Using a solvent for in-situ formation of fibers in an elastomer

A method of preparing a fiber reinforced elastomer by forming fibers therein in-situ and an elastomer made thereby are provided. In the method, a fiber forming material, preferably a high performance polymer, is dissolved in a compatible solvent to form a solvent/polymer mixture, and the mixture is added to the elastomer during compounding or mixing. The polymer is quickly dispersed into the elastomer, and the solvent rapidly evaporates. The shear of the mixer causes elongation of the polymer into fibers. The fibers may also be oriented by the shear of the mixer.

BACKGROUND OF THE INVENTION 
The invention relates to a method of preparing a fiber reinforced elastomer 
by the in-situ formation of fibers therein, and a reinforced elastomer 
made by the method. 
The use of short fiber reinforced elastomers in the preparation of many 
products is known in the art. Prior art fiber reinforced elastomers are 
prepared using various methods of dry blending crystalline fibers into an 
elastomer, melt blending thermoplastic polymers into an elastomer, or 
forming fibers in an elastomer by reacting fiber forming ingredients in 
the elastomer. For example, see U.S. Pat. Nos. 4,263,184 and 4,833,191. 
Dry blending fibers into an elastomer is difficult, and the friction caused 
by dry blending (if not carefully monitored) can cause overheating and 
degradation of the elastomer during mixing. Also, melt blending is limited 
in that thermoplastic polymers with a melting point above the degradation 
temperature of the elastomer cannot be used. 
There is a need in the art for a method of introducing high performance 
polymers which have a high melting point (greater than 200.degree. C.) or 
a high glass transition temperature (greater than 150.degree. C.) into an 
elastomer in fibrous form. By high performance polymer it is meant a 
polymer with good mechanical properties and heat stability. It is an 
object of the present invention to provide such a method. 
Other objects of the invention will be apparent from the following 
description and claims. 
SUMMARY OF THE INVENTION 
A method of forming high performance polymer fibers in-situ in an elastomer 
is provided. The method comprises the steps of at least partially 
dissolving the high performance polymer in a solvent to provide a 
solvent/polymer mixture (or solution), adding the mixture to a hot 
elastomer in a mixer, using the shear of the mixer to form said high 
performance polymer into fibrous reinforcement particles during mixing, 
and evaporating or stripping the solvent from the elastomer at rubber 
mixing temperatures. The fiber forming polymer may comprise a high melting 
thermoplastic or a polymer having a high glass transition temperature 
(Tg). Preferably, the polymer will comprise about 5-30% by weight of the 
solvent/polymer mixture. 
Also provided is a fiber reinforced elastomer made by the method of the 
invention. The reinforced elastomer of the invention demonstrates a 
10-150% improvement in modulus over a control compound made without 
fibers, the improvement in modulus being substantially in proportion to 
the fiber content.

DETAILED DESCRIPTION OF THE INVENTION 
In the method of the invention, a high performance polymer is mixed with 
solvent to form a solvent/polymer mixture. Separately, an elastomer (e.g. 
rubber) is compounded in a conventional Brabender mixer in a conventional 
manner. The solvent/polymer mixture is added to the elastomer in the mixer 
during mixing or compounding, and very quickly is homogeneously dispersed 
therein. The temperature of the rubber during compounding, generally about 
142.degree. F. to 392.degree. F., quickly causes the solvent to evaporate, 
permitting the polymer to coalesce in the elastomer. The evaporated 
solvent is stripped (vented) from the mixture by conventional means (e.g. 
a hood or vacuum exhaust system). The shear of the mixer causes elongation 
of the coalesced polymer into fiber form and may provide some orientation 
of the fiber. 
The fiber forming polymer of the invention may comprise a high performance 
polymer such as a high melting thermoplastic or a polymer having a high 
glass transition temperature. Examples of such polymers include 
polyphenylene oxide, polyester, polyarylate, polycarbonate, 
polyetherimide, polyamide, cellulose acetate, cellulose acetate butyrate, 
and mixtures thereof. The solvent used can be any solvent or plasticizer 
which is compatible with a particular polymer and may comprise methyl 
ethyl ketone, chloroform, acetone, methylene chloride and mixtures 
thereof, and mixtures of such solvents with other polar solvents such as 
methanol and dimethyl formamide. 
Elastomers that can be used in the method include any elastomer that can be 
blended in the conventional mixing equipment. Examples of such elastomers 
are polyisoprene, natural rubber, ethylene propylene rubber, butyl rubber, 
halobutyl rubber, nitrile rubber, polybutadiene rubber, polystyrene 
butadiene rubber, etc. 
The invention is further illustrated with reference to the following 
examples. 
EXAMPLE 1 
A 10% solution of polyphenylene oxide (PPO), in chloroform was slowly added 
to 45 g of poly cis 1,4 isoprene in a Brabender at about 140.degree. C. 
The sample was mixed for five minutes and discharged. The discharged 
elastomer contained 8.7 phr PPO. The fiber containing elastomer was used 
for further compounding as follows. 
______________________________________ 
Amount 
Ingredient 
Chemical Name Type in phr 
______________________________________ 
1. Duvalic cis,1,4-polyisoprene 
elastomer 
100 
or Natsyn 
2. pig 779 carbon black filler 45 
3. Sardine petroleum plasticizer 
9 
process oil 
4. Zonflax N-phenyl-N'-(1,3 
antidegradant 
2 
dimethyl/butyl) 
N-phenyl-P- 
phenylenediamine 
5. Nailax diaryl-P-phenylene 
antidegradant 
1 
diamine 
6. Sunolite paraffinic/micro 
processing aid 
1 
crystalline wax 
7. Sterax stearic acid activator 
3 
______________________________________ 
BRABENDER COMPOUNDING 
The high performance polymers (e.g. PPO) were added on top of the 100 parts 
of elastomer as described above. A Brabender mix at 70 rpm, using a 
120.degree. C. oil bath, was used for non-productives (ingredients 1-7). 
Mix time was 5 minutes, and the drop temperature was approximately 
270.degree. F. 
The non-productive mixes were used for further compounding by reloading the 
non-productives in the mixer and adding the following ingredients. 
______________________________________ 
Amount 
Ingredient Chemical Name Type in phr 
______________________________________ 
8. pig 1 zinc oxide activator 
3 
9. sponbax 2(morpholino-thio) 
accelerator 
0.8 
benzenethiazole 
10. phenax N,N' diphenyl accelerator 
0.4 
guanidine 
11. pig 4 sulfur vulcanizing 
1.6 
agent 
______________________________________ 
Productive mixes (non-productive plus the accelerators and vulcanizing 
agents (ingredients 8-11)) were carried out without external heating at 50 
rpm for 3 minutes. The compounded elastomers were cured at 150.degree. C. 
The vulcanizate physical properties of the reinforced elastomer (Natsyn or 
Duvalic) were compared to that of a control compound comprising the above 
formulation prepared without the addition of a fiber reinforcing polymer. 
Upon testing the compound of the invention for certain physical properties, 
it was determined that the elastomer composition made according to the 
invention showed improvements over a control compound (without fibers) as 
follows: 
______________________________________ 
% tensile modulus 
improvement 
over control 
______________________________________ 
at 50% elongation 
87% 
at 100% elongation 
129% 
at 200% elongation 
104% 
at 300% elongation 
48% 
______________________________________ 
EXAMPLE 2 
25 g of cellulose acetate butyrate was dissolved in 200 ml of mixed solvent 
(4:1/acetone : methanol). The solution was slowly added to 200 g of 
poly(cis-1,4-isoprene) in a Brabender set at 125.degree. C. and 40 RPM. 
The mixing was done in five minutes. The resultant elastomer was 
compounded according to the formula described in Example 1. The cured 
sample has an improved tensile modulus over a non-fibrous control as 
follows: 
______________________________________ 
% tensile modulus 
improvement 
over control 
______________________________________ 
at 50% elongation 
43% 
at 100% elongation 
26% 
at 200% elongation 
40% 
at 300% elongation 
17.6% 
______________________________________ 
EXAMPLE 3 
A 20% solution of polyphenylene oxide (PPO) in chloroform was slowly added 
to poly(cis-1,4-polyisoprene) in a Brabender at about 140.degree. C. The 
sample was mixed for 5 minutes and discharged. The elastomer contained 9 
phr PPO. The resultant elastomer was compounded using the compound 
formulation described in Example 1. The vulcanizate physical properties 
showed an improvement of tensile modulus as follows: 
______________________________________ 
% tensile modulus 
improvement 
over control 
______________________________________ 
at 50% elongation 
97% 
at 100% elongation 
103% 
at 200% elongation 
66% 
at 300% elongation 
50% 
______________________________________ 
While specific embodiments of the invention have been illustrated and 
described, those skilled in the art will recognize that the invention may 
be variously modified and practiced without departing from the spirit of 
the invention. The invention is limited only by the following claims.