**3.2 Effects of functional group type and number of plasticizers on the properties of biobased films**

Physicochemical properties of blend films are substantially affected by the functional groups of plasticizers used in PVA/starch biobased films. The total number of both carboxyl and hydroxyl groups in plasticizers were given in **Table 2** along with their behaviors in films. For instance, as regards the hydroxyl and carboxyl groups of glycerol (H.3, C.0) and succinic acid (H.0, C.2), the E% of the glycerol-added film has shown a high enhancement than that of the films containing succinic acid, contrarily to the TS behavior. However, when malic acid (H.1, C.2) in the same carboxyl number with succinic acid (H.0, C.2) was added to the film, the TS and E% were improved compared to glycerol (H.3, C.0) and sorbitol (H.6, C.0) because of the presence of two functional groups. Depending on the increasing functional groups of plasticizer, TS and E% of tartaric acid (H.2, C.2) added biobased films with two same functional groups were greater than those of malic acid, glycerol, and sorbitol [6, 30]. Furthermore, the biobased films containing citric acid (H.1, C.3) were stronger and more flexible than that of containing glycerol [7, 30] and xylitol (H.5, C.0) [31]. On the other hand, when the glycerol and xylitol added films were compared, it was found that xylitol-added biobased films had a higher strength and more elasticity than glycerol-added biobased films due to its 5 hydroxyl groups [31]. Even a few xylitol molecules can play an extra role in plasticizer than others [32]. Similarly, the comparison of glycerol- and sorbitoladded films showed that TS and E% of sorbitol-added film were greater than glycerol [7, 30]. Consequently, E% value increases while TS decreases with an increase in the total functional groups and the amount of these plasticizers in blend films.

The concept of plasticization could be understood with the analysis of different properties such as elongation at break (mentioned above) or glass transition point (Tg). For instance, Aydin et al. reported that the addition of plasticizers reduced the Tg point clearly and the change of plasticizing performances could be observed by increasing Tg point. Apart from the above-mentioned plasticizers, 1,4-Butanediol (H.2, C.0), 1,2,6-Hexanetriol (H.3, C.0), pentaerythritol (H.4, C.0), xylitol (H.5, C.0), and mannitol (H.6, C.0) from 2 to 6 hydroxyl groups have also been investigated based on the changes in Tg point. Among the investigated plasticizers, 1,4-butanediol demonstrated the maximum plasticizing effect for starch and PVA due to small molecular size and geometry [32]. **Table 2** shows the effects of the various plasticizers with different functional groups and number on the properties of PVA/starch films.


**7**

lower [7].

and PVA.

**Table 2.**

*The Effects of Novel Additives Used in PVA/Starch Biohybrid Films*

The different plasticizing effect of xylitol and mannitol was attributed to lower penetration capability. Due to larger molecular geometry and size of 1,2,6-Hexanetriol and pentaerythritol, further penetration into the chain fragment of starch and PVA was prevented. Moreover, the plasticizer efficiency of pentaerythritol was generally lower than that of 1,4-butanediol, 1,2,6-Hexanetriol, xylitol, and mannitol. Consequently, the increase in hydroxyl

*Effect of functional group type and number on the plasticization in PVA/starch films.*

**H1 C2**

**Numbers**

2 2

**Funct. groups Formula Reference**

1 2 [6, 30]

1 3 [31]

groups and molecular size of the plasticizers such as mannitol caused an improvement in the thermomechanical stability on the contrary of xylitol. For example, the maximum amount of mannitol (due to more hydroxyl number) in the films tends to interact more with the blend, on the contrary, with lower hydroxyl number plasticizers [32]. Based on the literature data obtained, it could be expressed that the molecular structure and geometry of plasticizers could inhibit or support their penetration into the molecular chain segments and reduce or increase inter- and intramolecular interactions, although the number of hydroxyl groups of plasticizers is hydrogen bonding quarters for starch

The presence of two type of functional groups could also significantly influence other properties of biobased films. For instance, the citric acid could improve the water stability and inhibit degradation of starch molecules [15]. Due to the very strong interaction of water with glycerol and sorbitol, the solubility values were higher than the plasticizer with carboxyl groups. While the solubility of tartaric and citric acids was easy in water, their solubility value was lower than that of glycerol and sorbitol [7]. Eventually, the degree of swelling and mechanical properties of biofilms could decrease or increase slightly with the increasing content of plasticizer depending on functional groups [30]. However, the degree of swelling of the films without plasticizer was higher than that of films containing additives, while the solubility of films without plasticizer was

*DOI: http://dx.doi.org/10.5772/intechopen.81727*

**characteristics and obtained improvement**

the TS and E% than those of glycerol, sorbitol, and succinic acid due to both hydroxyl and carboxyl

acid, glycerol, and sorbitol, it had a higher

carboxyl groups, its TS and E% were stronger than those of glycerol and xylitol.

TS and E%.

**Plasticizer added PVA/starch film** 

Malic acid It has a good effect on

groups.

Tartaric acid Compared to malic

Citric acid Due to hydroxyl and


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

**Table 2.**

*Fillers - Synthesis, Characterization and Industrial Application*

**H1 C2**

**Numbers**

4 —

**Funct. groups Formula Reference**

2 — [32]

3 — [6]

3 — [32]

5 — 1[31], 2[32]

6 — [30]

6 — [32]

— 2 [6]

**characteristics and obtained improvement**

investigated plasticizers with 2 and 6 hydroxyl groups, it showed the highest plasticizing effect for starch and PVA due to small molecular size and geometry.

glycerol-added film was higher than that of succinic acid on the contrary TS.

into the chain fragment of starch and PVA was prevented because of their larger molecular

**Plasticizer added PVA/starch film** 

1,4-Butanediol Among the

Glycerol The E% of the

1,2,6-Hexanetriol Further penetration

Pentaerythritol Due to molecular size

Xylitol Compared to the

Sorbitol Mechanical properties

films.

Mannitol It can enhance the

Succinic acid It is too fragile to be

geometry.

and geometry, its plasticizer efficiency was generally lower than 1,4-butanediol, 1,2,6-Hexanetriol, xylitol, and mannitol.

glycerol, its TS and E% had more potential1

of sorbitol-added films were higher than those of glycerol-added

thermal stability.

used in applications

However, after its continuous addition, penetration capability into molecular chains tended to be lower2

.

.

**6**

*Effect of functional group type and number on the plasticization in PVA/starch films.*

The different plasticizing effect of xylitol and mannitol was attributed to lower penetration capability. Due to larger molecular geometry and size of 1,2,6-Hexanetriol and pentaerythritol, further penetration into the chain fragment of starch and PVA was prevented. Moreover, the plasticizer efficiency of pentaerythritol was generally lower than that of 1,4-butanediol, 1,2,6-Hexanetriol, xylitol, and mannitol. Consequently, the increase in hydroxyl groups and molecular size of the plasticizers such as mannitol caused an improvement in the thermomechanical stability on the contrary of xylitol. For example, the maximum amount of mannitol (due to more hydroxyl number) in the films tends to interact more with the blend, on the contrary, with lower hydroxyl number plasticizers [32]. Based on the literature data obtained, it could be expressed that the molecular structure and geometry of plasticizers could inhibit or support their penetration into the molecular chain segments and reduce or increase inter- and intramolecular interactions, although the number of hydroxyl groups of plasticizers is hydrogen bonding quarters for starch and PVA.

The presence of two type of functional groups could also significantly influence other properties of biobased films. For instance, the citric acid could improve the water stability and inhibit degradation of starch molecules [15]. Due to the very strong interaction of water with glycerol and sorbitol, the solubility values were higher than the plasticizer with carboxyl groups. While the solubility of tartaric and citric acids was easy in water, their solubility value was lower than that of glycerol and sorbitol [7]. Eventually, the degree of swelling and mechanical properties of biofilms could decrease or increase slightly with the increasing content of plasticizer depending on functional groups [30]. However, the degree of swelling of the films without plasticizer was higher than that of films containing additives, while the solubility of films without plasticizer was lower [7].
