A Review of the Effect of Plasticizers on the Physical and Mechanical Properties of Alginate-Based Films

Abstract

In recent years, there has been a growing attempt to manipulate various properties of biodegradable materials to use them as alternatives to their synthetic plastic counterparts. Alginate is a polysaccharide extracted from seaweed or soil bacteria that is considered one of the most promising materials for numerous applications. However, alginate potential for various applications is relatively limited due to brittleness, poor mechanical properties, scaling-up difficulties, and high water vapor permeability (WVP). Choosing an appropriate plasticizer can alleviate the situation by providing higher flexibility, workability, processability, and in some cases, higher hydrophobicity. This review paper discusses the main results and developments regarding the effects of various plasticizers on the properties of alginate-based films during the last decades. The plasticizers used for plasticizing alginate were classified into different categories, and their behavior under different concentrations and conditions was studied. Moreover, the drawback effects of plasticizers on the mechanical properties and WVP of the films are discussed. Finally, the role of plasticizers in the improved processing of alginate and the lack of knowledge on some aspects of plasticized alginate films is clarified, and accordingly, some recommendations for more classical studies of the plasticized alginate films in the future are offered.

Keywords: alginate; films; hydrophilic and hydrophobic plasticizers; physical and mechanical properties; plasticization mechanisms; water vapor permeability.

Figure 1

Alginate structure: (a) arrangement of the molecules in alginate; (b) three regions of M-blocks, G-blocks, and alternating sequences of MG-blocks in alginate structure (after [14]).

Figure 2

Schematic illustration of the effect of the most common plasticizer, glycerol, on alginate chains (The color scheme is used for the sake of clarity).

Figure 3

Mechanism of anti-plasticization action (after [38]).

Figure 4

SEM and AFM results of alginate films dried at 25, 57, and 90 °C [77].