In situ analysis of sizing agents on fibre reinforcements by near-infrared light-fibre optics spectroscopy

SPECTROSCOPY ELSEVIER

Vibrational Spectroscopy 15 (1997) 43-51

In situ analysis of sizing agents on fibre reinforcements by near-infrared light-fibre optics spectroscopy K. Kitagawa a, S. Hayasaki b, y. Ozaki c,, a Department of Applied Chemistry, Kyoto Municipal Institute oflndustrial Research, Chudoji, Shimogyo-ku, Kyoto 600, Japan b Faculty of Textile Science, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606, Japan c School of Science, Kwansei Gakuin University, Uegahara, Nishinomiya 662, Japan

Received 24 January 1997; accepted 25 April 1997

Abstract

Sizing agents on sized fibre reinforcements were analyzed in situ by means of near-infrared (NIR) light-fibre optics spectroscopy. For the sized aramid knitted fabrics, characteristic NIR bands of epoxy and polyethylene types of sizing agents were superimposed on the spectrum of non-treated aramid fabrics. The spectra of non-treated aramid knitted fabrics and aramid fabrics with the two different sizing agents were clearly distinguished without using any chemometric analysis. In the case of sized glass strand, the formation of an amide bond between maleic anhydride-modified polypropylene binder and an amino silane coupling agent on glass fibers could be monitored by NIR light-fibre optics spectroscopy. © 1997 Elsevier Science B.V. Keywords: Near-infrared spectroscopy; In situ analysis; Light-fibre; Aramid fibre; Glass fibre; Sizing agent; Nondestructive analysis;

Composites

1. I n t r o d u c t i o n

It has been recognized that near-infrared (NIR) spectroscopy is very useful for textile research [ 1-7]. Since textile test specimens are in solid form, diffuse reflectance NIR spectroscopy provides a special advantage by saving extensive sample preparation for characterizing textile materials such as fibre, y a m and fabric. Previous investigations have shown that NIR spectroscopy is a simple, rapid and accurate technique for evaluating some properties and characteristics of textile materials. For example, Ghosh and Roy [8] investigated NIR spectra of cotton and developed calibration equations for monitoring the sugar content in it; Ticher and Luk [9] proposed calibration equations for several properties of cotton/polyester blends based upon their NIR spectra and Rodgers [10] reported a NIR analysis of moisture and finish-on-fibre as a lubricant for nylon fibre. High performance fibres such as glass, carbon and aramid fibres have been adopted as reinforcements in polymer composites. Basic mechanical properties of the fibre reinforced polymer composites depend not only on

*

Corresponding author. Fax: (81-798) 510-914.

0924-2031/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved. PII S0924-203 1(97)00022-2

44

K. Kitagawa et al. / Vibrational Spectroscopy 15 (1997) 43-51

fibre and matrix properties, but also on interfacial properties. Recently, the concept of 'interphase' has been widely recognized [11,12]. This concept is that the interface between fiber and matrix is not a surface but a region that has some amount of volume. The authors have been studying the interphase properties of aramid fibre reinforced composites [13-16]. Surface treatments for a reinforcement are very effective in making the useful interphase in the composite materials. Therefore, it is important to analyze in situ the surface properties of reinforcements after the treatments. Surface analytical methods, such as Fourier-transform (FT)-IR and X-ray photo-electronic spectroscopy (XPS), have been utilized for investigating the surface properties of treated reinforcement. However, FT-IR spectroscopy is not always suitable for the in situ analysis because aramid fibers have strong absorptions in the region of mid IR. In contrast, NIR spectroscopy holds considerable promise in the surface characterization because absorbances in the NIR region are generally not strong [1,2]. Another advantage of NIR spectroscopy over IR spectroscopy is the use of light-fibre probe; one can examine the surface properties of textiles in nondestructive manner by use of NIR light-fibre optics spectroscopy. However, to our best knowledge, NIR spectroscopy has never been employed for the surface analysis of high performance fibers. In this study, sizing agents on sized fibre reinforcements were directly analyzed without any sample pretreatments using NIR light-fibre optics spectroscopy. Furthermore, we discussed the relationship between the analytical results and the effects of sizing treatment on mechanical properties of composites.

2. Experimental Aramid yams (KEVLAR 49, l140d, 768 filaments, 12 ~ m in filament diameter, Du Pont-Toray Co.) were weft knitted on a flat knitting machine to produce plain knitted fabric. Fig. 1 shows the chemical structure of aramid and a photograph of the aramid knitted fabric. Usually, received fibres from a fibre manufacturing company were treated by a binder such as oils and surfactants to protect the fibre surface and improve handleability. In order to remove the binder the knitted fabric was immersed in cyclohexane under ultrasonic

H I

_•H

0 it

0-] ,~--------~ il|

N~N--C~C-~ [

,~----~,

Chemical structure of aramid.

_3n

Fig. 1. A chemicalstructureof the aramid and photographof the plain knittedfabric.

45

K. Kitagawa et al. / Vibrational Spectroscopy 15 (1997) 43-51

waves. This fabric was called 'refined' fabric. Two kinds of sizing treatments were performed on the refined knitted fabrics; one used a bisphenol-A epoxy dispersion-based sizing agent (EA-7) and the other employed a polyethylene type dispersion-based sizing agent (PE-400), supplied by Nippon-NSC. The bisphenol-A epoxy disperison-based sizing agent (EA-7) consisted of diglycidyl ether of bisphenol (DGEBA), reactive diluent agent, surfactant and water. The structure of DGEBA is shown below. o

F

c~

oN

/\

~

I

I

q

c~

"

I

CH,--CH - c ~ : - o ~ / ~ c ~ ¢ ~ o - - c ~ - c N - - a - ~ - I - o ~ Y c ~ / ~ o

o

/\.,

C~-CH-CN,

Mean molecular weight (M w = 388) of this compound was determined by gel permeation chromatography (GPC), If n = 0 and 1, M w is 340 and 624, respectively, so that in the present case, n can be calculated to be 0.17. The reactive diluent agent, which reduces the viscosity of DGEBA and is involved in the crosslinking reaction, was added to DGEBA to improve the impregnation into the aramid fabric. E-glass strand (100 filaments, 24 lxm in filament diameter) was obtained from Nippon Glass Fiber Co. The glass strand was treated at the company with both an amino silane coupling agent and a sizing agent which consists of maleic anhydride-modified polypropylene binder. Fig. 2 shows a photograph of the sized glass strand. In this study two kinds of sizing agents, L type and H10 type, were used for the glass strand; they were modified polypropylene of low (5000 in mean molecular weight) and high (20 000-40 000 in mean molecular weight) molecular weights, respectively. NIR spectra in the 1000-2500 nm region were measured by use of a Bran + Luebbe InfraProver II FT-NIR spectrometer equipped with an optical fibre probe. The optical fibre used was a fluoride glass fibre (KDD T-FF fibre; KDD Technology Co.) [17]. Diffuse reflectance measurements were carried out by putting the probe directly on either the sized aramid fabric placed on a ceramic plate or the sized glass strand wound round the plate. The NIR measurements were repeated five times for each part in one sample. Before the NIR measurements, the samples were dried in a oven for 40 min at 110°C. Except for this, no sample pretreatment was performed.

3. Results and discussion 3.1. In situ analysis o f sizing agents on aramid knitted fabrics

Fig. 3 shows NIR spectra of aramid knitted fabrics with the different sizing systems, together with the spectrum of the 'refined' fabric. The terms, 'Epoxy 5 wt% sized' and 'PE 5 wt% sized', indicate the spectra

Fig. 2. Sizedglass strand.

K. Kitagawa et al. / Vibrational Spectroscopy 15 (1997) 43-51

46 '

o.oo

~ " ,,0

0.4B" 0 . ~ "

........

B.,o .........

<

o.,,

.........

1000

:' . . . . . . . .

,

•

•

iiii/ •

) ........

:" . . . . . . . .

- :..........

-

•

i ........ i ........ i ........ i ......... i........

! ....

:: P E S w t % s i z e d

::

:,-.i

lll~

.......

i ....... ,

1200

1300

1400

:

:

....

"'"~

........

' ~~ . . . . . . . . .

1(~O

!

:

-! . . . . !---

,

.

.

~V..~i i : .

.

.

;~ ...... i ........ i .......

.

.

.

.

.

i...

• ........ i .....

::

:

11500

:

:

>:........ ~ ........ i ........ i ........ i ........

1700

IB00

1900

2000

2100

2200

2300

2400

W a v e l e n g t h (rim) Fig. 3. N I R s p e c t r a o f the 5 w t % e p o x y - a n d 5 w t % P E - s i z e d a r a m i d knitted a n d ' r e f i n e d ' fabrics. T h e b a n d s w i t h ~- a n d •

are d u e to the

e p o x y a n d p o l y e t h y l e n e sizes, r e s p e c t i v e l y .

obtained from 5 wt% epoxy- and 5 wt% polyethylene-sized fabrics, respectively. Comparison of the spectra of 'Epoxy 5 wt% sized' or 'PE 5 wt% sized' with that of 'refined' reveals that the aramid knitted fabrics were, indeed, treated by the sizing agent. Another notable point in Fig. 3 is that the use of fluoride glass fibre allows one to observe clearly the NIR spectra up to 2500 nm [17]. It is rather difficult to obtain the reliable spectra up to 2500 nm by means of quartz glass fibre. In order to characterize the sizing agents on the fabrics, NIR spectra of the epoxy and polyethylene sizes, directly recovered from each dispersion-based sizing agent by drying at 130°C, were obtained and shown in Fig. 4. Referring to these spectra, one can identify characteristic bands of the epoxy and polyethylene type of sizing agents in the NIR spectra of sized aramid knitted fabrics. They are marked by ~r and O, respectively. Assignments for the characteristic bands of the sized fabrics are summarized in Table 1 [18-23]. The observations in Fig. 3 clearly show that one can investigate in situ the sizing agents on the aramid knitted fabrics by means of NIR light-fibre optics spectroscopy. We examined the dependence of the NIR spectrum of the epoxy-sized fabrics on the concentration of the epoxy size. Fig. 5A and B exhibit the NIR spectra in the 1400-1800 nm and 1800-2400 nm regions of 0, 5, 10

....

,o

L -

' '

............. i i ........ i ........ i......... ~,. ..........i........i ........i........i.........

o.o II

"

i i ; '. ; ; i ; ; ilflO 12oo 13oo 1,1~1 11100 16oo 17~o 11[1~1 I ~

Wsvelength(nm)

(a) Epoxy size

........

......... i............. i ........ 7........ .i__....-.............. i........i........

; ~

i i i 211~ 2200 ~

; 1ooo

ilao

t~o

latlo

i,~1

t~

l~ao

1~o

two

19oo

~o

21oo

22oo

23oo

Wavelength(rim)

(b) Polyethylene size

Fig. 4. N I R s p e c t r a o f the sizes r e c o v e r e d f r o m the d i s p e r s i o n - b a s e d sizing a g e n t s b y d r y i n g at 130°C. (a) E p o x y size and (b) p o l y e t h y l e n e size.

47

K. Kitagawa et al. / Vibrational Spectroscopy 15 (1997) 43-51 Table 1 Assignments for the characteristic NIR bands in Fig. 3 of knitted fabrics after sizing Sizing agent

Band position (nm)

Assignments

Epoxy

1130 1429 1650 1685 1695 1735 2275

C - H str. second overtone 2 × C - H stret. + C - H def. (aromatic) C - H str. first overtone (epoxy ring) C - H str. first overtone (aromatic) C - H str. first overtone (CH 3) C - H str. first overtone (CH 2) C - H str. + C - H def.

Polyethylene

1215 1395, 1415 1725, 1765 2310

C - H str. second overtone (CH 2) 2 × C - H stret. C - H def. (CH 2) C - H str. first overtone (CH 2) C - H s t r . + C - H def. (CH 2)

~24"

0.210.100.16" 0.12'

Wavelength/nm o.,~ ............. i(Bii

O,Oo, i

............. !............. i............. i........ ~

...... i i ................... i.............

i ii \J;i

ee ~ .

O. "t2" O. 35" 0.28" 0,21"

0.14

.............

1800

; .................................................................................................

:. . . . . . . . . . . . . . . . . . . . . . . . . . .

i

1860

1920

1960

2040

2100

i 21e{O

2220

2280

2'34'0

2400

Wavelength/nm Fig. 5. N1R spectra the 1400-1800 (A) and 1800-2400 (B) nm regions of 0, 5, 10 and 20 wt% epoxy-sized fabrics.

K. Kitagawa et al. / Vibrational Spectroscopy 15 (1997) 43-51

48

o.7o ....................................

0 . ~ 3

. . . . . . . . .

, ........

•. . . . . . . . .

~ ........

i ............................

i .....................................

!

i

i .........

. .........

~ ........

" ........

~ ........

::......... i .........................

~ .........

: .........

i

i

i. . . . . .

; ........

= ........

, . . . . .

0 . 5 6 "

O. 4 9 "

O.21"

0.14"

0,07"

1000

I

I

i

1100

1200

1300

i

t'lO0

15130 1600

17(30

1800

1900

2000

2100

2200

2'300

2400

Wavelength(nm) Fig. 6. NIR spectra of 5 wt% epoxy-sizedfabrics dried at 110°Cfor 40 rain in an oven (a) and at 25°C for 5 h in air and 16 h in addition under vacuum(b). and 20 wt% epoxy-sized fabrics, respectively. Intensity changes are obvious for the bands near 1650, 1695, 1725, 1765, 2210 and 2275 nm. The intensity increases of these bands with the concentration confirm that all the bands are assignable to the epoxy size. The results in Fig. 5 indicate that the quantitative analysis of the sizing agent may also be possible with the aid of chemometrics. The effect of drying on the NIR spectrum was also investigated. Fig. 6 compares the NIR spectra of 5 wt% epoxy-sized fabrics dried at 110°C for 40 min in an oven and at 25°C for 5 h in air and 16 h in addition under vacuum. The spectral differences are very small between the two spectra except for the bands due to water, near 1415 and 1930 nm. Therefore, the effect of drying is very small. Probably, one can analyze the sizing agent on the aramid knitted fabrics without the process of drying by use of the NIR light-fibre spectroscopy. Tensile tests were carried out for the aramid knitted fabrics/epoxy resin composites in which the aramid knitted fabrics had been treated, as described above, with different sizing agents [15]. For the epoxy-sized specimen, the initial crack occurred at the section with extreme low fiber volume in the widthwise direction of the specimen. On the other hand, the initial crack took place at loop interlocking region for the polyethylene-sized specimen. Since the epoxy type sizing agent used was the same kind as matrix epoxy resin, it can be related to

Course "f

Tensile Modulus 6.5

5.5

5

.,,i 0

.... 1

i ....

i , , ,llllI

2

3

4

, , l li . 5

Concentration of Sizing Agent (wt%)

~

32

~

28

, ,

Tensile strength

o Eoxy,1l °

, ,

0

,,

1

2

3

4

, ,

5

6

Concentration of Sizing Agent (wt%)

Fig. 7. Relationship between the concentration of sizing agent and tensile modulus (a) or tensile strength (b) of weft knitted structural composites in course direction.

K. Kitagawa et al. / Vibrational Spectroscopy 15 (1997) 43-51

49 -0.02

0.065 0.060

L _

~

C H 2 -..........~

-0.03 -0.04

0.050

~

-

-0.05

0.045

--0.06

0.040 ,<

-0.07

0.035

-0.08

0.030 0.025

-0.09

H00

o.o20 0.015

-0.10

--

r

i

;

i

I

i

I00

10(30 1100 1200 1 O0 1400 1500 1600 17

I

i

i

I

I

I

I

-0.11

1800 1900 2000 2 1 0 0 2 2 0 0 2 3 0 0 2400 2 5 0 0

Wavelength (rim) Fig. 8. NIR spectra of sized glass strands, L, H10 and H00.

the curing reaction of the matrix resin with hardening catalyst. Therefore, after the mutual diffusion between the epoxy sizing agent and the matrix resin with hardening catalyst in the fabrication, it could make a crosslinking interphase [13]. However, the polyethylene type of sizing agent on the fibre was not soluble in the matrix epoxy resin and could not be related to the curing reaction. It is clear that the interphase made from the polyethylene sizing agent is poor. It can be seen from Fig. 7 that the tensile properties, tensile modules and tensile strength, of the epoxy specimen are higher than those of the polyethylene specimen. These different interphases made from the two kinds of sizing agents, which were directly identified on aramid fabric by NIR spectroscopy, produce the different fracture mechanisms, resulting in the different tensile properties of composites. 3.2. In situ analysis of sizing agent on the glass strand Fig. 8 shows NIR spectra of the L, H10 and H00 sized glass strands. The term H00 means the glass fibre strand was treated solely by silane coupling agent. Bands at 1725, 1944 and 2310 nm can be assigned to the first overtone of CH stretching modes, the combination of amide modes and the combination of CH stretching and CH bending modes, respectively [18,19,22,23]. Of particular note is that the amide band is observed only in the spectrum of the L type sized glass strand. The spectrum of the H00 sized glass strand, which was treated solely by the silane coupling agent, does not show a band in the 1900-2000 nm region where the combination mode of the amide group is expected to appear. The appearance of the amide band in the spectrum of the L type sized glass strand elucidated that the amide bond was formed between the amino silane coupling agent and modified polypropylene sizing agent as shown in Fig. 9 [24]. In this way NIR spectroscopy can probe the chemical Amide Bond

/

"~-'%'~CH-- C \ 0

~

_.

+

m

ICH2__C/

,o,

Modified polypropyte~ae sizingagent

I

I

CH,--c--OH

0

-: Amino silane coupling agent

Fig. 9. Formation of an amide bond between amino silane coupling agent and modified polypropylene sizing agent.

K. Kitagawa et al. / Vibrational Spectroscopy 15 (1997) 43-51

50

3°

A

25

~

20

g.

..... //] //////FA

NN" ///,,,','//..1 //////A

~ ,° m

HO0

L

HIO

Type of Sizing Agent

Fig. 10. Relationbetweenbendingstrengthand typesof sizingagentin glass/polypropylenecomposites.

reaction on the textile nondestructively. This may be the first time that the reaction of sizing agent on fabric is monitored directly. It was expected that H10 also gave a band due to the amide group in the region of 1900-2000 nm because the weight loss of both the L and H10 strands by washing with tetralin at 135°C was 0.0 wt%. Weak features in the 1900-2000 nm region of the spectrum of the H10 sized glass strand might be due to the amide mode.The H10 type material is an isotactic polypropylene with high molecular weight while the L type material is an atactic polypropylene with low molecular weight, so that the number of maleic anhydride per mass may be smaller in the former. Therefore, it seems that the number of the amide group in the H10 type sized glass strand is smaller than in the L type sized glass strand and thus the hand due to the amide groups is much weaker in the NIR spectrum of the H10 type sized strand. The formation of the amide bond should improve the interracial properties between the fibre reinforcement and matrix resin. Bending tests were performed for the glass fibre/polypropylene composites, which had been fabricated using sized glass reinforcements and polypropylene films as the matrix by a film stacking method [25]. The bending strength of H00, L and H10 is compared in Fig. 10. It is clearly shown that the bending strength of the L specimen is the highest among the three. This is due to the strong interphase with the amide bond in the L composites. The amide bond should, however, exist also in the H10 size glass strand, as discussed above.

4. Conclusions

This paper has demonstrated the potential of NIR light-fibre optics spectroscopy in the direct analysis of sizing agents on sized aramid knitted fabric and sized glass strand. The conclusions reached from the present study may be summarized as follows; (1) Characteristic NIR spectra were obtained for the two kinds of sizing agents directly from the sized aramid knitted fabrics. The agents could be identified by specific NIR bands. (2) The intensities of the bands due to the epoxy sizing agent increase with its concentration, indicating that the quantitative analysis of the agent may also be possible. (3) The formation of the amide bond between the maleic anhydride-modified polypropylene sizing agent and the amino silane coupling agent was revealed by the NIR spectral measurements of the sizing glass strand.

K. Kitagawa et al. / Vibrational Spectroscopy 15 (1997) 43-51

51

References [1] S. Ghosh, J. Rodgers, NIR analysis of textiles, in: D.A. Bums, E.W. Ciurczak (Eds.), Handbook of NIR Analysis, Marcel Dekker, New York, NY, 1992, p. 495. [2] S. Ghosh, D. Dilanni, T. Ebersole, Fundamental aspects of characterizing textile materials using NIRS, in: C.S. Creaser, A.M.C. Davies (Eds.), Analytical Applications of Spectroscopy, The Royal Society of Chemistry, London, 1988, p. 133. [3] S. Ghosh, J.R. Hassick, NIRS for the textile industry, in: C.S. Creaser, A.M.C. Davies (Eds.), Analytical Applications of Spectroscopy, The Royal Society of Chemistry, London, 1988, p. 147. [4] T. Malfait, L. Ruys, NIRA as production control of synthetic fibers, in: K.I. Hildrum, T. Isaksson, T. Naes, A. Tandberg (Eds.), Near Infrared Spectroscopy, Ellis Horwood, Chichester, 1992, p. 423. [5] J.E. Rodgers, S. Lee, Textile Res. J. 59 (1989) 513. [6] J.E. Rodgers, S. Lee, Textile Res. J. 61 (1991) 531. [7] S.L. Monfire, F.A. DeThomas, On-line reflectance analysis of fibre materials by near-infrared spectroscopy, in: K.I. Hildrum, T. Isaksson, T. Naes, A. Tandberg (Eds.), Near Infrared Spectroscopy, Ellis Horwood, Chichester, 1992, p. 447. [8] S. Ghosh, R. Roy, J. Textile Inst. 79 (1988) 504. [9] W. Tincher, A. Luk, Textile Chem. Color. 17 (1985) 200. [10] J. Rodgers, Specific applications of NIRA in the textile indus, presented at 7th International NIRA Symposium, Technicon Technical Center, Tarrytown, NY, 1984. [11] R.E. Allred, E.W. Merrill, D.K. Roylance, Polym. Sci. Technol. 27 (1985) 333. [12] J. Kalantar, L.T. Drzal, J. Mater. Sci. 25 (1990) 4186. [13] K. Kitagawa, Y. Kankawa, T. Shimamura, H. Maruyama, Y. Nakanishi, The mutual diffusion between sizing agent and epoxy resins, in: Proceedings of the International Symposium on Advanced Network-Polymers at Kansai University, Osaka, 1995, p. 71. [14] K. Kitagawa, H. Hamada, Z. Maekawa, N. Ikuta, M.G. Dobb, D.J. Johnson, J. Mater. Sci. Lett. 15 (1996) 2091. [15] K. Kitagawa, S. Hayasaki, N. Ikuta, Z. Maekawa, Composite Interfaces, in press. [16] K. Kitagawa, S. Hayasaki, N. Ikuta, Z. Maekawa, Adv. Composites Lett. 5 (1996) 175. [17] Y. Noda, Y. Mimura, T. Nakai, T. Tani, T. Sudo. S. Ohno, in: Proc. of llth Symposium of Nondestructive Measurements, Tsukuba, 1995, p. 81 (in Japanese). [18] B.G. Osborne, T. Feam, P.H. Hindle, Practical NIR Spectroscopy with Application in Food and Beverage Analysis, Longman Scientific and Technical, Harlow, 1993. [19] R.F. Goddu, D.A. Delker, Anal. Chem. 30 (1958) 2013. [20] H. Dannenberg, SPE Trans. 78 (1963). [21] S.E. Krikorian, M. Mahpour, Spectrochim. Acta 29A (1973) 1233. [22] C.E. Miller, Appl. Spectrosc. Rev. 26 (1991) 277. [23] G. Lachenal, Vib. Spectrosc. 9 (1995) 93. [24] H.A. Rijsdijk, M. Contant, A.A.J.M. Peijs, Compos. Sci. Tech. 48 (1993) 161. [25] A. Harada, Effect of interfacial properties on mechanical properties of glass fiber reinforced polypropylene composites, Graduation Thesis, Kyoto Institute of Technology, 1996.