EXPERIMENTAL
Materials
High density polyethylene (HDPE) molecular weight 2.2×105 g/mol, melt flow index 0.3g/min (190°C, 2.16kg), Borealis BS2581 was used as the matrix. Carbon Black was supplied by the Columbian Chemicals Company, talc (Luzenac A3 C) from Lusenac Europe SAS and zinc oxide from US Zinc.
Sample preparation and characterisation
A Haake PolyLab Rheomix was used to mix the HDPE with different amounts of carbon black. The mixing temperature was 180°C, mixing time was 10 minutes and rotational speed was 40 rpm. The materials were then made into sheets 1.5 mm thick by compression moulding at 180°C.
Microwave heating
A modified 800W domestic microwave oven was used for microwave heating experiments. The oven was modified so that the magnetron could be operated continuously on reduced power. Test specimens of filled polymer sheet (1 cm x 5 cm x 0.15 cm) were oriented vertically in the centre of the oven turntable using a block of ceramic foam as support. The initial and final temperature of the sample was recorded using a thermal imaging camera with the oven door opened to allow viewing (FLIR Systems Thermovision® A40).
Other tests
Mechanical properties of dumbbell specimens were measured using a tensile testing machine. Scanning electron microscopy was used to examine the fracture surfaces of the test specimens in order to establish the mode of failure.
RESULTS & DISCUSSION
Table 1 shows the relative temperature rise for carbon black, zinc oxide and talc at the same volume % loading for exposure to 200 W of microwave power for 60s. Tests on unfilled HDPE under the same conditions gave no significant temperature rise.