- Email: [email protected]
The mechanism of the modifying action of oligomers in filled compositions based on polyethylene
2862
V.I. SKRIPACHEVet al.
5. V. P. BUDTOV, N. G. PODOSENOVA, E. G. ZOTIKOV, V. M. BELYAYEV, Ye. N. KISLOV and Yu. M. DZHALIASHV1LI, Plast. massy, 2, 33, 1975 6. N. I. KONDRASHKINA, T. N. ZELENKOVA, M. Z. BORDULINA and B. I. SAZHIN, Zh. prikl, khimii, 1196, 1982 7. O. N. KARPUKHIN and Ye. M. SLOBODETSKAYA, Uspekhi khimii 42: 391, 1973 8. A. M. KOTLIAR and S. EICHENBAUM, Polymer Preprints, 9: 341, 1968 9. A. L. GOL'DENBERG, Plast. massy, 6, 29, 1963 10. Ye. M. SLOBODETSKAYA, Uspekhi khimii 49: 1596, 1980
Polymerr Science U.S.S.R. Vol. 26, No. 12, pp. 2862-2866, 1984 Printed in Poland
0032-3950/84 $10.00+.00 <~ 1986.Pergamon Press Ltd.
THE M E C H A N I S M OF THE MODIFYING ACTION OF OLIGOMERS IN FILLED COMPOSITIONS BASED ON POLYETHYLENE* V. I. SKRIPACHEV, V. N. KUZNETSOV and S. S. ]VANCHEV Okhta Scientific and Industrial Unit "Plastpolimer" (Received 5 May 1983)
The effect of oligomeric compounds containing functional groups on the properties of systems consisting of a dispersed filler in PE has been investigated. The results obtained indicate that the oligomers not only combine physically with the filler but also interact chemically with the functional groups located on the filler surface. Mechanisms, which depend on the structure of the oligomeric compound, are proposed for the formation of a transitional zone in filled PE. FILLED polymeric materials have found wide application in various sectors of the Soviet economy in the last decade. This is related to the fact that the introduction of fillers into polymers leads to substantial changes in th.eir properties which are largely determined by the interaction between the components. It should, however, be noted that organic polymers, especially polyolefins, do not combine well with inorganic fillers. One of the methods of improving the interaction between the components in a filled polymeric system is to use modifying additions that form an intermediate layer between the polymeric phase and the filler [1]. The following types of low-molecular weight compounds are used as such additions: organosilanes, surfactants and organotitanates [2, 3]. Up to now, oligomeric compounds have hardly been studied at all as modifiers for the filler surface and filler polyolefins. Information about the effect of * Vysokomol. soyed. A26: No. 12, 2553-2556, 1984.
Mechanism of modifying action of oligomers
2863
certain types of oligomers on the p r o p e r t e s of filled polyolefins has been reported [4, 5] but the question of the interaction between the filler and the polymer in the presence o f these additions was not discussed by the authors. In this connection, it is of current interest to establish the basic rules governing an effect of oligomeric compounds on the properties of filled composite materials and to determine the mechanism of their modifying action. The effect of oligomeric compounds, either with end functional groups or with functional groups along the main oligomeric chain, on the properties of filled PE is discussed in the present work. High-pressure PE with a melt-flow index of 2 g/10 min was used as the basic polymer. The filling of the PE with MMO grade chalk, KRKhS grade kaolin or with SMS-160 grade mica was carried out in a Banbury mixer having a mixing chamber 0.002 m a in volume, at 10-140°C for 7 rain. The modifying effect of the following oligomers was studied: the anhydride of alkenylsuceinie acid (ANAS), M=900-1100; bis-alkenylsuccinimide (BASI), M = 1900-2100 and a eopolymer of butadiene and methacrylic acid (SKD-1 A) with M=45{X)--5000. The oligomers ANAS and BASI have a polybutene hydrocarbon block and SKD-1A contains 3--4~. of carboxyl groups. The physico-mechanical, technological and electro-physical properties of the filled PE were determined by standard methods using moulded specimens. In order to determine the amount of the oligomer chemically combined with the filler, the latter was separated from the composition by dissolution of the PE and the free oligomer in boiling xylene. After the soluble part of the composition had been separated, the filler was extracted with p-xylene in a Soxhlet apparatus for 100 hr to remove residues of adsorbed oligomer. The amount of the oligomer combined with the filler was determined by weighing, the filler having been heated in a muffle furnace at 800°C. The chemical combination of ANAS with the filler was established by IR spectroscopy. The Table shows the properties of compositions based on PE, containing 30 wt. % of chalk and an oligomer. It may be seen that oligomers with end functional groups (ANAS and BASI) and those with functional groups positioned along the main chain (SKD-1A) affect the properties of filled PE in different ways. Thus the introduction of A N A S and BASI leads to a reduction in the tensile strength and to an increase in the relative elongation of failed PE. S K D - 1 A increases b o t h the tensile strength and also the relative elongation at rupture. An increase in filler content is known to lower the flowability of the melt so that definite difficulties arise in processing filled polymers to form components. In this connection it is interesting to note that all the types of oligomeric c o m p o u n d s that we have used, when introduced in small quantities, raise the melt flow index of filled PE. This appears to a greater extent in the case of oligomers containing end functional groups. The rules governing changes in the electrophysical properties of filled PE are of especial interest. As the concentration of a polar oligomei in the composition is increased, the tangent of the dielectric loss angle, tan & decreases and, having reached a minimum, increases once more (Fig. 1). The specific volumetric electric resistance, po, of the compositions is observed to increase in the same region of oligomer concentration. The various positions of the region of the m a x i m u m on the curves are determined by the specific
2864
V.I.
SKRIPACHEV
etaL
surface area, the particle shape, the chemical nature and concentration of the filler in PE. The minimum on the curves showing taxi J as a function of the amount of oligomer per gram o f filler does not depend on the filler concentration (Fig. 2). The way in which the water absorption of filled PE changes as a function of the oligomer concentration is similar to the way in which tan ~ changes.
tan 8,10s
logpv ,ohm.cm
',10J
/0
1
16'
"~Qn (
175
O~ ,17"0 3 0"5
1"0 l~o. 1
1"5 c, w t %
1
15.5
0
0"02
0'04
0.06
1~o. 2
Fio. 1. Dependence of: 1 - 3 - the tangent of the dielectric loss angle, tan J, and 4 - the specific volumetric electrical resistivity, pv, on the concentration of A S A N for PE compositions with 40 wt. % filler, the following being used:/-mica; 2 and 4-chalk and 3-kaolin. FIo. 2. Dependence of the tangent of the dielectric loss angle, tan J, of filler PE on q, the amount of A S A N per gram of filler, mica being used at the following concentrations: 1-70 wt. ~.; 2 - 4 0 wt. ~. and 3 - 2 0 wt. ~.. It may be assumed that the oligomer molecules in the filled polymer are localized in a transition zone close to the surface and are positioned at the phase interface, the polar groups being oriented towards the failer surface. Anhydride, imide and carboxyl groups in this orientation cannot only combine physically with the failer surface but can also interact with functional groups located at the filler surface. For example, in the case o f ANAS the interaction can occur with the hydroxyl groups of the filler, the anhydride ring being opened up. Confirmation that ANAS, chemically combined with the filler, is formed has b e e n obtained by IR spectroscopy. Absorption bands in the region 1720-1730 cm -1, which were not present in the initial filler sample, are observed in the IR spectrum o f the filler separated from filled PE. The amount of chemically combined oligomer, determined by combustion, was equal to 5-10, 2-5 and 2-4 wt. ~o for ANAS, BASI and SKD-1A respectively. I f oligomer molecules with end functional groups are oriented in the neighbourhood o f the filler-polymer interface with the hydrophilie part towards the filler and the hydrophobic part towards the polymer, one may estimate the surface area of the filler occupied by the oligomer, by analogy with the orientation of surfactants in condensed films. The cross-sectional area o f the PE maerochain is taken to be equal to 21 A 2 [6]. Since
Mechanism of modifying action of oligomers PROPERTIES OF L O W - D ~
PE nLLm~ WITH 30
WT.~.
2865
CHALK, AS A FUNCTION OF THE OLIOOMER
CONTENT OF THE COblP(~ITION
Parameter Tensile strength, MPa
Relative elongation at rupture,
% Melt flow index, g/10 min
Tangent of the dielectric loss angle, tan J x l 0 a, at a frequency of l0 s Hz Water absorption,
Oligomer ASAN BASI SKD-1A ASAN BASI SKD-1A ASAN BASI SKD-1A ASAN BASI SKD-IA ASAN BASI SKD-1A
Values of the parameter for the following oligomer concentrations in the composition, wt. ~, I 0"25 [ 0"50 [ 0.75 I 1.00 I 1.50 12.00 10"9 10"6 10"5 10.3 9-8] 9.5 I1'0 11"1 10"7 10"6 10-0 9.9 9.7 11.8 11"9 12.3 12.7 12.9 12.5 140 119 145 127 120 75 105 100 110 123 125 112 115 84 80 81 76 80 86 1"02 1 "07 1"19 1.35 1.47 1.60 1.7 1"05 1"11 1-27 1.38 1.50 1.6 1"02 1"09 1.11 1.15 1.19 1.2 2"1 1"7 1-5 1.1 1-2 1.0 0.9 1"8 1.3 1.4 1"6 1.1 1.1 1"8 1.5 1.7 1.8 1.5 1-6 0"50 0"38 0"22 0.19 0.18 0-20 0.2 0"42 0"30 0.25 0.25 0.26 0.2 0-47 0.45 0.41 0.41 0.43 0.4
the cross-sectional axea is not known for the polybutene block of the A N A S molecule, we shall roughly consider that it is equal to 21 A 2 although this value is rather too small. The specific surface area of the chalk being 14.7 m2/g, it is necessary to introduce 2"0 x 1021 molecules of A N A S into 100 grams of a composition containing 30 wt. ~o o f chalk in order that the oligomer should be in the f o r m of a condensed film and cover the entire surface o f the filler. The region in which the minimum on the curves for tan t~, the water-absorption and the resistivity po is observed corresponds to a concentration o f 1"0 wt. % A N A S in the composition, that is, 0.6 x 1021 molecules. This figure is 3 times less than the calculated n u m b e r of A N A S molecules necessary to satisfy the condition that the filler surface should be screened if the calculation is based on the principle used for surfactants, namely, that condensed films should be formed at the interface between the phases. If, however, we remember that the cross-sectional area o f the polybutene block is greater than that assumed in the calculation and the oligom e r i t block, because of its great length, can make it difficult for additionally introduced oligomeric molecules to have access to the free surface of the filler, we should recognize that there is agreement between the calculated figure and the figure obtained experimentally. BASI, in whose molecule there axe two polybutene blocks, acts similarly. Oligomers with end functional groups in filled PE isolate the filler particles so that they axe separated by, at most, two lengths of the oligomeric block. In this case, effects involving the formation of filler structures are completely absent. Because of the disruption of the filler structure, the conductivity of the system is reduced, and this leads to a reduction in tan t~ and to an increase in Pv. Oligomeric compounds with end functional groups in filled systems have a mainly plasticizing effect.
2866
V. I. SKRIPACHEV e t al.
By contrast to ANAS and BASI, the carboxyl groups in the SKD-1A oligomer a r e distributed along the main chain. In this case, the oligomer molecules are probably adsorbed at the filler surface along their entire length. The effectiveness of the screening is thus less and the screening effect of the filler particles is achieved at a lower oligomer concentration. The fact that only a small percent of the SKD-1A is chemically combined with the filler and the value of the water adsorption confirm the low density of the covering o f the filler. The positioning of the oligomer molecules in a felt-like manner is clearly characteristic of the use of SKD-1A. The thinness of the isolation layer between two filler particles, corresponding in the best case only to two diameters of the oligomeric chain's cross-section, as well as the existence of free surface can lead in the system to the formation of coagulation thixotropic filler structures, which are responsible for the increase in the strength properties of the polymer system [7]. In addition to this mechanism of reinforcement, it may be assumed that a definite contribution to the increase in the strength properties of filled PE is made by an effect involving the entrapment o f PE macromolecules by an oligomeric chain with the formation of an entanglement-type bond. The incorporation of a PE macrochain, gripped by the oligomer, within crystalline formations leads to reinforcement of the p o l y m e r - filler bond and, correspondingly, to an increase in the strength properties. The properties of filled PE thus depend essentially on the type of oligomeric modifier that participates in the formation of the transition zone between the filler and the polymeric matrix. The use of oligomers with end functional groups to modify filled polyolefins leads to the production of a composite material with improved technological properties, enhanced elasticity and with good dielectric properties. In similar systems, the use of oligomers containing functional groups along the main chain makes it possible to obtain filled compositions with improved physico-mechanical properties. Translated by G. F. MODLI~N
REFERENCES
1. Poverkhnosti razdela v polimernykh kompozitakh (Interfaces in Polymeric Composites), edited by E. P. Plueddemann, p. 9, Mir, Moscow, 1978 (Russian translation) 2. Ye. P. NIKULINA, Khim. prom-st' za rubezhom, 7, 24, 1977 3. S. N. TOLSTAYA, (book) Napolniteli polimernyk.h materialov (Fillers for Polymeric Materials), p. 11, Moscow, 1977 4. M. M. REVYAKO, A. Ya. MARKINA, T. V. DUNINA and L. A. ISAYENYA, (book) Khimiya i khim. tckhnol. (Chemistry and chemical technology), No. 10, p. 120, Vysshaya shkola, Minsk, 1976 5. I. A. KHLAVITSKAYA, L. A. TSINANKINA andE. A. SPORYAGIN, Plast. massy, 1, 29, 1978 6. S. S. VOYUTSKII, Kurs kolloidnoi khimii (Textbook of Colloid Chemistry). p. 135, Khimiya, Moscow, 1976 7. Yu. S. LIPATOV, Fizicheskaya khimiya napolnennykh polimerov (Physical Chemistry of Filled Polymers). p. 273, Khimiya, Moscow, 1977
V.I. SKRIPACHEVet al.
5. V. P. BUDTOV, N. G. PODOSENOVA, E. G. ZOTIKOV, V. M. BELYAYEV, Ye. N. KISLOV and Yu. M. DZHALIASHV1LI, Plast. massy, 2, 33, 1975 6. N. I. KONDRASHKINA, T. N. ZELENKOVA, M. Z. BORDULINA and B. I. SAZHIN, Zh. prikl, khimii, 1196, 1982 7. O. N. KARPUKHIN and Ye. M. SLOBODETSKAYA, Uspekhi khimii 42: 391, 1973 8. A. M. KOTLIAR and S. EICHENBAUM, Polymer Preprints, 9: 341, 1968 9. A. L. GOL'DENBERG, Plast. massy, 6, 29, 1963 10. Ye. M. SLOBODETSKAYA, Uspekhi khimii 49: 1596, 1980
Polymerr Science U.S.S.R. Vol. 26, No. 12, pp. 2862-2866, 1984 Printed in Poland
0032-3950/84 $10.00+.00 <~ 1986.Pergamon Press Ltd.
THE M E C H A N I S M OF THE MODIFYING ACTION OF OLIGOMERS IN FILLED COMPOSITIONS BASED ON POLYETHYLENE* V. I. SKRIPACHEV, V. N. KUZNETSOV and S. S. ]VANCHEV Okhta Scientific and Industrial Unit "Plastpolimer" (Received 5 May 1983)
The effect of oligomeric compounds containing functional groups on the properties of systems consisting of a dispersed filler in PE has been investigated. The results obtained indicate that the oligomers not only combine physically with the filler but also interact chemically with the functional groups located on the filler surface. Mechanisms, which depend on the structure of the oligomeric compound, are proposed for the formation of a transitional zone in filled PE. FILLED polymeric materials have found wide application in various sectors of the Soviet economy in the last decade. This is related to the fact that the introduction of fillers into polymers leads to substantial changes in th.eir properties which are largely determined by the interaction between the components. It should, however, be noted that organic polymers, especially polyolefins, do not combine well with inorganic fillers. One of the methods of improving the interaction between the components in a filled polymeric system is to use modifying additions that form an intermediate layer between the polymeric phase and the filler [1]. The following types of low-molecular weight compounds are used as such additions: organosilanes, surfactants and organotitanates [2, 3]. Up to now, oligomeric compounds have hardly been studied at all as modifiers for the filler surface and filler polyolefins. Information about the effect of * Vysokomol. soyed. A26: No. 12, 2553-2556, 1984.
Mechanism of modifying action of oligomers
2863
certain types of oligomers on the p r o p e r t e s of filled polyolefins has been reported [4, 5] but the question of the interaction between the filler and the polymer in the presence o f these additions was not discussed by the authors. In this connection, it is of current interest to establish the basic rules governing an effect of oligomeric compounds on the properties of filled composite materials and to determine the mechanism of their modifying action. The effect of oligomeric compounds, either with end functional groups or with functional groups along the main oligomeric chain, on the properties of filled PE is discussed in the present work. High-pressure PE with a melt-flow index of 2 g/10 min was used as the basic polymer. The filling of the PE with MMO grade chalk, KRKhS grade kaolin or with SMS-160 grade mica was carried out in a Banbury mixer having a mixing chamber 0.002 m a in volume, at 10-140°C for 7 rain. The modifying effect of the following oligomers was studied: the anhydride of alkenylsuceinie acid (ANAS), M=900-1100; bis-alkenylsuccinimide (BASI), M = 1900-2100 and a eopolymer of butadiene and methacrylic acid (SKD-1 A) with M=45{X)--5000. The oligomers ANAS and BASI have a polybutene hydrocarbon block and SKD-1A contains 3--4~. of carboxyl groups. The physico-mechanical, technological and electro-physical properties of the filled PE were determined by standard methods using moulded specimens. In order to determine the amount of the oligomer chemically combined with the filler, the latter was separated from the composition by dissolution of the PE and the free oligomer in boiling xylene. After the soluble part of the composition had been separated, the filler was extracted with p-xylene in a Soxhlet apparatus for 100 hr to remove residues of adsorbed oligomer. The amount of the oligomer combined with the filler was determined by weighing, the filler having been heated in a muffle furnace at 800°C. The chemical combination of ANAS with the filler was established by IR spectroscopy. The Table shows the properties of compositions based on PE, containing 30 wt. % of chalk and an oligomer. It may be seen that oligomers with end functional groups (ANAS and BASI) and those with functional groups positioned along the main chain (SKD-1A) affect the properties of filled PE in different ways. Thus the introduction of A N A S and BASI leads to a reduction in the tensile strength and to an increase in the relative elongation of failed PE. S K D - 1 A increases b o t h the tensile strength and also the relative elongation at rupture. An increase in filler content is known to lower the flowability of the melt so that definite difficulties arise in processing filled polymers to form components. In this connection it is interesting to note that all the types of oligomeric c o m p o u n d s that we have used, when introduced in small quantities, raise the melt flow index of filled PE. This appears to a greater extent in the case of oligomers containing end functional groups. The rules governing changes in the electrophysical properties of filled PE are of especial interest. As the concentration of a polar oligomei in the composition is increased, the tangent of the dielectric loss angle, tan & decreases and, having reached a minimum, increases once more (Fig. 1). The specific volumetric electric resistance, po, of the compositions is observed to increase in the same region of oligomer concentration. The various positions of the region of the m a x i m u m on the curves are determined by the specific
2864
V.I.
SKRIPACHEV
etaL
surface area, the particle shape, the chemical nature and concentration of the filler in PE. The minimum on the curves showing taxi J as a function of the amount of oligomer per gram o f filler does not depend on the filler concentration (Fig. 2). The way in which the water absorption of filled PE changes as a function of the oligomer concentration is similar to the way in which tan ~ changes.
tan 8,10s
logpv ,ohm.cm
',10J
/0
1
16'
"~Qn (
175
O~ ,17"0 3 0"5
1"0 l~o. 1
1"5 c, w t %
1
15.5
0
0"02
0'04
0.06
1~o. 2
Fio. 1. Dependence of: 1 - 3 - the tangent of the dielectric loss angle, tan J, and 4 - the specific volumetric electrical resistivity, pv, on the concentration of A S A N for PE compositions with 40 wt. % filler, the following being used:/-mica; 2 and 4-chalk and 3-kaolin. FIo. 2. Dependence of the tangent of the dielectric loss angle, tan J, of filler PE on q, the amount of A S A N per gram of filler, mica being used at the following concentrations: 1-70 wt. ~.; 2 - 4 0 wt. ~. and 3 - 2 0 wt. ~.. It may be assumed that the oligomer molecules in the filled polymer are localized in a transition zone close to the surface and are positioned at the phase interface, the polar groups being oriented towards the failer surface. Anhydride, imide and carboxyl groups in this orientation cannot only combine physically with the failer surface but can also interact with functional groups located at the filler surface. For example, in the case o f ANAS the interaction can occur with the hydroxyl groups of the filler, the anhydride ring being opened up. Confirmation that ANAS, chemically combined with the filler, is formed has b e e n obtained by IR spectroscopy. Absorption bands in the region 1720-1730 cm -1, which were not present in the initial filler sample, are observed in the IR spectrum o f the filler separated from filled PE. The amount of chemically combined oligomer, determined by combustion, was equal to 5-10, 2-5 and 2-4 wt. ~o for ANAS, BASI and SKD-1A respectively. I f oligomer molecules with end functional groups are oriented in the neighbourhood o f the filler-polymer interface with the hydrophilie part towards the filler and the hydrophobic part towards the polymer, one may estimate the surface area of the filler occupied by the oligomer, by analogy with the orientation of surfactants in condensed films. The cross-sectional area o f the PE maerochain is taken to be equal to 21 A 2 [6]. Since
Mechanism of modifying action of oligomers PROPERTIES OF L O W - D ~
PE nLLm~ WITH 30
WT.~.
2865
CHALK, AS A FUNCTION OF THE OLIOOMER
CONTENT OF THE COblP(~ITION
Parameter Tensile strength, MPa
Relative elongation at rupture,
% Melt flow index, g/10 min
Tangent of the dielectric loss angle, tan J x l 0 a, at a frequency of l0 s Hz Water absorption,
Oligomer ASAN BASI SKD-1A ASAN BASI SKD-1A ASAN BASI SKD-1A ASAN BASI SKD-IA ASAN BASI SKD-1A
Values of the parameter for the following oligomer concentrations in the composition, wt. ~, I 0"25 [ 0"50 [ 0.75 I 1.00 I 1.50 12.00 10"9 10"6 10"5 10.3 9-8] 9.5 I1'0 11"1 10"7 10"6 10-0 9.9 9.7 11.8 11"9 12.3 12.7 12.9 12.5 140 119 145 127 120 75 105 100 110 123 125 112 115 84 80 81 76 80 86 1"02 1 "07 1"19 1.35 1.47 1.60 1.7 1"05 1"11 1-27 1.38 1.50 1.6 1"02 1"09 1.11 1.15 1.19 1.2 2"1 1"7 1-5 1.1 1-2 1.0 0.9 1"8 1.3 1.4 1"6 1.1 1.1 1"8 1.5 1.7 1.8 1.5 1-6 0"50 0"38 0"22 0.19 0.18 0-20 0.2 0"42 0"30 0.25 0.25 0.26 0.2 0-47 0.45 0.41 0.41 0.43 0.4
the cross-sectional axea is not known for the polybutene block of the A N A S molecule, we shall roughly consider that it is equal to 21 A 2 although this value is rather too small. The specific surface area of the chalk being 14.7 m2/g, it is necessary to introduce 2"0 x 1021 molecules of A N A S into 100 grams of a composition containing 30 wt. ~o o f chalk in order that the oligomer should be in the f o r m of a condensed film and cover the entire surface o f the filler. The region in which the minimum on the curves for tan t~, the water-absorption and the resistivity po is observed corresponds to a concentration o f 1"0 wt. % A N A S in the composition, that is, 0.6 x 1021 molecules. This figure is 3 times less than the calculated n u m b e r of A N A S molecules necessary to satisfy the condition that the filler surface should be screened if the calculation is based on the principle used for surfactants, namely, that condensed films should be formed at the interface between the phases. If, however, we remember that the cross-sectional area o f the polybutene block is greater than that assumed in the calculation and the oligom e r i t block, because of its great length, can make it difficult for additionally introduced oligomeric molecules to have access to the free surface of the filler, we should recognize that there is agreement between the calculated figure and the figure obtained experimentally. BASI, in whose molecule there axe two polybutene blocks, acts similarly. Oligomers with end functional groups in filled PE isolate the filler particles so that they axe separated by, at most, two lengths of the oligomeric block. In this case, effects involving the formation of filler structures are completely absent. Because of the disruption of the filler structure, the conductivity of the system is reduced, and this leads to a reduction in tan t~ and to an increase in Pv. Oligomeric compounds with end functional groups in filled systems have a mainly plasticizing effect.
2866
V. I. SKRIPACHEV e t al.
By contrast to ANAS and BASI, the carboxyl groups in the SKD-1A oligomer a r e distributed along the main chain. In this case, the oligomer molecules are probably adsorbed at the filler surface along their entire length. The effectiveness of the screening is thus less and the screening effect of the filler particles is achieved at a lower oligomer concentration. The fact that only a small percent of the SKD-1A is chemically combined with the filler and the value of the water adsorption confirm the low density of the covering o f the filler. The positioning of the oligomer molecules in a felt-like manner is clearly characteristic of the use of SKD-1A. The thinness of the isolation layer between two filler particles, corresponding in the best case only to two diameters of the oligomeric chain's cross-section, as well as the existence of free surface can lead in the system to the formation of coagulation thixotropic filler structures, which are responsible for the increase in the strength properties of the polymer system [7]. In addition to this mechanism of reinforcement, it may be assumed that a definite contribution to the increase in the strength properties of filled PE is made by an effect involving the entrapment o f PE macromolecules by an oligomeric chain with the formation of an entanglement-type bond. The incorporation of a PE macrochain, gripped by the oligomer, within crystalline formations leads to reinforcement of the p o l y m e r - filler bond and, correspondingly, to an increase in the strength properties. The properties of filled PE thus depend essentially on the type of oligomeric modifier that participates in the formation of the transition zone between the filler and the polymeric matrix. The use of oligomers with end functional groups to modify filled polyolefins leads to the production of a composite material with improved technological properties, enhanced elasticity and with good dielectric properties. In similar systems, the use of oligomers containing functional groups along the main chain makes it possible to obtain filled compositions with improved physico-mechanical properties. Translated by G. F. MODLI~N
REFERENCES
1. Poverkhnosti razdela v polimernykh kompozitakh (Interfaces in Polymeric Composites), edited by E. P. Plueddemann, p. 9, Mir, Moscow, 1978 (Russian translation) 2. Ye. P. NIKULINA, Khim. prom-st' za rubezhom, 7, 24, 1977 3. S. N. TOLSTAYA, (book) Napolniteli polimernyk.h materialov (Fillers for Polymeric Materials), p. 11, Moscow, 1977 4. M. M. REVYAKO, A. Ya. MARKINA, T. V. DUNINA and L. A. ISAYENYA, (book) Khimiya i khim. tckhnol. (Chemistry and chemical technology), No. 10, p. 120, Vysshaya shkola, Minsk, 1976 5. I. A. KHLAVITSKAYA, L. A. TSINANKINA andE. A. SPORYAGIN, Plast. massy, 1, 29, 1978 6. S. S. VOYUTSKII, Kurs kolloidnoi khimii (Textbook of Colloid Chemistry). p. 135, Khimiya, Moscow, 1976 7. Yu. S. LIPATOV, Fizicheskaya khimiya napolnennykh polimerov (Physical Chemistry of Filled Polymers). p. 273, Khimiya, Moscow, 1977