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Hedrite growth in polyacrylonitrile.

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Die Angewandte Makromolekulare Chemie 20 (1971) 197-201 ( N r . 273)
From the Department of Chemistry, Sardar Pate1 University,
Vallabh Vidyanagar, Gujarat State, India
Kurzmitteilung
Hedrite Growth in Polyacrylonitrile
By R. M. GOHIL,K. C. PATEL,
and R. D. PATEL
(Eingegangenam 23. Januar 1971)
SUMMARY :
Hedrite growth has been observed in PAN from its solution in propylene carbonate in the concentration range 0.06y0 t o 0.5%.
A review of the literaturel-3 indicated that the hedrites could be grow either
by slow crystallization of molten thin films or from very dilute solutions of polymers. Further it is also noted that polyacrylonitrile (PAN) is considered t o exhibit poor morphological growth. HOLLAND
et a1.43 5 succeeded to grow crystalline
platelets of PAN in propylene carbonate. The platelets were ellipsoidal in shape.
KLEMENT
and GEIL~
using the technique described by HOLLAND
et al. (loc. cit.)
reported that the morphology of the full-grown crystal of PAN varied considerably with crystallization temperature. A little information is available on the
hedrite growth in PAN from solution. Previous works3$6suggested that different stages of growth of hedrites and spherulites are achieved simply by varying
the concentration of polymer and the temperature of crystallization. Hence an
attempt has been made to obtain hedrites of PAN from its solution in propylene
carbonate.
PAN used in the present work was prepared according to the method described by MINO and KAIZERMAN~
= 6.63 x 105). A series of experiments
were tried to obtain the various morphological forms of PAN from its solution
in propylene carbonate. The concentration of the PAN was varied from 0.06 to
0.5% and in the crystallization temperature range of 105 to 150°C. Using the
film formation techniques it was possible to get various morphological forms
of PAN. I n most of the cases crystals were coated with carbon and shadowed
with chromium. The carbon replica were transferred to the grids suitable for
electron microscopic work. These were then examined in the CARLZEISS model
(x,
197
R.M. GOHIL,K . C. PATEL,and R. D. PATEL
EF-4 electron optical plant. It was also possible to get different growth stages
of hedrites, in the concentration range employed in this study.
In the concentration range 0.06y0 to 0.08yo of PAN in propylene carbonate
isolated plates with a few lamellae are obtained (Fig. 1 and 2) which can be considered to represent the primary growth stage of hedrites. Fig. 1 indicates a
typical example of a penetration twinned crystal of PAN. Increasing the con-
Fig. 1. Primary growth stage of hedrites from 0.06y0 solution of PAN, grown at
105°C ( X 22,130).
Fig. 2.
Primary growth stage of hedrites from 0.06% solution of PAN, grown at
105°C ( X 11,690).
198
Hedrite Growth in Polyacrylonitrile
Fig. 3. Intermediate growth stage of hedrites from 0.1% solution of PAN, grown
at 105°C ( x 11,590).
Fig. 4. Intermediate growth stage of hedrites from 0.2% solution of PAN, grown
at 110°C ( X 11,450).
centration of PAN from 0.1 t o 0.15%a rossette shape of growth (Fig. 3) containing more than 20 lamellae is observed. This represents an intermediate growth
stage. On further increase of concentration a final growth stage of hedrites is
reached (Fig. 5, 6). It could be seen from Fig. 6, that sometimes it is not possible
to observe distinct lamellae in the final growth stage. This is because the electron beam cannot penetrate through such a thick hedrite. Ellipsoidal hedrites
199
R . M. GOHIL,K . C. PATEL,
and R. D. PATEL
Fig. 5. Final growth stage of hedrites from 0.5% solution of PAN, grown a t
115°C ( X 11,400).
Fig. 6. Final growth stage of hedrites from 0.4% solution of PAN, grown at 110°C
( X 12,240.4).
developed on ellipsoidal platelet as a basic lamella, were also observed. It was
noted that hedrites continued to exhibit the same axial symmetry of the bound
lamellae over a wide range of concentration. From the different growth stages
of hedrites, it is evident that the hedrites get thickened by spiral growth mechanism. Various morphological forms along with the growth mechanism of hedrites will be published elsewhere.
Hedrite Growth i n Polyacrylonitrile
Authors’ thanks are due to Prof. A. R. PATEL,Head of the Physics Department, and Dr. s. M. PATEL,
Dr. C. M. PATEL,
and Dr. C. K. PATEL
for their
help and valuable suggestions throughout the progress of the work.
1
2
3
4
5
6
7
8
P. H. GEIL, J. Polymer Sci. 47 (1960) 65.
H. D. KEITH,J. Polymer Sci. A-2 (1964) 4339.
G. N. PATELand R. D. PATEL,European Polymer J. 6 (1970) 657.
V. F. HOLLAND,
S . B. MITCHELL,W. L. HUNTER,and P. H. LINDENMEYER,
J.
Polymer Sci. 62 (1962) 145.
V. F. HOLLAND,
R. CHIANG,and J. H. RHODES,
J. Polymer Sci. A 3 (1965) 479.
J. J. KLEMENT
and P. H. GEIL, J. Polymer Sci. A-2, 6 (1968) 1381.
G. MINO and S . KAIZERMAN,
J. Polymer Sci. 31 (1958) 242.
R. D. PATEL
and G. N. PATEL,J. Polymer Sci. A-2, 8 (1970) 47.
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