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In-Depth Information
m thick, were prepared from poly(amic acid) (PAA) by cast-
ing onto soda lime glass plates and oven curing under air. Polymers of the BPDA-
TPER and (BPDA-TPER)TPER types could be obtained in the form of relatively
flexible and strong films (BPDA-TPER was an opaque film and (BPDA-
TPER)TPER was a transparent film), from NMP or N,N-dimethylacetamide
(DMAc) solutions. ODPA-BAPB and R-BAPB did not yield flexible films at all
from DMAc. The films of these polymers obtained from DMAc were opaque,
brown in color and very brittle after imidization at T = 280
PI films, 40-50
µ
C. According to XRD
and DSC data, an active crystallization of these PI's from PAA took place.
The sequence of the preparation of the composite based on semicrystalline PI
and low modulus (200 GPa) carbon fiber ELUR (NPO “Chimvolokno”, Moscow,
Russia) was as follows:
(1) Impregnation of the unidirectional carbon fabric with a 20-30% of the PAA
binder;
(2) Prepreg drying for complete solvent removal and thermal treatment up to ap-
proximately 100% imidization of the binder;
(3) Prepreg packing into a stack to obtain a composite of the required thickness.
(4) Composite molding above the matrix melting temperature to render the poly-
mer sufficiently fluid for uniform distribution throughout the fibers mass; and
(5) Mold cooling and annealing at temperature below the melting temperature of
the polymer and in the vicinity of its crystallization temperature in order to at-
tain the maximum degree of matrix crystallinity in the composite.
°
2.2. Measurements
DSC was performed using a Mettler DSC-30 Model on 5-10 mg samples con-
tained in aluminum pans with a heating rate of 10-20
C/ min under nitrogen.
Wide-angle XRD measurements were conducted on a diffractometer with a
Philips PW-1830 generator. A wavelength of 1.54 Å was generated from a CuK
°
source, with graphite as the monochromator. Samples were scanned in the angular
range of 10-40
α
.
Interlaminar fracture toughness G
1C
of the CFRC was measured by the double
cantilever beam method on a 1958U-10-1 (Russia) testing machine at a load
speed of 10 mm/min.
The storage shear modulus G' and loss modulus G'' of the CFRC were deter-
mined on a torsion pendulum MK-003 developed at the Institute of Macromolecu-
lar Compounds.
°
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