Fabrication of host–guest UV-blocking materials by intercalation of fluorescent anions into layered double hydroxides

Abstract

Materials for blocking UV light play important roles in a variety of areas such as protecting the human skin and increasing the lifetime of polymers. In this work, a new type of host-guest UV-blocking material has been synthesized by the introduction of a fluorescent anion, 2-[2-[4-[2-(4-carboxyphenyl)vinyl]phenyl]vinyl]benzoate (CPBA), into the interlayer galleries of a ZnAl-NO 3 layered double hydroxide (LDH) precursor by an anion-exchange method. The structure and the thermal and photostability of the intercalated ZnAl-CPBA-LDH were investigated by powder X-ray diffraction (XRD), infrared spectroscopy (FTIR), thermogravimetry and differential thermal analysis (TG-DTA), fluorescence spectroscopy and UVvis spectroscopy. The supramolecular layered host-guest structure of ZnAl-CPBA-LDH enables both physical shielding and absorption of UV light. Furthermore, in contrast to conventional UV blocking materials-which convert UV light into thermal energy-the CPBA anions in the LDH interlayer galleries convert UV light (in the range 250-380 nm) into lower energy fluorescence emission (l em max ¼ 430 nm), thus reducing the thermal aging of the polymer composite materials. Intercalation of the CPBA anionsinto the LDH host also markedly enhances the thermal stability of CPBA. In polypropylene (PP) aging performance tests, after adding 1-5 wt% ZnAl-CPBA-LDH to PP, the resistance to UV degradation of the resulting ZnAl-CPBA-LDH/PP composites is higher than that of pristine PP or a CPBA/PP composite. Therefore, this work provides a way to construct a new type of host-guest layered material for UVblocking applications.

Effects of a layered double hydroxide (LDH) on the photostability of wood flour/polypropylene composites during UV weathering

“…26 Previous studies have reported that LDH can inhibit the photo-oxidation of asphalt during weathering, especially at high loading levels. 28 For example, Wang et al 29 have developed several organic UVAs-intercalated LDH systems, which signicantly enhance the stability of polypropylene during UV weathering. 28 For example, Wang et al 29 have developed several organic UVAs-intercalated LDH systems, which signicantly enhance the stability of polypropylene during UV weathering.…”

Synthesis of 5‐sulfosalicylic acid‐intercalated layered double hydroxide and its effects on wood flour/polypropylene composites during accelerated UV weathering

“…After the ion‐exchange interaction of SA into the interlayer galleries of LDH, the three peaks mentioned above appeared at 2θ = 7.03° (003), 16.44° (006), and 17.16° (009), respectively. The corresponding interlayer distance d (003) was expanded to 1.260 nm, indicating that SA anions have successfully replaced in the interlayer galleries to form LDH‐SA . As commonly observed in the intercalation of large anions into LDH, the two reflections at (015) and (018) merged and broadened in the pattern of LDH‐SA, which might be related to a partial loss of crystallinity or turbostratic disorder .…”

“…The band around 3425 cm −1 shown in the spectrum of LDH was assigned to the stretching vibration of the hydroxyl groups of LDH layers and interlayer water molecules . The sharp band observed at 1364 cm −1 corresponded to the ν 3 stretching vibration of group, while the band at 450 cm −1 was the signal of OMO vibrations in the LDH layers . The spectrum of SA exhibited several distinctive bands, for example, the absorbance at 3490 cm −1 from the aromatic COH, 1670 and 1376 cm −1 from the vibration of COO − , 1175 and 1040 cm −1 from the characteristic absorption band of .…”

“…The transmission light will be transformed into heat, accelerating the degradation of composites. With intercalation of SA into interlayer galleries of LDH, LDH‐SA could block UV light by both physical shield effect (LDH layers) and chemical absorbability (interlayer SA anions) . The chemical structure of SA is similar to a kind of phenolic antioxidant named Vitamin E (Ve).…”

“…Fortunately, these problems can be overcome by incorporating organic UV absorbing materials in an inorganic host matrix . The resulting hybrid compound can block UV light not only by physical shield effect, but also by chemical absorbability …”