The majority of the published bio-based benzoxazine research has focused almost exclusively on different phenolic and amine compounds, while the aldehyde portion of the oxazine ring remains the same.
Chitosan/clay (nano)composites were prepared by using a special quaternary ammonium intercalating agent coupled with a silanol group to facilitate the organic clay formation. Exfoliated clay in the chitosan matrix was attained at the higher intercalant dosages through X-ray diffraction (XRD) and transmission electron microscope (TEM) analyses. Optical transmittance for the (nano)composites increased slightly with increasing the amount of intercalants in the clays. In light of the hydrophobic component on the intercalant and the effective clay content, the interfacial interaction between chitosan and modified clay may not be strong enough to render higher mechanical properties, even though the partially exfoliated clays were achieved to provide high interfacial area for the dispersed phase and the matrix. An optimum Young's modulus was thus found for (nano)composites using modified clay at a medium dosage of intercalant, which resulted from the balance of the dispersion status and interfacial interaction. This outcome indicated high dispersion of modified clay may not guarantee high mechanical properties of (nano)composites. The antimicrobial property of chitosan against Escherichia coli (E. coli) increased further with the addition of modified clays, in which the intercalant exhibiting the antimicrobial function. The modified clay at an optimum dosage of modifier to balance the mechanical properties and antimicrobial property was attained.
A nacre-mimetic brick-and-mortar structure was used to develop a new flame-retardant technology. A second biomimetic approach was utilized to develop a non-flammable elastomeric benzoxazine for use as a polymer matrix that effectively adheres to the hydrophilic laponite nanofiller. A combination of laponite and benzoxazine is used to apply an ultra-high nanofiller content, thin nanocomposite coating on a polyurethane foam. The technology used is made environmentally friendly by eliminating the need to add any undesirable flame retardants, such as phosphorus additives or halogenated compounds. The very-thin coating on the polyurethane foam (PUF) is obtained through a single dip-coating. The structure of the polymer has been confirmed by proton nuclear magnetic resonance spectroscopy (1H NMR) and Fourier transform infrared spectroscopy (FTIR). The flammability of the polymer and nanocomposite was evaluated by heat release capacity using microscale combustion calorimetry (MCC). A material with heat release capacity (HRC) lower than 100 J/Kg is considered non-ignitable. The nanocomposite developed exhibits HRC of 22 J/Kg, which is well within the classification of a non-ignitable material. The cone calorimeter test was also used to investigate the flame retardancy of the nanocomposite’s thin film on polyurethane foam. This test confirms that the second peak of the heat release rate (HRR) decreased 62% or completely disappeared for the coated PUF with different loadings. Compression tests show an increase in the modulus of the PUF by 88% for the 4 wt% coating concentration. Upon repeated modulus tests, the rigidity decreases, approaching the modulus of the uncoated PUF. However, the effect of this repeated mechanical loading does not significantly affect the flame retarding performance.
Correction for ‘A truly bio-based benzoxazine derived from three natural reactants obtained under environmentally friendly conditions and its polymer properties’ by Irlaine Machado et al., Green Chem., 2021, 23, 4051–4064, DOI: 10.1039/D1GC00951F.
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