INJECTION MOLDED BIODEGRADABLE STARCH POLYMER COMPOSITE

Abstract: An injection moldable biodegradable plastic formed of corn starch and low-density polyethylene. Ethylene acrylic acid co-polymer can be included in proportions ranging from 0-10 % by weight, and sodium hydroxide can be utilized to neutralize the acidic portions of the ethylene acrylic acid co-polymer. When no ethylene acrylic acid co-polymer is utilized, glycerol is added. To improve injection molding characteristics, the ethylene acrylic acid co-polymer and polyethylene are premixed before the addition of corn starch.

Description: INJECTION MOLDED BIODEGRADABLE STARCH POLYMER COMPOSITE BACKGROUND OF THE INVENTION This invention relates generally to biodegradable plastics and in particular to biodegradable plastics containing starch- Plastics, despite their many advantages, have one particular drawback that becomes more evident with each passing year, i.e.. the long-lasting quality of most plastics in common use makes safe and inexpensive disposal of discarded plastic goods difficult and problematic. This is particularly true of plastic goods, such as food product containers and wrappers, which are discarded after a single use. Although some plastics will, when left exposed to nature, undergo photodegradation or biodegradation, the rate of such degradation is often so slow that, for all practical purposes, the plastics seem to last forever. To combat these disposal problems, biodegradable plastics containing starch have been developed. Such starch- based biodegradable plastics are shown, for example, in U.S. Patents No. 4,337,181, No. 4,133,784 and No. 3,949,145, which issued to Otey, et al., on June 29, 2982, January 9, 1979 and April 6, 1976, respectively. These patents are incorporated by reference herein. Typically, such starch-based biodegradable plastics are produced by combining a starch with a water dis- persible plasticizer such as glycerol, or with a water dis- persible ethylene acrylic acid (EAA) co-polymer, in the presence of heat. To improve the qualities of the resulting plastic when formed into a blown film, polyethylene (PE) can also be combined with the starch, and ammonia, in either its anhydrous or aqueous form, can be added to neutralize part or all of the acidic portion of the EAA co-polymer. As set forth in one or more of the previously incorporated Otey patents, acceptable levels of EAA co-polymer are in the range of at least 10% and a maximum of 90% (dry weight), with the preferred amount being in the range of about 30-70%, depending upon the proportion of PE. Despite the improved qualities of current starch-based biodegradable plastics, some drawbacks still remain. EAA co¬ polymer is expensive, and thus EAA co-polymer adds substantially to the cost of the resulting plastic. EAA is also a metal adhesive and produces processing problems for injection molding machines. Ammonia-based neutralizers are subject to strict environmental regulation, require special handling during the manufacturing process and can impart a distinctive odor to the plastic, thereby rendering it unfit for certain applications, such as food product packaging. Finally, the emphasis in the past has been on biodegradable plastics suitable for the manu¬ facture of blown films, with little substantive work directed to injection molded products. In view of the foregoing, it is a general object of the present invention to provide a new and improved biodegrad¬ able starch-based plastic and method for producing the same. It is a further object of the present invention to provide a new and improved biodegradable starch-based plastic which can be manufactured with economy. It is a still further object of the present invention to provide a new and improved biodegradable starch-based plastic which is free of any distinctive odor making the material suit¬ able for food product packaging. It is a still further object of the present invention to provide a new and improved biodegradable starch-based plastic which is well adapted for injection molding. SUMMARY OF THE INVENTION In one form of the invention there is provided a bio¬ degradable injection moldable plastic, consisting essentially of corn starch, low density polyethylene, ammonium hydroxide and glycerol. The invention also provides an injection moldable bio¬ degradable plastic consisting essentially of corn starch, low density polyethylene, EAA co-polymer, and glycerol, the ethylene acrylic acid comprising less than 10% of the injection moldable biodegradable plastic. The invention also provides an improvement in a method for forming an injection moldable biodegradable plastic includ¬ ing corn starch, polyethylene and EAA co-polymer, the improve¬ ment comprising the step of neutralizing the acidic portion of the EAA co-polymer through addition of sodium hydroxide. The invention also provides a biodegradable injection moldable plastic consisting essentially of EAA co-polymer, low density polyethelene, urea and a corn starch sleeted from the group consisting of low percentage oxidate (such as 0.5% to 3%, preferably 1%) corn starch and acid modified corn starch. The invention also provides a method of forming an injection moldable biodegradable plastic comprising the steps of premixing a quantity of ethylene acrylic acid co-polymer with a quantity of polyethylene, adding to the premixed ethylene acrylic acid co-polymer and the polyethylene a quantity of starch and sodium hydroxide and adding and mixing with the ethylene acrylic acid co-polymer, the polyethylene, the starch and the sodium hydroxide. The invention also provides a method of forming an injection moldable biodegradable plastic comprising the steps of premixing a quantity of ethylene acrylic acid co-polymer with a quantity of polyethylene and adding to the premixed polyethylene and the ethylene acrylic acid co-polymer, a quantity of starch. The invention also provides a method of forming an injection moldable biodegradable plastic comprising the steps of premixing a quantity of corn starch and sodium hydroxide, adding to said premixed corn starch and sodium hydroxide a quantity of EAA co-polymer, and maintaining the temperature of the corn starch, the sodium hydroxide and the EAA co-polymer between approximately 160° F and 200° F during mixing. DETAILED DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION The present invention provides starch-based biodegrad¬ able plastics which are well suited for injection molding. As used herein, plastics which are "well suited for injection molding" are those which provide good fill and packing of the mold cavity, and avoid poor ejection or sticking to the mold, while exhibiting good biodegradability. In accordance with one aspect of the invention, the starch-based plastics of the present invention display improved injection molding charac¬ teristics and retained biodegradability at EAA co-polymer levels below 10% (dry weight) and at starch contents as high as about 80%. The plastics of the present inventions typically include various types of modified and unmodified corn starches in combination with one or more of low-density polyethylene (LDPE) , ethylene acrylic acid (EAA) co-polymer, glycerol and urea. Various additives can be included to improve the injec¬ tion molding characteristics of the resulting plastic, and either ammonium hydroxide (NH OH) or sodium hydroxide (NaOH) can be added to neutralize the acidic portion of the EAA co-polymer. In accordance with one aspect of the invention, EAA co-polymer levels between 0% and 10% (weight) can be utilized to achieve successful injection moldable biodegradable plastics. In those formulations containing no EAA co-polymer, corn starch and polyethylene are typically combined with glycerol as a plasticizer. Ammonium hydroxide can be added as a neutralizer, and a commercially available release agent (such as PEG 3350 from Harwich Company) can be added to improve ejection and avoid sticking to the molds. Preferably, in those formulations utilizing no EAA co-polymer, the corn starch and polyethylene are combined in substantially a one to one ratio, and the glycerol comprises approximately 0.2% by weight of the result¬ ing mixture. The ammonium hydroxide and the release agent preferably comprise 1% and 0.5%, respectively, of the resulting combination. In those formulations where EAA co-polymer is present in proportions less than 10%, the corn starch and low-density polyethylene are again preferably present in substantially a one to one ratio. EAA co-polymer and glycerol are also present and the quantities of each are such that the EAA co-polymer and the glycerol together comprise approximately 10% (by weight) of the resulting mixture. A monostearate can also be included, and preferably, the proportion of -the monostearate is roughly 3.0%. To avoid the previously cited problems associated with the use of ammonium hydroxide as a neutralizer for the acidic portion of the EAA co-polymer, sodium hydroxide is preferably utilized as a neutralizer. When so utilized, the corn starch and sodium hydroxide are preferably mixed together prior to the addition of the remaining ingredients. In addition, the tem¬ perature during mixing is kept relatively low, preferably in the range of 160° to 200° F. To further improve the thermal stability of the injec¬ tion moldable plastics described herein, a low percentage, preferably 1%, oxidate corn starch can be used. Alternatively, acid modified corn starch can be utilized to improve thermal stability. In accordance with another aspect of the present invention, beneficial results can be obtained by premixing the EAA co-polymer with the polyethylene and then adding corn starch as a next step. When sodium hydroxide is used as a neutralizer, a preferred blending sequence is to mix the poly¬ ethylene and EAA co-polymer for approximately one minute, thereafter to add the corn starch and sodium hydroxide and continuing mixing, and finally to add the selected release agent when mixing is about completed, approximately two and one-half to three and one-half minutes following the initial blending of the polyethylene and EAA co-polymer. In the examples that follow, initial compounding of all ingredients, unless otherwise indicated, was performed using Banbury produced batch mixtures. The resulting mixtures were next extruded using Killion and Brabender extruders. Following extrusion, the extrudates were pelletized, and the resulting pellets were injected molded in a Newbury injection molding unit. These examples are meant to be illustrative of the inventions and not limiting the scope thereof. EXAMPLE 1 In a Banbury batch mixer, 107.75 grams of corn starch (common pearl), 107.75 grams of low-density polyethylene (USI-3404), 16 grams of ethylene acrylic acid co-polymer (Dow-3460), 10.75 grams of glycerol, 7.5 grams of monostearate (Hobag 150-s) and 4.6 ml of NH.OH were combined. Mixing continued for a minimum of five minutes with a jacket tempera¬ ture of 200° Farenheit and a weight of 40-95 Psi. The mix was then extruded into strands on a Brabender plasti-corder using a mixing screw operating at 30 to 100 rpm with a mixture tempera¬ ture of 125° to 150° C. The strands were then pelletized using a Wiley mill and the pellets were injection molded on a Newbury 50-ton injection molding machine. This produced six satisfactory plaques. Some surface blotching occurred and was thought to be a result of starch on the surface. EXAMPLE 2 The following items were combined in the Banbury batch mixer in the proportions indicated: CORN STARCH 49.1% 122.9 grams LDPE 49.1% 122.9 grams NH 4 OH 1.0% 2.5 ml. Release Agent .5% 1.2 Glycerol .2% .6 These items were compounded for five minutes at a weight of 45-95 psi. The resulting compound was then cut into small pieces and then extruded on the Killion extruder at a speed of 140 rpm, with a zone 1 temperature of 150° C and a zone 2 temperature of 175°C. The resulting pellets were found to be suitable for injection molding carried out thereafter. EXAMPLE 3 In the Banbury mixer were combined the following items in the proportions indicated: CORN STARCH (1% oxidate-330-b) 100 parts per hundred resin (phr) EAA (5901) 62.5 (phr) LDPE (340b) 62.5 (phr) Urea(5319) 25 (phr) The resulting mix was extruded on the Brabender extruder and the extrudate was pelletized. The pelletized extrudate was then molded on the Newbury injection molder at 310° F and 700 psi back pressure. This produced a good plague showing few if any signs of thermal degradation. EXAMPLE 4 The following items, in the following proportions, were combined, extruded and injection molded in accordance with the process set forth in Example 3. Corn Starch (220-b acid modified) 100 phr EAA (5981) 62.5 phr LDPE (3404b) 62.5 phr Urea (5319) 25 phr Although problems were encountered with respect to mold release, the use of modified starch did, however, exhibit improved thermal stability. EXAMPLE 5 In the Banbury mixer, 140 grams of corn starch (un¬ modified) were combined with 6 grams of NaOH and mixed for one minute. Thereafter, 140 grams of LDPE (3404b), 35 grams of EAA co-polymer (5981), and 7 grams of peg 3350 as a release agent were added to the premixed corn starch and NaOH. The tempera¬ ture was kept between 160° - 205° F during compounding. The resulting mix did not discolor, released well and showed little gasing during injection molding. EXAMPLE 6 24.4 grams of LDPE (3404b) were combined with 5.4 grams of EAA co-polymer (5981) and were mixed for approximately one minute. Thereafter, 24.4 grams of unmodified corn starch and 2.7 grams of NaOH were added to the combined LDPE and EAA co-polymer. Mixing continued for additional one and one-half minutes where upon 0.48 grams of PEG 350, as a release agent, were added.

Claims: WHAT IS CLAIMED IS: 1. A biodegradable injection moldable plastic, con¬ sisting essentially of corn starch, IDW density polyethylene, ammonium hydroxide and glycerol. 2. An injection moldable biodegradable plastic con¬ sisting essentially of: corn starch; low density polyethylene; EAA co-polymer; and glycerol; said ethylene acrylic acid comprising less than 10% of said injection moldable biodegradable plastic. 3. An injection moldable biodegradable plastic as defined in Claim 2 further consisting of a monostearate and ammonium hydroxide. 4. In a method for forming an injection moldable biodegradable plastic including corn starch, polyethylene and EAA co-polymer, the improvement comprising the step of neutral¬ izing the acidic portion of the EAA co-polymer through addition of sodium hydroxide. 5. A method as defined in Claim 4 wherein the quantity of said sodium hydroxide is substantially 5% of the amount of said EAA co-polymer. 6. A method as defined in Claim 4 wherein the EAA co-polymer comprises less than 10% of the injection moldable biodegradable plastic. 7. A biodegradable injection moldable plastic con¬ sisting essentially of EAA co-polymer, low density polyethelene, urea and a corn starch sleeted from the group consisting of 1% oxidate corn starch and acid modified corn starch. 8. A method of forming an injection moldable bio¬ degradable plastic comprising the steps of: premixing a quantity of ethylene acrylic acid co-polymer with a quantity of polyethylene; adding to said premixed ethylene acrylic acid co-polymer and said polyethylene a quantity of starch and sodium hydroxide; and adding and mixing with said ethylene acrylic acid co-polymer, said polyethylene, said F rch and said sodium hydroxide. 9. A method of forming an injection moldable bio¬ degradable plastic comprising the steps of: premixing a quantity of ethylene acrylic acid co-polymer with a quantity of polyethylene; and adding to said premixed polyethylene and said ethylene acrylic acid co-polymer, a quantity of starch. 10. A method of forming an injection moldable bio¬ degradable plastic comprising the steps of: premixing a quantity of corn starch and sodium hydroxide; adding to said premixed corn starch and sodium hydroxide a quantity of EAA co polymer; and maintaining the temperature of said corn starch, said sodium hydroxide and said EAA co-polymer between substan¬ tially 160° F and 200° F during mixing.

Inventors: OELSCHLAEGER PETER, WILLETT JULIOS, WOOL RICHARD P, OELSCHLAEGER, PETER, WILLETT, JULIOS, WOOL, RICHARD, P.
Applicants: AGRI TECH IND INC, AGRI-TECH INDUSTRIES, INC.
Application year: 1990
Main classification: C08L3
IPC codes: B29C45, C08L3, C08L23