Swiss biochemicals group Lonza has extended its $1.4bn tender offer for US-based Arch Chemicals, the company behind the Purista fresh-finish for textiles and one of the world's largest manufacturers of antimicrobials.

The second extension in less than a month now sees the offer deadline pushed back to 14 October. The company says it is still waiting antitrust clearance in the US, although clearances have been obtained from the competition authorities in France and Germany.

The all-cash offer, equivalent to $47.20 per share, may be further extended, Lonza warns.

The acquisition, which was announced in July, will make Switzerland-based Lonza the world's largest company in the microbial biocides market, with annual sales of around $1.6bn.

Based on polyhexamethylenebiguanide hydrochloride (PHMB), Purista treatments protect clothing and other textiles from odour-causing bacteria, providing a long lasting "fresh finish."