Process for making highly dispersible polymeric reinforcing fibers

Abstract

Synthetic polymer reinforcing fibers provide dispersability and strength in matrix materials such as concrete, masonry, shotcrete, and asphalt. The individual fiber bodies, substantially free of stress fractures and substantially non-fibrillatable, have generally quadrilateral cross-sectional profiles along their elongated lengths.

Description

[0001] The invention relates to fibers for reinforcing matrix materials, and more particularly to a plurality of synthetic polymer fibers having excellent dispersibility and reinforcibility properties in hydratable cementitious compositions. Individual fiber bodies are elongated and highly bendable, with generally quadrilateral cross-sectional profiles, thereby minimizing fiber balling and maximizing fiber bond.[0002] Although fibers of the present invention are suitable for reinforcing various matrix materials, such as adhesives, asphalts, composites, plastics, rubbers, etc., and structures made from these, the fibers that will be described herein are especially suited for reinforcing hydratable cementitious compositions, such as ready-mix concrete, precast concrete, masonry concrete (mortar), shotcrete, bituminous concrete, gypsum compositions, gypsum- and / or Portland cement-based fireproofing compositions, and others.[0003] A major purpose of the fibers of the present invention i...

AI Technical Summary

Benefits of technology

[0020] Exemplary individual fiber bodies of the invention are also substantially free of internal and external stress fractures, such as might be created by clinker grinding or mechanical flattening. The general intent of the present inventors is to maintain integrity of the individual fiber bodies, not only in terms of structural fiber integrity, but also integrity and uniformity of total surface area and bendability characteristic from one batch to the next.

[0021] A generally quadrilateral cross-sectional profile provides a higher surface area to volume ratio (S.sub.a / V) compared to round or oval monofilaments comprising similar material and having a diameter of comparable dimension. The present inventors believe that a quadrilateral cross-sectional shape provides a better flexibility-to-volume ratio in comparison with round or elliptical cross-sectional shapes, and, more significantly, this improved flexibility characteristic translates into better "bendability" control. The individual fiber bodies of the invention will tend to bend predominantly in a bow shape with comparatively less minimal twisting and fiber-to-fiber entanglement, thereby facilitating dispersal. In contrast, for a given material modulus and cross-sectional area, the prior art fibers having circular or elliptical cross section with major axis / minor axis ratios of less than 3 will have greater resistance to bending, thereby having a greater tendency for fiber balling when compared to fibers of generally quadrilateral (e.g., rectangular) cross-section.

Problems solved by technology

They also sought to avoid extreme rigidity, which is often associated with strength, because this too can lead to undesirable fiber "balling."

Flexibility that is too high (such as in wet human hair) can be just as troublesome as stiffness (such as in the "pick-up-sticks" game played by children) because self-entanglement can arise in either case.

A high degree of fiber balling or entanglement means that substantially uniform dispersion has not been attained in the matrix material; and this, in turn, means that the fiber dosage will be inadequate and the material properties of the fiber reinforced material will be subject to significant variation.

As mentioned above, an increase in elastic modulus usually means a decrease in bendability, which has a negative impact on dispersion properties of the plurality of fibers.

Fibers added at these low dosage rates do not have a significant effect on the hardened properties of concrete.

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