PVA Beads Research Articles

Synthesis of high-molecular-weight poly(vinyl alcohol) with high yield by novel one-batch suspension polymerization of vinyl acetate and saponification

Generally, owing to tautomerism of vinyl alcohol monomer, poly(vinyl alcohol) (PVA) cannot be obtained by direct polymerization but it can be obtained by the saponification of poly(vinyl ester) precursors such as poly(vinyl acetate) (PVAc). In this study, to obtain high-molecular-weight (HMW) PVA with high yield through a one-batch method, we tried continuous saponification of PVAc prepared by suspension polymerization of vinyl acetate (VAc). We controlled various polymerization conditions, such as polymerization temperature, initiator concentration, suspending agent concentration, agitation speed, and VAc/water ratio, and obtained PVAc with a maximum conversion of VAc into PVAc of over 95–98%. PVA beads having various molecular parameters were prepared by continuous saponification of PVAc microspheres. Despite our employing a one-batch process, a maximum degree of saponification of 99.9% could be obtained. Continuous heterogeneous saponification of prepared PVAc yielded HMW PVA having a number-average degree of polymerization of 2,500–5,500, a syndiotactic diad content of 51–52%, and degree of saponification of 85.0–99.9%.

Immobilization of Alcaligenes eutrophus using PVA crosslinked with sodium nitrate

A new cell immobilization technique using polyvinyl alcohol crosslinked with sodium nitrate was developed. This new technique can simultaneously eliminate the agglomeration of PVA beads and the toxicity of boric acid caused by the PVA-boric acid and PVA-orthophosphate methods. Alcaligenes eutrophus was immobilized using four different PVA entrapment processes. The stability, swelling, relative mechanical strength and denitrification activity of the PVA beads were compared in this study. © Rapid Science Ltd. 1998

Immobilization of Thiol Proteases onto Porous Poly(vinyl alcohol) Beads

Water-insoluble enzymes were prepared by immobilizing thiol proteases such as, papain, ficin, and bromelain, onto the porous poly(vinyl alcohol) (PVA) beads by covalent fixation. The relative activity (RA) of the immobilized enzymes was found to be rather high toward small ester substrates, N-benzyl-L-arginine ethyl ester (BAEE), but rather low toward casein, a high molecular weight substrate. RA of the immobilized enzymes by the hexamethylene diisocianate (HMDI) method gave an almost constant activity in marked contrast with the immobilized enzymes by the cyanogen bromide (CNBr) method whose activity monotonous decreased with the decreasing amount of immobilized enzymes. The values of the Michaelis constant Km and maximum reaction velocity Vm for free and immobilized enzymes on the porous PVA beads are estimated. Apparent Km values were larger for immobilized enzymes than for the free ones, while Vm values were smaller for the immobilized enzymes. The pH, thermal, and storage stabilities of the immobilized enzymes were higher than those of the free ones. The initial enzymatic activity of the immobilized enzymes remained almost unchanged without any elimination and inactivation of the enzymes, when the batch enzymatic reaction was performed repeatedly, indicating excellent durability.

Synthesis and characterization of suspension‐polymerized poly(vinyl alcohol) beads with core–shell structure

AbstractA new method of preparing large spherical PVA beads (up to 1.5 mm diameter) with a core‐shell structure has been developed. This involves a stepwise saponification of suspension polymerized PVAc beads, followed by a stepwise crosslinking of the PVA core and shell with glutaraldehyde. The resulting composite PVA beads have thin, highly crosslinked outer shells and lightly to moderately crosslinked inner cores of different degrees of crosslinking. In addition to the characterization of structural parameters, the kinetics of solute release and the swelling dynamics, including the transient dimensional changes, have been investigated using proxyphylline as a model compound. © 1992 John Wiley & Sons, Inc.

Composite poly(vinyl alcohol) beads for controlled drug delivery.

A new method of preparing composite poly(vinyl alcohol) (PVA) beads with a double-layer structure has been developed, which involves a stepwise saponification of suspension polymerized poly(vinyl acetate) (PVAc) beads and subsequent stepwise cross-linking of the PVA core and shell with glutaraldehyde. This process results in PVA beads with thin, highly cross-linked outer shells and lightly cross-linked inner cores of different degrees of cross-linking. In addition to structural characterization of the polymer based on equilibrium swelling measurements, the kinetics of water swelling and drug release from these beads were studied at 37 degrees C using acetaminophen and proxyphylline as model drugs. The results show that the outer shell functions as a rate-controlling membrane upon increasing its cross-linking ratio, X, above 0.47. This aspect is reflected in the observed diffusional time lags and constant-rate regions during swelling and drug release. Based on observed time lags, the diffusion coefficient of water through the outer PVA shell with a high cross-linking ratio of X = 0.5 is estimated to be at least six times higher than that of acetaminophen and proxyphylline. In addition, drug diffusion coefficients in the lightly cross-linked PVA core appear to be at least 10 times larger than that in the highly cross-linked outer shell. At lower shell cross-linking ratios (X less than 0.4), the diffusional time lags appear to be absent and the diffusion profiles are apparently first-order (Fickian) in nature.

Preparation of magnetic ion exchangers by cerium-initiated graft polymerization on crosslinked poly (vinyl alcohol)

Magnetic ion-exchange resins, which offer a practicable means of operating ion-exchange processes continuously, can be prepared by graft polymerization of functional monomers on crosslinked poly(vinyl alcohol) (PVA) beads containing γ-Fe 2O 3. Cerium (IV)-initiated graft polymerization of acrylic acid gives weak-acid ion-exchange capacities of up to 5 meq/g. Grafting of acrylamide followed by hydrolysis gives capacities of up to 6 meq/g. Other functional monomers failed to graft to magnetic PVA beads. Grafting of acrylamide and acrylic acid is accompanied by extensive homopolymerization.The graft chains are attached to both the surface and the interior of the beads. The products are resistant to acid hydrolysis and have very high ion-exchange reaction rates. The mechanism of the grafting reaction is discussed.