The sterically expanded octamethyloctahydrodibenzofluorene moiety, C29H38 (Oct), has been incorporated into ansa-metallocenes and constrained geometry catalysts (CGC's). Utilization of this sterically expanded version of fluorene has resulted in solidstate anomalies for both systems. The ansa-metallocenes Me2C(n5-C5H4) (n5-C29H36)MCl2, M = Zr, Hf and Me2C(n5-C5H4)(n5-C29H36)ZrBn2 demonstrate crystal motifs expected for ansametallocenes while Me2C(n5-C5H4)(n5-C29H36)MMe2, M=Zr, Hf exhibit diffuse diffraction, a phenomenon that is extremely unusual for organometallic complexes. This crystalline anomaly is the result of a disorder restricted to two dimensions caused by the rare pillared motif of the system. The best solution for this system consists of parallel and anti-parallel pillars present in a 60:40 ratio. The solid state anomaly observed for the Oct-CGC's occurs on a molecular level. The parent Oct-CGC, Me2Si(1-C29H36)(1-N-tBu)ZrCl2·OEt2, demonstrates an unprecedented n1 ligation to the fluorenyl-based ring. Systematic derivatization of this system via halide substitution, alkylation, and exchange of Zr for Hf has revealed that the n1 ligation persists for systems with small substituents on the metal center capable of retaining a coordinated ether. It is hypothesized that the unusual structure of this new Oct-CGC results in Me2Si(1-C29H36)(1-N-tBu)ZrCl2·OEt2/MAO (MAO = methylaluminoxane) being six times more active in the homopolymerization of 1-octene than ethylene. When compared to the prototypical Ti-CGC Me2Si(n5-C5Me4)(n1-N-tBu)TiCl2/MAO, the Oct-CGC is 85 times more reactive in the homopolymerization of 1-octene and 52 times more active in the copolymerization of 1-octene and 4-methyl-1-pentene. The high reactivity of the Oct-CGC towards alpha-olefins results in the observation of an unyielding comonomer effect in the copolymerization of these olefins with ethylene. In addition, the Oct-CGC is perhaps the most syndioselective catalyst known. With an enantiofacial selectivity of 99.7% and a remarkably high activity towards alpha-olefins, the Oct-CGC is capable of producing the highest melting syndiotactic polypropylene (Tm = 165oC, annealed = 174oC) reported thus far. The high activity and syndioselectivity of the Oct-CGC can be extended to the production of syndiotactic poly(4-methyl-1-pentene) with the highest melting point thus far reported (Tm = 215oC).

Since odor-complaint events have been increased year by year in Taiwan, odor control has become an important issue in the air pollution control field. Thus, this paper attempted to investigate if ¡§ozone scrubbing-activation carbon adsorption¡¨ is feasible for efficiently reducing the odor intensity of vented gas from recycled polypropylene (PP) fusion operations. A pilot scrubber (0.17 m L ¡Ñ0.17 m W ¡Ñ1.2m H, packed with Intalox saddles to a total volume of around 0.018 m3) was used for the feasibility test. Odorous gases vented from the fusing operation kept at 200 ¢J in a temperature-controlled oven were used as the target waste gases. Results indicated that with operation conditions of VOCs (as methane) 10-40 ppm, an ozone concentration of 4.0 ppm in the influent gas, a liquid/gas (L/G) ratio of 0.030 L/m3 in the scrubber, and an empty bed retention time of around 9.7 s in the packed section, around 60% of the VOCs in the influent gas was removed. Most alkenes in the gas were converted into sweet-smell ketones in the ozonated gas. Vented gas from the scrubber was further treated by a granulated activated carbon (GAC) adsorption column with an EBRT of less than 1 s for the gas. An overall VOC removal of around 70% was observed for the full ozonation-GAC process. Only trace amounts of original fume-like and sweet-ketone smells were detected in the treated gases. A test indicated that the overall odor (expressed as the dilution to threshold D/T value) removal was around 70% and the D/T were 733, 309, and 232, respectively, for the influent, ozonation-scrubbing effluent, and GAC effluent. It was estimated that the cost is around NT$ 9.57 for treating 1,000 m3 of the teat gas by the system. Efforts should be made by decreasing the cost by other alternative technologies.

M. Tech. Polymer Technology. / This study was undertaken to investigate the effect of the addition of boehmite alumina (AlO(OH)) nanoparticles in polypropylene grafted maleic anhydride (PP-g-MA) compatibilized polypropylene (PP)/polyamide 12 (PA12) blend.

Traditionally ultrafine fibers below 1 dpf are produced by extrusion followed by mechanical drawing. A modified melt spinning apparatus with high-speed air nozzle was designed and fabricated to produce continuous polypropylene filaments by cold air drawing only. With this setup, the fiber is quenched and simultaneously attenuated by a symmetric cold air jet. Since the formation of fiber structure is highly dependent on the processing conditions, the new process will provide a unique operation window to study fiber attenuation and structural formation under high-speed cold air drawing. Based on computational fluid dynamics simulation results, a parametric study was carried out under different process conditions which include processing temperature, air velocity and polymer volume flow rate. Effects of changes in processing variables on the fiber diameter, molecular orientation, crystallinity, tensile strength and other properties were studied. Furthermore, a theoretical model was developed to analyze the non-isothermal fiber attenuation mechanisms. The new knowledge obtained in this study would likely yield a new process for producing innovative fiber products.

No description available.

Polypropylene continues to be the mainstream choice thermoplastic for automotive applications. In many applications PP is filled with mineral fillers for improvement of properties. Biobased natural fillers or fibres are attractive materials to reduce the weight because of the low specific gravity of the biobased materials compared to the mineral fillers. Our group has done extensive research on the development of wheat straw fiber in thermoplastics in the past years. It is very important to understand the behaviour of single fillers on composites before studying the effects of mixing fillers or fibers (hybridization). The objective of this study is to evaluate and compare systematically the effects of wheat straw and mineral fillers in the polypropylene matrix. The study includes two types of wheat straw (WS) categorized based on their size (fine WS and medium WS) and three different types of natural minerals (Talc, Mica and Wollastonite). Three types of polypropylene (PP), Homopolymer PP, High Impact Copolymer PP and Homopolymer-Copolymer Blend PP, were investigated as the matrix. This study also evaluates the effect of combining two fillers (WS and mineral filler) in the hybrid composite. The fillers were formulated in three different percentages (20, 30 and 40wt %) and compounded via extrusion. Samples for all formulations were prepared by injection molding. The mechanical properties (flexural modulus and strength, tensile modulus and strength, impact strength), water absorption and density were measured. The properties of hybrid composites were evaluated by varying the amounts of two fillers at 10wt%-20wt%, 15wt%-15wt% and 20wt%-10wt% each, keeping the overall filler content constant at 30wt%. The effect of type of filler, filler size and filler content were critical in this work. The results obtained from this study indicated that filler type and filler content greatly influenced the mechanical properties and water absorption characteristics of the composites. The flexural modulus increased with increasing filler content. It was interesting to observe that though the impact strength decreased with the addition of fillers, increasing the filler content from 20 to 40 wt% did not affect the property. With respect to all fillers, wollastonite improved the mechanical properties significantly. Increasing the amount of WS content reduced the composite’s resistance to water absorption. Among mineral fillers, mica showed significantly higher percentage gain in weight with water absorption. Combination of fillers at varying percentages did not have any synergy effect on the mechanical behaviour of the composite. The percentage increase in weight with water absorption was observed to be increasing with increasing WS content in hybrid composites, but significantly lower than pure WS composites. The morphological study on WS composites revealed improved interaction of filler with homopolymer and polypropylene blend.

The use of wheat straw and other agricultural by-product fibers in polymer composite materials offers many economical and environmental benefits. Wheat straw has been recently commercialized as new filler for polypropylene thermoplastic composites in automotive applications. However, to expand its application in the automotive industry and other sectors where highly-engineered materials are needed, a systematic database and reliable composite property models are needed. For this purpose, this research was systematically conducted. A product design approach is used in studying wheat straw polypropylene (WS-PP) composite. A set of thermoplastic composite specifications relevant to several automotive parts was used as a basis for the customer needs which give the direction to the entire product design of thermoplastic composites based on polypropylene and straw. Straw fibers were produced by grinding and sieving (without any other treatment). These fibers were used in the formulation of polypropylene thermoplastic composites to understand the variable that can contribute to minimize production cost, maximize product performance and maximize wheat straw utilization (fraction of renewable material). The variation in chemical composition due to plant variety (parts of the plant, location of harvesting and seasonality), the bonding incompatibility between hydrophobic polypropylene matrix and hydrophilic straw fiber, along with the heterogeneity of fiber size and shape, has made wheat straw polypropylene composite a complex system. This complexity causes the mechanistic approach of composite modeling in the well-established composite theory difficult to be applied, since modeling the contribution of natural fibers to the performance of thermoplastic composites is not as straightforward like in the case of homogenous glass fiber (with same shape, diameter and narrow length distribution). Alternatively, a statistical approach of modeling by using designed experiments was used in this research. The Mixture and Process-Mixture Experimental Design methodologies were applied to develop response surface models that can be used to correlate input properties and formulation of these thermoplastic composites to the final properties of the product. The models obtained can then be inverted to predict the required properties and formulations using fiber (straw), matrix (polypropylene), and additives (coupling agent) as the main components for a specified product performance. The prediction includes the fiber grading (size and aspect ratio) and classification in order to maximize fiber utilization for different needs of composite products. The experiments were designed based on the analysis of the existing data provided by previous research works of wheat straw polypropylene composite system in our laboratory and by experimental data generated during this research. The focus of the analysis was the determination of the factor(s), i.e., the independent variables of the experiments and their acceptable levels. The response variables being measured were chosen based on the required specifications of targeted products. A constrained three-component mixture design of experiment was conducted to develop models for flexural properties of WS-PP composite. The three independent mixture variables in this experiment were the weight proportions of: straw (as fiber), polypropylene (as matrix), and maleic anhydride polypropylene (as coupling agent). Statistical analysis results showed that the obtained models have met standard requirements of response surface models with good predictive capability. One of the important finding of this study was the formulation for optimum coupling agent proportion which gives the best flexural properties of composite. The effect of straw fiber size on composite properties was investigated by using fiber length and aspect ratio as parameters to describe fiber size, instead of the size of sieves used in fiber preparation. Two-stage separation method was applied in the straw fiber preparation process. In this method, width-based separation was followed by length-based separation to obtain fiber fractions with distinct fiber length and aspect ratio. Samples of thermoplastic composites for measurement of physical properties were produced from each fiber factions at two different levels of fiber loading. The samples were compounded by twin-screw extrusion and specimens were prepared by injection molding. The fibers were then extracted from the samples after injection molding (using solvent) and their sizes were measured to investigate the fiber size reduction during the compounding and molding process. A comprehensive analysis was then performed to study the responses of stiffness, impact resistance and specific properties of these composites by including initial fiber sizes, fiber chemical compositions (measured as cellulose, hemi-cellulose and lignin), fiber size reduction during compounding/molding process, and fiber loading as factors. One of the important contributions of this study is fiber grading in terms of their sizes and their respective contributions to the final composite product properties. Based on the previous results, a mixture design of experiment was performed on wheat straw – polypropylene / impact copolymer polypropylene (WS-PP/ICP) composite system. The objective of the experiment was to obtain response surface models that can be used to estimate some important properties required by a set of automotive product specifications. The optimum formulation of coupling agent obtained in the previous study was used to determine the fixed recipe of coupling agent; simplifying the composite system into a three-component mixture, i.e. straw (as fiber) and polypropylene (homopolymer and impact copolymer (polypropylene blend as matrix). Simulation of the models shows the superiority of using a blend of polypropylenes to balance the stiffness and impact strength of the composites and being able to reach three targeted product specifications. A case study was also performed to demonstrate that the models can be used to find optimum formulations to minimize material cost while meeting specifications of all targeted products. Finally, a framework for wheat straw polypropylene product design and development is presented in this thesis. The framework can be used for designing polypropylene-straw thermoplastic composites with various combinations of fiber - polymer matrix - additive systems with different product attributes and specifications suitable for several applications in the automotive industry.

Particulate filled polymer composites are gaining growing acceptance in the commodity industry because the properties can be adjusted according to the industry's requirements. As particulate filler, fly ash is ready to compete with other particular fillers in polymer composites industries. Although fly ash is a cheap material but the fact that fly ash is grey-black in colour, limits the application of fly ash only to product where colour is not important. As such, a method was needed to be developed to increase the whiteness of fly ash without reducing the advantages of it as a cheap material. In this research, twelve commercially provided fly ash samples from Australian thermal power stations were investigated with respect to composition. Seven of them were thermally modified and further investigated and characterized with respect to colour, size, size distribution, and density. Of these seven fly ashes a particular grade was modified to a whiteness of 93.3 in L*a*b* scale (using barium sulfate as standard), without changing other inherent properties such as particle size and density. By comparison L*a*b* value for Omy carb 20, based on calcium carbonate is 96.9. The whiteness of fly ash was increased using a one stage thermal method ensuring the related cost of production would be not a major hurdle. The next aspect of the thesis involved incorporating as-received and heat treated fly ash samples in isotactic polypropylene up to 80 parts of fly ash per hundred resins (phr), demonstrating that fly ash content in polypropylene composites can be quite high with properly maintained combination of mechanical properties -- in particular up to 200 % improvement in Young's modulus and 63 % gain in notched impact properties, as explained in the thesis. Whilst the Young's modulus properties of the fly ash PP composites match very well with Kerner model, they lie in between the Rule of Mixture series and parallel. The tensile strength properties obtained in this research are at least 25 % higher than those predicted by Nielsen, Landon and Nicolais; whereas the strain to failure values are between 25 - 50 % higher than those predicted by Nielsen, and Smith. Whilst tensile strength of the fly ash filled polypropylene composites were less than the original polypropylene samples, as normally reported in the literature, in this thesis surface modification of fly ash particles by using 10% vinyl triethoxy silane (VTES) coupling agent gave a nominal increase in tensile strength especially at higher fly ash content. The final aspect involved study of oxidation behavior of fly ash filled polypropylene composites. Fillers, including fly ash can shorten the life time of polymers from both chemical as well as physical factors. As-received fly ash contains iron based impurities which may catalyze the anti oxidant in polypropylene, therefore reducing the service life time of the polymer. In this work, thermal treatment studies showed that the iron in fly ash can be changed to a chemically inert material so the effective service life of the polymer will only be influenced by physical factors. Therefore thermal treatment of fly ash not only increases the whiteness but also it reduces the risk of the filler on the life time of the polymer, and hence the composites.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references. Also available via the Internet.

Thesis (M.S.)--University of Alabama at Birmingham, 2010. / Title from PDF t.p. (viewed July 19, 2010). Includes bibliographical references (p. 67-70).