The effects of bio-based plasticizing agent and plant-based filler on the mechanical and thermal properties of poly(lactic acid) (PLA)

• Author / Creator

  Momeni, Sina

• The overwhelming majority of the plastics that are currently used in commercial applications are petroleum-based polymers due to their exceptional properties and low cost. However, these polymers are non-degradable and their excessive use is leading to significant increase in global plastic waste. The environmental and health issues associated with petroleum-based polymers has raised the demand for bio-based and biodegradable polymers as an alternative to reduce the negative impacts of synthetic polymers on the environment. Poly(lactic acid) (PLA) is a bio-based, biodegradable, and biocompatible biopolymer which is considered as a promising alternative to petroleum-based polymers. It has great potential for applications in different areas such as food packaging, pharmaceuticals, and medical applications. However, the production cost for PLA is relatively high compared to its petroleum-based counterparts, and it suffers from high brittleness and low flexibility that limit its large-scale commercial applications.
  In this work, the effects of hemp hurds as inexpensive bio-based reinforcing filler on the mechanical and thermal properties of PLA biocomposites were investigated so as to determine the potential of the prepared materials to be used in commercial applications. Additionally, the incorporation of epoxidized canola oil (ECO) as a bioplasticizer (i.e. is bio-based plasticizer) into both neat PLA and PLA-hemp hurd composites was studied to determine whether the flexibility issues of PLA-based materials could be improved.
  For the purpose of this study, two different chemical treatments were performed on the hemp hurds to potentially improve the filler-matrix interaction once it is introduced into PLA matrix. Then neat PLA pellets were melted and compounded with varying amounts of hemp hurd powder and ECO using a twin-screw extruder. The extruded filaments were hot-pressed to obtain dumbbell-shaped samples for mechanical characterization according to international standards. The prepared specimens were characterized to determine the effect of hemp hurd powder and ECO on the mechanical and thermal properties of PLA.
  Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) analysis were carried out to study the effect of chemical treatments on the morphology and structure of the hemp hurd powder. Differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) measurements were used to evaluate the thermal properties, thermal stability, and crystallinity of the prepared biocomposites. Tensile testing was used to study the mechanical properties of the prepared samples. Plasticizer migration level was also evaluated according to an international standard.
  Characterizations showed that the chemical treatments were effective in removing undesirable components from hemp hurds, which resulted in an enhanced filler-matrix interaction once introduced into PLA matrix. The mechanical and thermal properties of the biocomposites formed with treated hemp hurd powder were improved as compared to the biocomposites containing untreated hemp hurd powder. For all of the biocomposites, the incorporation of hemp hurd powder – either treated or untreated – resulted in an increase in tensile modulus and a reduction in tensile strength compared to neat PLA due to the higher stiffness of the hemp hurds.
  The incorporation of epoxidized canola oil (ECO) as a bio-based plasticizer into PLA matrix showed significant improvement in the mechanical properties in terms of elongation at break as compared to neat PLA. The plasticizing effect of ECO was most evident in PLA sample containing 7.5 wt % ECO, as the sample showed an impressive 1732% increase in elongation at break compared to neat PLA. In terms of PLA/hemp hurd powder biocomposites plasticized with ECO, only the sample containing 10 wt % ECO showed elongation at break value higher than neat PLA. Nonetheless, all of the plasticized biocomposites containing hemp hurd powder showed improved flexibility compared to the samples without ECO, however, this improvement was not significant for the samples containing less than 10 wt % ECO. Moreover, none of the plasticized samples showed significant plasticizer migration levels. Considering the promising results regarding the plasticizing effect of ECO on PLA, it is possible to prepare completely bio-based PLA biocomposites that can be used in commercial applications without causing adverse environmental effects.

• Subjects / Keywords

  • Hemp hurds
  • PLA
  • Biocomposite
  • Chemical treatments
  • Epoxidized canola oil

• Graduation date

  Fall 2021

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-6stc-kb03

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.