Synthesis, Selective Infrared Absorption Property And Application Of Intercalated Layered Double Hydroxides

Layered double hydroxides (LDHs) are a class of anionic clay compounds. Its main features are:adjustable composition of its host layer, tunable layer charge density and exchangeable interlayer anions in a wide range. The layered structure of LDHs and the positively charge density of host sheets are responsible for their anionic exchange capacity which offers widely potential applications in a variety of fields, e.g., catalysis, electrochemistry, adsorption separation, biochemical medicine and functional additives in polymers.This dissertation relates to a systemic study on the preparation of intercalated layered supermolecular materials with highly selective IR absorption capacity and their applications in Low Density Polyethylene (LDPE). A detailed investigation has been carried out on the influence of the composition of LDHs precursor and the properties of functional guest anions on the selectivity and the efficiency of IR absorption, and of the LDHs structure on thermal stability of the guest species as well as IR absorption performance of LDHs/LDPE composite films when the prepared intercalated layered supermolecular materials with highly selective IR absorption capacity was incorporated into the LDPE. Additionally, a preliminary examination has also been taken on the dispersion degree of the prepared LDHs in the LDHs/LDPE films, the mechanical properties and the visible light transmittance of the LDHs/LDPE composite films.MgAl-CO3-LDHs and MgAl-NO3-LDHs, as the precursor of anion-exchange reaction, have been prepared by a method involving separate nucleation and aging steps (SNAS). Dihydrogen phosphate anion, Iminodiacetic acid, N,N-bis (phosphonomethyl) glycine and Amino trimethylene phosphonic acid anions which have promising IR absorption capacity in the wavelength ranges of 7～25μm, especially in the peak range of 9～11μm, have been intercalated into the interlayer of LDHs by anion exchange method. Four novel kinds of highly selective IR absorption intercalated LDHs:MgAl-H2PO4-LDHs, MgAl-IDA-LDHs, MgAl-GLYP-LDHs and MgAl-ATMP-LDHs have been prepared. The resulting intercalated LDHs were characterized by various techniques, such as XRD, FT-IR, TG-DTA-DTG, ICP and SEM. The obtained results show that the anion exchange method is an effective way to prepare these functional anions intercalated LDHs using MgAl-CO3-LDHs and MgAl-NO3-LDHs as the precursor; furthermore, the intercalation of guest anions into the galley of the LDHs favors to enhance the thermal stability of guest species.The IR absorption performances of these four intercalated LDHs and the relationship between the performance and the chemical composition of guest anions were investigated by FT-IR in detail. The obtained results indicate that the selectivity and the efficiency of IR absorption of the intercalated LDHs are mainly determined by the IR absorption features of the interlayer anions and the amount of the intercalated anions in the interlayer. Besides, the layered structure of the LDHs also has synergetic effects.MgAl-CO3-LDHs and four intercalated LDHs were mixed with LDPE to form the corresponding LDHs/LDPE films with a thickness of 120μm by the masterbatch technology. A variety of techniques such as TEM, XRD, TG-DTA and FT-IR have been used to characterize the LDHs/LDPE composite films. The results suggest that LDHs particles were uniformly dispersed in the LDPE matrix and the mixed process did not change structures of LDHs and LDPE matrix; the intercalated LDHs/LDPE films had highly selective IR absorption in the range of 9～11μm, in which the amount of heat radiated from the earth's surface to the atmosphere is a maximum. Therefore, the intercalated LDHs materials containing functional anions should enhance the heat retention properties of LDPE agricultural films. And among the four highly selective IR absorption intercalated LDHs, the H2PO4- intercalated LDHs has the best selective IR absorption capacity and the selective IR absorption capacity of the organic anions intercalated LDH materials decreases in the order:ATMP> GLYP>IDA.FT-IR, universal testing machine and TG-DTA techniques have been used to examine the influence of the addition of LDHs on the visible light transmittance, the mechanical properties and the thermal stability of the LDPE film. The investigated results show that the addition of the LDHs powder (4 wt%) has little adverse impact on the visible light transmittance and the mechanical properties, and significantly enhances the thermal stability of the LDPE matrix.