US20070129467A1

US20070129467A1 - Bio based biodegradable polymer compositions and use of same

Info

Publication number: US20070129467A1
Application number: US11/293,517
Authority: US
Inventors: Frederic Scheer
Original assignee: Cereplast Inc
Current assignee: Cereplast Inc
Priority date: 2005-12-02
Filing date: 2005-12-02
Publication date: 2007-06-07
Also published as: EP1966308A1; WO2007063361A1

Abstract

A biodegradable polymer composition useful for manufacturing biodegradable items or articles with improved mechanical properties comprising poly(lactic acid) polymer (PLA), starch and protein material, obtainable by providing poly(lactic acid) polymer (PLA), starch and protein material in such ratios that PLA/starch blend represents at least 95% weight of the above three components and that starch represents at least 23% weight of PLA; mixing the above three components at room temperature in a controlled moisture atmosphere to afford a homogeneous mixture; subjecting the above homogeneous mixture to extrusion compounding under controlled heat, speed and pressure conditions; and drying down to a maximum of approximately 1% weight of moisture and subsequently conditioning the extruded polymeric composition.

Description

FIELD

The present invention relates to bio based, biodegradable polymer compositions comprising poly(lactic acid) and further components of natural origin which exhibit improved mechanical properties as compared to currently available similar material. In addition, the present invention also relates to products, items or articles made on the basis of said compositions.

BACKGROUND

Packaging material and disposable beakers, cups and cutlery are used nowadays widely and allow that food material may be sold and/or consumed under hygienic conditions. Such disposable materials and objects are highly estimated by the consumers and the retailers, since they may be simply disposed after use and do not have to be washed and cleaned like conventional dishes, glasses or cutlery.
Yet, the widespread and even growing use of such materials result in a mounting amount of litter produced each day. Currently, the plastic waste is either provided to garbage incinerators or accumulates in refuse dumps, with both of the above-mentioned solutions for waste disposal being associated with problems for the environment.
For preparing the above mentioned items several biodegradable polymers are already known in the state of the art and comprise materials on the basis of e.g. poly(glycolic acid), poly(epsilon-caprolactone), poly(lactic acid), and polydioxanone. The production of these polymers is, however, rather cumbersome and expensive, so that the use thereof is presently mainly restricted to high value medical applications requiring bio absorbable materials. A few biodegradable resins have been used in applications such as described above but cost has made them unaffordable by the consumers.
Thus, there is a need in the art to obviate the above problem and to provide materials, which combine the advantages of currently used plastics material and do not add to environmental pollution and, also, which remain cost and price competitive.
It has been indeed observed that even if relevant costs could be sometimes reduced significantly, e.g. so that articles manufactured on the basis of such biodegradable resins are no longer more expensive than the current equivalent plastic articles, this did not provide real incentive to consumers for replacing the traditional plastic articles or goods by the new biodegradable articles or goods which have been proposed.
U.S. Pat. No. 6,235,815 provides biodegradable polymer compositions made of mixtures of native and thermoplastic starch in relatively high proportions (ca 50% weight), poly(lactic acid) and plasticizer like polyester amide type plasticizers. It has been observed, however, that the necessity to use plasticizers does not provide the expected reductions manufacture costs.
US 2004/0034128 discloses biodegradable polylactide resin compositions comprising at least one protein like e.g. silk protein, gelatin, keratin, elastin, gluten or zein so that a polylactide, in other terms a poly(lactic acid) composition having excellent biodegradability can be obtained while maintaining good physical properties and strengths.
This document further teaches, however, that when a naturally occurring polymer such as starch is blended into the polylactide the good mechanical strength or physical properties thereof are lost and merely provides examples of blends wherein poly(lactic acid) is by far the major component, i.e. represents 95 weight % or more of the composition.
Surprisingly, duly selected blends of poly(lactic acid), starch and proteins, namely blends comprising up to ca 50 weight % of starch, when processed according to the present invention lead to biodegradable polymer material having all the desired and necessary physical or mechanical features, which does not comprise any added plasticizer and which proves cost and price competitive.
Consequently, an object of the present invention is to provide a cost and price attractive composition or article, which composition or article is degraded in a natural environment in a time period which is significantly shorter as compared to the time period required for the degradation of conventional plastic materials, such as e.g. polyethylene or polypropylene. In a controlled environment such as a composting site the composition will allow biodegradation in period of time not to exceed 180 days, one of the time requirements set by the US specification set by ASTM (ASTM 6400 D99). Moreover, such a composition should also enable production of bags, bottles or cutlery, exhibiting desired properties for the respective purpose.
These and other objects which will become apparent from the subsequent detailed description of the present invention, which provides a composition comprising poly(lactic acid), starch and protein material like e.g. gluten and which is obtainable by the process according to claim 1 and following.

SUMMARY

A composition or an article of the present invention is biodegradable when exposed to specific environmental conditions, such as composting, which will result in a loss of some properties that may be measured by standard methods appropriate to the plastic and in the application in a period of time that determines its classification. For instance composting is a managed process that controls the biological decomposition and transformation of biodegradable materials into humus-like substance called compost: the aerobic mesophilic and thermophilic degradation of organic matter to make compost; the transformation of biologically decomposable material through a controlled process of bio oxidation that proceed through mesophilic and thermophilic phases and results in the production of carbon dioxide, water, minerals, and stabilized organic matter (compost or humus) (ASTM Terminology) Consequently all main components, poly(lactic acid), starch and proteins will be degraded to small organic fragments which will create stabilized organic matter and will not introduce any hazard or heavy metals into soil.
As a result, objects made from the composition of the present invention will not contribute to a further increase of refuse dumps; on the contrary they will allow creation of organic fertilizers such as compost, while such objects simultaneously provide all advantages of disposable objects highly estimated by the consumers and producer. Objects made of a composition according to the present invention may be disposed after use, are essentially of lightweight, and have not to be transported to a location where they have to be cleaned. In particular, objects made from a composition according to the present invention provide the advantage that objects thrown away in parks or at the beach will degrade and will vanish after some time. However this invention should not be publicize as a license to litter the environment.
Moreover, a composition or an article according to the present invention can be produced completely from renewable sources. In addition, a composition according to the present invention may be adapted to various processing methods known in the art.
Also, the compositions according to the present invention provide improved mechanical properties not inherent to poly(lactic acid) and provide improvements with respect to the processability, production costs and heat or mechanical resistance along with improved flexibility and ductility.

DETAILED DESCRIPTION

The present invention relates to a biodegradable polymer compositions or articles. The term “biodegradable polymer” pertains to a degradable polymer material in which the degradation results from the action of naturally occurring microorganisms such as bacteria, fungi, and algae. A degradable polymer material is a material designed to undergo a significant change in its chemical structure under specific environmental conditions, resulting in a loss of some properties that may be measured by standard tests methods appropriate to the plastic and the application in a period of time that determines its classification. Depending on the additional components present in the composition and the dimensions of the object made from said biodegradable material, the time period required for degradation will vary and may also be controlled when desired. Generally, the time span for biodegradation will be significantly shorter than the time span required for a degradation of objects made from conventional plastic materials having the same dimensions, such as e.g. polyethylene, which have been designed to last for as long as possible. For example, cellulose and Kraft paper is to biodegrade within 83 days in a compost environment. Our formulation is to biodegrade in a shorter period of time and will pass the tests required by ASTM 6400 D99, which demand that compostable plastic or polymer material would biodegrade within less than 180 days. Articles made from e.g. PE would not degrade under normal composting conditions and PLA-based article would degrade in compost environment in weeks (about 6 to 8 weeks).
Biodegradable polymers are comprised of components which are reduced in film or fiber strength by microbial catalyzed degradation. The biodegradable polymers are reduced to monomers or short chains, which are then assimilated by the microbes. In an aerobic environment, these monomers or short chains are ultimately oxidized to CO₂, H₂O, and new cell biomass. In an anaerobic environment the monomers or short chains are ultimately oxidized to CO₂, H₂O, acetate, methane, and cell biomass. Successful biodegradation requires direct physical contact between the biodegradable polymers and the active microbial population or the enzymes produced by the active microbial population. Moreover, certain minimal physical and chemical requirements such as suitable pH, temperature, oxygen concentration, proper nutrients, and moisture level must be met (cf. U.S. Pat. No. 6,020,393).
The present invention also relates to a substantially or totally bio based biodegradable article or composition. The term “bio based” means that the major weight portion if not the whole of such an article or composition consists of naturally occurring components like starch, e.g. corn or wheat starch, i.e. a material simply extracted from their natural source without any subsequent chemical treatment; or components such poly(lactic acid) or esters thereof which results from e.g. enzymatic treatment of naturally occurring material like starch and subsequent polymerization and/or subsequent ester formation if any.
The biodegradable polymer composition according to the present invention can be obtained by means of a process which comprises
i) providing poly(lactic acid) polymer (PLA), starch and protein material in such ratios that PLA/starch blend represents min. 95% weight of the above three components and that starch represents min. 23% weight of PLA;
ii) mixing the above three components at room temperature in a controlled moisture atmosphere, to afford a homogeneous mixture;
iii) subjecting the above homogeneous mixture to extrusion compounding under controlled heat, speed and pressure conditions;
iv) drying down the extruded polymer composition to a max. of ca 1% weight of moisture and subsequently conditioning it.
The invention further provides a process for improving processability of biodegradable polymers based on poly(lactic acid) polymer (PLA), starch and protein material, which comprises subjecting said components to a process defined here above.
The invention also provides a process for manufacturing substantially or totally bio based biodegradable items or articles with improved mechanical properties which comprises subjecting the polymeric composition prepared according to the process defined here above to an operation selected from the group of forming, molding, injection, molding, extrusion, extrusion coating and thermoform extrusion.
Surprisingly, these polymer compositions show significantly improved process ability and/or physical and/or mechanical properties when compared to prior known compositions made of same or similar components but processed in a quite different way and also present in quite different respective ratios (see e.g. U.S. Pat. No. 6,235,815 and US 2004/0034128).
Preferably, the composition here above is made of mixtures wherein the protein material is gluten, still more preferably corn gluten or wheat gluten and represents from min. 1 to max. 5 weight % of the PLA/starch blend.
Proportions of starch in the PLA/starch blend, e.g. wheat starch or corn starch represent preferably from min 15 to 55 weight % of the said blend and still more preferably from min. 25 to max. 45 weight % of the said blend. Starch can be either native or thermoplastic starch.
Poly(lactic acid) may be represented by the following structure:
wherein n for example can be an integer between 10 and 250. Poly(lactic acid) can be prepared according to any method known in the state of the art. For example, poly(lactic acid) can be prepared from lactic acid and/or from one or more of D-lactide (i.e. a dilactone, or a cyclic dimer of D-lactic acid), L-lactide (i.e. a dilactone, or a cyclic dimer of L-lactic acid), meso D,L-lactide (i.e. a cyclic dimer of D-, and L-lactic acid), and racemic D,L-lactide (racemic D,L-lactide comprises a 1/1 mixture of D-, and L-lactide). The preparation of polyesters and copolyesters of lactic acid is well known in the art, such as disclosed in U.S. Pat. No. 2,012,267.
The present biodegradable polymer composition may be used for various applications and should not be restricted to those the exemplarily disclosed herein. For example, also applications in the medical field, such as e.g. for sutures, and drug release matrices, or in the agricultural industry are conceivable.
According to the invention the selected components can be first subjected to drying operations provided they do not have the required moisture yet, i.e. a max. of about 1 weight % of moisture. Moisture control is in fact critical for achieving the necessary conditions, namely to improve or increase the processability of the biopolymer material used for blending
Mixing the above components is performed at room temperature by means of standard techniques like e.g. twin screw extrusion or ball milling until achieving a fully homogenized mass. During that operation the mixture can be further blended with additional polymer material like e.g. biodegradable polyester and/ or components like polymerization initiators and, optionally, inert mineral filler like a silicate or talc. Such a mixing operation is furthermore performed in a well controlled moisture atmosphere, preferably in a way that allows keeping moisture at a max. of ca 1% weight or even lower if ever necessary.
The homogenized blend is then further mixed by means of extrusion compounding like e.g. multiple screw extrusion, which is usually run at a temperature varying from about 95° C. to about 190° C. depending on the zones of the mixing, for a period extending from about 2 minutes to about 5 minutes in most cases. The extruded mass is subsequently cooled using e.g. water bath or ice cold air current and eventually dried to the required humidity content.
The extruded polymer composition can be transformed into pellets or balls or flakes or filaments depending on the necessity of its subsequent transformation into finished goods or articles; packaging and storage are done in such a way that the required humidity level is preserved.
The extruded polymer composition can also be directly used for the subsequent transformation without any preliminary packaging or storage.
A polymer composition of the present invention may be used for the production of various articles, such as e.g. molded articles and/or extruded articles. The term “molded article” (or “extruded article”) as used in the present invention comprises articles made according to a molding process (or an extrusion process). A “molded article” (or “extruded article”) can also be part of another object, such as e.g. an insert in a container or a knife blade or fork insert in a corresponding handle.
A molded article according to the present invention comprises a biodegradable composition, which biodegradable composition comprises between about 15 and about 55% by weight of starch and 45 and about 75% by weight of poly(lactic acid) polymer. As outlined in detail before, the composition for the preparation of such molded articles can comprise in addition to the above-mentioned components mineral particles comprising at least one of magnesium and silicium.
Examples for various molded article are utensils, forks, spoons, knives, chopsticks, containers, cups, foam material products, and pots.
Articles according to the present invention made from a thermoform extrusion method are e.g. sheets for producing cups, plates and bottles and other objects, which could be outside of the food service industry.
Injection molding, blown film extrusion, profile extrusion and thermoform extrusion are processes known to a skilled person and are described for example in Modem Plastics Encyclopedia, Published by McGraw-Hill, Inc. -mid-October 1991 edition.
The present invention will be described now in detail on the basis of the following non-limiting examples given by way of an example only.

EXAMPLE 1

Various formulations have been prepared within the frame of the present invention using the components mentioned here below; respective amounts (weight percent) of each of the selected component are adjusted to the eventual use of the resulting polymer composition and to the physical and/or mechanical properties which are required.



Ingredients	Composition A	Composition B	Composition C

Starch	15-25%	15-25%	14-45%
PLA	65-75%	65-75%	55-75%
Gluten	1-5%	1-5%	1-5%
Polyester	1-5%	1-5%	1-5%
Silicate	1-5%	0	0

Ingredients	Composition D	Composition E	Composition F

Starch	15-25%	15-25%	20-55%
PLA	55-65%	65-75%	45-55%
Gluten	1-5%	1-5%	1-5%
Silicate	1-5%	0	0

“PLA” is a polymer created from Lactic Acid a three carbon organic acid: one terminal carbon atom is part of an acid or carboxyl group; the other terminal carbon atom is part of a methyl or hydrocarbon group; and a central carbon atom having an alcohol carbon group. Lactic acid exists in two optically active isometric forms. Poly-Lactic Acid is commercially available from different sources. The principal source being NatureWorks, LLC, a wholly own subsidiary of Cargill, Inc., a U.S. company.
“Gluten” is corn gluten or wheat gluten. Both can be used in the formulations. Corn gluten is preferred because of its stability and consistency. Both products are available commercially from companies such as e.g. Sigma Aldrich, Penford Co., Archer Daniel Midlands (USA).
“Polyester” is a Co-Polyester commercially available like e.g. Bio-Eastar from Eastman Chemical (USA) or Ecoflex from BASF (Germany).

EXAMPLE 2

Injection Molding Formulation
An injection molding formulation is prepared which comprises the following components:

Ingredients Composition D Composition E Composition F

Starch 15-25% 15-25% 20-55%

PLA 55-65% 65-75% 45-55%

Gluten 1-5% 1-5% 1-5%

Silicate 1-5% 0 0
The selected components (humidity max. 1 weight %) are first blended in a rotating screw mixer at room temperature to afford a homogeneous powdered mass. That mass is then subjected to further mixing, heating and pressurizing in a twin screw extruder under the following conditions:
temperature: from min. 95° C. to max. 190° C.
speed: from 125 to 300 rpm
humidity: maximum 1% weight
The extruded plasticized polymer mass is cooled by means of a water bath, then converted into pellets using a strand pelletizer or an under water pelletizer and eventually dried under vacuum until reaching again a humidity of max. 1 weight % and then packed and stored until further processing. Drying of the pellets is done using a draying conveyor combining air blowing, vacuum and extraction; such a drying step is performed within milliseconds, in any case within a max. of 3 seconds after pellets move out of the water bath.
Pellets as collected here above are then filled in a conventional injection molding device at a temperature of about 160° C. and is injected into a mold at a temperature of about 20° C. in order to obtain an injection molded utensils or other shapes.
Further examples for various molded article are utensils, forks, spoons, knives, chopsticks, containers, cups and pots.

EXAMPLE 3

Thermoform Extrusion Formulation

A thermoform extrusion formulation is prepared which comprises:

The above-mentioned compounds are mixed and subjected to twin screw extrusion as defined in Example 2. The resulting polymer material is filled in a thermoform extrusion device at a temperature of 160° C. and a sheet having a thickness between 0.1 mm to 45mm is obtained which may be used for forming cups, plates or bottles.
It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present subject matter and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims.

Claims

1. A biodegradable polymer composition useful for manufacturing biodegradable items or articles with improved mechanical properties comprising poly(lactic acid) polymer (PLA), starch and protein material, obtainable by

i) providing poly(lactic acid) polymer (PLA), starch and protein material in such ratios that PLA/starch blend represents at least 95% weight of the above three components and that starch represents at least 23% weight of PLA;

ii) mixing the above three components at room temperature in a controlled moisture atmosphere to afford a homogeneous mixture;

iii) subjecting the above homogeneous mixture to extrusion compounding under controlled heat, speed and pressure conditions; and

iv) drying down to a maximum of approximately 1% weight of moisture and subsequently conditioning the extruded polymeric composition.

2. The biodegradable polymeric composition according to claim 1 wherein the protein material is gluten and wherein it represents from 1 to 5% weight of the PLA/starch blend.

3. The biodegradable polymeric composition according to claim 1 wherein starch is either native or thermoplastic starch and wherein it represents from 15 to 55% weight of the PLA/starch blend.

4. The biodegradable polymeric composition according to claim 3 wherein starch represents from 25 to 45% weight of the PLA/starch blend.

5. The biodegradable polymer composition according to claim 1 wherein PLA, starch and the protein material are further mixed with additional components selected from the group consisting of a polymerization initiator and an inert material.

6. The biodegradable polymer composition according to claim 1 wherein the components provided in step i) are dried down to a maximum of approximately 1% weight of moisture prior mixing.

7. The biodegradable polymer composition according to claim 1 wherein the components subjected to blending and subsequent extrusion compounding are dried down to a maximum of approximately 1 weight % of moisture prior to conditioning.

8. The biodegradable polymer composition according to claim 1 wherein extrusion compounding is multiple screw extrusion performed at a temperature of about 95° C. to about 190° C. for a period of about 1 to about 10 minutes.

9. A process for manufacturing substantially or totally bio based biodegradable items or articles with improved mechanical properties which comprises subjecting a biodegradable polymer composition useful for manufacturing biodegradable items or articles with improved mechanical properties comprising poly(lactic acid) polymer (PLA), starch and protein material, obtainable by

iv) drying down to a maximum of approximately 1% weight of moisture and subsequently conditioning the extruded polymeric composition to an operation selected from the group of forming, molding, injection, molding, extrusion coating and thermoform extrusion.

10. A substantially or totally bio based biodegradable item or article with improved mechanical properties obtainable by means of the process according to claim 9.

11. An item or an article according to claim 10 which is designed to be totally degraded in a natural environment, preferably in a time period that is significantly shorter than that required for the degradation of conventional polymer or plastic materials.

12. An item or an article according to claim 10 which is designed to be in contact with food material or food products.

13. An item or an article according to claim 10 which is selected from the group consisting of utensils, food service-ware, forks, spoon, knives, chopsticks, containers, bottles, foam material products, plates and pots or films, trash bags, grocery bags, container sealing films, pipes, drinking straws, spun-bonded non-woven material and sheets.

14. A process for preparing a biodegradable polymer composition useful for manufacturing bio based biodegradable items or articles, which comprises

15. A process for improving processability of biodegradable polymers based on poly(lactic acid) polymer (PLA), starch and protein material, which comprises