Hopf algebra appears in recent papers that systematize renormalization of quantum field theory (QFT). For example see Connes' work and citing papers or a paper referenced here on PSE:
R. E. Borcherds, "Renormalization and quantum field theory"
http://arxiv.org/abs/1008.0129
This seems to be an effort that is separate from string theory, but I wonder if they are compatible. Since "compatible" is perhaps too loose of a term, I'm asking:
Why do string theory and Hopf algebra renormalization seem to have no intersection?
If the reader feels the question could be improved by rewriting, please so assist.