I've just looked at the home pages of the two sites and they are pretty much the same apart from substituting plastics with bottles. I'm not an expert but I would have thought Google might think this is duplicate content.
In my opinion I would concentrate on one of the sites say plastics and have the bottle specific stuff as a subsection. I'm not sure how the sites rank etc so that may be easier said than done.
As for the site map / robot question, if you continue with two sites then I would recommend generating a new one for the copied site.
