Application of microwave energy in degumming of hemp stems for the processing of fibres

• Hemp stems were subjected to microwave-pretreatment before decortication.
• Found effective removal of impurities when compared to conventional method.
• MW retting/degumming was found to be efficient and time saving when compared to other methods.
• The process was optimized for maximum fibre quality.

Microwave assisted-degumming/retting of hemp stems was established and the changes in the components like cellulose, hemicellulose and lignin during microwave treatment were studied by near infrared (NIR) analysis of the fibres processed from the treated hemp stems. Pre-soaked hemp stems subjected to microwave assisted degumming/retting at various power levels showed significant increase in the cellulose content from 72.1% to 79.8% when compared with the control samples. The percentage of hemicellulose and lignin were the key factors in binding the fibres together, which showed significant decrease when subjected to microwave treatment. Hemicellulose decreased from 14.5% to 12.1% and lignin from 8% to 5.5%. These compositional changes proved the effect of microwave energy in fibre separation. Measurements of diameter distribution and tensile strength, and colorimetric analysis, were performed to verify the effect on the physical properties. Thirty five percent of control sample hemp fibre diameters were <23 μm whereas the microwave-assisted retted samples contained more than 50% of fibre diameter were <23 μm. Colorimetric tests and tensile strength tests did not show any specific trends but the results confirmed that the microwave energy did not have any significant influence in the changes of the physical qualities during the process. The above studies showed the efficiency of microwave treatments for the degumming of hemp fibres.

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