Synthesis of Bioresins from Plant Oil Epoxides

  • Author / Creator
    Patel, Vinay
  • The overall objective of this thesis is to develop bioresins from plant oil epoxides for use in biocomposites and other applications. Plant oil-based epoxides show promise as feedstocks to replace non-renewable epoxides used in many applications from biocomposite manufacturing to adhesives and coatings. However, plant oil epoxides are often not directly compatible with many hardeners, requiring a solvent to prepare one phase epoxide-hardener mixtures. The work described in this thesis is aimed at making plant-oil-based bioresins and biocomposites, without the use of solvents and catalysts. In order to achieve a one phase epoxide-curing agent mixture, this thesis explores two possibilities: 1. modification of the plant oil epoxides and 2. modification of the curing agent, specifically in the synthesis of biobased curing agents.
    In the first possibility, epoxidised triglycerides are transesterified into epoxidized methyl esters (EMS). These low viscosity EMS were found to act as reactive diluents for the curing agent. However, the curing agent still had limited miscibility in EMS, and so required the use of elevated temperatures to achieve a single phase. As a result, prepolymer mixtures containing EMS have a limited pot life because they start to polymerise, leading to increased viscosity and leads to major difficulties in manufacturing.
    In the second possibility, a biobased curing agent (citric acid) was modified into alkyl citrates via solvent- and catalyst-free esterification with the short- to medium-chain alcohols, ethanol, propanol, butanol and hexanol. The synthesized mixtures of, mono-,di-, trialkyl citrate esters and unreacted citric acid (CA-alkyl esters), were found to be fully miscible with plant-oil-epoxides.1 The resulting homogeneous mixtures of epoxides and curing agents have about 1 hour iii
    of pot life compared to less than 5 minutes for mixtures produced from epoxidized methyl esters. The optimum molar ratios of epoxy group to carboxylic acid group (Ep/Ac) were identified by the glass transition temperatures (Tg) measurements of bioresins that were prepared by using range of Ep/Ac ratios. Then, properties of the cured resins were measured and characterized. These novel biobased curing agents were found to be reactive at room temperature which could be utilized for certain new applications where low temperature curing is required. Furthermore, the Tg achieved for solvent-free curing of bioresins prepared from CA-alkyl esters were higher than those achieved using citric acid dissolved in solvent, for example 61 °C with epoxidized linseed oil, compared to 38 °C using a citric acid/acetone solution.
    Finally, the optimum epoxide-curing agent formulations were used to prepare natural fiber biocomposites without the use of solvents. The Tg of biocomposite prepared by using epoxidized hemp oil and the citric acid/acetone solution was 39 °C. Comparatively, a biocomposite prepared via a solvent-free process using CA-alkyl esters and its Tg of 46 °C was achieved.

    1 Jonathan M. Curtis, Vinay Patel, US provisional patent application serial no. 63/075,940, Biobased hardener for epoxy resins

  • Subjects / Keywords
  • Graduation date
    Fall 2021
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • 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.