Here's the first paper I could find referring to Lenzing's development of the solvent spun cellulose process. This paper doesn't appear in Lenzinger Berichte: the first mention of lyocell in this Journal appears in 1994.
The new cellulose fibre Lyocell has been developed by Lenzing AG as an attempt to solve problems expected in the future with raw material supplies due to a growing world population and increasing fibre consumption as well as to provide a new generation of fibre. Taking into account the strengths and weaknesses of existing fibres like synthetics, cotton and viscose, the merits and disadvantages of the new generation of Lyocell fibre are discussed. Fabric structures produced from Lyocell possess high tear resistance, uniformity, wear comfort and shrink very little during washing or lamination. Fibrillation presents a problem. Other advantages include biological degradability and an inexhaustible raw material resource.
Firgo H, International Man-Made Fibres Congress, 12-14 June 1991, at Dornbirn, Austria