ApplicationNews

No.A474

Thermal and Spectrophotometric Analysis

Analysis of Polyimide CFRP by TG-FTIR

LAAN-A-FT-E054

Epoxy resin is typically used in carbon fiber composite materials (carbon fiber reinforced plastic: CFRP), however, due to its limited heat resistance, high heat-resistant CFRP materials using polyimide resin are being developed. Here, we introduce the results of combined Thermogravimetric (TG) - Fourier Transform Infrared Spectroscopy (FTIR) analysis of thermoplastic polyimide and thermosetting polyimide prepregs, polyimide matrices impregnated with carbon fibers and formed into sheets ready for processing.

n Polyimide / Carbon Fiber CompositesCFRPs containing the base material epoxy have a temperature limit of approximately 120 ˚C, and are therefore not applicable for use in high-temperature materials. Studies using polyimide resin in CFRP materials which display excellent heat resistance are presently underway, but due to problems in workability, methods to improve their thermoplasticity are being considered. In this study, we analyzed thermoplastic polyimide and thermosetting polyimide prepregs by TG-FTIR to identify the types of gasses they generate. (Samples provided by the Advanced Composite Research Center, Aerospace Research and Development Directorate, Japan Aerospace Exploration Agency (JAXA).)

n TG-FTIR SystemFigure 1 shows an overview of the system used for measurement. The system comprises a DTG-60, a simultaneous TG - differential thermal analysis (DTA) instrument, and an IRAffinity-1 FTIR spectrophotometer connected via a gas cell and heated transfer line.

n Analytical ResultsMeasurements of thermoplastic and thermosetting polyimide prepreg samples weighing 36.8 mg and 30.9 mg, respectively, were conducted under the conditions shown in Table 1. Figures 2 and 3 show the TG-DTA curves obtained for the samples. Glass transitions are clearly observed in the vicinity of 250 ˚C in both DTA curves. Furthermore, in the TG curves, a slight weight loss is noticeable in the vicinity of 200 ˚C – 400 ˚C (between 500 to 1000 seconds). Also visible is the onset of decomposition, signified by the beginning of the large weight loss around 550 ˚C (at about 1500 seconds) in the TG curves. This decomposition onset temperature is a measure of heat resistance, which is higher in the thermosetting prepreg.

-0 500 1000 1500 2000Time [sec]

60.00

80.00

100.00

%TGA

-100.00

0.00

100.00

200.00

300.00uVDTA

246.0 ﾟC

-0.3 mg-0.8 %

Weight loss

-19.8 %Weight loss -7.3 mg

547.8 ﾟCTG

DTA

Thermoplastic PI Prepreg%

TGAuVDTA

-0.2 mg-0.6 %

Weight loss-11.0 %

Weight loss -3.4 mg

-0 500 1000 1500 2000Time [sec]

80.00

90.00

100.00

-100.00

0.00

100.00

200.00

300.00

248.5 ﾟC

567.3 ﾟCTG

DTA

Thermosetting PI Prepreg

Fig. 1 Overview of TG-FTIR System

FTIR Instrument : IRAffinity-1/IRTracer-100

Resolution : 8 cm-1

Accumulation : 10Interval : 30 secDetector : DLATGS

DTG Instrument : DTG-60Heating Rate : 20 °C/minHold Temperature : 800 °CAtmosphere : N2

Table 1 Instrument and Analytical Conditions

Fig. 2 TG-DTA Curves of Thermoplastic Polyimide Prepreg Fig. 3 TG-DTA Curves of Thermosetting Polyimide Prepreg

ApplicationNews

No.

For Research Use Only. Not for use in diagnostic procedures.The content of this publication shall not be reproduced, altered or sold for any commercial purpose without the written approval of Shimadzu. The information contained herein is provided to you "as is" without warranty of any kind including without limitation warranties as to its accuracy or completeness. Shimadzu does not assume any responsibility or liability for any damage, whether direct or indirect, relating to the use of this publication. This publication is based upon the information available to Shimadzu on or before the date of publication, and subject to change without notice.

© Shimadzu Corporation, 2013www.shimadzu.com/an/

A474

First Edition: Nov. 2013

Figures 4 and 5 show 3D infrared spectra of the two samples. The infrared spectra were analyzed to identify the components corresponding to the slight weight losses seen in the first half of the TG curves of the thermoplastic and thermosetting polyimide prepregs. Search results associated with the first arrow-marked positions in the infrared spectra of Figure 4 position (1) and Figure 5 position (2) are shown in Figures 6 and 7, respectively. The result shown in Figure 6 suggests that the gas generated at position (1) might be a phthalate ester. For posit ion (2), the IR spectrum of NMP (N-methyl-2-pyrrolidone) shows good agreement in Figure 7, which is consistent, because NMP is used as a solvent to dissolve the thermosetting polyimide. Not only does residual NMP create voids during forming, it also lowers the glass transition temperature.Also conducted was an infrared spectral search for the gas components that were generated in the latter stage of the analysis, Figure 5 position (3). As indicted in Figure 8, they were confirmed to consist of phenol, CO2 and CO. These components are assumed to be aromatic polyimide decomposition products, and were present in thermoplastic polyimide as well.As the above results show, combined TG-FTIR analysis is a powerful method for confirming the presence of residual solvents and identifying chemical products associated with thermal transitions.

wavenumbers4000 3500 3000 2500 2000 1500 1000 500

-1

-0.5

0

0.5

1

Spectrum (1140 s) obtained from generated gas (1)

Phthalate

wavenumbers4000 3500 3000 2500 2000 1500 1000 500

-1

-0.5

0

0.5

1

wavenumbers4000 3500 3000 2500 2000 1500 1000 500

-1

-0.5

0

0.5

1

ON

Spectrum (780 s) obtained from generated gas (2)

N-methylpyrrolidone

wavenumbers4000 3500 3000 2500 2000 1500 1000 500

-1

-0.5

0

0.5

1

OH

CO2CO

Spectrum (1740 s) obtained from generated gas (3)

Phenol（1）

（2）

（3）

Fig. 4 3D Display of IR Spectra of Thermoplastic Polyimide Prepreg

Fig. 5 3D Display of IR Spectra of Thermosetting Polyimide Prepreg

Fig. 8 Search Results for Generated Gas (3)

Fig. 7 Search Result for Generated Gas (2)

Fig. 6 Search Result for Generated Gas (1)