*The Effects of Novel Additives Used in PVA/Starch Biohybrid Films DOI: http://dx.doi.org/10.5772/intechopen.81727*

*Fillers - Synthesis, Characterization and Industrial Application*

**3.1 Plasticizers**

cross-linkers, fillers, and chemical and physical modifications.

modifications have been discussed under the following subheadings as plasticizers,

Plasticizers are additives that increase the elasticity. These are the ingredients for nonthermoplastic starch, which are added in order to alter their physical properties. Plasticization takes place in the amorphous zone, which has a higher molecular dynamism. The type and the amount of plasticizer have an important influence on the ability to hinder hydrogen bonding along the polymer chains. The major gain obtained from utilization of plasticizers is that the tensile strength (TS) is decreased, while the elongation at break (E%) increases as well as they become more flexible [26]. One of the most important properties of an efficient plasticizer is to be compatible with the polymer matrix. The plasticizers such as glycerol, polyethylene glycol, urea, ascorbic acid, sorbitol, citric acid, and tartaric acid are usually used [19]. However, the plasticizers in the biobased films cause an increase in permeability to moisture, oxygen, and aromatic compounds [27]. **Table 1** presents the various plasticizers and used methods along with the effects of plasticization on some properties of PVA/starch films.

Water is accepted as a basic plasticizer for PVA/starch biofilms. Physicochemical properties of films could differ based on the changing water content. At the same time, the water is also compatible with other plasticizers. When the plasticizers are added into biofilm formulations, the physical properties are affected due to the increasing relative moisture because of compatibility with water. Possibly, water is absorbed because of polarity compliance to the solubility of other plasticizers added as additives. The plasticizer effect of water could usually be effective when it is used also together or not with an above-mentioned plasticizer. Furthermore, glycerol, sorbitol, and citric acid are generally favored as an efficient plasticizer for PVA/starch films. According to previous studies, the E% increased while TS decreased because of increasing glycerol, sorbitol, and citric acid ratio from 10 to 50% in the biobased films. It was also reported that E% and TS of sorbitol or citric acid–added films were higher than those of the glycerol-added films. However, the water absorption property of the biobased film decreased with the increasing glycerol ratio due to its hydrophobicity [29]. Moreover, the swelling behavior of the film containing glycerol was the lowest compared to the sorbitol- and citric acid-added films due to weaker hydrogen bonding capabilities,

unlike the solubility value due to weaker hydrogen bonding capable [8].

recorded when the storage relative humidity increased from 15%

and degree of the compatibility with PVA and starch were lower compared to sorbitol and citric acid. However, solubility was

with PVA and starch in comparison with glycerol and sorbitol.

It exhibited synergistic effects and the compatibility, especially E%,

*Effect of plasticization on some characteristics of PVA/starch films along with obtained improvements.*

Water A large decrease in tensile strength in all the tested films was

Glycerol E% increased while TS decreased. TS, E%, swelling behavior,

Formamide It was not a good plasticizer and could not improve the compatibility and flexibility of the blend.

with simultaneously added urea in the blend.

Urea It had a good interaction, homogeneity, and sensitivity to the water

**Characteristics of PVA/starch film and obtained improvement Processing** 

**method**

Casting [8]

Casting [8]

Casting [28]

Casting [19]

**Reference**

**4**

**Table 1.**

**Plasticizers added**

to 33%.

higher.

The homogeneity of PVA/starch biobased films could also be enhanced with the addition of urea, like glycerol. However, urea as a plasticizer showed stronger interactions with starch and PVA in biofilms than those of glycerol and sorbitol [11, 28]. Consequently, urea was considered a better plasticizer to improve the flexibility of PVA/starch films [19]. Furthermore, the crystallinity of biobased films was also decreased by the addition of urea and formamide. These agents could penetrate into the crystallization zone of PVA/starch biobased films during the process forming new hydrogen bonds with starch and PVA molecules, which damage the crystal region of PVA in the biobased films. However, formamide is not a good plasticizer and could not develop the compatibility and flexibility of the biobased films, while the compatibility was improved when it combined with urea. When the additives containing both urea and formamide are simultaneously used, their synergistic effects and the compatibility could occur in the blend. Besides, while TS and young modulus of biobased films were significantly decreased, the E% was substantially improved. With the increasing amount of urea in the biobased films, the sensitivity to water increased, while the melting point of blends decreased. It was likely due to the facilitation of molecular ability of both urea and formamide as a plasticizer [19].
