Morphology Control And Surface Modification Of TiO₂ Pro-oxidant And The Application In LDPE Photo-oxidation And Biodegradation

The oxo-biodegradable mulch film is a kind of environmental film which can be completely degraded in the environment. In recent years, it has become a hot research topic at domestic and abroad. As an effective pro-oxidant, TiO₂ has been successfully applied for the oxo-biodegradation of plastics. So far, the practical application of TiO₂ in the degradable plastics field has been greatly limited due to the low photocatalytic efficiencies resulted from the easy recombination of photogenerated charge carriers, easy agglomeration and low utilization of sunlight. In this paper, the mesoporous TiO₂?M-TiO₂? with high specific area and the nano-fiber TiO₂?F-TiO₂? were prepared as photocatalysts. Furthermore, to improve their photocatalytic activity and the utilization of sunlight, the photocatalysts were modified by organic monomer, and the photo-catalytic oxidation and biodegradation properties of LDPE were studied. The contents of this paper include the following:Nanosized meso-TiO₂?M-TiO₂? was prepared by hydro-thermal method using tetrabutyl as material. The effects of hydrothermal time, hydrothermal temperature and aging time on the crystal form and specific surface properties of meso-TiO₂ were investigated. Nanosized TiO₂ fiber?F-TiO₂? was synthesized via a two-step heat-reactive alkali and hydrogen ion substitution process using titanium sulfate as titanium source and urea as a precipitating agent. The effects of different molar ratios of titanium sulfate and urea, and the order of the addition of alkali in the two steps of alkali thermal reaction on the morphology of titanium sulfate were investigated. The results show that the prepared M-TiO₂ has larger specific surface area, and the crystalline form is anatase mainly. The anatase nano-TiO₂ fiber can be obtained when the molar ratio of titanium sulfate to urea is 1:1, and the addition order of alkali is KOH first and then the Na OH.Nanosize M-TiO₂ partices were modified by grafting oleic acid?OA? via hydro-thermal method in situ. The effects of different content of oleic acid on the crystal form and specific surface properties of M-TiO₂-g-OA particles were studied. On the other side, nanosize M-TiO₂ and F-TiO₂ partices were modified by polyaniline?PANI? in situ polymerization. The effects of different contents of PANI on the crystal form, specific surface properties and absorption spectra of PANI/M-TiO₂ particles were studied. The results showed that the dispersion of F-TiO₂ and M-TiO₂ particles in the solvent were improved after the modification by OA and PANI. The modification by conjugated polymer PANI can obviously decrease the recombination efficiency of photogenerated charge carriers of nano M-TiO₂ and F-TiO₂ particles, and broaden the absorption range of the solar spectrum.The LDPE/TiO₂ and LDPE/TiO₂-g-OA composite films were prepared by an addition of M-TiO₂ and M-TiO₂-g-OA as pro-oxidants into LDPE. The effects of the amount of OA on the photocatalytic oxidation and biodegradation of composite films were studied. The results showed that: The photocatalytic degradation activity of the composite films showed a decreasing trend with the increase of the content of oleic acid. The photocatalytic degradation of the composite film was the best in the absence of grafting oleic acid. After UV irradiation for 792 h,The weight loss of LDPE/M-TiO₂ and LDPE/M-TiO₂-g-OA?0.6:1? composite films were 68.82% and 61.46%, weight average molecular weight?Mw? decreased by 97.9% and 97.6%, respectively. However, the biodegradable activity of pro-oxidative composite films was significantly increased due to the addition of oleic acid in microbial culture experiments or composting. After composting for 193 days, the mineralization rate of LDPE/M-TiO₂-g-OA?0.6:1? composite film reached 27.45%. The micro-organisms grew well on the films after microbial cultivation.The composite film was prepared by an addition of PANI/M-TiO₂ into LDPE. The effects of the amount of PANI on the photocatalytic oxidation and biodegradation of composite films were investigated. The results showed that: The photocatalytic oxidation of composite films was firstly increased and then decreased with the increasing amount of PANI. When the mass ratio of PANI to M-TiO₂ was 1/300, the LDPE/PANI/M-TiO₂ had the best photocatalytic degradation. After UV irradiation for 792 h, the weight loss of LDPE/ PANI/M-TiO₂?1/300? composite film reached 92.85%,the weight average molecular weight?Mw? decreased by 98.4%, and the crystallinity increased from 15.39% to 46.2% before and after UV irradiation, showing that many small molecule compounds were produced in photocatalytic oxidation lead to the orderliness improving. The microbial cultivation experiment showed that the microbial were growing well,and the mineralization rate reached 21.08% after composting 180 days.The composite films were prepared by an addition of F-TiO₂ and PANI/F-TiO₂ into LDPE. When the mass ratio of PANI to F-TiO₂ is 1/300,the time control properties of photocatalytic oxidation were investigated by the addition of different amount of light stabilizer in composite films. The results showed that:The elongation at breaks of LDPE/F-TiO₂ and LDPE/PANI/F-TiO₂ were 40% and 46% higher than that of LDPE, which indicating that fibrous orientation in processing improved the mechanical strength of the composite films. After UV irradiation for 792 h,The weight loss of LDPE/F-TiO₂ and LDPE/PANI/F-TiO₂?1/300? composite films were 59.03% and 68.05%, weight average molecular weight?Mw? decreased by 97.8%. After composting for 46 days, the mineralization rate of LDPE/F-TiO₂ and LDPE/PANI/F-TiO₂?1/300? composite films reached 7.96% and 8.59%. The microbes grew well after microbial cultivation.