Polylactic acid adhesive compositions and methods for their preparation and use

Patent metadata

Field	Value
Publication number	US-10442966-B2
Application number	US-201314443248-A
Country	US
Kind code	B2
Filing date	Nov 15, 2013
Priority date	Nov 15, 2012
Publication date	Oct 15, 2019
Grant date	Oct 15, 2019

Abstract

New adhesives and methods for preparing them are disclosed that include polylactic acid irradiated with gamma radiation, such as by a Co60 source. Irradiation times are used that improve the characteristics of the adhesive materials. Generally, the dose of radiation is from about 5 kGy to about 200 kGy of gamma irradiation. The adhesives generally have melting temperatures in the range of at least about 140 to about 148° C. such that they can be conveniently used in conventional glue guns and other glue equipment. The disclosed adhesives can provide bond strengths in the range of about 1,600 psi or more to about 2,500 psi or more. The disclosed adhesives can include a crosslinking agents. They can be used to join a wide range of substrates including wood, metal, plastic, ceramic, glass or combinations of substrates. They can be conveniently prepared by heating a polylactic acid (polylactic acid) preparation and mixing the molten polylactic acid with one or more crosslinkers when present. The molten mixture can then be and the polylactic acid can be irradiated with the desired dose of gamma radiation. Irradiation can occur before during or after mixing with the crosslinking agent and before or after shaping into the desired shape or even after use to join substrates. The adhesives can be used to join substrates by any known method once heated to a molten state.

First claim

The invention claimed is:

1. A method for producing an adhesive comprising melting an adhesive comprising a heated, irradiated, crosslinked polylactic acid, wherein the crosslinks are introduced by irradiation, and treating the melted adhesive at a temperature in range of about 240° C. to about 270° C. for about 10 minutes to about 100 minutes prior to use.

2. The method for producing an adhesive of claim 1 , wherein the polylactic acid is irradiated using an electron beam or an isotope.

3. The method for producing an adhesive of claim 1 , wherein the adhesive has a melting temperature in the range of about 140 to about 210° C.

4. The method for producing an adhesive of claim 1 further comprising adding a plasticizer ranging in concentration from about 0.5 wt. % to about 20 wt. %.

5. The method for producing an adhesive of claim 1 further comprising adding a plasticizer ranging in concentration from about 0.5 wt. % to about 20 wt. %, wherein the plasticizer is chosen from the group of biodegradable plasticizers consisting of di-tetrahydrofurfuryl-succinate, bis(tetrahydrofurfuryl-2-ylmethyl)butanedioate, ethoxylated aliphatic diester; and bis (2-(2-butoxyethoxy)ethyl)adipate.

6. The method for producing an adhesive of claim 1 , further comprising adding a crosslinking agent.

7. The method for producing an adhesive of claim 1 , wherein the adhesive produced is a particulate, a bead, in a spray form or in a vapor form.

8. The method for producing an adhesive of claim 1 , further comprising grinding a solid adhesive as prepared in claim 1 into a powder with a centrifugal blade impact generator to obtain a powder that can pass through a sieve having a pore size in the range of about 50 to about 1,000 microns.

9. The method for producing the adhesive of claim 1 , further comprising grinding a solid adhesive of claim 1 with a burr grinder to obtain flakes.

10. A method for filling cracks and holes in a substrate comprising obtaining an adhesive as produced in claim 1 , obtaining a substrate having a crack or hole, and applying the adhesive produced as in claim 1 to the crack or hole in the substrate.

11. The method for filling cracks and holes in a substrate of claim 10 further comprising removing the adhesive by subjecting adhesive to boiling water or by raising temperature to levels in the range of about 140° C. to about 270° C.

12. A method for joining substrates with an adhesive comprising obtaining a first substrate, heating the first substrate to a temperature in the range of 140° C. to about 260° C., applying the adhesive comprising a heated, irradiated, crosslinked polylactic acid, wherein the crosslinks are introduced by irradiation, to a surface of the first substrate, and placing a second substrate in contact with the surface of the first substrate having the applied adhesive to form a joined substrate.

13. The method for joining substrates of claim 12 , further comprising heating the adhesive of claim 1 to about 240° C. to about 270° C. for about 20 to about 75 minutes.

14. The method for joining substrates of claim 12 , wherein the applying of the adhesive is by spreading and coating of the first substrate with powdered adhesive granules having an average particle diameter in the range of about 50 to 1000 microns and heating the first substrate to about 160° C. to about 200° C.

15. The method for joining substrates of claim 12 , wherein the applying of the adhesive is by spreading and coating of the first substrate with powdered adhesive granules having an average particle diameter in the range of about 500 to 1000 microns and heating the first substrate to about 160° C. to about 200° C. with a PTFE sheet compressed overlay.

16. The method for joining substrates of claim 12 , wherein the adhesive is applied as a powdered adhesive in an aqueous slurry.

17. The method for joining substrates of claim 12 , further comprising placing the joined substrates under pressure, wherein the pressure can range from under 1 psig to over 600 psig.

18. The method for joining substrates of claim 12 , further comprising removing the adhesive by subjecting adhesive to boiling water or by raising temperature to levels in the range of about 140° C. to about 270° C.

Assignees

• Purdue Research Foundation

Inventors

• Taleyarkhan Rusi
• Bakken Alexander Charles
• Fisher Kevin F
• Hagen Alexander R
• Kostry Neal P

Classifications

• Y10T428/31794

  Of cross-linked polyester · CPC title

• B29K2067/06

  Unsaturated polyesters · CPC title

• B29C65/487

  characterised by their shape, e.g. being fibres or being spherical · CPC title

• B32B27/16

  specially treated, e.g. irradiated · CPC title

• B32B37/06

  characterised by the heating method · CPC title