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. 2020 Aug 24;12(9):1908. doi: 10.3390/polym12091908

Table 2.

Brief summary of different IPN based systems investigated in literature for epoxy modification as a function of different parameters.

Epoxy Toughener Morphology Objective Investigated Properties Key Findings Ref.
DGEBA/INN Polyurethane obtained from TDI and Desmophen 1200 No phase separation To investigate the effect of isocyanate content

  • Elemental analysis

  • Tensile strength

  • Impact strength

  • The better mechanical properties of the modified epoxy system was achieved by using toughener with higher isocyanate content.

  • The impact strength was maximally enhanced by adding 20% of polyurethane with highest isocyanate index while the addition of 15% of the toughener was enough to obtain the best tensile strength and elongation at break.

 [58]
DGEBA/TETA Polyurethane derived from PET waste by glycolysis Homogeneous morphology To analyze the influence of molecular weight ofpolyethylene glycol (600–1500 g·mol−1)

  • Fracture toughness

  • Tensile strength

  • Impact strength

  • The results showed the maximum increase of 61% and 212% in tensile strength and impact strength, respectively, by adding 10 wt % of polyurethane prepared with the glycol having molecular weight of 1000.

  • Moreover, the addition of toughener resulted in 45% and 184% increase in mode I fracture toughness and fracture energy, respectively, as compared to the neat epoxy system at room temperature.

 [57]
DGEBA/modified amine PUP Sea-island structure To understand the influence of different gravity accelerations of 0, 1, and 2 g

  • Elemental analysis

  • Bending stress

  • Thermal properties

  • The bending stress and coefficient of thermal expansion (CTE) of modified epoxy showed a decrease with the increasing acceleration of gravity which was attributed to the increase in diameter and decease in number of dispersed phase.

 [59]
DGEBA/PAMAM HBP-PU Two-phase morphology To study the impact of different generations (G) of HBPs (G1–G4)

  • Elemental analysis

  • Thermal properties

  • Flexural strength

  • Impact strength

  • The results showed an increase in the impact strength of modified epoxy till generation G3 and a decrease for G4, which was attributed to the formation of bigger particles. However, the flexural modulus and strength linearly increased as a function of generation because of the enhancement in the rigidity of the system.

  • The HBP-PU based epoxy samples displayed higher toughness as compared to the next epoxy and linear-PU based epoxy samples. While the thermal stability and flexural characteristics of HBP-PU based epoxy system were lower than the neat epoxy which was linked with the presence of flexible linkages and reduction in cross-linked density of epoxy.

 [13]
Bisphenol A type epoxy RTA Sea-island structure To examine the effect of different curing agents (G1–G3)

  • Elemental analysis

  • Thermal properties

  • Tensile strength

  • Impact strength

  • Fracture toughness

  • The results showed that the mixtures having G1 and G2 curing agent satisfied the technical index requirements of steel deck pavement. Moreover, the fatigue life of epoxy mixture cured with G1 was quite longer than the epoxy asphalt mixture.

 [55]
DGEBA SiMPU - To assess the influence of different curing agents (H-957, DADPE and DADPS)

  • Fracture toughness

  • Impact strength

  • The values of impact strength and fracture toughness (at room temperature) of epoxy system, cured by using H-957, were higher than the epoxy systems cured with other two hardeners (DADPE and DADPS).

  • The results showed an increase of 216% in fracture toughness by curing the epoxy with H-957 along with 16.7 wt % of SiMPU, as compared to the neat epoxy.

 [11]