Low temperature flexible side chain epoxy compound toughened cycloaliphatic epoxy resin: impact strength increased by nearly 280%, heat resistance simultaneously improved

Research background: The toughness weakness of low-temperature cured epoxy

Epoxy resin (CEP) cured at ≤ 100 ° C can avoid cracking problems caused by high-temperature curing at 120 ° C-180 ° C, but the toughness of the cured material is still insufficient. The conventional approach is to introduce a second phase modifier or embed flexible segments in the resin structure, but the second phase modifier often damages other properties such as heat resistance or is poorly dispersed in the epoxy matrix. In response to this contradiction, the research team designed and synthesized two epoxy compounds containing aliphatic side chains at the molecular level – BD-S-182 and DGEBDDBA. Through cross-linking network modification of the cycloaliphatic epoxy resin (brand 2021P), the mechanical properties and heat resistance were improved without changing the original low-temperature curing mechanism.

Performance data: Significant improvement in impact strength and elongation at break

Research results show that both modifiers can significantly improve the toughness of 2021P.

. The optimal impact strengths of the BD-S-182 and DGEBDDBA modified systems reached 45.1 kJ/m ² and 52.4 kJ/m ², respectively, which were 226.8% and 279.7% higher than those of the low-temperature cured pure resin, respectively; The elongation at break reached 43.71% and 51.36%, respectively, with an increase of 168.8% and 215.9%. In terms of heat resistance, improvements have also been made: the system with 10 wt% DGEBDDBA added increased the 5% thermal weight loss temperature (T_d5%) from 226.3 ° C to 275.1 ° C; the system with 30 wt% BD-S-182 added increased it to 241.7 ° C. This indicates that the introduction of flexible side chains did not sacrifice heat resistance, but achieved synchronous optimization of toughness and heat resistance at a specific addition amount.

Inspiration for the polymer additive industry

The core idea of this study – using epoxy compounds containing flexible long alkyl side chains as reactive modification components to participate in crosslinking – has reference value for rubber and tire formulation design.

. In the tire and rubber system, toughening, heat resistance, and aging resistance often require a synergistic balance: anti-aging agents and antioxidants are responsible for suppressing chain breakage and oxidation during the aging process, while the structural design of cross-linked networks determines the deformation and crack propagation behavior of materials under dynamic loads. The strategy of “embedding flexible side chains into cross-linked networks” demonstrated in this study is similar in methodology to the idea of adjusting cross-linking density through vulcanization systems and constructing a filler network through reinforcing fillers (such as white carbon black) to balance strength and elasticity in rubber. It is worth noting that the dispersion state of reinforcing fillers such as white carbon black in the rubber matrix has similar formulation difficulties as the “poor dispersion” problem of the second phase modifier mentioned in this article; Reactive flexible segment modification provides a molecular level solution pathway to avoid phase separation. For rubber products and refurbished tire compounds that require vulcanization or curing at lower temperatures, there is also a need to balance toughness and heat resistance under low-temperature curing conditions. The data from this study can provide reference for the formulation screening of related systems.

Summary of research points

• Two types of aliphatic side chain epoxy compounds, BD-S-182 and DGEBDDBA, were synthesized for low-temperature (≤ 100 ° C) curing modification of cycloaliphatic epoxy resin 2021P.

  . The optimal impact strength is 45.1 and 52.4 kJ/m ², which increase by 226.8% and 279.7% respectively; The elongation at break is 43.71% and 51.36%, respectively increasing by 168.8% and 215.9%.

• 10 wt% DGEBDDBA increased T_d5%from 226.3 ° C to 275.1 ° C; 30 wt% BD-S-182 increased it to 241.7 ° C.
• The modification does not change the original low-temperature curing mechanism, avoiding the problems of poor dispersibility and damage to heat resistance of traditional second phase modifiers.

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Explanation: The research object is an epoxy resin system, not a direct formula for tires or rubber; The reference significance for the rubber additive industry lies in the design of cross-linked network molecules and the idea of toughening heat balance. The migration of relevant conclusions to rubber systems still needs experimental verification.

Information source:Toughening Low‐Temperature Curing Alicyclic Epoxy Resin via Epoxy Compound Containing Flexible Side Chains， Organized by Herun Chemical.