Hydrolysis of tetracalcium phosphate in the presence of a poly(alkenoic acid)
- PDF / 492,106 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 38 Downloads / 184 Views
MATERIALS RESEARCH
Welcome
Comments
Help
Hydrolysis of tetracalcium phosphate in the presence of a poly(alkenoic acid) Y.E. Greish and P.W. Brown Intercollege Materials Research Laboratory, Pennsylvania State University, University Park, Pennsylvania 16802 (Received 21 August 1998; accepted 15 September 1999)
Ca4(PO4)2O (TetCP) reacts with an acidic polyelectrolyte in the absence of a solvent to form a composite composed of Ca10(PO4)6(OH)2 (hydroxyapatite, or HAp) and the Ca salt of the polyelectrolyte. Mixtures of an acrylic copolymer and TetCP powders were hot-pressed, and the effects of temperature, pressure, and time on HAp formation were studied. Reaction starts when the copolymer is heated to above Tg. Initial carboxyl site neutralization liberates water, continued TetCP hydrolysis, liberates Ca2+ ions, which react with the copolymer forming its Ca salt. When 90% conversion to HAp was achieved, the composite had an average tensile strength of 51 MPa, a Vickers hardness of 145 kg/mm2 and a Tg ∼ 250 °C.
I. INTRODUCTION
It is well known that acid-base reactions involving acidic polyelectrolytes and basic oxides take place in aqueous media.1 However, Nielsen and co-workers2– 4 found that a basic metal oxide can react with a polyelectrolyte if their powder mixture was treated at elevated temperatures and pressures, a fabrication technique that greatly resembles those used in powder metallurgy. The polyelectrolyte salts produced possessed improved properties over normal plastics and were characterized by higher shear moduli, lower thermal expansions, and good thermal stabilities. These composites remained rigid up to very high temperatures (>400 ° C). Although Nielsen’s work demonstrated that particulate basic oxide compounds would be consumed in the formation of salts of poly(alkenoic acids), conversion of the inorganic constituent from one compound to another had not been demonstrated. Thus, it was the objective of this study to establish whether Ca4(PO4)2O (TetCP) could be converted to Ca10(PO4)6(OH)2 (hydroxyapatite, or HAp) by solid-state reaction at high temperature in the presence of acidic polyelectrolytes. This reaction is anticipated to result in a new type of composites. Formation of a HAp– polymer composite was selected in an effort to develop a material with mechanical properties more closely approximating those of hard tissues than those currently available.5 The hydrolysis of TetCP is interesting because it is the only calcium phosphate more basic than HAp. Therefore TetCP is the base used in many aqueous processes forming HAp.6 Because of the Ca/P ratio difference between J. Mater. Res., Vol. 14, No. 12, Dec 1999
HAp and TetCP, complete hydration would also be expected to produce calcium hydroxide according to Eq. (1): 3Ca4共PO4兲2O + 3H2O → Ca10共PO4兲6共OH兲2 + 2Ca共OH兲2 . (1) The presence of a polymer that contains carboxylic acid groups in its structure is expected to participate in TetCP hydrolysis by reacting with the Ca(OH)2. For example, TenHusein et al.7 observed that acidic polyphosphazi
Data Loading...
