The kapok investigated exhibited excellent buoyancy,
high selectivity for various oils and excellent repellency
for water in its native form. It did not need chemical pretreatment,
unlike some other agro-based products which
need chemical pretreatment to enhance oil absorbency.
Its hydrophobic–oleophilic characteristics could be attributed
to its waxy fiber surface, which was evidenced by its
smaller contact angle with the different oils, but large contact
angle with water. Its large lumen contributed to excellent
oil absorbency and retention capacity. The mechanism
of oil sorption by its hollow fiber could be controlled by
sorption on the fiber surface and capillary action through
its lumen. The less viscous oil such as diesel drained out
at a faster rate but reached equilibrium sooner compared
to the more viscous oils. Though at loose packing, the
kapok might lose 30% of its oil sorption capacity when
reused, it still possessed higher oil sorption capacity than
PP. The oil absorbed by the kapok could be easily recovered,
and better recovery could be obtained with centrifugation,
which could achieve >83% oil recovery from the
densely packed assemblies. When absorbing oils spilled
on water, kapok could remove all oil spilled if the oil
amounts were considerably below its oil sorption capacity.
It demonstrated high water repellency, which is a favorable
characteristic as it optimizes the oil removal rate and
reduces the volume of absorbed liquid to be handled
afterward.
In summary, kapok can be a better alternative to the
widely used synthetic sorbent materials. Economically,
kapok is relatively cheap compared to PP and cotton. Environmentally,
it can be recovered from discarded bedding,
upholstery, and life preservers for reuse as oil sorbent. It
can be ultimately disposed of for biomass energy recovery
due to its biodegrability. Thus its use leaves no secondary
waste to the environment.