Flushability of nonwoven wet wipes

Particular hygiene applications, such as Moist Toilet Tissue (MTT), toddler
wipes, bathroom cleaning wipes 'and feminine hygiene wipes lend themselves
to convenient disposal via the sewer network. The high volume of wipes now
disposed of through the sewer network is increasing pressure on pipework
systems and wastewater treatment plants. The main objectives of this study
were to review the prior art and published literature on flushable nonwoven
technology, identifying the fundamental mechanisms of function, benchmark
the performance of currently available commercial flushable wipes and
through experimentation and empirical modeling, begin to form an
understanding of flushable wet wipe structure-property relationships.
Commercially available wet wipes were found to exhibit varying dispersibilities
when assessed using the industry-standard shake-flask test methodology, a test
designed to assess the disintegration of a wipe following disposal in the sewer
network. All were composed from cellulose, usually blends of wood pulp and
lyocell. It was observed that fibrillation of lyocell increased as a result of
mechanical agitation during dispersibility testing. These fibrils apparently
hindered the dispersion of the wipe into individual fibres. In experimental
wipes, fibre fibrillation was found to have a negative influence on the
dispersibility behaviour of both wetlaid and airlaid hydroentangled wipes.
Hydroentangled fabrics containing non-fibrillating regenerated cellulose fibres
exhibited the greatest resistance to fibrillation and also the highest
dispersibility. Experiments were performed to assess the wet strength and
dispersibility of both wetlaid and airlaid hydroentangled wipes composed of
wood pulp and regenerated cellulose. The influence of fabric structure
including fibre length, aspect ratio (fineness), blend composition and process
(specific energy and hydroentanglement forming belt open area) were studied.
Based on the findings from the present work, using an airlaid-hydroentangled
platform it is possible to produce a wet wipe with a wet strength as high as 22
N/50mm with dispersibility of 100% (<12.5 mm screen), which exceeds the
aspirational target of 15 N/50 mm and ?.95% dispersibility (12.5 mm screen).
Empirical models based on linear multiple regression methods suggested
specific energy and the total regenerated fibre length positively influence the
wet tensile strength of the fabrics. However, the total fibre length negatively
influences dispersibility. Fibres that are resistant to fibrillation were found to
benefit dispersibility. The model for wet tensile strength was found to have a
relatively good correlation with the experimental data, but less so for
dispersibility. Furthermore, it was established that the most likely dispersion
mechanism in the shake flask is the result of fibre slippage, meaning that wet
fibre-to-fibre cohesion and frictional resistance to sliding is critical in
governing the break-up of the substrate. To understand the magnitude of the
wet cohesive forces involved, a wet pull out test was devised. Airlaidhydroentangled
wipes with a carboxymethylcellulose (CMC)' binder exhibited
improved dispersibility performance but with decreased wet tensile strength.
This could be explained in terms of the modification of the coefficient of friction
by the CMC allowing the fibres to separate more easily when subjected to
mechanical forces during agitation. Optimum pH conditions and electrolyte
addition levels were established for the stabilisation of CMC binder in wetwipes.