Abstract
Abstract Blends of zein and poly(vinyl alcohol) (PVAl) were processed in an internal mixer (150oC, 50 rpm) for 5-8 minutes. Glycerol and oleic acid were used as plasticizers. The mixtures obtained were then compression molded and further characterized by Fourier transform infrared spectroscopy (FTIR), water-absorption experiments, mechanical tests, and scanning electron microscopy (SEM). FTIR analysis indicated the existence of hydrogen bonding interactions between zein and PVAl. Tensile tests showed that the addition of PVAl increased the flexibility of the blends. The tensile strength ranged from 1.7 to 5.7 MPa, elongation at break ranged from 2.7 to 32% and Young’s modulus ranged from 433 to 7371 MPa. Water absorption at equilibrium decreased with increasing zein content, which favored a brittle behavior in the zein/PVAl. The blends were immiscible in the composition studied and the presence of voids indicated poor interfacial interaction between the polymers.
Highlights
Zein is a corn protein that represents about 80% of the total proteins in corn grains[1]
In the poly(vinyl alcohol) (PVAl)/glycerol (0/100) mixture, the torque reached a stable value of around 0.3 ± 0.1 Nm, and no change was observed in the torque curve after the melting of polymer, indicating that no loss of plasticizer, crosslinking or degradation occurred during the processing of the PVAl / glycerol mixture
The torque values of the zein/PVAl blends at equilibrium were 1.1 ± 0.3 Nm, 2.4 ± 0.3 Nm, and 3.8 ± 0.3 Nm, respectively, for compositions 25/75, 50/50 and 75/25. These values were much lower than that of the plasticized zein, indicating that blend processing was facilitated by the addition of PVAl and glycerol, which reduced the viscosity
Summary
Zein is a corn protein that represents about 80% of the total proteins in corn grains[1]. As a hydrophobic molecule, is a primary plasticizer, meaning it can effectively plasticize the zein film on its own with a low level of water vapor barrier[14]. Xu et al.[15] studied the effect glycerol and oleic acid mixtures to plasticize zein films. To the best of author’s knowledge, only three papers dealing to zein/PVAl blends are reported in the literature[23,25,26]. In these studies, the zein/PVAl blends were prepared by casting and using glycerol as plasticizer. Oleic acid and glycerol were investigated as plasticizers to process the zein/PVAl blends
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