I was working on a project where I transform data, create and load a CSV for another system to process. The issue was non-conforming characters were breaking the endpoint system. I ensured that my php.ini configuration had the UTF8 character set defined as default, however the output from fputcsv() was still outputting non-UTF8 characters.
I found the a Stack Overflow conversation and saw that the fix was to issue the following definitions in the fputcsv() function.
fprintf($df, chr(0xEF).chr(0xBB).chr(0xBF)); writes file header for correct encoding.
Thanks goes to Hardy.