Elaboration and characterization of composites based on poly (lactic acid) and biomass fibers

Abstract

The aim of this research is to prepare, characterize and evaluate the thermo-physical properties of hybrid bio-composites where OpuntiaFicusIndica flour (OFI-F) as anorganic filler and talc as inorganic filler were used as reinforcing agents into PLA matrix, where the matrixis a polymer derived from renewable resources (PLA polymer). Bio-composites exhibit properties like many petrochemical-based polymers composites. They could be employed in the automobile and decking sector as well as biodegradablepackaging. However, their broad application has been limited because of their expensive cost and poor mechanical and thermal properties. Before bio-composites can be widely employed, there is a number of technological challenges that must be addressed. In this research, Polylactic acid (PLA) bio-composites, reinforced with organic fillers(OFI- F) and mineral fillers (talc), were investigated. The thermal properties of the bio-composites were studied by means of thermogravimetric analysis (TGA) while the characterization and morphology of the bio-composites were studied by Wide-angle X-ray scattering (WAXS) and Scanning Electron Microscope (SEM). PLA/Talc/OpuntiaFicusIndica flour (OFI-F) bio-composites were developed by mixing PLA with talc and OFI Flour in different ratios, using a melt compounding process. PLA/Talc (90/10), PLA/OFI-F (90/10), PLA/Talc/ OFI-F (80/10/10). All TGA curves are sigmoidal in shape whereas the DTG curves show only one peak. This indicates that thermal degradation occurred in a single step for all bio-composites.

The thermal degradation kinetics are studied using non-isothermal multiple heating rate techniques. As a result, model-free methods such as Flynn Wall Ozawa (FWO) and Kissinger AkahiraSunose (KAS) are utilized as well as model-fitting methods such as Kissinger method and Coats-Redfern technique. The results indicate that compared to neat PLA, the activation energy (Ea) of PLA/Talc bio-composites increases from 157.45 to 160.86 KJ/mol according to the FWO method.The talc distribution into the PLA matrix is homogeneous as observed by SEM. Thermal degradation PLA /Talc bio-composites showcompared to neat PLA, that talc particles at 10 wt % into the PLA matrix have a minor impact on the thermal stability of bio-composites. However, after the addition of OFI-F into the PLA matrix, all thermograms shifted to lower temperatures values. The addition of OFI-F into the PLA matrix reduces the Ea from 157.45 to 151.02 KJ/mol according to the FWO method. The decrease in Ea can be due to the incompatibility between OFI-F and PLA matrix as observed by SEM. When talc is present with the OFI-F mixture, the activation energy of the bio-composites decreases from 157.45 to is 143.40 KJ/mol according to the FWO method. This result demonstrates that the PLA/Talc/OFI-F hybrid bio-composites have a lower thermal stability; the voids adjacent shown by SEM between OFI-F and talc particles mean that the adhesion between the fillers and the polymer matrix needs to be improved. In Kissinger method the addition of talc marginally boosts the activation energy (142.33 KJ/mol) similar to what FWO method found.

The Coats-Redfern (C-R) approach yields higher activation energies than the FWO and KAS methods; nonetheless, the C-R method follows the same pattern as the FWO and KAS methods. Furthermore, in this work, the proposed degradation process of bio-composites utilizing Coats-Redfern and Criado techniques confirms that the F2 reaction model is the most accurate degradation mechanism.