It might be helpful to have a little more information about what you are trying to do. Latex is largely water. Polyethylene doesn't like water. So just putting them in a pot and stirring isn't going to do much. You will need to heat the mixture up, probably past the melting point of polyethylene (110-140 C depending on what kind you have), boil off most of the water, and hope the polymer phase of the latex is sufficiently compatible with the PE to mix in the melt, and stay mixed when you cool it back down. It's possible you still may get a phase separated mixture when you cool it down.