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Study On The Preparation, Characterization And Properties Of Poly(Vinyl Alcohol)/attapulgite Nanocomposties

Posted on:2007-08-28Degree:DoctorType:Dissertation
Country:ChinaCandidate:Z Q PengFull Text:PDF
GTID:1101360215962790Subject:Materials science
Abstract/Summary:PDF Full Text Request
Poly(vinyl alcohol)(PVA)/attapulgite(AT)nanocomposites were prepared by solution blending, in which PVA was used as polymer matrix and AT as inorganic components. The purification, nano-size dispersion and surface modification of AT and the structure and properties of PVA/AT nanocomposites were studied. Moreover, the dynamic rheological properties, crystallization kinetics, behaviors and kinetics of thermal decomposition were also investigated. Furthermore, PVA/AT composite fibers were prepared in laboratory and middle scale production lines by wet spinning, which were characterized and analyzed properly.The purchased AT was purified by suspending-sedimentation method. Then it was separated into nano-size rods by ultrasonic dispersion. The purified AT was treated by five different modifiers to get organically modified AT. The structure of untreated and treated AT were investigated by Fourier Transform Infrared-Ramen Spectrometer (FTIR), X-Ray Diffraction (XRD) and Dynamic Contact Angle Testing (DCAT), while the dispersion condition of AT nanorods was observed by means of Scanning Electronic Microscope(SEM), Atomic Force Microscope(AFM) and Transmission Electron Microscope(TEM). The results show that the impurities in AT were wiped off greatly, which ended in AT with bright grayish color. AT aggregations can be separated into nano-size rods with the length of 550~750nm and the diameter of 40~50nm mostly, whereas the length/diameter ratio will be smaller if the AT was exposed to ultrasonic dispersion too long. According to the analyses of FTIR and XRD, the AT itself has many active reaction sites, which forms such groups as Si-OH and (or) A1-0H, on its surface as a result of its imperfect crystal structure and (or) other special characters existing in its crystal structure. The FTIR and XRD patterns of modified AT get little change in the main peaks, where some new peaks appearing on the patterns of FTIR, which shows that the crystal structure of modified AT has no change while the organic modifiers exists on the surface of AT nano-rods. Thus the organic modifiers may not insert into the crystal layers of AT and just adsorb or bond on the surface of AT nano-rods. DCAT results show that nearly all the modified AT are more organophilic except one sample.According to the characterization of morphology and structure of PVA/AT nanocomposites, it is found that AT nano-rods are dispersed uniformly in the matrix of PVA, with closely combined interface between these two components. However, excessive AT may induce aggregation to part of AT nano-rods. The type of PVA crystal has no change whereas the crystallinity of PVA/AT nanocoposites is higher than pure PVA. It is also found that the onset thermal decomposition temperature, tensile strength, tensile modulus and storage modulus of PVA/AT nanocomposties are higher than that of pure PVA. As to the effects of AT treating, one can find that AT with different treatment has different influence on the mechanical properties of PVA/AT nanocomposites, while the KH590 modified AT has the best enhancement effect, followed by untreated AT. The modification mechanism of PVA/AT nanocomposites has been discussed according to the above results. AT has many active reaction sites (e.g. hydroxyl) on its surface and it can form hydrogen bonding with PVA matrix, which links those two components closely. So AT can share the load impressed from PVA matrix properly and enhance the mechanical strength of PVA/AT nanocomposite. Those AT treated by modifiers without polarity function groups on their organophilic sides to react with PVA have less reinforcement effect than untreated AT even though they are more organophilic. One possible reason may be the shielding of the surface reaction sites of AT by those modifiers.The investigation on the crystallization kinetics of PVA/AT composites indicates that Jeziorny method could describe this system very well. Comparing to the PVA bulk, PVA/AT nanocomposites have higher crystallinity, shorter semi-crystallization time and higher crystallization rate constant. It can be concluded that attapulgite can be used as an effective nucleating agent and has effects on the growth of crystallites in the crystallization process of PVA matrix.The thermal decomposition curve of PVA/AT composites showed that the initial temperature of thermal decomposition and the temperature of maximum thermo-gravimetric rate were all shifted towards high temperature. The studies of thermal decomposition kinetics indicated that the activation energy of thermal decomposition increased comparing to pure PVA, which also show that the PVA/AT composites have higher thermal stability.The rheological properties of PVA solution are influenced by AT nano-rods greatly. It is believed that nano-rods can prevent the entanglement of PVA molecular chains by reducing their hydrogen bonding. This may offer great help to the extending of PVA chains on the process of spinning and thus useful to the reinforcement of final fibers.PVA/AT composite fibers were prepared by wet spinning. It has been found that the loading of AT does not affect the spinning process. PVA/AT nanocomposite fibers show much higher tensile strength, initial modulus and work-to-break than that of pure PVA fibers in the same draw ratio. The observations of SEM display that the AT nanorods can align orderly along the fiber axis by stretching and have good adhesion to the fiber matrix. The results of birefringence measurements prove that the modified fibers have higher orientation than that of pure PVA fibers after stretching. Results of DSC analysis indicate that the crystallinity of the PVA fibers can be increased by adding AT. From the results of middle scale production experiment, one can find that the reinforcement of PVA/AT fibers without boric acid is more obvious than that of fibers with boric acid as crosslinking agent. So it is believed that AT may have similar function as boric acid, that is, as a kind of crosslinking agent. Hence it helps the extending of PVA chains, shares the load pressed from PVA matrix greatly and has great effect on the enhancement of mechanical properties. So the reinforcement of PVA/AT fibers is due to the effect of AT on the spinning solution, the orientation of PVA crystallines, the ability of chain extending and the linking between those two components.The investigation of this paper will exploit new applications for AT and enhance its value in industries. It will provide theory supports for the preparation of high performance PVA fibers. Moreover, it will be useful reference for the preparation and industrialization of nano-modification fibers.
Keywords/Search Tags:Poly(vinyl alcohol), Attapulgite, Nanocomposite, Kinetics of crystallization, Rheological properties, Wet spinning
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