Chapter 3

Chapter 3 RESULTS AND DISCUSSION 3.1 The Thermoplastic Starch Product The compressed material having been homogenized under high temperature is supposed to have underwent fragmentation, melting, destructurization, plastification and depolymerzation, as described by Averous (2004), forming the product which is plasticized starch is commonly known as thermoplastic starch (TPS). The products differed in terms of texture, hardness, and color. The results on the said observations are shown in Table 3 and Figure 1. Table 3. Observations on the thermoplastic starch extrudates. Treatment 1 2 3 4

Color Dark brown Dark brown Dark brown Dark brown

Observations Hardness Brittle, hard Brittle, hard Brittle, soft Brittle soft

texture Smooth Smooth Smooth Smooth

30

Fig. 6. Thermoplastic starch extrudates. (A) 20% glycerol blend extruded at 90°C; (B) 20% glycerol blend extruded at 110°C; (C) 40% glycerol blend extruded at 90°C; (D) 40% glycerol blend extruded at 110°C. Samples made with 20% (w/w) glycerol at 90°C were found to be hard, and smooth in texture, but were brittle and easily broke nonetheless. Samples with 40% (w/w) glycerol and extruded at 90°C and 110°C produced softer and brittle extrudates, but nonetheless were smooth. All samples were brown in color, which could be attributed possibly to the browning reaction of the sago starch, which was probably enhanced by the plasticizer and increased temperatures (Anthonysamy et al., 2004). Accordingly, sago starch is always associated with browning due to the presence of polyphenols and polyphenol oxidase (Okamoto et al., 1991; Anthonysamy et al., 2004). Generally, samples of lower glycerol content (i.e. 20% w/w) seemed tougher when extruded at lower temperatures, but those with higher glycerol content (i.e. 40% w/w) were soft at the same temperatures; at any rate, all samples extruded at such lower temperature conditions of 90°C and 110°C were smooth in texture. This was due to the fact that at such temperatures, steam was not profusely produced and had less tendency to cause expansion in the extrudates. When starch blends of lower glycerol content are extruded at higher temperatures, they tend to be brittle and soft; those blends of higher glycerol content extruded

31 at higher temperatures tend to be tougher. Probably it was caused by a plastification effect achieved in thermoplastic starch at high glycerol contents (30%-40%) and lower moisture content brought about by higher temperatures inside the barrel, according to Lourdin et al. (1999). However, at lower glycerol contents, the TPS was expected to be brittle as there is an antiplastification effect due to the low plasticizer content (Lourdin et al., 1995). Results obtained, however, were on the contrary.

3.2 Physical properties of the TPS extrudates Testing on tensile strength at break is one way of assessing possible packaging applications of the extrudates. It is proportional to the amount of force necessary to just break a TPS sample into two distinct species. Table 4 shows the results for the said test. Table 4. One-way Analysis of Variance for the Mean Tensile strength at Break of TPS. Treatment

Mean Tensile Strength* 0.34996a

T1 (20% glycerol; 90°C) T2 (20% glycerol; 0.34696a 110°C) T3 (40% glycerol; 90°C) 0.26346b T3 (40% glycerol; 0.26646b 110°C) p-value < 0.05 level of significance

Computed F-ratio

8.59

P-value

0.0323

* Means having different subscripts differ significantly from each other.

Using one-way Anova (Analysis of Variance), results showed that there was a significant difference among the four treatments used in this study. Results were then subjected to a pairwise comparison of means using Tukey’s HSD Test to determine which treatments are significantly different among the rest. Tensile strength at break of samples containing 20% glycerol extruded at 90°C and 110°C were not significantly with each other. This signifies that when samples containing the said amount of glycerol extruded at both temperatures will yield samples of comparable strengths at break. Similarly, samples containing 40% glycerol extruded at barrel temperatures of 90°C and 110°C yielded similar tensile strengths at break;

32 hence, at lower temperatures of extrusion (i.e. 90°C), TPS samples can carry specific amounts of load as good as that extruded at a higher temperature (i.e.110°C). For extruded samples with 20% glycerol (w/w), the tensile strength at break generally decreased as barrel temperature increased. For those samples containing higher glycerol content (i.e. 40%), tensile strength at break generally increased as the barrel temperature increased. The blend with 20% glycerol extruded at the lowest temperature (90°C) exhibit the greatest tensile strength at break, higher than any of the blends containing a higher amount of glycerol (40% w/w) extruded in all testing barrel temperatures. Similarly, the blend containing 20% glycerol extruded at 110°C had relatively higher tensile strength at break than all the extrudates with higher plasticizer content. According to Curvelo et al. (2001), TPS properties vary according to the type of starch used, emphasizing the amylose content. Sago starch contains about 214% to 31% amylose (Ahmad et al., 1999). The almost linear proportional increase of breaking forces and elongation according to the amylose content can be explained through the larger agglomeration capacity of linear amylose molecules; the ramified structures of amylopectin originate nodules. Hence, thermoplastic materials from sago starch have considerable tensile strength due to its low amylose content; the higher amylopectin content of starch is responsible for counteracting such agglomerations. However, even if the values of maximum forces for breaking are acceptable, materials have been fragile due to their low deformation, which accordingly is just about 6%. This property explains the reason why it is necessary to add plasticizers to enhance the plasticity of TPS (Lourdin et al., 1999). According to Lourdin et al. (1995 and 1999), the effect of the amylose content is considered a favorable factor when there is no plasticizer. Nonetheless, when plasticizers are added, there is a reverse effect, since films with a larger content of amylopectin react more and have a larger plasticity. In this case, starches with lower amylose content can be preferable (Averous et al., 2000). Hence, sago starch appeared to be favorable in terms of being a substrate, and can possibly be used in TPS materials. However, at higher glycerol contents, an antiplastification effect was noted. Moreover, at increased temperatures, there

33 was an increase in the force necessary to break the samples into two, although at smaller degrees only. Such can be attributed to the fact that at increasing plasticizer contents, interchain bonding strength is reduced and tensile strength decreased (Daniels, 1989; Ma and Yu, 2004-b). the interference of plasticizers in chain bonding is very crucial in determining the content of plasticizers which consequently affects the strength of the thermoplastic material. However, the higher temperatures may cause the volatilization may also be the reason why at higher temperatures for the extrusion of blends of lower glycerol content, the extrudates was brittle and smooth due to the lack of plasticizers.

3.3 Biodegradation of TPS Due to their nature, TPS materials are considered to be biodegradable polymer which can be acted upon by microorganisms (Averous et al., 2002; Averous et al., 2004). In the experiment, the results for biodegradation are preliminary, and tend to asses only the general biodegradation of the extrudates, regardless of the extent. As observed, there were losses in the integrity f the plasticized samples. This is one proof of the extruder’s success in plasticizing the sago starch-glycerol blends after the extrusion process. Table 5. Weight loss(%) of TPS samples after soil burial. Treatment 1 2 3 4

Weight loss (%) Garden Soil 0.417362 0.449294 0.574713 0.488759

3.4 Resistance to Water Disintegration The disintegration of TPS extrudates was determined, and results are presented below. The term disintegration in this context means the transformation of the plastic film into very small tiny pieces as visually judged. Samples in all treatments did not dissolve in 25°C water, using a mixing speed of 1000 rpm, within the specified cut-off time. This simply means that the extrudates are possibly insoluble in water, and have fewer tendencies to easily

34 get disintegrated by the said solvent. Nonetheless, at temperatures approaching the gelatinization temperatures of starch, the starch granules in the thermoplastic starch will tend to swell in an aqueous medium (Sim et al., 1991). The solubility of sago starch, and any starch for that matter, in aqueous medium increases with temperature (Ahmad and Williams, 1998), hence, the thermoplastic starch materials possibly disintegrate at higher temperatures. Nevertheless, a visual basis of disintegration is still inadequate to ascertain solubility in water, and other methods of chemical analysis may be employed to substantiate the claims. With the results, it can be said that the material is suitable as garbage liners with high moisture levels as they do not readily dissolve in such aqueous media. Table 6. Resistance of TPS extrudates to disintegration in water. Treatment Disintegration timez (s) 1 (20% glycerol; 90°C) > 1200 2 (20% glycerol; 110°C) > 1200 3 (40% glycerol; 90°C) > 1200 4 (40% glycerol; 110°C) > 1200 z time for dissolving exceeded the limit of 20 mins or 1200s; disc were considered insoluble in water.