R. Smith

Porous biodegradable polyesters. I. Preparation of porous poly(L-lactide) films by extraction of poly(ethylene oxide) from their blends

Porous poly(L-lactide) (PLLA) films were prepared by water extraction of poly(ethylene oxide) (PEO) from solution-cast PLLA and PEO blend films. The dependence of blend ratio and molecular weight of PEO on the porosity and pore size of films was investigated by gravimetry and scanning electron microscopy. The film porosity and extracted weight ratio were in good agreement with the expected for porous films prepared using PEO of low molecular weight (Mw = 1 × 103), but shifted to lower values than expected when high molecular weight PEO (Mw = 1 × 105) was utilized. The maximum pore size was larger for porous films prepared from PEO having higher molecular weight, when compared at the same blending ratio of PLLA and PEO before water extraction. Differential scanning calorimetry of as-cast PLLA and PEO blend films revealed that PLLA and PEO were phase-separated at least after solvent evaporation. On the other hand, comparison of blend films before and after extraction suggested that a small amount of PEO was trapped in the amorphous region between PLLA crystallites even after water extraction and hindered PLLA crystallization during solvent evaporation.

Effect of cross-linking agents on the dynamic mechanical properties of hydrogel blends of poly(acrylic acid)-poly(vinyl alcohol-vinyl acetate)

A range of hydrogels were prepared by blending aqueous solutions of poly(vinyl alcohol-vinyl acetate) with poly(acrylic acid) in various proportions. The effects of two cross-linking agents (glyoxal and glutaraldehyde) and subsequent thermal treatment on the properties of the blends are discussed. Dynamic mechanical analysis (DMA) of the xerogels indicated complete miscibility of the various blends which was evident from the appearance of a single glass transition temperature (Tg) in the presence of either glyoxal or glutaraldehyde at all thermal treatments studied. A 50/50% wt/wt blend was found to have the highest storage modulus and was thus selected for further study. Hydrogels prepared with glutaraldehyde without subsequent thermal treatment exhibited higher storage modulus values than those prepared using glyoxal when tested isothermally at 20 degrees C in a water bath. A further increase in the storage modulus was observed when these hydrogels were thermally treated at 120 or 150 degrees C. In a non-isothermal study on the cross-linked hydrogels, no variation in storage modulus was observed. Broad peaks were observed in tan delta plots, these peaks shifting towards higher frequencies as the degree of cross-linking increased in the hydrogel.

Characterization of hydrogel blends of poly(vinyl pyrrolidone) and poly(vinyl alcohol-vinyl acetate)

Hydrogel blends were prepared from water-soluble polymers of poly(vinyl alcohol-vinyl acetate) and poly(vinyl pyrrolidone). The method of preparation was optimized and different compositions of blends were characterized. The effect of thermal treatment and the introduction of an aldehydic crosslinking agent in the blend was also studied. The swelling characteristics of the various compositions, their thermal behaviour and the state of water was examined. Mechanical properties of the hydrogels were determined and it was observed that blends containing glutaraldehyde produced materials with good mechanical integrity and high water contents.