**3.3. PU as composites**

Composite materials from FADU have not been prepared yet. In their recent research, Zafar et al have developed composites from FADU using metal oxides and organo‐ montmorillonite clay [OMMT] (Cloisite 30B; modified by an alkyl ammonium cation bearing two primary hydroxyl functions, alkyl group is tallow containing ≈65% C18, ≈30% C16, and ≈5% C14, Southern Clay product) as modifiers added in very lower amounts to FADU matrix (unpublished work). The sole aim behind the development of these composites was the improvement in performance of FADU materials in terms of thermal stability, physico‐mechanical and corrosion or chemical resistance performance, and also antimicrobial behavior relative to the pristine material for high performance applications. MMT occurred as nano‐sized aggregates with size ranging from 37 to 100 nm as observed by Transmission Electron Micrography [TEM]. The thermal stability of FADU/ MMT was found to increase with increased MMT loading. These composites may be used as protective coatings in future. Zafar et al have also developed FADU/MnO composites, with good antifungal behavior. MnO occurred as needles self‐assembled in "lemon slices" morphology as observed in optical micrograph (Figure 8). The said composite material may find application as antimicrobial agent in coatings and paints.

PU composites were prepared by the dispersion of conducting polymer poly (1‐ naphthylamine) [PNA] in LFADU matrix in amount ranging from 0.5–2.5 wt% by conventional solution method as reported by Riaz et al [39]. At lower levels, the composites were very fragile in nature. The polymerization of PNA occurred through N–C(5) linkages of 1‐naphthylamine units as confirmed by FTIR spectra. PNA also reacted with free isocyanate groups of TDI forming urea linkages, as also supported by spectral analysis. UV visible spectra also confirmed the formation of urea linkages between LFADU and PNA. TEM micrographs showed the average particle size as 17–27 nm. Nanoparticles appeared as smaller aggregates which later on formed larger aggregates. XRD analysis revealed purely amorphous nature of composites. With the increase in the loading of PNA in the composites, the distortion and torsional strain increased in the composites due to higher urea linkages. It was found that as the percent loading of PNA in the composites increased, their electrical conductivity values also increased; however, these values fell in the semi‐conducting range, which was much higher relative to the conductivity values obtained with very high loading of PNA in previously reported composites. The improved electrical conductivity values of LFADU/PNA composites can be correlated to the hydrogen bonding and urea type linkages formed between the two polymers, which provide the path to charge conduction [40,41].

**Figure 8.** Optical micrographs of FADU/MnO (a) 100 X, (b) 200 X, (c) 500 X
