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Heat Treatment of Green Wood Accomplishes Crystal Hardening

Photo of Cross-section of wood cell wall. U.S. Department of Agriculture Forest Service.Cross-section of wood cell wall. U.S. Department of Agriculture Forest Service.Snapshot : After centuries of study, the structure of the woody cell wall remains poorly understood. Regarding cellulose crystals in green wood, X-ray methods demonstrate the repeating structure of a crystal, but Raman Spectroscopy methods reveal a high level of disorder within the crystal unit cell. Forest Service research demonstrates that with delignification (pulping) or heat treatments, the degree of disorder is decreased, resulting in a chemically robust crystal form in bleached pulps.

Principal Investigators(s) :
Agarwal, Umesh P. 
Research Station : Forest Products Laboratory (FPL)
Year : 2016
Highlight ID : 1048

Summary

There is considerable interest in high-strength cellulose nanocrystals (CNC) that can be used as a reinforcing phase in cellulose–plastic composites. Normally, these are produced by treatment of wood pulp, but when the treatment is carried out on wood, a very low yield of CNC is obtained. Although the repeating character of the crystal unit cell can be observed using X-ray methods, Raman methods reveal considerable disorder within the crystals or apparent crystals of green wood. These apparent crystals are permeable to acid and do not resist acid hydrolysis, the chemical method that successfully isolates crystals from other forms of cellulose. The chemical and thermal treatment in kraft pulping increases the internal hydrogen bonding in the crystals, resulting in less disorder and a chemically robust crystal. Forest Service research demonstrates heat treatment of green wood accomplishes the same crystal "hardening" and allows CNC to be obtained without the need for pulping and bleaching.

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