Poly(3-hydroxyalkanoate) foam particles and poly(3-hydroxyalkanoate) foam molded article
Provided are poly(3-hydroxyalkanoate) foam particles in which a gel fraction of the whole foam particles is from 30 to 80% by weight and a difference in gel fraction between inside and outside of the foam particles is 25% by weight or less. Preferably, the foam particles are particles crosslinked by an organic peroxide. Preferably, the organic peroxide has a 1 hour half-life temperature of 114 to 124° C., contains a carbonate group, and is liquid at room temperature.
1. A poly(3-hydroxyalkanoate) foam particle, wherein a gel fraction of a whole foam particle is from 30 to 80% by weight, and a difference between a gel fraction inside of the foam particle and a gel fraction outside of the foam particle is 25% by weight or less.
2. The poly(3-hydroxyalkanoate) foam particle according to claim 1 , wherein a weight per piece of the foam particle is from 0.3 to 10 mg, and a length/diameter ratio of the foam particle is from 0.5 to 2.5.
3. The poly(3-hydroxyalkanoate) foam particle according to claim 1 , wherein the poly(3-hydroxyalkanoate) is at least one selected from the group consisting of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), and poly(3-hydroxybutyrate-co-4-hydroxybutyrate).
4. The poly(3-hydroxyalkanoate) foam particle according to claim 1 , wherein the poly(3-hydroxyalkanoate) is a copolymer of 3-hydroxybutyrate and a comonomer, and a 3-hydroxybutyrate/comonomer ratio in the copolymer is from 99/1 to 80/20 (mol %/mol %).
5. The poly(3-hydroxyalkanoate) foam particle according to claim 1 , wherein the poly(3-hydroxyalkanoate) is crosslinked by an organic peroxide.
6. The poly(3-hydroxyalkanoate) foam particle according to claim 5 , wherein the organic peroxide has a 1 hour half-life temperature of 114 to 124° C., contains a carbonate group, and is liquid at room temperature.
7. The poly(3-hydroxyalkanoate) foam particle according to claim 1 , wherein an apparent density of the foam particle is from 20 to 150 g/L.
8. A poly(3-hydroxyalkanoate) foam molded article produced by molding a plurality of the foam particles according to claim 1 .
9. A method for producing the foam particle according to claim 1 , the method comprising:
dispersing poly(3-hydroxyalkanoate)-containing resin particles and a crosslinking agent into water in a pressure-resistant vessel;
subsequently introducing a blowing agent into the pressure-resistant vessel and heating the contents of the pressure-resistant vessel to or above a softening temperature of the resin particles; and
subsequently opening one end of the pressure-resistant vessel to discharge the contents of the pressure-resistant vessel into a low-pressure atmosphere and thus foam the resin particles, wherein
the crosslinking agent is an organic peroxide that has a 1 hour half-life temperature of 114 to 124° C., that contains a carbonate group, and that is liquid at room temperature, and
the crosslinking agent is used in an amount of 1.2 to 5 parts by weight per 100 parts by weight of the resin particles.
10. The method according to claim 9 , wherein the organic peroxide is a compound containing one carbonate group.
11. The method according to claim 9 , wherein in the heating of the contents of the pressure-resistant vessel to or above a softening temperature of the resin particles, the contents of the pressure-resistant vessel are subjected to a temperature of 100 to 140° C.
12. The poly(3-hydroxyalkanoate) foam particle according to claim 1 , wherein the gel fraction of the whole foam particle is from 50 to 78% by weight.
13. The poly(3-hydroxyalkanoate) foam particle according to claim 1 , wherein the difference between the gel fraction inside of the foam particle and the gel fraction outside of the foam particle is 10% by weight or less.
14. The poly(3-hydroxyalkanoate) foam particle according to claim 1 , wherein the difference between the gel fraction inside of the foam particle and the gel fraction outside of the foam particle is 5% by weight or less.
15. The poly(3-hydroxyalkanoate) foam particle according to claim 1 , wherein the foam particle has a cylindrical shape.
16. The method according to claim 9 , wherein the crosslinking agent is used in an amount of 1.5 to 3 parts by weight per 100 parts by weight of the resin particles.