There are many potential definitions of polymer processing.
One of my favorites is that given by Tadmor and Gogos
in their classic textbook: polymer processing concerns "operations
carried out on polymeric materials or systems to increase
their utility."  Personally, I prefer the use of the word
"value" in place of "utility." The goal of polymer processing
is to increase the value of the polymer or formulation.
I view polymer processing as a tool to achieve the desired
shape, properties, and performance for a polymer article.
It has broad applicability from packaging to aerospace.
1. Z. Tadmor and C.G. Gogos,
Principles of Polymer Processing,
John Wiley and Sons (1979).