Comparison of Thermal Properties in Composites of PHB Using Rice Husk Ash or Talc as Filler
Abstract
This study has been conducted in order to use rationally rice husk ash (RHA) since it is one of the most abundant industrial waste. With the purpose of comparing fillers, composites of PHB (polyhydroxybutyrate) with RHA and PHB with talc (TA), were obtain by twin-screw extrusion and injection molding techniques and characterized by the use of Laser Flash Method and Differential Scanning Calorimetry (DSC). The thermal conductivity value displayed by PHB polymer was 0.419 W∙m-1 ∙K -1 while the composites values were slightly higher, due to the increasing content of the filler. PHB/RHA composite showed maximum values 0.456 W∙m -1 ∙K -1 and, PHB/TA composite was 0.492 W∙m-1 ∙K -1 . As regards to the DSC it can be stated that the presence of filler does not change significantly the thermogram curve, as evidenced by the endothermic peak at 172.96°C, 173.61°C and 171.65°C to PHB, PHB/RHA (85/15) and PHB/TA (85/15), respectively. Fillers from waste contribute to sustainable materials.
Keywords
Download Options
Introduction
Composites have gained more space in various industry segments mostly because these materials make possible a good synergy in the interaction between the different components forming it, resulting in a range of properties inherent to the material and more interesting economic and environmentally friendly than the original components [1-5].
PHB is a biodegradable and biocompatible thermoplastic polymer that can be produced by bacteria from carbohydrates in bioreactors [6]. Its mechanical properties are generally restricted to certain uses due to its fragility. Furthermore, PHB has a narrow processing window and thermal instability near 180 °C [7-10]. In order to be accepted on a large scale, it is evident the need for improvement of its properties and processability is necessary. This can be obtained by adding functional fillers.
Rice husk ash (RHA) is an abundant waste generated from drying rice operation in several countries [11]. The world rice production in the period of 2006 to 2007 was approximately 600 million tons. These represent a generation of 145 million tons of rice husk residue [12]. RHA contends a large amount of silica (SiO2) at least 90% [13, 14]. Despite the great possibilities of using this residue [15], its main application remains as landfill, which is an unsatisfactory solution from both the environmental and economic points of view. Studies have been conducted in order to facilitate the RHA use in a more rational way [16-19]. The use of food waste in the production of bioplastic composite can be a good way to reduce cost of these polymers and the amount of residue to the environment [20].
Conclusion
Composites of PHB/RHA and PHB/TA were obtained with different fillers contents by extrusion and injection molding techniques. The melting temperature of the composites did not change significantly if compared to the pure PHB, and the composites with RHA showed values closer to PHB in DSC analysis. The thermoanalysis showed no indication of any interaction between the polymer and the filler, but a high thermal stability for composites. The pure PHB presented thermal conductivity of about 0.419 W m-1 .K-1 , the composites PHB/RHA increasing thermal conductivities in the range between 0.444 W m-1 .K-1 and 0.456 W m-1 .K-1 , and the composites PHB/TA thermal conductivities in the range of 0.456 W m-1K -1 to 0.492 W m-1 .K-1 , depending on the content of filler addition. The RHA with applications until 15wt% can be used as filler in composites of PHB. Because its influence on the properties examined is not significant, suggesting a better performance as thermal insulation if compared to conventional mineral fillers for polymers as talc. In this case, RHA as a natural filler represents a new category of green material, could be a good alternative under technical and sustainable points of view, since this is one waste, which is abundantly available in the world.