Rapid Determination of the Distribution of Cellulose Nanomaterial Aggregates in Composites Enabled by Multi-Channel Spectral Confocal Microscopy

Abstract

There is increased interest in the use of cellulose nanomaterials for the mechanical reinforcement of composites due to their high stiffness and strength. However, challenges remain in accurately determining their distribution within composite microstructures. We report the use of a range of techniques used to image aggregates of cellulose nanocrystals (CNCs) greater than 10 µm2 within a model thermoplastic polymer. While Raman imaging accurately determines CNC aggregate size, it requires extended periods of analysis and the limited observable area results in poor reproducibility. In contrast, staining the CNCs with a fluorophore enables rapid acquisition with high reproducibility, but overestimates the aggregate size as CNC content increases. Multi-channel spectral confocal laser scanning microscopy is presented as an alternative technique that combines the accuracy of Raman imaging with the speed and reproducibility of conventional confocal laser scanning microscopy, enabling the rapid determination of CNC aggregate distribution within composites.

Quantitative Analysis of Compatibility and Dispersibility in Nanocellulose-Reinforced Composites: Hansen Solubility and Raman Mapping

“…Several studies have reported the analysis of the CNC distribution by Raman intensity maps based on the characteristic Raman bands located at ca . 1092 cm –1 . − ,, However, the signaling peaks of polymer matrices are also located in the fingerprint region (400–1800 cm –1 ), inducing multiple Raman peak interference. Specifically, the Raman spectrum of HPC in the glycosidic linkage range 1000–1250 cm –1 coincides with the characteristic peaks of CNCs .…”

“…Univariate analyses are usually adopted in a binary or ternary composite system, which requires a constituent-specific spectral band free of interference from other system constituents. Several recent studies reported the qualitative analysis of the stress transfer effect in CNC-reinforced composites by Raman spectroscopy, − based on the characteristic of cellulose itself ( ca . 1095 cm –1 ).…”

The effect of the dispersion of microfibrillated cellulose on the mechanical properties of melt-compounded polypropylene–polyethylene copolymer

“…Previous research has confirmed that SCLSM can be used to identify cellulose aggregates in composite materials without the need for a fluorescent dye (Johns et al 2019). Here we confirmed the autofluorescence of microfibrillated cellulose (MFC), tannic acid (TA) and the MFC-TA-C 18 filler in composites.…”

Employing photoluminescence to rapidly follow aggregation and dispersion of cellulose nanofibrils

“…2,25,26 The autofluorescence of poly-and oligo-saccharides, from various sources, has previously been widely reported. 6,[27][28][29][30][31][32][33][34][35] This autofluorescence is generally attributed to contamination of the sample with aromatic compounds, i.e. lignin, or proteins, dependent on the source.…”

“…We previously took advantage of this phenomenon to track the dispersion of cellulose particles in polymer matrices, confirming that the observed autofluorescence was intrinsically linked to the presence of cellulose. 6,31 In relation to cellulosic nanomaterials with typical surface chemical modifications, Li et al investigated the autofluorescent properties of carboxymethylated nanocellulose. 33 They demonstrated that the particles exhibited two fluorescent bands with an approximate wavelength difference of 40 nm, the second of which increased with concentration.…”