You can freely build on How Stephanie Kwolek Invented the Liquid Crystal Solution for Kevlar
This patent expired in 1989. Every claim — 0 independent, 1 dependent — is now unenforceable. Anyone can use, reproduce, manufacture, sell, or offer for sale this technology without a license.
Original assignee
EI Du Pont de Nemours and Co
Patent granted
1972
Expired
1989
Forward citations
132
What this patent covers
The patent describes a chemical solution, or dope, containing specific aromatic polyamides that exhibit optical anisotropy. This means the molecules in the liquid align themselves in a structured, orderly way rather than floating randomly. When this liquid is spun into fibers, that internal order is preserved, resulting in a material with extreme tensile strength and stiffness. The patent specifically details using concentrated sulfuric acid as the solvent to achieve this unique molecular alignment.
What is now free to use
All 1 claims of US 3671542 are in the public domain. Specifically:
The 1 dependent claim add narrowing limitations and are also free.
What is NOT covered
Patent expiry frees this specific invention. Separately-patented improvements made after expiry may still be protected.
Does not cover the final solid fiber product itself, only the liquid dope composition.
Does not cover standard polymers that do not exhibit optical anisotropy in solution.
Does not cover spinning processes or mechanical equipment used to create the fibers.
Who is building on this today
DuPont remains the primary manufacturer of Kevlar, though many competitors in the high-performance fiber market, such as Teijin with their Twaron brand, utilize similar liquid-crystal spinning technologies.
Products built on expired version of this technology
Kevlar body armor
High-strength mooring lines for offshore oil rigs
Reinforcement in high-performance tires
Fiber-optic cable strength members
How to cite this patent in your documentation
EI Du Pont de Nemours and Co. US Patent 3671542. Optically anisotropic aromatic polyamide dopes. Granted 1972, expired 1989. Now in the public domain.
Note: This is a convenience citation. Consult a patent attorney for formal freedom-to-operate analysis.
PatentBrief is an educational resource and does not provide legal advice. Patent expiration information is derived from USPTO records and may not reflect continuation patents, divisional filings, or separately-patented improvements. For commercial use or production decisions, obtain a formal freedom-to-operate (FTO) opinion from a registered patent attorney.