In general:
xinput set-prop id-number "Device Enabled" 0
Specific example (if I wanted to disable my UVC Camera):
xinput set-prop 12 "Device Enabled" 0
You need to identify the id-number of the touchpad first.
Steps:
1. at the command prompt, use:
xinput list
Example output:
xinput list
⎡ Virtual core pointer id=2 [master pointer (3)]
⎜ ↳ Virtual core XTEST pointer id=4 [slave pointer (2)]
⎜ ↳ Razer Razer Ornata Chroma id=10 [slave pointer (2)]
⎜ ↳ Razer Razer Ornata Chroma id=11 [slave pointer (2)]
⎜ ↳ Logitech K330 id=13 [slave pointer (2)]
⎜ ↳ Logitech M215 2nd Gen id=14 [slave pointer (2)]
⎣ Virtual core keyboard id=3 [master keyboard (2)]
↳ Virtual core XTEST keyboard id=5 [slave keyboard (3)]
↳ Power Button id=6 [slave keyboard (3)]
↳ Power Button id=7 [slave keyboard (3)]
↳ Sleep Button id=8 [slave keyboard (3)]
↳ Razer Razer Ornata Chroma id=9 [slave keyboard (3)]
↳ UVC Camera (046d:0825) id=12 [slave keyboard (3)]
↳ Razer Razer Ornata Chroma id=15 [slave keyboard (3)]
↳ Logitech K330 id=16 [slave keyboard (3)]
From the output, determine the id of your device.