 |
Description  |
|
|
SUMMARY OF THE INVENTION
This invention relates generally to a biodegradable article and more
particularly to a biodegradable packing material and a process for making
the same.
Fragile articles, such as glassware, are commonly packed in containers for
shipping along with peanut-shaped, shock absorbing packing material made
from a lightweight plastic such as polystyrene foam. These foam "peanuts"
surround the article within the container and fill in the space between
the container walls and the article so that the article is protected
during transport. However, although polystyrene foam peanuts
satisfactorily protect articles from damage during shipping, they present
a disposal problem after use because they are not biodegradable.
Biodegradable packing material, such as the dunnage disclosed in U.S. Pat.
No. 4,997,091, has been developed to solve the environmental concerns
associated with polystyrene foam peanuts. However, the biodegradable
dunnage disclosed in U.S. Pat. No. 4,977,091 is deficient in that it is
too dense and too hard. Dunnage which is too dense unnecessarily increases
the weight of the container. If the dunnage material is too hard, the more
likely that the article may be scratched by the material or broken because
of the reduced shock absorbing capability of the material. Biodegradable
dunnage disclosed in U.S. Pat. No. 4,977,091 is produced by a heavy slurry
mix which is directly introduced into a forming machine. A large and
costly pumping system must be provided to pump the heavy slurry mix from a
mixing tank to the forming machine.
Moreover, there is presently a need for a process which is readily
controlled to produce biodegradable material of different density and
hardness so that the material could be used to make other biodegradable
products such as: disposable diapers, liquid containers (e.g., cups and
plates), appliance housings (e.g., for telephones and televisions), heat
sources such as cooking briquettes and fire logs, constructions panels,
and food packaging materials.
Among the several objects and features of this invention may be noted the
provision of process for making a shaped biodegradable cellulosic article
having a density and hardness suitable for shipping fragile articles, such
as glassware; the provision of such a process in which the density and
hardness are readily controlled to produce biodegradable material suitable
for different applications; and the provision of a biodegradable
cellulosic article which may be formed in the shape of a shipping peanut
which is easy and cost-efficient to manufacture.
Generally, a process for making a shaped biodegradable cellulosic article
from cellulose-containing material having a water content less than about
50 percent by weight comprises mixing the cellulose-containing material, a
bonding agent and an expander in a dry mix. The dry mix is pressurized by
the extruder. Water is injected into the pressurized dry mix and the
wetted mixture is extruded into a shaped article.
A shaped biodegradable product made according to the previously described
process comprises cellulose in an amount ranging from about 5 percent to
about 90 percent by weight, bonding agents in an amount ranging from about
3 percent to about 90 percent by weight, and expanders in an amount
ranging from about 3 percent to about 80 percent by weight. The product
has a water content of less than 40 percent by weight. The product has a
density of less than 1.0 pound per cubic foot.
Other objects and features will be in part apparent and in part pointed out
hereinafter.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
This invention particularly relates to an improved biodegradable material
and a process of making the same in the form of a peanut for use as
packing material. It is believed, however, that by changing the relative
concentration of certain components of the material to select a different
density and hardness, the process of the present invention can produce
material suitable for other applications, such as in disposable diapers,
containers (e.g., cups, plates and bowls), appliance housings (e.g., for
telephones and televisions), heat sources such as cooking briquettes and
fire logs, constructions panels, and food packaging.
The process, which is described in more detail hereinafter, includes the
step of mixing a cellulose containing material (e.g., newspaper) with a
bonding agent, an expander and, preferably, one or more performance
enhancing additives in a dry mix. The dry mix is fed to an extruder and
pressurized to a nominal pressure by the extruder. Water is injected into
the mix, which is then extruded into a shaped article, such as a packing
peanut.
The particles of cellulose in the mix are held together in the shaped
article by the bonding agent. The expanding or foaming agent expands the
volume of the article (which consequently decreases its density), and the
enhancers improve the performance of the article such as by preventing rot
or retarding fire.
Cellulose-containing source material may be obtained from used paper
products such as newsprint or computer paper. Newsprint and computer paper
are sanitary, therefore, no decontamination is required. Contaminated
cellulose-containing material, such as corrugated waste paper which has
toxic adhesives, may be used, but the contaminants must be removed. As one
alternative, cellulose may also be provided in a virgin state, e.g., tree
pulp, soybean stalks, corn stalks, peanut vines and hulls. However, to
conserve resources, recycling of used cellulose containing materials to
make the biodegradable article is more desirable.
Preferably, the cellulose-containing source material is pulverized to
particulate size for better blending with the additives. However, larger
pieces of cellulose such as newspaper torn into squares as large as about
2".times.2" may be used in the mix. Thus, while it is preferable that the
cellulose material be particulate, larger pieces may be used and fall
within the scope of the present invention.
Cellulose may be present in the composition of the article in amounts
ranging between 5 and 90 percent by weight, preferably in amounts ranging
between 5 and 80 percent by weight, and most preferably in amounts ranging
between 20 and 60 percent by weight. Before the cellulose is mixed with
the additives, its water content is reduced to less than 50 percent by
weight. More preferably, the water content of the cellulose prior to
mixing is less than 30 percent by weight, and most preferably the water
content of the cellulose is in a range of between 3 and 25 percent by
weight. The cellulose may be dried in unagitated equipment by indirect
heating or by contact with warm air. Tray dryers or screen-conveyor
dryers, as are known in the art, are suitable for accomplishing this step.
As previously stated, the components added to the cellulose-containing
source material fall into three categories, namely, bonding agents for
bonding the cellulose particles, expanders for expanding the volume of the
article and performance enhancing additives for enhancing the overall
quality of the article. Bonding agents may be selected from a group
including: casein, protein, gluten, starch, gelatin or flour. Casein,
which is the phosphoprotein of fresh milk, has been found to be
particularly well suited as a binder in the composition. Bonding agents
may be present in amounts ranging between 3 and 90 percent by weight,
preferably in amounts ranging between 15 and 80 percent by weight, and
most preferably between 15 and 45 percent by weight.
Expanders which may be used in the composition of the article consist of:
casein; starch; tataric acid; calcium carbonate; baking powder; and flour.
Starch and casein have been found to be an excellent expander of
cellulose. Expanders may be present in the composition of the article in
amounts ranging between 3 and 80 percent by weight, preferably in amounts
ranging between 3 and 50 percent by weight, and most preferably between 3
and 30 percent by weight.
It is believed that there is substantial flexibility in the choice of the
specific bonding agent(s) and expander(s) which are used in the
composition. Thus, the manufacturer may choose the bonding agent and
expander based on availability and cost at the time of manufacture. Most
of the additives are agricultural by-products from grains, cereals,
vegetables and dairy products. These products are priced daily, so that
the manufacturer may take advantage of the market to obtain the lowest
cost bonding agent and expander.
Performance enhancing additives in the composition may include: boron (for
fire retardancy), amino acids (for controlling bacteria and mold), nitrate
(for controlling bacteria and mold), lactic acid (for controlling bacteria
and mold), and carigenin (for added elasticity). Enhancers may be present
in the composition of the article in amounts of less than 50 percent by
weight, preferably in amounts of less than 40 percent by weight, and most
preferably in amounts less than 30 percent by weight. Amino acids, nitrate
or lactic acid are preferably added to the composition of packing peanuts
to prevent them from molding, especially if there is any likelihood that
the peanuts may be exposed to moisture. Boron or another fire retardant is
also desirably added to the composition when packing peanuts are produced.
In the process of the present invention, cellulose-containing source
material, such as newsprint, is first pulverized. The comminution of the
cellulose prior to its introduction into the mix may be performed, for
example, by a shredder or a hammer mill (e.g., Model 4W, manufactured by
J. B. Sedberry of Tyler, Tex.). The pulverized cellulose is then dry mixed
with one or more bonding agents, one or more expanders and one or more
performance enhancing additives. However, all of the additives (i.e.,
bonding agents, expanders and enhancers) can be introduced into the
cellulose at the shredder or hammer mill as the cellulose is being
pulverized. Introduction of the additives at this point might be done to
reduce the size of one or more of the additives, or to prepare the mix for
storage and later use.
Dry mixing of the ingredients is preferred over mixing in a water slurry. A
slurry mixture is too wet to be formed so that water must be removed prior
to its introduction into the extruder. Moreover, the water content of the
extruded article produced when the ingredients are mixed in a slurry is
higher than when they are dry mixed so that more time and energy is
required to dry the extruded product when a slurry mix is used. A dry mix
can be stored prior to usage for long periods of time, whereas a slurry
must be used in a relatively short time before the organic ingredients in
the mixture begin to mold. The dry mix can be fluidized and conveyed in
ducts to the extruder by a relatively inexpensive blower system, while a
slurry must be pumped into the extruder using a costly pumping system.
To mix the ingredients in a generally dry state, an air chamber may be used
in which circulating air within the chamber mixes the ingredients. The
mixed ingredients may then be stored in a separate container or hopper or
be transported directly (e.g., by an air duct) to an extruder forming
machine. It is also possible to add the ingredients directly into the
extruder wherein they are mixed by the action of the extruder.
In the extruder, the dry mix is pressurized to a nominal pressure in a
preferred range of between about 18 to 30 psi absolute for ensuring that
the bonding agents bind the cellulose particles together. The type of
extruder preferably used to to form the packing peanuts is a twin-screw
extruder, such as Baker-Perkins Model No. MPF-50 twin-screw extruder
manufactured by APV Chemical Machinery, Ltd. of Hanley, England. In a
twin-screw extruder, co-rotating or counter-rotating screws move the mix
from one end of the extruder which receives the mix to the other end of
the extruder which dispenses the mix. The extruder includes a mixing
chamber into which the dry mix is force fed for further mixing the dry
mix. Each screw has a plurality of blades which are in near contact with
the barrel wall and with blades on the other screw so that the material is
wiped away from the barrel wall and the blades. A more thorough mix is
achieved with a twin-screw extruder than with a single-screw extruder,
because a twin-screw extruder has two screws having interengaging blades
which cut and blend the ingredients, whereas a single-screw extruder
merely pressurizes and transports the mix. Unlike the barrel in a
single-screw extruder, the barrel in a twin-screw extruder is not
completely filled so there is more room in the barrel for mixing the
ingredients. In twin-screw extrusion, heat is primarily derived from the
energy developed by cutting the mix within the extruder, with the
remainder of the heat being added to the mix by heating elements located
outside the barrel wall.
Water is injected into the heated and pressurized dry mix after it exits
the mixing chamber. The water introduced into the extruder may have any
temperature but preferably should have a temperature of greater than
approximately 50.degree. F. and less than approximately 200.degree. F. The
temperature of the dry mix has previously been increased by the mechanical
action of the screws. The introduction of water starts chemical reactions
which produce more heat. It is not necessary that any additional heat be
added to the wetted mix. However, better bonding is achieved when the
temperature exceeds 100.degree. F., or more preferably, is at or in excess
of 180.degree. F. Additional heat may be required to reach the more
preferred range.
The water and heat activate the bonding agents and expanders in the dry mix
to bond the cellulose particles together and to decrease the density of
the final product, respectfully. Only a relatively small amount of water
need be injected into the mix to activate the bonding agents and
expanders. At the end of the extruder opposite the mixing chamber there is
a die for shaping the extruded mix as it is forced from the extruder. The
die forms the mix into the shape of the peanut, but may form the mix into
other shapes and still fall within the scope of the present invention. A
cutter separates the extruded mix from the mix in the extruder.
After the extruded mix is shaped and cut, the resultant product is dried. A
number of commercially available dryers are suitable for drying the
product. An example of such a dryer is a convection oven manufactured by
Wenger Manufacturing, Inc. of Sabetha, Kans. A micro-wave dryer may also
be used for drying the product. The resulting water content of the product
after drying should be less than 40 percent by weight, preferably be less
than 30 percent by weight, and most preferably be less than 20 percent
water by weight. The density of the finished biodegradable peanut is less
than 1.0 pound per cubic foot (lb./cu. ft.), with a preferred range
between 0.1-0.5 lb./cu. ft., and a most preferred range between 0.3-0.4
lb./cu. ft. However, when the product is used in other applications, the
process is adjusted to increase or decrease the density by increasing or
decreasing the percentage of expanders by weight.
This invention is illustrated by the following example which is merely for
the purpose of illustration and is not to be regarded as limiting the
scope of the invention or manner in which it may be practiced.
EXAMPLE
A biodegradable cellulosic material in the form of a shipping peanut was
prepared in accordance with the present invention. The following materials
were employed in the amounts indicated.
______________________________________
Material Quantity (in pounds)
______________________________________
newsprint (cellulose)
58.8 lbs.
wheat gluten (bonding agent)
25.0 lbs.
wheat starch (expander)
5.0 lbs.
baking powder (expander)
1.0 lbs.
corn flour (bonding agent)
30.3 lbs.
boron (fire retardant)
1.2 lbs.
______________________________________
The above quantities of ingredients were introduced directly into a
Baker-Perkins, Model No. MPF-50, twin-screw extruder, which has 50 mm
diameter bore. The cellulose material comprised shredded newsprint having
a fire retardant (boron) mixed therein. The ingredients were dry mixed
beforehand and then introduced into a mixing chamber provided in the
extruder. Water was then injected into the mix after it exited the mixing
chamber so that water comprised approximately 25 percent of the mix by
weight for activating the bonding agents for binding the particles and the
expanding agents (i.e., wheat starch and baking powder) for decreasing the
density of the product. During the course of the experiment, the extruder
was operated at temperatures between 180.degree. F. and 350.degree. F.,
and at pressures between approximately 18 to 25 psi absolute. In each
instance a satisfactory product was made. As stated previously, the
combinations of ingredients, temperatures and pressures may be varied for
obtaining a wide variety of finished product density and hardness,
depending upon the application for which the article is used.
In view of the above, it will be seen that the several objects of the
invention are achieved and other advantageous results attained.
As various changes could be made in the above constructions without
departing from the scope of the invention, it is intended that all matter
contained in the above description as shown in the accompanying drawing
shall be interpreted as illustrative and not in a limiting sense.
* * * * *
|
|
 |
|
 |
Description |
|
