Sheet molding compound resins from soybean oil: Thickening behavior and mechanical properties

Abstract

Thermosetting resins for sheet molding compound (SMC) and bulk molding compound applications were synthesized from soybean oil. The SMC resins were prepared from maleated hydroxylated soybean oil (MHSO) and maleated acrylated epoxidized soybean oil (MAESO) with styrene. When thickened with divalent cations such as MgO, these resins exhibited a substantial rise in viscosity at room temperature because of complexation of MgO with the terminal acid groups on maleic anhydride. The resulting high viscosity sheet upon heating rapidly reduced its viscosity as the labile MgO-acid groups thermally disassociated. The flexural strength r and moduli E of these polymers varied from 61 to 87 MPa and from 1.6 to 2.4 GPa, respectively and the tensile strength and moduli varied from 27 to 44 MPa and from 1.6 to 2.5 GPa, respectively. The mechanical and fracture properties of these polymers were related to the amount of functional groups f, on the fatty acid backbone, and followed the Rigidity Percolation and Twinkling Fractal Theories, r $ [Em] 1/2 , where m $ [f À 1]. The fracture energy G IC decreased significantly with increasing crosslink density, as G IC $ m À2 and the plastic zone r p decreased as r p $ m À3 . The new bio-based resins possessed mechanical and thermal properties comparable with petroleum-based unsaturated polyesters.

Research progress on bio‐based thermosetting resins

“…UPEs are commonly used in fiberglass composites, sheet molding compounds and bulk molding compounds. They have enjoyed a long‐term leadership in petroleum‐based composites since 1941 due to their low cost, ease of handling and good balance of mechanical, electrical, chemical and fire‐resistance properties …”

Soybean‐Oil‐Based Thermosetting Resins with Methacrylated Vanillyl Alcohol as Bio‐Based, Low‐Viscosity Comonomer

“…The resulting MAESO‐based thermosets exhibit improved properties compared to the corresponding AESO‐based thermosets because of the increased number of reactive sites (more double bonds available). However, pure MAESO resins exhibit extremely high viscosities at room temperature, which makes it difficult to use common processing technologies . Therefore, MAESO resins typically require ≈33% of low‐viscosity styrene as a comonomer prior to curing by free radical polymerization.…”

Bio-based reactive diluents as sustainable replacements for styrene in MAESO resin

“…Thus, MAESO resin possesses more reactive C]C double bonds than that of AESO resin. 20,21 Generally, pure MAESO resin is too viscous to use, and therefore demands approximately 35% of styrene as a reactive diluent before being cured by a free radical polymerization. However, new emission standards for composite manufacturing by the Environmental Protection Agency specically have targeted styrene as a regulated hazardous air pollutant (HAP) and volatile organic compound (VOC).…”