Calcium phosphate bioceramics synthesized from eggshell powders through a solid state reaction

Everyday millions of tons of eggshells are produced as biowaste around the world. Most of this waste is disposed of in landfills without any pretreatment. Eggshells in landfills produce odors and promote microbial growth as they biodegrade. The present invention provides an environmentally beneficial and cost-effective method of producing calcium phosphate bioceramics (hydroxyapatite or tricalcium phosphate) from eggshell waste. In this investigation, heat treatment produced solid state reactions between eggshell powders and dicalcium phosphate dihydrate (CaHPO₄·2H₂O, DCPD) or calcium pyrophosphate (Ca₂P₂O₇). When eggshell powders (CaO) and DCPD were heat treated at 1150 °C for 3 h, only a single hydroxyapatite (HA) phase was found; no diffraction peaks of starting materials and no β-TCP were observed. The XRD patterns of the product fabricated from raw eggshell powders (CaCO₃) and Ca₂P₂O₇ heat treated at 1100 °C for 3 h showed that almost only pure β-TCP remained with a trace amount of HA. The calcium phosphate ceramic synthesized from eggshell powders contains several important trace elements such as Na, Mg and Sr.     

Thermoreversible hydrogels XIII: Synthesis and swelling behaviors of [N-isopropylacrylamide-co-sodium 2-acrylamido-2-methylpropyl sulfonate-co-N,N-dimethyl(acrylamido propyl) ammonium propane sulfonate] copolymeric hydrogels

A series of copolymeric hydrogels were prepared from various molar ratios of N-isopropylacrylamide (NIPAAm), sodium-2-acrylamido-2-methylpropyl sulfonate (NaAMPS) and N,N′-dimethyl(acrylamido propyl) ammonium propane sulfonate (DMAAPS). The swelling behaviors of these copolymeric hydrogels were investigated in various saline solutions. The result showed that the phase transition temperatures of these gels changed insignificantly, and the thermosensitivity, in contrast, diminished. In addition, the copolymer gels exhibited polyelectrolytic behavior under lower salt concentration (10⁻⁵∼10⁻¹ M), exhibited a nonionic gel (like NIPAAm) behavior at the salt concentration from 0.1 to 0.4 M, and showed an antipolyelectrolytic behavior (polyzwitterionic effect) at a salt concentration over 0.4 M. Finally, the presented coplymeric gels are investigated for use in drug release application.     

Studies on graft copolymerization of glycidyl methacrylate onto poly(vinyl chloride) and curing behavior of its grafted copolymer

Poly(vinyl chloride) was dehydrochlorinated in an alkali solution and then grafted with glycidyl methacrylate (GMA) using benzol peroxide as the free-radical initator under a nitrogen atmosphere. The efficiency of grafting GMA under the influence of an alkali, GMA concentration, and duration of the grafting reaction, the viscosity properties, and the curing behavior with diamine were investigated. Maximum grafting to the extent of 46.4% was obtained. The optimum curing reaction condition were investigated. © 1995 John Wiley & Sons, Inc.     

Studies on graft copolymerization of 2-hydroxyethyl methacrylate onto poly(vinyl chloride)

Poly(vinyl chloride) was dehydrochlorinated in alkali solution and then grafted with 2-hydroxyethyl methacrylate (HEMA) using benzoyl peroxide as a free-radical initiator under a nitrogen atmosphere. The investigations involved examining the effects of grafting efficiency on various conditions, such as degree of dehydrochlorination, HEMA concentration, solvent effect, and reaction time. Maximum grafting to the extent of 57.2% was obtained. The mixed solvent grafting was attempted. © 1994 John Wiley & Sons, Inc.     

Poly[2-(hydroxyethyl methacrylate)-co-(sulfobetaine)]s hydrogels: 1. Synthesis and swelling behaviors of the 2-(hydroxyethyl methacrylate)-co-2-(vinyl-1-pyridinium propane sulfonate) hydrogels

A series of the 2-hydroxyethyl methacrylate/2-vinyl-l-pyridinium propane sulfonate (HEMA/VPPS) copolymeric gels have been prepared from HEMA and zwitterionic monomer VPPS of various molar ratios. The influence of the amount of VPPS in copolymeric gels on their swelling behavior in water and various saline solutions at different temperatures was investigated. Results indicate that the PHEMA hydrogels exhibit an overshooting phenomenon in their dynamic swelling behavior. The maximum overshooting value decreases with increasing temperature. The same results are also shown for the lower VPPS content HEMA/VPPS copolymeric gels. In the equilibrium swelling ratio, the PHEMA hydrogel exhibits a minimum swelling ratio at 55 °C. Then, the minimum swelling ratio disappears gradually with increasing VPPS content in HEMA/VPPS copolymeric gels. In the saline solution, the swelling ratios of HEMA/VPPS copolymeric gels increase rapidly with increasing salt concentration, for salts with a smaller ratio of charge/radius.     

pH/thermoreversible hydrogels III: Synthesis and swelling behaviors of (N-isopropylacrylamide-co-acrylic acid) copolymeric hydrogels

A series of pH-thermoreversible hydrogels exhibiting volume phase transition were synthesized by three degrees of neutralization (DN) of acrylic acid (AA) and N-isopropylacrylamide (NIPAAm). The influence of environmental conditions, such as temperature and pH, on the swelling behavior of these copolymeric gels is investigated in this article. Results show that the negatively charged hydrogels exhibit different equilibrium swelling ratios at different pH values depending on the ionic composition. The pH-sensitivities of these gels also strongly depend on the DN of AA in the copolymeric gels. The results show that the higher the DN, the higher the gel pH-sensitivity. These hydrogels based on a temperature-sensitive hydrogel demonstrate a larger change of equilibrium swelling in aqueous media between a highly solvated, swollen gel state and a collapsed dehydrated network in response to a variation of temperature. On the other hand, a significant phenomenon that was found in the gel swelling kinetics was an overshooting under high temperature conditions. The presented hydrogels were used for release of model drugs that occur at the changes of surrounding conditions, such as temperature and pH, in this study. It was also found that the higher the DN of AA, the higher the gel transition temperature and the larger the release in a high temperature environment and, at the same time, the larger the swelling ratios.     

Superabsorbent polymeric material. V. Synthesis and swelling behavior of sodium acrylate and sodium 2-acrylamido-2-methylpropanesulfonate copolymeric gels

A series of xerogels based on sodium acrylate (SA), sodium 2-acrylamido-2-methyl propanesulfonate (NaAMPS), and N,N-methylene-bis-acrylamide (NMBA) are prepared by inverse suspension polymerization. The water absorbency and swelling behavior for these high absorbent polymers in deionized water and transition salt solutions are investigated. Experimental results indicated that the absorbency in deionized water increases with an increase of the NaAMPS content in the copolymeric gels, which is related to the degree of charge density of the network and the strength of hydrophilic group. The extent of crosslinking agent also influenced the swelling capacity because of elastic chain force of the polymer chain. The absorbency in chloride salt solutions decreases with an increase in the ionic strength of salt. But the decrease of absorbency is different in monovalent and multivalent salt solution. This behavior can be accounted for in terms of counterion condensation or screening effect for monovalent cations, as well as complexation for multivalent cations. The swelling rates in various salt solutions for these xerogels are also investigated. At last, SA-NaAMPS copolymeric gels were used for ion adsorption. But the result showed that the adsorptive amount of transition metal ions for SA-NaAMPS copolymeric gels was lower than that for pure poly(SA) gel. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 229–237, 1998     

Poly(2-hydroxyethyl methacrylate-co-sulfobetaine) hydrogels. II. Synthesis and swelling behaviors of the [2-hydroxyethyl methacrylate-co-3-dimethyl(methacryloyloxyethyl)ammonium propane sulfonate] hydrogels

A series of the 2-hydroxyethyl methacrylate/3-dimethyl-(methacryloyloxyethyl)ammonium propane sulfonate (HEMA/DMAPS) copolymeric gels was prepared from various molar ratios of HEMA and the zwitterionic monomer DMAPS. The influence of the amount of the zwitterionic monomer in the copolymeric gels on the swelling behaviors in water, various saline solutions, and temperature was investigated. The results indicate that the PHEMA hydrogel (D0) and lower DMAPS content of the HEMA/DMAPS copolymeric gel (D1) exhibit overshooting phenomena in the dynamic swelling behavior. The maximum overshooting value decreases with increase in temperature. In the equilibrium swelling ratio, the PHEMA hydrogel exhibits a minimum swelling ratio at 55°C. Then, the minimum swelling ratio diminishes gradually with increasing of the DMAPS content in the HEMA/DMAPS copolymeric gels. In the saline solution, the swelling ratios of HEMA/DMAPS copolymeric gels increase rapidly with increasing of concentration of the salt with a smaller ratio of the charge/radius. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2021–2034, 1998     

Superabsorbent polymeric materials. II. Swelling behavior of crosslinked poly[sodium acrylate-co-3-dimethyl(methacryloyloxyethyl) ammonium propane sulfonate] in aqueous salt solution

A series of xerogels based on sodium acrylate (SA), 3-dimethyl (methacryloyloxyethyl) ammonium propane sulfonate (DMAPS), and N,N′-methylene-bis-acrylamide (NMBA) are prepared by inverse suspension polymerization. The water absorbencies or swelling behaviors for these xerogels in water or various saline solutions respectively exhibit a value of 1435 g H₂O/g sample and 96 g H₂O/g sample of deionized water and 0.9 wt % NaCl solution at a gel containing 1.88 × 10⁻³ molar ratio of DMAPS while the extent of 1.53 × 10⁻³ molar ratio (0.25 wt % based on total monomer) of NMBA was used in the polymerization. The absorbency in the chloride salt solutions decreases with an increase in the ionic strength of salt. For the same ionic strength of various salt solutions, the swelling amount has the following tendency: Na⁺ > Fe³⁺ > A1³⁺ > Ca²⁺ for the higher ionic strength of 5 × 10⁻³ −2 × 10⁻²M and Na⁺ > Fe³⁺ > Ca²⁺ > A1³⁺ for the lower ionic strength of < 2 × 10⁻⁴M. The bound water found by DSC investigation is approximately equal to 2 g H₂O/g sample. The pH effect and thermal effect on the water absorbency for these xerogels are also investigated. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1701–1712, 1997     

Superabsorbent polymeric materials III. Effect of initial total monomer concentration on the swelling behavior of crosslinked poly(sodium acrylate) in aqueous salt solution

A series of xerogels based on sodium acrylate (SA) and N,N′-methylene-bisacrylamide (NMBA) were prepared by inverse suspension polymerization. The water absorbency or swelling behaviors for these hydrogels in water or various saline solutions was investigated. Experimental results indicate that the absorbency of poly(SA) in deionized water increases with decrease in the initial total monomer concentration. Results obtained from this study show that the water absorbency, respectively, exhibited a value of 992 g H₂O/g sample and 106 g H₂O/g sample in deionized water and a 0.9 wt % NaCl solution at an initial total monomer concentration of 3.03M. The absorbency in the chloride salt solutions decreases with increase in the ionic strength of the salt. For the same ionic strength of various salt solutions, the swelling amount has the following tendency: Co²⁺ > Ni²⁺ > Cu²⁺ for the higher ionic strength of 6.25 × 10⁻⁴ to 2.0 × 10⁻³M, and Co²⁺, Ni²⁺, and Cu²⁺ approximately have the same swelling amount for the lower ionic strength of < 6.25 × 10⁻⁴M. The influence of monovalent, divalent, and trivalent anions with a common cationic ion (Na⁺) on the water absorbency shows the tendency of monovalent < divalent < trivalent anions for the same ionic strength. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 2371–2380, 1997