Celanese Corporation, Dallas, TX, a hybrid chemical company, has sold the Films business of its AT Plastics subsidiary to British Polythene Industries plc. The Films business manufactures products for the agricultural, horticultural and construction industries.   ; The sale is part of Celanese's plan to divest non-core businesses.   ; The Specialty Polymers business of AT Plastics, whose production and support facilities are located in Edmonton, remains with Celanese. The Polymers business concentrates on the development and supply of specialty resins and compounds.