**2.2. Preparation of RHF-reinforced biocomposites**

The pre-extruded TPB pellets were compounded with RHF and 3 phc of MAPE at temperature profiles of 170, 215, 210 and 195 °C and screw speed of 30 rpm. Prior to extrusion, RHF was oven-dried at 90 °C for 24 h to remove the moisture of RHF. After extrusion, the compression moulding was performed at 200 °C using a hot/cold press machine (LP50, Labtech Engineering Company Ltd.). The preheating, venting, full pressing and cold pressing times were set at 3, 2, 5 and 5 min, respectively. In this study, the experimental variables studied were polymer blend types (UTPB and CTPB) and rice husk flour content (50, 60, 70 and 80 wt%).

#### **2.3. Characterization**

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. 1 and 2:

$$\text{WA (\%)} = \frac{W\_\text{\tiny{}} - W\_\text{\tiny{}}}{W\_\text{\tiny{}}} \times 100\tag{1}$$

$$\text{TS}(\% \text{\textquotedblleft} \text{\textquotedblright}) = \frac{T\_\text{\textquotedblleft} - T\_\text{\textquotedblright}}{T\_\text{\textquotedblleft}} \times 100 \text{\textquotedblright} \tag{2}$$

where *W*0 and *Wt* represent the oven-dry weight (the initial weight) and weight after water exposure at time *t*, respectively, whereas *T*0 and *Tt* represent the oven-dry thickness and thickness after water exposure at time *t*, respectively. Three replicates of specimens were tested for each formulation to obtain the average results.

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 to obtain the average results.

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 equation of *V* = *L*/*t* where *V* is the burning rates (mm/s), *L* is the burned length (mm) and *t* is the burning time (seconds).

The morphology of the fracture surface of broken sample from tensile testing was analysed using SEM (VPSEM Philips XL-30). The samples were sputter-coated with gold before examination of SEM.
