Graphene nanoplatelet modified sheet molding compositions
A sheet molding compound (SMC) is provided with superior conductivity properties based on the use of graphitics. A process for exfoliation of GnP and turbostratic carbon is also provided. By exfoliating the graphitics, a reduced amount of material can confer comparable properties relative to native GnPs or turbostratic carbon thereby reducing the amount of material usage, but also reducing negative effects to the base resin formulation through inclusion of these additives. Particular utility is found in thermoset resin molding to produce articles that are amenable to electrostatic coating and other surface treatments that rely on surface conductivity and especially in the realm of vehicle body parts.
1. A thermoset molded article having a surface region and a central bulk region comprising:
a thermoset resin formulation cured to define a matrix with a shape of the article; and
a graphitic filler dispersed in the matrix, where said graphitic filler is functionalized to add covalently bonded hydrophilic moieties that promote preferential surface segregation of said graphitic filler, as opposed to homogenous dispersion through the central bulk region, where the surface region of the article has a greater concentration of said graphitic filler than the central bulk region.
2. The article of claim 1 wherein said graphitic filler is graphite nanoplatelets.
3. The article of claim 1 wherein said graphitic filler is exfoliated graphite nanoplatelets.
4. The article of claim 1 wherein said graphitic filler is turbostratic carbon.
5. The article of claim 1 further comprising a particulate filler of calcium carbonate, hollow micropheroids, or a combination thereof.
6. The article of claim 1 wherein said graphitic is present from 1 to 10 total weight percent.
7. The article of claim 1 wherein said graphitic is exfoliated and present from 0.01 to 1 total weight percent.
8. The article of claim 1 wherein the thermoset resin composition includes an unsaturated polyester or polyvinyl ester.
9. The article of claim 1 wherein the thermoset resin composition is a sheet molding composite paste.
10. The article of claim 1 wherein the surface region is adapted to receive a coating that renders the article with an automotive high gloss finish.
11. A method of electrostatically coating an article comprising:
forming an article of claim 1 ;
applying an electrical bias to the article to create a biased article;
exposing the biased article to a coating precursor having an opposing electrical charge relative to the electrical bias; and
allowing sufficient time for said coating precursor to form the electrostatic coating on the article.
12. A method for forming an exfoliated graphitic containing molded article comprising:
dispersing a graphitic in a solvent based dispersion or solution of a polyelectrolyte having a first counterion under conditions to allow said polyelectrolyte to intercalate to form a mixture;
exposing said mixture to a second counterion to form the exfoliated graphitic; and
admixing the exfoliated graphitic into a thermoset resin formulation as a graphitic filler; and
curing the thermoset resin formulation to form the thermoset molded article of claim 1 .
13. The method of claim 12 wherein said solvent is water or a majority by weight water.
14. The method of claim 12 wherein the graphitic is graphite nanoplatelets.
15. The method of claim 12 wherein said first counterion is cationic and second counterion is one or more of calcium, magnesium, or aluminum.
16. The method of claim 12 wherein said polyelectrolyte is one or more of polyacrylic acid, polyacrylates, peptides with ionic R groups, or poly(sodium 4-styrene sulfonate).
17. The method of claim 12 wherein said dispersing and said exposing occur at ambient temperature of between 10 and 25° Celsius.
18. The method of claim 12 further comprising removing said solvent.
19. The method of claim 18 wherein the exfoliated graphitic is not exposed to heating during the removing of said solvent.