How can you see graphene when blended with polymer? All you get is the diffraction pattern from the polymer or the coated metal surface. Your graphene has been actually coated with polymer and deeply buried under the layers of hydrocarbon.
Graphene oxide does not have sharp Bragg peaks because it's nanoparticulate and not very crystalline. So I would assume that 4% is well below the detection limit of XRD. Have you tried increasing the wt% of graphene oxide to 10% and 50% (or 100%)?
The comments by Dr.Pieter Bots are fully right.As graphene oxide is nanoparticulate material not fully crystalline , due to the strong disorder and irregular packing of the layers . Peaks in XRD patterns of small particles of nano-size graphene composites are wide and less intensity,also raring and weakness of peaks in FTIR and XRD spectra are associate with graphene composites . It´s difficult to select a limit, but increasing the wt% of graphene oxide to more than 10% ,XRD pattern may exhibits more distinctive peaks of graphene.
you have to increasing the wt% of graphene oxide ,just in one sample of your mixtuer then you will get the peaks , and mention that in the discussion .