss; II = migrated plasticizer by radioactivity of the alcohol; III = weight loss; IV ,= difference II -- III (diffused alcohol)

Measuremen t The radioactivity of the liquid medium, at a given time after immersion, was measured by transferring 0.5 ml of the content of the flasks to a glass measuring vial containing 10 ml of the scintillation solution, shaking to ensure complete solution, and measuring the radioactivity by means of a Packard Tri-Carb 3385 liquid scintillation spectrometer over a period of 10 min. The scintillation solution was made by dissolving 5 g of 2,5-diphenyloxazole (PPO) and 300 mg of 2,2'-p-phenylenebis(4-methyl-5-phenytoxazole)(Dimethyl-POPOP) in one litre of toluene. From each flask, two samples were taken thus each quoted result represents the average of four measurements. Corrections were made for background and quenching. The radioactivity loss was calculated from radioactivity measurements of the specimens before and after immersion. In both cases about I0 mg of the specimens were dissolved in 1 ml of tetrahydrofuran, 10 ml of the scintillation solution were added, and the radioactivity was measured in the usual way. Efforts were made to obtain representative samples; all measurements were made in fivefold and the average obtained.

RESULTS AND DISCUSSION Effect o f the nature of alcohols This effect was examined at 257C using k 65 PVC plasticized with 50 phr DBP or DOP. The results obtained are given in Tables 1 and 2. As the data in Table 1 indicate, the amount of migrated DBP is high in the case of n-alcohols

and much lower with iso-alcohols. In both cases the greater the molecular weight of the alcohol, the lower is the amount of plasticizer. In the case of DOP the greater migration rates also occur with n-alcohols, but the effect of the molecular weight of is different. Now the greater the molecular weight n- or iso-alcohols, the greater is the amount of migrated plasticizer. As the data in Table 2 indicate, the radioactivity loss method can give results approximately the same as obtained by measurements of the radioactivity of the liquid medium. Comparison between the results obtained by the weight loss method and that of the radioactivity of the liquid, for both DBP and DOP, indicates that in no case can the weight loss method be used for the measurement of the amount of migrated plasticizer. Correlation of the results of the two methods, supposing no other matter except plasticizer is migrated, can give quantitative information on the amount of the alcohol diffused into the polymer, during the migration process. In no case can the amount of diffused alcohol be related with the molecular weight. The only clear observation is that n-alcohols diffused in greater amounts than iso-alcohols both in the case of DBP and DOP. It also holds true that the lower alcohols diffused faster in PVC plasticized with DBP, while the higher alcohols diffused faster in PVC plasticized with DOP. In most cases the specimens gradually lose their transparency and become opaque to white, during the migration process. This can be explained by the fact that the plasticizer alcohol mixture, which plasticizes the polymer, becomes gradually a non-solvent for the polymer and

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Migration of PVC plasticizers into alcohols: E. M. Kampouris eta/.

hols exhibiting a selective action. As the data in Table 2 indicate, the lower alcohols diffuse faster in PVC plasticized with DBP, while the higher alcohols do so in PVC plasticized with DOP.

Effect of the amount of plasticizer

Figure I

Formation of a long hole, a number of small ones, and lines of differentiation in the mass of PVC plasticized with 50 phr DBP and immersed in ethanol (×35)

Table 3 Effect of the amount of plasticizer upon the migration of DBP from plasticized PVC into ethanol at 30°C

Migrated plasticizer (rag) Time (days)

20 phr

40 phr

60 phr

2 4 6 10 15 20 25 30 40 50 60 70 80

14 19 25 33 40 46 50 56 60 70 76 85 93

108 159 209 301 352 383 415 438 461 482 498 512 523

451 614 688 757 801 827 852 872 899 924 935 943 947

464

802

1050

371

179

' 103

16 78

9 180

6 517

15

343

430

Initial plasticizer content (mg) Final plasticizer content (mg) Final plasticizer content (phr) Weight loss (mg) Diffused alcohol (mg)

separates as a secon(1 phase in the mass. This is shown in the microphoto of Figure 1.

This effect was examined in the case of k 65 PVC plasticized with 20, 40 and 60 phr of DBP. The temperature of the test was 30°C, the duration 80 days, and the liquid medium ethanol. The results obtained are given in Table 3. As the data indicate the amount of plasticizer strongly affects the migration process and the greater the amount of plasticizer, the greater is the amount lost by migration. During the course of the process the migration rate was faster for the specimens plasticized with the greater amounts of plasticizer. The result was a reversal of the order and after a certain time the specimen with the greater amount of plasticizer ends up with the lowest amount. This behaviour can be explained only in cases of high diffusion rates. In the case examined it is evident that the greater the amount of plasticizer, the greater is the amount of diffused ethanol. At the end of the test the specimen plasticized with 20 phr DBP becomes plasticized with about 16 phr of a mixture containing 4% ethanol, the specimen plasticized with 40 phr becomes plasticized with about 26 phr of a mixture containing 65% ethanol, and finally the specimen plasticized with 60 phr DBP becomes plasticized with about 30 phr of a mixture containing 80% ethanol.

Effect of the molecular weight of the polymer For this test four samples of PVC (k values 55, 65, 70, and 73 respectively) were ]~lasticized with 50 phr DBP and immersed in ethanol at 30vC for 60 days. The results obtained are given in Table 4. As the data indicate the molecular weight of the polymer affects migration and the greater the molecular weight, the lower is the amount of migrated plasticizer.

Effect of th e th ickn ess of specimens In some cases ~°'H short-time tests led to the conclusion that the thickness of specimens has little or no effect on the migration of plasticizers. In this test specimens of k Table 4 Effect or the molecular weight of polymer upon the migration of DBP from plasticized PVC into ethanol at 30°C Migrated plasticizer (rag) Time (days)

k55

k65

k70

k73

2 4 6 10 15 20 25 30 35 40 45 50 55 60

256 330 377 410 435 450 459 464 469 473 476 480 483 486

203 275 327 370 401 419 425 435 440 445 450 453 457 480

156 205 244 285 324 348 360 370 376 381 385 392 398 405

90 135 170 199 235 260 276 284 298 310 319 326 331 335

Effect of the nature of phthalate plasticizer This effect was examined for both DBP and DOP, two common plasticizers with differences in molecular weight, viscosity and volatility. It is often stated, in examining the tendency of plasticizers to migrate, that the greater the molecular weight, the greater the viscosity, or the lower the volatility, the lower is the migration rate a-l°. The data in Table 1 indicate that there is no firm relationship between molecular weight, viscosity, or volatility of plasticizer and the rate of the migration process. Generally only in the case of contact with methanol does DBP migrate faster than DOP, while the opposite is true in the other cases. The nature of plasticizer affects the diffusion of alco-

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1975, V o l 16, N o v e m b e r

Migration of PVC plasticizers into alcohols: E. M. Kampouris et aL Table 5 Effect of the thickness of specimens upon the migration of DBP from plasticized PVC into ethanol

Migrated plasticizer (mg) Time (days) 1 2 4 6 10 15 20 25 30

3040 mg 317 531 688 738 778 796 814 834 843

Initial plasticizer content (mg) 1000 Final plasticizer content (rag) 157 Final plasticizer content (phr) 7.7

2381 mg

1785 mg

1483 mg

295 442 530 572 599 633 657 675 701

292 386 463 488 502 515 526 538 547

287 338 361 377 406 419 435 447 460

783

578

488

82

31

28

5.2

3.5

3.6

El]Oct of stabilization This effect was examined for k 65 PVC plasticized with 60 phr DBP or DOP and immersed in 96% ethanol for 30 days at 25°C. In the case of non-stabilized PVC, plasticized with 60 phr DOP, two series of samples were prepared with different plasticization times, i.e. 7 and 15 rain. The results in Table 8 indicate that stabilization affects strongly the migration process, and the greater amounts are migrating from the stabilized specimens. In the case of unstabilized specimens the effect of the plasticization time is greater than in the case of stabilized ones.

Effect of temperature The effect of temperature was studied in the case of k 65 PVC plasticized with 50 phr DBP and immersed in ethanol

Table 6 Effect of epoxy plasticizer upon the migration of DBP and DOP from plasticized PVC into ethanol

Migrated DBP (rag)

ranged from 2.5 to 15 min. As the data in Table 7 indicate, differences in the plasticization process (due to variations in plasticization time) affect migration and the greater the working time, the lower is the amount of migrated plasticizer.

Table 7 Effect of the plasticization process upon the migration of DBP from plasticized DBP ethanol

Migrated plasticizer

Migrated DOP (mg)

(rag)

Time (days)

0 phr

6 phr

0 phr

6 phr

2 4 6 10 15 20 25 30

186 244 270 302 317 327 333 342

219 269 296 331 360 373 381 384

178 240 282 327 349 360 377 383

223 297 347 402 437 451 460 469

65 PVC plasticized with 50 phr DBP were used immersed in ethanol at 30°C. For higher accuracy the weight of 20 x 50 mm specimens was used as an indication of thickness. The results in Table 5 indicate that the greater the thickness of the specimens, the greater is the amount of migrated plasticizer. At the end of the test the major part of the plasticizer had migrated and the amount remaining was greater for the thicker specimens.

Time (days)

2.5 min

5 rain

10 min

15 min

2 4 6 10 15 20 30 40 50 60

230 327 370 421 445 452 462 467 472 477

213 307 352 392 416 430 441 449 459 461

208 280 321 368 392 417 425 431 437 442

202 262 297 335 380 398 415 424 432 437

Weight loss (mg) Ethanol diffused (mg)

294

290

273

265

183

171

169

172

Table 8 Effect of the presence of stabilizers upon the migration of DBP and DOP from plasticized PVC into 96% alcohol

Migrated plasticizer (rag)

Effect o f the epoxv plasticizer In examining the effect of epoxy plasticizers upon the migration of the main (phthalate) plasticizer, specimens were made from k 65 PVC plasticized with 50 phr DBP or DOP and 6 phr of epoxy plasticizer (a commercial epoxidized soyabean oil). The specimens were immersed in ethanol for 30 days at 25°C. The results obtained are given in Table 6. As the data indicate, the epoxy plasticizer affects migration, promoting that of the main plasticizer. This behaviour seems to be selective: DOP migrates to a greater extent than does DBP.

Time (days)

I

II

III

IV

V

2 4 6 10 15 20 25 30

222 283 333 379 424 451 469 483

80 136 173 227 257 273 282 291

153 228 263 312 358 383 410 425

79 123 164 207 246 276 303 328

67 114 148 175 211 230 251 267

Lffect o f the plasticization process

I = Normally stabilized PVC plasticized with 60 phr DBP; II = unstabilized PVC plasticized with 60 phr DBP; III = normally stabilized PVC plasticized with 60 phr DOP, plasticization time 7 min; IV = unstabilized PVC plasticized with 60 phr DOP, plasticization time 7 min; V = unstabilized PVC plasticized with 60 phr DOP, plasticization time 15 rain

This effect was studied for k 65 PVC plasticized with 50 phr DBP and immersed in ethanol at 30°C for 60 days. The plasticization process generally used in this work was followed with variations in the time of hot working which

POLYMER, 1975, Vol 16, November 843

Migration of PVC plasticizers into alcohols: E. M. Karnpouris et aL Table 9 Effect of the temperature upon the migration of DBP from plasticized PVC into ethanol

Migrated plasticizer (rag) Time (days)

10°C

30 °C

60 °C

2 4 6 10 15 20 30

54 78 100 132 164 199 213

234 334 388 430 457 473 484

442 530 572 599 633 657 701

at temperatures ranging from 10° to 60°C. The results in Table 9 indicate that the temperature affects strongly the migration of plasticizer; any rise in temperature increases drastically the amount of migrated plasticizer. Thus 30 days of immersion at 10°C gave the same amount of migrated plasticizer, as 2 days at 30°C. Schematic presentation of the results leads to the conclusion that the relation temperature/amount of migrated plasticizer is not a linear one. E f f e c t o f time

Examining the effect of time, in all the above cases, we can conclude that there is no linear relation between the amount of migrated plasticizer and time, or the square root of time. Contradictory results in the literature may

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be explained by the small intervals of time. Generally the greatest migration rates occur in the first stages of the process. They become then lower and tend to minimize. For long enough periods the total amount of plasticizer can migrate, leaving the polymer plasticized, or swelled, by a mixture containing low amounts of plasticizer.

ACKNOWLEDGEMENTS The authors wish to express thanks to Dr G. Akoyunoglou and Mr S. Daousis of the Biology Dept. of N.R.C. Democritos for counting the samples. REFERENCES 1

2 3 4 5 6 7 8 9 10 11

Reed, M.C. andHarding, J. lnd. Eng. Chem., 1949,41,675 Kampouris, E. and Rokotas, S. unpublished data Rost, H. E. Fette, Seifen, Anstrichm. 1970, 72, 552 Rohleder, K. and Bruchhausen, B. V. Dsch. LebensmRundsch. 1972, 68, Gutsalyul, V. G. and Samonova, N. S. [zv. Akad. Nauk Kaz. SSR, Set. Khim. 1962, (2), 95 Woggon,H. and Koehler, U. Kunststoffe 1967, 57, 583 Figge,K. and Piater, H. Dsch. Lebensm-Rundsch. 1971, 67, 235 Kampouris, E. 4th Eur. Conf. Plast. Rubbers, Paris 1974, Paper 91 Knappe, W. Kunststoffe 1962, 52, 387 Quackenbos, H. M. Ind. Eng. Chem. 1954, 46, 1335 Reed, M. C., Klemm, H. F. and Schultz, E. F. Ind. Eng. Chem. 1954, 46, 1344