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The processes and mechanism of ageing of synthetic fibres—II. Investigation of the stabilization of polyamide fibres
Stabilization of polyamide fibres
473
Hence the data obtained show that pressure is one of the factors capable of affecting the direction of the elementary chain propagation step, and consequently the conformation of the polymer formed. CONCLUSIONS
The effect of high pressures applied during the process of polymerization of methylmethacrylate on the conformation of the polymer chains formed has been studied. It is shown that pressure is one of the factors capable of altering the fractions of the iso and syndio units in the polymer. The results obtained are explained on the basis of relationship arising from the theory of absolute rate processes. Translated by E. O. PHILLIPS REFERENCES 1. T. G. FOX, W. E. GOODE, S. GRATCH, H. M. HUGGETT, J. F. KINCAID, A. SPELL and J. D. STROUPE, J. Polymer Sci. 31: 173, 1958 2. M. G. GONIKBERG and A. I. KITAIGORODSKII, Dokl. Akad. Nauk SSSR 122: 231, 1958 3. P. P. KOBEKO, Amorfnye veshchestva. (Amorphous Substances.) Izd. Akad. Nauk SSSR, Foreign Literature Publishing House, 1952 4. U. BAUMANN, N. SCHERBER and K. TESSMAR, Makromol. Chem. 37: 81, 1959 5. N. G. G A ~ , O R D and H . F . MARK, Linear and Stereoregular Addition Polymers, New York-London, 1959
THE PROCESSES AND MECHANISM OF AGEING OF SYNTHETIC F I B R E S - - H . INVESTIGATION OF THE STABILIZATION OF POLYAMIDE FIBRES* L. G. T O K A R E V A , N . V. M I K H A I L O V , Z. I. P O T E M K I N A a n d M. V. K O V A L E V A All-Union Scientific-Research Institute of Synthetic Fibre
(Received 14 July, 1960)
THE loss cf mechanical and physico-chemical properties of fibres at 150-200°C depends on the time and conditions of application of the high temperatures. Under actual workirg conditions the high temperatures can act for periods of both short and lovg duration. Short-period action, particularly in an inert medium, results most often in changes in the physico-mechanical properties that charac* Vysokomol. soedin. 2: No. 11, 1728-1738, 1960.
474
L . G . TOKAREVA st a/.
texize the heat stability of polymeric materials, mainly as a result of reversible changes in the structure of the fibre and not of changes in chemical composition. The prolonged action of high temperatures on fibres and other articles based on polyamides in any medium, and particularly in the presence of oxygen, results in irreversible changes in their physico-mechanieal and physico-ehemical properties that characterize the heat stability of polymers, and these changes are connected not only with changes in the structure of the fibre but also with changes in its chemical composition. Polyamide fibres belong to a class of materials that are unstable not only to high temperatures but also to the action of light. Hence polyamide fibres and articles made from them need to be protected from the action of both high temperatures and light. Since no theory of the mechanism of ageiog of polyamides and polyamide fibres has been developed, work on their stabilization is mainly empirical in nature. Various organic substances are used as stabilizing additives for polyamides, possessing in the main inhibitirg properties of a reducing character. Examples of these are phenols, amines and their derivatives, and also salts mainly of complex-forming metals (Cu, Cr, Mg etc.) and organic and inorganic acids. For the purpose of making a more rational approach to a solution of the problem of stabilization of the properties of polyamid ~ fibres and articles a study has been made of the changes in properties of polyamides and fibres under the action of heat in an inert atmosphere and in an atmosphere of oxygen. On the basis of these results and those of previously published work on this problem [3] a mechanism of the degradation of polyamides has been suggested, from which it follows that in order to retard the irreversible changes in polyamide fibres the use of stabilizers with inhibiting action (antioxidants) is neeessary~ A lowering or prevention of the irreversible changes could probably be achieved by the addition of substances with active, bifunetional groups which should prevent changes in the structure of the fibre by chemical crosslinking of the polymer molecules. The present communication presents the results of a study of the possibility of preventing or retarding irreversible changes in the physico-mechanical properties of polyamide fibres (Kapron) by the addition of antioxidants. According to the present views of Semenov and his school [4], the activity of chain-reaction inhibitors is based on termination of the reaction chain as a result of interaction of the inhibitor with the molecules of the substance reacting. The effectiveness of an antioxidant is determined by the structure of its molecule. The relationship between the effectiveness of an antioxidant and the structure of its molecule has been studied by a number of authors [5]. As antioxidants substituted amines (primary and secondary aromatic amines) and phenols were used.
Stabilization of polyamide fibres
47.5
EXPERIMENTAL*
A large number of antioxidants and organic luminophores were investigated tbr stabilization of the properties of polyamide fibres, and the results of these tests are shown in Tables 1 and 2. In examining the experimental data of Tables 1 and 2 it should be noted that the most effective stabilizing activity is shown by the aromatic amines and their derivatives with cyclic radicals, the characteristic feature of which is the inhibition of oxidative processes, known from their application in rubbers. Tables 1 and 2 show the results of investigation of the changes in properties of fibres under conditions of accelerated thermal oxidation (t=200 ° for 2 hours). The additives were introduced in quantities from 0.1 to 1 ~o of the weight of polymer by dusting on to the granular polymer before spinning No. 300 fibre. As these results show the fibres on heating, as a result of the protective action of a number of additives against the thermal oxidation reactions taking place in polyamides, maintain 70-95% of their tensile strm~gth, with a small change in the specific viscosity of their 0"5~o solutions in tricresol. This means that the choice of the most suitable stabilizers would be controlled by the technological requirements of the particular application and probably 'by the amount ,*f additive involved. The interesting results on the stabilization of Kapron fibres against thermal oxidation reactions by means of luminophores should be noted. As is well known. these are inhibitors of photodegradation [6]. Of the luminophores investigated by us, some of which are included in Table 2. hydroxyphenylbenzoxazole (HPBO) shows the highest protective activity against thermal oxidative degradation. The data shown indicate t h a t luminophores can possess properties characteristie of thermophores. This is of great scientific and practical interest for the simultaneous protection of fibres against thermal and photo degradation, and shows the necessity of a more detailed s t u d y of both the luminophores used by us and new compounds of a similar type. In a number of cases, both with inhibitors of thermal oxidative degradation and with luminophores, the absence of an appreciable protective effect on heating the fibres in air is accompanied by a fall in the solubility of the polymer. This is evidently connected with the bifunctionality of these substances, leading to crosslinking of the polymer and consequently also to a loss of the inhibiting properties of these compounds. Under the conditions of our experiments the most effective stabilizer proved to be N,N'-di- fl-naphthyl-p-phenylene diamine (DNPDA)t and this was subjected to a more detailed investigation. Kapron fibre containing this stabilizer was prepared. * A. M. Glebova assisted in the experimental work. t We are grateful to A. I. Korolev and co-workers of the NIOP and K for the synthesis , ,f the DNPDA.
476
L . G . TOKAREVA et al.
TABLE
1,
VARIATION IN
PROPERTIES
OF K A P R O N
FIBRES P R E P A R E D W I T H VARIOUS
ANTIOXIDANTS Before heating
Additive
Structural formula
t
Physicomechanical eon stant_~s
After heating at 200 ° for 2 hours Physicomechanical ' constants
~ ' ~
Initial N,N'-di-fl-naphthyl-p-phenylene diamine 2,2'-Methylenebis-4-methyl-6tert-butylphenol
/
/\--N
m~
N
.705
50.0
26"3
0-57
0"658
45.6
38"4
44.2 37.0 0.722 87.---5 06.6
f
i 10-0 23-0 ~---~-13o.5
--N
CH.
CH,
OH
OH
0.595
54"5
25"~ i / r
[ 18s.2 13.5 33.4 52.3
C4H~--~--C4H9 CH C,HD
0-627
35"6
24"~ i/r
I 14.5 m.5 ~-s.~ ~.~
C4H~--~--C4H o OH
0"653
50.5
24"~
[R--~0]~P
0"869
59"I
17"7
0.704
56.4
35"6
i/r
]14--5_ 10-9 31.2 30.0
9.624
i2.0
36"2
p/h
21.o 12.6 52.7 34.7
)'702
t0.0
34.8
0.805[ 31.0 33.5
)'501
48"1
32.1
42-2 30-5 0-601 8 ~ 9%.o
CH~ 2,6-di-tert-butyl4-methylphenol
2,4,6-tri-(tertbutyl) phenol Polygard Dimethylphenylp-cresol
Reaction product from acetone and diphenylamine N,N'-phenylcyelohexyl.pphenylene diamine
117.__O9 11.6 35.5 47.2
0.296 l _~5_.2 12._3_ 25.8 69.5
CH3 I \
CH3 Dibutyldi. hydroxyphenyl . sulphide
i]r
/
OH OH C.H ~/--~--S--~C,H.
(C6Hs)~H+ CH3COCH~ CH2
/~N--\/---%--N--~C/~0H~ CH2
Stabilization of polyamide fibres
477
TABLE 1. (cntd.) Before heating
Additive
2,5-di-tert-butylhydro-quinone
Structural formula
Physieomechan ieal constants
OH (~C,H~--tert tcrt--II~C~/J OII
Reaction product of acetone and aminophenol N,N'-diphenylp -phenylene diamine
£
After heating at 200° for 2 hours
%/"
"\/
Physicomechanical constants
19.3 0.603 26.0 ~.~
0-707 52.3
29.8
0.697
19.2 0.597 s3.4
48.0
37.8
0-597 47-7
23.5
0.490 ~32'9
33.~ 17.3
22,5
Product of condensation of phenol with styrene
0.532
48.5
34.7
0.479 ~.~ 41-2
Phenyl-fl-naphthylamine
0"651 I 50.7
30.3
O.428 ~b:~ dT~
15.6
14.3
35.5
34.6
T h e spinning o f t h e fibre followed t h e n o r m a l routine a n d the fibre o b t a i n e d had t h e same initial physieo-mechanical c o n s t a n t s as the n o r m a l fibre (Table 3). All t h e fibres were s u b j e c t e d to prolonged h e a t i n g a t 150 a n d 180 ° for 8, 48 and 100 hours, a n d to a short period o f h e a t i r g for 30 m i n u t e s a t 200 ° in a c u r r e n t of n i t r o g e n a n d in air. T h e changes in the viscosity of 0-5% solutions o f the p o l y m e r in tricresol, a n d in the physico-mechanica] constants of t h e fibre were determined. I n Table 3 a n d Figures 1, 2 a n d 3 is p r e s e n t e d p a r t of the results, showing t h e i r good reproducibility. F r o m the results shown in Figure 1 on t h e changes in t h e physico-mechanical properties o f the fibres, d e t e r m i n e d a t n o r m a l t e m p e r a t u r e , it is seen t h a t during the short t e r m action o f high t e m p e r a t u r e s on n o r m a l fibre (without additive) in a m e d i u m o f n i t r c g e n (curve 2) a n d on t h e fibre stabilized with D N P D A b o t h in air a n d in n i t r c g e n (curves 5 a n d 6) o n l y a reversible change in the tensile s t r e n g t h o f the fibre a n d increase in extensibility takes place as a result of structural changes in the fibre.
47s
L.G.
T O K A R E V A et al.
T A B L E 2. V A R I A T I O N I N P R O P E R T I E S OF K A P R O N FIBRES P R E P A R E D W I T H VARIOUS LUMINOPHORES
Additive
Before heating Physieomechanieal constants
Structural formula
"~
After heating at 200° for 2 hours Physicomechanical constants
~
.= l
~°
N
Hydroxyphenylbenzoxazole ~ (HPBO) Light-yellow, i Lumogen,Water's°luble2hydroxy- 1na.phthaldehyde i azlne
/\/\ ,\/\/ o
......
, / ili:T- - - /
ctt-~=.x--tie ~1 "1/~oH, FIo--~!
33-8 24--5 0.642 43-2 27.9 0"642 T g.~ 9o.o
0.687 48.2 20.5
i/r
0. 737 38"0 43.3
i/r
T77~ 46-5 0.4
" /\" 0 /fi\/\/~.
i I! III Water-blue Lurnogen
c :1 c
f~'x/\/\\
II|
i
12.4
1_1.5
3~.g 26.6 i
In the short-term action in air of the same temperature on normal fibre (curve 3) an irreversible fall in the physico-meehanical properties of the fibre occurs, resulting from both structural changes and changes in the chemical composition of the polymer. Curves 1 and 4 show the physico-mechanical properties of the normal and stabilized fibres respectively. As is seen from the data shown in Figure 2 the viscosity of 0.5% solutions of normal fibre in trieresol falls sharply with increasing time of heating (curve 1). The viscosity of the fibre with D N P D A as additive increases a little after heading at 150 ° for 8 and 48 hours and then falls to the original value (curve 2). These investigations show that the addition of small amounts of N,N'-difl-naphlhyl-p-phenylene diamine (DNPDA) (0.2-1% of the weight of polymer} increases the heat stability of Kapron fibre considerably. The tensile strength of the fibre after prolorged heating is maintained at 80-85}/0 of the original value when this material is added, whereas without the additive only 20-25% of the tensile strength is maintained (Fig. 3).
S t a b i l i z a t i o n o f p o l y a m i d e fibres
479
TABLE 3. VARIATION IN PROPERTIES OF KAPRON FIBRES ON PROLONGED HEATING I
Before heating
tlsP
"~.~
Heated 8 hours a t 150 °
H e a t e d 48 h o u r s a t 150 °
~'~ ~
Elongation,
~_~
%
~
::::
~/sp
qsp
0-5 0"796 t
0.496 0.853
0"749
76.1 15.0 0"825
0.5 0"745
75.0! 17.9 0 . 8 5 i
Elonga. tion,
~ ~
%
44.7
15.1
75.0 74*5
21.9 161 20.5
-6U
13~.8
71.1
23.4
I ,
.i
o~
0"775
H e a t e d 100 h o u r s a t 150 °
I
0-333
25.1
10.0
-~
16.4
~g.~
1~
65.5
17.4
0.827
-s6~. 61.5
18.4
0.938
~82.5
-i03
0.827 0-769
1-~
~/~ --~
~-~
o~ /o
19.2 25.8 66.6
8-3 46.0 16.8
66.5 ~TTi.4 62-6 -ga.8
19.3 i28.~ 19.9"
r/sp
0.304
55.6
65*2
0.842
i
. .
0.825
* Not washed.
~ ~//mrgl 2
/
5g
5/7 ,
¢0
2
."/ //¢1// /d/
I
r/'"
30
212
lO
g
0
8
f
I
t
72
16
20
1
2'
t
1
28
32
E,% ~'IG. 1. V a r i a t i o n i n t h e p h y s i e o - e h e m i e a l p r o p e r t i e s o f K a p r o n fibres: 1 - - i n i tiM; 2 - - t h e s a m e , h e a t e d 30 m i n a t 200 ° i n n i t r o g e n ; 3 - - t h e s a m e , in air; d - - w i t h a d d i t i o n o f D N P D A ; 5 - - t h e s a m e , h e a t e d 30 r a i n a t 200 ~ i n n i t r o g e n ; 6 - - t h e s a m e , i n air. a2 P o l y m e r 3
Elongation,
Ill
480
L.G. TOKAREVAet al. I00
qsp
0.14
,
O3 8 #8 10o Time of" hea~ng, hears a~ 150°
FIO. 2. Viscosity of 0.5% solutions in tricresol of Kapron fibres dusted with DNPDA: /--initial; 2--with addition of DNPDA.
ZO I
8
I
#8
lOfO
Time of heating, hours
FIG. 3. Variation in strength of Kapron fibres dusted with DNPDA. 1--initial, heated at 150°; 2--the same, at 180°; 3--with addition of DNPDA, heated at 150°; 4--the same, at 180°.
The reduction in strength of the fibre stabilized with DNPDA is evidently due to irreversible charges in the structure of the fibre but not in its chemical composition, as is shown by the fact t h a t the viscosity of 0"5~/o solutions of the fibre in tricresol remains constant while at the same time the strength decreases and the elongation increases. I t is known t h a t monomer and other low-molecular products impair the properties of Kapron fibre. In order to remove these the fibre is washed with hot water, which could also remove the stabilizer (DNPDA). B y a comparative study of the heat stability of washed and unwashed stabilized fibres it was shown t h a t the DNPDA is not washed out of the fibre. The results shown in Figure 3 indicate t h a t the properties of the washed and unwashed fibres are the same. The additive in the fibre investigated by us was introduced by dusting on to the polymer but the simpler method of introducing the stabilizer before polymerization and thus stabilizing the polymer during preparation is of doubtful practical applicability in view of the prolonged action of the high polymerization temperature on the additive. Experiments were carried out on the addition c f DNPDA to molten caprolaetam before polymerization. The caprolactam was polymerized by the usual method. Water was used as calatyst and acetic or adipic acid as agent for the control of molecular weight. Some experimental batches were made without a chain terminating agent. Table 4 shows the visccsities of 0.5% solutions in tricresol of polymers prepared with and without terminating agents.
Stabilization of polyamide fibres
itt~i~
TABLE 4. VISCOSITIES OF 0"5 SOLUTIONS OF POLYMERS
Additive in ~o of the weight of polymer 0.1 0.1 0.2 0.2
~/sp
0-760"75 0"7~0"71 0"737 0.735
DNPDA DNPDA-b 0.075 acetic acid DNPDA+0.1 adipic acid DNPDA+0.05 acetic acid
T h e results g i v e n in T a b l e 4 show t h a t t h e v i s c o s i t y o f t h e solution o f t h e p o l y m e r p r e p a r e d w i t h o u t a t e r m i n a t i n g a g e n t is a little h i g h e r ' t h a n t h a t o f t h e p o ] y m e r s p r e p a r e d w i t h t e r m i n a t i r g agents. F i b r e s w i t h s a t i s f a c t o r y p h y s i c o - m e c h a n i c a l c o n s t a n t s were p r e p a r e d f r o m the p o l y m e r s , t h e c h a r a c t e r i s t i c s o f which are g i v e n in T a b l e 4. T h e fibres were h e a t e d a t 150 a n d 180 ° . T h e v a r i a t i o n in viscosity o f 0 . 5 % solutions o f t h e fibres in tricresol a n d t h e i r p h y s i c o - m e c h a n i c a l c h a r a c t e r i s t i c s a f t e r h e a t i n g a r e s h o w n in F i g u r e s 4 a n d 5. rlso
0"9 0"~ ~:" 8O
0"7 O~
U
0"5
~: zo 0..I
!
8 48 I00 Time of heatLng~hovrs ~zt 150 o
FIe. 4. Viscosity of 0.5% solutions in tricresol of Kapron fibres (DNPDA added during polymerization of the caprolactazn): 1 initial; 2--with addition of DNPDA.
8
#8 Time of" heating, ho~rs
i00
Fie. 5. Variation in strength of polyamide fibres (DNPDA added during polymerization of the caprolactam): /--initial, h e a t e d at 150°; 2--the same, at 180°; 3--with addition of DNPDA, heated at 150°; 4--the same, at 180 °.
I t is seen f r o m these results t h a t t h e v i s c o s i t y o f t h e solutions o f fibres h e a t e d a t 150 ° v a r i e s in t h e s a m e w a y as for fibres p r e p a r e d w i t h t h e a d d i t i o n o f D N P D A b y d u s t i n g (cf. Fig. 2). 32*
L. G. TOKAREVA e t
482
al.
The physico-mechanical characteristics also vary in the same w a y (el. Figs. 3 and 5). These data show that independently of the method of addition D N P D A is a fairly effective stabilizer that increases the heat stability of Kapron fibre considerably. •
Study of ihe heat and light resistance of Kapron fibres Investigation o f t h e heat resistance of the fibres, with and without stabilizers, was carried out on a thermomeehanical test apparatus of the Polyani type over a wide range of temperatures in air and in nitrogen• Figure 6 shows the 'i
i
'~
•
il
38 _55 37 35 -50 83 31 29
fi 35 •
1 i
i
ZJ /
_.'"
,21 /251
y3
I7 ¢5 t
i i
2l
15 I ZO
I 50
- i 80
L 170
, I/~O
i 770
200t:C
I
FIG. 6. tVariation inI physieo-meehanical properties of polyamide fibres: / - - s t r e n g t h of original fibre in nitrogen; 2--thee.same, in air; 3 - - s t r e n g t h of fibro with a d d e d D N P D A in nitrogen; d - - t h e same, in air.
deperidence Of tensile strength and elongation of the fibres on test temperature and ~the medium. /~s is seen from Figure 6 the tensile strength falls considerably with increasing temperature. The strength falls more sharply in the case of the Kapron fibre testec], in air (curve 2), which supports the conclusion drawn previously [2] conoerni~, g the role of oxidative processes in the variation in the physieo-mechanic~l properties of fibres.
Stabilization of polyamide fibres
483
The decrease in strength of the fibre under the action of heat is 'also connected with the occurrence of reversible structural processes, ;as a result of whieh~ the strength is restored on cooling the specimen. Hence the difference in the residual strength on testing the fibre in nitrogvn (curve 1) and air' (curve 2) must be due to the occurrence of irreversible chemical processes. I t follows from this that the coincidence of the results of testing the fibre stabilized with DN-PDA in nitrcgvn and in air (cvrves 3 and 4) indicates t h a t irreversible chemical processes do not occur in the stabilized fibre subjected to the action of high temperatures in air. This is very clearly confirmed b y the fact that the reduction in strength of the fibre stabilized with D N P D A is a little less than in the case of the unstabilized fibre tested in nitrogen (cf. curves 3 and 4 with 1). The difference in the results on the lowering of the strength of fibres stabilized with D N P D A and unstabilized (in nitrogen) can evidently be explained b y a small increase in heat resistance on account of the introduction of the add#tive. regards the cause of the stabilizing action of such inhibitors as D N P D A against the short-term action of heat, at the present time there are insufficient experimental data to explain it and in any consideration of this accountimust be taken of the possibility, if only partial, of strepgthenirg of the inter-molecular bonds or crosslinkirg in the polyamides by means of th~ stabilizer. The addition of small amounts of D N P D A or H P B O leads not only to the achievement of a considerable increase in the heat stability and some increase in the heat resistance of polyamide fibres b u t also a considerable increase in the light resistance of the fibres is brought about: ; ( ~ TABLE 5. EFFECT OF ADDITIVESON THE STRENGTHOF POLYAMIDESAND THE VISCOSITYOF THEIR SOLUTIONS Viscosity ~/sp Additive
W i t h o u t additive (normal) W i t h addition of 0.5% D N P D A With addition of 1% D N P D A With addition of 0.5% HPBO With addition of 1% HPBO
% fall in strength
% fall in elongation
40"9 21"9 19"7 16"8 12"8
45 34.1 32.5 24.4 31.4
before ] after irradiation irradiation 0"775 0.795 0-762 0.754 0.762
0"471 ~40 0"773 0'770 0"768
Table 5 shows the variation in viscosity of 5% solutions of the polyamide in tricresol, and the fall in strength and elongation of Kapron fibres, with and without additives, subjected to accelerated photodegradation in air by irradiation with a quartz lamp for 20 hours. ~ As is seen from Table 5 the viscosity of solutions of stabilized fibre in tricresol shows practically no fall after irradiation, whereas in the case of the fibre without
484
L. G. TOKAREVAet
al.
additive it falls sharply. The tensile strergth and elorgation of the fibre with additive fM1 almost half as much as in the case of the fibre without additive (Table 5). :This:interesting phenomenon, which requires special investigation, is in good egreement with the fact, described above, of the appearance in a luminophore of the properties of a thermophore, because if this is possible the converse ,would ~lso be expected i.e. the occurrence of photostabilizing activity in a typical antioxidant such as DNPDA. ': All this suggests the possibility, in principle, of a combined solution of the problem of the ageing of synthetic fibres which embraces simultaneously the protection: of the polymer from thermal and photo degradation and an improvement in heat resistance. A l l the data presented b y us relate to Kapron polyamide fibre but from preliminary results obtained it may be considered that all additives that increase the heat stability of Kapron fibre will also increase that of polyamide fibres such as Anid and Enant. The results of an investigation of these fibres will f o r m a separate communication. The authors express their gratitude to N. V. Demina and co-workers of the Laboratory of Textile Testing for assistance in the determination of the physicomechanical properties of the fibres.
" '
CONCLUSIONS
(1) Investigation of the effect of a large number of antioxidants and luminophores on the variation in properties of polyamide fibres has shown that aromatic amines and their derivatives possess effective stabilizirg activity. N,N'-di-flnaphthyl-p-phenylene diamine (DNPDA) and N,N'-phenylcyclohexyl-p-phenylene d i a m i n e are the most effective stabilizers for polyamide fibres. (2) It was found that the tensile strength of fibres stabilized with DNPDA after prolor~ged action of high temperatures (150° for 100-150 hours) is maintained t o the extent of 80-85% whereas that of the unstabflized fibre falls to only 205.25% of the original value. (3) The variation in the physico-mechanical properties of fibres stabilized with DNPDA has been studied over a wide rarge of temperatures. It is shown that short exposure of the normal fibre to high temperatures in an atmosphere of nitrogen and of the DNPDA-stabilized material in air also causes a reversible charge in the strength of the fibre, whereas irreversible changes in the properties of the fibre take place when the normal fibre is subjected to these temperatures in air and these chang3s are related to charges in the chemical composition of the polymer. It has been established that irreversible chemical processes do not occur on prolor.g3d heating of fibre stabilized with DNPDA, i.e. this antioxidant completely protects the polyamide fibre from oxidation.
Dehydroehlorination of polyvinylchloride
485
(4) It is shown that some luminophores, for example hydroxyphenylbenzoxazole (HI~BO) can at the same time possess properties characteristic of thermophores. The addition of DNPDA and H P B O to polyamides increases the light resistance of the polyamide fibres as well as their heat stability. Translated by E. O. PHILLIPS REFERENCES 1. HALLE, Texture, 3, 18-20, 1956 2. N. V. MIKHAILOV, L. G. TOKAREVA and M. V. KOVALEVA, Vysokomol. soedin. 2: 581, 1960 3. G. ACHI-IAMMER, W. REIGART and M. I~LINE, J. Applied Chem. 1: 301, 1951; L. URBANCOVA, Chem. prumysl. 5: 75-78, 1955; I. GUNDAVDA, J. Textile Inst. 5: 289, 1956 4. N. N. SEMENOV, O nekotorykh problemakh khimicheskoi kinetiki i reaktsionnoi sposobnosti. (Some Problems of Chemical Kinetics and Reactivity). Izd. Akad. Nauk SSSR, 1954 5. A. S. KUZ'MINSKII and A. G. ANGERT, Dokl. Akad. Nauk SSSR 82: 747, 1952; 96: 1147, 1954; P. P. MARSCH a n d M. L. BUTLER, Ind. Eng. Chem. 38: 701, 1946; G. S. HAMMAUND and {3. E. BOOSER, J. Amer. Chem. Soc. 77: 3238, 1955 6. V. V. KORSHAK, K. K. MOZGOVA and V. P. LAVRISHCHEV, Vysokomol. soedin, l : 1164, 1959
Letter to the Editor THE DEHYDROCHLORINATION OF POLYVINYLCHLORIDE BY POTASSIUM AMIDE IN LIQUID AMMONIA* I. V. A S T A F ' E V a n d A. K . P I S K U N O V
(Received 5 July 1960)
DEHYDROCHLORINATION of polyvinylchloride (PVC) is one of the methods of producing polymers with systems of conjugated double bonds, possessing heat stability and semiconductor properties [1]. We used for this purpose a solution of potassium amide in liquid ammonia and carried out the reaction under pressure at room temperature, considering that b y the action of the amide on secondary and tertiary halides olefines are produced exclusively [2]. From PVC (mol. ~ t > 75,000) the product obtained was a black powder, insoluble in benzene. On investigation of the electron spin resonance (ESR) at a frequency of~9370 m herz at room temperature the powder gives a single absorption line with weak a s y m m e t r y toward the side of high field strength. The width of the line between * Vysokomol. soedin. 2: No. 11, 1745, 1960.
473
Hence the data obtained show that pressure is one of the factors capable of affecting the direction of the elementary chain propagation step, and consequently the conformation of the polymer formed. CONCLUSIONS
The effect of high pressures applied during the process of polymerization of methylmethacrylate on the conformation of the polymer chains formed has been studied. It is shown that pressure is one of the factors capable of altering the fractions of the iso and syndio units in the polymer. The results obtained are explained on the basis of relationship arising from the theory of absolute rate processes. Translated by E. O. PHILLIPS REFERENCES 1. T. G. FOX, W. E. GOODE, S. GRATCH, H. M. HUGGETT, J. F. KINCAID, A. SPELL and J. D. STROUPE, J. Polymer Sci. 31: 173, 1958 2. M. G. GONIKBERG and A. I. KITAIGORODSKII, Dokl. Akad. Nauk SSSR 122: 231, 1958 3. P. P. KOBEKO, Amorfnye veshchestva. (Amorphous Substances.) Izd. Akad. Nauk SSSR, Foreign Literature Publishing House, 1952 4. U. BAUMANN, N. SCHERBER and K. TESSMAR, Makromol. Chem. 37: 81, 1959 5. N. G. G A ~ , O R D and H . F . MARK, Linear and Stereoregular Addition Polymers, New York-London, 1959
THE PROCESSES AND MECHANISM OF AGEING OF SYNTHETIC F I B R E S - - H . INVESTIGATION OF THE STABILIZATION OF POLYAMIDE FIBRES* L. G. T O K A R E V A , N . V. M I K H A I L O V , Z. I. P O T E M K I N A a n d M. V. K O V A L E V A All-Union Scientific-Research Institute of Synthetic Fibre
(Received 14 July, 1960)
THE loss cf mechanical and physico-chemical properties of fibres at 150-200°C depends on the time and conditions of application of the high temperatures. Under actual workirg conditions the high temperatures can act for periods of both short and lovg duration. Short-period action, particularly in an inert medium, results most often in changes in the physico-mechanical properties that charac* Vysokomol. soedin. 2: No. 11, 1728-1738, 1960.
474
L . G . TOKAREVA st a/.
texize the heat stability of polymeric materials, mainly as a result of reversible changes in the structure of the fibre and not of changes in chemical composition. The prolonged action of high temperatures on fibres and other articles based on polyamides in any medium, and particularly in the presence of oxygen, results in irreversible changes in their physico-mechanieal and physico-ehemical properties that characterize the heat stability of polymers, and these changes are connected not only with changes in the structure of the fibre but also with changes in its chemical composition. Polyamide fibres belong to a class of materials that are unstable not only to high temperatures but also to the action of light. Hence polyamide fibres and articles made from them need to be protected from the action of both high temperatures and light. Since no theory of the mechanism of ageiog of polyamides and polyamide fibres has been developed, work on their stabilization is mainly empirical in nature. Various organic substances are used as stabilizing additives for polyamides, possessing in the main inhibitirg properties of a reducing character. Examples of these are phenols, amines and their derivatives, and also salts mainly of complex-forming metals (Cu, Cr, Mg etc.) and organic and inorganic acids. For the purpose of making a more rational approach to a solution of the problem of stabilization of the properties of polyamid ~ fibres and articles a study has been made of the changes in properties of polyamides and fibres under the action of heat in an inert atmosphere and in an atmosphere of oxygen. On the basis of these results and those of previously published work on this problem [3] a mechanism of the degradation of polyamides has been suggested, from which it follows that in order to retard the irreversible changes in polyamide fibres the use of stabilizers with inhibiting action (antioxidants) is neeessary~ A lowering or prevention of the irreversible changes could probably be achieved by the addition of substances with active, bifunetional groups which should prevent changes in the structure of the fibre by chemical crosslinking of the polymer molecules. The present communication presents the results of a study of the possibility of preventing or retarding irreversible changes in the physico-mechanical properties of polyamide fibres (Kapron) by the addition of antioxidants. According to the present views of Semenov and his school [4], the activity of chain-reaction inhibitors is based on termination of the reaction chain as a result of interaction of the inhibitor with the molecules of the substance reacting. The effectiveness of an antioxidant is determined by the structure of its molecule. The relationship between the effectiveness of an antioxidant and the structure of its molecule has been studied by a number of authors [5]. As antioxidants substituted amines (primary and secondary aromatic amines) and phenols were used.
Stabilization of polyamide fibres
47.5
EXPERIMENTAL*
A large number of antioxidants and organic luminophores were investigated tbr stabilization of the properties of polyamide fibres, and the results of these tests are shown in Tables 1 and 2. In examining the experimental data of Tables 1 and 2 it should be noted that the most effective stabilizing activity is shown by the aromatic amines and their derivatives with cyclic radicals, the characteristic feature of which is the inhibition of oxidative processes, known from their application in rubbers. Tables 1 and 2 show the results of investigation of the changes in properties of fibres under conditions of accelerated thermal oxidation (t=200 ° for 2 hours). The additives were introduced in quantities from 0.1 to 1 ~o of the weight of polymer by dusting on to the granular polymer before spinning No. 300 fibre. As these results show the fibres on heating, as a result of the protective action of a number of additives against the thermal oxidation reactions taking place in polyamides, maintain 70-95% of their tensile strm~gth, with a small change in the specific viscosity of their 0"5~o solutions in tricresol. This means that the choice of the most suitable stabilizers would be controlled by the technological requirements of the particular application and probably 'by the amount ,*f additive involved. The interesting results on the stabilization of Kapron fibres against thermal oxidation reactions by means of luminophores should be noted. As is well known. these are inhibitors of photodegradation [6]. Of the luminophores investigated by us, some of which are included in Table 2. hydroxyphenylbenzoxazole (HPBO) shows the highest protective activity against thermal oxidative degradation. The data shown indicate t h a t luminophores can possess properties characteristie of thermophores. This is of great scientific and practical interest for the simultaneous protection of fibres against thermal and photo degradation, and shows the necessity of a more detailed s t u d y of both the luminophores used by us and new compounds of a similar type. In a number of cases, both with inhibitors of thermal oxidative degradation and with luminophores, the absence of an appreciable protective effect on heating the fibres in air is accompanied by a fall in the solubility of the polymer. This is evidently connected with the bifunctionality of these substances, leading to crosslinking of the polymer and consequently also to a loss of the inhibiting properties of these compounds. Under the conditions of our experiments the most effective stabilizer proved to be N,N'-di- fl-naphthyl-p-phenylene diamine (DNPDA)t and this was subjected to a more detailed investigation. Kapron fibre containing this stabilizer was prepared. * A. M. Glebova assisted in the experimental work. t We are grateful to A. I. Korolev and co-workers of the NIOP and K for the synthesis , ,f the DNPDA.
476
L . G . TOKAREVA et al.
TABLE
1,
VARIATION IN
PROPERTIES
OF K A P R O N
FIBRES P R E P A R E D W I T H VARIOUS
ANTIOXIDANTS Before heating
Additive
Structural formula
t
Physicomechanical eon stant_~s
After heating at 200 ° for 2 hours Physicomechanical ' constants
~ ' ~
Initial N,N'-di-fl-naphthyl-p-phenylene diamine 2,2'-Methylenebis-4-methyl-6tert-butylphenol
/
/\--N
m~
N
.705
50.0
26"3
0-57
0"658
45.6
38"4
44.2 37.0 0.722 87.---5 06.6
f
i 10-0 23-0 ~---~-13o.5
--N
CH.
CH,
OH
OH
0.595
54"5
25"~ i / r
[ 18s.2 13.5 33.4 52.3
C4H~--~--C4H9 CH C,HD
0-627
35"6
24"~ i/r
I 14.5 m.5 ~-s.~ ~.~
C4H~--~--C4H o OH
0"653
50.5
24"~
[R--~0]~P
0"869
59"I
17"7
0.704
56.4
35"6
i/r
]14--5_ 10-9 31.2 30.0
9.624
i2.0
36"2
p/h
21.o 12.6 52.7 34.7
)'702
t0.0
34.8
0.805[ 31.0 33.5
)'501
48"1
32.1
42-2 30-5 0-601 8 ~ 9%.o
CH~ 2,6-di-tert-butyl4-methylphenol
2,4,6-tri-(tertbutyl) phenol Polygard Dimethylphenylp-cresol
Reaction product from acetone and diphenylamine N,N'-phenylcyelohexyl.pphenylene diamine
117.__O9 11.6 35.5 47.2
0.296 l _~5_.2 12._3_ 25.8 69.5
CH3 I \
CH3 Dibutyldi. hydroxyphenyl . sulphide
i]r
/
OH OH C.H ~/--~--S--~C,H.
(C6Hs)~H+ CH3COCH~ CH2
/~N--\/---%--N--~C/~0H~ CH2
Stabilization of polyamide fibres
477
TABLE 1. (cntd.) Before heating
Additive
2,5-di-tert-butylhydro-quinone
Structural formula
Physieomechan ieal constants
OH (~C,H~--tert tcrt--II~C~/J OII
Reaction product of acetone and aminophenol N,N'-diphenylp -phenylene diamine
£
After heating at 200° for 2 hours
%/"
"\/
Physicomechanical constants
19.3 0.603 26.0 ~.~
0-707 52.3
29.8
0.697
19.2 0.597 s3.4
48.0
37.8
0-597 47-7
23.5
0.490 ~32'9
33.~ 17.3
22,5
Product of condensation of phenol with styrene
0.532
48.5
34.7
0.479 ~.~ 41-2
Phenyl-fl-naphthylamine
0"651 I 50.7
30.3
O.428 ~b:~ dT~
15.6
14.3
35.5
34.6
T h e spinning o f t h e fibre followed t h e n o r m a l routine a n d the fibre o b t a i n e d had t h e same initial physieo-mechanical c o n s t a n t s as the n o r m a l fibre (Table 3). All t h e fibres were s u b j e c t e d to prolonged h e a t i n g a t 150 a n d 180 ° for 8, 48 and 100 hours, a n d to a short period o f h e a t i r g for 30 m i n u t e s a t 200 ° in a c u r r e n t of n i t r o g e n a n d in air. T h e changes in the viscosity of 0-5% solutions o f the p o l y m e r in tricresol, a n d in the physico-mechanica] constants of t h e fibre were determined. I n Table 3 a n d Figures 1, 2 a n d 3 is p r e s e n t e d p a r t of the results, showing t h e i r good reproducibility. F r o m the results shown in Figure 1 on t h e changes in t h e physico-mechanical properties o f the fibres, d e t e r m i n e d a t n o r m a l t e m p e r a t u r e , it is seen t h a t during the short t e r m action o f high t e m p e r a t u r e s on n o r m a l fibre (without additive) in a m e d i u m o f n i t r c g e n (curve 2) a n d on t h e fibre stabilized with D N P D A b o t h in air a n d in n i t r c g e n (curves 5 a n d 6) o n l y a reversible change in the tensile s t r e n g t h o f the fibre a n d increase in extensibility takes place as a result of structural changes in the fibre.
47s
L.G.
T O K A R E V A et al.
T A B L E 2. V A R I A T I O N I N P R O P E R T I E S OF K A P R O N FIBRES P R E P A R E D W I T H VARIOUS LUMINOPHORES
Additive
Before heating Physieomechanieal constants
Structural formula
"~
After heating at 200° for 2 hours Physicomechanical constants
~
.= l
~°
N
Hydroxyphenylbenzoxazole ~ (HPBO) Light-yellow, i Lumogen,Water's°luble2hydroxy- 1na.phthaldehyde i azlne
/\/\ ,\/\/ o
......
, / ili:T- - - /
ctt-~=.x--tie ~1 "1/~oH, FIo--~!
33-8 24--5 0.642 43-2 27.9 0"642 T g.~ 9o.o
0.687 48.2 20.5
i/r
0. 737 38"0 43.3
i/r
T77~ 46-5 0.4
" /\" 0 /fi\/\/~.
i I! III Water-blue Lurnogen
c :1 c
f~'x/\/\\
II|
i
12.4
1_1.5
3~.g 26.6 i
In the short-term action in air of the same temperature on normal fibre (curve 3) an irreversible fall in the physico-meehanical properties of the fibre occurs, resulting from both structural changes and changes in the chemical composition of the polymer. Curves 1 and 4 show the physico-mechanical properties of the normal and stabilized fibres respectively. As is seen from the data shown in Figure 2 the viscosity of 0.5% solutions of normal fibre in trieresol falls sharply with increasing time of heating (curve 1). The viscosity of the fibre with D N P D A as additive increases a little after heading at 150 ° for 8 and 48 hours and then falls to the original value (curve 2). These investigations show that the addition of small amounts of N,N'-difl-naphlhyl-p-phenylene diamine (DNPDA) (0.2-1% of the weight of polymer} increases the heat stability of Kapron fibre considerably. The tensile strength of the fibre after prolorged heating is maintained at 80-85}/0 of the original value when this material is added, whereas without the additive only 20-25% of the tensile strength is maintained (Fig. 3).
S t a b i l i z a t i o n o f p o l y a m i d e fibres
479
TABLE 3. VARIATION IN PROPERTIES OF KAPRON FIBRES ON PROLONGED HEATING I
Before heating
tlsP
"~.~
Heated 8 hours a t 150 °
H e a t e d 48 h o u r s a t 150 °
~'~ ~
Elongation,
~_~
%
~
::::
~/sp
qsp
0-5 0"796 t
0.496 0.853
0"749
76.1 15.0 0"825
0.5 0"745
75.0! 17.9 0 . 8 5 i
Elonga. tion,
~ ~
%
44.7
15.1
75.0 74*5
21.9 161 20.5
-6U
13~.8
71.1
23.4
I ,
.i
o~
0"775
H e a t e d 100 h o u r s a t 150 °
I
0-333
25.1
10.0
-~
16.4
~g.~
1~
65.5
17.4
0.827
-s6~. 61.5
18.4
0.938
~82.5
-i03
0.827 0-769
1-~
~/~ --~
~-~
o~ /o
19.2 25.8 66.6
8-3 46.0 16.8
66.5 ~TTi.4 62-6 -ga.8
19.3 i28.~ 19.9"
r/sp
0.304
55.6
65*2
0.842
i
. .
0.825
* Not washed.
~ ~//mrgl 2
/
5g
5/7 ,
¢0
2
."/ //¢1// /d/
I
r/'"
30
212
lO
g
0
8
f
I
t
72
16
20
1
2'
t
1
28
32
E,% ~'IG. 1. V a r i a t i o n i n t h e p h y s i e o - e h e m i e a l p r o p e r t i e s o f K a p r o n fibres: 1 - - i n i tiM; 2 - - t h e s a m e , h e a t e d 30 m i n a t 200 ° i n n i t r o g e n ; 3 - - t h e s a m e , in air; d - - w i t h a d d i t i o n o f D N P D A ; 5 - - t h e s a m e , h e a t e d 30 r a i n a t 200 ~ i n n i t r o g e n ; 6 - - t h e s a m e , i n air. a2 P o l y m e r 3
Elongation,
Ill
480
L.G. TOKAREVAet al. I00
qsp
0.14
,
O3 8 #8 10o Time of" hea~ng, hears a~ 150°
FIO. 2. Viscosity of 0.5% solutions in tricresol of Kapron fibres dusted with DNPDA: /--initial; 2--with addition of DNPDA.
ZO I
8
I
#8
lOfO
Time of heating, hours
FIG. 3. Variation in strength of Kapron fibres dusted with DNPDA. 1--initial, heated at 150°; 2--the same, at 180°; 3--with addition of DNPDA, heated at 150°; 4--the same, at 180°.
The reduction in strength of the fibre stabilized with DNPDA is evidently due to irreversible charges in the structure of the fibre but not in its chemical composition, as is shown by the fact t h a t the viscosity of 0"5~/o solutions of the fibre in tricresol remains constant while at the same time the strength decreases and the elongation increases. I t is known t h a t monomer and other low-molecular products impair the properties of Kapron fibre. In order to remove these the fibre is washed with hot water, which could also remove the stabilizer (DNPDA). B y a comparative study of the heat stability of washed and unwashed stabilized fibres it was shown t h a t the DNPDA is not washed out of the fibre. The results shown in Figure 3 indicate t h a t the properties of the washed and unwashed fibres are the same. The additive in the fibre investigated by us was introduced by dusting on to the polymer but the simpler method of introducing the stabilizer before polymerization and thus stabilizing the polymer during preparation is of doubtful practical applicability in view of the prolonged action of the high polymerization temperature on the additive. Experiments were carried out on the addition c f DNPDA to molten caprolaetam before polymerization. The caprolactam was polymerized by the usual method. Water was used as calatyst and acetic or adipic acid as agent for the control of molecular weight. Some experimental batches were made without a chain terminating agent. Table 4 shows the visccsities of 0.5% solutions in tricresol of polymers prepared with and without terminating agents.
Stabilization of polyamide fibres
itt~i~
TABLE 4. VISCOSITIES OF 0"5 SOLUTIONS OF POLYMERS
Additive in ~o of the weight of polymer 0.1 0.1 0.2 0.2
~/sp
0-760"75 0"7~0"71 0"737 0.735
DNPDA DNPDA-b 0.075 acetic acid DNPDA+0.1 adipic acid DNPDA+0.05 acetic acid
T h e results g i v e n in T a b l e 4 show t h a t t h e v i s c o s i t y o f t h e solution o f t h e p o l y m e r p r e p a r e d w i t h o u t a t e r m i n a t i n g a g e n t is a little h i g h e r ' t h a n t h a t o f t h e p o ] y m e r s p r e p a r e d w i t h t e r m i n a t i r g agents. F i b r e s w i t h s a t i s f a c t o r y p h y s i c o - m e c h a n i c a l c o n s t a n t s were p r e p a r e d f r o m the p o l y m e r s , t h e c h a r a c t e r i s t i c s o f which are g i v e n in T a b l e 4. T h e fibres were h e a t e d a t 150 a n d 180 ° . T h e v a r i a t i o n in viscosity o f 0 . 5 % solutions o f t h e fibres in tricresol a n d t h e i r p h y s i c o - m e c h a n i c a l c h a r a c t e r i s t i c s a f t e r h e a t i n g a r e s h o w n in F i g u r e s 4 a n d 5. rlso
0"9 0"~ ~:" 8O
0"7 O~
U
0"5
~: zo 0..I
!
8 48 I00 Time of heatLng~hovrs ~zt 150 o
FIe. 4. Viscosity of 0.5% solutions in tricresol of Kapron fibres (DNPDA added during polymerization of the caprolactazn): 1 initial; 2--with addition of DNPDA.
8
#8 Time of" heating, ho~rs
i00
Fie. 5. Variation in strength of polyamide fibres (DNPDA added during polymerization of the caprolactam): /--initial, h e a t e d at 150°; 2--the same, at 180°; 3--with addition of DNPDA, heated at 150°; 4--the same, at 180 °.
I t is seen f r o m these results t h a t t h e v i s c o s i t y o f t h e solutions o f fibres h e a t e d a t 150 ° v a r i e s in t h e s a m e w a y as for fibres p r e p a r e d w i t h t h e a d d i t i o n o f D N P D A b y d u s t i n g (cf. Fig. 2). 32*
L. G. TOKAREVA e t
482
al.
The physico-mechanical characteristics also vary in the same w a y (el. Figs. 3 and 5). These data show that independently of the method of addition D N P D A is a fairly effective stabilizer that increases the heat stability of Kapron fibre considerably. •
Study of ihe heat and light resistance of Kapron fibres Investigation o f t h e heat resistance of the fibres, with and without stabilizers, was carried out on a thermomeehanical test apparatus of the Polyani type over a wide range of temperatures in air and in nitrogen• Figure 6 shows the 'i
i
'~
•
il
38 _55 37 35 -50 83 31 29
fi 35 •
1 i
i
ZJ /
_.'"
,21 /251
y3
I7 ¢5 t
i i
2l
15 I ZO
I 50
- i 80
L 170
, I/~O
i 770
200t:C
I
FIG. 6. tVariation inI physieo-meehanical properties of polyamide fibres: / - - s t r e n g t h of original fibre in nitrogen; 2--thee.same, in air; 3 - - s t r e n g t h of fibro with a d d e d D N P D A in nitrogen; d - - t h e same, in air.
deperidence Of tensile strength and elongation of the fibres on test temperature and ~the medium. /~s is seen from Figure 6 the tensile strength falls considerably with increasing temperature. The strength falls more sharply in the case of the Kapron fibre testec], in air (curve 2), which supports the conclusion drawn previously [2] conoerni~, g the role of oxidative processes in the variation in the physieo-mechanic~l properties of fibres.
Stabilization of polyamide fibres
483
The decrease in strength of the fibre under the action of heat is 'also connected with the occurrence of reversible structural processes, ;as a result of whieh~ the strength is restored on cooling the specimen. Hence the difference in the residual strength on testing the fibre in nitrogvn (curve 1) and air' (curve 2) must be due to the occurrence of irreversible chemical processes. I t follows from this that the coincidence of the results of testing the fibre stabilized with DN-PDA in nitrcgvn and in air (cvrves 3 and 4) indicates t h a t irreversible chemical processes do not occur in the stabilized fibre subjected to the action of high temperatures in air. This is very clearly confirmed b y the fact that the reduction in strength of the fibre stabilized with D N P D A is a little less than in the case of the unstabilized fibre tested in nitrogen (cf. curves 3 and 4 with 1). The difference in the results on the lowering of the strength of fibres stabilized with D N P D A and unstabilized (in nitrogen) can evidently be explained b y a small increase in heat resistance on account of the introduction of the add#tive. regards the cause of the stabilizing action of such inhibitors as D N P D A against the short-term action of heat, at the present time there are insufficient experimental data to explain it and in any consideration of this accountimust be taken of the possibility, if only partial, of strepgthenirg of the inter-molecular bonds or crosslinkirg in the polyamides by means of th~ stabilizer. The addition of small amounts of D N P D A or H P B O leads not only to the achievement of a considerable increase in the heat stability and some increase in the heat resistance of polyamide fibres b u t also a considerable increase in the light resistance of the fibres is brought about: ; ( ~ TABLE 5. EFFECT OF ADDITIVESON THE STRENGTHOF POLYAMIDESAND THE VISCOSITYOF THEIR SOLUTIONS Viscosity ~/sp Additive
W i t h o u t additive (normal) W i t h addition of 0.5% D N P D A With addition of 1% D N P D A With addition of 0.5% HPBO With addition of 1% HPBO
% fall in strength
% fall in elongation
40"9 21"9 19"7 16"8 12"8
45 34.1 32.5 24.4 31.4
before ] after irradiation irradiation 0"775 0.795 0-762 0.754 0.762
0"471 ~40 0"773 0'770 0"768
Table 5 shows the variation in viscosity of 5% solutions of the polyamide in tricresol, and the fall in strength and elongation of Kapron fibres, with and without additives, subjected to accelerated photodegradation in air by irradiation with a quartz lamp for 20 hours. ~ As is seen from Table 5 the viscosity of solutions of stabilized fibre in tricresol shows practically no fall after irradiation, whereas in the case of the fibre without
484
L. G. TOKAREVAet
al.
additive it falls sharply. The tensile strergth and elorgation of the fibre with additive fM1 almost half as much as in the case of the fibre without additive (Table 5). :This:interesting phenomenon, which requires special investigation, is in good egreement with the fact, described above, of the appearance in a luminophore of the properties of a thermophore, because if this is possible the converse ,would ~lso be expected i.e. the occurrence of photostabilizing activity in a typical antioxidant such as DNPDA. ': All this suggests the possibility, in principle, of a combined solution of the problem of the ageing of synthetic fibres which embraces simultaneously the protection: of the polymer from thermal and photo degradation and an improvement in heat resistance. A l l the data presented b y us relate to Kapron polyamide fibre but from preliminary results obtained it may be considered that all additives that increase the heat stability of Kapron fibre will also increase that of polyamide fibres such as Anid and Enant. The results of an investigation of these fibres will f o r m a separate communication. The authors express their gratitude to N. V. Demina and co-workers of the Laboratory of Textile Testing for assistance in the determination of the physicomechanical properties of the fibres.
" '
CONCLUSIONS
(1) Investigation of the effect of a large number of antioxidants and luminophores on the variation in properties of polyamide fibres has shown that aromatic amines and their derivatives possess effective stabilizirg activity. N,N'-di-flnaphthyl-p-phenylene diamine (DNPDA) and N,N'-phenylcyclohexyl-p-phenylene d i a m i n e are the most effective stabilizers for polyamide fibres. (2) It was found that the tensile strength of fibres stabilized with DNPDA after prolor~ged action of high temperatures (150° for 100-150 hours) is maintained t o the extent of 80-85% whereas that of the unstabflized fibre falls to only 205.25% of the original value. (3) The variation in the physico-mechanical properties of fibres stabilized with DNPDA has been studied over a wide rarge of temperatures. It is shown that short exposure of the normal fibre to high temperatures in an atmosphere of nitrogen and of the DNPDA-stabilized material in air also causes a reversible charge in the strength of the fibre, whereas irreversible changes in the properties of the fibre take place when the normal fibre is subjected to these temperatures in air and these chang3s are related to charges in the chemical composition of the polymer. It has been established that irreversible chemical processes do not occur on prolor.g3d heating of fibre stabilized with DNPDA, i.e. this antioxidant completely protects the polyamide fibre from oxidation.
Dehydroehlorination of polyvinylchloride
485
(4) It is shown that some luminophores, for example hydroxyphenylbenzoxazole (HI~BO) can at the same time possess properties characteristic of thermophores. The addition of DNPDA and H P B O to polyamides increases the light resistance of the polyamide fibres as well as their heat stability. Translated by E. O. PHILLIPS REFERENCES 1. HALLE, Texture, 3, 18-20, 1956 2. N. V. MIKHAILOV, L. G. TOKAREVA and M. V. KOVALEVA, Vysokomol. soedin. 2: 581, 1960 3. G. ACHI-IAMMER, W. REIGART and M. I~LINE, J. Applied Chem. 1: 301, 1951; L. URBANCOVA, Chem. prumysl. 5: 75-78, 1955; I. GUNDAVDA, J. Textile Inst. 5: 289, 1956 4. N. N. SEMENOV, O nekotorykh problemakh khimicheskoi kinetiki i reaktsionnoi sposobnosti. (Some Problems of Chemical Kinetics and Reactivity). Izd. Akad. Nauk SSSR, 1954 5. A. S. KUZ'MINSKII and A. G. ANGERT, Dokl. Akad. Nauk SSSR 82: 747, 1952; 96: 1147, 1954; P. P. MARSCH a n d M. L. BUTLER, Ind. Eng. Chem. 38: 701, 1946; G. S. HAMMAUND and {3. E. BOOSER, J. Amer. Chem. Soc. 77: 3238, 1955 6. V. V. KORSHAK, K. K. MOZGOVA and V. P. LAVRISHCHEV, Vysokomol. soedin, l : 1164, 1959
Letter to the Editor THE DEHYDROCHLORINATION OF POLYVINYLCHLORIDE BY POTASSIUM AMIDE IN LIQUID AMMONIA* I. V. A S T A F ' E V a n d A. K . P I S K U N O V
(Received 5 July 1960)
DEHYDROCHLORINATION of polyvinylchloride (PVC) is one of the methods of producing polymers with systems of conjugated double bonds, possessing heat stability and semiconductor properties [1]. We used for this purpose a solution of potassium amide in liquid ammonia and carried out the reaction under pressure at room temperature, considering that b y the action of the amide on secondary and tertiary halides olefines are produced exclusively [2]. From PVC (mol. ~ t > 75,000) the product obtained was a black powder, insoluble in benzene. On investigation of the electron spin resonance (ESR) at a frequency of~9370 m herz at room temperature the powder gives a single absorption line with weak a s y m m e t r y toward the side of high field strength. The width of the line between * Vysokomol. soedin. 2: No. 11, 1745, 1960.