No. | Pretreatments | Effect of pretreatments | References | Energy conservation requirement | Process & remarks |
1 | (a) Ozone at a charge level of at least about 0.1 wt/wt%, based on the dry weight of the cellulosic material for generating free radicals in the slurry (b) Cellulase enzyme at a concentration from about 0.1 to about 10 lbs/ton based on the dry weight of the cellulosic material A combination of both (a) and (b) mentioned above | Partial depolymerization of cellulose | [28] | >2% energy conserved | Comminution processing |
2 | Organic (morpholine, piperidine or mixtures) or inorganic (inorganic halide, an inorganic hydroxide, or mixtures thereof) swelling agent or a mixture thereof | Swelling of cellulose | [29] | 1400 kWh/t energy required 500 kWh/t energy required | Comminution processing 80% nanocellulose (defined as having an average diameter of less than 30 nm) 45% of the material having average diameters less than 30 nm |
3 | Carboxymethylation | Increases the anionic charges due to the formation of carboxyl groups in the surface | [30] | 5500 kWh/t without pretreatment (per pass through)- Minimum of 4 passes 2200 kWh/t with pretreatment (per pass through)-4 passes 30000 kW/t (total) without pretreatment | Microfluidization process Ultra-fine friction grinding |
4 | Carboxymethylation OR by irreversibly attaching CMC onto cellulose fibres | Increases the anionic charges due to the formation of carboxyl groups in the surface | [31] | 500 - 2300 kWh/t | Microfluidization process |
5 | Acid like sulfur dioxide, sulfurous acid, sulfur trioxide, sulfuric acid, lignosulfonic acid & their combinations or enzyme | Hydrolysis | [32] | <1000 kWh/t | Mechanical treatment |