Why can envelopes not be recycled?

Envelopes are not included in the paper recycling at the request of the paper merchants who take the paper for recycling. Highland Council have been informed that the adhesive gum on the envelopes in large quantities can cause problems for their equipment during the pulping process. Also, there is a contamination problem with plastic windows on envelopes. Because of this Highland Council have envelopes down under “no thank you” at the recycling banks.  

Envelopes with plastic windows removed can be composted.