No description available.

No description available.

Polytetrafluoroethylene (Teflon®) is encountered in many environments – frying pans, clothing, osmotic distillation membranes, to name a few – yet the solubility and clustering behaviour of water with this material was not found in the open literature. This information may be useful in applications where an absence of water is desired, such as in clothing and textiles. Previous work on polyethylene + water has shown that small water clusters form in the amorphous portion of the polymer. This work investigated this phenomenon for the case of polytetrafluoroethylene + water. Initially, a test system of light alcohols + water + n-dodecane was investigated using Gibbs Ensemble Monte Carlo simulations and compared to previous laboratory experiments. This test system was investigated in order to gain expertise in the methodologies and theory behind Monte Carlo simulation, as well as to gain experience with using the necessary software. For this test system, it was found that the TraPPE parameters representing the interactions between the alcohols and the n-dodecane were not adequate and lead to increasing deviations with increasing carbon number in the alcohol. To replicate the conditions of the amorphous polymer matrix, liquid-liquid equilibrium between water and the polymer was investigated. Gibbs Ensemble Monte Carlo simulations have been performed for systems of perfluoroalkanes and water to determine the influence of temperature and carbon number on the solubility and clustering behaviour of water within the perfluoroalkanes. The temperature range in this study was from 450 K to 600 K, and the perfluoroalkane carbon number range was from 8 to 300 carbon atoms. With increasing carbon number, it was found that there was an asymptotic value of 98.0 mole percent water in the polymer phase. With increasing temperatures it was found that there were exponential increases in solubility of water into the polymer matrix. Previous work on clustering and supramolecular structure of perfluoroalkanes described the rigidity of the perfluoroalkane chains in comparison to alkane chains, thus explaining the large increases in free volume with increasing temperature in the polymer matrix observed in this work. A discontinuity with regard to both solubility and clustering behavior was observed for a polymer carbon number of 10 to 12 carbon atoms. Prior work on the energy contributions towards the helical structure of perfluoroalkanes showed a shift in the energy contribution regime for carbon numbers larger than ~10 carbon atoms, which may explain this discontinuity. It was found that linear water clusters accounted for up to ~90 percent of the water clusters, concurring with previous work on water clustering in polyethylene. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2011.

No description available.

Digitized by Kansas Correctional Industries

The purpose of this thesis was to determine which contaminants were present in washed and dried shredded poly(ethylene terephthalate) (PET, flake) obtained from curbside collection and to determine whether their concentrations were above the US FDA threshold of 215 ppb. Over thirty semi-volatile contaminants were extracted from the treated flake by Soxhlet extraction using dichloromethane as a PET swelling solvent and gas chromatography-mass spectroscopy for identification and quantification. Soxhlet extraction of flake ground to 0-300 �m was effectively completed by 24 h, whereas sonication reduced the extraction time to 3 h. In contrast Soxhlet extractions on flake ground to a larger particle size range (>300-425 �m and >425-700 �m) were completed within four hours, possibly due to less aggregation in the extraction thimble. In the finely ground flake (0-300 �m) the levels of most contaminants were below 215 ppb, but six were not. Dodecanoic acid was present at about 1200 ppb, 2-butoxyethanol was approximately 1000 ppb, limonene, benzophenone and methylsalicylate were above 800 ppb and 2-methylnaphthalene near 215 ppb. After analogous method development the levels of all diffusible compounds in extruded PET pellets were below the threshold of 215 ppb. The Soxhlet extraction technique was validated by comparison with total dissolution by TFA for two of the three particle size ranges obtained by grinding the PET flake (>300-425 �m and >425-700 �m) and for the unground flake. Further validation was achieved by the comparison of contaminant levels determined by total dissolution with TFA and sonication with DCM using flake ground to the 0-300 �m size range. The levels of contaminants were found to increase with decreasing particle size range, but XRD measurements of degrees of crystallinity were similar for each PET particle size range, thus showing that the differences in contaminant levels were not due to variable percentages of the amorphous material from the tops and bottoms of shredded bottles, relative to the amounts of crystalline PET from the mid-sections of the bottles. Hence it was postulated that the variations in contaminant levels were due to selective grinding of the more highly contaminated surfaces, whilst the larger particles incorporated the less contaminated interior material. The analysis of the more homogenous annealed (extruded) pellets indicated that contaminant levels between the analogous particle size ranges were equivalent. This observation validated our interpretation of the high levels of contaminants found in finely ground flake being due to selective surface grinding where high levels are expected. When analysing volatiles, static headspace analysis was performed on flake and extruded pellets due to the limitations surrounding SPME. External standardisation was used as the method of quantification and the levels of toluene, undecane and p-xylene in extruded pellets were found to be below 38 ppb and therefore within the 215 ppb FDA-set threshold for flake and pellets.

Thesis (M.Phil)--University of Hong Kong, 1994. / Includes bibliographical references. Also available in print.

In a first step, the surfaces of polyethylene films have been modified by grafting urethane monoacrylate monomer under UV irradiation in ambient air. For native films, this grafting was successfully realized but the grafted surface was heterogeneous. To overcome this drawback and obtain a smooth and homogeneous coating, a wet oxidation method using sodium hypochlorite through two different processes was developed. The oxidation mechanism of the PE films has been established. As a consequence of the oxidation, the wettability of the grafted films was strongly increased as measured by sessile drop technique and Wilhelmy plate method. The hydrophilicity is due to carbonyl and carboxylic groups created on the treated surface. Grafting of several formulations containing different amounts of monomer, carrier and photosensitizer was successfully evidenced by analyzing the residues obtained from PE extraction in hot toluene. Indeed, FTIR, XPS, DSC and elementary analysis showed that the polyacrylate was effectively grafted on PE pre-oxidized films. Moreover, the obtained grafted surfaces corresponding to important oxidation time were homogeneous as shown by SEM and AFM. In a second step, acrylate grafting was used to induce specific properties onto the surface. This study was focused on antibacterial effect. The process starts by a dissolution of poly(4-vinylbenzyl chloride) (PVBC) in the urethane monoacrylate monomer followed by photopolymerisation of the latter. Anchoring of different PVBC based formulations was confirmed by FTIR analysis, performed onto obtained residues after extraction in hot toluene and dichloromethane. In a last step, the grafted coatings were quaternized by using triethylamine in N, N-dimethyl formamide by a nucleophilic displacement reaction. Antibacterial effect of the quaternized samples was measured by Kirby Bauer method.

In a first step, the surfaces of polyethylene films have been modified by grafting urethane monoacrylate monomer under UV irradiation in ambient air. For native films, this grafting was successfully realized but the grafted surface was heterogeneous. To overcome this drawback and obtain a smooth and homogeneous coating, a wet oxidation method using sodium hypochlorite through two different processes was developed. The oxidation mechanism of the PE films has been established. As a consequence of the oxidation, the wettability of the grafted films was strongly increased as measured by sessile drop technique and Wilhelmy plate method. The hydrophilicity is due to carbonyl and carboxylic groups created on the treated surface. Grafting of several formulations containing different amounts of monomer, carrier and photosensitizer was successfully evidenced by analyzing the residues obtained from PE extraction in hot toluene. Indeed, FTIR, XPS, DSC and elementary analysis showed that the polyacrylate was effectively grafted on PE pre-oxidized films. Moreover, the obtained grafted surfaces corresponding to important oxidation time were homogeneous as shown by SEM and AFM. In a second step, acrylate grafting was used to induce specific properties onto the surface. This study was focused on antibacterial effect. The process starts by a dissolution of poly(4-vinylbenzyl chloride) (PVBC) in the urethane monoacrylate monomer followed by photopolymerisation of the latter. Anchoring of different PVBC based formulations was confirmed by FTIR analysis, performed onto obtained residues after extraction in hot toluene and dichloromethane. In a last step, the grafted coatings were quaternized by using triethylamine in N, N-dimethyl formamide by a nucleophilic displacement reaction. Antibacterial effect of the quaternized samples was measured by Kirby Bauer method.

Single-site catalysts revolutionized the polyolefin manufacturing industry and research with their ability to make polymers with uniform microstructural properties. Several of these catalysts are currently used commercially to produce commodity and differentiated-commodity resins. The key to their rapid success and industrial implementation resides in the fact that they can be used without major modifications in the polymerization reactors that previously used heterogeneous Ziegler-Natta and Phillips catalysts. Since most of these industrial processes use slurry or gas-phase reactors, soluble single-site catalysts must be supported on adequate carriers that ensure not only high activity, but also the formation of polymer particles with the proper morphology and bulk densities. Metallocene catalysts have been supported on a variety of carriers, but supporting late transition metal catalysts has not been investigated in detail, despite their very interesting properties such as tolerance to polar comonomers and impurities, activity in the absence of MAO, and the formation of short chain branches by the chain walking mechanism. The research work of this PhD thesis intends to fill this gap, by developing supported late transition metal catalysts with high catalyst activities towards ethylene polymerization and good polymer particle morphology. The effects of catalyst structure and polymerization conditions on silica-supported nickel diimine catalysts are discussed in Chapter 3. Compared with the equivalent homogeneous catalysts, the covalently-attached supported catalysts had high activities, produced spherical polyethylene particles with good morphologies, and polyethylene with higher melting temperatures, higher molecular weight averages, and broader molecular weight distributions. Borates used as internal activators during the synthesis of these supported catalysts successfully activated the nickel diimine complexes. In Chapter 4, MgCl2/alcohol adducts are recrystallized with alkylaluminum compounds and used as catalysts supports for nickel diimine complexes functionalized with amine groups. Polymerization results were compared with those of the equivalent SiO2-supported nickel diimine catalysts. MgCl2-based supported nickel diimine catalysts had high catalyst activity without the use of activators, and it was possible to control polymer molecular weight averages by changing the support composition. Although linear low density polyethylene made with metallocenes offers superior mechanical properties such as excellent toughness, impact strength and clarity, it suffers from poor processability. To overcome some of these disadvantages, Chapter 5 introduces methods to produce bimodal polyethylene resins using supported hybrid early and late transition metal catalyst systems. The presence of short chain branches in the higher molecular weight component is attributable to the incorporation of alpha-olefin molecules by the metallocene sites, while the nickel diimine catalyst sites produce chains with a distribution of short chain branch sizes through the chain walking mechanism. Finally, in Chapter 6 supporting a nickel diimine catalyst onto organo-modified montmorillonite (MMT) to prepare polyethylene/clay nanocomposites through in-situ polymerization is described. The thermal properties and crystallinity of the nanocomposites could be controlled by varying the fraction of MMT in the nanocomposite, and the dispersion of the MMT layers in the polymer matrix were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM).