VISCOELASTIC AND THERMAL-PROPERTIES OF COLLAGEN POLY(VINYL ALCOHOL) BLENDS

Blends of poly(vinyl alcohol) (PVA) with collagen and gelatin, prepare d from aqueous solution by solvent casting, were investigated by diffe rential scanning calorimetry (DSC) and dynamic mechanical thermal anal ysis (DMTA). After conditioning at 51% relative humidity, collagen and PVA show nearly coincident glass transition temperatures (T-g approxi mate to 35 degrees C), while gelatin has a higher T-g(approximate to 7 0 degrees C). Gelatin/PVA blends show two invariant T(g)s, whose tempe rature and associated specific heat increment clearly indicate the coe xistence of two amorphous phases composed of the pure components. Owin g to similarity of the T(g)s of collagen and PVA after humidity condit ioning, DSC offers no indication on miscibility of collagen/PVA blends . In DMTA experiments, where absorbed water freely evaporates from the samples during the thermal scan, PVA shows a glass transition relaxat ion at about 50 degrees C, while both gelatin and collagen display an intense glass transition in the vicinity of 230 degrees C. The DMTA sp ectra of collagen/PVA and gelatin/PVA blends show two invariant glass transition relaxations at about 50 and 230 degrees C. Absence of any T -g shift with composition demonstrates that the blend components are i mmiscible. However, blends of PVA with collagen and gelatin form optic ally clear films with good mechanical properties over the whole range of compositions. It is found that at T > T-g (PVA) the elastic modulus (E') of the blends strongly increases with increasing content of the biopolymer. In the case of collagen/PVA blends, experimental E' values agree with the predictions of a simple two-phase composite model with phases connected in parallel. It is concluded that, though thermodyna mically immiscible with both native and denatured collagen, PVA forms mechanically compatible blends with collagen and gelatin.