Does synthetic blend use petrochemicals?
Many do if hydrocarbons are the basics.
10W40 is just a blend oils, likely from hydrocarbons.
Synthetic liquids in the petroleum world are made by taking the hydrocarbon chain of crude and natural gas apart and rearranging thru chemical reactions
One method, Fischer-Tropsch, converts natural gas or coal into a variety of liquids such as gasoline, diesel, kerosene and aviation fuels. The Nazis uses this to generate fuels from coal to power their tanks.
The synthetic aviation fuels are particularly found useful as these synthetics, unlike fuel made from crude oil, are completely free of contaminants - jet engines love that.
Biomass can also be used to manufacture hydrocarbon and synthetic liquids.