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Laboratory Assessment of Delaminated Polyimide Cable · PDF file Laboratory Assessment of Delaminated Polyimide Cable Personnel Sandia Personnel participating in this laboratory assessment

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    Laboratory Assessment of Delaminated Polyimide Cable

    Personnel

    Sandia Personnel participating in this laboratory assessment were: Robert Bernstein, Roger L. Clough, Kenneth T. Gillen, G. Michael Malone, Dora K. Derzon, Alex R. Griego, David Tallant, Manuel Garica, David Wheeler, and Douglas J. Harris. Sandia received cooperation from Airbus Industries’ Jean-Luc Ballenghien, Dominique Mazzarino, Alcatel Cable’s Jean Pierre Ferlier, Dupont’s James Edman (Dupont),

    Background General: Using the Lectromec DelTest®, a breech was found in the LCL-Midspan of the A300 aircraft. This bundle was then carefully ‘opened up’ at Sandia National Laboratories by Bill Lindsey and Robert Bernstein. The bundle was discovered to possess a region that was atypical. A more lengthy description (with pictures), of this can be found in the Chapter 4 of the report provided to the working group by Sandia National Laboratories, and will not be repeated in this document.1

    Kapton®: Kapton® is a polyimide made by DuPont, sythnesized by the condensation polymerization of a diamine and dianhydride and can be hydrolyzed, reversibly, by (usually base catalyzed) H2O (Scheme 1).2

    Scheme 1

    OO

    O

    O

    O

    O

    n

    OH3N

    2H2O

    NN

    O

    O

    O

    O

    O

    OH2N

    NH2

    R

    N

    O

    O

    O

    O

    OH

    O

    n

    Kapton

    _ +

    4,4'-Oxydianiline1, 2, 4, 5- Benzenetetracarboxylic dianhydride

    n

    -nH2O

    -2H2O

    Kapton® film was obtained from DuPont and the Infrared (IR) spectrum obtained (Figure 1).3

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    0

    .5

    1

    1.5 A

    bs or

    ba nc

    e

    3500 3000 2500 2000 1500 1000 Wavenumber (cm-1)

    17 75

    17 20

    15 00

    13 75 12 43

    16 00

    Figure 1: IR spectrum of Kapton film.3

    Chemical Analysis of A300 LCL-Midspan ‘Flakes’ The flakes were initially examined via a light microscope and two distinct parts were observed. It is predominately one material(s) with fragments of a white material (Figure 2).

    Figure 2: Microscope picture of A300 LCL-Midspan flake (7X). Insert is magnification illustrating the white material (90X).

    White Material: The white material was subjected to transmission Infrared (IR) analysis by a Nicolet Nexus IR spectrometer with a microscope attachment. The white specs within the flakes

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    were quickly determined to be FEP (fluorinated ethylene-propylene polymer) via IR analysis by comparing the spectrum to FEP obtained from DuPont (Error! Reference source not found.).4

    It is most likely that these FEP flakes came from the outer coat of the wire insulation but there is not enough data to determine how and why this FEP came apart; thus we will refrain from speculating on this matter.

    Major Flake Material(s), IR Studies: The IR spectrum of the major flake material(s) (non-FEP component) of the compounds(s) was obtained (Figure 3). This spectrum clearly has an -O-H or an -N-H functional group (3700-3000 cm-1) and possibly an amide functional group (1650 cm-1).

    0

    .5

    1

    1.5

    A bs

    or ba

    nc e

    3500 3000 2500 2000 1500 1000 Wavenumber (cm-1)

    16 00

    15 00

    16 50

    15 50

    13 45

    14 08

    12 43

    , 1 22

    0

    Figure 3: IR spectrum of the major constituent(s) of the unknown flakes.

    Major Flake Material(s), NMR Studies: The majority of the flake was readily soluble in deionized water, which lead to the ability to perform hydrogen Nuclear Magnetic Resonance (1H NMR) studies on the material. The 1H NMR spectrum of the unknown flakes was obtained by dissolving in D2O and filtering to remove the insoluble component(s) (Figure 4).

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    Figure 4: 1H NMR spectrum of major constituent(s) of the unknown flakes. Note the large peak at ca. 4.6 ppm is due to H2O.

    The NMR spectrum displays peaks in the aromatic region (ca. 7 ppm) which is what is expected from Kapton® degradation products (Figure 5).

    Figure 5: Part of 1H NMR spectrum of major constituent(s) of the unknown flakes focusing on the aromatic region.

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    The unknown spectrum contains very broad peaks. Two possible explanations for this are a ‘tumbling effect’ due to a high molecular weight, or a paramagnetic impurity. Either of these would result in the broadened peaks.

    Comparison Studies, IR Studies: The IR spectrum of Kapton® (DuPont) was obtained, and comparison of the unknown spectra clearly show that the flake is not Kapton® in its pristine state (Figure 1 vs. Figure 3). This lead to the hypothesis that the flakes could be some derivative or degradation product of Kapton®.

    A piece of Kapton® was subjected to refluxing 0.1M NaOH solution, and within 12 hours the material had completely dissolved. The water was evaporated and the IR spectrum obtained. Comparison of this spectrum to that of the unknown flake showed similarities, but due to the massive NaOH (and carbonate) peaks it is difficult to draw a conclusion from the comparison (Figure 6).

    0

    .2

    .4

    .6

    .8

    1

    1.2

    1.4

    A bs

    or ba

    nc e

    3500 3000 2500 2000 1500 1000 Wavenumber (cm-1)

    RB-I-18 "Unknown Material"

    NaOH-degraded Kapton

    hydroxyl carbonate

    1600

    1220

    Figure 6: IR spectra comparing the unknown flakes (red) and the NaOH exposed Kapton® (green)

    In order to avoid this problem, NH3(aq) was chosen as the base. NH3 is a gas that can readily be removed from the solution upon evaporating the water. When a piece of Kapton® film was allowed to sit at room temperature (refluxing would have removed all the NH3(g)) over ca. 3 days, the Kapton® dissolved. To make this similar to the NaOH experiment, the solution was then refluxed overnight. The IR spectrum of this NH3(aq) degraded Kapton® showed ‘striking similarities’ to that of the unknown flakes (Figure 7).

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    0

    .2

    .4

    .6

    .8

    1

    1.2

    1.4

    A bs

    or ba

    nc e

    3500 3000 2500 2000 1500 1000 Wavenumber (cm-1)

    RB-I-18 "Unknown Material"

    NH4OH-degraded Kapton

    ammonium

    N-H

    1600

    1500

    1220

    Figure 7: IR spectra comparing the unknown flakes (red) and the NH3(aq) exposed Kapton® (blue).

    This is strong evidence to support the conclusion that the unknown flakes are some form of degraded/modified Kapton®.

    Comparison Studies, NMR Studies: The 1H NMR spectra of the NH3(aq) exposed Kapton® was obtained.

    Figure 8: 1H NMR spectrum of NH3(aq) exposed Kapton®. Note the large peak at ca.4.6 ppm is due to H2O.

    This spectrum contains aromatic peaks as expected for a Kapton® derivative (Figure 9).

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    Figure 9: Part of 1H NMR spectrum of NH3(aq) exposed Kapton® focusing on the aromatic region.

    Comparison of the 1H NMR spectrum of NH3(aq) exposed Kapton® and that of the major constituent(s) of the unknown flakes show a great deal of similarities (Figure 10).

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    Figure 10: 1H NMR spectrum of NH3(aq) exposed Kapton® (upper spectra) and that of the major constituent(s) of the unknown flakes (lower spectra).

    Although the unknown peaks are broad and the splitting pattern indiscernible, it is clear that the peak positions and the approximate integration of the aromatic region of the two spectra are very similar.

    Comparison Studies, Conclusion for Flakes Analysis: It is concluded that the unknown flakes are composed of a Kapton® degradation or derivative product. The IR spectrum and the 1H NMR spectrum both show striking similarity to that of the Kapton® exposed to heat and basic conditions. This data does not lead to how the Kapton® transformed into the flakes, it supports the hypothesis however, that the flakes are derived from Kapton® and suggests that a hydrolytic degradation process is a possible mechanism for this transformation.

    Wire Cross Section Analysis In order to determine the integrity of the insulation, examination of cross-sections of one of the wires from the LCL-Midspan was performed. The wire bundle was arbitrarily assigned a ‘North’ and ‘South’ to give a frame of reference. At specific distances from the northern end, the wire was cut into seven pieces (Figure 11).

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    203.2

    174.6

    15.2

    59.7

    80.0

    91.4

    106.7

    N 123456

    Atypical Region

    75.0 26.7 Wire

    S 7

    Figure 11: Schematic of A300 from LCL Midspan (Kapton®, FEP) wire which was cross-sectioned as marked. Examined surfaces were on the northern ends of the numbered sections. Units are in cm.

    Photographs of the outsides of the wires near the northern ends of each section were taken (Figure 12) so that the outside visual condition could be compared to the cross section. Sections 3 and 4 are in the atypical region on the wire. All other sections of the wire appeared typical by visual inspection of the exterior surface of the wire.

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    Figure 12: Side views of north ends of cut wire pieces in approximate locations where cross-section photos were taken. The number in the figure corresponds to the section number.

    Small pieces of wire with the conductor (approximately 2.54 cm long) were cut off of the “northern” ends of each numb

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