Starch as fuel in gas generating compositions

Starch is used as a fuel/binder in pyrotechnic propellant compositions suitable for use in vehicle safety restraint systems.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to the use of starch as a fuel/binder in pyrotechnic 
compositions, especially those propellants suitable for use in inflating 
an infltable device, such as a vehicle safety restraint. 
2. Description of the Prior Art 
Various pyrotechnic propellants have been prepared for generating a gas 
upon combustion in order to inflate an air bag or similar safety restraint 
in a vehicle so as to restrain movement of an occupant in the event of a 
sudden deceleration of the vehicle, such as caused by a collision. In 
order to be employed as a pyrotechnic gas generating composition for 
inflatable occupant restraints, several criteria must be met. The 
pyrotechnic must be capable of producing non-toxic, non-flammable and 
essentially smokeless gases over a wide variety of temperatures and other 
environmental conditions. The gases that are generated must be totally 
ignited at a sufficiently low temperature so as not to destroy the 
restraint or injure the occupant. The pyrotechnic must also be safe to 
handle and must be capable of generating a substantial amount of gas 
within a very short period of time, e.g., less than about 100 
milliseconds. 
A wide variety of pyrotechnic compositions have been suggested for possible 
use for inflating vehicle occupant safety restraints. A typical 
pyrotechnic composition is disclosed in U.S. Pat. No. 3,897,285 to 
Hamilton et al., and is comprised of a fuel such as carbonaceous material, 
aluminum or magnesium; and an inorganic oxidizer such as metal chlorate, a 
metal perchlorate, or a metal nitrate. 
Another typical pyrotechnic composition is described in co-pending 
application Ser. No. 767,726, filed Feb. 11, 1977 and incorporated herein 
by reference. The pyrotechnic composition disclosed therein is comprised 
of an inorganic oxidizer such as a metal perchlorate and a highly 
oxygenated organic binder such as a polyester resin or polyacetal resin. 
Although pyrotechnic compositions can be produced using a wide variety of 
ingredients, to obtain a wide variety of results, there is still a need to 
develop a fuel/binder which can offer both economic advantages as well as 
pyrotechnic advantages, such as higher burn rates at lower energy levels. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, starch is provided as a 
fuel/binder for use in pyrotechnic compositions wherein the compositions 
are comprised of about 0 to 5 wt. %, preferably about 1 to 2 wt. % binder 
such as polyvinyl acetate; about 30 to 95 wt. %, preferably 45 to 50 wt. % 
inorganic oxidizer, about 2 to 20 wt. %, preferably 8 to 13 wt. % starch, 
about 0 to 50 wt. %, preferably about 35 to 45 wt. % coolant such as 
calcium hydroxide; and about 0 to 1 wt. %, preferably about 0.4 to 0.6 wt. 
% carbon black. 
The use of starch in such compositions increases the burn rate over other 
conventionally used fuel/binders at any given energy level. Starch is also 
more economical to use than other more exotic fuel/binders. 
DETAILED DESCRIPTION 
Pyrotechnic compositions for which the presently claimed binder is suitable 
for use are generally any of those pyrotechnic compositions containing an 
oxidizer known in the art. Such pyrotechnic compositions generate a gas 
upon combustion and are generally comprised of mixtures of chemical 
components such as fuels, oxidizers, coolants, opacifiers, and other 
propellant adjuvants. These compositions are capable of being activated 
by, for example, an electrically energized squib to generate substantial 
volumes of gas for inflating such devices as automobile crash bags. 
Oxidizing compounds suitable for use in pyrotechnic compositions include 
metal peroxides such as sodium peroxide, potassium peroxide, rubidium 
peroxide, cesium peroxide, calcium peroxide, strontium peroxide, and 
varium peroxide; inorganic chlorate such as sodium chlorate, potassium 
chlorate, lithium chlorate, rubidium chlorate, magnesium chlorate, 
strontium chlorate, barium chlorate; inorganic perchlorate such as lithium 
perchlorate, sodium perchlorate, potassium perchlorate, rubidium 
perchlorate, magnesium perchlorate, calcium perchlorate, strontium 
perchlorate, barium perchlorate, ferric perchlorate, and cobalt 
perchlorate; and metal nitrates such as lithium nitrate, sodium nitrate, 
potassium nitrate, copper nitrate, silver nitrate, magnesium nitrate, 
barium nitrate, zinc nitrate, aluminum nitrate, thallium nitrate, stannic 
nitrate, bismuth nitrate, manganese nitrate, ferric nitrate, ferrous 
nitrate and nickel nitrate. Also suitable for use are ammonium chlorate, 
ammonium perchlorate, ammonium nitrate, and the like. 
It is also within the scope of the present invention that a coolant such as 
calcium hydroxide, magnesium chloride, calcium carbonate, or magnesium 
carbonate, as well as opacifiers such as carbon black can be incorporated 
into the presently claimed compositions. 
Starch suitable for use in the present invention can be any of the 
conventionally known high-polymeric carbohydrates such as corn starch, 
wheat starch, potato starch, rice starch, tapioca starch, arrowroot 
starch, etc. When used in the pyrotechnic compositions herein, the starch 
should be of a particle size of about 4 to 30.mu.. These small particle 
sizes can be acquired by any conventional grinding means such as 
ball-milling. 
Although the starch can be used as the sole binder in the pyrotechnic 
compositions of the present invention it is preferred to also use up to 
about 5 wt. % of a traditional binder such as the oxygen-containing 
polymeric compounds. Non-limiting examples of such compounds include 
polyacetal resins including both homopolymer and copolymers, polyvinyl 
acetate resins, polyesters, polyurethanes, polyester & polyurethane 
copolymers, polycarbonates and polymers based on cellulose compounds such 
as cellulose acetate, and the like. Preferred are the polyacetal resins 
and polyvinyl acetate, more preferred is polyvinyl acetate. 
The method of preparing the pyrotechnic compositions of the present 
invention is not critical. One preferred method is to intimately mix the 
ingredients by ball-milling under an appropriate solvent such as methylene 
chloride. The admixture is then dried and pressed into pellets. 
The pyrotechnic compositions of this invention may be employed with any 
suitable gas generator apparatus for use in inflating a variety of 
inflatable devices, preferably vehicle occupant restraint devices, such as 
air bags.

In order to further describe the present invention, the following 
non-limiting examples are given. 
EXAMPLE I 
A composition consisting of 0.5 wt. % carbon black, 2 wt. % polyvinyl 
acetate, 7 wt. % corn starch, 48.5 wt. % sodium chlorate and 42 wt. % 
calcium hydroxide was intimately mixed under methylene chloride, dried, 
and pressed into pellets. The aforementioned weight percents are based on 
the total weight of the composition. 
The pellets were pressed into a slug measuring about 2 inches long and 1 
inch in diameter. The slug was inserted into a cylindrical steel casing 
and the exposed end of the slug, to which a nozzle was attached, was 
ignited. A burn rate of 0.78 inches per second at 1000 psi was measured. 
This rate is acceptable for safety restraint pyrotechnic compositions 
wherein any rate over about 0.5 inches per second is generally acceptable. 
COMATIVE EXAMPLE 
A composition consisting of 0.5 wt. % carbon black, 9 wt. % polyvinyl 
acetate 48.5 wt. % sodium chlorate, and 42 wt. % calcium hydroxide was 
intimately mixed under methylene chloride, dried, and pressed into 
pellets. All weight percents are based on the total weight of the 
composition. 
The pellets were pressed into a slug and the burn rate measured as in 
Example I. The burn rate was found to be 0.5 inches per second at 1000 
psi. 
It is to be understood that variations and modifications of the present 
invention may be made without departing from the scope thereof. It is also 
understood that the present invention is not to be limited by the specific 
embodiments disclosed herein but only in accordance with the appended 
claims when read in light of the foregoing specifications.