Surface modification of alumina hydrate with liquid fatty acids

A surface modified alumina hydrate composition compatible with thermoplastic resins when used as a flame retardant and smoke suppressing filler. Surface modification is accomplished by treating powdered alumina hydrate with about 0.2 to 5 percent by weight of a liquid mixture of C.sub.10 -C.sub.20 carboxylic acids having a titer below about 30.degree. C. and an iodine value of about 15 or less. In a preferred embodiment, the alumina hydrate has a particle size of less than about two microns, and the liquid mixture of acids comprises isostearic acid.

BACKGROUND OF THE INVENTION 
The present invention relates to alumina hydrate used as a filler for 
thermoplastic resins. More specifically, the invention concerns surface 
modification of alumina hydrate to render the hydrate compatible with 
thermoplastic resins. 
Inorganic materials, such as alumina hydrates, talc and calcium carbonate, 
are frequently employed as fillers in thermoplastic resins, including 
polypropylene, polyethylene and polyvinyl chloride (rigid and flexible). 
The fillers can impart increased mechanical strength, stiffness and, in 
the case of alumina hydrate, increased flame retardancy and decreased 
smoke generation. Filled thermoplastic resins are widely used as molded 
components in automobiles, appliances and machine housings and as extruded 
components in sheet and tube form, for example, in wire and cable 
jacketing. 
When alumina hydrates are added to thermoplastic resins in amounts needed 
to achieve a reasonable degree of flame retardancy (about 35 to 65 percent 
by weight), the hydrates can detrimentally influence physical properties 
even where uniformly dispersed. For example, when incorporated into 
polypropylene, they reduce flexibility and impact strength. Even more 
detrimental to physical properties is the difficulty of realizing uniform 
dispersions of alumina hydrate in the resins. Gross heterogeneities caused 
by undispersed agglomerates can seriously compromise physical properties, 
especially impact strength and cosmetic qualities, such as gloss and 
surface smoothness. Consequently, the use of alumina hydrate, which is 
otherwise an excellent and low cost flame retardant filler, is considered 
less desirable than other fillers for most applications where retention of 
physical properties is required. 
It is a principal object of the present invention to provide powdered 
alumina hydrate with a surface coating that will cause filled 
thermoplastic compounds made with the hydrate to exhibit satisfactory 
flame retardancy and smoke suppressive qualities and improved final 
physical properties compared with thermoplastic compounds filled with an 
equivalent amount of unmodified alumina hydrate. 
It is a related object of the invention to provide a surface modified 
alumina hydrate composition that possesses improved processing 
characteristics. 
Additional objects and advantages of the invention will become apparent to 
persons skilled in the art from the following specification. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, powdered alumina hydrate is 
combined with about 0.2 to 5 percent, based on the weight of the alumina 
hydrate, of a liquid mixture of carboxylic acids having a titer 
(congealing temperature) below about 30.degree. C. Mixtures of saturated 
carboxylic acids having an iodine value of about 15 or less, and 
preferably about 12 or less, are preferred. A particularly preferred fatty 
acid mixture has an iodine value of about three or less and is sold 
commercially under the designation "isostearic acid". 
Mixtures of C.sub.10 -C.sub.20 saturated carboxylic acids are useful, with 
C.sub.16 -C.sub.20 saturated acids being preferred. The particularly 
preferred isostearic acid is a mixture of saturated, mostly C.sub.18 
carboxylic acids. Titer of the acid mixture is preferably below about 
20.degree. C. and optimally about 8.degree. to 10.degree. C. 
A surface modified alumina hydrate composition made in accordance with the 
invention preferably contains about 0.2 to 2 percent isostearic acid, 
based on the weight of the hydrate. A particularly preferred alumina 
hydrate composition described in the examples contains about one percent 
isostearic acid. 
The powdered alumina hydrate preferably has an average particle size less 
than about 15 microns, more preferably less than about five microns, and 
most preferably less than about two microns. Optimally, essentially all of 
the alumina hydrate has a particle size less than about two microns, with 
a nominal particle size of about one micron. The alumina hydrate may 
contain about 15 to 35 percent by weight water as determined by 
calcination at 1000.degree. F. for one hour. 
The surface modified, isostearic acid coated alumina hydrate composition is 
mixed with a thermoplastic resin to form filled thermoplastic resin 
compounds. Suitable resins are polyethylene, polypropylene, polyvinyl 
chloride and mixtures and copolymers thereof. Up to about 190 parts by 
weight of thermoplastic resin are mixed with 100 parts by weight of the 
coated hydrate composition to form a filled thermoplastic compound. Filled 
thermoplastic compounds made in accordance with the invention have 
improved flexibility, impact strength and appearance compared with filled 
resin compounds in which unmodified alumina hydrate is used. 
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
This invention relates to surface modified alumina hydrates employed as 
fillers for thermoplastic resins. 
For purposes of this description, the expression "alumina hydrate" refers 
to Al.sub.2 O.sub.3.xH.sub.2 O, wherein x varies from 1 to 3; in other 
words, the water of the alumina hydrate varies between 15 and 35 percent 
by weight of the alumina hydrate, determined by calcination of the alumina 
hydrate at 1000.degree. F. for one hour. Alumina hydrate which is modified 
according to the invention can be obtained from many sources, most 
commonly as the product of the well-known Bayer process. 
The expression "thermoplastic resin" as used herein refers to polymeric 
compositions which can be heated and softened numerous times without 
suffering any basic alteration in characteristics. 
The term "isostearic acid" as used herein is not intended to be restricted 
to its literal translation of 16-methylheptadecanoic acid, but rather is 
intended in its more common meaning, as is normally associated with a 
coined name, in this case, for mixtures of C.sub.18 saturated fatty acids 
of the general formula C.sub.17 H.sub.35 COOH. These are rather complex 
mixtures of isomers, liquid at room temperature and primarily of the 
methyl-branched series, which are mutually soluble and virtually 
inseparable. While most of the branched chains contain a total of 18 
carbon atoms, not necessarily all of the molecules contain exactly that 
number. The branch is primarily methyl but may possibly include some 
ethyl, and the distribution is typically primarily towards the center of 
the chain but is still fairly random. Methods pertaining to the production 
of isostearic acid are contained in U.S. Pat. Nos. 2,664,429 and 
2,812,342. One source of isostearic acid suitable in practicing the 
invention is marketed commercially by Emery Industries, Inc. under the 
trade name Emersol 875 Isostearic Acid. Typical characteristics of this 
acid are listed in the following table: 
______________________________________ 
Minimum Maximum 
______________________________________ 
Titer .degree.C. 10.0 
Iodine value 3.0 
Acid value 191 201 
Saponification value 
197 204 
Molecular weight 
(approx.) 284 
______________________________________ 
The surface modified alumina hydrate described herein can be produced quite 
economically by blending or mixing, employing more or less conventional 
means, particulate alumina hydrate with the appropriate amount of 
isostearic acid, thereby applying to the particulate surfaces a coating of 
isostearic acid. The isostearic acid is liquid at room temperature and 
thus can be applied directly to the alumina hydrate. Double-cone mixers, 
rotating disc mixers and ribbon blenders can be used as well as medium and 
high intensity powder blending equipment. The coating may be done at room 
temperature or at higher temperatures if more convenient. 
The following examples and tables are presented for further illustration of 
the effects of the novel alumina hydrate-isostearic acid coated 
compositions when used as fillers for thermoplastic resins.

EXAMPLES 
An alumina hydrate, the composition of which is shown in Table I, was used 
for all comparative tests used in these examples. The alumina hydrate, 
Hydral 710 (Aluminum Company of America), where indicated, was surface 
coated with one percent of isostearic acid (Emery Industries Emersol 875 
Isostearic Acid) in a high intensity PVC powder blender (Welex) for 15 
minutes with the temperature of mixing allowed to rise to 150.degree. F. 
TABLE I 
______________________________________ 
Typical Composition and Characteristics 
of Alumina Hydrate (Hydral 710) 
Typical Properties 
______________________________________ 
Al.sub.2 O.sub.3, % by weight 
64.7 
SiO.sub.2, % by weight 0.04 
Fe.sub.2 O.sub.3, % by weight 
0.01 
Na.sub.2 O (total), % by weight 
0.45 
Na.sub.2 O (soluble), % by weight 
0.10 
Moisture (110.degree. C.), % by weight 
0.3 
Bulk density, loose, lb./ft..sup.3 
8-14 
Bulk density, packed, lb./ft..sup.3 
16-28 
Specific gravity 2.40 
Specific surface area, m.sup.2 /g 
6-8 
Particle distribution, cumulative, 
as determined by electron 
microscope on a weight basis 
% less than 2 microns 100 
% less than 1 micron 85 
% less than 0.5 micron 28 
______________________________________ 
EXAMPLE 1 
Effect of Isostearic Acid Coating for Alumina Hydrate on Impact Strength of 
Filled Polypropylene 
Alumina hydrate (Hydral 710-Alcoa) was compounded into a high impact grade 
of polypropylene, Shell Chemical Co. 7328 (melt flow 2.0 dg/min, ASTM 
D1238-70) on a laboratory two-roll mill at 390.degree. F. for seven 
minutes. The sheeted compound was removed, cooled, granulated, then 
compression molded at 380.degree. F. into 0.125 inch test placques. Impact 
strengths were determined according to ASTM D-256-78, Method A (except 
unnotched). 
TABLE II 
______________________________________ 
Impact Strength of Filled Polypropylene 
Alumina Hydrate Oxygen Impact Strength 
(parts per 100 
Alumina Index Izod Impact.sup.a 
Test parts polypropy- 
Hydrate ASTM (Unnotched, 
Sample 
lene resin) Coating D2863-77 
ft. lb./in.) 
______________________________________ 
C-5.sup.b 
45 None 21 2.3 
C-6.sup.b 
45 1% 21 3.3 
isostearic 
acid 
C-2 100 None 24 0.9 
C-7 100 1% 23.5 1.8 
isostearic 
acid 
______________________________________ 
.sup.a by ASTM D25678, Method A, except unnotched 
.sup.b also contains 6 parts reinforcing mineral fiber per 100 parts 
polypropylene resin 
EXAMPLE 2 
Effect of Isostearic Acid Surface Modified Alumina Hydrate on Physical 
Properties of Filled Polypropylene 
The procedure of Example 1 was followed. The polypropylene base plastic was 
Shell Chemical Co.'s 7328, high impact grade. 
TABLE III 
__________________________________________________________________________ 
Physical Properties of Filled Polypropylene 
Alumina Hydrate.sup.a 
(parts per 
Alumina 
Test 
100 parts 
Hydrate 
Izod Impact Strength.sup.c 
Oxygen 
UL-94 
Tensile Strength (psi).sup.f 
Sample 
polypropylene) 
Coating 
Unnotched 
Notched 
Index.sup.d 
VBT.sup.e 
At Yield 
At Break 
% Elongation 
__________________________________________________________________________ 
H-1 50 None 2.25 0.43 21.5 Fail 
5180 2661 4.3 
G-2 50 1% isostearic 
5.1 0.51 21.5 Fail 
2590 1984 15.7 
acid.sup.b 
I-4 150 None 0.19 0.06 29.0 V-O 1604 1604 1.0 
I-9 150 1% isostearic 
1.05 0.32 26.5 V-O 2071 2071 1.0 
acid.sup.b 
__________________________________________________________________________ 
.sup.a Hydral 710 (Alcoa) 
.sup.b Emersol 875 isostearic acid (Emery Industries) 
.sup.c Foot-pounds/inch ASTM D25678, Method A 
.sup.d ASTM D2863-77 
.sup.e Underwriters Laboratories Vertical Burn Test 
.sup.f ASTM D63877a 
Elongation and impact strength are seen to be enhanced for the filled 
polypropylene containing the isostearic acid surface modified alumina 
hydrate. 
EXAMPLE 3 
Effect of Isostearic Acid Surface Modified Alumina Hydrate on Spiral Mold 
Flow Properties of Filled Polypropylene and Polyethylene 
A comparative ranking was made of filled polyethylene and polypropylene as 
related to melt flow travel in a spiral mold flow injection molder. The 
polypropylene (PP) used was Shell Chemical Co. high impact grade 7328 of 
melt flow 2.0 dg/g ASTM D1238-70 and the polyethylene (PE) used was 
Super-Dylan 7180 of ARCO Polymers of melt index 18. For this test mold 
temperature was 380.degree.-385.degree. F. with the same injection 
pressure being used for all samples. 
TABLE IV 
__________________________________________________________________________ 
Spiral Mold Melt Flow of Filled Polyethylene and Polypropylene 
Alumina Hydrate 
Alumina 
Mold 
Plastic 
(parts per 100 
Hydrate 
Flow 
Sample 
Resin 
parts resin) 
Coating 
(inches) 
Appearance 
__________________________________________________________________________ 
N3B PE 67 None 24.1 Brittle, rough surface 
N2B PE 67 1% isostearic 
32.8 Smooth 
acid 
N6B PE 150 None 9.4 Many voids, crumbly 
N5B PE 150 1% isostearic 
28.8 Smooth, brittle 
acid 
N10A 
PP 67 None 9.4 Rough finish, voids 
N9B PP 67 1% isostearic 
10.0 Good fill 
acid 
N13B 
PP 150 None 6.2 Rough large air voids, 
slight degradation 
N12A 
PP 150 1% isostearic 
9.3 Rough finish 
acid 
__________________________________________________________________________ 
In general, significantly improved melt flow occurred for the filled 
polyethylene and polypropylene when the alumina hydrate was surface 
modified with isostearic acid. Simplistically, the improved melt flow can 
be translated into improved mold filling ability with better surface 
characteristics, such as gloss and smoothness. 
EXAMPLE 4 
Effect of Isostearic Acid Surface Coating of Alumina Hydrates on Melt 
Processing Behavior of Rigid PVC Compounds 
A standard PVC rigid vinyl compound was prepared according to the following 
formula: 
______________________________________ 
Component Parts by Weight 
______________________________________ 
PVC resin (B.F. Goodrich Geon 
103 EPF-76) 100 
Thermal stabilizer 2 
Processing Aid 1.5 
Impact modifier 6.0 
Titania pigment 3.0 
Lubricants (calcium stearate and 
polyethylene wax) 3.0 
______________________________________ 
This mix was dry blended with alumina hydrate (Hydral 710) at 35 parts per 
100 parts resin. The dry blend was then evaluated for melt fusion behavior 
in a torque rheometer. A Brabender Plasticorder torque rheometer (C. W. 
Brabender, Hackensack, New Jersey) was used. Fusion data was obtained with 
the #6 roller head under the following conditions: 
______________________________________ 
Sensitivity 1:5 .times. 5 
Damp 6 seconds 
Speed 50 rpm 
Temperature 228.degree. C. 
Loading 55 grams. 
______________________________________ 
The results are collected in Table V. 
TABLE V 
__________________________________________________________________________ 
Melt Fusion Behavoir of Rigid PVC Compounds 
Containing Alumina Hydrates 
Time to 
Torque at Time to 
Torque at 
Time to 
Torque at 
Time to 
Melt Melt Temp. at 
Fuse Fusion 
Stabilize 
Stabilization 
Degrade 
Sample (min.) 
(m-g) Melt (min.) 
(m-g) (min.) 
(m-g) (min.) 
__________________________________________________________________________ 
100 parts 
PVC + 35 
parts alumina 
hydrate 
0.65 880 172.degree. C. 
1.0 2525 6.5 1350 8.4 
100 parts 
PVC + 35 
parts alumina 
hydrate with 
1% isostearic 
acid 0.6 600 171.degree. C. 
1.0 2400 8.8 1350 10.8 
__________________________________________________________________________ 
The above data demonstrate that a lower melt torque is developed at melt 
and at fusion with the isostearic acid surface modified alumina hydrate. 
Also significant is the improved thermal stability (longer time to 
degrade) for the isostearic acid surface modified alumina hydrate filled 
PVC compound. 
EXAMPLE 5 
The effect of isostearic acid surface modified alumina hydrate as a filler 
in rigid PVC compound was examined at two levels, 20 phr (parts alumina 
hydrate per 100 parts resin) and 40 phr. Rigid PVC compound powder blends 
were made up according to Example 4. The powder blends were extruded in 
3-inch wide strips at a thickness of about 0.035 inch. The extruder was a 
3/4" single screw type associated with the torque rheometer. Temperature 
of extrusion was 380.degree.-385.degree. F. 
Physical properties of the extruded strips are given in Table VI. 
TABLE VI 
__________________________________________________________________________ 
Physical Properties of Rigid PVC Compounds Containing Alumina Hydrate 
Falling 
Alumina Hydrate 
Thickness 
Density 
Tensile 
Dart Impact 
Sample 
(phr) (inches) 
(g/cm.sup.3) 
Strength (psi) 
(in. lb./.001 in.) 
% Elongation 
__________________________________________________________________________ 
W-1-29-1 
none (control) 
0.032 1.51 7875 3.00 125 
W-1-29-2 
20 (uncoated) 
0.032 1.41 5488 &lt;0.32 25 
W-1-29-6 
20 (1% Isostearic 
0.036 1.54 5944 0.65 54 
Acid Coated) 
W-1-29-3 
40 (uncoated) 
0.037 1.14 2940 &lt;0.27 8.4 
W-1-29-7 
40 (1% Isostearic 
0.038 1.49 5326 0.74 125 
Acid Coated) 
__________________________________________________________________________ 
Of most interest is the very low density of the rigid PVC compounds filled 
with uncoated alumina hydrate as compared to the density of the same 
compound filled with isostearic acid surface modified alumina hydrate. The 
much lower density can be explained by an air foamed structure probably 
resulting from poor compatibility of the uncoated alumina hydrate with the 
PVC resin matrix, i.e. an undisplaced surface occluded shell of air 
associated with the uncoated alumina hydrate filler. The isostearic acid 
surface modified alumina hydrate gives a filled composite of density more 
in line with that expected by proportionate ratios of densities of the 
alumina hydrate (2.42 g/cm.sup.3) and of the PVC compound (1.37 
g/cm.sup.3). The significantly improved impact strength, tensile strength 
and elongation of the PVC compound containing isostearic acid surface 
coated alumina hydrate as compared to the same PVC compound containing the 
uncoated alumina hydrate is also noteworthy. 
The foregoing description of my invention has been made with reference to a 
particularly preferred embodiment. Persons skilled in the art will 
understand that numerous changes and modifications can be made therein 
without departing from the spirit and scope of the following claims.