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. 2021 Aug 17;26(16):4972.
doi: 10.3390/molecules26164972.

Microwave-Assisted Defibrillation of Microalgae

Frederik L Zitzmann  1 , Ewan Ward  1 , Xiangju Meng  1 , Avtar S Matharu  1
Affiliations

Microwave-Assisted Defibrillation of Microalgae

Frederik L Zitzmann et al. Molecules. .

Abstract

The first production of defibrillated celluloses from microalgal biomass using acid-free, TEMPO-free and bleach-free hydrothermal microwave processing is reported. Two routes were explored: i. direct microwave process of native microalgae ("standard"), and ii. scCO2 pre-treatment followed by microwave processing. ScCO2 was investigated as it is commonly used to extract lipids and generates considerable quantities of spent algal biomass. Defibrillation was evidenced in both cases to afford cellulosic strands, which progressively decreased in their width and length as the microwave processing temperature increased from 160 °C to 220 °C. Lower temperatures revealed aspect ratios similar to microfibrillated cellulose whilst at the highest temperature (220 °C), a mixture of microfibrillated cellulose and nanocrystals were evidenced. XRD studies showed similar patterns to cellulose I but also some unresolved peaks. The crystallinity index (CrI), determined by XRD, increased with increasing microwave processing temperature. The water holding capacity (WHC) of all materials was approximately 4.5 g H2O/g sample. The materials were able to form partially stable hydrogels, but only with those processed above 200 °C and at a concentration of 3 wt% in water. This unique work provides a new set of materials with potential applications in the packaging, food, pharmaceutical and cosmetic industries.

Keywords: defibrillated cellulose; microalgae; microwave processing; zero waste biorefinery.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Process flow diagram of a potential biorefinery route of microalgal biomass. NB. ‘Standard’ refers to without any scCO2 pretreatment.
Figure 2
Figure 2
Microfibrillated cellulose (MFC) obtained via microwave treatment at temperatures of 160, 180, 200 and 220 °C for a total of 30 min (50:50 ramp:hold). Obtained from: Left—standard method using spray-dried microalgal biomass. Right: supercritical treated method using residual microalgal biomass post scCO2 extraction. NB. ‘Standard’ refers to without any scCO2 pretreatment.
Figure 3
Figure 3
MFC yield (line chart) and carbohydrate yield (bar chart) of standard and supercritical treated microalgal biomass at different microwave temperatures. NB. ‘Standard’ refers to without any scCO2 pretreatment.
Figure 4
Figure 4
Carbohydrate split obtained from HPLC for standard method (left) and supercritical method (right). The numbers 160, 180, 200 and 220 refer to the microwave processing temperature (°C). NB. ‘Standard’ refers to without any scCO2 pretreatment.
Figure 5
Figure 5
DTG thermograms of standard and scCO2 treated MFC. NB. ‘Standard’ refers to without any scCO2 pretreatment.
Figure 6
Figure 6
X-ray diffractograms of (a) standard method MFC and (b) scCO2 method MFC. Black numbers indicate cellulose planes, red numbers indicate CaC2O4 planes. NB. where ‘standard’ refers to without any scCO2 pretreatment.
Figure 7
Figure 7
Crystallinity index (CrI) of MFC from standard and scCO2 methods at different MW temperatures calculated from XRD traces in Figure 6 via Segal’s method. NB. ‘Standard’ refers to without any scCO2 pretreatment.
Figure 8
Figure 8
Solid state 13C CPMAS NMR spectra of (a) standard method MFC and (b) scCO2 method MFC. NB. ‘Standard’ refers to without any scCO2 pretreatment.
Figure 9
Figure 9
TEM images of MFC samples at different temperatures as labelled. MFCXXX corresponds to microfibrillated cellulose processed at XXX °C.
Figure 10
Figure 10
Water holding capacities (WHC) of MFC of both standard and scCO2 methods. NB. ‘Standard’ refers to without any scCO2 pretreatment.
See this image and copyright information in PMC

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