Lightweight particles and compositions containing them
Disclosed are particles that have an exterior surface coated with a thin polymeric coating, such as a coating that includes a sulfur-containing polymer. Also disclosed are compositions, such as fuel-resistant sealant and coating compositions, which include such particles. Aerospace vehicles having an aperture at least partially sealed with a sealant deposited from such a sealant composition are also disclosed.
1. A particle comprising an exterior surface having a coating thereon, wherein the coating comprises:
(a) a reaction product of an aminoplast resin and the exterior surface; and
(b) the reaction product of (a) and a sulfur-containing polymer wherein the sulfur-containing polymer comprises:
functional groups reactive with the aminoplast resin; and
functional groups reactive with a film forming binder, a cross-linking agent, or both a film forming binder and a cross-linking agent, wherein the sulfur-containing polymer comprises a thiol-terminated polythioether of Formula (II):
HS—R 1 —[—S—(CH 2 ) p —O—[—R 2 —O—] m —(CH 2 ) 2 —S—R 1 —]—SH (II)
wherein,
R 1 is selected from a C 2-6 n-alkylene group; a C 3-6 branched alkylene group having one or more pendent groups; a C 6-8 cycloalkylene; C 6-10 alkylcycloalkylene group; heteroatomic substituted analogs of any of the foregoing, —[(—CHR 3 —) s —O—] q —(—CHR 3 —) r —, and —[(—CHR 3 —) s —S—] q —(—CHR 3 —) r —;
each R 3 is hydrogen;
m is a rational number having a value ranging from 0 to 50;
s is an integer having a value ranging from 2 to 6;
q is an integer having a value ranging from 1 to 5; and
r is an integer having a value ranging from 2 to 10.
2. The particle of claim 1 , wherein the particle comprises a thermally expandable capsule.
3. The particle of claim 2 , wherein the thermally expandable capsule comprises a thermally expandable thermoplastic capsule.
4. The particle of claim 1 , wherein the particle comprises a polystyrene foam, a polyacrylate microsphere, a polyolefin microsphere, a silica microsphere, an alumina/silica microsphere, an aluminum silicate microsphere, a calcium carbonate-coated polyvinylidene copolymer microsphere, or a thermally expandable capsule.
5. The particle of claim 1 , wherein the coating is substantially continuous from 70 percent to 100 percent of the exterior surface.
6. The particle of claim 1 , wherein the aminoplast resin is coupled to the exterior surface of the particle prior to reaction with the compound.
7. A composition comprising:
a cross-linking agent;
a plurality of the particles of claim 1 comprising functional groups reactive with the cross-linking agent; and
a sulfur-containing polymer comprising terminal groups reactive with the cross-linking agent.
8. The composition of claim 7 , wherein the sulfur-containing polymer is selected from a polythioether, a polysulfide, a sulfur-containing polyformal, and a combination of any of the foregoing.
9. The composition of claim 7 , wherein the crosslinking agent comprises a polyepoxy.
10. The composition of claim 7 , formulated as a sealant having a specific gravity less than 1.0.
11. A cured sealant prepared from the composition of claim 10 .
12. The cured sealant of claim 11 , formulated as a sealant having a specific gravity less than 1.0.
13. The cured sealant of claim 11 , wherein the cured sealant exhibits:
a percent volume swell of not greater than 40% after immersion for one week at 140° F. (60° C.) and ambient pressure in Jet Reference Fuel Type 1;
an elongation of at least 80% when measured as described in AMS 3269a; and
a tensile strength of at least 2000 mega-Pascals when measured according to AS 5127/1a7.7.
14. A method of using the particle of claim 1 , comprising dispersing the particle in a composition comprising a sulfur-containing polymer.
15. The particle of claim 1 , wherein the functional groups reactive with a film forming binder, a cross-linking agent, or both a film forming binder and a cross-linking agent comprise thiol groups.
16. The particle of claim 1 , wherein the functional groups reactive with a cross-linking agent are selected from thiol groups, vinyl groups, isocyanate groups, amine groups, and hydroxy groups.
17. The particle of claim 1 , wherein the functional groups reactive with a film-forming binder are selected from olefinic groups, acrylate groups, and epoxy groups.
18. The particle of claim 1 , wherein between functional groups reactive are reactive with a cross-linking agent.