Gluing Melamine to Melamine can be difficult and we would suggest using some form of manual fixing such as screws or dowelling to support and strengthen the joint.
A polyurethane glue such as Aquadhere Durabond super durable woodworking Glue would give best results.
This glue is a treacle/honey colour and dries to a white colour. It will foam or expand as it cures. It is best to trim or sand any excess glue off once it has cured.
To assist adhesion, we suggest sanding the melamine surfaces first.