Photo-degradation Behaviors Of Polypropylene With Different Crystal Modifications And Photo-stabilization Of Polymer

The graduate thesis centers on the photo-degradation behaviors of a-andβ-phase polypropylene (PP) as well as modification of traditional light stabilizers with rare earth.The change of product species and chemi-crystallization in amorphous phase of PP with different polymorphs during photo-degradation were investigated, with the aim of understanding the influence of crystalline structure on degradation product species as well as chemi-crystallization on further photo-degradation behaviors. On the other hand, we combined rare earth with hindered amine light stabilizer (HALS) and UV absorbor (UVA) to obtain novel light stabilizers based on rare earth complex. Due to the unique properties of rare earth, the complexes exhibited attractive stabilizing effect in polymer.The thesis contains five chapters.Chapter one is an introduction of the entire work, which discussed the mechanism and detactation of polymer photo-degradation, especially the photo-degradation of PP, the categories and development of light stabilizer, and further covered the application of rare earth complex in photo and thermal stabilization of polymer.In cheapter two, the evolution of various photo-degradation carbonyl products in a-andβ-PP was investigated by using Fourier transform infrared spectra (FTIR) and two-dimensional infrared spactra (2D-IR).A control sample containingβ-nucleating agent but with dominant a-phase was photo-degraded and investigated as well to discern the influence of nucleating agent.These samples were characterized by differential scanning calorimetry (DSC), polarized microscope (POM) and dynamic mechanical analysis (DMA) before photo-degradation.As indicated by FTIR spectra, the photo-degradability ofβ-PP was lower than that of pristine a-PP and control sample.Based on the transform sequence in 2D-IR analysis results, the main carbonyl products generated during photo-degradation were ketones for pristine a-PP and control sample, while those forβ-PP were acids.According to these results, the different photo-degradation behavior of a-andβ-PP has been discussed in terms of the main competitive degradation routes. It was suggested to be related with the different activation of the chain mobility in theβ-crystal and gas diffusion rate. The structure change ofα-andβ-PP crystalline was studied by DSC and surface morphologies observation in chapter three. During photo-degradation,β-PP showed slighter decrease in the melting point and longer period of chemi-crystallyzation as compared with a-PP. With regard toα-andβ-phase in P-PP, it was found that the increase of overall crystallinity degree was mainly happened on lamellar ofβ-crystal, while the content of a-crystal kept decreasing and disappeared after irradiated for 12 days, which also suggested the greater chemi-crystallyzation degree inβ-phase.We proposed that the species of degradation product and the ac-relaxation temperature of amorphous phase in crystal should be responsible for this difference.Meanwhile, the different crystallization ability on lamellar ofα-andβ-crystal was also verified during thermal oxidation. According to above results, the influence of re-crystallization or chemi-crystallization on the oxidation behavior of polypropylene was discussed. Two different effects were proposed. On one hand, decrease in crystallinity degree would lower the density of amorphous phase, and cause the formation of microvoids, which may further accelerate the diffusion of oxygen and oxidation reaction in PP material. On the other hand, crystallization in amorphous phase would make it possible for crystalline phase to act as radical scavengers and thus contribute to stabilize PP.In chapter four, a novel approach to modificate traditional light stabilizers based on rare earth complex was introduced. Firstly, a series of lanthanide complexes with a low molecular weight HALS were synthesized by a simply solvent-free solid state reaction. Elemental, thermo analysis and FTIR indicated that the lanthanide ions were coordinated with oxygen atoms of the carbonyl group in ligand. Photo-stabilizing efficiency of the complexes and ligand was measured in PP before and after ethanol extraction. The measurement of carbonyl index, thermal stability and tensile properties of irradiated samples revealed that these complexes have comparable photo-stabilizing efficiency and improved extraction resistance compared to the ligand alone. Secondly, rare earth complex with UVA and staric acid was synthesized and characterized by Elemental, thermo gravimetry, FTIR, UV-vis spactra and fluorescence analysis.The stabilizing efficiency of ligand and complex were studied in polyvinyl choride.The results suggested that coordination with rare earth could improve the ability of UVA to absorbe ultraviolet irradiation ranged from 300 to 400 nm, and retarde the thermal decomposition of UVA.Such effects together with the thermal stabilizing effect of rare earth steric should be responsible for better photo-stabilizing efficiency and weaker oxidative catalysis effect of complex as compared with UVA.Chapter five is the conclution to the whole research work.Our study on photo-degradation of polypropylene with different polymorphs not only opened the application field of 2D-IR in characterizing polymer photo-degradation, but also developed the mechanism of interaction between degradation and crystalline structure in polymer system. On the other hand, we introduced rare earth complex into modification of traditional light stabilizers, which provide a novel approach to the cheap and efficient light stabilizer.