Biodegradable cellulosic material and process for making such material

A process for making a shaped biodegradable cellulosic article from cellulose-containing material having a water content of less than about 50 percent by weight. The process includes forming a dry mix of the material, a bonding agent and an expander. The dry mix is fed to a screw extruder and pressurized to a nominal pressure in the extruder. Water is injected into the pressurized dry mix. The wetted mixture is then extruded into a shaped article. A biodegradable product is also disclosed herein.

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.