Abstract
Phenolic foams (PFs) as thermal insulation material with outstanding flame retardancy are required to match society’s ever expanding safety expectations; however, a trade off exists between flame retardancy and toughness. Here, for the first time, we synthesized a novel reactive phosphorus containing tung oil based derivative and used it to toughen PF, resulting in PFs with a combination of excellent mechanical properties and flame retardancy. Compared with pure PF, the modified PFs exhibit enhanced mechanical properties, with specific compressive and flexural strengths as high as 5.67 MPa and 12.46 MPa, which represent increases of 90.67% and 178.7% over those of pure PF, respectively. Meanwhile, the limiting oxygen index (LOI) values of the modified PFs are improved as much as 40.83%. Scanning electron microscopy micrographs show that the microstructure of the modified PFs is better than that of pure PF, with a more uniform cell morphology, a narrower pore size distribution range, and a smaller average pore size, all of which are beneficial to the foam’s mechanical properties. This study provides a scientific paradigm for the development of advanced PFs based on renewable biological resources.
Highlights
Because of their flammability, tendency to generate of large amounts of highly toxic fumes, and tendency to drip during combustion, conventional thermal insulation foams are increasingly unable to meet the strict safety requirements being imposed worldwide [3,4]
In the Fourier transform infrared (FT-IR) spectrum of to synthesize Ntungacyl diethylenetriamine (TA) (Fig. 1(a),I), characteristic peaks are observed at approximately 3287 cm-1 and 1555 cm-1; these peaks are attributed to N-H stretching and bending vibrations, respectively
These results strongly demonstrate the toughening effect of TAPC on the foam and indicate that an optimal content of TAPC exists that best improves the mechanical properties of phenolic foams (PFs)
Summary
Tendency to generate of large amounts of highly toxic fumes, and tendency to drip during combustion, conventional thermal insulation foams (e.g., polystyrene [1] and polyurethane [2]) are increasingly unable to meet the strict safety requirements being imposed worldwide [3,4]. The conjugated triene bonds and ester group exhibit strong reactivity and can undergo various reactions including amidation, transesterification, Friedel-Crafts, Diels-Alder, epoxidation, and click reactions [21]. Through these reactions, tung oil has been developed into a range of products, including polyurethane foams [2], epoxy resins [22], unsaturated co-esters [23], and plasticizers [24]. To the best of our knowledge, the literature contains no studies reporting the application of tung oils to synthesize flame retardants for toughening PFs. In this study, a novel reactive phosphorus-containing tung-oil-based derivative was designed and synthesized.
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