Sarti B, Scandola M
Dipartimento di Chimica G. Ciamician dell'Università di Bologna, Italy.
Biomaterials. 1995 Jul;16(10):785-92. doi: 10.1016/0142-9612(95)99641-x.
Blends of poly(vinyl alcohol) (PVA) with collagen and gelatin, prepared from aqueous solution by solvent casting, were investigated by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). After conditioning at 51% relative humidity, collagen and PVA show nearly coincident glass transition temperatures (Tg approximately 35 degrees C), while gelatin has a higher Tg (approximately 70 degrees C). Gelatin/PVA blends show two invariant Tgs, whose temperature and associated specific heat increment clearly indicate the coexistence of two amorphous phases composed of the pure components. Owing to similarity of the Tgs of collagen and PVA after humidity conditioning, 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 relaxation at about 50 degrees C, while both gelatin and collagen display an intense glass transition in the vicinity of 230 degrees C. The DMTA spectra of collagen/PVA and gelatin/PVA blends show two invariant glass transition relaxations at about 50 and 230 degrees C. Absence of any Tg shift with composition demonstrates that the blend components are immiscible. However, blends of PVA with collagen and gelatin form optically clear films with good mechanical properties over the whole range of compositions. It is found that at T > Tg (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 thermodynamically immiscible with both native and denatured collagen, PVA forms mechanically compatible blends with collagen and gelatin.
通过溶液浇铸法从水溶液中制备的聚乙烯醇（PVA）与胶原蛋白和明胶的共混物，采用差示扫描量热法（DSC）和动态热机械分析（DMTA）进行了研究。在相对湿度为51%的条件下进行调湿后，胶原蛋白和PVA的玻璃化转变温度（Tg约为35℃）几乎重合，而明胶的Tg较高（约为70℃）。明胶/PVA共混物显示出两个不变的Tg，其温度和相关的比热增量清楚地表明由纯组分组成的两个非晶相共存。由于调湿后胶原蛋白和PVA的Tg相似，DSC无法表明胶原蛋白/PVA共混物的混溶性。在DMTA实验中，热扫描过程中样品中的吸附水会自由蒸发，PVA在约50℃处显示出玻璃化转变弛豫，而明胶和胶原蛋白在230℃附近均显示出强烈的玻璃化转变。胶原蛋白/PVA和明胶/PVA共混物的DMTA光谱在约50℃和230℃处显示出两个不变的玻璃化转变弛豫。Tg不随组成变化表明共混物组分是不混溶的。然而，PVA与胶原蛋白和明胶的共混物在整个组成范围内形成了具有良好机械性能的光学透明薄膜。研究发现，在T>Tg（PVA）时，共混物的弹性模量（E'）随生物聚合物含量的增加而强烈增加。对于胶原蛋白/PVA共混物，实验得到的E'值与具有并联相的简单两相复合模型的预测结果一致。得出的结论是，尽管PVA与天然和变性胶原蛋白在热力学上是不混溶的，但它与胶原蛋白和明胶形成了机械相容的共混物。
