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Preparation and behaviour of combined fibres
Preparation and behaviour of combined fibres
1985
3. L. ]~EI.I,~kI"YlY,Infrared Spectra of Complex Molecules, p. 215, Foreign Lit. Pub. House, 1963 4. R. B. WOODWARD and T. J. KATZ, Tetrahedron 5: 70, 1959 5. L. V. GINZBURG, V. A. SHERSHNEV and B. A. DOGADKIN, Dokl. AN SSSR 152: 355, 1963
PREPARATION AND BEHAVIOUR OF COMBINED FIBRES* YE. P . DANILOV, .A.I. I{.10RILENKO, V. A. TEMNIKOVSKII, I. G. NIKULINA a n d V. L. K ~ P o v
(Received 12 July 1968)
THE preparation of bonded fibrous materials in which the fibres are bonded together at the places of contact by their own surface layer involves the use of combined fibres [1, 2]. The nature and polymeric structm-e of the combined fibres are not the same in volume as on the surface. These combined materials are produced by various methods of coating a layer of thermoplastic polymer on an oriented fibre surface. This polymer is capable of softening (on heating, in solvents) under conditions that will not affect the structure and properties of the initial fibre. The synthesis of homopolymers on fibre surface is common practice. Many papers have appeared in connection with methods of synthesizing graft polymers on fibres [3] but insufficient study has been made of the mechanical behaviour and adhesion of fibres modified by grafting. T A B L E 1. CHARACTERISTICS OF MATERIALS
Code for material Films PP-80 PP-30 PP-10 Fibres PP PETP PCA
A Fibre diameter,
Crystallinity found by AP,* X-ray % method
Amount of BP
AP1,? el /o
AP, %
v,~ rag/ /cmmg/10~ /cm~.hr
1.01
80 30 10
26 54 54
17-0 9"5 4'8
23 20.6 10.8
0.38 0-85 2.2
1.4 1.2 1-0
0.26 0.07
30
71 63 69
20.0 8-5 3.2
72-0 22.8 10.6
2.9 1-07 0-86
2.0 0.71 0.5
0-06 0.011 0-0018
20 20
* Steady state sorption of St from the licluid phase at 25 °. t DittO, converting for an amorphous polymer. :~ Average rate of polymerization in the first 10 hr.
* Vysokomol. soyed. A l l : No. 8, 1747-1753, 1969.
K,
rel. units
1.0 1.6 1.0
1986
yv,. p. D ~ ' ~ o v et al.
This p a p e r is a r e p o r t on the results of s t u d y i n g the p r e p a r a t i o n o f c o m b i n e d fibres a n d films b y p o l y m e r i z i n g s t y r e n e (St) on the surface o f s y n t h e t i c fibres a n d films. T h e m e c h a n i c a l b e h a v i o u r a n d the adhesion o f t h e m a t e r i a l s were also investigated. EXPERIMENTAL
The experiments were conducted with different sorts of industrial synthetic fibres including polycaproamide (PCA), polyethylene terephthalate (PETP) and polypropylene (PP) fibres. Tests were also carried out with PP films of different thicknesses to determine how the structure of the material affected the synthesis of polystyrene (PS). The polymerization of St from the gas phase was initiated by benzoyl peroxide (BP) applied to the surface of the materials [4]. St is a convenient monomer for use in the preparation of model fibres: PS is readily soluble in substances in which synthetic fibres swell only slightly and with no change in their structure or properties. The characteristics of the fibres and films have been tabulated (Table 1). The film thickness A is reduced approximately in proportion to the degree of extension, and the structure and properties of the films differ accordingly. The degree of orientation of PP determined from the value of amax in the isometric heating diagram (IHD) is twice as high for the film with J =301~ (PP-30) compared with the film with A = 8 0 # (PP-80). The samples were kept for 5 rain in a 0.5~/o solution of BP in benzene. The BP content was determined by iodometry after the samples had been washed in chloroform. After the removal of benzene from the fibres the samples were kept for different periods of time in saturated St vapour at 95 °. The same ampoules also contained reference samples that had not been treated with BP solution. The samples had the PS homopolymer removed by washing with benzene in a Soxhlet apparatus for 60-80 hr. The amount of PS synthesized (AP) was expressed as a percentage on the initial weight of the samples. The degree of crystallinity (Cr) was determined by the X-ray method. The procedure for studying the mechanical and thermomechanieal properties of the fibres and films was described in reference [5], and adhesion testing was similar to that in [6]. All the measurements were carried out with individual monofibres. DISCUSSION OF RESULTS
I t has a l r e a d y b e e n said t h a t the a i m in the e x p e r i m e n t s was to s t u d y t h e possibility of synthesizing P S h o m o p o l y m e r in the sm'face l a y e r o f m a t e r i a l s u n d e r conditions which will p r e s e r v e their s t r u c t u r e a n d m e c h a n i c a l properties. I t was essential to d e t e r m i n e the f o r m a t i o n a n d d i s t r i b u t i o n o f P S in t h e m a t e r i a l , a n d this can be done m o r e easily w i t h films. Conclusions r e a c h e d as a result o f these e x p e r i m e n t s are also applicable to fibres, b u t w i t h certain restrictions. T h e f o r m a t i o n of P S in P P films containing B P p r o c e e d s a t a r a t e t h a t is higher b y a p p r o x i m a t e l y t w o orders t h a n t h a t for the initial films (Fig. 1); t h e r a t e increases w i t h increasing film thickness, so t h a t a t A = 8 0 / ~ it is a l m o s t double t h e r a t e for A - - 10/~. W h e n the film is m a d e into a p a c k a g e (with t h e edges o f the films welded) t h e m a x i m u m a m o u n t of P S decreases in p r o p o r t i o n to the reduction in t h e specific surface of t h e s a m p l e (Table 2), so it is m a i n l y in t h e surface l a y e r o f t h e m a t e r i a l t h a t P S is formed. T h e a m o u n t o f B P t r a p p e d b y t h e m a t e r i a l is p r o p o r t i o n a l to its specific surface. Since t h e r a t e of sorption o f St,
1987
Preparation and behaviour of combined fibres
e.g. b y the PP-80 film, is higher b y one order than the polymerization rate in the initial period of synthesis there is an approximately equilibrium concentration of St in the films during the synthesis (Figs. 1 and 3). A considerably amount of PS is washed out of the film on simply immersing AP, % AP, %
x/
300
a
b 1
o 1
8
2 3
200 6
100
~ I~x 0
x
o
I
I
I
5
10
15
I
20 Time
Ilv
0
I
I
I
I,
5
fO
~5
20
. hr
:FIG. 1. Weight increment of initial (a) and BP-containing (b) PP films vs. time kept ia St vapour. Film thickness: 1--10, 2--30 and 3--80/L. the latter in benzene at 20 °, the amount in question being proportional to the film thickness, i.e. PS forms a layer on the surface of the material. Boiling in benzene will remove PS from the film layer immediately adjacent to the surface, and this method is naturally more effective with thin films. Further prolonged extraction does not reduce the amount of PS in P P , though this is not to say that PS has been chemically grafted to the film. Some of the PS m a y be formed in the volume of the material, and this portion is not extracted. The reference experiment showed that the weight of PS ( m o l . w t . = 3 . 6 × 105) in the package made from T A B L E 2. M A X I M U M INCREASE I3r W E I G H T OF P S R E L A T I V E TO THICKNESS OF T H E
Film PP-80 PP-30
Number of film layers in package
FILM PACKAGE
A,/z
AP, %
80 160 30 60 90
53'7 24"4 33'7 12'7 8-6
1988
Y s . P. D , ~ o v
et al.
PP-30 remained constant in the course of 30 hours' boiling in benzene, i.e. the PS homopolymer cannot diffuse through PP under these conditions. The results of removing PS from the PP films by washing were as follows: Films A P after synthesis of PS, % AP after being k e p t for 40 min in benzene at 20 °, % AP after 3 hr extraction in benzene in a Soxhlet apparatus, % Grafting efficiency, % before fractionation after fractionation
PP-10 195 55 15.6
PP-30 220 150 86
8 5
PP-80 194 160 ,94
39 16.4
40 19
The results of the fractionation of P P films in boiling toluene show that about one half of the PS remaining after the films have been washed is PS homopolymer. Similar data were obtained in [7] with a polyethyle~e-PS system. It follows that only quite a small portion of the synthesized polymer (5-19%) is grafted, partly on account of the peroxides present in the PP macromo]ecules, and partly as a result of chain transfer to the substrate. Most of the grafted chains will probably be in the surface layer of the material. 4P,%
a
/
300
¢
b 20
.o.
75
~o/2~
,8o-
/
/
! 5
0
5
lO
15
20
0
10 20 30 T i m e , hr
#0
0
lO
20
30
~0
FIG. 2. Weight increment of P P fibres (a), P E T P fibres (b) and PCA fibres (c) vs. time k e p t in St vapour. Fibres with (1, 2) and without B P (3, 4) before (1, 3) and after (2, 4) the PS has been washed off.
The polymerization process is similar in the case of fibres (Fig. 2). A large amount of PS is washed out of the fibres, and practically all the PS synthesized during the first hours is washed out of the P P fibres (PS forms a homopolymer "jacket" on the fibres ). In the polymerization of St the initiator completely decomposes during the first hours. (The energy of activation of decomposition is 30 kcal/mole). However, the reaction rate remr,ins constaut for 20-40 hr, which shows that there is no change in the number of growing chains. This conclusion is confirmed by the fact that the molecular weight (Mw)* of the PS removed from the P E T P * Determined b y the light-scattering method, using a "Sofica" device.
Preparation and behaviour of combined fibres
1989
fibres b y washing increases w i t h t h e p o l y m e r i z a t i o n t i m e f r o m 3 . 8 × 10 ~ a f t e r 10 hr to 8.6 x 105 a f t e r 40 hr, i.e. t h e rise in AP is t o a considerable e x t e n t due to t h e increased l e n g t h of t h e molecules. TABLE 3. CRYSTALLINITY(Cr) OF PP FILMS CONTAININGPS Film PP-80
PP-30
ziP, ~o 0 1.7" 23.4 200.0 0 0'9* 27.0 183
Heating time, hr
Cr, ~/o
0 24 4 24 0 24 4 24
26 47 42 33 54 60 57 44
* Films without BP. T h e effect o f t h e fibre n a t u r e on t h e p o l y m e r i z a t i o n r a t e is reflected in changes in t h e St c o n c e n t r a t i o n in t h e p o l y m e r i z a t i o n zone, since molecules s o r b e d b y a m o r p h o u s regions of t h e m a t e r i a l come into t h e reaction. A s s u m i n g t h a t t h e
AP/Po,%
~!
30
0"0
fO ~ 0[
z~ 10I0 Time, m[n FIC. 3
3
0"2 200 "
0
v,Sg
100
I T, °C 150
I~G. 4
Fio. 3. Sorption of styrene on PP films at 95 ° (1, 2) and 25 ° (3, 4) : from gas phase: 1--PP-10, 2--PP-80; from liquid phase: 3--PP-80, 4--PP-30. FIO. 4. Isometric heating diagram for PP fibres: /--initial, 2--zIP=33~/o, 3 - - A P = 5 1 % . r e a c t i o n is described b y t h e usual e q u a t i o n for h o m o g e n e o u s p o l y m e r i z a t i o n v=K'[M]'Vin w h e r e Vin is p r o p o r t i o n a l to t h e a m o u n t of initiator, a n d [1V[] is p r o p o r t i o n a l to t h e s t e a d y - s t a t e sorption, we f o u n d K , i.e. t h e coefficient p r o p o r -
1990
Y~.. P. D~'~iLOVeta/.
tional to the constant rate of polymerization. The K values (expressed in relative units in Table 1) are similar for the different sorts of fibre, though there is a 30-fold difference in the rates at which PS is formed on P P and PCA. Inconsiderable amounts of PS are formed on the P P films that have not been treated with BP, and the polymerization rate increases with reduction in the film thickness, although [lVl], on the other hand, is reduced. This m a y be due to the higher concentration of peroxide groups [8, 9] formed through the rupturing of macromolecules in the stretching of the film. The anomalously high rate of St polymerization on P P fibres with no BP (Fig. 3) is probably caused by the increased concentration of peroxides formed in P P when the latter is stretched beyond a certain limit in which case the large crystals are converted into small ones (the total crystallinity remaining unaltered), which is accompanied by chain breakage and by increase in the inner surface of the crystallites [8]. The results of studying the structure and properties of fibres and films with PS synthesized on them are presented in Tables 3-5 and Figs. 4 and 5. The rise in Cr (Table 3), the lower degree of orientation and the reduction in areax in the I H D c~,l~~/mm z 0.0#.
!
0'02
0
120
I
-4oc
180
Fie. 5. Isometric heating diagram for PP films: PP-30: /--initial, 2--z/P=l16%; PP-80 3-- initial, 4--ztP = 148%. of the films (Fig. 5) is the result of the increased mobility of the P P chains during prolonged heating of P P saturated with St, which is a plasticizer. The slight reduction in Cr at z/P----200% is caused by the shielding effect of PS during the recording of the X-ray pictures, not by actual breakdown of the crystalline
regions. Particularly noteworthy is the altered shape of the I H D for P P fibres (Fig. 4) showing a second maximum a~ax at ~ 60 ° after the synthesis of PS. At the same time the value of the first maximum is reduced and it is displaced into the higher temperature region as a result of the partial disorientation of PP, as was noted above in respect to the films. The value of the second maximum increases with increase in the amount of PS in the fibre. The appearance of a second maximum m a y be attributed to PS structures
Preparation and behaviour of combined fibres
1991
~ABLE 4 . M E C H A N I C A L B E H A V I O U R OF F I B R E S W I T H P S
Mechanical properties Fibre
~P, % after wash-
ing
at,
6t,
Elnlt,
kg/ /mm'
%
kg/
IHD
Tia~,
Ear,
kg/ /n~-~ /mm'
°C
TI~a,~, Tm.p., O"max,
°C
°C
kg/ /mm z
(TP'max~
kg/ mm
[
PP
PCA
PETP
0 33* 51 0 6'9* 16.6 0 8.2* 45.0
29 30 25 87 85 78 69 71 50
28 90 80 19-51 22 18 25
160 110 130 560
590 1050 98O i 820
95 35 40 415 390 275 480 290 380
50 38 34 49 25 25 30 35 35
112 128 130 186 195 --
142 ---
-148 59 151 65 157 79 210 57 210 110 211 75 239 78 243 85 238
0'43 0"I5 0'25 1'15 0"50 2"00 1'75 2'10 2"60
0.10
0.35 2.10 1.30 1.40
* No initiator.
oriented along the fibre axis [10, 11] a n d i b r m e d s p o n t a n e o u s l y on the surface and in t h e v o l u m e of the fibres during the synthesis. The absence o f a second m a x i m u m in respect to the films is due to the weak orienting effect of the material (amax for the initial P P - 3 0 film is lower b y one order t h a n %ax for the fibre). S t r u c t u r a l changes in the fibres are reflected in their mechanical b e h a v i o u r : in respect to changes in their properties a n d in their St sorption c a p a c i t y the order of t h e fibres is the same in b o t h cases: P P > P E T P > P C A . I t is seen f r o m Table 4 t h a t the s t r e n g t h o f P P a n d P E T P with A P ~ 50 % is r e d u c e d b y 20 %. As the fibre cross section is increased at the same time b y ~ 50% owing to the weight increase, the a p p a r e n t r e d u c t i o n in s t r e n g t h is due to the fact t h a t the s t r e n g t h of the synthesized P S is below t h a t o f the fibres, b u t higher t h a n t h a t o f bulk u n o r i e n t e d PS; this confirms the conclusion arrived a t in regard to the f o r m a t i o n of oriented P S structures. I f this were n o t so there would h a v e to be a r e d u c t i o n in a t equal to the increase in the fibre cross section. TABLE
Fibre PP
PETP
5.
ADHESION
AP, %* 0 5"9 51 75 0 3.4 33
OF P S
TO F I B R E S
aadh'
kg/em 2 36±3 66±3 97'6±5 Cohesion 54.8±3 53__2 90±4
* After the PS has been washed out.
ac°hes'
kg/em ~
71'7 85"8 84'8
~1992
YE. P . DANILOV et ~ .
The initial moduli El~ t of the fibres are reduced. Particularly marked is the change in the breaking elongation ~t for PP: there is a section of considerable deformation (forced high-elasticity) on the tensile curve of the latter appearing when the stress approaches the breaking level. In this case it appears that PS acts as a plasticizer. The formation of grafted PS chains on the surface considerably increases the adhesion of the fibres to PS. Even at A P = 5 . 9 % the adhesion is doubled, while at z i P = 5 1 % it is trebled, and at A P = 7 8 % the fibre breaks on attempting to remove it. Similarly increased adhesion was observed with P E T P fibres also. This effect is understandable from the standpoint of the diffusion theory of adhesion. PS chains grafted on fibre surfaces dissolve in the binding agent applied to the fibre and on removal of the solvent a bond is formed with virtually no welldefined interface between the fibre surface and the binder. This ensures maximum fibre-binder bond strength. I t therefore appears that the structure and properties of combined fibres obtained b y polymerizing St from the gas phase on synthetic oriented fibres are not the same in the volume of the material as they are on the surface. The surface layer of homopolymer may serve as a binding agent. Beneath it there is the layer of P S chains grafted to the surfaces of the initial fibre molecules and this ensures greater fibre-binder bond strength. At the same time there is virtually no impairment of the good mechanical properties of the initial fibres as PS homop o l y m e r synthesized mainly on the surface has no effect on the structure and properties of the initial fibres. The authors thank N. 1~I. Bol'bit for measuring the molecular weights. CONCLUSIONS
(1) A study has been made of the preparation of combined fibres and films by means of the polymerization of styrene from the gas phase, using benzoyl peroxide applied to the surface of oriented synthetic materials as initiator. (2) The thermomechanical, mechanical and adhesion behavi0ur of the combined fibres has been investigated. The adhesion of the fibre to PS is increased several times, without impairing the mechanical properties of the fibres. Oriented polystyrene structures are formed in the synthesis. Translated by R. J. A. HENDRY REFERENCES 1. M. K A T Z and M. ~ S I , U. S. Pat. 3121698, 1964; Ref. Zh. 12S895P, 1965 2. H. L U C I ~ , Adhesion, No. 12, 501, 1964
3. A. A. KONKIN and M. P. ZVEREV, Polyolefin Fibres, Izd. "Khimiya", 1966 4. Z. MANASEK, M. LAZAR eta/., Czech. Pat. 108720, 1963 5. S. L. DOBRETSOV, A. I. KURILENKO and V. A. TEMNIKOVSI~II~ Mekhanika polimerov, 944, 1966 6. A. I. KURILENKO and G. V. SHIRYAYEVA, Vysokomol. soyed. 8: 578, 1966 (Translated in Polymer Sci. U.S.S.R. 8: 4, 633, 1966)
Effect of pigments on kinetics of photoaging of polyethylene
1993
7. V. CHEN and G. FRIDLENDER, Khim. i tekhnologiya polimerov, 1~o. 12, 46, 1963 8. F. GELEDZHI and L. ODOR, Khim. i. tekhnologiya polimerov, No. 12, 30, 1963 9. R. A. VESELOVSKII, S. S. LESHCHENKO and V. L. KARPOV, Vysokomol. soyed. 8: 744, 1966 (Translated in Polymer Sci. U.S.S.R. 8: 4, 817, 1966) 10. A. V. VLASOV, N. V. MTKHAILOV eta/., Khim. volokna, No. 6, 24, 1963 11. A. I. KURILENKO, Ye, P. DANILOV and V.A. TEMNIKOVSKII, Vysokomol. soyed. 8: 2024, 1966 (Translated in Polymer Sei. U.S.S.R. 8: 11, 2235, 1966); Ye. P. DANILOV and A. I. KURILENKO, Vysokomol. soyed. Ag: 2697, 1967 (Translated in Polymer Sci. U.S.S.R. 9: 12, 3052, 1967); N. Kh. FAIZI, N. A. SLOVOKHOTOVA, Ye. P. DANILOV, A. I. KURILENKO and V. L. KARPOV, Vysokomol. soyed. B9: 879, 1967 (Not translated in Polymer Sei. U.S.S.R.)
EFFECT OF PIGMENTS ON THE KINETICS OF PHOTOAGING OF POLYETHYLENE* Y~. A. Y~.Rs~ov and R. K. ANKUNDINOVA Moscow Textile Institute, Lit.S.S.R. Aeademy~of Sciences
(Received 12 July 1968)
DIFFERENT effects are observed on adding pigments to polymers undergoing photoaging: the amount of light absorbed by the polymer may be reduced by screening, the rate of initiation of radicals may be increased or reduced owing to sensitization or desensitization; the rate of initiation of radicals may also be reduced by the extinction of the excited states of polymer molecules [1]. The effects referred to above may appear simultaneously, and whether the particular processes underlying the kinetics of photoaging will be accelerated or retarded by the addition of pigment additives will depend on the ratio of the effects in question. This paper is a study of effects arising in the accelerated photoaging of polyethylene (PE) coloured by pigments widely used in polymer technology: phthalocyanine blue (PB), phthalocyanine green (PG), bright red (dZh) and yellow (SK). EXPERIMENTAL
Samples intended for irradiation were prepared in the form of films 50/z thick by press-moulding, using unstabillzed PE (melt index 0.43g/10min, density 0.96g/era 8, Mw=17,000, M,----22,O00, crystallinity 55%, degree of branching 0.7 methyl groups per 1000 atoms of C). The pigments were as follows: PB--GOST (State Standard) 6220-52, PG~--TO (Teeh. Specification) 3289-52,bright red--TUTSMKh, 51-59,yellow--STU P.570-64. The irradiation was performed using the equipment described in reference [2] with a PRK-2 * Vysokomol. soyed. A l l : No. 8, 1754-1759, 1969.
1985
3. L. ]~EI.I,~kI"YlY,Infrared Spectra of Complex Molecules, p. 215, Foreign Lit. Pub. House, 1963 4. R. B. WOODWARD and T. J. KATZ, Tetrahedron 5: 70, 1959 5. L. V. GINZBURG, V. A. SHERSHNEV and B. A. DOGADKIN, Dokl. AN SSSR 152: 355, 1963
PREPARATION AND BEHAVIOUR OF COMBINED FIBRES* YE. P . DANILOV, .A.I. I{.10RILENKO, V. A. TEMNIKOVSKII, I. G. NIKULINA a n d V. L. K ~ P o v
(Received 12 July 1968)
THE preparation of bonded fibrous materials in which the fibres are bonded together at the places of contact by their own surface layer involves the use of combined fibres [1, 2]. The nature and polymeric structm-e of the combined fibres are not the same in volume as on the surface. These combined materials are produced by various methods of coating a layer of thermoplastic polymer on an oriented fibre surface. This polymer is capable of softening (on heating, in solvents) under conditions that will not affect the structure and properties of the initial fibre. The synthesis of homopolymers on fibre surface is common practice. Many papers have appeared in connection with methods of synthesizing graft polymers on fibres [3] but insufficient study has been made of the mechanical behaviour and adhesion of fibres modified by grafting. T A B L E 1. CHARACTERISTICS OF MATERIALS
Code for material Films PP-80 PP-30 PP-10 Fibres PP PETP PCA
A Fibre diameter,
Crystallinity found by AP,* X-ray % method
Amount of BP
AP1,? el /o
AP, %
v,~ rag/ /cmmg/10~ /cm~.hr
1.01
80 30 10
26 54 54
17-0 9"5 4'8
23 20.6 10.8
0.38 0-85 2.2
1.4 1.2 1-0
0.26 0.07
30
71 63 69
20.0 8-5 3.2
72-0 22.8 10.6
2.9 1-07 0-86
2.0 0.71 0.5
0-06 0.011 0-0018
20 20
* Steady state sorption of St from the licluid phase at 25 °. t DittO, converting for an amorphous polymer. :~ Average rate of polymerization in the first 10 hr.
* Vysokomol. soyed. A l l : No. 8, 1747-1753, 1969.
K,
rel. units
1.0 1.6 1.0
1986
yv,. p. D ~ ' ~ o v et al.
This p a p e r is a r e p o r t on the results of s t u d y i n g the p r e p a r a t i o n o f c o m b i n e d fibres a n d films b y p o l y m e r i z i n g s t y r e n e (St) on the surface o f s y n t h e t i c fibres a n d films. T h e m e c h a n i c a l b e h a v i o u r a n d the adhesion o f t h e m a t e r i a l s were also investigated. EXPERIMENTAL
The experiments were conducted with different sorts of industrial synthetic fibres including polycaproamide (PCA), polyethylene terephthalate (PETP) and polypropylene (PP) fibres. Tests were also carried out with PP films of different thicknesses to determine how the structure of the material affected the synthesis of polystyrene (PS). The polymerization of St from the gas phase was initiated by benzoyl peroxide (BP) applied to the surface of the materials [4]. St is a convenient monomer for use in the preparation of model fibres: PS is readily soluble in substances in which synthetic fibres swell only slightly and with no change in their structure or properties. The characteristics of the fibres and films have been tabulated (Table 1). The film thickness A is reduced approximately in proportion to the degree of extension, and the structure and properties of the films differ accordingly. The degree of orientation of PP determined from the value of amax in the isometric heating diagram (IHD) is twice as high for the film with J =301~ (PP-30) compared with the film with A = 8 0 # (PP-80). The samples were kept for 5 rain in a 0.5~/o solution of BP in benzene. The BP content was determined by iodometry after the samples had been washed in chloroform. After the removal of benzene from the fibres the samples were kept for different periods of time in saturated St vapour at 95 °. The same ampoules also contained reference samples that had not been treated with BP solution. The samples had the PS homopolymer removed by washing with benzene in a Soxhlet apparatus for 60-80 hr. The amount of PS synthesized (AP) was expressed as a percentage on the initial weight of the samples. The degree of crystallinity (Cr) was determined by the X-ray method. The procedure for studying the mechanical and thermomechanieal properties of the fibres and films was described in reference [5], and adhesion testing was similar to that in [6]. All the measurements were carried out with individual monofibres. DISCUSSION OF RESULTS
I t has a l r e a d y b e e n said t h a t the a i m in the e x p e r i m e n t s was to s t u d y t h e possibility of synthesizing P S h o m o p o l y m e r in the sm'face l a y e r o f m a t e r i a l s u n d e r conditions which will p r e s e r v e their s t r u c t u r e a n d m e c h a n i c a l properties. I t was essential to d e t e r m i n e the f o r m a t i o n a n d d i s t r i b u t i o n o f P S in t h e m a t e r i a l , a n d this can be done m o r e easily w i t h films. Conclusions r e a c h e d as a result o f these e x p e r i m e n t s are also applicable to fibres, b u t w i t h certain restrictions. T h e f o r m a t i o n of P S in P P films containing B P p r o c e e d s a t a r a t e t h a t is higher b y a p p r o x i m a t e l y t w o orders t h a n t h a t for the initial films (Fig. 1); t h e r a t e increases w i t h increasing film thickness, so t h a t a t A = 8 0 / ~ it is a l m o s t double t h e r a t e for A - - 10/~. W h e n the film is m a d e into a p a c k a g e (with t h e edges o f the films welded) t h e m a x i m u m a m o u n t of P S decreases in p r o p o r t i o n to the reduction in t h e specific surface of t h e s a m p l e (Table 2), so it is m a i n l y in t h e surface l a y e r o f t h e m a t e r i a l t h a t P S is formed. T h e a m o u n t o f B P t r a p p e d b y t h e m a t e r i a l is p r o p o r t i o n a l to its specific surface. Since t h e r a t e of sorption o f St,
1987
Preparation and behaviour of combined fibres
e.g. b y the PP-80 film, is higher b y one order than the polymerization rate in the initial period of synthesis there is an approximately equilibrium concentration of St in the films during the synthesis (Figs. 1 and 3). A considerably amount of PS is washed out of the film on simply immersing AP, % AP, %
x/
300
a
b 1
o 1
8
2 3
200 6
100
~ I~x 0
x
o
I
I
I
5
10
15
I
20 Time
Ilv
0
I
I
I
I,
5
fO
~5
20
. hr
:FIG. 1. Weight increment of initial (a) and BP-containing (b) PP films vs. time kept ia St vapour. Film thickness: 1--10, 2--30 and 3--80/L. the latter in benzene at 20 °, the amount in question being proportional to the film thickness, i.e. PS forms a layer on the surface of the material. Boiling in benzene will remove PS from the film layer immediately adjacent to the surface, and this method is naturally more effective with thin films. Further prolonged extraction does not reduce the amount of PS in P P , though this is not to say that PS has been chemically grafted to the film. Some of the PS m a y be formed in the volume of the material, and this portion is not extracted. The reference experiment showed that the weight of PS ( m o l . w t . = 3 . 6 × 105) in the package made from T A B L E 2. M A X I M U M INCREASE I3r W E I G H T OF P S R E L A T I V E TO THICKNESS OF T H E
Film PP-80 PP-30
Number of film layers in package
FILM PACKAGE
A,/z
AP, %
80 160 30 60 90
53'7 24"4 33'7 12'7 8-6
1988
Y s . P. D , ~ o v
et al.
PP-30 remained constant in the course of 30 hours' boiling in benzene, i.e. the PS homopolymer cannot diffuse through PP under these conditions. The results of removing PS from the PP films by washing were as follows: Films A P after synthesis of PS, % AP after being k e p t for 40 min in benzene at 20 °, % AP after 3 hr extraction in benzene in a Soxhlet apparatus, % Grafting efficiency, % before fractionation after fractionation
PP-10 195 55 15.6
PP-30 220 150 86
8 5
PP-80 194 160 ,94
39 16.4
40 19
The results of the fractionation of P P films in boiling toluene show that about one half of the PS remaining after the films have been washed is PS homopolymer. Similar data were obtained in [7] with a polyethyle~e-PS system. It follows that only quite a small portion of the synthesized polymer (5-19%) is grafted, partly on account of the peroxides present in the PP macromo]ecules, and partly as a result of chain transfer to the substrate. Most of the grafted chains will probably be in the surface layer of the material. 4P,%
a
/
300
¢
b 20
.o.
75
~o/2~
,8o-
/
/
! 5
0
5
lO
15
20
0
10 20 30 T i m e , hr
#0
0
lO
20
30
~0
FIG. 2. Weight increment of P P fibres (a), P E T P fibres (b) and PCA fibres (c) vs. time k e p t in St vapour. Fibres with (1, 2) and without B P (3, 4) before (1, 3) and after (2, 4) the PS has been washed off.
The polymerization process is similar in the case of fibres (Fig. 2). A large amount of PS is washed out of the fibres, and practically all the PS synthesized during the first hours is washed out of the P P fibres (PS forms a homopolymer "jacket" on the fibres ). In the polymerization of St the initiator completely decomposes during the first hours. (The energy of activation of decomposition is 30 kcal/mole). However, the reaction rate remr,ins constaut for 20-40 hr, which shows that there is no change in the number of growing chains. This conclusion is confirmed by the fact that the molecular weight (Mw)* of the PS removed from the P E T P * Determined b y the light-scattering method, using a "Sofica" device.
Preparation and behaviour of combined fibres
1989
fibres b y washing increases w i t h t h e p o l y m e r i z a t i o n t i m e f r o m 3 . 8 × 10 ~ a f t e r 10 hr to 8.6 x 105 a f t e r 40 hr, i.e. t h e rise in AP is t o a considerable e x t e n t due to t h e increased l e n g t h of t h e molecules. TABLE 3. CRYSTALLINITY(Cr) OF PP FILMS CONTAININGPS Film PP-80
PP-30
ziP, ~o 0 1.7" 23.4 200.0 0 0'9* 27.0 183
Heating time, hr
Cr, ~/o
0 24 4 24 0 24 4 24
26 47 42 33 54 60 57 44
* Films without BP. T h e effect o f t h e fibre n a t u r e on t h e p o l y m e r i z a t i o n r a t e is reflected in changes in t h e St c o n c e n t r a t i o n in t h e p o l y m e r i z a t i o n zone, since molecules s o r b e d b y a m o r p h o u s regions of t h e m a t e r i a l come into t h e reaction. A s s u m i n g t h a t t h e
AP/Po,%
~!
30
0"0
fO ~ 0[
z~ 10I0 Time, m[n FIC. 3
3
0"2 200 "
0
v,Sg
100
I T, °C 150
I~G. 4
Fio. 3. Sorption of styrene on PP films at 95 ° (1, 2) and 25 ° (3, 4) : from gas phase: 1--PP-10, 2--PP-80; from liquid phase: 3--PP-80, 4--PP-30. FIO. 4. Isometric heating diagram for PP fibres: /--initial, 2--zIP=33~/o, 3 - - A P = 5 1 % . r e a c t i o n is described b y t h e usual e q u a t i o n for h o m o g e n e o u s p o l y m e r i z a t i o n v=K'[M]'Vin w h e r e Vin is p r o p o r t i o n a l to t h e a m o u n t of initiator, a n d [1V[] is p r o p o r t i o n a l to t h e s t e a d y - s t a t e sorption, we f o u n d K , i.e. t h e coefficient p r o p o r -
1990
Y~.. P. D~'~iLOVeta/.
tional to the constant rate of polymerization. The K values (expressed in relative units in Table 1) are similar for the different sorts of fibre, though there is a 30-fold difference in the rates at which PS is formed on P P and PCA. Inconsiderable amounts of PS are formed on the P P films that have not been treated with BP, and the polymerization rate increases with reduction in the film thickness, although [lVl], on the other hand, is reduced. This m a y be due to the higher concentration of peroxide groups [8, 9] formed through the rupturing of macromolecules in the stretching of the film. The anomalously high rate of St polymerization on P P fibres with no BP (Fig. 3) is probably caused by the increased concentration of peroxides formed in P P when the latter is stretched beyond a certain limit in which case the large crystals are converted into small ones (the total crystallinity remaining unaltered), which is accompanied by chain breakage and by increase in the inner surface of the crystallites [8]. The results of studying the structure and properties of fibres and films with PS synthesized on them are presented in Tables 3-5 and Figs. 4 and 5. The rise in Cr (Table 3), the lower degree of orientation and the reduction in areax in the I H D c~,l~~/mm z 0.0#.
!
0'02
0
120
I
-4oc
180
Fie. 5. Isometric heating diagram for PP films: PP-30: /--initial, 2--z/P=l16%; PP-80 3-- initial, 4--ztP = 148%. of the films (Fig. 5) is the result of the increased mobility of the P P chains during prolonged heating of P P saturated with St, which is a plasticizer. The slight reduction in Cr at z/P----200% is caused by the shielding effect of PS during the recording of the X-ray pictures, not by actual breakdown of the crystalline
regions. Particularly noteworthy is the altered shape of the I H D for P P fibres (Fig. 4) showing a second maximum a~ax at ~ 60 ° after the synthesis of PS. At the same time the value of the first maximum is reduced and it is displaced into the higher temperature region as a result of the partial disorientation of PP, as was noted above in respect to the films. The value of the second maximum increases with increase in the amount of PS in the fibre. The appearance of a second maximum m a y be attributed to PS structures
Preparation and behaviour of combined fibres
1991
~ABLE 4 . M E C H A N I C A L B E H A V I O U R OF F I B R E S W I T H P S
Mechanical properties Fibre
~P, % after wash-
ing
at,
6t,
Elnlt,
kg/ /mm'
%
kg/
IHD
Tia~,
Ear,
kg/ /n~-~ /mm'
°C
TI~a,~, Tm.p., O"max,
°C
°C
kg/ /mm z
(TP'max~
kg/ mm
[
PP
PCA
PETP
0 33* 51 0 6'9* 16.6 0 8.2* 45.0
29 30 25 87 85 78 69 71 50
28 90 80 19-51 22 18 25
160 110 130 560
590 1050 98O i 820
95 35 40 415 390 275 480 290 380
50 38 34 49 25 25 30 35 35
112 128 130 186 195 --
142 ---
-148 59 151 65 157 79 210 57 210 110 211 75 239 78 243 85 238
0'43 0"I5 0'25 1'15 0"50 2"00 1'75 2'10 2"60
0.10
0.35 2.10 1.30 1.40
* No initiator.
oriented along the fibre axis [10, 11] a n d i b r m e d s p o n t a n e o u s l y on the surface and in t h e v o l u m e of the fibres during the synthesis. The absence o f a second m a x i m u m in respect to the films is due to the weak orienting effect of the material (amax for the initial P P - 3 0 film is lower b y one order t h a n %ax for the fibre). S t r u c t u r a l changes in the fibres are reflected in their mechanical b e h a v i o u r : in respect to changes in their properties a n d in their St sorption c a p a c i t y the order of t h e fibres is the same in b o t h cases: P P > P E T P > P C A . I t is seen f r o m Table 4 t h a t the s t r e n g t h o f P P a n d P E T P with A P ~ 50 % is r e d u c e d b y 20 %. As the fibre cross section is increased at the same time b y ~ 50% owing to the weight increase, the a p p a r e n t r e d u c t i o n in s t r e n g t h is due to the fact t h a t the s t r e n g t h of the synthesized P S is below t h a t o f the fibres, b u t higher t h a n t h a t o f bulk u n o r i e n t e d PS; this confirms the conclusion arrived a t in regard to the f o r m a t i o n of oriented P S structures. I f this were n o t so there would h a v e to be a r e d u c t i o n in a t equal to the increase in the fibre cross section. TABLE
Fibre PP
PETP
5.
ADHESION
AP, %* 0 5"9 51 75 0 3.4 33
OF P S
TO F I B R E S
aadh'
kg/em 2 36±3 66±3 97'6±5 Cohesion 54.8±3 53__2 90±4
* After the PS has been washed out.
ac°hes'
kg/em ~
71'7 85"8 84'8
~1992
YE. P . DANILOV et ~ .
The initial moduli El~ t of the fibres are reduced. Particularly marked is the change in the breaking elongation ~t for PP: there is a section of considerable deformation (forced high-elasticity) on the tensile curve of the latter appearing when the stress approaches the breaking level. In this case it appears that PS acts as a plasticizer. The formation of grafted PS chains on the surface considerably increases the adhesion of the fibres to PS. Even at A P = 5 . 9 % the adhesion is doubled, while at z i P = 5 1 % it is trebled, and at A P = 7 8 % the fibre breaks on attempting to remove it. Similarly increased adhesion was observed with P E T P fibres also. This effect is understandable from the standpoint of the diffusion theory of adhesion. PS chains grafted on fibre surfaces dissolve in the binding agent applied to the fibre and on removal of the solvent a bond is formed with virtually no welldefined interface between the fibre surface and the binder. This ensures maximum fibre-binder bond strength. I t therefore appears that the structure and properties of combined fibres obtained b y polymerizing St from the gas phase on synthetic oriented fibres are not the same in the volume of the material as they are on the surface. The surface layer of homopolymer may serve as a binding agent. Beneath it there is the layer of P S chains grafted to the surfaces of the initial fibre molecules and this ensures greater fibre-binder bond strength. At the same time there is virtually no impairment of the good mechanical properties of the initial fibres as PS homop o l y m e r synthesized mainly on the surface has no effect on the structure and properties of the initial fibres. The authors thank N. 1~I. Bol'bit for measuring the molecular weights. CONCLUSIONS
(1) A study has been made of the preparation of combined fibres and films by means of the polymerization of styrene from the gas phase, using benzoyl peroxide applied to the surface of oriented synthetic materials as initiator. (2) The thermomechanical, mechanical and adhesion behavi0ur of the combined fibres has been investigated. The adhesion of the fibre to PS is increased several times, without impairing the mechanical properties of the fibres. Oriented polystyrene structures are formed in the synthesis. Translated by R. J. A. HENDRY REFERENCES 1. M. K A T Z and M. ~ S I , U. S. Pat. 3121698, 1964; Ref. Zh. 12S895P, 1965 2. H. L U C I ~ , Adhesion, No. 12, 501, 1964
3. A. A. KONKIN and M. P. ZVEREV, Polyolefin Fibres, Izd. "Khimiya", 1966 4. Z. MANASEK, M. LAZAR eta/., Czech. Pat. 108720, 1963 5. S. L. DOBRETSOV, A. I. KURILENKO and V. A. TEMNIKOVSI~II~ Mekhanika polimerov, 944, 1966 6. A. I. KURILENKO and G. V. SHIRYAYEVA, Vysokomol. soyed. 8: 578, 1966 (Translated in Polymer Sci. U.S.S.R. 8: 4, 633, 1966)
Effect of pigments on kinetics of photoaging of polyethylene
1993
7. V. CHEN and G. FRIDLENDER, Khim. i tekhnologiya polimerov, 1~o. 12, 46, 1963 8. F. GELEDZHI and L. ODOR, Khim. i. tekhnologiya polimerov, No. 12, 30, 1963 9. R. A. VESELOVSKII, S. S. LESHCHENKO and V. L. KARPOV, Vysokomol. soyed. 8: 744, 1966 (Translated in Polymer Sci. U.S.S.R. 8: 4, 817, 1966) 10. A. V. VLASOV, N. V. MTKHAILOV eta/., Khim. volokna, No. 6, 24, 1963 11. A. I. KURILENKO, Ye, P. DANILOV and V.A. TEMNIKOVSKII, Vysokomol. soyed. 8: 2024, 1966 (Translated in Polymer Sei. U.S.S.R. 8: 11, 2235, 1966); Ye. P. DANILOV and A. I. KURILENKO, Vysokomol. soyed. Ag: 2697, 1967 (Translated in Polymer Sci. U.S.S.R. 9: 12, 3052, 1967); N. Kh. FAIZI, N. A. SLOVOKHOTOVA, Ye. P. DANILOV, A. I. KURILENKO and V. L. KARPOV, Vysokomol. soyed. B9: 879, 1967 (Not translated in Polymer Sei. U.S.S.R.)
EFFECT OF PIGMENTS ON THE KINETICS OF PHOTOAGING OF POLYETHYLENE* Y~. A. Y~.Rs~ov and R. K. ANKUNDINOVA Moscow Textile Institute, Lit.S.S.R. Aeademy~of Sciences
(Received 12 July 1968)
DIFFERENT effects are observed on adding pigments to polymers undergoing photoaging: the amount of light absorbed by the polymer may be reduced by screening, the rate of initiation of radicals may be increased or reduced owing to sensitization or desensitization; the rate of initiation of radicals may also be reduced by the extinction of the excited states of polymer molecules [1]. The effects referred to above may appear simultaneously, and whether the particular processes underlying the kinetics of photoaging will be accelerated or retarded by the addition of pigment additives will depend on the ratio of the effects in question. This paper is a study of effects arising in the accelerated photoaging of polyethylene (PE) coloured by pigments widely used in polymer technology: phthalocyanine blue (PB), phthalocyanine green (PG), bright red (dZh) and yellow (SK). EXPERIMENTAL
Samples intended for irradiation were prepared in the form of films 50/z thick by press-moulding, using unstabillzed PE (melt index 0.43g/10min, density 0.96g/era 8, Mw=17,000, M,----22,O00, crystallinity 55%, degree of branching 0.7 methyl groups per 1000 atoms of C). The pigments were as follows: PB--GOST (State Standard) 6220-52, PG~--TO (Teeh. Specification) 3289-52,bright red--TUTSMKh, 51-59,yellow--STU P.570-64. The irradiation was performed using the equipment described in reference [2] with a PRK-2 * Vysokomol. soyed. A l l : No. 8, 1754-1759, 1969.