Nonbrittle Nanocomposite Materials Prepared by Coprecipitation of TEMPO-Oxidized Cellulose Nanofibers and Hydroxyapatite

Organic-inorganic nanocomposites were prepared by crystallization of hydroxyapatite in an aqueous dispersion of cellulose nanofibers. The addition of aqueous calcium chloride to an aqueous dispersion of cellulose nanofibers and disodium hydrogen phosphate yielded white precipitates, in which hydroxyapatite and cellulose nanofibers were hybridized in a weight ratio of ca. 70:30. Uniaxial pressing at 120 degrees C and 120 MPa of the nanocomposite powder afforded the compressed nanocomposite blocks. A three-point bending test revealed that the nanocomposite had a bending strength of up to 57 MPa and an elastic modulus of up to 4.1 GPa. The mechanical properties increased as the coprecipitation temperature was increased up to 70 degrees C. A further increase in temperature to 90 degrees C resulted in the reduction of bending strength. After the bending test, the compressed nanocomposites did not break in half. The fracture surface showed fibrous structures of ca. 140 mu m long, indicating that cellulose nanofibers are aggregated to form a fibrous structure of submillimeter length, and the formation of the aggregates contributed to the nonbrittle fracture.

Automated summary

Organic-inorganic nanocomposites were prepared by crystallizing hydroxyapatite in an aqueous dispersion of cellulose nanofibers. The resulting composite showed bending strength and elastic modulus, with mechanical properties increasing as the co-precipitation temperature rose.