Indian Journal or Textile ResearchVol. 4, September 1979, pp. 99-105

Hydrolysis and Aminolysis of Polyethylene Terephthalate

M R PADHYE & A N NADAFCentre of Advanced Studies, Department of

Chemical Technology, University of Bombay,Bombay 400019

Received 12 July 1978; accepted 24 March 1979

The effect of hydrolytic and amino lytic degradation on the structure of polyethylene terephthalate (PET) films has beeninvestigated. Changes in IR crystallinity, number ofOH and COOH end groups, and development of opacity have been takenas measures of the morphological changes occurring on hydrolysis. Increase in crystallinity occurs on treatment with acids,alkalis and amines. End group analysis shows that chain scission takes place only under drastic conditions (high reagentconcentration and high temperature of treatment). With all other reagents tried, except sulphuric acid, the film developsopacity, indicating that these reagents diffuse into the body of the film. In the case of hydrochloric acid, the attack seems tocause random depolymerization, while with sulphuric acid and alkalis, the end monomers seem to be liberated.

Hydrolytic degradation has a pronounced effect on theproperties and structures of fibres. Both cellulosic andprotein fibres were studied quite early, but in recentyears with increasing use of synthetics, such a study onsynthetics is essential. Limited literature is available onthe changes in surface and morphological structure asalso other physical properties of poly(ethyleneterephthalate)(PET) fibres on progressive hydrolysis.

The results reported so far in the literature on thechemical reactivity of polyester fibres are mainlykinetics oriented 1- 9 and there is obvious need toinvestigate the morphological changes taking placedue to hydrolysis.

Revens! reported that in the acid hydrolysis of PETfibres, the order of hydrolytic degradation is asfollows: Unoriented amorphous > unorientedcrystalline (48 %) > oriented crystalline (30 %). Healso proposed a mechanism for the hydrolytic attack.Hydrolysis by HCl and H2S04 shows characteristicdifferences!" 3; the former gives a random scissionwhich is not true in the case of H2SO 4'

Waters4 found the alkaline hydrolysis (20 % KOHsolution at 98°C) reaction to be heterogeneous withrespect to the polymer and not homogeneous as in thecase of neutral and acid hydrolysis. The alkaline attackis primarily a surface reactions. Hydrolysis of PETfilms has been studied as a function of temperature andconcentration for various film thicknesses and it hasbeen shown that hydrolysis occurs only on the surfaceand follows a zero-order reaction>.

The aminolysis of ester is reported to take placeaccording to. the following reaction»:

R'COOR+H2NR"-+ R'- CONHR" + ROHwhere R' = C6H4, R = CH2-CH2-O-, R" =-CH3

Kurita« suggested that the aminolysis reaction isselective, starting with the amorphous region andextending to the crystalline region on prolongedtreatment. The polymer shows progressive loss inweight. More recently, Overton and Haynes? andMehta and Bell8 came to a similar conclusion.Characterization of oriented samples after de-gradation was reported by Mocheria and Be1l9.

In the present investigation, a number of methodshave been used to study the various structural andmorphological changes taking place on controlledalkali and acid hydrolysis as well as aminolysis of PETfilms.

Materials and MethodsThe PET film used was obtained from Dupont de

Nemours through the courtesy of Dr Heffelfinger. Thetransparent films were completely amorphous andunoriented, as shown by polarized infraredspectroscopy and X-ray study.

Filament- These were semidull monofilaments(denier, 80; twist, 0; and fils, 34) supplied by NirlonSynthetic Fibres and Chemicals, Bombay.

The chemicals used were all of ANALAR grade andwere not purified further.

Instruments- The infrared spectra were recordedon a Perkin Elmer 21 spectrophotometer. X-raydiffraction scans were recorded employing a Geigercounter and rate meter charts using Ni-filtered CuKradiation from a Philips X-ray diffraction unitoperated at 35 kV and 30 mA. Chart speed was 150mm/hr and Goniometer speed was 1/4°Imino TheDT A/scans were taken on an Aminco thermalanalyzer unit; heating rate, lOoC/min. For tensile

99

INDIAN J. TEXT. RES., VOL. 4,SEPTEMBER 1979

strength measurement, Instron tensile tester modelTM-M metric standard was used; chart speed, lOcm/rn; gauge length, 1 em; and full scale adjusted for20 g.

Treatments-PET film strips of size 4 x I cm weretaken and treated with acids, alkalis and amines ofdifferent concentrations at different temperatures andfor different periods. After treatment, the films werewashed thoroughly and tested with BDH UniversalIndicator for complete removal of acid or base. Thefilms were then dried and kept in a vacuum desiccatorfor 24 hr. Filaments were treated in a similar manner.

Measuremcnts- The method of Sheldon et al. 10 wasemployed to determine the density of the polymerfilms. In the case of differential thermal analysis(DT A), the film was cut into I x I mm pieces whichwere sandwiched between two layers of calcinedalumina (reference material) in the sample holder.Scans were taken between 25° and 300°C; the heatingrate was lOoC/min. Infrared spectra and X-raydiffraction scans were recorded by the usual method.Crystallinity was calculated by the method of BhamaIyer and Padhye U.

Change in the number of OH and COOH endgroups in untreated PET films as well as in thosetreated with acids, alkalis and amines was studied bythe method of Addleman and Zichy+-.

Tensile strength measurement-For the elongationtest, samples of hydrolyzed PET filaments were

allowed to condition overnight at 65 % RH and 23'C.Ten readings were taken for each sample. Load-elongation curves of single filaments were obtained at atest length of I cm.

To examine the extent and nature of changes in thestructure of the polymer on hydrolysis and aminolysis,a series of experiments were conducted varying theacid, alkali or the amine and the conditions oftreatment. The following aspects were studied: (i)change in density, (ii) change in the number ofOH andCOOH end groups in the PET film, (iii) change ininfrared crystallinity, (iv) change in melting point andheat of fusion by DTA (relative), (v) change in orderfactor by X-ray analysis, (vi) development of opacity,and (vii) effect on breaking strength.

Results and DiscussionThe data obtained are presented in Tables 1-7. The

changes in tensile strength of PET filaments whensubjected to different treatments are shown in Figs. 1-3.

Acid treatment at room temperature-It is observed(Table 1) that HCl up to 35 % concentration and 6 hrtreatment at room temperature does not cause anyappreciable change in density. Though the infraredcrystallinity index shows a slight increase, there is nochange in X-ray order factor. End group estimationshows that with 20 and 35 % HCl there is an increase inthe number of end groups. The OH:COOH ratio,however, remains the same as for the original sample,

Table I-Effect of HCI Treatment on the Characteristics of PET (Amorphous) Film

Temp. Duration of Concentration Density IR End group estimation°C treatment % (wt/vol.) at 23°C crystallinity g equiv/106 g polymer

hr gjcm3 % No.orOH NO.ofCOOHgroups groups

5 1.334 35 94.0 47.7

30 3.0 10 1.334 35 94.0 48.020 1.335 37 120.0 58.535 1.335 37.5 122.5 61.05 1.334 35 102.0 48

30 6.0\0 1.334 38.5 110.0 5220 1.335 37.5 125.0 58.735 1.336 38.0 141.0 73

5 1.342 38.7 107.0 49.8

60 6.0 10 1.344 40.5 121.0 67.520 1.345 42.0 140.0 7235 1.345 47.2 148.0 96.5

5 1.346 50.9 94.0 47.7

90 3.010 \.354 52.6 120.5 58.520 1.356 53.0 125.5 6135 1.364 53.8 148.0 109

5 1.360 51.3 138 '64.2

90 6.010 1.362 51.5 141 68.520 1.370 57.8 159 9235 1.385 58.6 170 99

Control 1.334 91.50 45.5

100

PADHYE & NADAF:HYDROLYSIS & AMINOLYSIS OF POLYETHYLENE TEREPHTHALATE

viz. 2: 1. It follows that though no appreciablemorphological changes have taken place, acid hasdiffused into the film and some chain scission has takenplace at the ester linkage. The proportion of the endgroups gives an indication of the type of scissionprocess. Each scission should normally give a hydroxy

and a carboxy group on the fragments. Since the ratioof the number of OH to COOH groups remains thesame, it means an addition of two OH groups for eachCOOH group added. This can be explained only on theassumption that one in every three scissions gives OHgroups on each fragment. There is no appreciable fall

Table 2- Effect of Treatment with H2S04 on the Characteristics of PET (Amorphous) Film

Temp Duration of Concentration Density IR End group estimation°C treatment % (wt/vol.) at 23°C crystallinity g equiv/106 g polymer

hr gjcm3 % No.ofOH No.ofCOOHgroups groups

10 1.340 26 91.4 47.7

3.020 1.345 35 90.3 48.8

30 40 1.347 38 90.5 49.060 1.347 40 91.0 50.080 Dissolution of film completely

10 1.344 33.4 91.5 51.620 1.346 36.6 92.0 49:0

60 3.0 40 1.350 40.0 91.8 60.060 1.350 45.0 91.0 91.0

10 1.350 33.5 93.8 50.8

60 6.0 20 1.351 37.0 92.9 51.540 1.355 41.0 94.4 59.260 1.357 46.0 98.0 88.0

10 1.370 42 118 50

90 3.0 20 1.373 43 132 5140 1.378 44 133 6360 1.379 48 133 84

10 1.370 43.0 125 52.0

90 3.0 20 1.373 44.7 139 52.940 1.325 45.3 136 70.050 1.36 48.6 167 101.060 Dissolution of film completely

Control 1.334 91.5 45.5

90

Table 3-Effect of NaOH Treatment on the Characteristics of PET (Amorphous) Film

Duration of Concentration Density IR End groups estimationtreatment % (wt/vol.) at 23°C crystallinity g equiv/106 g polymer

hr gjcm3 x No.ofOH No.ofCOOHgroups groups

5 5 1.335 30 91.7 46.03.0 10 1.335 31 91.9 50.015 15 1.337 32 92.0 51.0

5 1.340 30 92.0 48.83.0 10 1.341 32 93.0 57.0

IS 1.342 35 93.5 60.2

5 1.349 47 104.0 47.36.0 10 1.350 50 105.0 51.5

IS 1.351 55 105.0 50.0

3.0 5 1.353 48 106.0 50.010 1.350 50 110.0 60.0

6.0 2.5 1.356 50 145.0 120.05.0 Destruction of film completely

1.334 91.5 45.5

101

Temp.°C

30

60

60

90

Control

INDIAN 1. TEXT. RES., VOL. 4, SEPTEMBER 1979

in tensile strength, though there is fall in the degree ofpolymerization (DP). A more drastic treatment causesfall in strength due to further reduction in DP.

Sulphuric acid even at room temperature shows amore drastic degradative action on PET. There is apronounced increase in density, whereas IR and X-raystudies show the order of change to be the same as withHCl. There is no change in the number of end groups.A thermogram of amorphous PET shows a coldcrystallization exotherm around 120°,which, however,disappears once the film is heat treated to about l60°Cand gets equilibrium thermal crystallinity. It is henceobvious that the enhanced increase in density is notgenuinely' due to crystallization, because IR and X-raydata as also persistence of cold crystallization

exotherm after acid treatment do not indicate anypronounced change in crystallinity. It is possible toexplain these results on the basis that H2SO 4 does notdiffuse into the film, due possibly to the large size of thehydrated sulphate ion. The action takes placepreferably on the surface. Acid extracts some lowmolecular weight fraction and oligomers from theamorphous region on the surface, indicating anapparent increase in density. This conclusion isconfirmed by the fact that there is no change in thenumber of end groups and that there is no fall in tensilestrength on H2S04 treatment at room temperature.

Acid treatment at higher temperatures-Treatmentwith both HCl and H2SO 4 at higher temperatures (60°and 90°C) causes more pronounced degradation. With

Table 4-Etfect of Treatment with Methylamine on the Characteristics of PET (Amorphous) Film

Temp. Duration of Concentration Density IR End group estimation°C treatment % (wt/vol.) at 23°e crystallinity g equiv/106 g polymer

hr g/cm ' % No.ofOH NO.ofCOOHgroups groups

2.5 1.350 32.2 98.5 47.830 3.0 5 1.354 35.3 102 47.9

10 1.355 37.8 112 49.5

2.5 1.350 33.0 99 49.230 6.0 5 1.355 45.0 104.5 53.7

10 1.355 48.0 105 49.8

2.5 1.356 35.0 98 45.560 6.0 5.0 1.358 46.5 98.5 45.9

10.0 1.362 47.0 107 47.2

2.5 1.350 35.0 110 4890 3.0 5.0 1.355 47.0 112.2 52

10.0 1.355 48.0 114 55

2.5 1.357 48.0 1-35 6990 6.0 5.0 1.358 49.5 135 70

10.0 1.460 49.0 140 75

Control 1.334 91.5 45.5

Table 5-Etfect of Treatment with Ethylamine on the Characteristics of PET (Amorphous) FilmTemp. Duration of Concentration Density IR End group estimation

°C treatment % (wt/vol.) at 23°C crystallinity g equiv/106 g polymerhr g/cm ' % No. of OH No. of COOH

groups groups

10 1.339 33 95 5020 1.344 34 110 5540 1.348 39 120 5650 1.350 41 140 70

10 1.340 38 96 5120 1.348 41 III 5640 1.350 43 120 7050 1.355 45 150 75

2.5 1.350 40 96.5 5010 1.353 47 150 80

2.5 1.365 49 120 75

1.334 91.5 45.5

30 3.0

30 6.0

60 3.0

90 3.0

Control

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PADHYE & NADAF:HYDROLYSIS & AMINOLYSIS OF POLYETHYLENE TEREPHTHALA'l'E

Table 6-Elfect of Treatment with Piperidine on the Characteristics of PET (Amorphous) Film

Temp Duration of Concentration Density IR End group estimation°C treatment % (wtjvol.) at 23°C crystallinity g equiv/106 g polymer

hr g/cm3 % No.ofOH NO.ofCOOHgroups groups

2.5 1.355 30 85.0 675 1.355 26 75.0 72

30 3.0 10 1.359 24 58.0 4720 1.365 22 43.2 6140 1.366 22 41.0 5550 1.368 21 40.0 50

2.5 1.362 28 77.0 705 1.363 25 76.0 75

30 6.0 20 1.364 21 60.0 5840 1.365 21 52.7 4950 1.370 20 46.0 50

60 3.02.5 1.363 9.75 55.2 25.75 1.365 9.00 35.4 30.6

Control 1.334 91.5 45.5

12r-------------------------------~-- HCI, 27·C,24 nr---- Hel, 80·C,6 hr'"~ 12

: ~---~ -0--~ _e -----e 0-'" --- ....: 90~----~------~------~------~~~ 5 10 20 40

Cone., .,. (wt/vol )

Fig.1 ~ Breaking load vs concentration of HCI for differenttemperatures of treatment

both the acids, crystallinity increases, as indicated bydensity, IR and X-ray data. However, the quantitativechanges with H2SO 4 treatment are uncertain becauseof the partial dissolution of the amorphous material.The cold crystallization exotherm is lost for filmstreated at higher temperature in the case of both theacids, which confirms that equilibrium crystallizationhas set in. End group analysis shows an interestingtrend. In the case of treatment with H2SO 4 at 60°C, theproportion of COOH groups increases. However withthe same acid at 90°C, there is increase in theproportion of OH groups. As expected, the tensilestrength falls in both the cases, but more steeply withsulphuric acid treatment. These changes show that athigher temperatures, H2SO 4 is able to diffuse into thefilm. There is, however, an important difference- thefilm develops opacity and becomes brittle with HCltreatment, whereas it remains clear and supple withH2SO 4 treatment. Opacity is possibly due tomicrocrystallinity or microvoids.

Alkali treatment-The effect of sodium hydroxidetreatment is evident from the data presented inTable 3. The increase in density in this case is less thanthat in the case of acid treatment, but IR and X-ray

----.....--- --'"•..9~"o

-- NaOH, 27·C, 6 hr

---- MethYlamine, 27 ·C, 24hr

3~ ~ ~~ ~~----~~o 10 20

conc-, Of. (wt Ivol )

Fig.2-Breaking load vs concentration of NaOH and methylaminefor different conditions of treatment

12r---------------------------------,.---.- --- .•...-.--...--- ---o -.

9

o~, 6

"'fm

---- Piperidine, 27 ·C, 24 hr

-- Piperidine, 80·C, lhr3

o 60 80 100conc -, .,. (wt/vol)

Fig.3-Breaking load vs concentration of piperidine

103

INDIAN J. TEXT. RES., VOL. 4,SEPTEMBER 1979

Table 7- Values of X-Ray Order Factor for PET(Amorphous) Film Treated with Acids, Alkali and Amines

Agent Concen-tration

%(wt/vol.)

Tempe- Duration X-Rayrature of order

°C treatment factorhr

Hydrochloric acid 35 90 6.0 0.34

Sulphuric acid 40 90 6.0 0.2450 90 6.0 0.25

Methylamine 2.5 90 6.0 0.205 90 6.0 0.22

10 90 6.0 0.25

Ethylamine 2.5 60 3.0 0.2010 60 3.0 0.21

Sodium hydroxide 2.5 90 6.0 0.32Untreated film

(control) 0

order factor-show higher increase in crystallinity thanthat expected from density data. The film treated athigh concentration and at 60°C or a highertemperature develops opacity. This shows that alkalidiffuses into the film and creates micro voids. Thesusceptibility of PET to alkali attack is greater than toacid attack. This is obvious from the fact that over 5 %alkali at 90°C completely disintegrates the film. Endgroup analysis shows that the number of end groupsdoes not change appreciably until 90°C and 6 hrtreatment. But this is about the condition when the filmbegins to disintegrate. It thus means that chainscission does not take place until the structure isbroken down. It may not even be an indication of chainscission but of liberation of bonded groups. It is henceprobable that PET chain scission is not possible inalkali treatment.

Alkali treatment causes a pronounced fall in tensilestrength even at room temperature. This loss ofstrength is more pronounced than with acid. At roomtemperature, 20% NaOH in 24 hr shows 20% loss,whereas at 60°C, a loss of this magnitude is caused evenby 5 % alkali.

The above observations do not corroborate theearlier finding of Waters- that the alkali- PET reactionis a heterogeneous one and that principally it takesplace on the surface. End group analysis shows thatalkali does not give random chain scission as in thecase ofHC!. The film develops uniform cloudiness andthere is a rapid fall in tensile strength, indicating thatalkali diffuses inside and acts throughout the entirethickness of the film.

Amine treatment-Data pertaining to the effect oftreatment with methylamine and ethylamine arepresented in Tables 4 and 5 respectively. It is obvious

104

that crystallinity increases, as indicated by density, IRand X-ray data. The action is more pronounced athigher concentrations and higher temperatures. Undercomparable conditions ethylamine is less reactive thanmethylamine and needs higher concentration for thesame degree of degradation. The action of amines haspreviously been attributed to the removal of theamorphous portions. It is shown here to be moredrastic than that.

End group analysis shows marked increase in thenumber of end groups at high temperatures only andaround 10 % concentration. This shows that action atlower concentrations and at lower temperatures maybe restricted to the amorphous regions, since endgroup analysis and tensile strength data show verylittle change. Tensile strength, however, falls steeply inthe case of treatment at high temperatures and highconcentrations.

In the case of ethylamine, the diffusion coefficientseems to be low because of the larger molecular sizeand hence needs more vigorous conditions in terms ofconcentration and temperature for the same degree ofdegradation as in methylamine treatment. Thesuggested mechanism of chain scission is that an amidegroup is formed. However, this needs confirmation.End group analysis shows proportionate increase inCOOH and OH groups compared to untreated film,but the effect of CONH groups, if formed, on themethod of end group estimation has not yet beenstudied.

Piperidine treatment-Piperidine behaves as a cyclicaliphatic secondary amine and has a comparativelysmaller size. The action of piperidine, as seen from theresults presented in Table 6, is characteristicallydifferent and complex. Even at room temperature,there is a marked increase in density, but IRcrystallinity data show that at higher concentrationand temperature, the density increases, but the IRcrystallinity falls. The X-ray order factor does notshow any change even for sample of higher density.The results of end group analysis show interestingtrends. At lower concentration and at roomtemperature, the number of OH groups decreases,while the number of COOH groups increases. Forlonger duration of treatment, the number of OH andCOOH groups falls and the proportion ofOH groupsis less compared to that in the starting material.

Infrared spectrum does not show any piperidinebound and left in the film, so that there is no likelihoodof solvent remaining in complexed form. On treatmentat room temperature there is a slight fall in tensilestrength, but at high temperature, when the number ofend groups is much less, the fall in tensile strength isappreciable. The possibility that due to the action ofpiperidine the polymer has formed a complex

PADHYE & NADAF:HYDROLYSIS & AMINOLYSIS OF POLYETHYLENE TEREPHTHALATf

interchain bonded compact amorphous mass cannotexplain the fall in breaking strength. The action ofpiperidine on PET, though interesting, is yet to beunderstood.

ConclusionThree types of effects take place simultaneously

when PET film is treated with acids, alkalis, aminesand piperidine: (i) change in IR crystallinity, (ii)change in the number ofOH and COOH end groups,and (iii) development of opacity.

Treatment with acids, alkalis and amines causesincrease in crystallinity, as shown by X-ray, IR anddensity data. End group estimations show that chainscission takes place only under drastic conditions (highconcentrations of the reactants and high temperatureof treatment). For different reagents, chain scissionstarts under different conditions.

Except in the case of sulphuric acid treatment, in allother treatments, the film develops opacity, indicating

that all other reagents except H2S04 diffuse into thebody of the film. In the case of HCI, the attack seems tocause random depolymerization, while with H2S04

and alkalis, the end monomers seem to get liberated.

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Wiley and Sons Inc., New York), 1964.3 Davies T. Goldsmith P L, Revens D A S & Ward I M, J phys

Chem, 66 (1962) 175.4 Waters E, J Soc Dyers Colour, 66 (1950) 609.5 Rudakova T E, Moiseev Yu V, Chelykh A F & Zaikov G E,

World Text Abstr, 4 (1972) 2823.6 Kurita T, J Polym Sci, Polymer Phys edn, 13 (1975) 765.7 Overton J R & Haynes S K, J Polym Sci, 43 (Pt.C) (1973) 9.8 Mehta R E & Bell J p, J Polym Sci, II (A-2) (1973) 1793.9 Mocherla K K & Bell J P, J Po/ym Sci, II (A-2) (1973) 1779.

10 Sheldon R P & Blakey P R, Nature, Lond, 195 (1962) 172.II Padhye M R & Bhama Iyer P, Angew makromol Chern, 39(1974)

149.12 Addleman R L & Zichy V J, Polymer, 13 (1972) 391.

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