A MD80 Captain reported a burning plastic smell developed after selecting engine and wing anti-ice during climb. The smell dissipated at cruise but reoccurred during descent when anti icing was reestablished.

Narrative

On departure; while climbing in icing conditions with engine and wing anti icing on; a burning plastic odor (was) present in the cockpit and cabin. We turned off galley power and cabin recirculation fan; but smell continued. Shortly after turning off engine and wing anti icing; the odor abated. We concluded that the cause was something to do with anti ice system. We called Dispatch to advise and requested a mechanic meet the flight. We returned galley power and recirculation fan to normal operation. On descent; prior to entering precipitation; flight attendants once again reported smelling the odor; and that was corroborated by the First Officer. We took initial steps of donning O2 masks and establishing communication; turned off galley power; recirculation fan and high pressure bleed off on AC packs. We declared an emergency with ATC and requested priority for the airport. I communicated with the flight attendants to keep me advised of any changes in the cabin odor and that we were getting priority handling. I gave them a 'test' briefing for a normal landing and no evacuation unless the situation deteriorated; and then I'd use the term 'easy victor.' I made a PA to the passengers to explain that we'd be getting priority handling into the airport and to not be alarmed if they see airport safety equipment around the aircraft on landing. We asked ATC to advise company and provided them with fuel on board and souls on board information. We advised ATC that we'd be maintaining 300 KTS inbound until necessary to slow for approach. Since we [encountered] ice on approach; and in consultation with QRH; we landed with flaps 28 and added 10 KTS to our minimum speeds. First Officer made a normal landing and we rolled out to end of runway where ARFF looked us over. We communicated with ARFF and all was normal; then made a PA to the passengers that we'd be taxiing to the gate and to remain seated unless otherwise advised by a uniformed crew member. We parked at the gate then released the ARFF (who had followed us); and accomplished all normal checklists; pulling the CRV Circuit Breaker. I called Dispatch to advise we were at the gate and then we briefed the mechanic and the outbound crew.