Vinyl ester resins (VERs) are widely used in various industries owing to their excellent mechanical properties and chemical resistance. However, their inherent flammability severely restricts further application, and conventional flame retardants often enhance fire safety at the cost of mechanical and thermal performance. Herein, a reactive ammonium polyphosphate (APP) derivative (MDO) with abundant C=C bonds was synthesized by grafting maleic anhydride onto the surface of an amine-modified APP (DO). The resulting MDO not only acts as an efficient flame retardant but also participates in the curing of VER through radical copolymerization. With the addition of only 22 wt% MDO, the 22% MDO/VER composite achieves a vertical burning (UL-94) V-0 rating and a high limiting oxygen index (LOI) of 28.5%, accompanied by remarkable reductions in peak heat release rate (PHRR), total heat release (THR), peak smoke production rate (PSPR) and total smoke production (TSP) compared to the neat VER. More importantly, introducing MDO enhances the tensile strength (49% improvement), flexural strength (56% improvement), and impact strength (19% improvement) of VER while effectively maintaining the glass transition temperature ( T g , 115 °C). The dual enhancement originates from the reactive crosslink sites of MDO that improve the interfacial compatibility and promote condensed-phase charring. This work provides a rational strategy to fabricate high-performance VER composites with superior fire retardancy, outstanding mechanical properties and well-preserved thermal performance.

Employing proper algorithms to process the acquired thermal sequences in either the spatial or frequency domain plays a crucial role in enhancing the defect/damage detectability in composite materials by means of Infrared Thermography. However, the performance of these algorithms may be questioned when inspecting woven composites, as their weave pattern can hinder the defect identification, thereby making their characterization very challenging. In this regard, the aim of this paper is to develop an effective thermographic procedure that first removes the periodic weave disturbance and reduces the temporal noise from the sequence and then post-processes it to obtain quantitative information on the depth and size of the damaged area. The procedure has been applied to natural hybrid woven composites made of flax and basalt fiber reinforced polypropylene matrix. In particular, two different matrices have been compared: neat and with the addition of a coupling agent, which have been subjected to drop weight impacts using masses of 3, 6, and 9 kg while maintaining a constant energy level of 3 J. The damage was characterized by using profilometric results and processing thermographic data derived from pulse thermography tests. The obtained outcomes were critically discussed to assess how the impact velocity values affect the damaged area.