Assessing Thermal Characteristics of Polyhydroxybutyrate Based Composites Reinforced with Different Natural Fibres Mikael Skrifvars 1 , Rathish Rajan 2 and Kuruvilla Joseph 3 1) School of Engineering, University of Borås, S-501 90 Borås, Sweden 2) St. Berchmans College , Mahatma Gandhi University, Kerala, India 3) Indian Institute of Space Science and Technology, ISRO.P.O, Thiruvananthapuram, Kerala, India