Ghost fishing, caused by lost fishing lines and nets,
has become
a severe problem in marine environments. To eliminate ghost fishing
in the ocean, the environmental degradation behavior of fishing lines
must be understood. In this study, the environmental degradation of
biodegradable nylon 4 fishing lines and commercial nylon 6, poly(ethylene
terephthalate) (PET), and poly(vinylidene fluoride) (PVDF) fishing
lines was simulated in the laboratory using an artificial weathering
tester
and biodegradation test in extracted seawater. To understand the degradation
mechanism, the chemical and structural changes induced by photo-oxidation
and biodegradation were investigated using tensile test, scanning
electron microscopy, differential scanning calorimetry, gel permeation
chromatography, infrared spectroscopy, and wide- and small-angle X-ray
scattering. The results indicated that photo-oxidation occurred in
the amorphous phase of the nylon 4, nylon 6, and PET fishing lines
during ultraviolet (UV) exposure. The nylon 4 fishing lines exhibited
excellent biodegradability, whereas the nylon 6, PET, and PVDF fishing
lines could not be degraded by microorganisms in the extracted seawater.
Both processes, i.e., photo-oxidation and biodegradation, were confined
to the amorphous regions of nylon 4. Note that the PVDF fishing lines
could not be degraded by UV exposure and biodegradation and, hence,
should be recycled after use.