**3. Results and discussion**

2, 5 and 5 min, respectively. In this study, the experimental variables studied were polymer

Water absorption and thickness swelling (TS) tests were performed according to the ASTM D 570-98 method. The specimen (dimension: 76.2 × 25.4 × 3.2 mm) for each formulation was ovendried for 24 h at 100 °C. Each oven-dried specimen was weighed using an analytical balance with a precision of 1 mg; the thickness of each oven-dried specimen was measured using a digital calliper with a precision of 0.01 mm. The specimens were then soaked in distilled water at 25 °C. The weight and thickness changes were determined periodically until 119 days. Specimens were removed from the water, wiped dry with tissue paper and measured. The percentages of water absorption (WA) and thickness swelling (TS) were calculated using Eqs.

> 0 0 WA (%) 100 *W W <sup>t</sup> W*

0 0 TS(%) 100 *T T <sup>t</sup> T*

thickness after water exposure at time *t*, respectively. Three replicates of specimens were tested

Compression-moulded composite panels were cut according to ASTM D 638-03 (type I) for tensile testing, ASTM D 790-03 for flexural testing and ASTM D 256-05 for impact strength. Both tensile and flexural testings are carried out using a universal testing machine (model Testometric M350-10CT) at 5 mm/min. The notched Izod impact testing was performed using the Ray-Ran Universal Pendulum Impact System at 3.46 ms−1 and 2.765 J with a load weight of 0.452 kg. In mechanical tests, five replicates of specimens were tested for each formulation

Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were conducted using a Mettler Toledo TGA/SDTA851e and DSC 882e, respectively, on the samples of about 10–15 mg. Samples of TGA were tested at a heating rate of 10 °C/min over the temperature range from 25 °C to 600 °C, the temperature of complete degradation. Balance accuracy of TGA is ± 0.1 %. The DSC samples were scanned from 25 °C to 300 °C at heating rate of 10 °C/ min, under atmospheric air flow condition. Burning test was carried out in accordance to ASTM D 5048-90 (procedure A—test of bar specimens) to determine the relative burning characteristics and flame-resistance properties. The burning rates of specimens are calculated using the

represent the oven-dry weight (the initial weight) and weight after water



represent the oven-dry thickness and

blend types (UTPB and CTPB) and rice husk flour content (50, 60, 70 and 80 wt%).

**2.3. Characterization**

28 Composites from Renewable and Sustainable Materials

1 and 2:

where *W*0 and *Wt*

to obtain the average results.

exposure at time *t*, respectively, whereas *T*0 and *Tt*

for each formulation to obtain the average results.
