Polylactic acid bioplastics

Abstract

Compositions and uses of polylactic acid biobased polymer plastic compositions are presented having increased strength and flexibility as well as improved heat tolerance relative to other biodegradable plastics. Methods of making these improved plastics are also disclosed.

Description

[0001] POLYLACTIC ACID BIOPLASTICS

[0002] CROSS REFERENCE TO RELATED APPLICATION

[0003] [1] This application claims the benefit of priority from U.S. Provisional Application No. 63 / 674,051 , hied July 22, 2024, the contents of which are herein incorporated by reference in their entirety.

[0004] FIELD

[0005] [2] The present application concerns plastics that can be aerobically composted.

[0006] BACKGROUND

[0007] [3] Most “biogenic” plastic articles are only functional with silicate fillers, such as talc. See, e.g., CN 110128806 (Zhongshan Perfect Color Resource Co.), CN 101602884 (Zhejiang Hisun Biological Material Co.), or US 2008 / 0108742 (Asahi Kasei Life Corp.). Talc provides an inexpensive solution to thermal instability issues that are common to all types of biogenic plastics. Talc is also easy to source worldwide. However, Talc has been proven to be harmful to the environment. For this reason, ecotoxicity standards like ASTM El 676- 12 that exclude silicates are currently being considered at the international level.

[0008] [4] Various attempts have been made to produce biogenic plastics without silicates, but such products do not tolerate heat stress. See, e.g., FR 3098519 (Carbiolice SAS). Thus, there remains a need for a biogenic plastic composition that can tolerate heat stress, but which does not include more than trace amounts of silicate filler.

[0009] SUMMARY

[0010] [5] Disclosed herein are plastic compositions, comprising 8-10%(w / w) compatibilizing agent e.g., polybutylene adipate-co-terephthalate or “PBAT”), approximately 50%(w / w) polylactic acid (PLA), and starch. In some aspects, the composition comprises no more than trace amounts of silicate filler (e.g. , talc). In some aspects, the starch includes cellulose with a melt-flow index (MFI) at 190°C of at least 2 g / 10 min. In some aspects, the composition comprises approximately 20%(w / w) of the cellulose. In some aspects, the plastic is 40-50% crystalline. By way of non-limiting example, the composition may consist of 21 %(w / w) cellulose with an MFI of at least 5 g / 10 min., 49%(w / w) PLA, 9%(w / w) PBAT, starch, and optionally a dye, pigment, or nacre. [6] Also disclosed herein are aspects in which the plastic is in the form of an extruded article, such as a straw, a bag, a sheet, or a table covering. Also disclosed herein are aspects in which the plastic is in the form of a molded article, such as a fork, spoon, knife, or spork. Also disclosed herein are aspects in which the plastic is in the form of a thermoformed article, such as a bowl, plate, or cup.

[0011] [7] Also disclosed herein are methods of making a plastic article, the method comprising: (a) blending approximately 30%(w / w) of a pre-compounded starch mix, approximately 20%(w / w) cellulose, and approximately 50% PLA to make pellets for extrusion, wherein the pre-compounded starch mix comprises approximately 30%(w / w) of a compatibilizing agent (e.g., PBAT) and approximately 70%(w / w) starch, and wherein the cellulose has an MFI of at least 5 g / 10 min; (b) processing the pellets by extrusion or molding in a machine to make the article; and (c) heating the article at 100-275°F until the plastic is approximately 40% to approximately 50% crystalline. In some aspects, the article is heated at 100-275°F for approximately 30 sec. to approximately 15 min e.g., 2 min. at approximately 250°F). In some aspects, the heat source is a heat lamp, a water bath, or an oven. In some aspects, the article is heated by the machine of step (b).

[0012] [8] In some aspects of these methods, the blend comprises 21%(w / w) of the cellulose. In some aspects, the blend comprises 49%(w / w) PLA.

[0013] [9] In some aspects, the method further comprises (d) extruding the pellets into a straw, a sheet, or a film. In some aspects, the method further comprises (d) thermoforming the sheet or film into a plate, a cup, or a bowl. In some aspects, the method further comprises (d) molding the pellets into tableware e.g., a fork, a knife, a spoon, or a spork).

[0014] DETAILED DESCRIPTION

[0015]

[0010] A polylactic acid (PLA) plastic composition is disclosed herein that constitutes an effectively compostable plastic to replace or reduce the use of non-renewable resources as well as the use of petroleum-based plastics. The plastic composition of crystalized PLA disclosed herein are blended with starch and a compatibilizing agent (e.g., polybutylene adipate-co-terephthalate or “PBAT”) to thereby reduce the use of non-renewable plastic fillers. Plastic articles (tableware, films, etc.) manufactured with these compostable plastics are also disclosed herein. By replacing or displacing petroleum-based polymers, the PLAs disclosed herein are capable of reducing the plastic industry’s reliance on petroleum-based plastics for the stronger and denser plastic products.

[0016] Polylactic Acid

[0017]

[0011] PLA is a thermoplastic polyester with backbone formula [-C(CH3)HC(=O)O-]n. It is usually made by condensing lactic acid [C(CH3)(0H)HC00H], with a corresponding loss of water. The PLA compositions disclosed herein have an effective hardness, strength, and flexural modulus (stiffness) that is sufficient to serve in (e.g.) disposable tableware, while being free of any petroleum-based polymers. However, in some aspects, depending on the desired properties for a plastic product, the PLA compositions disclosed herein may also be blended with one or more petroleum-based polymers to obtain a PLA composition capable of replacing a plastic product that is made of more or exclusively petroleum-based polymers.

[0018]

[0012] The PLA plastic composition of the present disclosure comprises a blend of PLA, starch (e.g. , cellulose), and a compatibilizing agent, (e.g., PBAT). The concentration of PLA in the compensation must be between 40%(w / w) and 60%(w / w), for example between 45%(w / w) and 55%(w / w), e.g., 45%(w / w), 46%(w / w), 47%(w / w), 48%(w / w), 49%(w / w), 50%(w / w), 51%(w / w), 52%(w / w), 53%(w / w), 54%(w / w), 55%(w / w), 56%(w / w), 57%(w / w), 58%(w / w), or 59%(w / w). If the PLA content is too little, the resulting plastic will be too soft, while if it is too much then the plastic will be brittle.

[0019]

[0013] In some aspects, the biobased content of the PLA composition can be measured and compared with other comparable petroleum-based compositions using the ASTM D6866 method certify the biologically derived content of bioplastics in view of the amount of carbon- 14 (14C) in the product. Biomass products can have relatively high amounts of14C, whereas exclusively petroleum-derived compositions will not have any14C.

[0020]

[0014] The PLA plastic compositions disclosed herein contain no more than trace amounts of silicate filler (e.g. , talc). For example, in some aspects the PLA plastic compositions comprise less than 100 parts per million (ppm) of silicate filler, e.g., <50 ppm, <25 ppm, <10 ppm, <8 ppm, <6 ppm, <4 ppm, or even <2 ppm.

[0021] Compatibilizer

[0022]

[0015] The PLA compositions disclosed herein require some quantity of compatibilizer lest the resulting plastic be too rigid and brittle. However, the amount required can be quite small, not exceeding 15%(w / w), for example <14%(w / w), <13%(w / w), <12%(w / w), <ll%(w / w), <10%(w / w), <9%(w / w), <8%(w / w), <7%(w / w), <6%(w / w), or <5%(w / w). By way of nonlimiting examples, suitable compatibilizers include PBAT, as well as polyethylene-grafted maleic anhydride (PE-g-MAH), PE-co-octene (PEO), and PP-based olefin block copolymers (PP-OBC).

[0023]

[0016] PBAT is a biodegradable, random copolyester of adipic acid, 1 ,4-butanediol and terephthalic acid. The structure is a random-block polymer consisting of butanediol-adipic acid and butanediol-terephthalic acid blocks. PBAT is a nucleation inhibitor, but also an excellent compatibilizer to provide flexibility. PBAT is produced by many different manufacturers and may be known by the brand names EASTAR BIO, ECOFLEX, ECOWORLD, ORIGO-BI, and WANGO. It is generally marketed as a fully biodegradable alternative to low-density polyethylene, as PBAT and low-density polyethylene have similar flexibility and resilience. PB AT can be used for many similar uses as low-density polyethylene, such as plastic bags and wraps. Where PBAT is used as the compatibilizer, one should not use more than 10%(w / w) because the nucleation inhibition effect will obstruct crystallization of the PLA.

[0024] Starch

[0025]

[0017] In addition to the PLA and compatibilizer, the PLA plastic compositions disclosed herein require additional bulk agents. Starch is an economical, biodegradable source of bulk for use in the PLA compositions of the present disclosure. In addition, PLA and cellulose are thermodynamically diphasic components — i.e., while one is molten, the other is not. This diphasic pairing facilitates nucleation of the resulting composition.

[0026]

[0018] The PLA plastic compositions disclosed herein comprise starch as the bulk that supplies most of whatever mass percent of the composition is not accounted by the PLA and the compatibilizer. Suitable starches include cellulose, as well as other starches. In order for the resulting PLA plastic composition to be of use in injection molding, the starch used must have a sufficiently high melt flow index (MFI) at 190°F. The starch used should have an MFI at 190°F of at least 2 g / 10 min., for example >3 g / 10 min., >5 g / 10 min., >10 g / 10 min., >12 g / 10 min., >15 g / 10 min., >20 g / 10 min., or even >21 g / 10 min.

[0027]

[0019] In some aspects, the PLA plastic composition comprises 15%(w / w) to 25%(w / w) (e.g. , 20%(w / w)) cellulose with an MFI at 190°F >2 g / 10 min. By way of non-limiting example, a PLA plastic composition as disclosed herein may comprise about 21%(w / w) cellulose with an MFI at 190' F >5 g / 10 min., about 49%(w / w) PLA, about 9%(w / w) PBAT, and starch. In a particular aspect, the PLA plastic composition may consist of 21%(w / w) cellulose with an MFI at 190°F >5 g / 10 min., 49%(w / w) PLA, 9%(w / w) PBAT, and starch.

[0028] Additives

[0029]

[0020] In certain aspects, the PLA plastic compositions disclosed herein may comprise various additives, such as a dye or other coloring agent, or a nacre (e.g., colored particles of any form, which may optionally be iridescent or pearlescent).

[0030]

[0021] Examples of coloring agents suitable for use in the PLA composition disclosed herein include, by way of non-limiting examples, iron-bearing pigments, copper compounds, and minerals. Examples of nacres that may be mentioned are nacre pigments such as mica titanium (i.e., mica coated with TiO ) coated with iron oxide, mica coated with bismuth oxychloride, mica titanium coated with chromium oxide, mica titanium coated with an organic colorant, and nacre pigments based on bismuth oxychloride. Suitable nacres may also include particles of mica with at least two successive layers of metal oxides and / or organic coloring substances superimposed on their surfaces.

[0031] Crystallinity

[0032]

[0022] Once the PLA plastic compositions disclosed herein have been shaped, molded, or extruded into their final shape, they must be heat treated to crystalize the PLA and harden the plastic into the finished article. The PLA plastic compositions disclosed herein should be about 35% to about 55% crystalline in their final form, for example about 40% to about 52% crystalline, for example about 48% to about 50% crystalline. Because the PLA and the starch are thermodynamically diphasic, it is possible to nucleate the plastic isothermally (z.e., solid phase to solid phase). The isothermal nucleation process increases crystallinity without melting.

[0033]

[0023] The degree of crystallinity is controlled by reducing the time of heat treatment (to achieve lower crystallinity) or increasing the time of heat treatment (to achieve higher crystallinity). Isothermal nucleation proceeds by application of a heat source at 100°F to 275°F for about 30 sec. to 15 min. In certain aspects, the isothermal nucleation proceeds for about 30 sec., about 45 sec., about 60 sec., about 90 sec., about 2 min. about 5 min., about 10 min., or about 15 min. In certain aspects, the temperature used can be about 100°F, about 110°F, about 125°F, about 150°F, about 200°F, about 225°F, or about 250°F. By way of non-limiting example, the isothermal nucleation can proceed for about 2 min. at 250°F.

[0034]

[0024] The means of heat application is not particularly limiting. Heat lamps, water baths, ovens, and molding chambers are all suitable for this purpose, along with other heat sources known to those familiar with plastic making. In some aspects, the shaped article is heated in the same machine that molded or extruded the plastic.

[0035] Methods of Making

[0036]

[0025] Disclosed herein are methods of making plastic articles with the PLA plastic compositions disclosed herein. Accordingly, the PLA, compatibilizer, starch, and optionally additives are combined according to the proportions described above and blended. The blending can be achieved by any known means and methods customary and familiar to those skilled in plastic making. By way of non-limiting example, the PLA, compatibilizer, and starch can be blended in a Farrel Pomini CP250 twin screw compounder, with a gravimetric feed, according to ordinary blending protocols. The result of the blending is pellets of PLA plastic.

[0037]

[0026] The pellets can be processed by extrusion, molding, thermoforming, or any other process for shaping plastic that is familiar to plastic makers. In certain aspects the pellets are injection molded. In certain aspects, the pellets are extruded into sheets and films. In certain aspects, the pellets are thermoformed.

[0038]

[0027] Once the plastic is shaped into the form desired, the method is completed by heating the article at a temperature from 100°F to 275°F for about 30 sec. to 15 min. until the plastic has achieved approximately 35% to 55% crystallinity (e.g., about 40% to about 52% crystallinity, or about 48% to about 50% crystallinity).

[0039] Shaping and Shaped Articles

[0040]

[0028] The PLA plastic compositions disclosed herein can be processed to recrystallize and / or reform in various shapes for various uses while taking advantage of the mechanical and chemical properties of the plastic compositions. For example, in some aspects, the PLA plastic compositions disclosed herein can be molded (e.g., injection molded) to make forks, knives (e.g., serrated knives), spoons, sporks, and other such tableware items. Additionally or alternatively, in some aspects, the PLA plastic compositions disclosed herein can be thermoformed to make cups, plates, bowls, and other such plastic dishware. Additionally or alternatively, in some aspects the PLA plastic compositions disclosed herein can be extruded into sheets or films. In some aspects, these sheets and films can be further shaped into bags, table coverings, straws, and other such useful plastic items.

[0041]

[0029] In particular aspects, the PLA composition is capable of replacing the hard petroleumbased plastic compositions as a more environmentally friendly substitute in respective products. In some aspects, the PLA plastic compositions disclosed herein have a flexural strength (MPa) of or between 45 MPa to 270 MPa. In still other aspects, the PLA composition has a flexural strength of or between 45 to 200 MPA, 45 to 150 MPa, 45 to 125 MPa, 45 to 100 MPa, 45 to 90 MPa, 45 to 85 MPa, 45 to 80, 45 to 75, 50 to 200, 50 to 150 MPa, 50 to 125 MPa, 50 to 100 MPa, 50 to 90 MPa, 50 to 85 MPa, 50 to 80 MPa, 50 to 75 MPa, 50 to 70 MPa, 60 to 200 MPa 60 to 150 MPa, 60 to 125 MPa, 60 to 100 MPa, 60 to 90 MPa, 60 to 85 MPa, 60 to 80 MPa, 60 to 75 MPa, 60 to 70 MPa, 65 to 200, 65 to 150 MPa, 65 to 125 MPa, 65 to 100 MPa, 65 to 90 MPa, 65 to 85 MPa, 65 to 80 MPa, 65 to 75 MPa, 65 to 70 MPa, 70 to 150 MPa, 70 to 125 MPa, 70 to 100 MPa, 70 to 90 MPa, 70 to 85 MPa, 70 to 80 MPa, or 70 to 75 MPa.

[0042]

[0030] Additionally or alternatively, the PLA composition may have a flexural modulus (GPa) of or between 2.0 to 7.5 GPa. In more specific aspects, the PLA composition has a flexural modulus of or between 2.0 to 6.5 GPa, 2.0 to 6.0 GPA, 2.0 to 5.5 GPa, 2.0 to 5.0 GPa, 2.0 to 4.5 GPa, 2.0 to 4.0 GPa, 2.0 to 3.5 GPa, 2.0 to 3.0 GPa, or 2.0 to 2.5 GPa.

[0043]

[0031] The PLA plastic compositions disclosed herein are advantageously resistant to heat. For example, the PLA plastic compositions dislcosed herein can safely contain foods and drinks heated to a temperature above 90°F, for example >100°F, >120°F, >140°F, >150°F, > 160°F, >180°F, >200°F, >220°F, or even 250°F and above.

[0044] Recycling, Biodegredation, & Compost

[0045]

[0032] In further advantageous aspects of the present disclosure, the PLA composition has increased recyclability and / or biodegradability. While recyclability and biodegradability can be related, they are indeed distinct properties and both are desirable for any plastic composition

[0046]

[0033] Recyclability of a plastic is the capability to break down the polymer or polymers in the plastic to a re-useable / reformable form. Accordingly, with respect to recyclability, a plastic composition that is made of one type of a biobased polymer is often more easily recyclable because it does not require separation of blended polymers.

[0047]

[0034] The PLA plastic compositions disclosed herein are advantageously biodegradable. Biodegradability may be measured using any conventional calculation. For example, aerobic compostability can be measured according to ASTM D6400-21, “Specifications for Labeling of Plastics Designed to be Aerobically Composted in Municipal or Industrial Facilities,” while anaerobic biodegradability may be measured following ASTM D5511-02 and / or ASTM D5526. More specifically, ASTM D5511-12 and ASTM D5526-12 are testing methods that comply with international standards such as the ISO DIS 15985 for the biodegradability of plastic. Accordingly, in some aspects, the PLA plastic compositions disclosed herein are effectively capable of replacing (e.g., substituting for) an exclusively petroleum-based plastic (e.g., ABS) for plastic products and has improved biodegradability compared to an exclusively petroleum-based plastic. In still further aspects, the PLA plastic compositions (1) are effectively capable of replacing an exclusively petroleum-based plastic for plastic products, (2) have improved biodegradability compared to an exclusively petroleum-based plastic, and (3) have a comparable (e.g., within 10%) flexural strength and / or flexural modulus of the exclusively petroleum-based plastic.

[0048] EXAMPLES

[0049] Example 1.

[0050]

[0035] PLA and high-flow cellulose at the proportions shown in Table 1 below were compounded in a Farrel Pomini CP250 twin screw compounder with a gravimetric feed. The PLA and high-flow cellulose were compounded into pellets with a density of 1.2415 g / mL. The extruded pellets were injection molded into test bars with cycle times averaging 44 seconds. Test bars were allowed to sit 24 hours before any testing or temperature manipulation. They were then heated in increments of 0 sec, 30sec, 1 min, 2 min, 3 min, and 4 min. at 250°F for nucleation and cooled for a minimum of 15 minutes before the initiation of any test for izod impact and heat deformation temperature. Test results are summarized in Table 1.

[0051] Table 1. Composition of plastic with 1.6 g / 10 min. MFI at 190°F

[0052]

[0036] In view of the results summarized in Table 1 above, this blend was rejected as unrealistic for manufacturing because of its low MFI and poor flexural modulus.

[0053] Example 2.

[0054]

[0037] PLA, high-flow cellulose, and methylene acrylate as a co-polymer at the proportions shown in Table 2 below were compounded as described in Example 1 above. The PLA, PBAT, and high-flow cellulose were compounded into pellets with a density of 1.2222 g / mL. The pellets were injection molded and subjected to heat stress at 250°F for testing as in Example 1. The results are summarized in Table 2.

[0055] Table 2. Composition of plastic with 0.8 g / 10 min. MFI at 190°F

[0056]

[0038] A methylene acrylate copolymer was added as a coupling agent to the Example 1 blend to improve flexural modulus. Although Example 2 saw an improvement in flexural modulus relative to Example 1 above, this blend was also rejected as unrealistic for manufacturing because of its low MFI.

[0057] Example 3.

[0058]

[0039] PLA, PBAT, and high-flow cellulose at the proportions shown in Table 3 below were compounded as described in Example 1 above. The PLA, PBAT, and high-flow cellulose were compounded into pellets with a density of 1.2429 g / mL. The pellets were injection molded and subjected to heat stress at 250°F for testing as in Example 1. The results are summarized in Table 3.

[0059] Table 3. Composition of plastic with 0.4 g / 10 min. MFI at 190°F

[0060]

[0040] Although Example 3 saw an improvement in flexural modulus relative to Example 1 above, this blend was also rejected as unrealistic for manufacturing because of its low MFI.

[0061] Example 4.

[0062]

[0041] PLA, BioBlend BC 27132, and high-flow cellulose at the proportions shown in Table 4 below were compounded in a Farrel Pomini CP250 twin screw compounder with a gravimetric feed. NuPlastiq BioBlend BC 27132 is a pre-compounded mixture of 30% polybutylene adipate- co-terephthalate (PBAT) / 70% starch blend. The PLA, PBAT, starch, and high-flow cellulose were compounded into pellets with a density of 1.2590 g / mL. The pellets were injection molded and subjected to heat stress at 250°F for testing as in Example 1. The results are summarized in Table 4.

[0063] Table 4. Composition of plastic with 21.2 g / 10 min. MFI at 190°F

[0064]

[0042] The MFI in Example 4 was much improved relative to the previous Examples. The flexural modulus was also high enough to take forward to manufacturing.

[0065]

[0043] Many more modifications besides those already described are possible without departing from the inventive concepts herein. The invention disclosed, therefore, is not to be restricted except in the spirit of the appended claims. The terms “comprises” and “comprising” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced. Where the specification or claims refer to at least one of something selected from the group consisting of A, B, C,. . . and N, the text should be interpreted as requiring only one element from the group, not A & N, or B & N, etc.

Claims

CLAIMSWhat is claimed is:

1. A plastic composition, comprising 8-10%(w / w) compatibilizing agent, approximately 50%(w / w) polylactic acid (PLA), and starch, and optionally wherein the composition comprises no more than trace amounts of silicate filler.

2. The composition of claim 1, wherein the starch includes cellulose with a melt- flow index (MFI) at 190°C of at least 2 g / 10 min.

3. The composition of claim 1 or claim 2, wherein the compatibilizing agent is polybutylene adipate-co-terephthalate (PBAT).

4. The composition of claim 2 or claim 3, wherein the composition comprises approximately 20%(w / w) of the cellulose.

5. The composition of any one of the previous claims, wherein the plastic is 40-50% crystalline.

6. The composition of any one of the previous claims, wherein the composition consists of 21%(w / w) cellulose with an MFI of at least 5 g / 10 min., 49%(w / w) PLA, 9%(w / w) PBAT, and starch.

7. The composition of any one of the previous claims, wherein the plastic is in the form of an extruded article.

8. The composition of any one of claims 1 to 6, wherein the plastic is in the form of a molded article.

9. A method of making a plastic article, the method comprising: a. blending approximately 30%(w / w) of a pre-compounded starch mix, approximately 20%(w / w) cellulose, and approximately 50% PLA to make pellets for extrusion, wherein the pre-compounded starch mix comprises approximately 30%(w / w) of a compatibilizing agent and approximately 70%(w / w) starch, and wherein the cellulose has an MFI of at least 5 g / 10 min;b. processing the pellets by extrusion or molding in a machine to make the article; and c. heating the article at 100-275°F until the plastic is approximately 40% to approximately 50% crystalline.

10. The method of claim 9, wherein the article is heated at 100-275°F for approximately 30 sec. to approximately 15 min.

11. The method of claim 9 or claim 10, wherein the heat source is a heat lamp, a water bath, or an oven.

12. The method of claim 9 or claim 10, wherein the article is heated by the machine of step (b).

13. The method of any one of claims 9 to 12, wherein the article is heated for approximately 2 min.

14. The method of any one of claims 9 to 13, wherein the article is heated at approximately 250°F.

15. The method of any one of claims 9 to 14, wherein the blend comprises 21%(w / w) of the cellulose.

16. The method of any one of claims 9 to 15, wherein the compatibilizing agent is PBAT.

17. The method of any one of claims 9 to 16, wherein the blend comprises 49%(w / w) PLA.

18. The method of any one of claims 9 to 17, wherein the pellets are extruded into a straw, a sheet, or a Him.

19. The method of claim 18, wherein the sheet or film is thermoformed into a plate, a cup, or a bowl.

20. The method of any one of claims 9 to 17, wherein the pellets are molded into tableware.

21. The method of claim 20, wherein the tableware is selected from the group consisting of a fork, a knife, and a spoon.

22. A plastic article made by the method of any one of claims 9 to 21.

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