There's not much I can offer in this area, never having been exposed to
the chemistry of adhesives.  It's a complex area, usually considered as
materials science,  something you'd pick up only if you are working in
the area of adhesives.

I know that some glues work because of reactive surface hydroxyl groups
(which may or may not be there, depending on what the surface is) which
upon drying form an oxide bond linkage with the release of a molecule
of water.

In other words, two surfaces with -OH (hydroxyl) groups come together, and
go to -O- (oxygen) upon drying, yielding an oxide bonding two surfaces
together, and H2O (water).  It's a form of condensation reaction, and at
least one of the adhesion mechanisms.  I can't say that this is how hide
glue works; I just don't know.
•
  Surface-----OH + HO------Surface (e.g. glue molecules and wood)
                   |
                   |
                   v
       Surface-----O-------Surface + H2O
•
Certainly epoxy cements work more on surface tension principles, being
able to "wet" a surface sufficiently and then form a hard bond between
them upon drying.

Sorry I can't help more, Robbie.

Frank Himpsl