A Systematic Review of Epoxidation Methods and Mechanical Properties of Sustainable Bio-Based Epoxy Resins

Abstract

There has been a growing interest in polymer-based materials in recent years, and current research is focused on reducing fossil-derived epoxy compounds. This review examines the potential of epoxidised vegetable oils (EVOs) as sustainable alternatives to these systems. Epoxidation processes have been systematically analysed and their influence on chemical, thermal, and mechanical properties has been assessed. Results indicate that basic, low-toxicity epoxidation methods resulted in resins with comparable performance to those obtained through more complex common/commercial procedures. In total, 5-7% oxirane oxygen content (OOC) was found to be optimal to achieve a balanced crosslink density, thus enhancing tensile strength. Furthermore, mechanical properties have been insufficiently studied, as less than half of the studies were conducted at least tensile or flexural strength. Reinforcement strategies were also explored, with nano-reinforcing carbon nanotubes (CBNTs) showing the best mechanical and thermal results. Natural fibres reported better mechanical performance when mixed with EVOs than conventional systems. On the other hand, one of the main constraints observed is the lack of consistency in reporting key chemical and mechanical parameters across studies. Environmental properties and end-of-life use are significant challenges to be addressed in future studies, as there remains a significant gap in understanding the end-of-life of these materials. Future research should focus on the exploration of eco-friendly epoxidation reagents and standardise protocols to compare and measure oil properties before and after being epoxidised.

Keywords: epoxidation process; epoxidised vegetable oils; mechanical properties; systematic review.

Figure 1

Keywords word cloud. (a) Keywords wordcloud; (b) percentage of keywords referred to each group.

Figure 2

Origin of the studies analysed.

Figure 3

Oil use distribution.

Figure 4

Tensile strength over oxirane oxygen content dispersion chart.

Figure 5

Prileschajew reaction process. Chemical structure of (a) hydrogen peroxide; (b) formic acid; (c) performic acid; (d) triglyceride molecule; and (e) epoxidised vegetable oil. Own elaboration.

Figure 6

Epoxidation complexity level distribution.

Figure 7

Tests topic appearances across the references.

Figure 8

Bulk density data found in references [29,37,38,75,77,91,92].

Figure 9

Tensile strength values according to type of oil used (MPa) [19,29,30,32,33,35,36,37,40,42,44,49].

Figure 10

Tensile strength over strain at break results [18,19,29,31,32,33,34,36,37,40,47,81].

Figure 11

Flexural strength values grouped by type of oil used [35,36,42,54,57,66,71].

Figure 12

Reinforced bio-based resins tensile strength values grouped by type of reinforcement [28,31,34,35,38,41,43,46,69,75,89,95].

Figure 13

Tensile strength over glass transition temperature values [18,19,28,29,30,31,32,33,34,35,36,38,39,44,45,47].

Figure 14

T_g values over T_5%.