The northbound side at Exit 164, reopened about 6 p.m.
The southbound lanes were closed for two hours but reopened around 2:40 p.m. on Monday.
Orange County officials told ABC11 that the tractor hauling two trailers was carrying resin, paper and rolls of cloth.
Investigators say the truck hit a mattress which sparked a fire that moved to the truck's first trailer.
Once the highly-explosive resin was consumed by the fire, firefighters moved in to extinguish the rest of the fire, which was still burning the load of paper and cloth.
A camera from the North Carolina Department of Transportation showed the vehicle erupting into flames.
The explosion and resin spill led to evacuations of businesses within 1,000 feet. The closures were a precaution because of the high-density vapors.
I-85 closed in both directions in Orange County due to truck fire
Two firefighters from the Efland Fire Department were injured when they took off gear that had resin on it, Hillsborough officials said in a news release.
The truck driver was not injured.
"Secure your loads," deputy Fire Chief Mac Cabe said. "If you lose something on the interstate, it's dangerous."