Investigation and development of techniques for the characterisation of the synthetic/biological interface

The purpose of this study is to increase our knowledge of the nature of the surface properties of polymeric materials and improve our understanding of how these factors influence the deposition of proteins to form a reactive biological/synthetic interface. A number of surface analytical techniques were identified as being of potential benefit to this investigation and included in a multidisciplinary research program. Cell adhesion in culture was the primary biological sensor of surface properties, and it showed that the cell response to different materials can be modified by adhesion promoting protein layers: cell adhesion is a protein-mediated event. A range of surface rugosity can be produced on polystyrene, and the results presented here show that surface rugosity does not play a major role in determining a material's cell adhesiveness. Contact angle measurements showed that surface energy (specifically the polar fraction) is important in promoting cell spreading on surfaces. The immunogold labelling technique indicated that there were small, but noticeable differences, between the distribution of proteins on a range of surfaces. This study has shown that surface analysis techniques have different sensitivities in terms of detection limits and depth probed, and these are important in determining the usefulness of the information obtained. The techniques provide information on differing aspects of the biological/synthetic interface, and the consequence of this is that a range of techniques is needed in any full study of such a complex field as the biomaterials area.

The separation of hydrogen and carbon monoxide using polymer membranes

This work studies the development of polymer membranes for the separation of hydrogen and carbon monoxide from a syngas produced by the partial oxidation of natural gas. The CO product is then used for the large scale manufacture of acetic acid by reaction with methanol. A method of economic evaluation has been developed for the process as a whole and a comparison is made between separation of the H2/CO mixture by a membrane system and the conventional method of cryogenic distillation. Costs are based on bids obtained from suppliers for several different specifications for the purity of the CO fed to the acetic acid reactor. When the purity of the CO is set at that obtained by cryogenic distillation it is shown that the membrane separator offers only a marginal cost advantage. Cost parameters for the membrane separation systems have been defined in terms of effective selectivity and cost permeability. These new parameters, obtained from an analysis of the bids, are then used in a procedure which defines the optimum degree of separation and recovery of carbon monoxide for a minimum cost of manufacture of acetic acid. It is shown that a significant cost reduction is achieved with a membrane separator at the optimum process conditions. A method of "targeting" the properties of new membranes has been developed. This involves defining the properties for new (hypothetical -yet to be developed) membranes such that their use for the hydrogen/carbon monoxide separation will produce a reduced cost of acetic acid manufacture. The use of the targeting method is illustrated in the development of new membranes for the separation of hydrogen and carbon monoxide. The selection of polymeric materials for new membranes is based on molecular design methods which predict the polymer properties from the molecular groups making up the polymer molecule. Two approaches have been used. One method develops the analogy between gas solubility in liquids and that in polymers. The UNIFAC group contribution method is then used to predict gas solubility in liquids. In the second method the polymer Permachor number, developed by Salame, has been correlated with hydrogen and carbon monoxide permeabilities. These correlations are used to predict the permeabilities of gases through polymers. Materials have been tested for hydrogen and carbon monoxide permeabilities and improvements in expected economic performance have been achieved.

Protein deposition at polymer surfaces:the bulk and surface structure-property effects of hydrogels

The primary objective of this research has been to investigate the interfacial phenomenon of protein adsorption in relation to the bulk and surface structure-property effect s of hydrogel polymers. In order to achieve this it was first necessary to characterise the bulk and surface properties of the hydrogels, with regard to the structural chemistry of their component monomers. The bulk properties of the hydrogels were established using equilibrium water content measurements, together with water-binding studies by differential scanning calorimetry (D.S.C.). Hamilton and captive air bubble-contact angle techniques were employed to characterise the hydrogel-water interface and from which by a mathematical derivation, the interfacial free energy (ðsw) and the surface free energy components (ð psv, ðdsv, ðsv) were obtained. From the adsorption studies using the radio labelled iodinated (125I) proteins of human serum albumin (H.S.A.) and human fibrinogen (H.Fb.), it was Found that multi-layered adsorption was occurring and that the rate and type of this adsorption was dependent on the physico-chemical behaviour of the adsorbing protein (and its bulk concentration in solution), together with the surface energetics of the adsorbent polymer. A potential method for the invitro evaluation of a material's 'biocompatibility' was also investigated, based on an empirically observed relationship between the adsorption of albumin and fibrinogen and the 'biocompatibility' of polymeric materials. Furthermore, some consideration was also given to the biocompatibility problem of proteinaceous deposit formation on hydrophilic soft' contact lenses and in addition a number of potential continual wear contact lens formulations now undergoing clinical trials,were characterised by the above techniques.

Fabrication and characterization of macroporous poly(ethylene glycol) hydrogels generated by several types of porogens

Polymer scaffolds play an important role in tissue engineering applications. Poly(ethylene glycol) based hydrogels have received a lot of attention in this field because of their high biocompatibility and ease of processing. However, in many cases they do not exhibit proper tissue invasion and nutrient transport because of their dense structure. In the present work, several approaches were developed and compared to each other to produce interconnected macroporous poly(ethylene glycol) hydrogels by including different types of porogens in the photocrosslinking reaction. The swelling capacity of the resulting hydrogels was analyzed and compared to non-porous hydrogel samples. Moreover, the obtained materials were characterized by means of mechanical properties and porosity using rheometry, scanning electron microscopy, and mercury intrusion porosimetry. Results showed that interconnected and uniform pores were obtained when a porogen template was used during hydrogel fabrication by photocrosslinking. On the other side, when the porogen particles were dispersed into the macromer solution before matrix photocrosslinking the interconnexion was negligible. The templates must be dissolved before the hydrogel's cell-seeding in vitro, while the dispersed porogen can be used in situ in the in vitro seeding tests. Copyright © 2013 Taylor & Francis Group, LLC.

Synthesis and evaluation of nanoparticle-polymer composites

This thesis describes the synthesis of functionalised polymeric material by variety of free-radical mediated polymerisation techniques including dispersion emulsion, seeded emulsion, suspension and bulk polymerisation reactions. Organic fluorophores and nanoparticles such as quantum dots were incorporated within polymeric materials, in particular, thiol-functionalised polymer microspheres, which were fluorescently labelled either during synthesis or by covalent attachment post synthesis. The resultant fluorescent polymeric conjugates were then assessed for their utility in biological systems as an analytical tool for cells or biological structures. Quantum dot labelled, thiol-functionalised microspheres were assessed for their utility in the visualisation and tracking of red blood cells. Determination of the possible internalisation of fluorescent microspheres into red blood cells was required before successful tracking of red blood cells could take place. Initial work appeared to indicate the presence of fluorescent microspheres inside red blood cells by the process of beadfection. A range of parameters were also investigated in order to optimise beadfection. Thiol-functionalised microspheres labelled successfully with organic fluorophores were used to image the tear film of the eye. A description of problems encountered with the covalent attachment of hydrophilic, thiol-reactive fluorescent dyes to a variety of modified polymer microspheres is also included in this section. Results indicated large microspheres were particularly useful when tracking the movement of fluid along the tear meniscus. Functional bulk polymers were synthesised for assessment of their interaction with titanium dioxide nanoparticles. Thiol-functionalised polymethyl methacrylate and spincoated thiouronium-functionalised polystyrene appeared to facilitate the attachment of titanium dioxide nanoparticles. Interaction assays included the use of XPS analysis and processes such as centrifugation. Attempts to synthesise 4-vinyl catechol, a compound containing hydroxyl moieties with potential for coordination with titanium dioxide nanoparticles, were also carried out using 3,4-dihydroxybenzaldehyde as the starting material.

Novel Ni-Mg-Al-Ca catalyst for enhanced hydrogen production for the pyrolysis-gasification of a biomass/plastic mixture

A Ni-Mg-Al-Ca catalyst was prepared by a co-precipitation method for hydrogen production from polymeric materials. The prepared catalyst was designed for both the steam cracking of hydrocarbons and for the in situ absorption of CO2 via enhancement of the water-gas shift reaction. The influence of Ca content in the catalyst and catalyst calcination temperature in relation to the pyrolysis-gasification of a wood sawdust/polypropylene mixture was investigated. The highest hydrogen yield of 39.6molH2/g Ni with H2/CO ratio of 1.90 was obtained in the presence of the Ca containing catalyst of molar ratio Ni:Mg:Al:Ca=1:1:1:4, calcined at 500°C. In addition, thermogravimetric and morphology analyses of the reacted catalysts revealed that Ca introduction into the Ni-Mg-Al catalyst prevented the deposition of filamentous carbon on the catalyst surface. Furthermore, all metals were well dispersed in the catalyst after the pyrolysis-gasification process with 20-30nm of NiO sized particles observed after the gasification without significant aggregation.

Preparation of a poly(L-lactide-co-caprolactone) copolymer using a novel tin(II) alkoxide initiator and its fiber processing for potential use as an absorbable monofilament surgical suture

A poly(L-lactide-co-caprolactone) copolymer, P(LL-co-CL), of composition 75:25 mol% was synthesized via the bulk ring-opening copolymerization of L-lactide and ε-caprolactone using a novel bis[tin(II) monooctoate] diethylene glycol coordination-insertion initiator, OctSn-OCH2CH2OCH2CH2O-SnOct. The P(LL-co-CL) copolymer obtained was characterized by a combination of analytical techniques, namely nuclear magnetic resonance spectroscopy, gel permeation chromatography, dilute-solution viscometry, differential scanning calorimetry, and thermogravimetric analysis. For processing into a monofilament fiber, the copolymer was melt spun with minimal draw to give a largely amorphous and unoriented as-spun fiber. The fiber's oriented semicrystalline morphology, necessary to give the required balance of mechanical properties, was then developed via a sequence of controlled offline hot-drawing and annealing steps. Depending on the final draw ratio, the fibers obtained had tensile strengths in the region of 200–400 MPa.

Aditivo polimérico derivado de fonte renovável para aplicação em cimento asfáltico de petróleo

This study evaluated the effects of incorporating an additive from an agro-industrial residue, after some chemical modification reactions, to petroleum asphalt cement (CAP) through the polymerization reaction of a viscous polyol obtained by bagasse biomass oxypropylation reaction sugarcane with anhydrides. The polyol is obtained by biomass oxypropylation reaction with propylene oxide, the reaction was performed in an autoclave sealed with pressure and temperature control using 25 mL of OP for every 5 grams of biomass 200°C, which time reaction was two hours. The reaction is revealed by varying the system pressure, initially at atmospheric pressure to reach a maximum pressure value and its subsequent return to atmospheric pressure. For the choice of the most suitable reaction time for polymerization of the polyol with pyromellitic anhydride, the reaction was also conducted in an autoclave sealed with temperature controller (150 ° C) using 20 g of polyol, 1 g of sodium acetate (catalyst) and 8 g of pyromellitic anhydride with the times 30 and 60 minutes. The polymerized materials with different times were characterized by determining the relative viscosity and percentage content of extractable in cyclohexane / ethanol. Given the results with the polymerized material 30 minutes showed the lowest percentage content of extractives and an increased viscosity relative indicating that this time is highlighted with respect to time 60 minutes, because the material is possibly in the form of a crosslinked polymer. Given the choice of time of 30 minutes other polymerization reactions were performed with various anhydrides and other conditions employed different proportions by mass of polyol anhydrides we were referred to as condition I (20 g anhydride and 8 g of polyol), II (20 g anhydride and 20 g of polyol) and III (8 g anhydride and 20 g of polyol). The FTIR spectra of polymeric materials with different polymerization conditions used to prove the occurrence of chemical modification due to the appearance of a characteristic band ester groups (1750 cm-1) present in the polymerized material. He chose to work with the condition III, as is the condition which employs a larger amount of polyol, and even with the smaller amount of anhydride used FTIR spectra revealed that the polymerization reaction was performed. Among the various anhydrides (phthalic, maleic and pyromellitic) of the different conditions used that stood out before the solubility test with solvents analyzed was polymerized material with pyromellitic anhydride because the polymerized material likely in the form of a crosslinked polymer because it was insoluble or poorly soluble in the solvents tested. Polymerization of the polyol with pyromellitic anhydride using condition III, that is, BCPP30, CSPP30, PCPP30 e BCPPG30, provided an increase in thermal stability relative to material in the form of polyol. Applicability tests concerning the incorporation of 16% m / m BCPP30, CSPP30, PCPP30 e BCPPG30 additive in relation to the mass of 600 g CAP showed through characterization tests used, softening point, elastic recovery and marshall dosage, it is possible to use BCPP30 as an additive the conventional CAP, because even with the incorporation of this new additive modified CAP met the specifications of the appropriate standard.

Componentes poliméricos de alto desempenho para a indústria automóvel

Atualmente, a utilização e as diversas aplicações de materiais poliméricos seguem tendências crescentes, pelo que se torna necessário aprofundar a compreensão do seu comportamento e funcionalidades. Neste contexto, na presente dissertação analisa-se a fabricação e características de rolamentos poliméricos para a suspensão automóvel. Estes rolamentos visam a substituição dos clássicos rolamentos metálicos. Esta substituição tem por objetivos garantir a melhoria do funcionamento dos rolamentos, bem como o seu usufruto, contribuindo para um maior conforto e segurança dos passageiros e para uma redução do peso do veículo, com consequente diminuição do consumo do combustível e melhoria da eficiência. Sendo o poliacetal (POM) e a poliamida (PA) considerados polímeros de alto desempenho, estes polímeros reúnem boas características para aplicação na fabricação de dispositivos com funcionalidades exigentes como é o caso dos rolamentos. O presente trabalho aborda o estudo de algumas das suas propriedades, de modo a obter informações relevantes quanto à respetiva aplicação em rolamentos de suspensão, tendo como foco principal a análise da matéria-prima utilizada. Deste modo, alteraram-se as formulações variando-se os teores de material virgem e reciclado, estudou-se o ser comportamento mecânico, reológico e térmico: fizeram-se análises reológicas através do estudo do MFI a fim de se obterem informações complementares ao estudo mecânico, realizaram-se análises térmicas para avaliar a possibilidade de degradação térmica do material e, no caso da PA66-30GF, recorreu-se à microscopia eletrónica de varrimento para se estudar os aspetos microestruturais deste compósito reforçado com fibra de vidro. Adicionalmente, procedeu-se à análise da rugosidade superficial dos componentes dos rolamentos e quantificou-se o torque dos mesmos. A partir dos estudos anteriores, foi possível concluir que o POM apresenta um comportamento mecânico estável mesmo utilizando uma formulação com 100% de material reciclado. Este comportamento não se verificou na PA6630GF, dado que as suas propriedades mecânicas são afetadas de forma significativa pelo teor de reciclado na formulação. Com o estudo do torque determinou-se o valor limite do momento de torsão do rolamento que garante o seu bom funcionamento e eficácia.

Characterization of Non-linear Polymer Properties to Predict Process Induced Warpage and Residual Stress of Electronic Packages

Nonlinear thermo-mechanical properties of advanced polymers are crucial to accurate prediction of the process induced warpage and residual stress of electronics packages. The Fiber Bragg grating (FBG) sensor based method is advanced and implemented to determine temperature and time dependent nonlinear properties. The FBG sensor is embedded in the center of the cylindrical specimen, which deforms together with the specimen. The strains of the specimen at different loading conditions are monitored by the FBG sensor. Two main sources of the warpage are considered: curing induced warpage and coefficient of thermal expansion (CTE) mismatch induced warpage. The effective chemical shrinkage and the equilibrium modulus are needed for the curing induced warpage prediction. Considering various polymeric materials used in microelectronic packages, unique curing setups and procedures are developed for elastomers (extremely low modulus, medium viscosity, room temperature curing), underfill materials (medium modulus, low viscosity, high temperature curing), and epoxy molding compound (EMC: high modulus, high viscosity, high temperature pressure curing), most notably, (1) zero-constraint mold for elastomers; (2) a two-stage curing procedure for underfill materials and (3) an air-cylinder based novel setup for EMC. For the CTE mismatch induced warpage, the temperature dependent CTE and the comprehensive viscoelastic properties are measured. The cured cylindrical specimen with a FBG sensor embedded in the center is further used for viscoelastic property measurements. A uni-axial compressive loading is applied to the specimen to measure the time dependent Young’s modulus. The test is repeated from room temperature to the reflow temperature to capture the time-temperature dependent Young’s modulus. A separate high pressure system is developed for the bulk modulus measurement. The time temperature dependent bulk modulus is measured at the same temperatures as the Young’s modulus. The master curve of the Young’s modulus and bulk modulus of the EMC is created and a single set of the shift factors is determined from the time temperature superposition. The supplementary experiments are conducted to verify the validity of the assumptions associated with the linear viscoelasticity. The measured time-temperature dependent properties are further verified by a shadow moiré and Twyman/Green test.

Size effects on self-assembly and melting of silver-alkanethiolate on inert surfaces

Self-assembled materials produced in the reaction between alkanethiol and Ag are characterized and compared. It is revealed that the size of the Ag substrate has a significant role in the self-assembly process and determines the reaction products. Alkanethiol adsorbs on the surface of Ag continuous planar thin films and only forms self-assembled monolayers (SAMs), while the reaction between alkanethiol and Ag clusters on inert surfaces is more aggressive and generates a significantly larger amount of alkanethiolate. Two dissimilar products are yielded depending on the size of the clusters. Small Ag clusters are more likely to be converted into multilayer silver-alkanethiolate (AgSR, R = CnH2n+1) crystals, while larger Ag clusters form monolayer-protected clusters (MPCs). The AgSR crystals are initially small and can ripen into large lamellae during thermal annealing. The crystals have facets and flat terraces with extended area, and have a strong preferred orientation in parallel with the substrate surface. The MPCs move laterally upon annealing and reorganize into a single-layer network with their separation distance approximately equal to the length of an extended alkyl chain. AgSR lamellar crystals grown on inert surfaces provide an excellent platform to study the melting characteristics of crystalline lamellae of polymeric materials with the thickness in the nanometer scale. This system is also unique in that each crystal has integer number of layers – magic-number size (thickness). The size of the crystals is controlled by adjusting the amount of Ag and the annealing temperature. X-ray diffraction (XRD) and atomic force microscopy (AFM) are combined to accurately determine the size (number of layers) of the lamellar crystals. The melting characteristics are measured with nanocalorimetry and show discrete melting transitions which are attributed to the magic-number sizes of the lamellar crystals. The discrete melting temperatures are intrinsic properties of the crystals with particular sizes. Smaller lamellar crystals with less number of layers melt at lower temperatures. The melting point depression is inversely proportional to the total thickness of the lamellae – the product of the number of layers and the layer thickness.

Evaluación de las propiedades mecánicas de materiales compuestos elaborados a partir de cenizas volantes y polímeros reciclados

En el presente artículo se evalúan las propiedades mecánicas de los materiales compuestos basados en cenizas volantes de carbón de la central termoeléctrica de Termozipa combinadas con los película extensible (Stretch film), polietilenos de baja densidad lineal de pos-consumo y polímero termoplástico parcialmente cristalino pos- industrial. Se obtuvieron mezclas variando el contenido de cenizas volantes de 0 a 50 % en peso en cada uno de los tres materiales poliméricos, dentro de una máquina mezcladora tipo Brabender. Las propiedades mecánicas evaluadas fueron: resistencia a la tracción, dureza Shore D, y absorción de energía. Los resultados obtenidos indican que en todos los casos a medida que se agrega ceniza volante las propiedades mecánicas aumentan.