Preparation And Properties Of Mg-based LDH Anti-photoaging Material

Polypropylene(PP)has been widely used in light industry,automotive industry,aerospace and other fields because of its low price,corrosion resistance,excellent mechanical properties.However,PP is prone to aging under sun light.In order to prevent the photoaging of PP,light stabilizers are usually added in the production process.These commercial light stabilizers are small molecular organic compounds with disadvantages of poor thermal stability and easy extraction,which greatly limits the wide use in PP.Layered double hydroxides(LDH)are a kind of layered anionic clays with many unique properties.The light stabilizers can be assembled into the interlayer of LDH to form inorganic-organic composite functional materials relying on the anion exchange ability of LDH,which will enhance the thermal stability,migration resistance and photo resistance of light stabilizers.Sole light stabilizer intercalated LDH usually suffer from limited UV-shielding performance because the UV absorber present in the interlayer can only selectively absorb finite waveband UV rays,which limits the application of anti-photoaging additives in PP.In order to further improve the photo aging resistance of light stabilizer intercalated LDH materials,in this work,two complementary UV absorbers co-intercalated into LDH layers is proposed according to the composition adjustability and intercalation assemblability of LDH.A new type of light-stabilized material with strong thermal stability and UV shielding ability was obtained by taking advantage of the synergistic effects of interlayer guests.Moreover,a neutral molecule light stabilizer was co-assembled with surfactant into LDH by making use of intermolecular forces prevalent between guests in LDH.The migration resistance ability of the light stabilizer was enhanced after intercalation into LDH.Moreover,the green preparation process of MgAl-LDH at normal pressure were optimized,indicating the potential industrial application value of the green process.The main research contents and conclusions are as follows.1.UV-284(HMBA)and cinnamic acid(CA)were successfully co-intercalated into the interlayer of Mg2ZnAl layered double hydroxides(LDH)with mole ratio of 1:1 by modified coprecipitation method to prepare novel UV-shielding material HMBA-CA-LDH.The characterization results reveal the presence of host-guest interactions between the LDH host layers and HMBA/CA guest anions as well as guest-guest interactions between guest anions in HMBA-CA-LDH,and HMBA-CA-LDH has much stronger UV absorption capability than HMBA intercalated LDH(HMBA-LDH)in the whole UV band and much broader UV absorption band than CA intercalated LDH(CA-LDH).A series of LDH/PP composites with evenly dispersed LDHs nanosheets,as expected,LDH/PP composites show higher thermal stability and better anti-photoaging performance than pristine PP.Furthermore,HMBA-CA-LDH/PP shows better anti-photoaging ability in comparison with HMBA-LDH/PP and CA-LDH/PP.2.Dodecyl sulfate(SDS)was intercalated into the interlayer of Mg3Al-LDH and then a UV absorber UV-531 was co-intercalated into the interlayer of SDS-LDH by utilizing the intermolecular forces between UV-531 and SDS to form UV-SDS-LDH.The characterization results show that UV-531 can effectively exert its UV absorption ability,which can significantly reinforce the UV shielding performance of SDS-LDH.Besides,the migration resistance capacity of UV-531 is effectively strengthened by LDH layers.UV-SDS-LDH can significantly improve the UV shielding performance and thermal stability of PP,thereby improving the anti-photoaging performance of PP.3.Stearic acid(STA)was intercalated into the interlayer of Mg3Al-LDH and then a hindered amine light stabilizer 770(HALS)was co-intercalated into the interlayer of STA-LDH according to the intermolecular forces in STA-LDH interlayer guests to prepare HALS and STA co-intercalated LDH(HALS-STA-LDH).The characterization results show that the UV shielding ability of HALS and HALS-STA-LDH is very weak,which can not improve the UV barrier performance of PP.However,HALS can effectively exert its anti-photoaging ability,which can significantly improve the anti-photoaging performance and thermal stability of PP.4.Nano sized Mg(OH)2 prepared from abundant MgCl2 in Qinghai Salt Lake and cheap Ca(OH)2 and AlOOH were used as the raw materials to prepare MgAl-LDH through a green preparation process under atmospheric pressure.It was found that UV absorber intercalated MgAl-LDH with nanosheet structure,high purity and crystallinity can be prepared by crystallizing at 95? for 6 h.Subsequently,the preparation method was successfully extended to synthesize surfactant,CO32-,and NO3-intercalated LDHs,indicating the universality of this green preparation process in synthesizing MgAl-LDH.