Air carrier cargo Captain reported loss of pitch trim control after takeoff. The Captain returned to the departure airport. After a maintenance inspection the cause of the malfunction was suspected to be ice in the control system.

Narrative

After deicing (TYPE I&IV) application; conducted physical check at gate. Taxied to Runway XXC. Took about 12 minutes. (HOT was 2 hrs). Set icing level to 2. Took off and rotated at Vr. The aircraft started pitch up without normal back pressure and kept pitching up quicker and higher without PF (Pilot Flying) input. Yolk needed to be pushed forward to maintain normal 9 degree pitch. Pitch trim was not responding from both switches on Yolk and STBY. CCAS (Centralized Crew Alerting System) announced icing and selected level 3 at 3000 ft. Hard to maintain altitude and advised ATC to return to ILSXXC. After landing and taxing to[ramp] observed ice accumulation on many aircraft surfaces during post flight. After takeoff rotation; aircraft kept pitching up without PF input.Maintenance suspected that there was ice inside of the pitch trim system. Manually flew aircraft without pitch trim and requested to return to ILSXXC at ZZZ.Should observe all flight control surface movements from outside after deicing application.