I'm not sure if you're trying to do this. Here's my solution:
- Hide all lights in your scene by selecting lights and pressing H.
- Set your world to white. If there's no color selection, you may check "Use Nodes" to create nodes before you change the world color.
- Use Node Wrangler. It's a built-in plug-in. Ctrl+Alt+U to call User Preferences. Go to Addons and search "Node Wrangler", and tick it, then save user settings.
- Go to Node Editor, and build up your materials for the object. Once finished, you want to make a solo preview of your texture, so press Ctrl+Shift+LMB on an image node of your diffuse BSDF to make it solo in preview.
(The dotted line was the original line in final, but I make a solo preview of the texture, as you can see the Material Output receives input from a Viewer, followed with Image node.)
- Render, or make a viewport render, by Shift+Z.
Alternatively, You can also make screenshots in Material viewport.
Hope that helps.