Mussel-Inspired General Interface Modification Method and Its Application in Polymer Reinforcement and as a Flame Retardant

Abstract

Inspired by the remarkable adhesion of mussels, the mimicking of natural adhesive molecules has been widely used for surface modification. In the present study, an economical and easily available biomimic material named as tannic acid–Fe 3+ (TA–Fe 3+ ) was first directly used as a surface modifier, carbonization agent, smoke inhibitor, and flame-retardant synergist. Compared with the flame-retardant magnesium hydroxide (Mg(OH) 2 ), TA–Fe 3+ -modified Mg(OH) 2 endowed polyamide 6 (PA 6) with improved mechanical performance and flame-retardant properties. The flame-retardant and smoke-suppressant properties were tested by the limiting oxygen index and cone calorimeter tests. The flame-retardation mechanism was investigated by thermogravimetric analysis, scanning electron microscopy, and X-ray photoelectron spectroscopy. The tensile strength could increase up to 90%, and the modified flame retardant was found to have higher UL-94 grade with the same dosage of flame-retardant additives. The peak heat release rate, total heat release, peak of smoke production rate, and total smoke production were significantly reduced. The synergistic effect between TA–Fe 3+ and Mg(OH) 2 was also discussed. This study provides new insights into the direct utilization of a biomimicking adhesive molecule, TA–Fe 3+ , to realize simultaneous composite reinforcement and flame-retardant property enhancement. Meanwhile, because of the extensive synergies of flame-retardant metal oxide with iron element and the universal growth characteristics of TA–Fe 3+ , it has potential applications in the preparation of various flame-retardant polymers.

Recent Advances in Bio-Based Flame Retardant Additives for Synthetic Polymeric Materials

“…However, polymer composites of metal hydroxides can exhibit poor adhesion to surfaces. Taking inspiration from mussels (in which catechol and amino groups are important for adhesion), it was recently shown that this problem could be addressed in a synergistic manner, by the incorporation of tannic acid-Fe(III) complexes and Mg(OH) 2 into a polyamide-6 (PA 6, an industrially-important polymer) matrix [ 19 ]. Tannic acid-Fe complexes can be used to coat materials on the surface because of their strong chelating properties and were used in this study to stabilize polymer–hydroxide composites through non-covalent interactions.…”

Bio-Based Flame Retardation of Acrylonitrile–Butadiene–Styrene

“…Tannic acid (TA) acts mainly in the solid phase as a char former due to its polyphenolic structure, shown in Figure a. It is an inherently intumescent compound, possessing the three characteristics required for that function: it is an acid source (containing many ester groups), a good carbon source and char former (composed mainly of benzene rings), and a blowing agent (releasing CO 2 during decomposition). , Researchers have used tannic acid, either alone or in combination with other additives, to reduce the flammability of epoxy aerogels, , PLA aerogels, , PLA resin, PA6, , polyesters and polyester/ABS blends, and polyolefins such as LDPE and PS . Another naturally occurring polyphenolic compound, lignin, has been used in ABS to reduce its flammability; ,, tannic acid has a similar structure and char-forming capacity as lignin, with the advantage of having a greater structural and compositional regularity, making it a promising candidate for use in ABS.…”

“…Magnesium hydroxide (MH) and alumina trihydrate (ATH) act mainly in the solid phase as "heat sinks", lowering the burning material's temperature as they endothermically decompose and release water. A drawback related to their use is that these additives are normally needed in large quantities to be effective, which often diminishes the polymer's mechanical properties; 26 this can potentially be mitigated using them in lower quantities in combination with other FRs. Wang et al 26 used MH together with TA−iron complexes in PA6, improving both the flame resistance and the mechanical properties of the polymer.…”

“…Tannic acid (TA), a naturally occurring polyphenolic compound found abundantly throughout the plant kingdom, is one of the key elements protecting trees from fires: it is a good char former, a strong antioxidant, and an inherently intumescent compound. Researchers have used TA to reduce the flammability of aerogels, − poly­(lactic acid) (PLA), nylon-6 (PA6), , polyester/acrylonitrile–butadiene–styrene (ABS) blends, and polyolefins such as low-density polyethylene (LDPE) and polystyrene (PS) . Phytic acid (PA) is the main storage form of phosphorus in plant seeds; its high P content (28 wt % and P/C atomic ratio of 1), readily carbonizable glucose ring, and natural intumescence make it attractive as an FR agent. , PA or its salts have been used in FR coatings for cotton, , PLA, and wood and as bulk FR additives in PLA ,,, and polypropylene (PP) .…”

“…Mineral hydroxides are good candidates for this purpose, being amongst the most widely used of all FRs but often needed in concentrations greater than 50 wt % when used independently . Examples of this family are alumina trihydrate (ATH) and magnesium hydroxide (MH), the latter of which has been used synergistically with TA to flame-retard LDPE, PS, and PA6. , Melamine (ME), a strong blowing agent, can potentially be used with natural char formers and phosphate-rich compounds (such as TA, PA, and/or DNA) to produce intumescence and/or combine P and N atoms. ME has been used synergistically with TA and FG in polyolefins .…”