Chapter 2

Chapter 2 METHODOLOGY

2.1 Preparation of Materials Sago flour (100-mesh, 83% starch) was provided by Prof. Dulce Flores sourced from the province of Agusan del Sur. Glycerol that was used in the experiment was of analytical grade, available from commercial suppliers.

2.2 Preparation of Thermoplastic Sago Starch The thermoplastic starch material was prepared using a method similar to that of Soest and Borger (1996). Starch-plasticized blend formulations consisting of sago starch, water, and glycerol in ratios of 20:80:40 and 40:60:40 were fed into the extruder using the treatments shown in Table 2. The extrudates were tubular due to the round die. Consequently, rectangular samples, 3 cm long and varying thickness and widths based on extrudate properties, were prepared from the tubular extrudates. Three samples were used for each treatment. The samples were subsequently placed in aluminum trays and cooled in an airconditioned environment at 20OC (50 ±5% RH), as suggested by Forssell et al. (1999), for 24 hours before analysis. This was to ensure that there was a constant level of temperature for conditioning the samples. Afterwards, samples were subjected to physical strength testing and biodegradation tests. Table 2. Production conditions of the thermoplastic sago starch sheets.

Treatment

Formulation (glycerol : starch : water)

Glycerol (% wt glycerol/wt starch)

Barrel Temperature(°C)

1

20:80:40

20%

90

2

20:80:40

20%

110

3

40:60:40

40%

90

4

40:60:40

40%

110

25 2. 3 Testing of Tensile Strength Tensile strength is defined as the maximum strength of a material without breaking when a certain load is trying to pull it apart (Daniels, 1989). Using an improvised tensile testing setup patterned after ASTM D638, tensile strength and elongation at break of samples were measured. The testing setup is shown in Figure 7. Three samples were tested per treatment. The upper part of the sample was attached to an iron clamp on an iron stand, whereas on the lower tip a screw clamp was attached. The spring scale was affixed on the screw clamp, and a pulling force was made on the scale hook. The hook was pulled until the material broke into two distinct pieces. The readings in the scale, in kilograms, just before breaking were estimated. The tensile strength was computed using the following formula: (MT x 9.8 m/s2) Strength (in Pa) = -----------------------------------HxW Where MT was the mass reading on the scale just before breaking; 9.8 m/s2 is the acceleration due to gravity; H was the thickness of the sample in meters; and W was the width of the sample in meters (Rosen, 1982).

clamp Iron stand TPS sheet

Screw clamp Spring scale

Fig. 2. The improvised tensile strength testing setup: (A) actual testing setup, with inset showing a close-up view of the polymer attached to the iron clamp; (B) schematic diagram of the testing setup, with x as the length of the TPS sample.

26 2.4 Biodegradability Test

Fig. 3. Sample of compost pile. A compost pile was prepared using garden soil placed in a box of dimensions 2m x 0.7 x 0.4m. A method by Kale et al. (2007) was followed in tracking the degration of TPS samples in the soil, with minor adaptations from Mohee et al. (2007). Two samples each for every treatment, approximately 3 centimeters long each, will be placed in 0.12m x 0.09m mesh bags, and buried 0.25m deep in the compost pile. Weights of every sample for each treatment will be recorded at zero time and after 7 days or until the starch films disappeared. The samples will be taken from the compost every 24 hours for visual observations of appearance and weight or mass reduction. Weight loss will be used as an indication of biodegradability, based on the method by Lai et.al. 2005, using the formula on the next page.

(wo - wf) Weight loss (%) = -------------------wo

x 100

Where wo is the original sample weight and wf is the final sample weight after the soil burial.

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2.5 Resistance to Water Disintegration The resistance of the thermoplastic starch samples to disintegration in water was determined using the method of Fishman et al. (1996) and as suggested by Sitohy and Ramadan (2001). Circular samples resembling discs were made, approximately 0.007 m in diameter; it was ensured that these weighed almost the same (±0.005 kg differences). These were submerged in 100 mL distilled water at 25OC in a beaker. The water was stirred using a magnetic stirring bar at 1000 rpm. The time required for each disc to visually disappear was measured through a stopwatch. However, if the discs remained undissolved after 20 minutes, they were considered resistant to disintegration. There were three discs used for each treatment.

Fig. 4. The resistance to water disintegration setup. 2.6 Statistical Analysis The following statistical tests were employed to analyze and interpret the results of the study: Mean. This was used to determine the average tensile strength at break and the average percent weight loss of the TPS samples.

28 One-Way Analysis of Variance. This was used to determine significance of the difference on the mean tensile strength at break and the mean percent weight loss of the TPS samples. Tukey’s Honestly Significant Difference. This post hoc multiple comparison procedure for analysis of variance was used to determine whether a significant difference between different treatments. All data are computerized using the Mega Stat Menu. In a 95% confidence interval, paired groups with significance level of ≤ 0.05 were considered to be significantly different.