Mechanically robust and flame-retarded EPDM composites with high loading of Mg(OH)2 based on reversible crosslinking network from Diels-Alder reactions

Abstract

Crosslinked EPDM/magnesium hydroxide (MH) composites are commercially materials, but the crosslinked EPDM/MH composites with high MH loading reported so far are difficult to achieve good flame retardant and mechanical properties at same time. In this paper, a thermoreversible crosslinking network based on Diels-Alder reaction between furan/acrylic acid and the Mg2+-carboxyl coordination between MH/carboxylic acid group was constructed in flame retardant EPDM composites containing high loading of MH. The composites were prepared via two steps, first, the EPDM-g-MAH was modified with furfurylamine to obtain furan functionalized EPDM(EPDM-g-FA), then a series of EPDM-g-FA/MH composites were prepared by blending EPDM-g-FA, MH and acrylic acid (AC) via two-roll milling and hot pressing process. It was revealed that the introduction of AC could not only promote the formation of thermoreversible crosslinking network, but also the coordination between MH/carboxylic acid group significantly restricts the MH agglomeration and improved the compatibility between MH and polymer matrix. Moreover, AC could act as a synergistic flame retardant, compared with AC-free composite (AC-0), the tensile strength of the composite containing 10 phr AC (AC-10) was increased from 10.5 to 13.9 MPa, and the Young's modulus increased from 41.8 MPa to 46.8 MPa. The LOI of the composite containing 15 phr AC (AC-15) was increased from 29.8 to 33.3%, and the char residue yield at 700 °C of AC-15 increased from 36.2 to 39.9% compared to AC-0, meanwhile the char residues of AC-15 was more compact and continuous. All samples with AC loading showed higher thermal stability and activation energy of degradation. More importantly, the EPDM-g-FA/MH composites with thermoreversibly crosslinking showed good reprocessability.