A sign says, “Waste paper”. Underneath the sign is a box. You have to put your used paper in the box for recycling.

But, should the sign say “Waste paper” or “Paper Waste”?

The idea is that the first noun is a “noun modifier”, or, a “non-adjective”. This is like saying “wooden spoon”, or “plastic fork”. It's a spoon (second noun), not a “wood”. So when you say:

• Waste Paper –> you mean it is paper, but that it is waste (垃圾 紙).
• Paper Waste –> you mean it is waste, but it must be paper (所有垃圾必須是紙本的).

There's just one problem. If you say “Waste Paper”, then waste has waste-n and waste-v. Are you saying, “Please waste paper”? So, some people like to say “paper waste”.

However, maybe you could use the word “recycle”.

• Recycled Paper (再生紙, “Zàishēng zhǐ”)

or

• Paper Recycling (紙張回收, “Zhǐzhāng huíshōu”)

is great!