|Waterproofing of paper cup|
Originally, paper cups for hot drinks were glued together and made waterproof by dropping a small amount of clay in the bottom of the cup, and then spinning at high speed so that clay would travel up the walls of the cup, making the paper water-resistant. However, this resulted in drinks smelling and tasting of cardboard.
Cups for cold drinks could not be treated in the same way, as condensation forms on the outside, then soaks into the board, making the cup unstable. To remedy this, cup manufacturers developed the technique of spraying both the inside and outside of the cup with wax. Clay- and wax-coated cups disappeared with the invention of polyethylene (PE)-coated cups; this process covers the surface of the board with a very thin layer of PE, waterproofing the board and welding the seams together.
In 2017, the Finnish board manufacturer Kotkamills launched a new kind of cup (food service) board which uses no wax or plastic for waterproofing, and thus can be recycled as part of the normal paper and board waste stream, biodegraded, or even composted in small quantities.
in 2017, the Newport Beach CA company Smart Planet Technologies, launched "reCUP" for the UK market, a recyclable paper cup using a polyethylene and mineral-blended coating, that is engineered to be recycled through traditional paper recycling systems.