Growth of calcium phosphate onto chemically-functionalized cottons

The growth of calcium phosphate onto both cotton fibers and chemically-modified cotton fibers with three different degrees of carbonyl groups contents, immersed in saturated calciumphosphate solutions at 60°C and 7.4 pH for 6, 9 and 12 days, has been investigated by scanning electron microscopy, energy dispersed spectrometry and transmission electron microscopy as a function of the type and amount of functionalized groups. The functionalized cotton fibers were obtained through the reaction of alkali cellulose with sodium chloroacetate and the immersion solution was changed every three days. Without modification no crystallization in the cotton sample was observed, whereas in the functionalized samples, with higher substitution we obtained calcium phosphate crystallization onto the fibers as long vesicles with sizes ranging from 1 μm to 24 μm wide; these vesicles are formed by long platelets with certain orientation and ordered arrangement. In the presence of the most functionalized cotton fibers we observed the highest calcium phosphate crystallization onto the fibers; the Ca/P molar ratio obtained by EDS was 1.58. One of the calcium phosphate identified by transmission microscopy was octacalcium phosphate (Ca8H2(PO4) · 6.5H2O, OCP). The chemical functionalization of the cotton via carbonyl group determined the growth and the amount of calcium phosphate onto the fiber.