STABILIZERS FOR POLYHYDROXYALKONOATES
A composition comprising a polyhydroxyalkonoate (PHA) and a stabilizer comprising one or more of an aliphatic carboxylic acid having a hydroxyl or thiol group, a cyclic anhydride, or a halo carboxylic acid may be formed by contacting the PHA and stabilizer and intermixing them so that the stabilizer is incorporated into the PHA to stabilize PHA. Typically, the PHA is melted, and the stabilizer added before much if any degradation (i.e., reduction of molecular weight occurs). The aliphatic carboxylic acid having a hydroxyl group may be naturally occurring and may be particularly useful for applications having human or food contact or particular environmental constraints.
1 . A composition comprising a polyhydroxyalkanoate formed from the ring opening of a lactone and a stabilizer comprising of one or more of an aliphatic carboxylic acid having a hydroxyl or thiol group, a cyclic anhydride; having a 5 member ring or a halo carboxylic acid wherein amount of the stabilizer is about 0.0001 to about 10 percent by weight or less based on the weight of the polyhydroxyalkanoate and the stabilizer.
2 . The composition of claim 1 , wherein the aliphatic carboxylic acid has at least one hydroxyl or thiol in an α, β, or γ position of a carbonyl of the aliphatic acid.
3 - 7 . (canceled)
8 . The composition of claim 1 , wherein the aliphatic carboxylic acid has 2 to 4 carboxylic acid groups.
9 . The composition of claim 8 , wherein the aliphatic carboxylic acid is comprised of at least one of: malic acid, citric acid and their thiol analogs.
10 . The composition of claim 1 , wherein the cyclic anhydride is maleic anhydride.
11 . A composition of claim 1 , wherein the halo carboxylic acid is comprised of aromatic groups.
12 . A composition of claim 1 , wherein the halo carboxylic acid is aliphatic.
13 - 14 . (canceled)
15 . The composition of claim 1 , wherein the aliphatic carboxylic acid is malic acid.
16 . The composition of claim 1 wherein the stabilizer is phthalic anhydride or a substituted phthalic anhydride.
17 . A method comprising (i) contacting a polyhydroxyalkanoate formed from the ring opening of a lactone and at least one stabilizer comprising of one or more of an aliphatic carboxylic acid having a hydroxyl or thiol group, a cyclic anhydride, and a halo carboxylic acid and
(ii) intermixing the polyhydroxyalkanoate and the stabilizer; wherein amount of the stabilizer is about 0.0001 to about 10 percent by weight or less based on the weight of the polyhydroxyalkanoate and the stabilizer.
18 . The method of claim 17 , wherein the intermixing is carried out by heating.
19 . The method of claim 17 , wherein the intermixing is aided by mechanical agitation.
20 . The method of claim 19 , wherein the intermixing is performed at least in part by solubilizing in a solvent at least one of the polyhydroxyalkanoate and stabilizer.
21 - 22 . (canceled)
23 . The method of claim 17 , wherein polyhydroxyalkanoate is comprised of a residue of a beta propiolactone or substituted beta lactone.
24 . The method of claim 23 , wherein the residue is comprised of the beta propiolactone residue.
25 - 26 . (canceled)
27 . The method of claim 17 , wherein the polyhydroxyalkanoate is a polyhydroxypropionate, polyhydroxybutyrate, copolymers or blends of these.
28 . The method of claim 17 , wherein the stabilizer is used in an amount of about 0.01 to about 5 percent by weight or less based on the weight of the polyhydroxyalkanoate and the stabilizer.
29 . The composition of claim 1 , wherein the stabilizer is used in an amount of about 0.01 to about 5 percent by weight or less based on the weight of the polyhydroxyalkanoate and the stabilizer.
30 . A composition comprising a polyhydroxyalkanoate and a stabilizer comprising of one or more of an aliphatic carboxylic acid having a hydroxyl or thiol group selected from malic acid and its thiol analogs; phthalic anhydride or a substituted phthalic anhydride or a halo carboxylic acid wherein the stabilizer is used in an amount of about 0.0001 to about 10 percent by weight or less based on the weight of the polyhydroxyalkanoate and the stabilizer.
31 . The composition of claim 30 , wherein the stabilizer is used in an amount of about 0.01 to about 5 percent by weight or less based on the weight of the polyhydroxyalkanoate and the stabilizer.