- Email: [email protected]
Characterization of EPDM rubber modified with maleic anhydride (MAH) by diffuse reflectance FTIR (DRIFT)
Polymer Testing 13 (1994) 25-34
Characterization of EPDM Rubber Modified with Maleic Anhydride (MAH) by Diffuse Reflectance FTIR (DRIFT) F. M. B. Coutinho* & M. I. P. Ferreira Instituto de Macromol6culas, Universidade Federal do Rio de Janeiro, CP 68.525, Rio de Janeiro, Brazil (Received 19 November 1992; accepted 10 March 1993)
ABSTRACT A rapid technique for determining bound M A H content in maleated EPDM rubbers has been established. It is based on the application of diffuse reflectance F T I R which permits the analysis of such products directly without any sample preparation other than removin 9 unreacted monomer and initiator. The spectrum obtained also allows the evaluation of the rubber's relative oxidation extent. Baseline and band choices as well as calculation methods required are discussed.
1 INTRODUCTION The synthesis of maleated E P D M elastomers basically aims at the modification of the apolar character of this rubber in order to improve its performance in specific applications such as compatibilization of polymer blends, 1 manufacture of thermoplastic elastomers, 2 and production of multipurpose lubricating oil additives. 3 The knowledge of bound MAH content in the grafted rubber is necessary not only to assign its end use, but also to choose the best grafting conditions. Three main techniques for analysing MAH content in modified polymers have been reported in the literature: direct titration of acid groups, 4 gravimetry, 5 and transmission infrared spectrometry. 6 7 The first method implies previous hydrolysis of the sample which cannot have any other source of carboxylic groups in order to provide correct * To whom correspondence should be addressed. 25 Polymer Testing 0142-9418/94/$07.00 © 1994 Elsevier Science Limited, England. Printed in Malta by Interprint Ltd.
26
F. M. B. Coutinho, M. I. P. Ferreira
values; furthermore, sample solubility in titrating media is required. Gravimetric determination is not a specific method to analyse succinic units content in the rubber because any gain or loss in weight can alter the results obtained. In the case of transmission IR (or FTIR) the main drawback is the sample preparation seeing that the sample shall be soluble, able to form transparent films or homogeneous mixtures with a nonabsorbing matrix. Up to now samples of maleated polymers have been quantitatively analysed by transmission infrared spectroscopy, applying standard solutions of pure succinic acid or esters, 6 and films of the modified copolymer. 7 It has been previously verified that oxidation is a side reaction that occurs when maleated EPDM is prepared by a bulk process using peroxide-type initiator. 8 Low-molecular-weight EPDM partially dissolves during sample purification, and the amount of weight lost varies according to the reaction conditions. Moreover, samples often have high insoluble content, thus presenting difficulty in moulding and obtaining transparent films (probably due to gelation). For the reasons cited above, current methods described in literature are not always adequate to evaluate the MAH content in modified EPDMs. Particularly in the case of products designed for impact modification of rigid plastics (in which a high gel content is desirable) alternative methods should be developed. It is known that the DRIFT accessory is used for samples that cannot be handled by transmittance such as IR-opaque or highly scattering materials, and samples sensitive to other preparations like KBr disks. This accessory has also high sensitivity and ability to analyse insoluble samples 'as is'. 9 However, quantitative analysis applying the DRIFT accessory is sometimes complicated by nonproportional relationships between concentration and pseudo-absorbance (A = - l o g R, R = reflectance). The low levels of MAH content in common maleated EPDM products could also make quantitative determination difficult. Thus, the objective of this work was to verify the adequacy of the DRIFT technique in determining the bound MAH content of modified EPDM elastomers, whether hydrolysed or not.
2 EXPERIMENTAL Varying amounts of standard succinic acid or succinic anhydride (purity more than 99.9%) were added to 40 g of EPDM rubbers in a Rheomix 600 internal mixer chamber (Haake Plastograph $40) at 100°C and 60 rpm. Ten minutes after that addition the system was opened, and the residues of acid (or anhydride) were carefully removed and weighed in order to
EPDM rubber modified with maleic anhydride
27
obtain the correct content of succinic groups in the rubber mixture. The main features of the E P D M s tested are listed in Table 1. Exxon's ASTM E P M standards 1° were also analysed in order to ratify the validity of the D R I F T method for quantitative characterization of ethylene-propylene copolymers. FTIR runs were carried out in a Perkin Elmer 1720 spectrometer equipped with the diffuse reflectance accessory, with 2 cm-1 resolution and 50 scans.
3 RESULTS AND DISCUSSION In the application of diffuse reflection in quantitative determinations the K u b e l k a - M u n k relationship between concentration and reflectance is often followed: 9 K F(R)= s -
(1-R~) 2 2R~
where F(R) = K u b e l k a - M u n k function
R~ =diffuse reflectance of an infinitely deep sample relative to a transparent matrix S = scattering coefficient K = absorption coefficient (proportional to concentration) However pseudo-absorbance (A) values can also show linear dependence on functional group concentration depending on the size and shape of the particles concerned. Thus, it was decided to check whether the usual K u b e l k a - M u n k transformation F(R) could be applied in the case of E P D M - g - M A H analysis, as well as to verify the adequacy of simpler pseudo-absorbance relationships before considering the technique a valid TABLE 1
Characteristics of EPDM Grades Used in DRIF'T Calibration Curves
Feature Propylene content (%w) Termonomer Iodine number Molecular weight (1VIn × 10- 3) Mw/Mn
EPDM A
EPDM B
EPDM C
43.0 ENB 6.0 51.0 2.8
27.0 ENB 15'0 66'0 2-9
40-0 ENB 29.0 58-0 3'6
28
F. M. B. Coutinho, M. I. P. Ferreira
tool for this q u a n t i t a t i v e c h a r a c t e r i z a t i o n . It was also i m p o r t a n t to check the possibility of q u a n t i f y i n g low c o n t e n t s of b o u n d succinic g r o u p s (as in c o m m e r c i a l samples) o n c e it is k n o w n that the D R I F T m e t h o d often amplifies certain c a r b o n y l reflectances.11 T h e linear c o r r e l a t i o n coefficient (r) o b t a i n e d with p s e u d o - a b s o r b a n c e (A) a n d K u b e l k a - M u n k (F(R)) b a n d ratios can be seen in T a b l e s 2 a n d 3 respectively. T h e b a n d ratio m e t h o d was c h o s e n in o r d e r to eliminate differences d u e to sample a m o u n t , shape a n d size, b y a p p l y i n g one characteristic b a n d of E P D M as an internal s t a n d a r d . TABLE 2
Pseudo-absorbance and Oxidation Index Results for DRIFT Analysis of EPDM Rubber Sample
ASTM stands EPDM B + SA EPDM B+SA EPDM B+SAH EPDM A+SAH EPDM B+SAH EPDM C+SAH EPDM A+SAH EPDM B+SAH EPDM C+SAH EPDM B-g-MAH
Baseline
Band ratio
Linear r
1220-642 1962-655 1803-1405 1962-655 1820-1405 1820-1405 1820-1405 1962-1405 1962-1405 1962-1405 1962-1405
A1156/A722
0-9945 0"8393 0"8981 0"9855 0'9920 0"9903 0"9834 1'29 a 1"42a 1-53a
A169o/A722 A169o/AI465 AtTao/A722 A178o/A1465 A17ao/At,65
AtTso/A1,6s A1713/At,65 A1713/At,6s A171a/A1465 AITI3/AI46S
1"50b
a Mean oxidation number. bTypical oxidation index. SA - Succinic acid. SAH - Succinic anhydride. TABLE 3
Kubelka-Munk Results for DRIFT Quantitative Analysis of EPDM Rubbers Containing Succinic Groups Sample
EPDM EPDM EPDM EPDM EPDM EPDM
B+SA B+SA B + SAH A+SAH B+SAH C+SAH
Baseline
1962-655 1803-1405 1962-655 1820-1405 1820-1405 1820-1405
SA - Succinic acid. SAH - Succinic anhydride.
Band ratio
F(R)169o/F(R)722 F(R)t69o/F(R)1465 F(R)t 7ao/F(R)722 F(R)tTso/F(R)1465 F(R)t7so/F(R)t465
F(R)17so/F(R)t465
Linear r
-0-7561 -0"8688 - 0-7250 -0"7004 -0"7463 -0"7900
EPDM rubber modified with maleic anhydride 0,7 A
I
bl
0.6 _
I
bz
bz
/,L~ F,~
_
3
29
I
b
.
[4
_
- "~'¢V
0.5 I
0.4 0.3 0.2
I
2000
I
1600
Notes Ib 1Ib z Ib]-
I
t200 CM-1
800
400
: Base-line at 1962. cm "t Base-line at t820 cm -I Base-line of t465 cm-4
Ib 4- Base-line at 655 cm -1 b1- Absortion band at t 7 8 0 cm -t b2- Absortion
band
b3- Abs0rtion
band at 1465 cm "1
b - Absortion
bond
4
at 171.?, cm "1 at
722 cm -t
Fig. 1. Typical spectrum of EPDM containing succinic anhydride used in DRIFT calibration curves.
0.9472
I
I
I
A 0,7672 0,5872 0.4072
0.2272 t 0.0472 2000
1
I
I
4600
t200
800
400
CM -1
Fig. 2. Typical spectrum of EPDM-g-MAH to be analysed by DRIFT technique.
F. M. B. Coutinho, M. L. P. Ferreira
30
z
/""0 ...z" ./"
/
, iz
J .d
.t" .J ../
0
z" e"
2J
/:
J
/
J
e,z" .'e/ 0 fJ
/ /
.Ij i"
/
/
d"
/
/
/
/
f"
I
~tccinic ~Mdrido Content (weigM 2) Fig. 3. DRIFT calibration curve for EPDM A.
It was noticed that pseudo-absorbance calibration curves produced better correlations than the Kubelka-Munk equation. The values of correlation coefficient (r) were strongly dependent on baseline choice. The use of global instead of individual baselines led to better fittings as well as the use of spectral bands closer in frequency. Although the 722 cm- ~ band (long -(CH2).- sequences) has been adequate as an internal standard for unmodified rubber, the pseudo-absorbance at 1465 cm- t (methylene rocking vibration) exhibits r values higher than those of the 722 cm- 1 band for standards containing succinic groups. When EPDM-g-MAH samples produced by a bulk technique were analysed they showed values higher than possible either for A I69o/A722 (in the case of partially hydrolysed samples) or for A~vso/A,722 (non-
E P D M rubber modified with maleic anhydride
31
I A
tt ¢
./"
\
/
..."
j"'" 0
2~
/
¢~
...."
0...-" ...-
0
.~...........
,~
/"¢ ./ j-
IJ ~
.~" /." . ...-
1.
~,
.!
o
..-" .." ..../
o
0O J
~
[
Succinic AnNdride Content (weight. 2)
Fig. 4. DRIFT c a l i b r a t i o n curve for EPDM B.
hydrolysed materials). This result indicates that the non-quantitative character of the 722 cm-1 band ratios of EPDMs containing succinic groups can be due not only to changing of the scattering coefficient with frequency, but also to the decrease of long ethylene sequences content caused by chain breaking. Carbonyl bands attributed to degradative oxidation by-products (1710-1742 cm-1) can be seen in typical spectra shown in Figs 1 and 2. The extent of oxidation can be infered from the maximum pseudo-absorbance value (at 1713cm -1) using the band at 1465cm -1 as internal standard (Table 2). Thus, AI713/A1465 ratio indicates that oxidation is more intense in EPDMgoMAH samples (produced with peroxide initiator) than in succinic standards.
32
F. M. B. Coutinho, M. I. P. Ferreira
The presence of oxidation by-products even in the standards used for preparing the calibration curves also explains why succinic-anhydridecontaining mixtures gave better fittings than their succinic-acid counterparts. Carbonyl bands due to oxidation overlap with succinic acid pseudoabsorption at 1690cm -1 and consequently generates higher deviation from linear behaviour of A 1 6 9 o band ratios. It is also noticed that the higher the diene content of E P D M rubber in the standard samples the worse were the r values obtained. This is in agreement with the fact that high bound diene in E P D M reduces its resistance to oxidation 12 and causes more disturbance in the whole spectrum. ~3 Furthermore, it can be noticed in Figs 3 to 5 that as the
/
/. /
/ /y"./
/
2~
/
/
S
/ I i
/
i
/
./
/
..~/"
/
/
0/" /
/ ./'/ /
/
j/ ./" /..
Succinic ~l~dride Content (weight Z) Fig. 5. D R I F T calibration curve for E P D M C.
EPDM rubber modified with maleic anhydride
33
diene content of the base rubber increases the linear coefficient (b) of the adjusted straight line also increases. The b value indicates the error due to baseline drawing (residual pseudo-absorbance at 1780 c m - 1) once the (0,0) theoretical point was included in all the fittings. The increase in carbonyl absorptions derived from oxidation by-products can be confirmed in Table 2 by the oxidation index of the three E P D M s used.
4 CONCLUSION The determination of bound MAH content in E P D M - g - M A H polymers can be satisfactorily achieved by applying the D R I F T technique. To establish good fittings for calibration curves, not only the correct choice of baseline and bands are critical, but so also is the application of correct treatment of data. In this study the best procedure was to use global baselines, spectral bands close in frequency, and pseudo-absorbance instead of KubelkaMunk values. Linear correlations obtained for succinic anhydride samples were better than those of succinic acid ones mainly because of degradative oxidation by-products interference in the spectra. The method described in this work permits evaluation of succinicgroup content in insoluble E P D M - g - M A H polymers which otherwise would be very difficult.
ACKNOWLEDGEMENTS To Conselho Nacional de Desenvolvimento Cientifico e Tecnol6gico (CNPq), to Nitriflex SA Industria e Com6rcio, and to Pirelli Cabos SA for the financial support of this work. To professor Elisabeth E. C. Monteiro for the helpful discussion on infrared quantitative determinations.
REFERENCES 1. Gaylord, N. G., Use surfactants to blend polymers. Chemtech, July (1989) 435--8. 2. Caywood, S. W., Thermoplastic elastomers containing an adduct prepared from maleic anhydride and an elastomeric copolymer. Patent DE 2.401.149 to Du Pont (US Appl. l0 Jan. 1973). 3. Elliot, R. L. & Gardiner, J. B., Improved lubricating oil additives. Patent DE 2.818.012 to Exxon R&D Co. (US Appl. 29 Apr. 1977).
34
F. M. B. Coutinho, M. L. P. Ferreira
4. De Vito, G., Lanzetta, G. M., Malinconico, M., Musto, P. & Palumbo, R., Functionalization of an amorphous ethylene-propylene copolymer by free radical initiated grafting of unsaturated molecules. J. Polymer Science, Polym. Chem. Ed., 22 (1984) 1335-47. 5. Minoura, Y., Minoru, U., Mizunuma, S. & Mareo, O., The reaction of polypropylene with maleic anhydride. J. Applied Polymer Science, 13 (1969) 1625-40. 6. Saier, E. L., Petrkis, L., Cousins, L. R., Heilman, W. J. & Itzel, J. F., Infrared and nuclear magnetic resonance of maleic anhydride copolymers and their half esters. J. Applied Polymer Science, 12 (1968) 2191-200. 7. Oosterbrink, A. J., Borggreve, R. J. M. & Gaymans, R. J., The modification of EPDM rubber with maleic anhydride by reaction blending. Proc. Int. Meeting Polym. Sci. Tech., Limburg, Netherlands, 1988, pp. 123-7. 8. Ferreira, M. I. P. & Coutinho, F. M. B., Chemical modification of EPDM rubbers with maleic anhydride I. Characterization of reaction by-products. Simpbsio lberoamericano de Pol~meros, Madrid, Spain, July 1992, pp. 444-6. 9. Cole, K. C., Noel, D. & Hechler, J. J., Crystallinity in PPS-carbon composites: a study using diffuse reflection FTIR spectroscopy and differential scanning calorimetry. J. Applied Polymer Science, 39 (1990) 1887-902. 10. ASTM D3900-86, Rubber, Raw - - determination of ethylene units in EPM and EPDM, ASTM Standards for Rubbers, V.09.01. American Society for Testing and Materials, MO, USA, 1986, pp. 905-15. 11. Graf, R. T., Koenig, J. L. & Ishida H., Quantitative analysis of polymeric fibres by drifts using optical data. In Fourier Transform Infrared Characterization of Polymers. Plenum Press, NY, USA, 1987, pp. 357-413. 12. Sant'Anna, C. M. R., Abarca, J. R. & Monteiro, E. E. C., Study of termonomer influence on synthesis and properties of EPDM terpolymers. MSc Thesis, Instituto de Macromol6culas, UFRJ, Rio de Janeiro, Brazil, 1990.
Characterization of EPDM Rubber Modified with Maleic Anhydride (MAH) by Diffuse Reflectance FTIR (DRIFT) F. M. B. Coutinho* & M. I. P. Ferreira Instituto de Macromol6culas, Universidade Federal do Rio de Janeiro, CP 68.525, Rio de Janeiro, Brazil (Received 19 November 1992; accepted 10 March 1993)
ABSTRACT A rapid technique for determining bound M A H content in maleated EPDM rubbers has been established. It is based on the application of diffuse reflectance F T I R which permits the analysis of such products directly without any sample preparation other than removin 9 unreacted monomer and initiator. The spectrum obtained also allows the evaluation of the rubber's relative oxidation extent. Baseline and band choices as well as calculation methods required are discussed.
1 INTRODUCTION The synthesis of maleated E P D M elastomers basically aims at the modification of the apolar character of this rubber in order to improve its performance in specific applications such as compatibilization of polymer blends, 1 manufacture of thermoplastic elastomers, 2 and production of multipurpose lubricating oil additives. 3 The knowledge of bound MAH content in the grafted rubber is necessary not only to assign its end use, but also to choose the best grafting conditions. Three main techniques for analysing MAH content in modified polymers have been reported in the literature: direct titration of acid groups, 4 gravimetry, 5 and transmission infrared spectrometry. 6 7 The first method implies previous hydrolysis of the sample which cannot have any other source of carboxylic groups in order to provide correct * To whom correspondence should be addressed. 25 Polymer Testing 0142-9418/94/$07.00 © 1994 Elsevier Science Limited, England. Printed in Malta by Interprint Ltd.
26
F. M. B. Coutinho, M. I. P. Ferreira
values; furthermore, sample solubility in titrating media is required. Gravimetric determination is not a specific method to analyse succinic units content in the rubber because any gain or loss in weight can alter the results obtained. In the case of transmission IR (or FTIR) the main drawback is the sample preparation seeing that the sample shall be soluble, able to form transparent films or homogeneous mixtures with a nonabsorbing matrix. Up to now samples of maleated polymers have been quantitatively analysed by transmission infrared spectroscopy, applying standard solutions of pure succinic acid or esters, 6 and films of the modified copolymer. 7 It has been previously verified that oxidation is a side reaction that occurs when maleated EPDM is prepared by a bulk process using peroxide-type initiator. 8 Low-molecular-weight EPDM partially dissolves during sample purification, and the amount of weight lost varies according to the reaction conditions. Moreover, samples often have high insoluble content, thus presenting difficulty in moulding and obtaining transparent films (probably due to gelation). For the reasons cited above, current methods described in literature are not always adequate to evaluate the MAH content in modified EPDMs. Particularly in the case of products designed for impact modification of rigid plastics (in which a high gel content is desirable) alternative methods should be developed. It is known that the DRIFT accessory is used for samples that cannot be handled by transmittance such as IR-opaque or highly scattering materials, and samples sensitive to other preparations like KBr disks. This accessory has also high sensitivity and ability to analyse insoluble samples 'as is'. 9 However, quantitative analysis applying the DRIFT accessory is sometimes complicated by nonproportional relationships between concentration and pseudo-absorbance (A = - l o g R, R = reflectance). The low levels of MAH content in common maleated EPDM products could also make quantitative determination difficult. Thus, the objective of this work was to verify the adequacy of the DRIFT technique in determining the bound MAH content of modified EPDM elastomers, whether hydrolysed or not.
2 EXPERIMENTAL Varying amounts of standard succinic acid or succinic anhydride (purity more than 99.9%) were added to 40 g of EPDM rubbers in a Rheomix 600 internal mixer chamber (Haake Plastograph $40) at 100°C and 60 rpm. Ten minutes after that addition the system was opened, and the residues of acid (or anhydride) were carefully removed and weighed in order to
EPDM rubber modified with maleic anhydride
27
obtain the correct content of succinic groups in the rubber mixture. The main features of the E P D M s tested are listed in Table 1. Exxon's ASTM E P M standards 1° were also analysed in order to ratify the validity of the D R I F T method for quantitative characterization of ethylene-propylene copolymers. FTIR runs were carried out in a Perkin Elmer 1720 spectrometer equipped with the diffuse reflectance accessory, with 2 cm-1 resolution and 50 scans.
3 RESULTS AND DISCUSSION In the application of diffuse reflection in quantitative determinations the K u b e l k a - M u n k relationship between concentration and reflectance is often followed: 9 K F(R)= s -
(1-R~) 2 2R~
where F(R) = K u b e l k a - M u n k function
R~ =diffuse reflectance of an infinitely deep sample relative to a transparent matrix S = scattering coefficient K = absorption coefficient (proportional to concentration) However pseudo-absorbance (A) values can also show linear dependence on functional group concentration depending on the size and shape of the particles concerned. Thus, it was decided to check whether the usual K u b e l k a - M u n k transformation F(R) could be applied in the case of E P D M - g - M A H analysis, as well as to verify the adequacy of simpler pseudo-absorbance relationships before considering the technique a valid TABLE 1
Characteristics of EPDM Grades Used in DRIF'T Calibration Curves
Feature Propylene content (%w) Termonomer Iodine number Molecular weight (1VIn × 10- 3) Mw/Mn
EPDM A
EPDM B
EPDM C
43.0 ENB 6.0 51.0 2.8
27.0 ENB 15'0 66'0 2-9
40-0 ENB 29.0 58-0 3'6
28
F. M. B. Coutinho, M. I. P. Ferreira
tool for this q u a n t i t a t i v e c h a r a c t e r i z a t i o n . It was also i m p o r t a n t to check the possibility of q u a n t i f y i n g low c o n t e n t s of b o u n d succinic g r o u p s (as in c o m m e r c i a l samples) o n c e it is k n o w n that the D R I F T m e t h o d often amplifies certain c a r b o n y l reflectances.11 T h e linear c o r r e l a t i o n coefficient (r) o b t a i n e d with p s e u d o - a b s o r b a n c e (A) a n d K u b e l k a - M u n k (F(R)) b a n d ratios can be seen in T a b l e s 2 a n d 3 respectively. T h e b a n d ratio m e t h o d was c h o s e n in o r d e r to eliminate differences d u e to sample a m o u n t , shape a n d size, b y a p p l y i n g one characteristic b a n d of E P D M as an internal s t a n d a r d . TABLE 2
Pseudo-absorbance and Oxidation Index Results for DRIFT Analysis of EPDM Rubber Sample
ASTM stands EPDM B + SA EPDM B+SA EPDM B+SAH EPDM A+SAH EPDM B+SAH EPDM C+SAH EPDM A+SAH EPDM B+SAH EPDM C+SAH EPDM B-g-MAH
Baseline
Band ratio
Linear r
1220-642 1962-655 1803-1405 1962-655 1820-1405 1820-1405 1820-1405 1962-1405 1962-1405 1962-1405 1962-1405
A1156/A722
0-9945 0"8393 0"8981 0"9855 0'9920 0"9903 0"9834 1'29 a 1"42a 1-53a
A169o/A722 A169o/AI465 AtTao/A722 A178o/A1465 A17ao/At,65
AtTso/A1,6s A1713/At,65 A1713/At,6s A171a/A1465 AITI3/AI46S
1"50b
a Mean oxidation number. bTypical oxidation index. SA - Succinic acid. SAH - Succinic anhydride. TABLE 3
Kubelka-Munk Results for DRIFT Quantitative Analysis of EPDM Rubbers Containing Succinic Groups Sample
EPDM EPDM EPDM EPDM EPDM EPDM
B+SA B+SA B + SAH A+SAH B+SAH C+SAH
Baseline
1962-655 1803-1405 1962-655 1820-1405 1820-1405 1820-1405
SA - Succinic acid. SAH - Succinic anhydride.
Band ratio
F(R)169o/F(R)722 F(R)t69o/F(R)1465 F(R)t 7ao/F(R)722 F(R)tTso/F(R)1465 F(R)t7so/F(R)t465
F(R)17so/F(R)t465
Linear r
-0-7561 -0"8688 - 0-7250 -0"7004 -0"7463 -0"7900
EPDM rubber modified with maleic anhydride 0,7 A
I
bl
0.6 _
I
bz
bz
/,L~ F,~
_
3
29
I
b
.
[4
_
- "~'¢V
0.5 I
0.4 0.3 0.2
I
2000
I
1600
Notes Ib 1Ib z Ib]-
I
t200 CM-1
800
400
: Base-line at 1962. cm "t Base-line at t820 cm -I Base-line of t465 cm-4
Ib 4- Base-line at 655 cm -1 b1- Absortion band at t 7 8 0 cm -t b2- Absortion
band
b3- Abs0rtion
band at 1465 cm "1
b - Absortion
bond
4
at 171.?, cm "1 at
722 cm -t
Fig. 1. Typical spectrum of EPDM containing succinic anhydride used in DRIFT calibration curves.
0.9472
I
I
I
A 0,7672 0,5872 0.4072
0.2272 t 0.0472 2000
1
I
I
4600
t200
800
400
CM -1
Fig. 2. Typical spectrum of EPDM-g-MAH to be analysed by DRIFT technique.
F. M. B. Coutinho, M. L. P. Ferreira
30
z
/""0 ...z" ./"
/
, iz
J .d
.t" .J ../
0
z" e"
2J
/:
J
/
J
e,z" .'e/ 0 fJ
/ /
.Ij i"
/
/
d"
/
/
/
/
f"
I
~tccinic ~Mdrido Content (weigM 2) Fig. 3. DRIFT calibration curve for EPDM A.
It was noticed that pseudo-absorbance calibration curves produced better correlations than the Kubelka-Munk equation. The values of correlation coefficient (r) were strongly dependent on baseline choice. The use of global instead of individual baselines led to better fittings as well as the use of spectral bands closer in frequency. Although the 722 cm- ~ band (long -(CH2).- sequences) has been adequate as an internal standard for unmodified rubber, the pseudo-absorbance at 1465 cm- t (methylene rocking vibration) exhibits r values higher than those of the 722 cm- 1 band for standards containing succinic groups. When EPDM-g-MAH samples produced by a bulk technique were analysed they showed values higher than possible either for A I69o/A722 (in the case of partially hydrolysed samples) or for A~vso/A,722 (non-
E P D M rubber modified with maleic anhydride
31
I A
tt ¢
./"
\
/
..."
j"'" 0
2~
/
¢~
...."
0...-" ...-
0
.~...........
,~
/"¢ ./ j-
IJ ~
.~" /." . ...-
1.
~,
.!
o
..-" .." ..../
o
0O J
~
[
Succinic AnNdride Content (weight. 2)
Fig. 4. DRIFT c a l i b r a t i o n curve for EPDM B.
hydrolysed materials). This result indicates that the non-quantitative character of the 722 cm-1 band ratios of EPDMs containing succinic groups can be due not only to changing of the scattering coefficient with frequency, but also to the decrease of long ethylene sequences content caused by chain breaking. Carbonyl bands attributed to degradative oxidation by-products (1710-1742 cm-1) can be seen in typical spectra shown in Figs 1 and 2. The extent of oxidation can be infered from the maximum pseudo-absorbance value (at 1713cm -1) using the band at 1465cm -1 as internal standard (Table 2). Thus, AI713/A1465 ratio indicates that oxidation is more intense in EPDMgoMAH samples (produced with peroxide initiator) than in succinic standards.
32
F. M. B. Coutinho, M. I. P. Ferreira
The presence of oxidation by-products even in the standards used for preparing the calibration curves also explains why succinic-anhydridecontaining mixtures gave better fittings than their succinic-acid counterparts. Carbonyl bands due to oxidation overlap with succinic acid pseudoabsorption at 1690cm -1 and consequently generates higher deviation from linear behaviour of A 1 6 9 o band ratios. It is also noticed that the higher the diene content of E P D M rubber in the standard samples the worse were the r values obtained. This is in agreement with the fact that high bound diene in E P D M reduces its resistance to oxidation 12 and causes more disturbance in the whole spectrum. ~3 Furthermore, it can be noticed in Figs 3 to 5 that as the
/
/. /
/ /y"./
/
2~
/
/
S
/ I i
/
i
/
./
/
..~/"
/
/
0/" /
/ ./'/ /
/
j/ ./" /..
Succinic ~l~dride Content (weight Z) Fig. 5. D R I F T calibration curve for E P D M C.
EPDM rubber modified with maleic anhydride
33
diene content of the base rubber increases the linear coefficient (b) of the adjusted straight line also increases. The b value indicates the error due to baseline drawing (residual pseudo-absorbance at 1780 c m - 1) once the (0,0) theoretical point was included in all the fittings. The increase in carbonyl absorptions derived from oxidation by-products can be confirmed in Table 2 by the oxidation index of the three E P D M s used.
4 CONCLUSION The determination of bound MAH content in E P D M - g - M A H polymers can be satisfactorily achieved by applying the D R I F T technique. To establish good fittings for calibration curves, not only the correct choice of baseline and bands are critical, but so also is the application of correct treatment of data. In this study the best procedure was to use global baselines, spectral bands close in frequency, and pseudo-absorbance instead of KubelkaMunk values. Linear correlations obtained for succinic anhydride samples were better than those of succinic acid ones mainly because of degradative oxidation by-products interference in the spectra. The method described in this work permits evaluation of succinicgroup content in insoluble E P D M - g - M A H polymers which otherwise would be very difficult.
ACKNOWLEDGEMENTS To Conselho Nacional de Desenvolvimento Cientifico e Tecnol6gico (CNPq), to Nitriflex SA Industria e Com6rcio, and to Pirelli Cabos SA for the financial support of this work. To professor Elisabeth E. C. Monteiro for the helpful discussion on infrared quantitative determinations.
REFERENCES 1. Gaylord, N. G., Use surfactants to blend polymers. Chemtech, July (1989) 435--8. 2. Caywood, S. W., Thermoplastic elastomers containing an adduct prepared from maleic anhydride and an elastomeric copolymer. Patent DE 2.401.149 to Du Pont (US Appl. l0 Jan. 1973). 3. Elliot, R. L. & Gardiner, J. B., Improved lubricating oil additives. Patent DE 2.818.012 to Exxon R&D Co. (US Appl. 29 Apr. 1977).
34
F. M. B. Coutinho, M. L. P. Ferreira
4. De Vito, G., Lanzetta, G. M., Malinconico, M., Musto, P. & Palumbo, R., Functionalization of an amorphous ethylene-propylene copolymer by free radical initiated grafting of unsaturated molecules. J. Polymer Science, Polym. Chem. Ed., 22 (1984) 1335-47. 5. Minoura, Y., Minoru, U., Mizunuma, S. & Mareo, O., The reaction of polypropylene with maleic anhydride. J. Applied Polymer Science, 13 (1969) 1625-40. 6. Saier, E. L., Petrkis, L., Cousins, L. R., Heilman, W. J. & Itzel, J. F., Infrared and nuclear magnetic resonance of maleic anhydride copolymers and their half esters. J. Applied Polymer Science, 12 (1968) 2191-200. 7. Oosterbrink, A. J., Borggreve, R. J. M. & Gaymans, R. J., The modification of EPDM rubber with maleic anhydride by reaction blending. Proc. Int. Meeting Polym. Sci. Tech., Limburg, Netherlands, 1988, pp. 123-7. 8. Ferreira, M. I. P. & Coutinho, F. M. B., Chemical modification of EPDM rubbers with maleic anhydride I. Characterization of reaction by-products. Simpbsio lberoamericano de Pol~meros, Madrid, Spain, July 1992, pp. 444-6. 9. Cole, K. C., Noel, D. & Hechler, J. J., Crystallinity in PPS-carbon composites: a study using diffuse reflection FTIR spectroscopy and differential scanning calorimetry. J. Applied Polymer Science, 39 (1990) 1887-902. 10. ASTM D3900-86, Rubber, Raw - - determination of ethylene units in EPM and EPDM, ASTM Standards for Rubbers, V.09.01. American Society for Testing and Materials, MO, USA, 1986, pp. 905-15. 11. Graf, R. T., Koenig, J. L. & Ishida H., Quantitative analysis of polymeric fibres by drifts using optical data. In Fourier Transform Infrared Characterization of Polymers. Plenum Press, NY, USA, 1987, pp. 357-413. 12. Sant'Anna, C. M. R., Abarca, J. R. & Monteiro, E. E. C., Study of termonomer influence on synthesis and properties of EPDM terpolymers. MSc Thesis, Instituto de Macromol6culas, UFRJ, Rio de Janeiro, Brazil, 1990.