## 3 Results and Discussion
### DMA Analysis  
The impact of SA incorporation, with different viscosities, and its crosslinking on the viscoelastic properties of the PW-based matrix was evaluated using dynamic mechanical analysis (DMA). One practical datum obtained from DMA analysis is the glass transition temperature (Tg) of the films, as listed in Table 1. This was determined from the main peak temperature in the Tan \(\delta\) versus temperature curve, as shown in Figure 4. Tg is an important parameter for understanding the flexibility of polymeric materials, defining the temperature range in which the material transitions from a rigid to a flexible state. In the case of packaging applications, Tg provides insights into the material's brittleness and the temperature range in which the material can be used effectively.  
Figure 4: DMA graph of PW, PW/SA (PAlv, PAhv), and crosslinked PW/SA films (PAlv, PAhvx).  
Across all samples, a distinct peak in Tan \(\delta\) was observed at approximately \(-50\)\({}^{\circ}\)C. This peak corresponds to the relaxation temperature of the glycerol-rich phase, indicating that glycerol had a similar effect on all formulations. The primary Tg values of each composite were identified at temperatures above \(0\)\({}^{\circ}\)C [42].  
The pure PW film exhibited a Tg of 60 \({}^{\circ}\)C. The incorporation of SA, regardless of its viscosity, caused a decrease in Tg, indicating increased flexibility at ambient temperatures. This reduction can be attributed to the higher hydrophilic nature of SA, which leads to increased moisture absorption in the composite. Water molecules act as plasticizers, enhancing polymer chain mobility and consequently lowering Tg [43]. Additionally, SA incorporation increases the free volume within the PW/SA matrix due to the irregular shape and size of SA molecules, further contributing to the decrease in Tg [44].  
Typically, a higher molecular weight in polymers leads to an increased Tg due to greater chain entanglement. However, despite its higher molecular weight, PAhv exhibited a lower Tg (38 \({}^{\circ}\)C) compared to PAlv (48 \({}^{\circ}\)C). This discrepancy is attributed to the greater hydrophilicity of hvSA relative to lvSA. The longer chain length of hvSA contributes to increased moisture absorption, as the higher number of carboxyl groups in these extended chains enhances the material's hydrophilic properties.  
Crosslinking further influenced the Tg of the composites. Compared to their non-crosslinked counterparts, Tg decreased by 3 \({}^{\circ}\)C in PAlvx and by 8 \({}^{\circ}\)C in PAhvx composites. Generally, crosslinking is expected to increase Tg due to restricted polymer chain mobility. However, in this case, a significant increase was not observed. This behavior can be explained by the dual effects of crosslinking in polymer systems: increasing free volume and restricting chain mobility. On one hand, crosslinking increases free volume, allowing greater chain mobility and potentially lowering Tg [45]. On the other hand, crosslinking by Ca\({}^{2+}\) ions restricts polymer chain movement due to the formation of an \"egg-box\" structure between SA chains and calcium ions, which would typically increase Tg [46]. The overall effect of crosslinking on Tg depends on the balance between these two opposing factors.