**4.1 Effect of glycerol content on morphology**

PE/TPS blends display a discrete morphology where LDPE is the matrix, especially at low TPS content. The combined effect of glycerol content and the elongational flow exerted on PE/TPS blends (TPS concentration 30 wt%) during quenching can be observed in Figure 6. PE1 blends prepared with TPS40 and TPS36 (Figures 6a and 6b) show a high level of deformation in the machine direction. Conversely, blends compounded with TPS29 show very little deformation (Figure 6c) and even less when prepared with PE2 (Figure 6d). The singular morphologies displayed by PE/TPS blends are closely related to the differences in viscosity of both TPS and PE. As mentioned in section 3, it was found that 30% glycerol is required to effectively plasticize starch (Rodriguez-Gonzalez et al., 2004). From Figure 6, it can be seen that below that limit, the viscosity and elasticity of TPS are too high to allow the LDPE matrix to greatly deform the TPS dispersed phase. When the Low-viscosity PE2 is used, it can be seen (Figure 6d) that the dispersed particles of TPS are of a spherical nature and that the particle size has increased compared to those of PE2/TPS29 blends (Figure 6c). These results clearly demonstrate that a high degree of morphological control is possible for this system and that the full range from spherical dispersed phase to that of a highly deformed fibrillar phase can be obtained at a given TPS concentration level. In fact, it is apparent that the control of the glycerol concentration allows one to modify the state of the starch from that of a solid particle to that of a quasi crosslinked dispersed phase to that of a highly deformable material.

#### **4.2 Effect of TPS concentration on morphology**

The axial direction morphology of PE1/TPS36 blends was a combination of large fiber-like structures with small spherical-like particles (Figure 7). Increasing the TPS concentration reduces the number of small spherical particles due to particle-particle coalescence. The larger particle size of the TPS domains plus particle coalescence leads to the lengthening of TPS fibers in the machine direction. At high TPS loadings (above 45 wt%), it was difficult to distinguish whether LDPE or TPS constituted the matrix. Both components appear to be fully continuous in the axial draw direction. The orientation imposed by the elongational flow field at the die exit plays an important role in the continuity development of starch in these PE/TPS blends.

The starch domain size increases in PE1/TPS29 as the TPS29 content increases (Figure 8). In contrast to the high continuity observed for the low-viscosity low-elasticity TPS36, TPS29 particles remain dispersed in a PE1 matrix, even at high loadings (conc. of TPS 49 wt%). It can be observed from Figure 8 that increasing the concentration of the TPS at low glycerol contents has little effect on the particle shape.

fed to the hopper of the twin-screw extruder and, as described in section 3, water-free TPS having 29, 36 and 40% glycerol (TPS29, TPS36 and TPS40, respectively) were prepared and melt blended with the LDPE as depicted in Figure 5. In order to evaluate the effect of PE and TPS viscosities on the morphology of LDPE/TPS blends two commercial LDPE resins, LDPE2040 (PE1, MFI = 12g/10min) and LDPE2049 (PE2, MFI = 20g/10min), and the three

PE/TPS blends display a discrete morphology where LDPE is the matrix, especially at low TPS content. The combined effect of glycerol content and the elongational flow exerted on PE/TPS blends (TPS concentration 30 wt%) during quenching can be observed in Figure 6. PE1 blends prepared with TPS40 and TPS36 (Figures 6a and 6b) show a high level of deformation in the machine direction. Conversely, blends compounded with TPS29 show very little deformation (Figure 6c) and even less when prepared with PE2 (Figure 6d). The singular morphologies displayed by PE/TPS blends are closely related to the differences in viscosity of both TPS and PE. As mentioned in section 3, it was found that 30% glycerol is required to effectively plasticize starch (Rodriguez-Gonzalez et al., 2004). From Figure 6, it can be seen that below that limit, the viscosity and elasticity of TPS are too high to allow the LDPE matrix to greatly deform the TPS dispersed phase. When the Low-viscosity PE2 is used, it can be seen (Figure 6d) that the dispersed particles of TPS are of a spherical nature and that the particle size has increased compared to those of PE2/TPS29 blends (Figure 6c). These results clearly demonstrate that a high degree of morphological control is possible for this system and that the full range from spherical dispersed phase to that of a highly deformed fibrillar phase can be obtained at a given TPS concentration level. In fact, it is apparent that the control of the glycerol concentration allows one to modify the state of the starch from that of a solid particle to that of a quasi crosslinked dispersed phase to that of a

The axial direction morphology of PE1/TPS36 blends was a combination of large fiber-like structures with small spherical-like particles (Figure 7). Increasing the TPS concentration reduces the number of small spherical particles due to particle-particle coalescence. The larger particle size of the TPS domains plus particle coalescence leads to the lengthening of TPS fibers in the machine direction. At high TPS loadings (above 45 wt%), it was difficult to distinguish whether LDPE or TPS constituted the matrix. Both components appear to be fully continuous in the axial draw direction. The orientation imposed by the elongational flow field at the die exit plays an important role in the continuity development of starch in

The starch domain size increases in PE1/TPS29 as the TPS29 content increases (Figure 8). In contrast to the high continuity observed for the low-viscosity low-elasticity TPS36, TPS29 particles remain dispersed in a PE1 matrix, even at high loadings (conc. of TPS 49 wt%). It can be observed from Figure 8 that increasing the concentration of the TPS at low glycerol

TPS were used.

highly deformable material.

these PE/TPS blends.

**4.2 Effect of TPS concentration on morphology** 

contents has little effect on the particle shape.

**4.1 Effect of glycerol content on morphology** 

Fig. 6. Effect of glycerol content and LDPE viscosity on the morphology of microtomed PE/TPS (70/30) blends. PE1/TPS blends: a) 40% glycerol, b) 36% glycerol, and c) 29% glycerol. d) PE2/TPS at 29% glycerol content. The black bar below the micrographs represents 10m.

Melt Blending with Thermoplastic Starch 13

Fig. 9. (a) Relative elongation at break (b/b0) and (b) relative Young's Modulus (E/E0) of PE1/TPS blends as a function of TPS concentration (wt%). Terms with subscript 0 refer to

the pure LDPE.

Fig. 7. Influence of TPS concentration on the morphology of PE1/TPS36 blends. a) 29 wt% TPS, b) 36 wt% TPS, c) 45 wt% TPS, and d) 53 wt% TPS. The black bar below the micrographs represents 10m.

Fig. 8. Influence of TPS concentration on the morphology of PE1/TPS29 blends. a) 30 wt% TPS, b) 41 wt% TPS, and c) 49 wt% TPS. The black bar below the micrographs represents 10m.

Fig. 7. Influence of TPS concentration on the morphology of PE1/TPS36 blends. a) 29 wt%

Fig. 8. Influence of TPS concentration on the morphology of PE1/TPS29 blends. a) 30 wt% TPS, b) 41 wt% TPS, and c) 49 wt% TPS. The black bar below the micrographs represents 10m.

TPS, b) 36 wt% TPS, c) 45 wt% TPS, and d) 53 wt% TPS. The black bar below the

micrographs represents 10m.

Fig. 9. (a) Relative elongation at break (b/b0) and (b) relative Young's Modulus (E/E0) of PE1/TPS blends as a function of TPS concentration (wt%). Terms with subscript 0 refer to the pure LDPE.

Melt Blending with Thermoplastic Starch 15

morphology plays an important role on percent continuity of LDPE/TPS40 blends. Blends depicting elongated particles show higher percent continuity at comparative concentrations than those displaying spherical morphology. For instance, PE1/TPS40 blends containing 32% TPS40 have 66% continuity while PE2/TPS40 blends composing of 31% TPS40 have only 38% continuity. Above 50% TPS40, at almost 95% continuity, blend morphology does not make any significant difference. At 62 wt% TPS40 the percent continuity of starch domains reaches 100% and the starch phase could be completely extracted. This is indicative of the full connectivity of starch particles through the entirely sample (Figure 10). The use of hydrolytic degradation as previous technique to biodegradation studies could be an

Fig. 10. Accessibility of starch domains LDPE/TPS40 blends exposed in solution of HCl 6N

Numerous studies have been done to investigate the enzymatic hydrolysis of starch-based materials. These works involve blends system with synthetic polymers like LDPE (Danjaji, 2002), ethylene vinyl acetate (EVA) (Simons & Thomas, 1995; Araujo et al., 2004) and polycaprolactone (PCL) (Seretoudi et al., 2002). The kinetic of enzymatic degradation of TPS40 and LDPE/TPS40 blends is shown in Figure 11. Amylase from the enzymatic cocktail triggers the cleavage of 1-4 acetal link while glucoamylase attacks the 1-6 links of

**4.4.2 Enzymatic degradation of LDPE/TPS40 blends** 

for 72 hours.

important tool to predict enzymatic and bacterial biodegradation.

## **4.3 Mechanical properties**
