Rheological Behavior of Polyvinyl Alcohol/Starch Blends: Influence of the Sorbitol Citrate Content

Problems associated with non-biodegradable materials are well known. Polyvinyl alcohol (PVOH)/starch (ST) blend has been reported as a good alternative to replacing non-biodegradable materials in packaging applications. However, this blend is incompatible. Thus, the first aim of this study was to use the sorbitol citrate (SC) as a plasticizing and compatibilizing agent in film-forming solutions composed of 25% w/w PVOH and 75% w/w ST. The second aim was to determine the effect of SC content (0.5, 10, 15 and 20% w/w) on the rheological properties of this blend. The steady shear analysis was carried out at 60, 70, 80, and 90 degrees C, while the sweep amplitude and the frequency analyses were carried out at 90 degrees C. The power law flow index (n) showed no dependence on the SC content, but the consistency index (k) followed the opposite behavior. On the other hand, the values of the reduction percentage of the activation energy (E-a) of the flow (%rE(a)) caused by SC were between 63.56 and 70.12%. This means that SC ostensibly increased the flow of these materials. Viscosity (eta) and E-a values of the PVOH/ST blends prepared with SC were lower than 1000 Pa.s and 2.60 kJ.mol(-1) respectively. All samples showed a thixotropic behavior and it increased with the SC content. The areas of the hysteresis region of these materials were between 101.11 and 192.14 Pa.s. It indicates that these materials have a good elastic recovery. Cole-Cole graphs showed that SC improved the miscibility of the PVOH/ST blend.

Automated summary

By adding 0.5-20% sorbitol citrate (SC) to film-forming solutions composed of 25% polyvinyl alcohol (PVOH) and 75% starch (ST), the compatibility and flowability of PVOH/ST blend can be improved, with reduced viscosity and activation energy, and good elastic recovery.