Novel Bio-based Branched Unsaturated Polyester Resins for High-Temperature Applications

Abstract

Unsaturated polyester resins, one of the most important thermosets, are invariably produced from oil-based monomers. Their application is limited in areas where high thermal stability is required due to their low Tg. Besides, these resins contain 30–40% hazardous styrene as a reactive solvent. Therefore, developing bio-based solventless unsaturated polyester resin with medium to high thermomechanical properties compared to petrochemical-based counterparts is important. In order to achieve this, a series of branched bio-based unsaturated polyester resins were synthesized using bulk polymerization method in two steps. In the first step, four different intermediates were prepared by reacting glycerol (as a core molecule) with either isosorbide (diol), 1,3-propanediol (diol), 2,5-furandicarboxylic acid (saturated diacid), or adipic acid (saturated diacid). In the second step, the branched intermediate was end capped with methacrylic anhydride to introduce reactive sites for cross-linking on the branch ends. The chemical structure of the resins was characterized by 13C-NMR. FT-IR confirmed the polycondensation reaction in the first step and the end functionalization of the resins with methacrylic anhydride in the second step. The effect of 2,5-furandicarboxylic acid and isosorbide on thermomechanical and thermal properties was investigated using dynamic mechanical analysis, differential scanning calorimetry, and thermo-gravimetric analysis. Results indicated that 2,5-furandicarboxylic acid based resins had superior thermomechanical properties compared to a commercial reference unsaturated polyester resin, making them promising resins for high-temperature composite applications. For example, the resin based on 2,5-furandicarboxylic acid and isosorbide and the resin based on 2,5-furandicarboxylic acid and 1,3-propanediol gave glass transition temperatures of 173 °C and 148 °C, respectively. Although the synthesized 2,5-furandicarboxylic acid based resins had higher viscosity (22.7 Pas) than conventional unsaturated polyester (0.4–0.5 Pas) at room temperature, preheated resins can be used for making high-temperature-tolerance fiber-reinforced composite.

Synthesis of Bio-Based Polyester Resins for Vat Photopolymerization 3D Printing

“…Acrylicmodified unsaturated polyester resins often show improved tensile strength due to acrylic functionalities which lead to intermolecular interactions and crosslinking within the polymer matrix, yielding materials with higher stiffness and strength. On the other hand, itaconic acid-modified unsaturated polyester resins can also cause increased tensile strength, albeit to a lesser extent than acrylic modification [41,58]. From the results, it can be seen that PEA-BIO-1 is an interesting alternative polyester resin for DLP 3D printing as it combines a higher content of bio-derived building blocks with decent printability and mechanical properties, which are superior to the purely petroleum-based counterpart PEA.…”

“…Acrylic-modified unsaturated polyester resins often show improved tensile strength due to acrylic functionalities which lead to intermolecular interactions and crosslinking within the polymer matrix, yielding materials with higher stiffness and strength. On the other hand, itaconic acid-modified unsaturated polyester resins can also cause increased tensile strength, albeit to a lesser extent than acrylic modification [41,58]. Along with the thermomechanical properties, the mechanical performance of the 3Dprinted test specimens was tested and the stress-strain curves are provided in Figure 6.…”

Flame-Retardant and Transparent Unsaturated Polyester Based on P/N Liquid Flame Retardants and Modified Halloysite Nanotubes

“…In this way, the problem of poor compatibility can be avoided, and even the mechanical properties of composite materials will be improved [27]. Most reactive flame retardants for UPR are designed to contain C=C structures with phosphorous or nitrogen [27,28]. Organic phosphorous compounds that are suitable for modification as reactive flame retardants include phosphate esters, ammonium polyphosphate (APP), phosphine oxide, and 9-10-dihydro-9-oxygen-10-phosphate-10-oxide (DOPO) [29][30][31][32][33][34].…”