Mitigation of poly (hydroxyalkanoate) degradation in polymer compositions
By using end-capping and grafting reactions, and treating poly(hydroxyalkanoates) with end-capping agents, acid anhydrides, and peroxides, the degradation problems of polymers under heat, shear, and hydrolysis are solved, thereby improving the stability and performance of the materials.
Patent Information
- Application Number
- CN202480012993.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2023-02-15
- Filing Date
- 2024-02-14
- Publication Date
- 2025-11-07
AI Technical Summary
Poly(hydroxyalkanoates) are susceptible to degradation by heat, shear and hydrolysis at the end of their life cycle, leading to loss of material properties and regulatory issues.
A reaction mixture is formed by combining poly(hydroxyalkanoates) with a capping agent, an acid anhydride, and a peroxide, wherein the capping agent includes carbodiimide, diisocyanate, or epoxide, the acid anhydride includes maleic anhydride, and the peroxide includes lauryl peroxide, to carry out a capping and grafting reaction, preferably in an extruder or a continuous mixer.
It significantly slows down the degradation of poly(hydroxyalkanoates), improves the stability and performance of materials, and reduces sensory problems and regulatory risks.
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Abstract
Description
TECHNICAL FIELD
[0001] The present invention relates to biodegradable polymer compositions. More specifically, the present disclosure relates to biodegradable polymer compositions comprising poly(hydroxyalkanoate) wherein degradation of the poly(hydroxyalkanoate) is mitigated. BACKGROUND
[0002] Poly(hydroxyalkanoate) (PHA) is a class of polymers that are ideally biodegradable and / or compostable. As a result, products made from poly(hydroxyalkanoate) will degrade when the product reaches its end of life. However, poly(hydroxyalkanoate) is also susceptible to degradation by heat, shear, and hydrolysis in other instances outside of end of life disposal. When this occurs, the material degrades to form monomeric components of the polymer. This degradation can result in loss of material properties, organoleptic issues, and regulatory issues.
[0003] Accordingly, it is desirable to provide poly(hydroxyalkanoate) compositions wherein degradation of the poly(hydroxyalkanoate) due to heat, shear, and hydrolysis is mitigated or even eliminated, which is also an object of the present invention. SUMMARY
[0004] According to the present invention, the above and other needs are met by a method for mitigating polymer degradation in poly(hydroxyalkanoate).
[0005] In a first aspect, the present disclosure provides a method for mitigating polymer degradation in poly(hydroxyalkanoate). According to one embodiment, the method comprises a first step of combining at least one poly(hydroxyalkanoate) with an endcapping agent, at least one anhydride, and a peroxide to form a reaction mixture comprising at least 50 wt% of the at least one poly(hydroxyalkanoate), about 0.01 wt% to about 15 wt% of the endcapping agent, about 0.01 wt% to about 15 wt% of the cyclic anhydride, and about 0.01 wt% to about 0.5 wt% of the peroxide. The at least one poly(hydroxyalkanoate) in the mixture comprises carboxylic acid end groups and monomeric repeat units that are susceptible to degradation to form unsaturated carboxylic acid byproducts.
[0006] The method comprises a step of reacting the endcapping agent with the carboxylic acid end groups to form endcapping groups on the at least one poly(hydroxyalkanoate). The method also comprises a step of reacting the at least one anhydride and the peroxide with the at least one poly(hydroxyalkanoate) to graft side chains formed from the anhydride onto the at least one poly(hydroxyalkanoate). According to the present invention, the endcapping agent consists of at least one compound selected from the group consisting of carbodiimides, diisocyanates, epoxides, and mixtures thereof, and the at least one anhydride consists of cyclic or acyclic anhydrides having 3 to 40 carbon atoms.
[0007] According to certain embodiments, the at least one poly(hydroxyalkanoate) preferably has an initial weight average molecular weight of at least 10,000 Daltons, as determined by ASTM 5296-19, prior to combination with the endcapping agent and the acid anhydride. More preferably, the at least one poly(hydroxyalkanoate) has an initial weight average molecular weight of from about 20,000 Daltons to about 2,500,000 Daltons, as determined by ASTM 5296-19, prior to combination with the endcapping agent and the acid anhydride.
[0008] In certain embodiments, the at least one poly(hydroxyalkanoate) preferably includes 3-hydroxybutyrate monomer repeat units, which are prone to degradation to form crotonic acid. In some embodiments, the at least one poly(hydroxyalkanoate) preferably includes 3-hydroxyhexanoate monomer repeat units, which are prone to degradation to form hexenoic acid. In other embodiments, the at least one poly(hydroxyalkanoate) preferably includes 3-hydroxypropionate monomer repeat units, which are prone to degradation to form propenoic acid. In further embodiments, the at least one poly(hydroxyalkanoate) preferably includes 4-hydroxybutyrate monomer repeat units, which are prone to degradation to form 4-hydroxybutyric acid.
[0009] In some cases, the at least one poly(hydroxyalkanoate) includes a polyhydroxybutyrate homopolymer. In other embodiments, the at least one poly(hydroxyalkanoate) includes a poly-3-hydroxybutyrate-co-3-hydroxyvalerate. In still further embodiments, the at least one poly(hydroxyalkanoate) includes a poly-3-hydroxybutyrate-co-3-hydroxyvalerate.
[0010] According to certain embodiments, the at least one poly(hydroxyalkanoate) preferably includes from about 0.1 mole % to about 25 mole % of monomer residues of 3-hydroxyalkanoate selected from the group consisting of 3-hydroxyhexanoate, 3-hydroxyoctanoate, 3-hydroxydecanoate, and mixtures thereof.
[0011] In some embodiments, the at least one poly(hydroxyalkanoate) preferably includes a polyhydroxyalkanoate terpolymer consisting of from about 75 mole % to about 99.9 mole % of monomer residues of 3-hydroxybutyrate, from about 0.1 mole % to about 25 mole % of monomer residues of 3-hydroxyhexanoate, and from about 0.1 mole % to about 25 mole % of monomer residues of a third 3-hydroxyalkanoate selected from the group consisting of 3-hydroxyoctanoate, 3-hydroxydecanoate, and mixtures thereof.
[0012] In some embodiments, the endcapping agent preferably includes at least one carbodiimide according to Formula (I).
[0013] R 1 -N=C=N-R 2
[0014] Formula (I)
[0015] wherein R 1 and R 2 independently comprise an aliphatic or aromatic group optionally substituted with one or more heteroatoms selected from the group consisting of N, O, S, and P.
[0016] According to some embodiments, the end-capping agent preferably comprises at least one polymeric carbodiimide having a molecular weight of about 20 to about 2000 Daltons (as determined by ASTM 5296-19).
[0017] In other embodiments, the end-capping agent preferably comprises at least one diisocyanate according to Formula (II):
[0018] O=C=N-R 3 -N=C=O
[0019] Formula (II)
[0020] wherein R 3 comprises an aliphatic or aromatic group having 1 to 20 carbon atoms.
[0021] In some embodiments, the end-capping agent preferably comprises at least one aliphatic or aromatic epoxide having 2 to 200 carbon atoms.
[0022] In some cases, the end-capping agent preferably comprises at least one poly(epoxide) having a molecular weight of about 40 to about 5000 Daltons (as determined by ASTM 5296-19).
[0023] According to certain embodiments of the present disclosure, the at least one anhydride preferably comprises an aliphatic cyclic anhydride having 3 to 40 carbon atoms. In some embodiments, the at least one anhydride preferably comprises at least one cyclic anhydride selected from the group consisting of maleic anhydride, succinic anhydride, octadecenyl succinic anhydride, and mixtures thereof.
[0024] In some embodiments, the peroxide is preferably an organic peroxide. More preferably, the peroxide is selected from the group consisting of lauryl peroxide, dicumyl peroxide, and 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane.
[0025] According to certain embodiments, the reaction step is preferably performed in an extruder. In other embodiments, the reaction step is preferably performed in a continuous mixer. In some embodiments, the reaction step is preferably performed at a temperature of about 120 °C to about 200 °C.
[0026] In another embodiment, the present disclosure provides a polymeric composition consisting of at least 50 wt% of a capped and grafted poly(hydroxyalkanoate) formed according to the above-described method.
[0027] In some embodiments, the reaction of the carbodiimide with the poly(hydroxyalkanoate) is characterized by an increase in molecular weight measured by ASTM 5296-19, a decrease in acid value measured by titration with potassium hydroxide (KOH) solution, and the formation of new carbon-nitrogen bonds observed by FT-IR spectroscopy. BRIEF DESCRIPTION OF DRAWINGS
[0028] Other advantages of the present disclosure will be readily apparent from the detailed description when considered in connection with the accompanying drawings, in which:
[0029] Figure 1 is a set of FT-IR spectra of a poly(hydroxyalkanoate) reacted with a carbodiimide capping agent and a poly(hydroxyalkanoate) not reacted with a carbodiimide capping agent according to one embodiment of the present disclosure. DETAILED DESCRIPTION
[0030] The present disclosure provides methods of making biodegradable polymeric compositions comprising poly(hydroxyalkanoate) wherein the poly(hydroxyalkanoate) has improved resistance to undesirable degradation. The present disclosure also provides biodegradable polymeric compositions made according to these methods.
[0031] Poly(hydroxyalkanoate)s are susceptible to degradation by heat, shear, and hydrolysis, resulting in the degradation of the material into monomeric components of the polymer. For example, if the poly(hydroxyalkanoate) comprises 3-hydroxybutyrate monomeric repeat units, these repeat units are susceptible to degradation to form crotonic acid. If the poly(hydroxyalkanoate) comprises 3-hydroxyhexanoate monomeric repeat units, these repeat units are susceptible to degradation to form hexenoic acid. If the poly(hydroxyalkanoate) comprises 3-hydroxypropionate monomeric repeat units, these repeat units are susceptible to degradation to form acrylic acid. If the poly(hydroxyalkanoate) comprises 4-hydroxybutyrate monomeric repeat units, these repeat units are susceptible to degradation to form 4-hydroxybutyric acid.
[0032] The formation of such degradation products can result in a loss of material properties such as strength and molecular weight, organoleptic issues, and regulatory issues due to the presence of materials such as crotonic acid in the polymeric composition.
[0033] To address these difficulties, the present disclosure first provides a method of mitigating polymer degradation in poly(hydroxyalkanoates) using endcapping and grafting. According to one embodiment, the method includes at least a first step of combining at least one poly(hydroxyalkanoate) with an endcapping agent, at least one anhydride, and a peroxide to form a reaction mixture comprising at least 50 wt.% of the at least one poly(hydroxyalkanoate), from about 0.01 wt.% to about 15 wt.% of the endcapping agent, from about 0.01 wt.% to about 15 wt.% of the cyclic anhydride, and from about 0.01 wt.% to about 0.5 wt.% of the peroxide.
[0034] The method includes a step of reacting the endcapping agent with the carboxylic acid end groups to form endcapping groups on the at least one poly(hydroxyalkanoate). The method also includes a step of reacting the at least one anhydride and the peroxide with the at least one poly(hydroxyalkanoate) to graft side chains formed from the anhydride onto the at least one poly(hydroxyalkanoate). According to the present invention, the endcapping agent consists of at least one compound selected from the group consisting of carbodiimides, diisocyanates, epoxides, and mixtures thereof, and the at least one anhydride consists of cyclic or acyclic anhydrides having from 3 to 40 carbon atoms.
[0035] Various poly(hydroxyalkanoates), including homopolymers, copolymers, and terpolymers, can be endcapped according to the present invention.
[0036] For example, in certain embodiments, the at least one poly(hydroxyalkanoate) can include a polyhydroxybutyrate homopolymer.
[0037] In other embodiments, the at least one poly(hydroxyalkanoate) can include a copolymer, such as a poly-3-hydroxybutyrate-co-3-hydroxyvalerate or a poly-3-hydroxybutyrate-co-3-hydroxyvalerate. More generally, in some embodiments, the poly(hydroxyalkanoate) copolymer can comprise from about 0.1 mole % to about 25 mole % of monomeric residues of 3-hydroxyalkanoate selected from the group consisting of 3-hydroxyhexanoate, 3-hydroxyoctanoate, 3-hydroxydecanoate, and mixtures thereof.
[0038] In other embodiments, the at least one poly(hydroxyalkanoate) can include a polyhydroxyalkanoate terpolymer consisting of from about 75 mole % to about 99.9 mole % of monomeric residues of 3-hydroxybutyrate, from about 0.1 mole % to about 25 mole % of monomeric residues of 3-hydroxyhexanoate, and from about 0.1 mole % to about 25 mole % of monomeric residues of a third 3-hydroxyalkanoate selected from the group consisting of 3-hydroxyoctanoate, 3-hydroxydecanoate, and mixtures thereof.
[0039] Mixtures of two or more of the above poly(hydroxyalkanoates) can also be endcapped according to the methods of the present invention.
[0040] The at least one poly(hydroxyalkanoate) generally has an initial weight average molecular weight of at least 10,000 Daltons, as determined by ASTM 5296-19, prior to combination with the endcapping agent, acid anhydride, and peroxide. More preferably, the at least one poly(hydroxyalkanoate) has an initial weight average molecular weight of from about 20,000 Daltons to about 2,500,000 Daltons, as determined by ASTM 5296-19, prior to combination with the endcapping agent, acid anhydride, and peroxide.
[0041] With respect to the endcapping agent, the endcapping agent includes at least one compound selected from the group consisting of carbodiimides, diisocyanates, epoxides, and mixtures thereof.
[0042] For example, in certain embodiments, the endcapping agent can include at least one carbodiimide according to Formula (I)
[0043] R 1 -N=C=N-R 2
[0044] Formula (I)
[0045] In this carbodiimide, R 1 and R 2 each independently includes an aliphatic or aromatic group optionally substituted with one or more heteroatoms selected from the group consisting of N, O, S, and P. Although the overall size of this carbodiimide can vary, in some embodiments, the carbodiimide is a polycarbodiimide having a molecular weight of from about 20 to about 5000 Daltons, more preferably from about 300 to about 2000 Daltons, as determined by ASTM 5296-19.
[0046] In some embodiments, R 1 and R 2 each more preferably includes an aromatic group. An example of a suitable carbodiimide is STABAXOL P available from Lanxess AG of Germany. Although the exact composition of STABAXOL P is unknown, it is believed to include an aromatic carbodiimide in which the aromatic group is substituted with an isopropyl group.
[0047] In other embodiments, the endcapping agent can include at least one diisocyanate according to Formula (II):
[0048] O=C=N-R 3 -N=C=O
[0049] Formula (II)
[0050] wherein R 3 includes an aliphatic or aromatic group having from 1 to 20 carbon atoms.
[0051] In some embodiments, the endcapping agent preferably comprises at least one aliphatic or aromatic epoxide having from 2 to 200 carbon atoms.
[0052] In other embodiments, the endcapping agent can comprise at least one poly(epoxide) having a molecular weight of from about 40 to about 5000 Daltons, more preferably from about 500 to about 3000 Daltons, as determined by ASTM 5296-19.
[0053] As noted above, grafting is performed with an anhydride and a peroxide. Generally, the anhydride can be a cyclic or acyclic anhydride having from 3 to 40 carbon atoms. In some cases, the at least one anhydride preferably includes at least one cyclic anhydride selected from the group consisting of maleic anhydride, succinic anhydride, octadecenyl succinic anhydride, and mixtures thereof.
[0054] In some embodiments, the peroxide is preferably an organic peroxide. More preferably, the peroxide is selected from the group consisting of lauryl peroxide, dicumyl peroxide, and 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane.
[0055] Both the endcapping reaction and the anhydride grafting reaction are preferably performed at a temperature of from about 120 °C to about 200 °C, more preferably from about 130 °C to about 170 °C.
[0056] According to certain embodiments, one or both of these reaction steps are preferably performed in an extruder. In other embodiments, one or both of these reaction steps are preferably performed in a continuous mixer.
[0057] In another embodiment, the present disclosure provides a polymeric composition consisting of at least 50 wt.% of an endcapped and grafted poly(hydroxyalkanoate) formed according to the above-described method.
[0058] In certain embodiments, the grafting reaction step of the grafting method is preferably performed in an extruder. In other embodiments, the grafting reaction step is preferably performed in a continuous mixer. In some embodiments, the reaction step is preferably performed at a temperature of from about 120 °C to about 200 °C, more preferably from about 130 °C to about 170 °C.
[0059] In some embodiments, the polymer and other reactive components further include other additives including, but not limited to, nucleating agents, lubricants, other biodegradable polymers, processing aids, fillers, antioxidants, and mixtures thereof.
[0060] In other embodiments, the extent of preventing degradation / mitigating the acid is determined by the percent change in molecular weight as determined by ASTM 5296-19, the change in refractive index as determined by ASTM E1347, the change in FTIR spectrum as determined by ASTM E168-16, and the change in acid number as determined by ASTM D7253-16.
[0061] The present disclosure is further illustrated by the following embodiments:
[0062] Embodiment 1. A method for mitigating polymer degradation in a poly(hydroxyalkanoate), the method comprising:
[0063] combining at least one poly(hydroxyalkanoate) with an endcapping agent, at least one acid anhydride, and a peroxide to form a reaction mixture comprising at least 50 wt.% of the at least one poly(hydroxyalkanoate), about 0.01 wt.% to about 15 wt.% of the endcapping agent, about 0.01 wt.% to about 15 wt.% of the cyclic acid anhydride, and about 0.01 wt.% to about 0.5 wt.% of the peroxide, wherein the at least one poly(hydroxyalkanoate) comprises carboxylic acid end groups and monomeric repeat units susceptible to degradation to form unsaturated carboxylic acid byproducts;
[0064] reacting the endcapping agent with the carboxylic acid end groups to form endcapping groups on the at least one poly(hydroxyalkanoate); and
[0065] reacting the at least one acid anhydride and the peroxide with the at least one poly(hydroxyalkanoate) to graft side chains formed from the acid anhydride onto the at least one poly(hydroxyalkanoate),
[0066] wherein the endcapping agent comprises at least one compound selected from the group consisting of carbodiimides, diisocyanates, epoxides, and mixtures thereof, and
[0067] wherein the at least one acid anhydride comprises a cyclic or acyclic acid anhydride having 3 to 40 carbon atoms.
[0068] Embodiment 2. The method of embodiment 1, wherein the at least one poly(hydroxyalkanoate) has an initial weight average molecular weight of at least 10,000 Daltons as determined by ASTM 5296-19 prior to combining with the endcapping agent and the acid anhydride.
[0069] Embodiment 3. The method of embodiment 1 or 2, wherein the at least one poly(hydroxyalkanoate) has an initial weight average molecular weight of about 20,000 Daltons to about 2,500,000 Daltons as determined by ASTM 5296-19 prior to combining with the endcapping agent and the acid anhydride.
[0070] Embodiment 4. The method of any of the preceding embodiments, wherein the at least one poly(hydroxyalkanoate) comprises 3-hydroxybutyrate monomer repeat units that are prone to degradation to form crotonic acid.
[0071] Embodiment 5. The method of any of the preceding embodiments, wherein the at least one poly(hydroxyalkanoate) comprises 3-hydroxyhexanoate monomer repeat units that are prone to degradation to form hexenoic acid.
[0072] Embodiment 6. The method of any of the preceding embodiments, wherein the at least one poly(hydroxyalkanoate) comprises 3-hydroxypropionate monomer repeat units that are prone to degradation to form acrylic acid.
[0073] Embodiment 7. The method of any of the preceding embodiments, wherein the at least one poly(hydroxyalkanoate) comprises 4-hydroxybutyrate monomer repeat units that are prone to degradation to form 4-hydroxybutyric acid.
[0074] Embodiment 8. The method of any of the preceding embodiments, wherein the at least one poly(hydroxyalkanoate) comprises poly-3-hydroxybutyrate-co-3-hydroxyhexanoate (P3HB-co-P3HHx).
[0075] Embodiment 9. The method of any of the preceding embodiments, wherein the at least one poly(hydroxyalkanoate) comprises polyhydroxybutyrate homopolymer.
[0076] Embodiment 10. The method of any of the preceding embodiments, wherein the at least one poly(hydroxyalkanoate) comprises poly-3-hydroxybutyrate-co-3-hydroxyvalerate.
[0077] Embodiment 11. The method of any of the preceding embodiments, wherein the at least one poly(hydroxyalkanoate) comprises from about 0.1 mole percent to about 25 mole percent of monomeric residues of 3-hydroxyalkanoate selected from the group consisting of 3-hydroxyhexanoate, 3-hydroxyoctanoate, 3-hydroxydecanoate, and mixtures thereof.
[0078] Embodiment 12. The method of any of the preceding embodiments, wherein the at least one poly(hydroxyalkanoate) comprises a polyhydroxyalkanoate terpolymer consisting of from about 75 mole percent to about 99.9 mole percent of monomeric residues of 3-hydroxybutyrate, from about 0.1 mole percent to about 25 mole percent of monomeric residues of 3-hydroxyhexanoate, and from about 0.1 mole percent to about 25 mole percent of monomeric residues of a third 3-hydroxyalkanoate selected from the group consisting of 3-hydroxyoctanoate, 3-hydroxydecanoate, and mixtures thereof.
[0079] Embodiment 13. The method of any of the preceding embodiments, wherein the end-capping agent comprises at least one carbodiimide according to Formula (I)
[0080] R 1 -N=C=N-R 2
[0081] Formula (I)
[0082] wherein R 1 and R 2 independently comprise an aliphatic or aromatic group optionally substituted with one or more heteroatoms selected from the group consisting of N, O, S, and P.
[0083] Embodiment 14. The method of any of the preceding embodiments, wherein the end-capping agent comprises at least one polycarbodiimide having a molecular weight of about 20 to about 5000 Daltons as determined according to ASTM 5296-19.
[0084] Embodiment 15. The method of any of the preceding embodiments, wherein the end-capping agent comprises at least one diisocyanate according to Formula (II)
[0085] O=C=N-R 3 -N=C=O
[0086] Formula (II)
[0087] wherein R 3 comprises an aliphatic or aromatic group having 1 to 20 carbon atoms.
[0088] Embodiment 16. The method of any of the preceding embodiments, wherein the end-capping agent comprises at least one aliphatic or aromatic epoxide having 2 to 200 carbon atoms.
[0089] Embodiment 17. The method of any of the preceding embodiments, wherein the end-capping agent comprises at least one poly(epoxide) having a molecular weight of about 40 to about 5000 Daltons as determined by ASTM 5296-19.
[0090] Embodiment 18. The method of any of the preceding embodiments, wherein the at least one acid anhydride is an aliphatic cyclic acid anhydride having 3 to 40 carbon atoms.
[0091] Embodiment 19. The method of any of the preceding embodiments, wherein the at least one acid anhydride comprises at least one cyclic acid anhydride selected from the group consisting of maleic anhydride, succinic anhydride, octadecenyl succinic anhydride, and mixtures thereof.
[0092] Embodiment 20. The method of any of the preceding embodiments, wherein the reacting step is conducted at a temperature of about 120 °C to about 200 °C.
[0093] Embodiment 21. The method of any of the preceding embodiments, wherein the peroxide is an organic peroxide.
[0094] Embodiment 22. The method of any of the preceding embodiments, wherein the peroxide is selected from the group consisting of lauryl peroxide, dicumyl peroxide, and 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane.
[0095] Embodiment 23. The method of any of the preceding embodiments, wherein the reacting step is conducted in an extruder.
[0096] Embodiment 24. The method of any of the preceding embodiments, wherein the reacting step is conducted in a continuous mixer.
[0097] Embodiment 25. The method of any of the preceding embodiments, wherein the reacting step is conducted at a temperature of about 120 °C to about 200 °C.
[0098] Embodiment 26. A polymer composition comprising at least 50 wt% of a capped and grafted poly(hydroxyalkanoate) formed according to any of the preceding embodiments.
[0099] Examples
[0100] The following non-limiting examples illustrate various other aspects of the present application. Unless otherwise indicated, temperatures are in degrees Celsius, and percentages are weight percentages based on the dry weight of the formulation.
[0101] Example 1. A poly(hydroxyalkanoate) consisting of 94% hydroxybutyrate repeat units and 6% hydroxyhexanoate repeat units was compounded in a twin-screw extruder with 1% of a nucleating agent (pentaerythritol) at a melt temperature of about 182 °C. The resulting pellets were analyzed for molecular weight according to ASTM 5296-19. The pellets were then converted into molded plaques by injection molding, and the haze and molecular weight were measured according to ASTM E1347 and ASTM 5296-19, respectively. The percent change in molecular weight after molding was calculated, and this value was used along with the haze as a control for comparison in Table 1.
[0102] Example 2. A poly(hydroxyalkanoate) consisting of 94% hydroxybutyrate repeat units and 6% hydroxyhexanoate repeat units was added to a twin-screw extruder along with 1% nucleating agent (pentaerythritol) and 2% Stabaxol P, a commercially available carbodiimide, and compounded at a melt temperature of about 182 °C. The molecular weight of the resulting pellets was analyzed according to ASTM 5296-19. The pellets were then converted into molded plaques by injection molding, and the yellowness index was measured by both the Hunter color and the molecular weight ASTM E1347 and ASTM 5296-19, respectively. The percent change in molecular weight after molding was calculated, and this value along with the Hunter color was compared to the control (Example 1) in Table 1. The sample had a lower percent change in molecular weight and a lower yellowness index compared to the control, indicating successful acid / degradation mitigation.
[0103] Example 3. A poly(hydroxyalkanoate) consisting of 94% hydroxybutyrate repeat units and 6% hydroxyhexanoate repeat units was added to a twin-screw extruder along with 1% nucleating agent (pentaerythritol) and 0.1% dicumyl peroxide, and compounded at a melt temperature of about 182 °C. The molecular weight of the resulting pellets was analyzed according to ASTM 5296-19. The pellets were then converted into molded plaques by injection molding, and the yellowness index was measured by both the Hunter color and the molecular weight ASTM E1347 and ASTM 5296-19, respectively. The percent change in molecular weight after molding was calculated, and this value along with the Hunter color was compared to the control in Table 1. The sample had a lower percent change in molecular weight and a lower yellowness index compared to the control, indicating successful acid / degradation mitigation.
[0104] Example 4. A poly(hydroxyalkanoate) consisting of 94% hydroxybutyrate repeat units and 6% hydroxyhexanoate repeat units was added to a twin-screw extruder along with 1% nucleating agent (pentaerythritol), 0.1% dicumyl peroxide, and 2.0% succinic anhydride, and compounded at a melt temperature of about 182 °C. The molecular weight of the resulting pellets was analyzed according to ASTM 5296-19. The pellets were then converted into molded plaques by injection molding, and the yellowness index was measured by both the Hunter color and the molecular weight ASTM E1347 and ASTM 5296-19, respectively. The percent change in molecular weight after molding was calculated, and this value along with the Hunter color was compared to the control in Table 1. The sample had a lower percent change in molecular weight and a lower yellowness index compared to the control, indicating successful acid / degradation mitigation.
[0105] Example 5. A poly(hydroxyalkanoate) consisting of 94% hydroxybutyrate repeat units and 6% hydroxyhexanoate repeat units was added to a twin-screw extruder along with 1% of a nucleating agent (pentaerythritol), 0.1% of dicumyl peroxide, and 1.0% of maleic anhydride and compounded at a melt temperature of about 182 °C. The molecular weight of the resulting pellets was analyzed according to ASTM 5296-19. The pellets were then converted into molded plaques by injection molding and the yellowness index was measured by the Hunter color and molecular weight ASTM E1347 and ASTM 5296-19, respectively. The percent change in molecular weight after molding was calculated and this value was compared to the controls in Table 1 along with the Hunter color. The sample had a lower percent change in molecular weight and a lower yellowness index compared to the controls, indicating that the acid / degradation was successfully slowed.
[0106] Table 1
[0107] Sample Change in weight average molecular weight % Hunter color values Example 1 65.97％ 55.32 Example 2 17.16％ 26.12 Example 3 10.78％ 27.45 Example 4 9.28％ 27.29 Example 5 11.92％ 32.33
[0108] Example 6. A poly(hydroxyalkanoate) consisting of 94% hydroxybutyrate repeat units and 6% hydroxyhexanoate repeat units was added to a twin-screw extruder along with 1% of a nucleating agent (pentaerythritol) and 2.0% of a polycarbodiimide and compounded at a melt temperature of about 182 °C. This reaction with the polycarbodiimide was characterized by an increase in molecular weight measured by ASTM 5296-19 and a decrease in acid value from about 0.7 to 0.2 measured by titration with potassium hydroxide (KOH) solution compared to the control sample (Example 1), as shown in Table 2 below. In addition, the formation of new carbon-nitrogen (C-N) bonds captured by FT-IR spectroscopy confirmed the endcapping reaction, as shown in Table 2 below. In the FT-IR spectrum of the 2% endcapped poly(hydroxyalkanoate), a new C-N stretch appeared near 1250 cm Figure 1 -1 -1
[0109] Table 2
[0110]
[0111] The foregoing description of preferred embodiments of the present disclosure has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the present disclosure to the precise form disclosed. Obvious modifications or variations are possible in light of the above teachings. The implementations were chosen and described in order to provide the best illustration of the principles of the present disclosure and its practical application to thereby enable one of ordinary skill in the art to utilize the present disclosure in various implementations and with various modifications being suited to the particular use contemplated.
Claims
1. A method of mitigating polymer degradation in a poly(hydroxyalkanoate), the method comprising: combining at least one poly(hydroxyalkanoate) with an endcapping agent, at least one acid anhydride, and a peroxide to form a reaction mixture, the reaction mixture comprising at least 50 wt% of the at least one poly(hydroxyalkanoate), 0.01 wt% to 15 wt% of the endcapping agent, 0.01 wt% to 15 wt% of the cyclic acid anhydride, and 0.01 wt% to 0.5 wt% of the peroxide, wherein the at least one poly(hydroxyalkanoate) comprises carboxylic acid end groups and monomeric repeat units susceptible to degradation to form an unsaturated carboxylic acid byproduct; reacting the endcapping agent with the carboxylic acid end groups to form endcapping groups on the at least one poly(hydroxyalkanoate); and reacting the at least one acid anhydride and the peroxide with the at least one poly(hydroxyalkanoate) to graft side chains formed from the acid anhydride onto the at least one poly(hydroxyalkanoate), wherein the endcapping agent comprises at least one compound selected from the group consisting of carbodiimides, diisocyanates, epoxides, and mixtures thereof, and wherein the at least one acid anhydride comprises a cyclic or acyclic acid anhydride having 3 to 40 carbon atoms.
2. The method of claim 1, wherein the at least one poly(hydroxyalkanoate) has an initial weight average molecular weight of at least 10,000 Daltons as determined by ASTM 5296-19 prior to being combined with the endcapping agent and the acid anhydride.
3. The method of claim 1, wherein the at least one poly(hydroxyalkanoate) has an initial weight average molecular weight of 20,000 Daltons to 2,500,000 Daltons as determined by ASTM 5296-19 prior to being combined with the endcapping agent and the acid anhydride.
4. The method of claim 1, wherein the at least one poly(hydroxyalkanoate) comprises 3-hydroxybutyrate monomeric repeat units susceptible to degradation to form crotonic acid.
5. The method of claim 1, wherein the at least one poly(hydroxyalkanoate) comprises 3-hydroxyhexanoate monomeric repeat units susceptible to degradation to form hexenoic acid.
6. The method of claim 1, wherein the at least one poly(hydroxyalkanoate) comprises 3-hydroxypropionate monomeric repeat units susceptible to degradation to form acrylic acid.
7. The method of claim 1, wherein the at least one poly(hydroxyalkanoate) comprises 4-hydroxybutyrate monomeric repeat units susceptible to degradation to form 4-hydroxybutyric acid.
8. The method of claim 1, wherein the at least one poly(hydroxyalkanoate) comprises poly-3-hydroxybutyrate-co-3-hydroxyhexanoate (P3HB-co-P3HHx).
9. The method of claim 1, wherein the at least one poly(hydroxyalkanoate) comprises polyhydroxybutyrate homopolymer.
10. The method of claim 1, wherein the at least one poly(hydroxyalkanoate) comprises poly-3-hydroxybutyrate-co-3-hydroxyvalerate.
11. The method of claim 1, wherein the at least one poly(hydroxyalkanoate) comprises 0.1 mole % to 25 mole % of monomeric residues of 3-hydroxyalkanoate selected from the group consisting of 3-hydroxyhexanoate, 3-hydroxyoctanoate, 3-hydroxydecanoate, and mixtures thereof.
12. The method of claim 1, wherein the at least one poly(hydroxyalkanoate) comprises a polyhydroxyalkanoate terpolymer consisting of 75 mole % to 99.9 mole % of monomeric residues of 3-hydroxybutyrate, 0.1 mole % to 25 mole % of monomeric residues of 3-hydroxyhexanoate, and 0.1 mole % to 25 mole % of monomeric residues of a third 3-hydroxyalkanoate selected from the group consisting of 3-hydroxyoctanoate, 3-hydroxydecanoate, and mixtures thereof.
13. The method of claim 1, wherein the endcapping agent comprises at least one carbodiimide according to Formula (I) R 1 -N=C=N-R 2 Formula (I) wherein R 1 and R 2 independently comprise an aliphatic or aromatic group optionally substituted with one or more heteroatoms selected from the group consisting of N, O, S, and P.
14. The method of claim 1, wherein the endcapping agent comprises at least one polycarbodiimide having a molecular weight of 20 to 5000 Daltons as determined according to ASTM 5296-19.
15. The method of claim 1, wherein the endcapping agent comprises at least one diisocyanate according to Formula (II) O=C=N-R 3 -N=C=O Formula (II) wherein R 3 comprises an aliphatic or aromatic group having 1 to 20 carbon atoms.
16. The method of claim 1, wherein the endcapping agent comprises at least one aliphatic or aromatic epoxide having 2 to 200 carbon atoms.
17. The method of claim 1, wherein the endcapping agent comprises at least one poly(epoxide) having a molecular weight of 40 to 5000 Daltons as determined by ASTM 5296-19.
18. The method of claim 1, wherein the at least one anhydride is an aliphatic cyclic anhydride having 3 to 40 carbon atoms.
19. The method of claim 1, wherein the at least one anhydride comprises at least one cyclic anhydride selected from the group consisting of maleic anhydride, succinic anhydride, octadecenyl succinic anhydride, and mixtures thereof.
20. The method of claim 1, wherein the reacting step is conducted at a temperature of 120 °C to 200 °C.
21. The method of claim 1, wherein the peroxide is an organic peroxide.
22. The method of claim 1, wherein the peroxide is selected from the group consisting of lauryl peroxide, dicumyl peroxide, and 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane.
23. The method of claim 1, wherein the reacting step is conducted in an extruder.
24. The method of claim 1, wherein the reacting step is conducted in a continuous mixer.
25. The method of claim 1, wherein the reacting step is conducted at a temperature of 120 °C to 200 °C.
26. A polymer composition comprising at least 50 wt% of the end-capped and grafted poly(hydroxyalkanoate) formed according to claim 1.