Nonwovens with anisotropic water-penetration properties
are of significant academic and practical importance. However, existing
materials suffer from inherent limitations, because of which the use
of chemicals is inevitable and the proportion of hydrophobic contents
is largely confined. Herein, we report for the first time, the chemical-free
and large-scale fabrication of nonwoven composites having anisotropic
water-penetration features. A layer of chitosan (hydrophobic) fibers
is consolidated with a layer of viscose (hydrophilic) fibers via the
hydroentanglement technique. The high-pressure water jets from hydroentanglement
achieve the vertical movement of fibers, thus generating a gradient
fiber distribution across nonwoven thickness. This gradient fiber
distribution enables fast water-penetration from the hydrophobic side,
even when 90% of the fibers are hydrophobic and the hydrophobic layer
exceeds a record-high thickness of 1.6 mm. Versatility of our method
is further demonstrated by realizing similar water penetration in
nonwovens formed by other types of fibers. Moreover, because no chemical
has been applied throughout the manufacture process, fiber properties
(such as distinct wettability difference, high antibacterial rate,
and good cell viability) can be well inherited by the nonwoven, which
ensures the water-penetration effect to be permanent. Taken together,
we believe that the green fabrication strategy developed in this study
would make the resultant nonwovens competitive in areas where swift
water transportation/absorption, high body/environmental safety, and
amphiphilic properties are desired.
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