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Properties of polyethylene-kaolin composites synthesized by polymerization of ethylene on the particulate surface of kaolin treated with organoaluminium compounds
Polymer Science U.S.S.R. Vol. 27, No. 11, pp. 2552-2559, 1985 Printed in Poland
0032-3950/85 $10.00+ .00 ~ Pergamon Journals Ltd.
PROPERTIES OF POLYETHYLENE-KAOLIN C O M P O S I T E S SYNTHESIZED BY POLYMERIZATION OF ETHYLENE ON THE PARTICULATE SURFACE OF KAOLIN TREATED WITH ORGANOALUMINIUM C O M P O U N D S * N. N. VLASOVA,V. I. SERGEYEV,P. YE. MATKOVSKII,N. S. YENIKOLOPYAN, A. T. PAPOYAN, B. Y~. VOSTORGOV,L. N. GRIGOROV, S. A. BUKANOVA, L. O. BUNINA, N. S. KOGARKO, L. A. TKACHENKOand V. V. SMIRNOV Department of the Institute of Chemical Physics, U.S.S.R. Academy of Sciences (Received 6 March 1984)
The influence of the conditions of polymerization on the dispersity, agglomeration of particles and the rheological and physicomechanical properties of polyethylene--kaolin composites obtained by polymerizing ethylene on the surface of kaolin treated with organoaluminium compounds has been studied. IT HAS been established [1, 2] that on polymerization of ethylene on the surface o f particles of disperse mineral fillers-kaolin, calcite and g i b b c i t e - i t is possible to obtain highly filled composites of uniform composition of ultra-high molecular PE characterized by high indices of the physicomechanical properties. Serving as catalysts here were combinations of ZrR4 and AIR3 which were evenly fixed on the surface of the filler particles. In these studies [1, 2] it is noted that materials of the same type also form on polymerization of ethylene on the stlrface of particles of kaolin treated with organoaluminium compounds (OAC). Detailed information on these processes has still not been published. In view of the great theoretical and practical importance of elucidating the mechanism and characteristics of polymerization of ethylene on the surface of kaolin particles using as catalyst the constitutional oxides of the transitional metals activated with OAC and continuing the investigations, to devise methods of polymerization synthesis of polyethylene-kaolin composites (PEKC) [3-5] we studied in detail the influence of the conditions of polymerization and other factors on the kinetic patterns o f expenditure of ethylene during polymerization [6] and the properties of the composites obtained by this method. Some results of these investigations formed the subject of the present work. The characteristics of the kaolins of the Glukhovetskii (KG) and Yeleninskii (KY) deposits used in the work, the methods of preparing and drying the raw material and also the technique of studying the kinetic patterns of polymerization of ethylene on the surface of the particles of kaolin treated with OAC are described in [6]. KG kaolin was dried at 873 K. The density of dried kaolin * Vysokomol. soyed. A27: No. 11, 2274-2280, 1985. 2552
Properties of polyethylene-kaolin composites
2553
was 2.5-2.6 g/cm 3. The PEKCs formed during polymerization after its completion were unloaded from the reactor, separated on a filter from the solvent and dried in a vacuum cupboard at temperatures not exceeding 353 K. The filling of PEKC with kaolin (wt. 7.) was determined from the consumption of ethylene, gravimetrically and from the ash yield after combustion of the samples by the standard technique. The mass and numerical distribution of the PEKC samples and the initial kaolin over the equivalent diameter of the particles was obtained in the same way as in [6] with the "Malvern ST-1800" instrument. The continuity of coverage of the surface of the kaolin particles with PE was determined by the method of electron spectroscopy for chemical analysis (ESCA) with the ES-2401 instrument. The specimens for the investigations by this method were prepared by fixing the powders on an indium support at pressures not exceeding 0-5 MPa. The fluidity index of the melt of the PEKC samples was determined with an instrument for measuring the index of the melt of the IIRT thermoplasts at the temperature 463 K and for a load 0"5 MPa. The samples to determine the physicomechanical characteristics of the PEKC were obtained from plates 1.5-2.0 mm thick prepared by hot pressing in the form of a closed type. The specific pressure for pressing was 10 MPa; pressing temperature 463 K, time of holding under pressure 30 min and rate of cooling 10 degrees/min. The physicomechanical characteristics of the PEKC were determined with the Instron-1185 machine. The rate of displacement of the active capture of the machine in the tests of the materials was 1 rain- 1.
ND,Zll q0 20
100
200
300
D,~rn
400
FIG. 1. Number distribution equivalent particle diameter of KG kaolin (1) and PEKC obtained during suspension polymerization of ethylene (2-4). [(iso-C4Hg)aA1]=0 (•); 0.15 (2); 0.03 (3) and 0.0085 kaolin (4) g/g. Ethylene pressure 1-0 MPa; temperature of polymerization 313 K; time 3 hr. A s a result o f s u s p e n s i o n p o l y m e r i z a t i o n o f ethylene on the surface o f the particles o f k a o l i n t r e a t e d w i t h O A C in relatively m i l d c o n d i t i o n s ( t e m p e r a t u r e 293-373 K , e t h y l e n e p r e s s u r e 0-3-1.0 M P a ) for 1-3 h r P E K C s f o r m with a d e g r e e o f filling f r o m 90 t o 25 ~ b y weight. A f t e r i s o l a t i o n a n d d r y i n g the P E K C s c o n s t i t u t e friable, c o l o u r less (in t h e case o f K G k a o l i n ) or p a l e p i n k (in the case o f K ¥ k a o l i n ) d i s p e r s e p r o d u c t s c h a r a c t e r i z e d by a v e r y wide m a s s a n d n u m e r i c a l d i s t r i b u t i o n o v e r t h e e q u i v a l e n t d i a m e t e r o f t h e p a r t i c l e s (Fig. 1, T a b l e 1). I t is w o r t h n o t i n g t h a t the m e a n n u m e r i c a l e q u i v a l e n t d i a m e t e r DN o f the P E K C p a r t i c l e s exceeds b y m o r e t h a n one o r d e r t h a t o f t h e initial d r i e d kaolin. S i m p l e calc u l a t i o n s show t h a t as a result o f c o v e r a g e o f t h e k a o l i n p a r t i c l e s w i t h P E for t h e fillings i n d i c a t e d in T a b l e 1 / ~ o u g h t to rise n o t m o r e t h a n 2 - 3 times.
2554
N.N. VLASOVAet al.
Comparison of the calculated with the experimental values of/)N invites the conclusion that the nascent PEKC particles represent agglomerates of smaller particles. This conclusion was confirmed by us experimentally. In the optical microscope with 50 fold magnification it is clearly seen that the nascent PEKC particles with a diameter 200-300/~m represent associates of a large number of primary particles with an equivalent diameter from 10 to 50/zm. On exposure to ethanol the PEKC associates like the agglomerates of the kaolin particles (Table 1) partially diaggregate. From this it follows that the primary PEKC particles in the associates are not bound by the through PE chains. The degree of aggregation of the primary PEKC particles is determined by the nature and degree of drying of kaolin, depends on the nature and concentration of the OAC, the temperature of polymerization and many other factors not easy to estimate. In particular, in the case of KY the mean numerical equivalent diameter of the PEKC associates (1-3 mm) with no change in the other conditions exceeds by one order DN of the PEKC obtained on the basis of KG kaolin. We would also note that rise in the concentration of Al(iso-C4H9)3 (from 0-0085 to 0.15 g/g kaolin) leads to fall in/)N (from 300 to 200 pro). It is known [1] that treatment with OAC is accompanied by disaggregation of the kaolin particles. Therefore there are grounds for assuming that the association of the particles during polymerization synthesis of PEKC is due to physical processes the progress of which leads to fall in the free energy of the developed surface of the primary PEKC particles. The nature of this process is still not clear. Comparative analysis of the distribution histograms of the kaolin and PEKC particles over the equivalent diameter (Fig. 1) indicates that practically all the kaolin particles for degrees of filling to 60 7oo by weight are covered by PE. This conclusion is confirmed by electron spectroscopy. Comparison of the intensity of the silicon, aluminium and oxygen lines in the electron spectra of the samples of dried kaolin and PEKC shows that the fraction of the surface of the kaolin particles not covered with PE for degrees of filling up to 60 % by weight does not exceed 2-5 %. From the data on the influence of the degree of filling of PEKC with KG kaolin on the completeness TABLE 1. CHARACTERIZATION
OF D I S T R I B U T I O N OF K A O L I N A N D
PEKC
OVER THE EQUIVALENT PARTICLE
DIAMETER
Kaolin
Txv,
K*
i
OAC
J KG KY KG
*
293 873 293 293 873 873 873 873
Dispersion medium Heptane ,)
(iso-C4Hg)3A1
Heptane Ethanol Heptane
))
))
B
(C2Hs)2A1CI
))
T,o-Temperature of drying o f k a o l i n . characterizing the width of the distribution.
~" y-Parameter
Filling, 70 100 100 100 100 27"3 38"9 59"2 44"7
/)N, pm 17"0 14"0 29"0 9"0
300 248 198 293
7' 1'1 1"0 1"0 1"1 3"6 4"3 3"4 3"0
Properties of polyethylene-kaolin composites
2555
of coverage of the surface of the kaolin particles with PE it will be seen that even for degrees of filling of the PEKC of 70-90 % by weight the surface of the kaolin particles is covered with PE to 50-75)o. Filling, wt.~ Completeness of coverage, ~
54'7 40"0 87.8 88"3 89"9 97 98 75.5 69'8 54.7
In the PEKC samples with a degree of filling up to 60 ~ by weight PE not bound to kaolin and particles of uncovered kaolin were not detected by the method of gradient tubes. On the other hand, in thin films of PEKC obtained by the method of hot pressing at 470-480 K clusters of kaolin particles for degrees of filling of 25-30,% by weight are not observed in the optical microscope for a 50-fold magnification. These results indicate that during polymerization of ethylene on the surface of the particles of kaolin treated with OAC with use as basis of the complex catalyst of the constituent oxides of titanium, vanadium and/or chromium, PEKCs form with practically ideal (i.e. uniform and continuous) coverage of the kaolin particles. The fluidity index of the PEKC melt in standard conditions (463 K, load 2.0 MPa) for all degrees of filling is equal to zero, which is due to the extremely high molecular mass of PE formed on the surface of the kaolin particles. The characteristic viscosity of the PE fraction soluble in decaline at 408 K exceeds 20 dl/g. This considerably narrows the areas of application of the PEKCs obtained by the method considered since they can be processed only by pressing. To elucidate the possibility of regulating the fluidity index of the PEKC melt (i.e. M and branching of the PE chain) we studied the polymerization of ethylene on the surface of the particles of kaolin treated with triisobutylaluminium in presence of hydrogen or 1-butene. The effect of the partial pressure of hydrogen and 1-butene on the kinetics of expenditure of ethylene during polymerization is indicated in Fig. 2. In both cases the introduction of a regulator into the reactor was accompanied by fall in the rate of consumption of ethylene during polymerization and limiting coverage of the kaolin particles with PE which was particularly noticeable in the case of 1-butene. Table 2 shows that with rise in the partial hydrogen pressure in the reaction zone the fluidity index of the melt, as to be expected, monotonically rises. In contrast 1-butene practically does not influence it. The sharp fall in the relative elongation e of the PEKCs obtained in presence of 1-butene indicates that it is also a chain transfer agent though less effective than hydrogen. The results obtained in the experiments with hydrogen indicate the possibility of obtaining PEKCs of casting and extrusion grades. One of the important advantages of the polymerization method of obtaining composite materials is the possibility of obtaining highly filled composites with a uniform distribution of polymer. This is particularly true of composites based on the ultra-high molecular weight PE characterized by extremely high viscosity of the melt. Blend composites of ultra-high molecular weight PE and kaolin even for degrees of filling 2 0 - 3 0 ~ by weight are heterogeneous and brittle [1, 2].
2556
N.N. VLASOVAet al.
According to Table 3, the PEI(Cs obtained by the polymerization method using as the basis of the complex catalyst of the polymerization of ethylene constitutional oxides of the transitional metals with degrees of filling up to 55% by weight are characterized by high rupture strength, considerable relative elongation e and high values of elasticity modulus E and toughness. From Table 3 it will be seen that rise in the content of kaolin in PEKC to 55 % by weight practically does not change the fluidity limit of the material a r (on reaching 10% deformation) but is accompanied by some fall in strength and relative elongation at rupture. With further increase in the content of kaolin in PEKC (from 55 to 70 % by weight) sharp fall in all the main indicators of the physico-mechanical properties is observed with highly unsatisfactory reproducibility of the results from sample to sample.
a
Z~v,I.
,50F
°
3
Zz~v,l.i l I
so tC~
so;
2 ~ _ _° _ _ ~[ 15
I J
2~
tI
~b
I0 ~
0
.
5
7
~
lO i
30
I
Time,rain
80
dO
Tt'me, min
80
FIO. 2. Effect of partial hydrogen (a) and 1-butene (b) pressure on the kinetics of consumption of ethylene during polymerization on the surface of particles of KG kaolin dried at 873 K and activated with triisobutylaluminium (3 mmole) in a heptane medium. Hydrogen pressure 0 (1); 0.13 (2); 0.3 (3); 0.6 (4) and 1.1 (5) MPa; pressure of 1-butene 0 (1); 0.15 (2); 0.2 (3); 0.3 (4) and 0.4 (5) MPa; temperature of polymerization 353 K, kaolin 20 g, heptane 0.21., ethylene pressure 1.0 MPa. At these degrees of filling in the PEKC samples by the ESCA method uncovered PE-particles of kaolin are found. Comparative analysis of thin sections of the material directly at the site of rupture and in the nearby layer by the method of microphotometry shows that the local concentration of filler at the site of rupture exceeds 2-4 times the concentration of filler in the nearby layer. This suggests that the sharp decline in the physico-mechanical properties of the PEKC for degrees of filling > 55 % by weight is due to the appreciable microheterogeneity of these composites. The deformation of the PEKC samples with degrees of filling from 40 to 55 % by weight proceeds with formation of a neck and a clearly pronounced portion of orientation consolidation the angle of slope of which rises with increase in the content of kaolin while its extent decreases. This essentially corresponds to the course of the dependence of the limiting parameters of the material during disruption on the degree
Properties of polyethylene-kaolin composites
2557
TABLE 2. EFFECT OF PARTIAL PRESSURE OF HYDROGEN AND I-BUTENE ON THE FLUIDITY INDEX OF THE MELT AND THE PHYSICOMECHANICAL PROPERTIES OF
PEKC
OBTAINED BY POLYMERIZATION OF ETHYLI~NE
ON THE SURFACE OF PARTICLES OF KAOLIN TREATED WITH TRUSOBUTYLALUM]NIUM IN HEPTANE AT AND ETHYLENE PRESSURE 1"0
(kaolin-20
g, h e p t a n e - 0 . 2
Conditions of polymerization I(iso-C4H9)3A1],
PH I
PC~II*,
filling,
mmole
MPa
MPa
wt. ~o
3"0 3"0 1'5 3-0 3"0 3.0 3-0
6 6 11 --
3"0
-
1"5 2'0
-
53 62.5 53 57 58 46 47
353 K
MPa 1.)
Properties of MFI, oF, g/10 rain MPa 0 21 0'033 0.066 0.160 0 0 0 -
PEKC aR, e, o/ /o E, G P a MPa 29.0 360 1"53 23'0 2 3"60 1 20.5 3"80 20.0 2 20-0 6 20'6 6
o f filling-fall in rupture at elongation and insignificant decline in strength. The elasticity modulus of the material regularly rises with inerease in the content of the filler in the polymer matrix. Comparison of the results given in Tables 2 and 3 indicates that fall in the M o f polyethylene in P E K C for identical degrees of filling substantially reduces the elasticity of the material. Change in the conditions of polymerization of ethylene on the surface o f the particles of kaolin treated with OAC allows one even in absence of specially introduced regulators to change the properties of the PEKCs obtained within wide limits. Table 4 shows that the PEKCs based on K G kaolin are characterized by higher indices o f the physicomechanical properties as compared with those of the same composition based on K ¥ kaolin. For the PEKCs based on K Y kaolin the same tendencies in the dependence of the properties on the degree of the filler are discerned although sharp fall in the indices of the physicomechanical properties is observed for a higher content o f kaolin in the region of fillings from 66 to 75 ~ by weight. These differences may be related to the characteristics of the distribution of filler over the dispersity of the particles; the higher the dispersity of the filler and the narrower its distribution over the equivalent diameter of the particles in the region/~N < 20 pro, the lower the degrees o f filling and the narrower the range of fillings in which there is sharp fall in the elasticity of the material. In line with this conclusion (which still must be regarded as a working hypothesis) the PE-silica gel composites obtained by the same method as P E K C based on SiO2-LS (surface 300 m2/g,/~N "~ 1 pm) already for degree of filling of 31.5 by weight are characterized by CrR----27"9 MPa and e = 9 ~ (for a degree of filling 5 5 ~ by weight aR = 18 MPa and e = 4 ~o). The nature of the OAC, other conditions being equal, weakly influences the properties of the P E K C (Table 4). But having regard to the character of change in the stability of the P E K C on storage of the material and use of the products and also the corrosive activity of the composites on processing OACs not containing chlorine atoms are to be preferred. Their consumption on synthesis of P E K C with a desired degree o f filling changes within the limits from 1.5 to 3.0 ~ by weight on conversion to kaolin.
2558
N . N . VLASOVAet aL
TABLE 3.
INFLUENCE OF THE DEGREE OF FILLING OF
P E K C WiTH K G
KOALIN ON ITS PHYSlCOMECHANICAL
PROPERTIES
(Regime of polymerization: [(iso-C, Hg)3A1]=0'02 g/g kaolin, Pc=e4=l MPa, 313 K; kaolin 100g; benzene 1 1.) Filling, w t . ~ 0* 0t 39.8 42.3 45.3 53-0 55.3 55-5 66.8 69.0
e,%
MPa 25 22 20.0 20.5 21.0 19.5 22-0 19-0 16.5
25 44 32'5 28"5 29"0 22"0 23"5 18"5 16"5 12'0
Toughness, MPa
E, G P a
600 450 265 260 210 140 150 10 10 5
1"30 1"60
m
D
3"05 3"10 3"60 4"•5
66 78 86
3"75
M . * 500,000; i" ~ 4,000.000.
* PE with
TABLE 4.
INFLUENCE OF THE CONDITIONS OF POLYMERIZATION OF ETHYLENE ON THE SURFACE OF KAOLIN
PARTICLES ON THE DEGREE OF FILLING AND THE PHYSICO-MECHANICAL PROPERTIES OF P E K C
(Kaolin (dried at 873 K for 5 h r ) - 2 0 g; h e x a n e - 0 . 2 1.; duration of p o l y m e r i z a t i o n - 2 hr)
OAC
[OAC], mmoles
T, K
PC2H4 MPa
Filling, wt. %
Properties O'F
I
of
PEKC
O'R
MPa KG (C2I-I5)2AIC1
(iso-C,*Hg)zAI
(iso'CaHg)zAI
3"0 3"0 3"0 1"5 3"0 6'0 9"0 12"0 •2"O 12"0 12'0 12'0 6"0
kaolin 1.0 0.5 0.3 1.0 1.0 1.0 1.0 2'0 2.0 1.0 1.0 1.0 0-5
38 44"7 58"4 44 39"8 54'7 62"5 42"3 45"3 53"0 55"3 66"8 69'0
20'0 17"2 18"0 20"0 20"0 18'5
41 "6 54"7 60"0 63"7 66"6 75-3
18"2 17"0 16"5 17"5 17"0
20"7 21"0 19"5 22"0 16"2
28"0 28"5 23"5 24 32"5 29"0 16"5 28"5 29"0 22"0 23"5 16'4 12"0
240 216 210 240 265 245 6"5 260 210 140 150 9 5
24"0 18"5 17"0 18"5 18"0 15"0
105 45 21 45 28 10
K Y kaolin (C2Hs)2A ICI
3'0 3"0 10"0 3"0 6"0 3-0
313 293 333 353 333 333
1"0 1"0 1'0 1'0 1.0 1"0
Properties of polyethylene-kaolin composites
2559
I n conclusion, we w o u l d n o t e t h a t the results p r e s e n t e d in r e f e r e n c e [6] a n d t h e present communication confirm the possibility of obtaining synthetic composite materials o f the d e s i r e d d e g r e e o f filling with a c o m p l e x o f high p h y s i c o m e c h a n i c a l p r o p erties as a result o f catalysis o f p o l y m e r i z a t i o n o f e t h y l e n e w i t h a c t i v a t e d O A C s cont a i n i n g c o n s t i t u t i o n a l t i t a n i u m , v a n a d i u m a n d / o r c h r o m i u m oxides in mild, t e c h n o l o gically f a v o u r a b l e conditions. Translated by A. CROZY REFERENCES
1. E. G. HOWARD, R. D. LIPSCOMB, R. N. MAC DONALD, B. L. GLAZAR, C. W. TULLOK and J. W. COLLETTE, Industr. and Engng. Chem. Product Res. and Development 20: 429, 1981 2. E. G. HOWARD, B. L. GLAZAR and J. W. COLLETTE, Industr. and Engng. Chem. Product Res. and Development 20: 429, 1981 3. N. S. YENIKOLOPYAN, F. S. D'YACHKOVSKII, L. I. CHERNAYA, P. Ye. MATKOVSKII, Yu. N. KOLESNIKOV, G. P. BELOV and N. N. BOKII, Dokl. Akad. Nauk SSSR 257: 633, 1981 4. L . I . CHERNAYA, P. Ye. MATKOVSKII, M. G. STUNZHAS, Yu. N. KOLESNIKOV, Kh. M. A. BRIKENSHTEIN, G. P. TOLSTOV and S. S. SHISHLOV, Kompleksnye metalloorganicheskiye katalizatory polimerizatsii olefinov (Complex Organometallic Polymerization Catalysts of Olefines), No. 9, p. 33, Akad. Nauk SSSR, OIKhF, 1982 5. N. S. YENIKOLOPYAN, Yu. N. KOLESNIKOV, F. S. D'YACHKOVSKII, Ye. I. YEVSYUKOV, Kh. M. A. BRIKENSHTEIN, A. I. MAKHIN'KO, L. K. SHEVTSOVA, S. S. SHISHLOV, G. P. TOLSTOV, L. A. NOVOKSHONOVA, G. P. BELOV, P. Ye. MATKOVSKII, V. M. RUDAKOV, M. P. GERASINA, F. N. AIVAZYAN and V. Ya. GOMENYUK, U.S.S.R. Pat. 1004407; Publ. in Byul. izobr., No. 10, 110, 1983 6. N. N. VLASOVA, P. Ye. MATKOVSKII, N. S. YENIKOLOPYAN, A. T. PAPOYAN, B. Ye. VOSTORGOV and V. I. SERGEYEV, Vysokomol. soyed. 27: 2120, 1985 (Translated in Polymer Sci. U.S.S.R. 27: 10, 2380, 1985)
0032-3950/85 $10.00+ .00 ~ Pergamon Journals Ltd.
PROPERTIES OF POLYETHYLENE-KAOLIN C O M P O S I T E S SYNTHESIZED BY POLYMERIZATION OF ETHYLENE ON THE PARTICULATE SURFACE OF KAOLIN TREATED WITH ORGANOALUMINIUM C O M P O U N D S * N. N. VLASOVA,V. I. SERGEYEV,P. YE. MATKOVSKII,N. S. YENIKOLOPYAN, A. T. PAPOYAN, B. Y~. VOSTORGOV,L. N. GRIGOROV, S. A. BUKANOVA, L. O. BUNINA, N. S. KOGARKO, L. A. TKACHENKOand V. V. SMIRNOV Department of the Institute of Chemical Physics, U.S.S.R. Academy of Sciences (Received 6 March 1984)
The influence of the conditions of polymerization on the dispersity, agglomeration of particles and the rheological and physicomechanical properties of polyethylene--kaolin composites obtained by polymerizing ethylene on the surface of kaolin treated with organoaluminium compounds has been studied. IT HAS been established [1, 2] that on polymerization of ethylene on the surface o f particles of disperse mineral fillers-kaolin, calcite and g i b b c i t e - i t is possible to obtain highly filled composites of uniform composition of ultra-high molecular PE characterized by high indices of the physicomechanical properties. Serving as catalysts here were combinations of ZrR4 and AIR3 which were evenly fixed on the surface of the filler particles. In these studies [1, 2] it is noted that materials of the same type also form on polymerization of ethylene on the stlrface of particles of kaolin treated with organoaluminium compounds (OAC). Detailed information on these processes has still not been published. In view of the great theoretical and practical importance of elucidating the mechanism and characteristics of polymerization of ethylene on the surface of kaolin particles using as catalyst the constitutional oxides of the transitional metals activated with OAC and continuing the investigations, to devise methods of polymerization synthesis of polyethylene-kaolin composites (PEKC) [3-5] we studied in detail the influence of the conditions of polymerization and other factors on the kinetic patterns o f expenditure of ethylene during polymerization [6] and the properties of the composites obtained by this method. Some results of these investigations formed the subject of the present work. The characteristics of the kaolins of the Glukhovetskii (KG) and Yeleninskii (KY) deposits used in the work, the methods of preparing and drying the raw material and also the technique of studying the kinetic patterns of polymerization of ethylene on the surface of the particles of kaolin treated with OAC are described in [6]. KG kaolin was dried at 873 K. The density of dried kaolin * Vysokomol. soyed. A27: No. 11, 2274-2280, 1985. 2552
Properties of polyethylene-kaolin composites
2553
was 2.5-2.6 g/cm 3. The PEKCs formed during polymerization after its completion were unloaded from the reactor, separated on a filter from the solvent and dried in a vacuum cupboard at temperatures not exceeding 353 K. The filling of PEKC with kaolin (wt. 7.) was determined from the consumption of ethylene, gravimetrically and from the ash yield after combustion of the samples by the standard technique. The mass and numerical distribution of the PEKC samples and the initial kaolin over the equivalent diameter of the particles was obtained in the same way as in [6] with the "Malvern ST-1800" instrument. The continuity of coverage of the surface of the kaolin particles with PE was determined by the method of electron spectroscopy for chemical analysis (ESCA) with the ES-2401 instrument. The specimens for the investigations by this method were prepared by fixing the powders on an indium support at pressures not exceeding 0-5 MPa. The fluidity index of the melt of the PEKC samples was determined with an instrument for measuring the index of the melt of the IIRT thermoplasts at the temperature 463 K and for a load 0"5 MPa. The samples to determine the physicomechanical characteristics of the PEKC were obtained from plates 1.5-2.0 mm thick prepared by hot pressing in the form of a closed type. The specific pressure for pressing was 10 MPa; pressing temperature 463 K, time of holding under pressure 30 min and rate of cooling 10 degrees/min. The physicomechanical characteristics of the PEKC were determined with the Instron-1185 machine. The rate of displacement of the active capture of the machine in the tests of the materials was 1 rain- 1.
ND,Zll q0 20
100
200
300
D,~rn
400
FIG. 1. Number distribution equivalent particle diameter of KG kaolin (1) and PEKC obtained during suspension polymerization of ethylene (2-4). [(iso-C4Hg)aA1]=0 (•); 0.15 (2); 0.03 (3) and 0.0085 kaolin (4) g/g. Ethylene pressure 1-0 MPa; temperature of polymerization 313 K; time 3 hr. A s a result o f s u s p e n s i o n p o l y m e r i z a t i o n o f ethylene on the surface o f the particles o f k a o l i n t r e a t e d w i t h O A C in relatively m i l d c o n d i t i o n s ( t e m p e r a t u r e 293-373 K , e t h y l e n e p r e s s u r e 0-3-1.0 M P a ) for 1-3 h r P E K C s f o r m with a d e g r e e o f filling f r o m 90 t o 25 ~ b y weight. A f t e r i s o l a t i o n a n d d r y i n g the P E K C s c o n s t i t u t e friable, c o l o u r less (in t h e case o f K G k a o l i n ) or p a l e p i n k (in the case o f K ¥ k a o l i n ) d i s p e r s e p r o d u c t s c h a r a c t e r i z e d by a v e r y wide m a s s a n d n u m e r i c a l d i s t r i b u t i o n o v e r t h e e q u i v a l e n t d i a m e t e r o f t h e p a r t i c l e s (Fig. 1, T a b l e 1). I t is w o r t h n o t i n g t h a t the m e a n n u m e r i c a l e q u i v a l e n t d i a m e t e r DN o f the P E K C p a r t i c l e s exceeds b y m o r e t h a n one o r d e r t h a t o f t h e initial d r i e d kaolin. S i m p l e calc u l a t i o n s show t h a t as a result o f c o v e r a g e o f t h e k a o l i n p a r t i c l e s w i t h P E for t h e fillings i n d i c a t e d in T a b l e 1 / ~ o u g h t to rise n o t m o r e t h a n 2 - 3 times.
2554
N.N. VLASOVAet al.
Comparison of the calculated with the experimental values of/)N invites the conclusion that the nascent PEKC particles represent agglomerates of smaller particles. This conclusion was confirmed by us experimentally. In the optical microscope with 50 fold magnification it is clearly seen that the nascent PEKC particles with a diameter 200-300/~m represent associates of a large number of primary particles with an equivalent diameter from 10 to 50/zm. On exposure to ethanol the PEKC associates like the agglomerates of the kaolin particles (Table 1) partially diaggregate. From this it follows that the primary PEKC particles in the associates are not bound by the through PE chains. The degree of aggregation of the primary PEKC particles is determined by the nature and degree of drying of kaolin, depends on the nature and concentration of the OAC, the temperature of polymerization and many other factors not easy to estimate. In particular, in the case of KY the mean numerical equivalent diameter of the PEKC associates (1-3 mm) with no change in the other conditions exceeds by one order DN of the PEKC obtained on the basis of KG kaolin. We would also note that rise in the concentration of Al(iso-C4H9)3 (from 0-0085 to 0.15 g/g kaolin) leads to fall in/)N (from 300 to 200 pro). It is known [1] that treatment with OAC is accompanied by disaggregation of the kaolin particles. Therefore there are grounds for assuming that the association of the particles during polymerization synthesis of PEKC is due to physical processes the progress of which leads to fall in the free energy of the developed surface of the primary PEKC particles. The nature of this process is still not clear. Comparative analysis of the distribution histograms of the kaolin and PEKC particles over the equivalent diameter (Fig. 1) indicates that practically all the kaolin particles for degrees of filling to 60 7oo by weight are covered by PE. This conclusion is confirmed by electron spectroscopy. Comparison of the intensity of the silicon, aluminium and oxygen lines in the electron spectra of the samples of dried kaolin and PEKC shows that the fraction of the surface of the kaolin particles not covered with PE for degrees of filling up to 60 % by weight does not exceed 2-5 %. From the data on the influence of the degree of filling of PEKC with KG kaolin on the completeness TABLE 1. CHARACTERIZATION
OF D I S T R I B U T I O N OF K A O L I N A N D
PEKC
OVER THE EQUIVALENT PARTICLE
DIAMETER
Kaolin
Txv,
K*
i
OAC
J KG KY KG
*
293 873 293 293 873 873 873 873
Dispersion medium Heptane ,)
(iso-C4Hg)3A1
Heptane Ethanol Heptane
))
))
B
(C2Hs)2A1CI
))
T,o-Temperature of drying o f k a o l i n . characterizing the width of the distribution.
~" y-Parameter
Filling, 70 100 100 100 100 27"3 38"9 59"2 44"7
/)N, pm 17"0 14"0 29"0 9"0
300 248 198 293
7' 1'1 1"0 1"0 1"1 3"6 4"3 3"4 3"0
Properties of polyethylene-kaolin composites
2555
of coverage of the surface of the kaolin particles with PE it will be seen that even for degrees of filling of the PEKC of 70-90 % by weight the surface of the kaolin particles is covered with PE to 50-75)o. Filling, wt.~ Completeness of coverage, ~
54'7 40"0 87.8 88"3 89"9 97 98 75.5 69'8 54.7
In the PEKC samples with a degree of filling up to 60 ~ by weight PE not bound to kaolin and particles of uncovered kaolin were not detected by the method of gradient tubes. On the other hand, in thin films of PEKC obtained by the method of hot pressing at 470-480 K clusters of kaolin particles for degrees of filling of 25-30,% by weight are not observed in the optical microscope for a 50-fold magnification. These results indicate that during polymerization of ethylene on the surface of the particles of kaolin treated with OAC with use as basis of the complex catalyst of the constituent oxides of titanium, vanadium and/or chromium, PEKCs form with practically ideal (i.e. uniform and continuous) coverage of the kaolin particles. The fluidity index of the PEKC melt in standard conditions (463 K, load 2.0 MPa) for all degrees of filling is equal to zero, which is due to the extremely high molecular mass of PE formed on the surface of the kaolin particles. The characteristic viscosity of the PE fraction soluble in decaline at 408 K exceeds 20 dl/g. This considerably narrows the areas of application of the PEKCs obtained by the method considered since they can be processed only by pressing. To elucidate the possibility of regulating the fluidity index of the PEKC melt (i.e. M and branching of the PE chain) we studied the polymerization of ethylene on the surface of the particles of kaolin treated with triisobutylaluminium in presence of hydrogen or 1-butene. The effect of the partial pressure of hydrogen and 1-butene on the kinetics of expenditure of ethylene during polymerization is indicated in Fig. 2. In both cases the introduction of a regulator into the reactor was accompanied by fall in the rate of consumption of ethylene during polymerization and limiting coverage of the kaolin particles with PE which was particularly noticeable in the case of 1-butene. Table 2 shows that with rise in the partial hydrogen pressure in the reaction zone the fluidity index of the melt, as to be expected, monotonically rises. In contrast 1-butene practically does not influence it. The sharp fall in the relative elongation e of the PEKCs obtained in presence of 1-butene indicates that it is also a chain transfer agent though less effective than hydrogen. The results obtained in the experiments with hydrogen indicate the possibility of obtaining PEKCs of casting and extrusion grades. One of the important advantages of the polymerization method of obtaining composite materials is the possibility of obtaining highly filled composites with a uniform distribution of polymer. This is particularly true of composites based on the ultra-high molecular weight PE characterized by extremely high viscosity of the melt. Blend composites of ultra-high molecular weight PE and kaolin even for degrees of filling 2 0 - 3 0 ~ by weight are heterogeneous and brittle [1, 2].
2556
N.N. VLASOVAet al.
According to Table 3, the PEI(Cs obtained by the polymerization method using as the basis of the complex catalyst of the polymerization of ethylene constitutional oxides of the transitional metals with degrees of filling up to 55% by weight are characterized by high rupture strength, considerable relative elongation e and high values of elasticity modulus E and toughness. From Table 3 it will be seen that rise in the content of kaolin in PEKC to 55 % by weight practically does not change the fluidity limit of the material a r (on reaching 10% deformation) but is accompanied by some fall in strength and relative elongation at rupture. With further increase in the content of kaolin in PEKC (from 55 to 70 % by weight) sharp fall in all the main indicators of the physico-mechanical properties is observed with highly unsatisfactory reproducibility of the results from sample to sample.
a
Z~v,I.
,50F
°
3
Zz~v,l.i l I
so tC~
so;
2 ~ _ _° _ _ ~[ 15
I J
2~
tI
~b
I0 ~
0
.
5
7
~
lO i
30
I
Time,rain
80
dO
Tt'me, min
80
FIO. 2. Effect of partial hydrogen (a) and 1-butene (b) pressure on the kinetics of consumption of ethylene during polymerization on the surface of particles of KG kaolin dried at 873 K and activated with triisobutylaluminium (3 mmole) in a heptane medium. Hydrogen pressure 0 (1); 0.13 (2); 0.3 (3); 0.6 (4) and 1.1 (5) MPa; pressure of 1-butene 0 (1); 0.15 (2); 0.2 (3); 0.3 (4) and 0.4 (5) MPa; temperature of polymerization 353 K, kaolin 20 g, heptane 0.21., ethylene pressure 1.0 MPa. At these degrees of filling in the PEKC samples by the ESCA method uncovered PE-particles of kaolin are found. Comparative analysis of thin sections of the material directly at the site of rupture and in the nearby layer by the method of microphotometry shows that the local concentration of filler at the site of rupture exceeds 2-4 times the concentration of filler in the nearby layer. This suggests that the sharp decline in the physico-mechanical properties of the PEKC for degrees of filling > 55 % by weight is due to the appreciable microheterogeneity of these composites. The deformation of the PEKC samples with degrees of filling from 40 to 55 % by weight proceeds with formation of a neck and a clearly pronounced portion of orientation consolidation the angle of slope of which rises with increase in the content of kaolin while its extent decreases. This essentially corresponds to the course of the dependence of the limiting parameters of the material during disruption on the degree
Properties of polyethylene-kaolin composites
2557
TABLE 2. EFFECT OF PARTIAL PRESSURE OF HYDROGEN AND I-BUTENE ON THE FLUIDITY INDEX OF THE MELT AND THE PHYSICOMECHANICAL PROPERTIES OF
PEKC
OBTAINED BY POLYMERIZATION OF ETHYLI~NE
ON THE SURFACE OF PARTICLES OF KAOLIN TREATED WITH TRUSOBUTYLALUM]NIUM IN HEPTANE AT AND ETHYLENE PRESSURE 1"0
(kaolin-20
g, h e p t a n e - 0 . 2
Conditions of polymerization I(iso-C4H9)3A1],
PH I
PC~II*,
filling,
mmole
MPa
MPa
wt. ~o
3"0 3"0 1'5 3-0 3"0 3.0 3-0
6 6 11 --
3"0
-
1"5 2'0
-
53 62.5 53 57 58 46 47
353 K
MPa 1.)
Properties of MFI, oF, g/10 rain MPa 0 21 0'033 0.066 0.160 0 0 0 -
PEKC aR, e, o/ /o E, G P a MPa 29.0 360 1"53 23'0 2 3"60 1 20.5 3"80 20.0 2 20-0 6 20'6 6
o f filling-fall in rupture at elongation and insignificant decline in strength. The elasticity modulus of the material regularly rises with inerease in the content of the filler in the polymer matrix. Comparison of the results given in Tables 2 and 3 indicates that fall in the M o f polyethylene in P E K C for identical degrees of filling substantially reduces the elasticity of the material. Change in the conditions of polymerization of ethylene on the surface o f the particles of kaolin treated with OAC allows one even in absence of specially introduced regulators to change the properties of the PEKCs obtained within wide limits. Table 4 shows that the PEKCs based on K G kaolin are characterized by higher indices o f the physicomechanical properties as compared with those of the same composition based on K ¥ kaolin. For the PEKCs based on K Y kaolin the same tendencies in the dependence of the properties on the degree of the filler are discerned although sharp fall in the indices of the physicomechanical properties is observed for a higher content o f kaolin in the region of fillings from 66 to 75 ~ by weight. These differences may be related to the characteristics of the distribution of filler over the dispersity of the particles; the higher the dispersity of the filler and the narrower its distribution over the equivalent diameter of the particles in the region/~N < 20 pro, the lower the degrees o f filling and the narrower the range of fillings in which there is sharp fall in the elasticity of the material. In line with this conclusion (which still must be regarded as a working hypothesis) the PE-silica gel composites obtained by the same method as P E K C based on SiO2-LS (surface 300 m2/g,/~N "~ 1 pm) already for degree of filling of 31.5 by weight are characterized by CrR----27"9 MPa and e = 9 ~ (for a degree of filling 5 5 ~ by weight aR = 18 MPa and e = 4 ~o). The nature of the OAC, other conditions being equal, weakly influences the properties of the P E K C (Table 4). But having regard to the character of change in the stability of the P E K C on storage of the material and use of the products and also the corrosive activity of the composites on processing OACs not containing chlorine atoms are to be preferred. Their consumption on synthesis of P E K C with a desired degree o f filling changes within the limits from 1.5 to 3.0 ~ by weight on conversion to kaolin.
2558
N . N . VLASOVAet aL
TABLE 3.
INFLUENCE OF THE DEGREE OF FILLING OF
P E K C WiTH K G
KOALIN ON ITS PHYSlCOMECHANICAL
PROPERTIES
(Regime of polymerization: [(iso-C, Hg)3A1]=0'02 g/g kaolin, Pc=e4=l MPa, 313 K; kaolin 100g; benzene 1 1.) Filling, w t . ~ 0* 0t 39.8 42.3 45.3 53-0 55.3 55-5 66.8 69.0
e,%
MPa 25 22 20.0 20.5 21.0 19.5 22-0 19-0 16.5
25 44 32'5 28"5 29"0 22"0 23"5 18"5 16"5 12'0
Toughness, MPa
E, G P a
600 450 265 260 210 140 150 10 10 5
1"30 1"60
m
D
3"05 3"10 3"60 4"•5
66 78 86
3"75
M . * 500,000; i" ~ 4,000.000.
* PE with
TABLE 4.
INFLUENCE OF THE CONDITIONS OF POLYMERIZATION OF ETHYLENE ON THE SURFACE OF KAOLIN
PARTICLES ON THE DEGREE OF FILLING AND THE PHYSICO-MECHANICAL PROPERTIES OF P E K C
(Kaolin (dried at 873 K for 5 h r ) - 2 0 g; h e x a n e - 0 . 2 1.; duration of p o l y m e r i z a t i o n - 2 hr)
OAC
[OAC], mmoles
T, K
PC2H4 MPa
Filling, wt. %
Properties O'F
I
of
PEKC
O'R
MPa KG (C2I-I5)2AIC1
(iso-C,*Hg)zAI
(iso'CaHg)zAI
3"0 3"0 3"0 1"5 3"0 6'0 9"0 12"0 •2"O 12"0 12'0 12'0 6"0
kaolin 1.0 0.5 0.3 1.0 1.0 1.0 1.0 2'0 2.0 1.0 1.0 1.0 0-5
38 44"7 58"4 44 39"8 54'7 62"5 42"3 45"3 53"0 55"3 66"8 69'0
20'0 17"2 18"0 20"0 20"0 18'5
41 "6 54"7 60"0 63"7 66"6 75-3
18"2 17"0 16"5 17"5 17"0
20"7 21"0 19"5 22"0 16"2
28"0 28"5 23"5 24 32"5 29"0 16"5 28"5 29"0 22"0 23"5 16'4 12"0
240 216 210 240 265 245 6"5 260 210 140 150 9 5
24"0 18"5 17"0 18"5 18"0 15"0
105 45 21 45 28 10
K Y kaolin (C2Hs)2A ICI
3'0 3"0 10"0 3"0 6"0 3-0
313 293 333 353 333 333
1"0 1"0 1'0 1'0 1.0 1"0
Properties of polyethylene-kaolin composites
2559
I n conclusion, we w o u l d n o t e t h a t the results p r e s e n t e d in r e f e r e n c e [6] a n d t h e present communication confirm the possibility of obtaining synthetic composite materials o f the d e s i r e d d e g r e e o f filling with a c o m p l e x o f high p h y s i c o m e c h a n i c a l p r o p erties as a result o f catalysis o f p o l y m e r i z a t i o n o f e t h y l e n e w i t h a c t i v a t e d O A C s cont a i n i n g c o n s t i t u t i o n a l t i t a n i u m , v a n a d i u m a n d / o r c h r o m i u m oxides in mild, t e c h n o l o gically f a v o u r a b l e conditions. Translated by A. CROZY REFERENCES
1. E. G. HOWARD, R. D. LIPSCOMB, R. N. MAC DONALD, B. L. GLAZAR, C. W. TULLOK and J. W. COLLETTE, Industr. and Engng. Chem. Product Res. and Development 20: 429, 1981 2. E. G. HOWARD, B. L. GLAZAR and J. W. COLLETTE, Industr. and Engng. Chem. Product Res. and Development 20: 429, 1981 3. N. S. YENIKOLOPYAN, F. S. D'YACHKOVSKII, L. I. CHERNAYA, P. Ye. MATKOVSKII, Yu. N. KOLESNIKOV, G. P. BELOV and N. N. BOKII, Dokl. Akad. Nauk SSSR 257: 633, 1981 4. L . I . CHERNAYA, P. Ye. MATKOVSKII, M. G. STUNZHAS, Yu. N. KOLESNIKOV, Kh. M. A. BRIKENSHTEIN, G. P. TOLSTOV and S. S. SHISHLOV, Kompleksnye metalloorganicheskiye katalizatory polimerizatsii olefinov (Complex Organometallic Polymerization Catalysts of Olefines), No. 9, p. 33, Akad. Nauk SSSR, OIKhF, 1982 5. N. S. YENIKOLOPYAN, Yu. N. KOLESNIKOV, F. S. D'YACHKOVSKII, Ye. I. YEVSYUKOV, Kh. M. A. BRIKENSHTEIN, A. I. MAKHIN'KO, L. K. SHEVTSOVA, S. S. SHISHLOV, G. P. TOLSTOV, L. A. NOVOKSHONOVA, G. P. BELOV, P. Ye. MATKOVSKII, V. M. RUDAKOV, M. P. GERASINA, F. N. AIVAZYAN and V. Ya. GOMENYUK, U.S.S.R. Pat. 1004407; Publ. in Byul. izobr., No. 10, 110, 1983 6. N. N. VLASOVA, P. Ye. MATKOVSKII, N. S. YENIKOLOPYAN, A. T. PAPOYAN, B. Ye. VOSTORGOV and V. I. SERGEYEV, Vysokomol. soyed. 27: 2120, 1985 (Translated in Polymer Sci. U.S.S.R. 27: 10, 2380, 1985)