Narrative:

Normal take off from runway xxr at ZZZ with first officer flying. Fairly heavy B737NG at 174;000 lbs; 35;000 lbs of fuel bound for ZZZ1. At approximately 2;000 MSL I began to detect a burning or melting plastic odor; smelling identical to what a piece of tupperware that had fallen onto the heating element in a dishwasher and melted would smell like. I asked the first officer if he smelled it and he replied 'yes'. We were still sterile cockpit; but the flight attendants called from the back and were very concerned with the same odor that was 'filling the cabin.' I told them to search the cabin to see if the source of the odor could be isolated; lavatories; ovens; coffee maker etc.; and call back. We had leveled at 5;000 feet and when ZZZ departure issued us another climb; I declined the climb and told ATC we had an issue and would get back with them. At this point the first officer's audio control panel went haywire with extremely loud static being broadcast into his headset and speaker; regardless of what radio was selected and he was unable to transmit. The purser called back and said that the source of the odor could not be determined but it was strong; and she now smelled what she described as 'burning paper.' this aircraft had just returned to service after a change of the #2 engine and this was the first flight after the change. The engine in terms of performance was operating normally but the possibility of it being involved in creating this situation did give me further concern. With the combination of the unidentifiable odor and failure of communication equipment; I made the decision to [advise ATC] and return back to ZZZ.once [advised]; ATC was very efficient in getting us back around for a landing on one of the long western facing runways and things happened rapidly. We were landing overweight and I wanted a long runway for braking and winds which were quite gusty with a crosswind component. The first officer remained as the flying pilot and executed a normal approach and landing to runway xxr. Upon exiting the runway; we had fire and emergency personnel inspect the aircraft for a potential fire source. No abnormal heat source could be detected; and we returned to [the] gate without further incident.

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Original NASA ASRS Text

Title: B737NG flight crew reported a return to departure airport due to smelling a 'burning plastic' odor throughout the aircraft during initial climb.

Narrative: Normal take off from Runway XXR at ZZZ with First Officer flying. Fairly heavy B737NG at 174;000 lbs; 35;000 lbs of fuel bound for ZZZ1. At approximately 2;000 MSL I began to detect a burning or melting plastic odor; smelling identical to what a piece of Tupperware that had fallen onto the heating element in a dishwasher and melted would smell like. I asked the First Officer if he smelled it and he replied 'YES'. We were still sterile cockpit; but the flight attendants called from the back and were very concerned with the same odor that was 'filling the cabin.' I told them to search the cabin to see if the source of the odor could be isolated; lavatories; ovens; coffee maker etc.; and call back. We had leveled at 5;000 feet and when ZZZ Departure issued us another climb; I declined the climb and told ATC we had an issue and would get back with them. At this point the First Officer's audio control panel went haywire with extremely loud static being broadcast into his headset and speaker; regardless of what radio was selected and he was unable to transmit. The Purser called back and said that the source of the odor could not be determined but it was strong; and she now smelled what she described as 'burning paper.' This aircraft had just returned to service after a change of the #2 engine and this was the first flight after the change. The engine in terms of performance was operating normally but the possibility of it being involved in creating this situation did give me further concern. With the combination of the unidentifiable odor and failure of communication equipment; I made the decision to [advise ATC] and return back to ZZZ.Once [advised]; ATC was very efficient in getting us back around for a landing on one of the long western facing runways and things happened rapidly. We were landing overweight and I wanted a long runway for braking and winds which were quite gusty with a crosswind component. The First Officer remained as the Flying Pilot and executed a normal approach and landing to Runway XXR. Upon exiting the runway; we had fire and emergency personnel inspect the aircraft for a potential fire source. No abnormal heat source could be detected; and we returned to [the] gate without further incident.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.