Rapid ReportPreparation of polyetherimide/carbon fibrecomposites by a cataphoresis processHoussain Qariouh, Rossitza Schue, Nabil Raklaoui and Francois Schue*Universite Montpellier II, Laboratoire de Chimie Macromoleculaire CC 009, Place Eugene Bataillon, 34095 Montpellier Cedex 5, France

Abstract: Preliminary results in this study show that it is possible to achieve a good Ultem 1000/carbon

®bres covering by means of electrophoretical deposition. The expected amount of deposited polymer is

well controlled and the deposited ®lms have a good appearance. In this way a variety of carbon ®bre

composite materials can be manufactured.

# 1999 Society of Chemical Industry

Keywords: polyimide; carbon ®bre; cataphoresis process; composites

INTRODUCTIONCataphoretic electrodeposition is an excellent coating

technique, enabling the coating of an object of any

shape with a high quality ®lm in a single processing

step.1 The technique also obviates the need for organic

solvents, making it environmentally benign. The

application of this method to polyimides could

increase their utility considerably.2±5 In a previous

paper we described an optimized cataphoretic process

of deposition of polyetherimide on to aluminium and

steel surfaces.6 Because this process is suitable for all

conductive substrates, it can be applied to the

preparation of polyetherimide/carbon ®bre com-

posites. Such materials may be produced as pre-

pregs by electrodeposition followed by stacking a

number of them together to obtain thick pieces. This

publication reports the results of our initial investiga-

tions.

EXPERIMENTAL80g of polyetherimide Ultem 1000 (product of GEC

Plastics), 165.3g of N-methylpyrrolidone and 20.6g

acetophenone were charged in a reaction ¯ask. The

polymer was dissolved with stirring at approximately

85±90°C under a blanket of nitrogen. When the

polymer was completely dissolved, a mixture of 18.9g

N-methylpiperazine and 61.8g acetophenone was

added over a period of 2h. Vigourous stirring was

maintained throughout. The temperature was kept at

85±90°C during the addition. After the addition was

complete, the mixture was stirred and warmed to

110°C and held at that temperature for 2h 30min.

The resulting solution of modi®ed polymer was then

used to prepare the electrophoretic deposition emul-

sion as detailed below.

5.98g of acetophenone and 1.48g of 50% aqueous

lactic acid were added to 30g of the modi®ed polymer

solution. The mixture was stirred vigorously while 78g

of deionized water was added slowly. The stirred

mixture became quite viscous and then thinned out as

the addition of water was completed.

Solvents (N-methylpyrrolidinone, acetophenone)

and reagents (1-methylpiperazine, lactic acid) were

purchased from Aldrich Chemical Co without addi-

tional puri®cation. The ®laments used to braid the

carbon ®bre fabrics had a diameter of about 8mm. All

electrodeposition experiments were carried out at

constant applied voltages using a Consort E425

apparatus. A multimeter with a data storage option

(Metrix) was used to monitor current decay.

The emulsion was placed in a constant temperature

bath at room temperature equipped with a Te¯on

stirbar and submersible magnetic stirrer. Carbon ®bre

fabric test pieces (60mm�60mm) were pretreated in

N-methylpyrrolidone and placed in the emulsion

together with an aluminium anode measuring

15mm�15mm. The distance between the cathode

and the anode was about 40mm. The test piece was

removed, rinsed rapidly in deionized water and placed

in a warm (60°C) dry chamber to evaporate solvents

from the ®lm. The coated fabrics were baked in several

steps in an oven (Eurotherm818P, Thermolyte) to

effect the reimidization reaction.

Polymer International Polym Int 48:1065±1067 (1999)

* Correspondence to: Francois Schue, Universite Montpellier II, Laboratoire de Chimie Macromoleculaire CC 009, Place Eugene Bataillon,34095 Montpellier Cedex 5, France(Received 6 August 1999; accepted 12 August 1999)

# 1999 Society of Chemical Industry. Polym Int 0959±8103/99/$17.50 1065

DEPOSITION MECHANISMIn aqueous emulsions, the passage of an electric

current results in the electrolysis of water and the

discharge of the various ionic species. The following

scheme shows such processes relevant to the system

under study:6

Anode:

2H2O! O"2 � 4H� � 4eÿ

4RCOOÿ � 4H� ! 4RCOOH

Cathode:

4H2O� 4eÿ ! 2H"2 � 4OHÿ

Because gas formation occurs during the coating

process, the coagulated (so called `wet') ®lm contains

some hydrogen which leads to bubbles and pinholes.

The successful use of this process depends on

Figure 1. Current density and polymer yield at different voltages plottedversus deposition time.

Figure 2. SEM of the surface (a, c) and the cross-section (b, d) of non-coated carbon fibre fabric and coated carbon fibre fabric, respectively, at 68V and 240sdeposition time.

1066 Polym Int 48:1065±1067 (1999)

H Qariouh et al

minimizing both the amount and the effects of this

gassing.

RESULTS AND DISCUSSIONElectrodeposition processClearly, it is important to verify that electrodeposition

occurs effectively with carbon ®bre. Thus, different

applied voltages (45, 68 and 80V) and deposition

times were used. Figure 1 shows the evolution of the

current density and the polymer yield with deposition

time.

The current decay curves at various voltages can be

attributed to the insulating effect of the coating.

During deposition, a coherent layer of material is

formed on the cathode, the ®lm resistance leading to a

decrease in current to a limiting value (residual current

density) depending on the applied voltage. For

example, for voltages of 45 and 68V, the residual

current was recorded to be 1 and 2.5mAcmÿ2,

respectively. One may observe that the decrease is

very similar compared to E-coating systems previously

studied.6

Figure 1 shows also the yield of polymer deposited

on the cathode as a function of deposition time and

voltage (45, 68 and 80V); electrodeposition of poly-

etherimide on carbon ®bres obeys Faraday's law. The

yield of polymer increases with increasing voltage and

grows linearly, even for very long deposition times.

The rate of deposition increases with increasing

voltage and takes values of 0.048, 0.066 and

0.098mgcmÿ2sÿ1 at 45, 68 and 80V, respectively.

Usually, with classical E-coating systems, the deposi-

tion yield grows linearly for a given period before

tending towards a maximum. Here, with this system,

the saturation effect is observed after a longer deposi-

tion time than we expected (more than 15min). This

difference could be attributed to a highly developed

®bre surface recovering due to a large number of

assembled ®laments in each ®bre.

SEM studyThe deposited layer was studied in terms of its ability

to form a ®lm homogeneous in thickness and density

(hole free). Figure 2 shows the surfaces and cross-

sections of carbon ®bres before and after deposition.

Figure 2(c, d) shows perfect coverage of the surface by

the polymer and good penetration of the polymer

between the ®bres and ®laments. The imperfections,

such as craters, seen in the ®lm surface could mostly be

avoided by adjusting the electrical parameters. The

desired ®lm thickness could be obtained by choosing

the appropriate electrodeposition conditions; for

example, in Fig 2(d) the ®lm thickness is 55mm which

was obtained at 68V and 240s deposition time.

CONCLUSIONSThe preliminary results in this study show that it is

possible to achieve a good Ultem 1000/carbon ®bre

covering by electrophoretic deposition. The expected

amount of deposited polymer is well controlled and

the deposited ®lms have a good appearance. In this

way a variety of carbon ®bre composite materials can

be manufactured.

REFERENCES1 Mark HF, Bikales NM, Overberger CG, Menges G and

Kroschwitz JI, Encyclopedia of Polymer Science and Engineering,

2nd Edn, John Wiley and Sons, New York. Vol 3 p 675 (1985).

2 Buchwalter SL, Polym Mater Sci Eng, 59:61 (1988).

3 Uebner M and Ng K, J Appl Polym Sci 36:1525 (1988).

4 Alvino WM, Fuller TJ and Scala LC, J Appl Polym Sci 28:267

(1983).

5 Alvino WM and Scala LC, J Appl Polym Sci 27:341 (1982).

6 Qariouh H, Raklaoui N, Schue R, Schue F and Bailly C, Polym Int

48(11): (1999) (accepted).

Polym Int 48:1065±1067 (1999) 1067

Preparation of polyetherimide/carbon ®bre composites