Thermal Degradation Studies of Some Strongly Acidic Ca-tion Exchange Resins

doi:10.4236/ojpc.2011.12007

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Open Journal of Physical Chemistry, 2011, 1, 45-54

doi:10.4236/ojpc.2011.12007 Published Online August 2011 (http://www.SciRP.org/journal/ojpc)

Thermal Degradation Studies of Some Strongly Acidic

Cation Exchange Resins

Pravin U. Singare*1, Ram S. Lokhande2, Rupa S. Madyal3

1Department of Chemistry, Bhavan’s College, Andheri, Mumbai, India

2Department of Chemistry, University of Mumbai, Vidyanagari, Santacruz, Mumbai, India

3Department of Chemistry, South Indians’ Welfare Society College, Sion, Mumbai, India

E-mail: [email protected]

Received April 19, 2011; revised June 13, 2011; accepted July 22, 2011

Abstract

The thermal degradation of some sulfonic cationites namely Amberlite IR-120, Indion-223 and Indion-225

was investigated using instrumental techniques like thermal analysis (TG) and Scanning Electron Micros-

copy (SEM). Fourier Transform Infrared Spectroscopy (FTIR) was used to characterize the resins degrada-

tion steps. The sulfonic cationites undergo degradation through dehydration, followed by decomposition of

sulfonic acid functional groups liberating SO2. The thermogravimetric analysis of above cationites at higher

temperature up to 520˚C, show mass loss of 61.61% and 25.43% respectively for Indion-223 and Indion-225,

while Amberlite IR-120 cationite get burned off completely.

Keywords: Sulfonic Cationites, Thermal Degradation, FTIR, SEM, Nuclear Resin, Thermal Analysis

1. Introduction

Ion-exchange resins are produced and commercialized in

a wide range of formulations with different characteris-

tics, and have now a large practical applicability in vari-

ous industrial processes, such as chemical, and nuclear

industry for treatment of liquid waste [1-16]. For their

versatile properties, the cationic resins are used both in

the ion exchange area and in the heterogeneous catalysis

field [17]. These resins exhibit a high exchange capacity

and an excellent osmotic shock resistance. So, the cati-

onic resins, produced with a high degree of purity, be-

came important as catalysts in various food technologies

[18] and for purification in heavy-water moderated nu-

clear reactors in nuclear industries [19-21]. In many

cases their use is limited by the relatively low thermal

stability [22]. Hence, knowledge of the thermal behavior

of cation exchange resins is necessary. Abundant data

exist on the thermal degradation of anion exchange res-

ins [23-25] and on carboxylic cationites with low acidity

[26-27]; literature seems to offer relatively poor informa-

tion on polystyrene-divinylbenzene sulfonic cationites

[28-33]. Therefore, in the present investigation thermal

degradation of strongly acidic sulfonic cationites was

performed to understand the degradation steps and to

compare the relative thermal stability.

2. Experimental

2.1. Materials

The following commercial cationites were used:

· Strongly acidic gel-type resin with sulfonic acid

functionality based on styrene-divinylbenzene matrix:

Amberlite IR-120 (Rohm and Haas Co, USA).

· Nuclear grade strongly acidic gel-type resin with

sulfonic acid functionality based on styrene-divinyl-

benzene matrix: Indion-223 (Ion Exchange India Ltd.,

Mumbai).

· Strongly acidic gel-type resin with sulfonic acid fun-

ctionality based on styrene-divinylbenzene matrix:

Indion-225 (Ion Exchange India Ltd., Mumbai).

The details regarding the physical properties of catio-

nites used are given in Table 1.

The soluble impurities of the resins were removed by

repeated soxhlet extraction using water and occasionally

with distilled methanol to remove non polymerized im-

purities. The resins were then dried over P2O5 in desic-

cators at room temperature.

2.2. Thermal Analysis

The thermogravimetric experiments were performed on a

46 P. U. SINGARE ET AL.

Table 1. The main characteristics of the investigated catio-

nites.

Cationites

Exchange

Capacity

(mEq./mL)

Particle size Moisture

Content (%)

Maximum

Temperature

Stability ˚C

Amberlite

IR-120 1.9 16 - 50 mesh 45 121

Indion-223 1.8 0.3 - 1.2 mm 53 120

Indion-225 2.0 0.3 - 1.2 mm 50 120

DTG-60H, (Shimadzu, Japan) thermal analysis system

between 30˚C - 550˚C using aluminum cell (6 mm in

diameter and 2.5 mm in depth). The measurements of

resin samples were carried out in nitrogen flow (50

mL· mi n –1) at heating rate (β = 10 K·min–1). The mass of

resin sample used was ~5 - 20 mg. In order to character-

ize the decomposition steps of the investigated ion-ex-

change resins, FTIR and Scanning Electron Microscopy

(SEM) were used in addition to thermal analysis.

2.3. FTIR Spectra

FTIR spectra (in 4000 - 450 cm–1 range) of thermal de-

composed samples, up to the characteristics mass-loss

steps temperatures, were recorded in KBr pellets (2 mg

cationite/200 mg KBr) using a FTIR PerkinElmer 1750

spectrophotometer.

Since in the thermal analysis, the major weight loss

was observed between 200˚C - 400˚C, the resin samples

were heated in an oven for 3h at 10˚C higher tempera-

tures above the maximum operating temperature, and

also at 200 and 400˚C. The thermal degradation of resin

was studied by comparing the spectra of fresh and heated

resin samples.

2.4. Scanning Electron Microscopy (SEM)

The thermal degradation studies of ion exchange resins

was also studied by examining the surface morphology

of fresh resin samples and samples heated at 400˚C using

JSM-6380LA Scanning Electron Microscope (Jeol Ltd.,

Japan).The powders were precisely fixed on an alumi-

num stub using double-sided graphite tape and then were

made electrically conductive by coating in a vaccum

with a thin layer of carbon, for 30 seconds and at 30 W.

The pictures were taken at an excitation voltage of 10 -

15 KV and a magnification of ×100 and ×130.

3. Results and Discussion

3.1. Characterization and Thermal Degradation

Study of Amberlite IR-120:

3.1.1. TGA Analysis

Figure 1 represents a dynamic weight loss profile of

Amberlite IR-120 from room temperature to 550˚C.

Thermogravimetric curve of Amberlite IR 120 shows

22% weight loss up to 200˚C due to moisture content and

the weight decreased gradually till 400˚C. Above 400˚C

whole compound burned off completely and weight loss

measurement was not possible.

3.1.2. FT IR Analysis

Figure 2 shows the IR spectrum of the fresh resin sam-

ple Amberlite IR-120. The bands at 2923 and 2876 cm–1

are due to the aliphatic C-H stretching absorbance of

methyl group in the main chain and in aromatic rings and

of methylene group respectively. SO2 asymmetric stre-

tching at 1382 cm–1. Strong band at 1652 cm–1 indicates

aromatic C=C bond. The four sharp peaks at 1009 cm–1

1037 cm–1, 1126 cm–1, 1186 cm–1 are due to SO3 sym-

metric stretching. The peaks at 1500 - 1600 cm–1 are due

to deformation and skeletal vibrations of C-H in DVB.

Bands appear at 2366 cm–1 which may be assigned to

O-H stretching vibration originating from the polymer.

At 200˚C, the 21% weight loss was observed without

any loss of peak in the IR spectra. At 400˚C IR investi-

gation indicates that the peaks in the region 1500 - 1000

cm–1 either shows a general broadening or no longer ex-

ists (Figure 3). Non-existence of the SO unit was con-

firmed by the absence of the peaks from 1500 - 1000cm–1,

with decomposition of the functional group i.e. sulfonic

portions of the ring. But slight broadening of the band is

observed at 1652 cm–1 for aromatic C=C bond remained

unchanged. This corresponds to the few chain scissions

in the DVB matrix.

3.1.3. SEM Anal ysi s

Figure 4, shows the surface morphology of Amberlite

IR-120 resins at room temperature indicating plane sph-

erical structure. At 400˚C, resin show large cracks and

thread like appearance on the surface (Figure 5).

3.2. Characterization and Thermal Degradation

Study of Indion-223:

3.2.1. TGA Analysis

Thermogravimetric curve of Indion—223H+ shown in

Figure 6. The 30% weight loss up to 200˚C can be at-

tributed to moisture content. The second major weight

loss begins at 270˚C and ends at 400˚C, which might be

due to slow degradation of side chain and loss of sul-

phonic functional group. The mass loss from 400˚C to

521˚C was gradual which might be due to degradation of

styrene/DVB matrix.

3.2.2. FT IR Analysis

he IR spectrum of Indion-223 in the 3700 - 400 cm−1

P. U. SINGARE ET AL.

Figure 1. TG curve of Amberlite IR-120.

Figure 2. IR spectrum of Amberlite IR-120 at room temperture.

P. U. SINGARE ET AL.

Figure 3. IR spectrum of Amberlite IR-120 at different tem-

perture.

Figure 4. Scanning electron micrograph of the surface of

the Amberlite IR-120 at room temperature.

Figure 5. Scanning electron micrograph of the surface of

the Amberlite IR-120 at 400˚C.

region is shown in Figure 7. FTIR spectral analysis

shows SO3 sharp symmetric stretching band at 1005 -

1126 cm–1. O-H stretching at 2364 cm–1. S-O stretching

at 668 cm–1. SO2 asymmetric stretching at 1382 cm–1.

C=C aromatic nucleus skeletal vibration band at 1500 -

1600 cm–1 and OH hydrogen bonded broad stretching

band at 3200 - 3500 cm–1. The band at 2900 cm–1 attrib-

uted to C-H stretching vibrations in the main chain and

in aromatic rings; the peaks at 1500 - 1600 cm–1 are due

to deformation and skeletal vibrations of C-H in Poly-

styrene/DVB.

FTIR investigation shows that that strong bands at 668

cm–1, 1019cm–1 and 1382 cm–1 which are related to SO

and 2364cm–1 stretching frequency of C-H units re-

mained upto 200˚C, but at 400˚C both the groups disap-

peared (Figure 8). This indicates that at 200˚C the 29.7%

weight loss is due to moisture, whereas 31.8% loss is due

to the functional group i.e. SO and breaking of C-H

bond.

3.2.3. SEM Anal ysi s

Surfaces of resins at room temperature (Figure 9) and at

400˚C (Figure 10) were examined by a Jeol JSM-

6380LA scanning electron microscope. It was found that

at 400˚C resin showed crack in the spherical structure

which supports breaking of polymer matrix at that tem-

perature.

3.3. Characterization and Thermal Degradation

Study of Indion-225:

3.3.1. TGA Analysis

Thermogravimetric curve of Indion-225 H+ is shown in

Figure 11. Thermogravimetric curve shows ~13% weight

loss up to 200˚C, corresponding to the moisture content.

Degradation of resin between 270˚C - 340˚C takes place

sharply and further gradually up to 521˚C which might

be due to decomposition of the sulphonic functional

group with rapid evolution of SO3 or SO2 showing mass

loss of ~12.5%.

3.3.2. FT IR Analysis

The IR spectrum of Indion-225 H+ in the 3700 - 400

cm–1 region is shown in Figure 12. FTIR spectral analy-

sis shows four sharp peaks at 1009 cm–1

, 1037 cm–1, 1126

cm–1, 1186 cm–1 are due to SO3 symmetric stretching. O-

H stretching at 2900 - 2400 cm–1. S-O stretching at 672

cm–1. C=C aromatic nucleus skeletal vibration band at

1550 - 1670 cm–1 and OH hydrogen bonded broad

stretching band at 3200 - 3500 cm–1. The sharp peak at

2900 cm–1 range attributed to C-H stretching skeletal

vibrations of C-H in Polystyrene/DVB.

The degradation occurs in a single step and mass loss

is 25% up to 521˚C. SO2 is the dominate product evolved

at 190˚C and 380˚C while water is also present during

the entire degradation pathway but in relatively small

amount. Loss of SO unit can also be confirmed by IR

investigation. The characteristic band for SO unit at 1009

cm–1

, 1037 cm–1, 1126 cm–1,1186 cm–1 are no longer exist

(Figure 13). The evolution of water occurs in the same

temperature regime as SO2, between 185 and 400˚C, as

spectrum at 200˚C shows broadened bands indicating

light decrease in SO content. This is likely due to the s

P. U. SINGARE ET AL.

Figure 6. TG curve of Indion-223.

Figure 7. IR spectrum of Indion-2223 at room temperature.

50 P. U. SINGARE ET AL.

Figure 8. IR spectrum of Indion-2223 at different temperature.

Figure 9. Scanning electron micrograph of the surface of

the Indion-223 at room temperature.

Figure 10. Scanning electron micrograph of the surface of

the Indion-223 at 400˚C.

formation of sulfurous acid by the process noted above.

Water is also evolved early in the degradation and this is

likely due to the loss of physically combined water as

has been observed for the other compounds [34].

3.3.3. SEM Anal ysi s

Figure 14 shows the surface morphology of the In-

dion-225 H+ at room temperature indicating plane sph-

erical structure. Similar to Indion-223 H+; Indion-225 H+

also shows crack on the spherical surface when heated at

400˚C (Figure 15)

4. Conclusions

From the FTIR analysis of three sulfonic acid cationites,

it was observed that the degradation takes place through

dehydration, followed by decomposition of sulfonic acid

functional groups. The thermal analysis shows that up to

200˚C, Indion-225 cationite shows mass loss of only

13%, as against mass loss of 21% and 30% shown by

Amberlite IR-120 and Indion-223 respectively. The

thermal analysis at a higher temperature up to 520˚C,

Amberlite IR-120 cationite gets completely burned,

while Indion-225 and Indion-223 shows total mass loss

of 25% and 62% respectively. Hence the thermal stabil-

ty of three cationites increases in the order of Amberlite i

P. U. SINGARE ET AL.

Figure 11. TG curve of Indion-225.

Figure 12. IR spectrum of Indion-2223 at room temperature.

52 P. U. SINGARE ET AL.

Figure 13. IR spectrum of Indion-2223 at different temperature.

Figure 14. Scanning electron micrograph of the surface of

the Indion-225 at room temperature.

Figure 15. Scanning electron micrograph of the surface of

the Indion-225 at 400˚C.

IR-120 < Indion-223 < Indion-225.

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