Abstract: The present invention relates to a high tenacity, high modulus and low shrinkage lyocell multifilament yarn suitable for use in tire cords and MRG (mechanical rubber goods). The lyocell multifilament yarn is a cellulose-based fiber for industrial applications, which is produced by dissolving pulp having a degree of polymerization (DPW) of 700-2,000 and preferably 800-1,400, and a ?-cellulose content of more than 90% and preferably more than 92%, in N-methylmorpholine N-oxide (NMMO) hydrate, at a pulp concentration of 5-15% by weight and preferably 8-13% by weight. The lyocell monofilament according to the present invention is characterized by the following stress-strain profile: (1) the lyocell monofilament analyzed after drying is elongated by less than 3.0% and has an initial modulus of 150-400 g/d, when it was subjected to an initial stress of 3.0 g/d; (2) it is elongated by 3.0-7.0% when it was subjected to a stress greater than the initial stress but smaller than 6.

Abstract: The present invention relates to a high tenacity polyethylene naphthalate fiber containing a silica compound. This fiber is produced by a method comprising the steps of: (A) melt-spinning a solid phase-polymerized polyethylene-2,6-naphthalate chip containing ethylene-2,6-naphthalate units at more than 85 mole % and a silica compound and having an intrinsic viscosity of 0.70-1.20, to produce a melt-spun yarn; (B) passing the melt-spun yarn through a retarded cooling zone and a cooling zone to solidify the yarn; (C) withdrawing the yarn at such a speed that the undrawn yarn has a birefringence of 0.001-0.1; and (D) subjecting the undrawn yarn to multi-stage drawing at a total draw ratio of at least 1.5 and a drawing temperature of 50-250° C.