Effect of Microwave Cure on the Thermo-Mechanical Properties of Tung Oil-Based/Carbon Nanotube Composites

Abstract

Tung oil is uniquely reactive among plant-based natural oils due to the series of conjugated carbon-carbon double bonds in its fatty acid chains. These conjugated carbon-carbon double bonds impart a high reactivity towards cationic polymerization in the presence of other reactive co-monomers, such as divinylbenzene and styrene. An impressive decrease in the cure time of tung oil-based thermosets has been achieved when the resins investigated were microwaved in the presence of carbon nanotubes (CNTs). However, the fast cure compromised the overall thermo-mechanical properties of the materials investigated. Microwave power, exposure time, and CNT loading effects have been assessed by means of dielectric analysis (DEA), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and proton nuclear magnetic resonance ( 1 H NMR) spectroscopy of extracts obtained by Soxhlet extraction. Possible reasons were proposed to explain the overall inferior properties observed whenever faster cure rates were achieved.

Synthesis and Properties of Thermosets from Tung Oil and Furfuryl Methacrylate

“…F50-T50-F showed a higher storage modulus (540 MPa) than F40-T60-F (340 MPa) and F30-T70-F (60MPa) at room temperature (Table 2). These values are comparable to the reported storage modulus values of other tung oil polymers [2,9,25]. It was difficult to run F30-T70-F samples, as these samples were too brittle to continue in tension mode, and broke above 45 °C.…”

“…The broad range of peaks in the 5.5-6.5 ppm (highlighted with green square shape in Figure 10a) region suggested a conjugated triene structure for TO, which was absent in soluble portions of FMA-TO polymers [32]. The absence of any characteristic peaks of FMA in the 5-6 ppm region confirmed that the predominant TO-related compounds in the soluble portions of FMA-TO polymers might be TO oligomers [2]. A similar conclusion was reached from 13 C spectra of FMA-TO polymers, as the TO-related carbon predominated in the 120-150 ppm and 10-40 ppm regions (highlighted with a green square shape in Figure 10b).…”

“…This helped in development of more cross-linking sites, which consequently led to rigidity in structure as well as brittleness in the materials. This resulted in polymers with low mechanical properties [2,25]. In Figure 7b, F40-T60-F exhibited broad tan δ transition compared to F50-T50-F, which indicated the presence of a heterogeneous polymer network in the system [14].…”

“…In Figure 10a, the proton signals of TO at δ 4.05-4.10 ppm and 4.27-4.31 ppm correspond to glycerol methylene units in TO. The multiplets appearing at δ 5.33-6.59 ppm are attributed to the olefinic protons in TO [2,29]. For FMA, the methylene proton (-CH 2 -OCO-) signal appears as a singlet δ 4.96 ppm, the vinyl and furan-ring protons in the downfield region (δ 6.03-7.05 ppm) and the α-CH 3 protons at δ 1.79 [30].…”

“…Major advantages of this bio-based resource include low cost, availability, renewability and biodegradability. Vegetable oil-derived polymeric materials with good thermomechanical and excellent damping properties will help to replace petroleum-based products in the near future [1,2]. Highly cross-linked thermoset-type materials can be produced from fatty acid unsaturation [1].…”