Ind. Eng. Chem. Prod. Res. Dev. 1981, 20, 421-428
421
111. Symposium on World-Wide Progress of the Petro, Organic, and Polymer Chemical Industries N. Platzer and S. Inoue, Chairmen ACS/CSJ Chemical Congress, Honolulu, Hawaii, April 1979 (Continued from December 1979 and September 1980 Issues)
Homogeneous Composites of Ultrahigh Molecular Weight Polyethylene and Minerals. 1. Synthesis' Edward 0. Howard,' Robert D. Llpscomb, Robert N. MacDonald, Barbara L. Glazar, Charles W. Tullock, and John W. Collette Central Research 8nd Development Department, E. Wllmington, Deleware 19898
I. Du Pont de " O u r s & Company, Experlnmntal Statlon,
High levels of minerals (clay, CaC03, Ai203*3H20)can be Incorporated homogeneously into ultrahigh molecular weight polyethylene by polymerizing ethylene onto catalytically activated mlneral surfaces. The homogeneity is achieved by deaggregating the mineral prior to polymerization and by the use of combination of R,Zr and RSAI as catalysts which are uniformly and Irreversibly attached to the mineral surface. The process leads to no uncoated mineral or polymer free of mineral, both of which can have a deleterious effect on mechanical properties. In contrast to most filed plastics which are brittle, these composites retain the ductile faUure characteristics of the unfilled ultrahigh molecular polyethylene, providing a unique combination of reinforcement and impact toughness in a mineral-filled polyolefin. Polymer molecular weight must be in excess of 10' for optimum properties.
Introduction Minerals are added to polymers to modify selected physical properties and reduce cost. This blend technology has been mainly developed in the elastomers field where high levels of fillers (especially carbon black) can provide increased tensile strength, modulus, and hardness. Adding high levels of minerals or fillers to plastics, especially crystalline plastics, has been less successful. A frequent problem in the plastic field is that large concentrations of minerals bring about dramatic and commercially unacceptable decreases in elongation and impact strength leading to brittle parts. This brittleness is usually attributed to stress concentrations either because of inhomogeneous mineral dispersion (Nielsen, 1962) or poor mineral-polymer adhesion. Based on the decrease in surface free energy, polyethylene should wet a clean mineral surface and have good adhesion. Fowkes (1968) has calculated that polyethylene in close contact with iron surface (0.4 nm separation) would have an interfacial tensile strength of over 100000 psi. Low interfacial strength can be the result of preferential adsorption at the interface of moisture or low molecular weight fractions, or adsorption may be kinetically slow. Efforts to toughen filled polyethylenes by modifying the filler have met with little success; examples are the use of titanate esters (Monte and Bruins, 1974), or aluminum acrylates as coupling agents (Hawthorn and Solomon, 1974), or by Contribution No. 2689. 0 196-4321I 8 111 220-042 1$0 1.2510
preencapsulation of the filler to provide an immobilized polymeric coating between the filler and polymer (Hausslein and Fallick, 1969). The data in Table I show these deleterious effects for blends of various minerals with polyethylene. The mineral increases the modulus but elongation and impact strength are drastically reduced. Results on blends with ultrahigh molecular weight polyethylene (UHMWPE) with 56 wt % clay are included for comparison. This is a special case. This polymer has outstanding impact toughness, but it is too viscous to mix with reinforcing fillers. The blends in Table I, prepared by blending fine powders, are heterogeneous and brittle. Homogeneous UHMWPE-Mineral Composites We have made highly mineral-filled polyethylene composites which retain high elongations and fail in impact tests in a ductile rather than a brittle fashion. These composites are prepared by polymerizing ethylene to molecular weights >los onto catalytically activated minerals so that substantially all the polymer is formed on the mineral surface. These products are called homogeneous composites. Polymerization on the surface offers several advantages. (a) It favors a uniform distribution of mineral throughout the polymer. (b) It provides optimum opportunity for the polymer to be adsorbed and wet the mineral surface as all the polymer grows at the surface. The coordination polymerization process used requires that the mineral surface be free from moisture or polar impurities which can also 0 1981 American Chemlcai Society
422
Ind. Eng. Chem. Prod. Res. Dev.. Vd. 20. No. 3. 1981
Propertien of Polyethylene Mineral M i x t u r e initial modulus GPa KPSI HDPED 0.69 (100) 409b kaolinite 3.1 (450) calcined kaolinite 3.1 (450) CaSO, 28 (410) mica 6.5 (942) CaCO, 2.7 (390)
Table 1. Ph*eal
UHMW-PEE (90) + 56%kaolinite 0.62 Alathon 7040 (Du Pont) M.I. 6.4 qm 1.7 (M, -90000). Chemical) 9.0 (M, > lo6).
'I,,,,,
PROPERTIESOF FILLED POIYEIHYIENE GUTH-GOLD
I + 2.54
+ 14.1+2
_y.__---
I
Izod 25 "C
JIM 79.5 17
20 15 20 21 1060 106
ultimate eloneation. % "
(ft-lblin.) . .
I
900 1.6
(1.5) (0.32) (0.37) (0.29) (0.38) (0.40)
2.7 1.3 0.3 3 1000
(20)
3.0
(2.0)
All percentages are by weight.
e
AC1220 (Allied
(Howard, 1980). The clay must be calcined above 400 OC. Water is lost irreversibly in the process, and the clay particles are no longer crystalline to X-rays even though the visual appearance of the stack plate-like A120~2Si02-2H20 A1203.2Si02 + 2H2O
n u) Y Y n 80 w . n c ~ m Figure 1. Properties of RUed polyethylene w. 70clay.
interfere with polymer-mineral adhesion (Fowkes, 1968). (c) It is the only process for the preparation of composites based on very high molecular weight polymers as the mixing is done in the polymerization. A. Polymerization with Calcined Kaolinites. The process is exemplified hy the preparation of homogeneous polyethylene-kaolinite clay composites. Coordination polymerization activity has not been generally reported for clays. Montmorillonite clay has been reported to polymerize styrene and methyl methacrylate both by a radical ion mechanism (Solomon and Rosser, 1965) and a freeradical mechanism (Solomon and Loft, 1968); these clays have also polymerized cis-2-butene and butadiene (Friedlander, 1964). Clay polymerization activity has been enhanced by y-irradiation (Blumstein and Billmeyer, 1966). Yields in all these examples are very low, on the order of 1-2%. (See Figure 1.) While virgin kaolinite is inert to Olefins, calcined kaolinite is a rather active ethylene polymerization catalyst
2. A.
structure is unchanged (see Figure 2A). The catalytic activity of the calcined clay is undoubtedly centered around the adventitious titanium dioxide that is present from 0.6-2% in most clays, and is known to be a coordination polymerization catalyst, particularly when associated with alumina. Thin conveniently provides a catalyst site locked into the mineral surface. Polymerization of ethylene onto this calcined kaolinite, however, results in a grossly nonuniform material with many aggregates of mineral in a polymer-rich matrix. Hot pressed films are heterogeneous, brittle, and weak, attempts to orient these films result in tears and breaks a t mineral-rich areas. Clays, especially when freshly activated, are extensively aggregated. This is true in dry state but is especially apparent when the clays are slurried in a hydrocarbon; thus 10% (g/mL) of calcined kaolinite in hexane forms a mayonnaise-like suspension presumably as a result of hydrogen bonding of exposed surface hydroxyls leading to an extended structure. Candlin and Thomas (1972) observed similar aggregation when attempting to measure the hydroxyl concentration on fine particle silicas in hexane. These aggregates must be separated prior to polymerization if the mineral surfaces are to be uniformly coated. This can be accomplished hy reaction of the surface hydroxyl groups with an organophilic reagent such as an
R. PE- COMPOSITE A. CLAY SEM of calcined clar. B,SEM of calcined clay/polyetbylene mmposite particlea.
Ind. Eng. Cham. Rod. Res. Dev.. Vol. 20. No. 9. IS81 4 a
Tabk n. Comparimn of Composite Properties Made by TiO, and TiCl, Catalyst PE/60% Clay' clay/TiL1,/ clayli-Bu,Al i-Bu,Al prCUXSS 3.3 (480) 27 (390) flexural modulus, GPa (kpsi) 21 (3) tensile, MPa (kpei) 21 (3) 48 ultimate elongation. % 350 notched Izod.
VlSmSlTYff UAY-HEIANE DISPERSMS 4000
k01 2000
J/m (ft-Lbli6) 23 "C -18°C
954 (18.0) 530 (10)
196 (3.7) 48 (0.9)
Gardner impact,= J (in .lhi . I
1
0
2 0 3 0 4 0 m n R,A1/100p CLAY
5
c
>27 (>240) >27 (>240)
23 "C -40 "C
Figure 8. Viaoosity of clay-hexane dispersions.
aluminum alkyl (Howard, 1978). Thia deaggregatea the particles leading to a uniform low viscosity dispersion of mineral particles in the hexane.
The effectiveneas of aluminum slkyls in dispersing clay
is shown in Figure 3. The viscosity of a 15% clay/hexane dispersion is very high (2000 to 3000 cP). The viscosity drops precipitously to 4 0 0 P on addition of an alkyl aluminum. i-Bud1 and i-BudC1 are the most effective alkyls; thus 100 g of clay free of adsorbed water (surface
3.6 (32)
Harwick GK Clay ( H d c k Chemical Co.) calcined at Catalyst is presumably "io, present in the 600 "C. clay. Measured on a 0.125 in. thick sample.
OH concentration -4 mequiv/100 g) requires only 400 mg (2.0 mequiv) of i-Bu& to reduce viscosity to that of the solvent. Larger (hexyl) or smaller (methyl) alkyl groups are pot as effective as the isobutyl group. Ethylene polymerization using this calcined clay dispersed in cyclohexane with the aid of i-Bu& produced a granular product in which the polymer was uniformly coated on nonagglomerated clay particles. Hot pressed thin films were homogeneous even when hot drawn five diameters to pinhole-free limp films. The physical p r o p erties are enormously improved when compared to those of the melt blended mixtures of Table I. The elongation and impact resistance are those of a tough plastic (Table 11). Quite m e r e n t physical pmpertiea are obtained if Tic4 or TiC1, is used in conjunction with i - B u a l as the polymerization catalyst. These catalysts,which were extensively investigated hy Herman and eo-workers for polymerization of ethylene onto cellulose and carbon black (Herman, 1965,1968; Orsino et al., 1964). give heterogeneous products with clay either as a result of polymer formed free of mineral or of mineral with no polymer coating. The resulting products are significantly more brittle (Table 11) than the homogeneous composites. 7.a' \
-
A
Ficltua 4.
A, "EM of composite partide3 (lOooOX
PE/day); B. TEM of day particles after polyethylene haa been extracted.
424
Ind. Eng. Chem. Prod. Res. Dev., Vol. 20, No. 3, 1981
Table 111. Micronization Fractionation of Polyethylene/Clay % clay original first sample fraction blend clay-TiCI,/Et,Al clay-TiClJi-Bu, AI calcined clayli-Bu,Al Table IV. PE/Clay-Catalyst
50 45 40 48
99 84 16 42
max fraction
min fraction
dispersity,
99 84 51 61
6 14 16 42
93 70 35 19
A
and Properties"
catalyst
17 inh
% clay
ultimate elongation, %
h o d (-18 "C), J / m (ft-lb/in.)
gardner impact -40 'C, J (in-lb)
a-TiCI,-Et,Al @-TiCl,-Et,Al calcined clay b/Et,Al composite b + free clay C
15 17 18 18
55 46 50 50
95 140 24 0 84
80 (1.5) 310 (5.9) 737 (13.9) 340 (6.4)
0.9 ( 8 ) 1.7 (15) 12.4 (110) 2.9 (26)
a Measured on 3.18 mm (0.125 in.) thick sample. Kaolinite clay calcined at 600 "C. polyethylene/clay composite (41.5% clay) with 16.4 g of calcined clay.
Microscopic details of the homogeneous clay/polyethylene composites are shown in Figures 2 and 4. Figure 2A shows an SEM of calcined clay prior to polymerization; the stacked plate structure of the clay particle is clearly evident; Figure 2B shows the polyethylene composite from this clay; no free mineral is observed. Figure 4A shows a transmission electron micrograph of these composite particles; the polymer appears to be formed both on the exterior surfaces and between the plates. If the polymer is extracted, many of the clay particles have been fragmented by the polymer growth (Figure 4B). B. Homogeneity. The uniformity or homogeneity of the composites can be evaluated in several ways. The simplest is to convert the powdery product to a film by hot compression molding and to inspect the film with transmitted light. Mineral-rich areas are very dark and mineral-poor areas more translucent. The film's heterogeneity can be further demonstrated by drawing a strip of film over a 160 "C hot pin. Holes will develop where the mineral pockets are located. A more direct method is based on fractionation of particles with density differences. Mineral-rich particles will sink in a 1:l carbon tetrachloridebromoform mixture (density, 2.27 g/mL) and polymer-rich material will float on a propanol-carbon tetrachloride mixture (density, 1.30 g/mL). A final method developed to compare the heterogeneity of various composites uses the centrifugal force and grinding action of an air micronizer. This method is applicable to composite powders directly from the polymerization; it cannot be used after the polymer has been heated or coalesced. The apparatus is illustrated in Figure 5. The sample powder is introduced into the air stream of the micronizer where the particles are ground by highspeed impaction and fractionated according to size and density. Samples collected at intervals throughout the micronization provide a measure of the range of particle compositions present. Thus a blend of polyethylene and mineral will separate completely; the early fractions are virtually pure mineral and the later fractions pure polymer. The change in composition throughout the fractionation is shown in Figure 5. In contrast, a composite prepared by surface polymerization of ethylene onto the clay gives fractions which differ little in mineral content. The micronization is a particularly useful method for comparing samples of significantly differing heterogeneity and for detecting the presence of free mineral. The particles must, however, be free flowing; if the polymer is sticky or stringy, as can occur when low-molecular-weight free polymer is
h a d e by combining 100 g of
HOMOG ENNTY
MICRON IZER FRACTIONATION BLEND a
w Y
40
10"
,
2.1,
o /'
,
,m
20 40 60 80 100 OF RECOVERED MATERIAL
Figure 5. Micronization fractionation.
present, the particles may not separate. The degree of heterogeneity for products made with various catalysts is illustrated in Table 111. Two values are measured: the composition of the first fraction and the dispersity (A) or breadth of the distribution. With a blend of PE and mineral, the first fraction is nearly pure mineral, the last, pure polymer; hence the dispenity is very large. With TiC13as a catalyst, free mineral is present, and the dispersity is very large, presumably as the polymerization occurs on the catalyst particles independent of the mineral surface. With TiC14as a catalyst, free polymer is present; TiC14would be expected to react with the surface of the mineral but will form an active catalyst in the solution independent of the surface. The final example is of a homogeneous composite; this shows no free mineral or polymer and has the narrowest compositional distribution. Table IV compares the properties of three 50% clay composites. All the polymers are high molecular weight. The homogeneous composite made with a calcined kaolinite catalyst has a much higher elongation and impact resistance than the samples made with titanium trichloride. As also shown in Table IV, the addition of clay to a 41.5% clay composite shows that free mineral significantly decreases elongation and impact resistance.
Ind. Eng. Chem. Prod. Res. Dev., Vol. 20, No. 3, 1981 425 Table V. Properties of Composites Made with Attached Catalysts mineral A1 0 .3H,0a claj clay b c1aT talcc catalyst Ti& Ti Ti e Cr Crg % mineral 69 66 69 49 59 notched Izod impact, 390 (7.4) 280 (5.3) 318 (6) 795h (15) 186 (3.5) J / m (ft-lb/in.) (-18 “C) elongation, ( b ) % 160 23 0 110 500 150 tensile, MPa (psi) 1 4 (2800) 20 (2950) 17 (2500) 23 (3300) 18 (2640) 2.5 (360) 4.0 (580) 4.1 (600) 3 (430) 4.4 (630) modulus( i), GPa (kpsi) a C-33 Alumina Hydrate, Alcoa Co. “Harwick” GK clay (A1,O3.2Si0,~2H,0). Hydrated magnesium silicate [Mg,Si,O,,.( OH),]. Hydrolyzed TiCl,. e Hydrolyzed Ti( OC,H,),. Cr( OAc),. g Methacrylatochromium chloride (Volan L, Du Pont). Izod impact at 73 O F .
COMPOSITE PROPERTIES
,\\
ULTIMATE ELONGATION
40] 200
30
NOTCHED IZOD IMPACT (-18OC)
70
50 % CLAY
% CLAY
Figure 6. Composite particles, elongation, and Izod impact vs. % clay.
One consequence of distributing mineral more homogeneously in the matrix is that a higher level of filler can be added before the composite becomes brittle. This is shown in Figure 6, which compares the ultimate tensile elongation and Izod impact of clay-polyethylene samples made using a T i c 4 catalyst and the titania catalyst in the clay. The TiC14 samples are brittle at 50% clay whereas the homogeneous clay are ductile and retain toughness even at 60% mineral. C. Synthesis of Composites with Other Minerals. It was of interest to extend the discoveries made with calcined clays to other minerals to determine the effect of chemical structure, particle size, shape, and surface characteristics on the properties of the composite. Alumina trihydrate was of special interest as a filler because of its fire-retardant characteristics with polyethylene (Collette, 1981). Most of these minerals do not contain catalyst sites as an integral part of their structure. Two general techniques were developed to attach coordination catalysts to such minerals. These involve attaching the catalyst irreversibly to the surface and using catalysts which are active only on the surface of the mineral. 1. Catalyst Fixed on the Surface. Titanium oxide, the probable active center in calcined clays, can be incorporated into the surfaces of many minerals by reaction with TiC14or an alkyl titanate followed by hydrolysis and heat treatment (Figure 7). It is essential that the unreacted reagent be removed prior to hydrolysis to avoid
OH
Figure 7. Catalyst fixed to surface.
subsequent formation of free polymer. With TiC14, this can be done by passing dry Nzthrough the mineral; excess alkyl titanates can be removed by washing with solvent. After hydrolysis, drying, and addition of an aluminum alkyl, the titanium-modified mineral forms an active coordination catalyst for ethylene yielding homogeneous composites (Howard, 1980). In the case of A1z03.3Hz0, 0.5% Ti is incorporated into the mineral by treatment with TiC1,; the polymer formed is high molecular weight (7 > 20), and micronization tests show excellent compositional homogeneity. Typical properties for these composites are summarized in Table V; even at 70% A1z03-3H20,the products have high impact strength and show ductile failure. Figure 8A shows an SEM of the original A1z03.3Hz0 particles and the resulting polyethylene composite particles (Figure 8B). This composite has the unusual characteristic that it can be expanded to a foam structure by heating sheets under pressure at about 300 OC to drive off the water of hydration from the mineral. A micrograph of such blown foam (Figure 9) shows the excellent mineral dispersion in the polymer and the adhesion of the polymer to the mineral surfaces. Transition metals other than titanium can be used similarly. Chromium chelates and esters are adsorbed strongly by many mineral surfaces to form chromium esters with the silanol groups on the surface (Figure 7). After hydrolysis and heat treatment to remove excess water, the chromium can be activated by aluminum alkyls and will polymerize ethylene (Lipscomb, 1976). These chromium catalysts complement the titania systems as they are more active on minerals containing silica (e.g., clay, Al2O3.2SiO2.2H20,talc; Mg0.SiOz*2H20;Wollastonite, m-CaSi03) than on alumina; they also generally give lower molecular weight polymers than Ti catalysts. Both of the above catalysts allow preparation of composites from uncalcined clays. The uncalcined clays are less reinforcing than the calcined clays and higher levels can be incorporated while ductile impact properties are retained (Howard et al., 1981). Typical physical properties for several composites are in Table V. 2. Catalysts Active Only on the Surface. A major deficiency with the preceding process is that all the mineral must be chemically treated and dried prior to polymerization. A simpler and more practical route involves tet-
428
I d . E-.
Chem. Rod. Res. Dev.. Vd. 20. No. 3. 1981
Scheme I
AI&
3H20
7
"\AI
I
R
Table VI. Ethylene Polymerization on Gl%bsite (AI20,.3H,O) with [PhCHJ,Zr composite properties [F'hCH,].Zr, polymer mol % Izod impact (-18 "C) mM/100 g ntnb elongation (b) J/m (it-lblin.)
*,
0.14 0.29
7.4 22 22
0.43
1.1
200
.._ .
250
408(7.7)
340
550(10.4)
B
n
notes inactive
heterogeneous
PE A1203.XH20 I
rOAM
8. A. SEM of AI&3HpO B, SEM of PE/72% AI20s3H20.
Figure 9. SEM of polyethylene/A1,0~3H20blown fmm.
raalkyl transition metals which are active catalysts only when adsorbed onto the surface of the mineral. In the early 1970's Ballard and co-workers showed that (PhCH3,Zr is a poor homogeneous catalysts for ethylene polymerization, but becomes extremely active when reacted with a colloidal silica or alumina support. The active catalyst was shown to be a supported alkyl (Ballard et al., 1974; Ballard, 1973).
\ISi-OH
/
O\Si-OH
/I
t ZrR.
-
\I
/Si-O 0
'si-0
/I
Aa catalysts for ethylene polymerization were emphasized, this work generally used high surface area supports (5&100
m2/g) and relatively high ratios of transition metal/mpprt (0.1-1.0 mm/g). We have found that these transition metal alkyls can be used alone or, better, in conjunction with an aluminum alkyl to catalyze ethylene polymerization onto many mineral surfaces. See Scheme I. When tetrabenylzirconium is used alone to polymerize ethylene onto alumina hydrate, concentrations of 0.51.0 mM of catalyst/100 g of mineral are required for tough homogeneous composites. A t lower concentrations, no polymer is formed, or the product is heterogeneous (Table VI). It is possible that part of the zirconium alkyl is being used for mineral deaggregation. The transition metal compound can be reduced five- to tenfold if used in conjunction with an aluminum alkyl. The combination of i-Bu&l/(PhCHJ,Zr is not active for ethylene polymeri-
Ind. Eng. Chem. Prod. Res. Dev., Vol. 20, No. 3, 1981 427
Table IX. Polymerization on Basic Minerals
Table VII. Active Catalysts M = Ti, Zr, Hf R4M Cr
R = PhCH,, CH,
I I
substrate
Ph-C-CH,,
CaCO , CaC0,-Al,O, CaC0,-H,PO, CaCO,-Si0 , CaSO, CaS0,-Al,O,
CH, (CH3)3CCH2-, (CH,),SiCH,R,ML,.,
L = -NMe,, -OR, AcAc, Cp -OSiPh,, -N(SiR,), a
Table VIII. Comparative Activity of Alkyl Transition Metal Catalysts time (h) under ethylene pressure (MPa)
a
0.4 (69) 0.6 (69) 0.7 (69) 1.1(69)
0.1
-goa
0.1
50 70 72 trace polymer 50
0.3 0.3 0.1 0.1
0.05 2.5 2.7 1.1
--
0.6
Table X. Mineral Oxides Requiring Acid Coating CaCO,, CaSO,, CaF,, CaSiO, BaCO,, BaSO. ZnCOi dawsonite (Na20~2C0;2H,0) basic silicas. micas. feldspar glass fabric
> 2 (69) 1.7 (2800) slow reaction 3.13 ( 2800)a
Table XI. Polymer Characteristics
Some uncoated mineral,
zation in solution but becomes extremely active when a mineral substrate is added. At constant Zr, the polymerization activity increases with alkyl aluminum up to an Al/Zr ratio of 20-30/L and then decreases rapidly at higher ratios. This may reflect competition for surface sites or inhibition of the active center by complexation with excess aluminum alkyl. The Zr catalyst is about 100-200 times more active than a titania catalyst prepared by hydrolysis of TiC14 or Ti(OR)4 on the same substrate. A variety of transition metal alkyls and related transition metal complexes are effective catalysts for ethylene polymerization on mineral when used with an aluminum alkyl in this manner. Examples of titanium, zirconium, hafnium, and chromium alkyls are given in Table VII. The compounds do not have to be peralkylated; active catalysts have been obtained with dimethylamino, alkoxy, acetoacetonate, aminosilylamines,and cyclopentadiene ligands. Not all combinations are useful; both the polymerization activity and the properties of the resulting composite can vary with the mineral and catalyst. Table VI11 compares the rates of polymerization onto clay and A1203-3H20with various zirconium species. The most active in both cases are the peralkylated zirconiums. Al2O3+iH20is clearly a more difficult surface from which to initiate than is clay, requiring longer times or higher pressures; also a dimethylamido complex gave some uncoated mineral. The peralkyl transition metals can be used as polymerization catalysts on a variety of mineral surfaces. For example, pigments such as Ti02, carbon black (Adelman and Howard, 1979), and aluminum flake all form active substrates. 3. Basic Minerals. Some minerals do not give active catalysts and cannot be used directly for composite synthesis. These minerals are either basic, such as calcium carbonate, or have absorbed alkali metal ions, such as feldspar or mica. This problem can be solved by surface coating the mineral with alumina or silica or other nonvolatile acidic substance according to the following equations (Howard, 1980). CaCO3
product % mineral
Reaction stopped after 10% polymer formed.
50% clay 70% A120,~3H,0 [PhCH,],Zr [PhCH,I,Cp,Zr Cp ,ZrC1 , [(CH,),CCH,],[NMe,],Zr
rate, g of C,H,/g of mineralh
Zr, mml 100 g
no polymerization
50% clay 17C polymer mp, "C as polymerized remelt crystallinity as polymerized remelt polymer qinh
M"
70% A1,0,. 3H,O 15A
138 132
137 134
78 54
85 67
16.8 ?r 1.8 3.2 X lo6 2.78 f 0.37 x l o 6 0.44 X lo6 6.7
26.1 7 x 106 1.66 X lo6 0.35 X l o 6 4.7
One to two percent alumina or silica is incorporated on the mineral surface in this process. Table IX shows the effect on polymerization rate of treating a CaC03 or CaS04 surface with an acidic oxide. Table X lists the minerals that responded to this procedure. Composite Characterization Polymer Molecular Weight and Crystallinity. Data on the molecular weight, melting point, and crystallinity of polymers in two typical composites are listed in Table XI. Precise molecular weights were difficult to obtain with these high molecular weight polymers. Inherent viscosities were measured on solutions of 0.50 mg/mL in 1,2,4-trichlorobenzene at 135 "C after dissolution at 180 "C for 2 h. Antioxidant was added and the solutions were blanketed under nitrogen. For difficultly soluble ultrahigh molecular weight samples, the concentration was reduced to 0.25 mg/mL. Control experiments demonstrated that the presence of suspended mineral did not affect the results, so the mineral was not removed. M, was calculated using the relationship of Francis et al. (1958), based on viscosity measured on 0.1% solutions in decahydronaphthalene at 135 "C. )linh = 6.7 x io4h!f,0'67 GPC measurements confirmed the high molecular weights, but experimental difficulties with the procedure do not allow use of the results to calibrate the inherent viscosity measurement. For GPC, the polymer was dissolved in 1,2,4-trichlorobenzene at 180 "C (1.25 mg of polyethylene/ (mL) and hot centrifuged to remove the mineral. The GPC measurement and calibration procedure have been reported previously (Ferguson et al., 1978).
428
Ind. Eng. Chem. Prod. Res. Dev., Vol. 20, No. 3, 1981
The precision of the GPC measurements was poor with standard deviations as large as 100% of the mean; this is probably because of degradation during dissolution, centrifugation, or injection into the GPC column. The M, calculated from inherent viscosity correlated with but did not numerically agree with M,from GPC (Table XI). The correlation for clay composites was different from that for A12O3.3H20 composites; this may reflect the significant differences in molecular weights. Melting points and crystallinity were determined by DSC on a du Pont 900 Thermal Analyzer with heating and cooling rates of 10 "C/min. The as-polymerized powders have melting points of >136 "C and are -80% crystalline. After melting or fabrication, crystallinity and melting point decrease to values in the range observed with unfilled UHMW PE. The high melting points probably result from nonequilibrium crystallization similar to that observed in some nascent UHMW polyethylenes. Experimental Section Polymerization Procedure (Howard, 1980). The polymerizations were carried out by first preparing thoroughly dried mineral by heating under nitrogen purge for 2 to 20 h. The temperature depended on the mineral, for example Al2O3.3H20,190 "C because it decomposes at higher temperatures, up to 1000 "C for calcined clay and alumina. The mineral was suspended in cyclohexane freed of oxygen by nitrogen purging and of water by passage through an alumina or silica absorption bed. Aluminum alkyl was added to the energetically stirred mixture at levels of 2 to 4 mmol of R3Al to 1000 g of mineral which normally gave a very low viscosity suspension. After adding 0.2 to 0.5 mmol of tetrabenzylzirconium, the reaction mixture was transferred by nitrogen pressure through polyethylene tubing into an autoclave. The polymerizations were carried out from 30 to 70 "C under 100 to 200 psi for 15 min to 1h, depending on the amount of polymer desired. Ethylene consumption was monitored by weight loss of the supply cylinder. The product was isolated by filtration and drying to a free-flowing powder passing through a 16 mesh screen. In the case of some basic solids such as CaC0, or BaCO,, it was necessary to change the nature of the surface. This was done by adding aluminum nitrate solution in an aqueous suspension of the carbonate, probably according to the equation (CaCO,),
+ 2Al(N03),
HzO
A1203(CaC03)n-3 + 3Ca(N03)2+ 3 c 0 2
In the case of CaS04,ammonia was used to precipitate the alumina
The minerals required about 0.2 to 0.5% aluminum. Physical Properties. The powders were compression molded at 180 "C for physical tests. The powders were held in the heated mold for 2 min at zero pressure, then 3000 psi (21 MPa) was applied for 1min. For tensile tests, tensile bars of Type I and '&pe V of ASTM 63&71A were used. Izod impact was measured according to ASTM D-256. Heat distortion temperature was determined by ASTM D-648. Gardner impact was measured on 0.125 in. thick pieces. Acknowledgment GPC measurements and crystallinity studies were carried out by R. C. Ferguson. Dr. C. A. Sperati, Professor B. Wunderlich, and Dr. B. C. Anderson provided helpful advice and encouragement. Literature Cited Adeknan, R. L.; Howard, E. G. US. Patent 4 151 126, 1979. Ballard, D. G. A&. Catel. 1973, 23, 263. Ballard, D. 0.; Jones, E.; Wyatt, R. J.; Mwray, R. T.; Robinson, P. A. Polymer 1974. 15, 169. Blumsteln, A.; Bllmeyer, F. W. J. fo&m. Sci. 1966, A4, 465. Candlin, J. P.; Thomas, H. A&. Chem. Ser. 1972, No. 732, 222. Collette, J. W.; CUazar, 8. L.; Guggenberpr, L. J.; Howard, E. G.; Lipscomb, R. D. Proceedings of the 1979 Intetnatbnal Symposium on Flammability and Fire retardants, In press. Ferguson, R. C., Stoklosa, H. J.; Yaw, W. W.; Hoehn, H. H. J. Appl. Polym. Sci., Appl. folym. Symp. 1970, 34, 119. Fowkes, F. M. J. Colbkl Interface Sci. 1960. 28, 493. Francis, P. S.; Cook, R. C., Jr.; EHlot, J. E. J. Polym. Sci. 1956, 37, 453. Friedlander, H. 2. J. folym. Sci. 1964, C4, 1291. Hausslein. A. W.; Faliick, G. J. Appl. pdym. Synp. 1969, 1 7 , 119. Hawthorn, D. G.; Solomon, D. H. J. Memmol. Sci. Chem. 1974, AS, 659. Herman, D. F. "Encyclopedia of Polymer Sclence Technology", Voi. 8, WlleyInterscience: New Y&, 1968. p 736. Herman, D. F.; Kurse, U.; Brancato, J. J. J . Polym. Scl. 1965, 11, 75. Howard, E. 0. U.S. Patent 4 104243, 1978. Howard, E. G. U.S. Patent 4 187210, 1980. Howard, E. G.; Glazer, B. L; Collette, J. W. I d . Eng. Chem. Prod. Res. Ow. following paper in this Issue, 1981. Upscomb, R. D. US. Patent 3950303, 1976. Monte, S. J.; Muns, P. F. Mod. Plast. 1974, 68. Nieisen, L. E. "Mechanlcal Properties of Polymers", Reinhold Publishing Corp.: New Ydtc, I 9 6 2 pp 126-135. Orslno, J. A,; Herman, D. F.; Brancato, J. J. U.S. Patent 3121698, 1964. Solomon, D.H.; Rosser, M. J. J . Appl. Pmm. Sd. 1965, 9 , 1261. Solomon, D. H.; Loft, B. C. J. Appl. Polym. Sci. 1966, 72, 1253.
Received for review April 7 , 1980 Accepted March 30, 1981 Presented at the ACS/CSJ Chemical Congress, Honolulu, Hawaii, April 1979, Division of Industrial and Engineering Chemistry.
