Assuming this is the plastic pressure, this would not necessarily cause machine damage. This will consume a large amount of energy and create a large amount of shear during recovery. The potential for material and additive degradation may be high depending on the material being processed. 

You may wish to consider a new screw designed specifically to address the complication you are encountering during recovery. For instance you may need a longer transition zone if the shear is necessary for melting, or you may need a mixing element in the metering zone if the back pressure is used for additive mixing.

This may be  great application for a shot-pot style of molding machine. This would allow a properly designed material-specific screw to be used to melt and convey the material while a plunger is used to inject the melted polymer.

-Andy