Investigating mechanisms deteriorating the dispersibility of biodegradable and flushable wet wipes

Wet wipe dispersibility is broadly discussed since they have been detected in massive fatbergs that were found in sewer systems of big cities, e.g., London. Dispersibility describes a wet wipe's ability to disintegrate into its fibres after being flushed in the toilet. Recently it has been found that this dispersibility of pilot-scale produced wet wipes can reduce when stored in a wet condition. This phenomenon is called dispersibility ageing. With this work we give a first approach on analysing the underlying mechanisms causing this solidification of wet wipes by measurement of the water-fibre-interactions and the mechanical strength of the wipes. Long-term swelling of the wood pulp is discussed as a possible root cause for the observed loss in dispersibility. Wet strength theory was used to find three possible mechanisms that are able to explain increased strength as a result of swelling: knot-tightening, increased friction and interdiffusion. To investigate the strength behaviour of wet wipes over wet storage time, tensile testing and a new approach to measure the disintegration energy of these fabrics were used to find a time-dependent increased mechanical characteristic. Surprisingly no increase in wet strength or disintegration energy-measured by short span, low test speed wet tensile energy absorption-over wet storage time was found. The dispersibility ageing effect of wet wipes is seemingly not measurable using mechanical testing. It seems that these test methods are not representative for the loading situation during disintegration in the sewer system and in the standard disintegration tester.