Introduction: With rising environmental awareness, biodegradable polymer material use has also risen.The aliphatic polyesters are high molecular weight biodegradable compounds, easily processable and thus have been extensively investigated. The optimization of structure property relationships of these biomaterials have been achieved by various methods including copolymerization. Blending of these materials offers an innovative and less investigated method of achieving the material properties.
Materials and Methods: In this study, PLA (grade 4032D, NatureWorks LLC), PCL (grade CAPA 6800, Perstorp) and PGA (grade Kuredux100R60) are used. The entire study is performed as follows: Initially PLA/PGA and PLA/PCL are blended in co-rotating twin screw extruder. These hygroscopic materials are desiccated thoroughly before using them for blending as well as all characterisation studies. The blend compositions are 100/0wt%, 95/5wt%, 90/10wt%, 85/15wt% for PLA/PGA and PLA/PCL respectively and extrusion is done. The extruded blends in pellet form is characterised for thermal, rheological and degradation analysis to study the structure property relationship. Thermal characterisation involves differential scanning calorimetry (DSC) and thermo gravimetric analysis (TGA) to study the effect of temperature on blends and understand the processing parameters. Rheological studies include melt flow index (MFI), parallel plate rheometer study and steady shear rheological study from which shear rate and viscosity data is obtained for optimising the extrusion parameters. Degradation studies evaluate the change in mass of blend samples in PBS solution. Based on overall structure-property analysis, composition [1] and processing parameters are optimized for tube extrusion using a single screw extruder.
Results and Discussion: The results for PLA/PCL blends are available while PLA/PGA blends are in the characterisation process. The DSC thermogram shows that the Tc values in the PLA/PCL blend shift to lower temperatures as PCL content increases. It can be deduced that with an increasing of PCL content, the Tc value of PLA/PCL blends decreases indicating that the crystallization of PLA may be affected by the addition of PCL [2]. TGA reveals that blends of PLA/PCL have higher initial degradation temperature than neat PLA because of the addition of PCL which has a high degradation temperature. Melt flow index of PLA/PCL blend decreases with increase in PCL content. In parallel plate rheometer study at a particular frequency and strain amplitude of 0.01, both G’ and G’’ increase with increase in PCL content. PLA95PCL05 represents Newtonian fluid like behaviour as that of PCL and also lowest viscosity among all compositions giving idea of better dispersion and miscibility of the two phases.There is difference in tan delta values at particular frequency of PLA95PCL05 . In degradation studies, it is observed that actual degradation begins after two months for PLA/PCL blends and 1-2% degradation occurs in 3 months. Based on overall structure-property analysis, composition and processing parameters are optimized for tube extrusion using a single screw extruder.
Conclusion: PLA95PCL05 show better dispersion of PCL in PLA and hence some amount of miscibility is observed. While rheological properties explains behavior of melt such as shear viscosity, melt relaxation etc. for the better processability of tubes out of blends.
References:
[1] Llanlal Zhanc, Chencdong Xionc, and Xianmo Denc, Biodegradable Polyester Blends for Bio-medical Application, Journal of Applied Polymer Science, Vol. 56, 1995, 103-112 .
[2] N. Lo´pez-Rodr´ıguez, A. Lo´pez-Arraiza, E. Meaurio, J.R. Sarasua, Crystallization, Morphology, and Mechanical Behavior of Polylactide/Poly(caprolactone) Blends, Polymer Engineering And Science—2006, 1301-1308.