Lignin poly(lactic acid) copolymers
Provided herein are graft co-polymers of lignin and poly(lactic acid) (lignin-g-PLA copolymer), thermoset and thermoplastic polymers including them, methods of preparing these polymers, and articles of manufacture including such polymers.
1. A process of preparing a graft polymer comprising lignin and poly(lactic acid) (lignin-g-PLA copolymer), the process comprising reacting a lignin with a lactide and an organic base to provide the lignin-g-PLA copolymer, wherein the organic base is of formula:
wherein
m is 0, 1, 2, or 3; n is 0, 1, 2, or 3; and R 1 is C 1 -C 6 alkyl optionally substituted with 1-3 hydroxy, aryl, or C 1 -C 6 alkoxy groups.
2. The process of claim 1 , which is performed in the absence of a Lewis acid metal catalyst.
3. The process of claim 1 , wherein the lactide is D-lactide, L-lactide, DL-lactide, or a mixture of 2 or more thereof.
4. The process of claim 1 , which is performed at about 100° C. to about 140° C.
5. The process of claim 1 , where the lignin-g-PLA copolymer comprises by weight about 1% to about 50% lignin.
6. The process of claim 1 , wherein the lignin-g-PLA copolymer has a number average molecular weight of about 1000 Da to about 100,000 Da.
7. The process of claim 1 , wherein the poly(lactic acid) chain length on the lignin-g-PLA copolymer has a degree of polymerization of about 2 to about 240.
8. The process of claim 1 , further comprising reacting the lignin with a second co-monomer selected from caprolactone and other cyclic lactone and carbonate monomers.
9. The process of claim 1 , wherein the lignin-g-PLA copolymer comprises about 0.15-about 1.10 mmole/g of aliphatic hydroxy groups.
10. The process of claim 1 , wherein the lignin is partially acylated, and the lignin-g-PLA copolymer comprises about 0.1-about 0.2 mmole/g of aliphatic hydroxy groups.
11. The process of claim 1 , further comprising reacting the lignin-g-PLA copolymer with a crosslinker to provide a thermoset polymer.
12. The process of claim 11 , wherein the crosslinker is of formula OCN-L-NCO, wherein L is a C 2 -C 20 alkylene or heteroalkylene optionally substituted with 1-5 C 1 -C 6 alkyl groups, or L is a bivalent aromatic group or a linker containing a bivalent aromatic group.
13. The process of claim 12 , wherein L is selected from —(CH 2 ) 6 —, di-epoxides and polyanhydrides.
14. The lignin-g-PLA copolymer prepared by the process of claim 1 .
15. The thermoset polymer prepared by the process of claim 11 .
16. The lignin-g-PLA copolymer of claim 14 admixed to form a blend with a thermoplastic polymer.
17. An article of manufacture comprising the lignin-g-PLA copolymer of claim 14 which is:
a packaging material for light-sensitive products, ornamental flowers, and plants;
a mobile phone case;
a mulch film for weed control, increased soil temperature, and moisture retention;
an ultraviolet blocking material for sunglasses and windows;
a colorant or a coating material for paper;
an ultraviolet-resistant roof shingle, tile, or container;
a coating material; or
an adhesive.
18. The process of claim 1 , wherein the lignin is partially acetylated.
19. The process of claim 1 , wherein the lignin is partially acylated, and the lignin-g-PLA copolymer comprises up to about 0.1 mmole/g of COOH groups.