| United States Patent |
5,496,895 |
|
Chinnaswamy
, et al.
|
March 5, 1996
|
Biodegradable polymers
Abstract
To prepare a biodegradable plastic, biodegradable materials such as
starches and a non-biodegradable polymer such as a polystyrene,
polyurethane, polyethylene, polypropylene, or polycarbonate are treated:
(1) under heat, pressure and reagents to break the polymers; and (2) by
adding to them an oxidizing agent. This treatment forms and/or makes
available reactive groups for bonding: (1) on the biodegradable material
groups such as aldehyde or hydroxyl groups in the case of the
carbohydrates and amine groups in the case of proteins and certain other
compounds such as urea; and (2) on the non-biodegradable plastic groups
such as aldehydes, methyl, propyl, ethyl, benzyl or hyroxyl groups. In one
embodiment, plastic and starch are processed in an extruder by: (1) mixing
a starch in a range of between 15 percent and 80 percent, an oxidizing
agent and an agent to break up the starch and the plastics; and (2)
subjecting the combination to sufficient heat and/or pressure to break the
plastic into shorter chains and bond monosaccharides to monomers from the
non-biodegradable polymer.
| Inventors: |
Chinnaswamy; Rangaswamy (Lincoln, NE), Hanna; Milford A. (Lincoln, NE) |
| Assignee: |
The Board of Regents of the University of Nebraska
(Lincoln,
NE)
|
| Appl. No.:
|
07/942,132 |
| Filed:
|
September 8, 1992 |
Related U.S. Patent Documents
| | | | | |
|
| Application Number | Filing Date | Patent Number | Issue Date | |
| | 393373 | Aug., 1989 | | | |
|
|
| Current U.S. Class: |
525/54.2 ; 525/326.1; 525/374; 525/379; 525/380; 525/382; 525/54.3; 527/300 |
| Current International Class: |
C08L
3/00 (20060101); C08L 89/00 (20060101); C08F
8/00 (20060101); C08L 101/00 (20060101); C08L
3/10 (20060101); C08G 063/48 (); C08G 063/91 (); C08F
008/00 (); C08F 032/00 () |
| Field of Search: |
525/54.2,54.3,326.1,374,379,380,382 527/300
|
References Cited [Referenced By]
U.S. Patent Documents
Primary Examiner: Nutter; Nathan M.
Attorney, Agent or Firm: Carney; Vincent L.
Parent Case Text
This application is a continuation of application Ser. No. 07/393,373,
filed Aug. 14, 1989, now abandoned.
Claims
What is claimed is:
1.
A biodegradable polymer comprising polymeric chains that include both
monosaccharides from a starch feedstock and hydrocarbon monomers from a
feedstock non-biodegradable
plastic covalently bound to each other in ratios by weight of between
15 and 80 percent monosaccharide from starch feedstock to hydrocarbon
from the feedstock non-biodegradable plastic, wherein at least some of
the monosaccharides are bound by covalent
bonds within the hydrocarbon chain of the biodegradable polymer.
2. A method of making a biodegradable polymer comprising the
steps of: combining a carbohydrate and a non-biodegradable polymer with
material that breaks up the carbohydrate and causing a reaction under
heat and pressure which substitutes at
least some monosaccharide groups from the carbohydrate into the
non-biodegradable polymer chain wherein the percentage by weight of
substituted carbohydrate to non-biodegradable polymer is between 15 to
80 percent.
3. A process according to claim 2 wherein the non-biodegradable polymer is a polystyrene and the carbohydrate is a starch.
4. A method of making a biodegradable polymer comprising the
steps of: combining a carbohydrate and non-biodegradable polymer with
material that breaks up he carbohydrate and causing a reaction under
heat and pressure which substitutes at least
some monosaccharide groups from the carbohydrate into the
non-biodegradable polymer chain wherein the percentage by weight of
substituted carbohydrate to non-biodegradable polymer is between 15 to
80 percent;
the non-biodegradable polymer is a polystyrene and the carbohydrate is a starch;
the combination is injection molded in a dispersion pressurized
reactor; the carbohydrate to polystyrene ratio is 60 percent to 40
percent and includes 10 to 20 grams of citric acid and sodium
bicarbonate and is extrusion processed at a
temperature of substantially 140 degrees Centigrade and a pressure of
approximately 20 mega-Pascals.
Description
BACKGROUND OF THE INVENTION
This invention relates to biodegradable polymers and to methods
of making them from non-biodegradable polymers such as petroleum -based
plastics combined with other biodegradable polymers, such as for
example, carbohydrates, proteins, lipids or
the like.
It is known to alter polymers such as petroleum-based plastics
by the incorporation of some carbohydrates to increase their
biodegradability. One prior art biodegradable polymer and method of
making it is disclosed in U.S. Pat. No. 4,016,117
to Griffin, issued Apr. 5, 1977. In this product, a synthetic resin
incorporates particles of biodegradable substances and an
auto-oxidizable substance. The processing preserves the starch granules
in the final product. This polymer, when it contacts
a transition metallic salt, auto-oxidizes to generate a peroxide or a
hydroperoxide.
Other biodegradable products are disclosed in U.S. Pat. Nos.
4,405,731 to Carter issued Sep. 20, 1983; 3,778,392 to Hughes issued
Dec. 11, 1973; 3,949,145 to Otey et al. issued Apr. 6, 1979; and
4,280,920 to Kesting.
The biodegradable plastics disclosed in these United States
patents have the disadvantages of only containing from approximately 5
percent to 15 percent carbohydrate while retaining its characteristics
as a plastic although they may have up to 50
percent starch but become paperlike at such high levels and lose the
typical characteristics of thermoplastic or thermosetting plastics. The
altered structure reduces the elasticity and shear strength.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide a novel biodegradable polymer.
It is a further object of the invention to provide a novel process for making biodegradable polymers.
It is a still further object of the invention to provide a
novel biodegradable polymer in which a carbohydrate or protein or
possibly lipids may be substituted in percentages between 15 percent
and 80 percent while preserving a substantial number
of the desirable properties of the polymer.
It is a still further object of the invention to make a novel
biodegradable polymer using a process which causes chemical
modification of a carbohydrate or protein or possibly lipids or urea
and a non-biodegradable polymer to make a biodegradable
polymer.
It is a still further object of the invention to provide a
novel biodegradable plastic and process for incorporating carbohydrates
or proteins or possibly lipids into polystyrene, polyurethane,
polyethylene, polypropylene, or polycarbonate
plastics in quantities greater than 15 percent while preserving many of
the functional characteristics of the plastic.
It is a still further object of the invention to provide a novel foam plastic product and method of making it.
It is a still further object of the invention to provide a novel film plastic product and method of making it.
In accordance with the above and further objects of the
invention, a biodegradable polymer is provided having polymeric chains
that include both hydrocarbon monomers from a non-biodegradable polymer
and other biodegradable groups such as
monosaccharides or amino acids or the like that render the polymer
biodegradable. In these polymers, the biodegradable groups and
hydrocarbon monomers are bonded or interconnected by single and/or
double bond covalent linkages, hydrocarbon or bridge
bonds, Van der Waals' forces or the like to each other. The
biodegradable groups may be obtained from carbohydrates, proteins,
lipids, urea or other materials that can result in groups that combine
with the hydrocarbon monomers from the plastic while
retaining biodegradability.
In preparing the biodegradable plastic, the biodegradable
group and a non-biodegradable polymer such as a polystyrene,
polyurethane, polyethylene, polypropylene, or polycarbonate are
treated: (1) under heat, pressure and reagents to break the
polymers; and (2) by adding to them an oxidizing agent. This treatment
forms and/or makes available reactive groups for bonding: (1) on the
biodegradable material such as aldehyde or hydroxyl groups in the case
of the carbohydrates and amine groups in
the case of proteins and certain other compounds such as urea; and (2)
on the non-biodegradable polymers such as aldehydes, methyl, propyl,
ethyl, benzyl or hyroxyl groups.
In one embodiment, the non-biodegradable polymer is treated
by: (1) adding to it a carbohydrate in a range of between 15 percent
and 80 percent, an oxidizing agent and an agent to break up the starch
or similar carbohydrates; and (2) subjecting
the combination to sufficient heat and/or pressure to break the polymer
into shorter chains and bond monosaccharides to monomers from the
non-biodegradable polymer.
In one example of this embodiment, the non-biodegradable
polymer is polystyrene, the oxidizing agent is citric acid and the
substance for degrading the starch is sodium bicarbonate. The heat and
pressure is provided by extruding the combination
at high temperatures to form a biodegradable foam plastic in which the
sodium bicarbonate and citric acid: (1) release carbon dioxide as a
foaming agent; (2) oxidize the methyl groups of the styrene to form
groups such as aldehyde groups which react with
groups on the starch; and (3) form sodium hydroxide to degrade the
starch and thus to form aldehydes such as formaldehyde or hydroxyl
groups to react with the styrene. Similarly, proteins can be degraded
to amino acids or aldehyde compounds having
reactive amine or carboxyl groups to react with the hydroxyl or
aldehyde groups of the oxidized carbohydrate.
As can be understood from the above description, the
biodegradable polymer of this invention and the method of making it
have several advantages, such as for example: (1) the biodegradable
polymer retains its physical characteristics with a large
percentage of carbohydrate added or protein or other biodegradable
material; (2) the biodegradable polymer effectively degrades when
discarded; (3) the process permits the inclusion of a large amount of
carbohydrate; and (4) the biodegradable polymer is
less expensive than other biodegradable polymers.
DETAILED DESCRIPTION
A carbohydrate, protein or lipid substituted biodegradable
polymer or other substituted biodegradable polymer such as a urea
substituted biodegradable polymer includes a polymeric chain including
both hydrocarbon monomers such as alkyne and
alkene polymers derived from petroleum and biodegradable monomers, such
as amino acids or monosaccharides or lipids, preferably obtained from
agricultural products, such as wheat or corn, in a molecule. The
hydrocarbon monomers and monosaccharides or
amino acids or other such groups are covalently bound to each other.
More specifically, the monosaccharides or amino groups or
carboxyl groups of lipids are bound in groups or chains of units or as
a single monomer side-chains or branches of the feedstock to
hydrocarbon polymers and/or within the hydrocarbon chain
to pairs of monomers such as glucose, styrene, ethylene, benzyl, acetyl
(for lipids) and amino acids. The monosaccharide, amino or carboxyl
groups or group are bonded to hydrocarbon monomers from the feedstock
non-biodegradable polymer and similarly the
hydrocarbon monomers from the feedstock non-biodegradable polymer may
be connected as single monomers to monosaccharides or amino acids or
the like or be bonded as chains of hydrocarbon monomers. The different
types of monomers are distributed
throughout the polymer molecules of the biodegradable polymer. The
monomers originating from the petroleum based polymer and from the
biodgradable carbohydrate, protein, lipid or urea may be interconnected
by single and/or double bond covalent linkages,
hydrocarbon or bridge bonds, Van der Waals' forces or the like but most
commonly by covalent bonds.
The biodegradable polymers are prepared by a high-temperature
short-time, high-shear extrusion process in which one or more
biodegradable material such as carbohydrate or protein or lipid or urea
or the like and one or more non-biodegradable
polymer such as petroleum based plastics are mixed with an oxidizing
agent and a mild acid or alkali that breaks the biodegradable polymer
into chains of between 1,000 to 100,000 daltons or approximately 500 to
50,000 monosaccharide groups in the case of
starch or other carbohydrates or the equivalent length in proteins or
lipids.
The non-biodegradable polymer may be any alkyne or alkene
chain with a substituted methyl and/or other functional groups such as
ethene, ethyne, propylene, propyne, butadiene and the like groups on
plastics such as polystyrene, polyurethane,
polyethylene, polypropylene, and polycarbonate among others. The
proportion of amino acid or carbohydrate to non-degradable polymer w/w
(weight to weight) is between 15 and 80 percent carbohydrate or amino
acid and the carbohydrate, protein or starch
should have a chain length greater than 1,000 daltons.
Suitable compounds that degrade the carbohydrates include
sodium hydroxide, citric acid, sodium chloride, sodium bisulfite, urea,
acrylic acid, acrylonitrile, adipic acid, aluminum trichloride, amino
resins, analeic acid, phthalic acid,
azo-bis-isobutyronitrile, berleculite, benzoyl peroxide, bisphenol A,
boron triflouride, butadiene, casein, cellophate, acetate, butyrate,
triacetate, tanthate, chloroprenyl, decamelhylene glycol, diethyl
maleate, diethyl phthalate, ethylene glycol,
propylene glycol, epichlorohydrin, epoxy resins, ethane, ethylene,
ethylene oxide, formaldehyde, fumaric acid, glycerol, hemomethylene
diamine, hexamine, isobutene, isobutylene, melamine, methacrylic acid,
methyl vinyl acetone, polyehylene terephthalate,
phenol, polyamides, potassium amide, sebacoyl chloride, sodium
napthalide, styrene, titanium tetrachloride, vinyl chloride, vinyl
sulphonic acid, zieglar catalyst.
Compounds for degrading carbohydrates are known in the art and
differ from each other in their reactions with starch in known ways.
Instead of a compound that degrades carbohydrates, compounds that form
such carbohydrate-degrading compounds,
such as sodium bicarbonate and citric acid, may also be used.
In manufacturing one suitable biodegradable polymer, a
carbohydrate such as starch and non-biodegradable polymer are combined
in a range of weight-to-weight ratios from approximately 4 parts
non-biodegradable polymer to one part carbohydrates at
one end to one part non-biodegradable polymer to two parts carbohydrate
at the other end of the range and with 1 to 10 percent each of an
oxidizing agent and carbohydrate degrader, and in some embodiments, a
foaming agent, The combination is subjected to
heat at a selected temperature falling within the range of 110 to 180
degrees Centigrade and a selected pressure falling within the range of
3 to 55 mega-Pascals.
As a result of this process, the carbohydrate molecules
degrade and then react with the non-biodegradable polymer molecules to
form a new polymer having interconnected chemical groups from the
carbohyrate and from the original non-biodegradable
polymer. The reaction under these conditions is believed to be as shown
in equation 1.
In the reaction of equation 1: MS indicates any monosaccharide
or amino or lipid group; R1 is any group attached to the alkyl group of
a monomer of the non-biodegradable polymer; and M is any unit or
monomer of the basic feedstock
non-biodegradable polymer.
In equation 2, there is shown a general reaction between a
carbohydrate and a non-biodegradable petroleum-based polymer. In this
equation, L represents any carbohydrate monomer, M is a monomer of the
non-biodegradable polymer such as
polystyrene, polyethylene or the like and R1, R2, R3 are any other
hydrocarbon group such as for example any acetyl, methyl, propyl, butyl
or the like. Proteins or amino acids and probably lipids may be
substituted into non-biodegradable polymers to
further increase the degradability.
For example, as shown in equation 4 a protein or amino acid,
shown as P with connected reactive groups, can react with polystyrene
or other non-biodegradable polymer have n monomers to obtain the
biodegradable polymer and as shown in equation 5,
a lipid, shown as F with a reactant group is combined with a
non-biodegradable polymer having n monomers M ##STR1## and a reactive
group R1 or R2 either of which may be a carboxyl group to obtain a
biodegradable polymer.
In this specification, the term "non-biodegradable" means a
material, which when incubated at room temperature and 50 percent
humidity for a time period of two months, shows no substantial growth
of bacteria or fungi nor an increase of less than
a multiple of 4 in bacteria or fungi if the initial product already
contained some growth. It should suffer less than 50 percent loss of
its integrity and physical strength by conversion of the polymer to
carbon dioxide and lower molecular weight
hydrcarbons within six months in a landfill. In this specification, the
term "biodegradable material" means that after incubation at a moisture
of 50 percent at room temperature for two months, the material is
substantially degraded and has lost its
mechanical strength or, if it has not reached that stage, that there
has been an increase in microbial growth on the material of at least
four times the starting growth. It should loose at least 50 percent of
its physical integrity and strength within
six months in a landfill.
Also biodegradable polymer in this specification includes
those polymers that are ##STR2## degradable through a process by which
fungi or bacteria secretes enzymes to convert a complex molecular
structure of the compound to simple gasses and
organic compounds and compounds capable of decomposing or deteriorating
through a natural chemical process into harmless components after
exposure to natural elements for not more than one year.
In the preferred embodiment, a starch based biodegradable
polymer is prepared by a high-temperature short-time, high shear
extrusion processes. Starch and polystyrene are combined in a ratio of
60 percent to 40 percent and with 1 to 10 percent
each of citric acid and sodium bicarbonate when extrusion-cooked at a
temperature of 140 decrees Centigrade and a pressure of approximately
20 mega-Pascals.
The starch molecules degrade and then react with polystyrene
molecules to form a network. The citric acid controls the molecular
degradation and interactions. The sodium bicarbonate decomposes to NaOH
and CO.sub.2. The NaOH degrades the starch
molecules and the CO.sub.2 contributes to the uniform foam structure of
the product. A reaction under these conditions is believed to be
illustrated as shown in equation 3 in which the left-hand top formula
is that of a polystyrene, the top right
formula is that of a starch and the bottom formula is the formula of
the new biodegradable polystyrene.
The process of choice appears to be high-temperature
short-time extrusion. This process, including the steps for forming
containers is described in "Foam, Extruded Polystyrene", Encyclopedia
of Packaging Technology by Bakker, copyright 1986,
published by John Wiley & Sons, Inc, N.Y. N.Y., USA, page 345, the
disclosure of which is incorporated herein by reference. However,
techniques such as thermosetting, injection molding and dispersion
pressurized reactors may also provide satisfactory
reaction conditions to form a similar starch-polystyrene network.
The resultant product may find use as meat trays, cups, egg
cartons, plates, bowls, loose-fill packaging materials, insulation and
sound proofing materials. In other words, it can be used in areas where
expanded plastics are currently being
used. Moreover, other plastic products such as bottles and wrapping
materials, may be made using corresponding non-biodegradable plastics
as a feedstock. For some uses a rodenticide or repellant and an
insecticide or repellant or antimicrobial agents
may be included.
The invention is illustrated by the following examples:
EXAMPLES
GENERAL
The temperatures and pressures in the examples are applied
during extrusion of the combination of ingredients. The starch in the
actual examples was obtained from corn and wheat but can also be
obtained from sorghum, potato, rice and tapioca.
EXAMPLE 1
Wheat starch and polystyrene are mixed in a ratio of 66 percent
wheat starch by weight to 27 percent polystyrene and combined with 3
percent c acid and 6 percent sodium bicarbonate. They are
extrusion-cooked at a temperature of 140 degrees
Centigrade and a pressure of approximately 20 mega-Pascals.
The resulting product has the appearance of the original expanded polystyrene.
EXAMPLE 2
Wheat starch and polystyrene are mixed in a ratio of 38.1
percent wheat starch by weight to 57.1 percent polystyrene and combined
with 1.6 percent citric acid and 3.2 percent sodium bicarbonate. They
are extrusion-cooked at a temperature of 140
degrees Centigrade and a pressure of approximately 20 mega-Pascals.
The resulting product has the appearance of the original expanded polystyrene.
EXAMPLE 3
Wheat starch and polystyrene are mixed in a ratio of 52.9
percent wheat starch by weight to 35.3 percent polystyrene and combined
with 4.4 percent citric acid and 7.4 percent sodium bicarbonate. They
are extrusion-cooked at a temperature of 140
degrees Centigrade and a pressure of approximately 20 mega-Pascals.
The resulting product has the appearance of the original expanded polystyrene.
EXAMPLE 4
Wheat starch and polystyrene are mixed in a ratio of 23.4
percent wheat starch by weight to 70.3 percent polystyrene and combined
with 1.6 percent citric acid and 4.7 percent sodium bicarbonate. They
are extrusion-cooked at a temperature of 140
degrees Centigrade and a pressure of approximately 20 mega-Pascals.
The resulting product has the appearance of the original expanded polystyrene.
EXAMPLE 5
One percent milk protein and 20 percent corn starch and/or
wheat starch are combined with 79 percent polystryene, 1.6 percent
citric acid and 4.7 percent sodium bicarbonate. They are
extrusion-cooked at a temperature of 140 degrees Centigrade
and a pressure of approximately 20 mega-Pascals.
The resulting product has the appearance of the original expanded polystyrene.
EXAMPLE 6
One percent wheat protein (isolated) and 20 percent corn starch
and/or wheat starch are combined with 79 percent polystryene combined
with 1.6 percent citric acid and 4.7 percent sodium bicarbonate. They
are extrusion-cooked at a temperature of
140 degrees Centigrade and a pressure of approximately 20 mega-Pascals.
The resulting product has the appearance of the original expanded polystyrene.
As can be understood from the above description, the
biodegradable polymer of this invention and the method of making it
have several advantages, such as for example: (1) the biodegradable
polymer is less expensive than other biodegradable
polymers; (2) the biodegradable polymer retains its physical
characteristics with a large percentage of carbohydrate added; (3) the
biodegradable polymer effectively degrades when discarded; and (4) the
process permits the inclusion of a larger amount of
carbohydrate.
Although a preferred embodiment of the invention has been
described with some particularity, many modification and variations in
the preferred embodiment may be made without deviating from the
invention. Accordingly, it is to understood that,
within the scope of the appended claims, the invention may be practiced
other than as specifically described.
* * * * *
