Rapid Identification of Cellulose Nanomaterial Interactions and Distribution Within Composite Materials Using Confocal Microscopy

The rise of the circular economy, and increased environmental awareness, has seen biomaterials come to the fore of innovation as evidenced by the circular design challenge winners announced earlier this year. This has led to substantial interest in the use of cellulosic nanomaterials, CNMs, across a wide range of application areas. For example, their nanoscale dimensions, high mechanical properties, ease of functionalisation, and sustainability have resulted in publications exploring their use as reinforcement in various polymer composite materials. However, it is a challenge to track the bulk distribution of CNMs in the composite, which is required to ensure material homogeneity and maximise mechanical performance. Here, we demonstrate that two forms of CNMs (cellulose nanocrystals and oxidised cellulose nanofibres) autofluoresce under excitation at 405 nm and report on how the interactions of solvents and ionic compounds affect the peak emission wavelength. This forms the basis of a technique that may rapidly determine the bulk distribution of CNMs within a composite material and provide additional information on the CNM environment.