Characterisation and processing of PLA/PEG/Curcumin microfiber drawn via melt spinning method

Abstract

Poly (lactic acid) (PLA) has been recognized as an excellent candidate to be used as bioplastic and biomaterial due to its biodegradability and biocompatibility with excellent tensile strength. However, PLA has inherent brittleness and has low percentage of elongation at break that may limit its suitability to be used for specific geometrical shape such as fibers for biomedical application. The addition of plasticizer to improve brittleness also results with decrease in strength. Hence, particulates are often added as reinforcement filler. The main objective of this research is to characterize the properties of various PLA/PEG and PLA/PEG/cur blends and investigate the resultant properties of the melt spun microfiber. This research has two main stages. The first stage involved in investigating the effect of polyethylene glycol (PEG) additions into PLA with increments of 5 wt. % up to 30 wt. % to improve the brittleness of PLA. These compositions were then prepared via two blending methods i.e. solvent cast and melt blend. These PLA/PEG blends were structurally and thermally characterized using Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA). Results from the studies showed that as the incorporation of PEG (wt. %) into PLA increases, the IR spectra for O-H band stretching became broader and sharper proposing that hydrogen bonding interaction between the network chains of PEG and PLA. DSC thermograms showed that the incorporations of PEG (wt.%) into PLA blends led to significant decrease in the glass transition temperature (Tg) and the crystallization temperature (Tc). TGA thermograms indicated that the initial degradation temperature for all the PLA/PEG composition shifted systematically to lower temperature with further additions of PEG (wt.%). All PLA/PEG blends were then successfully drawn via an in-house built fiber drawing tower with diameter ranging from 15µm to 112µm. These fibers were further characterized using optical microscope (OM) and scanning electron microscopy (SEM). The images obtained showed that the surface of the PLA/PEG microfibers were bead-free and had uniformly circular cross-sections. The surface of the fiber transitioned from smooth to slightly rough with increasing PEG content (wt.%) regardless of the blending method postulated due to thermally induced phase separation of PLA and PEG. It was noted that PLA/PEG microfiber prepared via melt blending were more brittle and fractured easily. Thus, only fibers obtained from solvent cast PLA/PEG blends were further tested for single fiber tensile test (SFTT). The SFTT results revealed that adding PEG up to 25 wt.% resulted with microfibers having fair strength, modulus, and elongation properties, thus was selected to be added with curcumin particulates. In the second stage of the study, PLA/PEG/cur blends were thermally and structurally characterized using DSC, TGA, and FTIR. The incorporation of curcumin into the PLA/PEG blends resulted with noticeable shift in peaks for O-H stretching vibration. Thermal studies showed that the incorporation of curcumin (wt. %) into PLA/PEG blends did not affect the Tg and the final degradation temperature. SFTT for PLA/PEG/curcumin microfibers further curcumin loadings beyond 1wt.% had resulted with decreasing strength, Young’s modulus and elongation (%) possibly due to particulate agglomeration and inhomogeneous dispersion in the polymer matrix. PLA/PEG/cur microfibers were successfully drawn using an in-house-built fiber drawing tower with average diameters of 31μm to 36μm. The OM images showed bead-free and, uniformly circular in cross section microfibers.