The effect of various inorganic and organic additives as possible nucleating agents on the crystallisation behaviour of P. E. T. and the suosequent influence on the morphological and mechanical properties has been examined. Various methods of mixing(: the polymer and additive were investigated and a method involving the screw-Extrusion of the polymer and the additive was ultimately adopted. Crystallisation studies were carried out using differential scanning calorimetry under dynamic and isothermal modes. The results produced under conditions of isothermal crystallisation were analysed by means of a computer. Despite differences between batches of polymer all the additives with the exception of indigo produced a nucleating effect in the polymer as indicated by an increase in the rate of crystallisation compared with that of the base polymer. Two organo-metallic substances (sodium benzoate and sodium stearate) proved to be the most effective in this respect by decreasing the degree of supercooling of the polymer by 20 [degrees]. Morphological studies were carried out on isothermally crystallised samples, after etching and replication using a transmission electron microscope. A nodular structure whose dimensions were sensitive to both the nucleating agent and the temperature of crystallisation was observed. Mechanical testing of samples direct from the D. S. C. was carried out using a compression method. The breaking loads were found to vary with both the type of nucleating agent used and the crystallisation temperature chosen. A separate study involving the exanination of the resulting fracture surfaces by scanning electron microscopy revealed that a, high breaking load was associated with a fine discontinuous structure whereas lower breaking loads were characterised by a more continuous linear appearance. This implies a higher energy of fracture due to the increased surface area of the fracture surface of the former.

Thesis (MTech. degree: Polymer Technology.)--Tshwane University of Technology, 2012. / Aims to use the recently developed Flow Injection Polymer Analysis (FIPA) for the development of a method which will be used to characterise the hexane extractable portions from selected grades of LLDPE and LDPE

Traumatic neuronal injury inevitably causes plasmalemmal damage, and sometimes leads to axonal severance. For any eukaryotic cell to survive following traumatic injury, the plasmalemma must be repaired (sealed). Plasmalemmal sealing occurs via a Ca²⁺-dependent accumulation of vesicles or other membranous structures that form a plug at the damage site. Using uniquely identified and damaged rat hippocampal B104 cells that extend neurites with axonal properties, or rat sciatic nerves, plasmalemmal sealing is assessed by exclusion of an extracellular dye from each damaged B104 cell, or sciatic nerves ex vivo. B104 cells with neurites transected nearer (<50 [micrometres]) to the soma seal at a lower frequency and slower rate compared to cells with neurites transected farther (>50 [micrometres]) from the soma. Sealing in B104 cells is enhanced by 1) increased [cAMP], 2) increased PKA activity, 3) increased Epac activity, 4) H₂O₂ and 5) Poly-ethylene glycol (PEG). Sealing is decreased by 1) PKA inhibition, 2), Botulinum toxins A, B, E, 3) Tetanus toxin 4), NEM, 5) Brefeldin A, 6) nPKC inhibition, 7) DTT, 8) Melatonin and 9) Methylene Blue. Substances (NEM, Bref A, PKI, db-cAMP, PEG) that affect plasmalemmal sealing in B104 cells in vitro have similar effects on plasmalemmal sealing in rat sciatic nerves ex vivo. Based on data from co-application of enhancers and inhibitors of sealing, I propose a plasmalemmal sealing model having four partly redundant, parallel pathways mediated by 1) PKA, 2) Epac, 3) cytosolic oxidation and 4) nPKCs. The identification and confirmation of these pathways may provide novel clinical targets for repairing and/or recovery from traumatic injury. The fusogenic compound PEG rapidly repairs axonal continuity of severed axons, potentially by rejoining severed proximal and distal axons. PEG-fusion is influenced by plasmalemmal sealing, since unsealed axons are easier to PEG fuse. I demonstrate that PEG restores morphological continuity, and improves behavioral recovery following crush-severance to sciatic nerves in rats in vivo. Co-application of Mel or MB prior to PEG application further improves PEG fusion (as measured by electrophysiology) and behavioral recovery following crush-severance in vivo. These PEG data may provide novel clinical techniques for rapidly repairing axonal severance. / text

Acute injury of major epithelial organ systems (kidney, liver, lung, etc.) is collectively a principal cause of death worldwide. Regenerative medicine promises to meet these human health challenges by harnessing intrinsic cellular processes to repair or replace damaged tissues. Epithelial morphogenesis is a hard-wired, multicellular differentiation program that dynamically integrates microenvironmental cues to coordinate cell fate processes including adhesion, migration, proliferation, and polarization. Thus, epithelial morphogenesis is an instructive mode of tissue assembly, maintenance, and repair. Three-dimensional epithelial cell cultures in natural basement membrane (BM) extracts produce hollow, spherical cyst structures and have indicated that the BM provides the critical cell adhesion ligands to facilitate cell survival, stimulate proliferation, and promote polarization and lumen formation. However, the utility of natural BMs for detailed studies is generally limited by lot-to-lot variations, uncontrolled cell adhesive interactions, or growth factor contamination. The goal of this thesis was to engineer bioartificial extracellular matrices (ECM) that would support and modulate epithelial cyst morphogenesis. We have engineered hydrogels, based on a multi-arm maleimide-terminated poly (ethylene glycol) (PEG-4MAL), that present cell adhesive molecules and enzymatic degradation substrates and promote polarized epithelial cyst differentiation in vitro. To investigate the influence of matrix physical and biochemical signals on cyst morphogenesis, we independently varied the polymer weight percentage (wt%), the density of a cell adhesion ligand (RGD), and crosslink degradation rates of the hydrogels. Then, we evaluated functional outcomes including Madin-Darby canine kidney (MDCK II) epithelial cell survival, proliferation, cyst polarization, and lumen formation. We found that cell proliferation, but not cell survival, was sensitive to the polymer wt%, which is related to elastic modulus and crosslink density. This result defined a working range of PEG-4MAL concentration (3.5% - 4.5%) that promotes robust proliferation. Analysis of mature cysts indicated that 4.0% and 4.5% gels produced cysts resembling those typically grown in type I collagen gels while 3.5% gels produced cysts with higher incidence of inverted polarity and multiple lumens. Perturbation of matrix degradability using a slow-degrading crosslink peptide or matrix metalloproteinase inhibitors showed that the rate of matrix degradation exerts major influence on cyst growth in PEG-4MAL gels. We employed 4.0% PEG-4MAL hydrogels with RGD ligand density ranging over 0 – 2000 uM to discover that (1) lumen formation was eliminated in the absence of RGD, (2) extent of lumen formation increased with increasing RGD concentration, and (3) cyst polarity was inverted below a threshold of integrin binding to RGD. Together, these results show that the biochemical and physical properties of the matrix, particularly integrin binding and matrix degradability, effectively modulate establishment of apico-basal polarity and lumen phenotypes in MDCK II epithelial cyst structures. Furthermore, these studies validate PEG-4MAL hydrogels as a powerful culture platform to enable detailed investigation of matrix-directed modulation of epithelial morphogenesis.

No description available.

The purpose of this research was to synthesize the constrained geometry catalyst Ti[(C5Me4)SiMe2(tBuN)]Cl2 (1) with MAO as a cocatalyst for ethylene homopolymerization and copolymerizations with 1-TMSO-alkenes to produce a copolymer with polar functionality. Three 1-alkenols of varying length were purchased and derivatized and used for the copolymerization experiments: 2-propen-1-ol, 3-buten-1-ol and 9-decen-1-ol. Several variables were tested to determine their effects on comonomer incorporation such as temperature, equivalents of comonomer, equivalents of MAO and two different solvents. Higher catalytic activities were correlated with fewer equivalents of polar comonomer, lower temperatures, and no fewer than 1000 equivalents of MAO. Toluene was found to be a far more effective reaction solvent than dichloromethane, as polymer yields were on average thirteen times higher. All polymer samples were analyzed by high temperature 1H NMR spectroscopy and selected samples were analyzed by DSC and IR spectroscopy. DSC determined that the polyethylene produced by 1 was substantially linear HDPE with long chain branching and that comonomer incorporation reduced the Tc and Tm, probably due to increased short chain branching. 1-TMSO-9-Decene was the most effective comonomer, as it had the highest incorporation rates (8.0 mol%) of all three of the polar comonomers. The two shorter comonomers exhibited no incorporation at all. This confirmed the hypothesis that polar comonomers with longer chains would be less prone to poisoning the electrophilic catalyst. / Thesis (Master, Chemistry) -- Queen's University, 2009-04-27 10:16:46.356

No description available.

No description available.

The gas phase polyethylene production process is the most recently developed and boasts many / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, 2006

A computational model for the prediction of articular and backside polyethylene (PE) wear of total knee replacements (TKRs) could enable the optimization of TKRs for the reduction of polyethylene wear, thereby improving the long term success of TKRs. A finite element model was developed for the TKR and the results were implemented in a computational wear model to assess PE wear. The wear factors of Archard’s wear law were identified by implementing the finite element simulation results along with knee simulator wear test results. Archard’s wear law was found to have insufficient accuracy for the purpose of optimization. Therefore, a novel computational wear model was developed by the author based on a theoretical understanding of the molecular behavior of PE. The model predicted result fell within the standard deviation of the independent knee simulator wear test results, indicating a high level of accuracy for the novel computational wear model.