Patent ID: 7749352

Claim:
A process for making bi-tapered fibers, comprising: extruding polymer through an extrusion device to form monofilament fibers or a polymer sheet, and, if in sheet form, slitting said sheet to form separate fibers; stretching the fibers in the longitudinal direction to increase modulus of elasticity; and drawing the polymer between opposed rollers thereby shaping said fibers, and cutting the fibers into individual lengths; said polymer extruding, stretching, and cutting into individual lengths being accomplished so as to obtain fiber bodies having two opposed ends defining therebetween an intermediate elongated fiber body portion which is substantially non-fractured and non-fibrillatable when mixed into a matrix material comprising concrete, shotcrete, mortar, grout, synthetic polymer, or mixture thereof, the fiber body portions having a length of 5 mm-100 mm; the body portion defining longitudinal major axis Z and comprising a transverse cross-sectional profile having two tapering dimensions for pull out-resistance from the concrete or other matrix material, the first tapering dimension occurring in a first transverse minor axis X that is perpendicular to axis Z, the second tapering dimension occurring in a second transverse minor axis Y that is perpendicular to both axes X and Z; the first and second tapering dimensions having inverted tapering behaviors wherein, along axis Z, the first tapering dimension along axis X increases as the second tapering dimension along axis Y decreases, and the first tapering dimension along axis X decreases as the second tapering dimension along axis Y increases; the transverse cross-sectional area remaining substantially uniform along axis Z having said inverted tapering dimensional behaviors; and said fibers having an aspect ratio in terms of length to equivalent diameter of not less than 10 and not greater than 500, a modulus of elasticity not less than 5 Gigapascals and not greater than 250 Gigapascals, a tensile strength not less than 400 Megapascals and not greater than 2,500 Megapascals, and a load carrying capacity of not less than 50 Newtons per fiber and not greater than 5,000 Newtons per fiber; said tapering being achieved by (a) at least one of said two opposed rollers having undulations to form said fiber tapering in said fiber bodies or (b) both rollers having circular circumferential dimensions and oscillating at least one of said two opposed rollers in a direction perpendicular to the fiber axis being drawn between said rollers, whereby said fibers acquire said tapering dimensions.