As the popularity of nanocellulose grows, reliable detection strategies to quantify migration and leaching under conditions of realistic usage are becoming increasingly important, especially in the context of biomaterial and food contact applications. In this work, a proof of concept approach is described using fluorescently-labelled cellulose nanofibrils (CNFs) to quantify leaching from CNF-containing papers under usage scenarios typically encountered in food packaging applications. To do this, enzymatically pre-treated pulp was first labelled with 5-([4,6-Dichlorotriazin-2-yl]amino)fluorescein hydrochloride (DTAF), followed by microfluidization to generate fluorescent CNFs of different qualities by varying the pass number through the microfluidizer (1, 3, or 10 passes). Fluorescent labelling at the μmolar DTAF/g cellulose level was achieved, enough to impart quantitative ppb fluorescence detection (20 ppb limit of detection) without significant change to other properties. The DTAF-labelled CNFs were processed into nanopapers and into blended CNF-fiber papers, where CNFs were included as a strengthening agent.  The leachate obtained after cold and hot-water extractions of the papers was analyzed by fluorescence spectroscopy to quantify fluorescent material loss. In all cases, loss values below 3 wt% were observed, with materials produced from finer CNF qualities experiencing the lowest leaching and conditions of hot water extractions giving the highest leaching. Fluorescence microscopy of the leachate suggested large micrometer-scale fluorescent aggregates rather than individualized fibrils. Overall, the DTAF-labelling of CNFs is a promising strategy that can be used to address questions related to CNF distribution, localization, and loss in papermaking applications, including for food packaging.

Fluorescently-labelled cellulose nanofibrils for proof-of-concept leaching detection under conditons of food contact

ACS Spring Meeting 2021

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