Effects Of Aging And Photocatalytic Processes On The Physical And Chemical Properties Of Titanium Dioxide Microplastics

Microplastic pollution is an important issue on a global scale.The endogenous and exogenous pollution of microplastics has been valued by many countries and regions.Microplastic fragments and micropollutants adsorbed on their surfaces and additives carried by themselves If released into the environment,it may pose a certain threat to ecosystems and human health.In this thesis,the effects of the aging process on the surface characteristics of microplastics and the release of additives are studied by using a simulated aging box.The microplastics selected in this paper are pigmented titanium dioxide-containing low-density polyethylene plastic masterbatches.And imaging,spectrophotometric instruments,scanning electron microscopy combined with energy dispersive X-ray spectroscopy(SEM-EDS)and thermogravimetric analysis(TGA)and other technical analysis methods to characterize the microplastics before and after aging,and studied the release rule of pigment titanium dioxide and The particle size distribution of the released particles.The atomic force nano-infrared(nano IR2 AFM-IR)technology is used to explore the performance changes of microplastics in the sub-micron and nano-ranges.The specific detection indicators include: surface morphology,chemical composition changes,glass transition temperature,and Loren Hereby contact resonance force performance.Finally,the effect of photocatalysis on the properties of polypropylene(PP)and low density polyethylene(LDPE)plastic films supported by nano-titanium dioxide was studied by atomic force infrared(AFM-IR).The research results obtained are as follows:(1)During the aging process of microplastics: First,the surface chemical composition changes,and carbon-oxycarbonyl bonds are formed;the surface brightness and color difference change greatly.Secondly,obvious cracks appear on the surface,and the content of oxygen element on the surface is obviously larger than that of titanium element.Finally,the microplastic matrix low-density polyethylene has a significant quality loss.(2)It can be seen from the additive leaching experiment that the leaching concentration of titanium dioxide in the aged microplastics is about 15.89 times that of the unaged at 12 h.The amount of titanium dioxide particles leached from the aged microplastics is about 15.4 times that of the unaged.It shows that the aging process has promoted the release of additives,and the effect is obvious.(3)Characterization of microplastics by AFM-IR: It is found that the surface of the microplastics after aging is relatively rough,showing a grainy feel,and the particle sizes are different.The nano-infrared imaging image shows obvious oxidation and uniform distribution.From the nano-thermal analysis(Nano-TA),it can be concluded that the glass transition temperature of the unaged microplastic surface is209.50 ± 11.48 °C,and the glass transition temperature of the microplastic surface that is aged for 6 weeks is 94.91 ± 4.40 °C.The melting temperature decreased by approximately 114.59 °C.The Lorenz contact resonance(LCR)analysis of the surface of the sample was used to analyze the nano-mechanical spectrum,and the results showed that the aged microplastic surface hardened.(4)Nano-titanium dioxide on the surface of PP and LDPE plastic films is uniformly dispersed.Except for a small amount of agglomeration,the equivalent diameter of the nanoparticles is about 81.5 nm.The photocatalytic action of nano-titanium dioxide causes C=O stretching vibration bonds and ·OH stretching vibration bonds in intramolecular hydrogen bonds to appear on the surface of both membrane materials,and their signal intensity is affected by the photocatalytic time and distance gradient(the distance from the nano-titanium dioxide)influences.Nano-TA analysis showed that the average glass transition temperature of the surface of the PP film gradually decreased,and its glass transition temperature decreased from126.7 °C at 0 h to 108.5 °C at 4 h.The analysis of the LDPE film found that the average glass transition temperature on the surface of the LDPE film fluctuated within95 °C to 97 °C with the increase of the photocatalytic time,without significant change.It was observed by LCR analysis that with the extension of the photocatalytic time,both the PP and LDPE film materials became hardened by the photocatalytic effect.The photocatalytic effect of nano-titanium dioxide has a certain effect on the stiffness of the surrounding plastic film material,and the closer the PP and LDPE substrates are to the titanium dioxide,the stronger the resonance frequency signal.In this thesis,traditional techniques such as infrared spectroscopy,micro Raman spectroscopy and imaging,spectrophotometric instruments,scanning electron microscopy combined with energy dispersive X-ray spectroscopy(SEM-EDS)and thermogravimetric analysis(TGA)are used to treat the surface of aging microplastics.The characteristics and release laws of additives were studied,and the performance of microplastics in the sub-micron and nanometer range was analyzed using the new atomic force nano-infrared technology,which provided a new basis for the formation of microplastics and the release of additives.And additive pollution provide newideas.