I haven’t been able to find an abstract for this article but JBL is widely available so have a look.
Lappenga, Benjamin J. “Misdirected Emulation and Paradoxical Zeal: Paul’s Redefinition of ‘The Good’ as Object of ζῆλος in Galatians 4:12-20. Journal of Biblical Literature. 131:4 (2012): 775-796.