This thesis aims to improve the performance of latex-based pressure-sensitive adhesives (PSAs). PSA performance is usually evaluated by tack, peel strength and shear strength. Tack and peel strength characterize a PSA’s bonding strength to a substrate while shear strength reflects a PSA’s capability to resist shear deformation. In general, increasing shear strength leads to a decrease in tack and peel strength. While there are several commercial PSA synthesis methods, the two most important methods consist of either solvent-based or latex-based techniques. While latex-based PSAs are more environmentally compliant than solvent-based PSAs, they tend to have much lower shear strength, at similar tack and peel strength levels. Therefore, the goal in this thesis was to greatly improve the shear strength of latex-based PSAs at little to no sacrifice to tack and peel strength. In this study, controlling the polymer microstructure of latexes or their corresponding PSA films was used as the main method for improving the PSA performance. The research was sub-divided into four parts. First, the influence of chain transfer agent (CTA) and cross-linker on latex polymer microstructure was studied via seeded semi-batch emulsion polymerization of butyl acrylate (BA) and methyl methacrylate (MMA). Three techniques were used to produce the latexes: (1) adding CTA only, (2) adding cross-linker only, and (3) adding both CTA and cross-linker. It was found that using CTA and cross-linker simultaneously allows one to expand the range of latex microstructural possibilities. For example, latexes with similar gel contents but different Mc (molecular weight between cross-links) and Mw (molecular weight of sol polymers) could be produced if CTA and cross-linker concentration are both increased. However, for the corresponding PSAs with similar gel contents, the relationship between their polymer microstructure and performance was difficult to establish as almost all of the medium and high gel content PSAs showed very low tack and peel strength as well as extremely large shear strength readings. In the second part of this thesis, in order to improve the tack and peel strength of medium and high gel content PSAs, the monomer composition and emulsifier concentration were varied. It was found that changing the monomer mixture from BA/MMA to BA/acrylic acid (AA)/2-hydroxyethyl methacrylate (HEMA) while simultaneously decreasing emulsifier concentration dramatically improved the corresponding PSAs’ shear strength as well as tack and peel strength. The addition of polar groups to the PSA increased its cohesive strength due to the presence of strong hydrogen bonding; meanwhile, PSA films’ surface tension increased. In the third part, two series of BA/AA/HEMA latexes were generated by varying the amounts of CTA either in the absence or presence of cross-linker. The latexes produced in the absence of cross-linker exhibited significantly larger Mc and Mw compared to their counterparts with similar gel contents prepared with cross-linker. The PSAs with the larger Mc and Mw showed much larger shear strengths due to improved entanglements between the polymer chains. In the final part of the thesis, the performance of the BA/AA/HEMA PSAs was further improved by post-heating. Compared with original latex-based PSAs with similar gel contents, heat-treated PSAs showed not only significantly improved shear strengths, but also much larger tack and peel strengths. The different shear strengths were related to the PSAs’ gel structures, which were discrete in the original PSAs but continuous in the heat-treated PSAs. The improved tack and peel strengths were related to the PSA films’ surface smoothness. During the post-heating process, the PSA polymer flowed, resulting in much smoother surfaces than the original PSA films. In addition, the effect of post-heating was related to the polymer microstructure of the untreated PSAs. Decreasing the amount of very small or very big polymers or simultaneously increasing Mc and Mw could lead to post-treated PSAs with significantly better performance. Moreover, it was found that by optimizing the polymer microstructure of the original latex-based PSAs, it was possible to obtain a treated PSA with similar or even better performance than a solvent-based PSA with similar polymer microstructure. Our original objective was surpassed: in two cases, not only was shear strength greatly improved, but so were tack and peel strength due to the simultaneous modification of PSA bulk and surface properties.

Yes / Polymer extrusion is an important but an energy intensive method of processing polymeric materials. The rapid increase in demand of polymeric products has forced manufactures to rethink their processing efficiencies to manufacture good quality products with low-unit-cost. Here, analyzing the operational conditions has become a key strategy to achieve both energy and thermal efficiencies simultaneously. This study aims to explore the effects of polymers' rheology on the energy consumption and melt thermal quality (ie, a thermally homogeneous melt flow in both radial and axil directions) of extruders. Six commodity grades of polymers (LDPE, LLDPE, PP, PET, PS, and PMMA) were processed at different conditions in two types of continuous screw extruders. Total power, motor power, and melt temperature profiles were analyzed in an industrial scale single-screw extruder. Moreover, the active power (AP), mass throughput, torque, and power factor were measured in a laboratory scale twin-screw extruder. The results confirmed that the specific energy consumption for both single and twin screw extruders tends to decrease with the processing speed. However, this action deteriorates the thermal stability of the melt regardless the nature of the polymer. Rheological characterization results showed that the viscosity of LDPE and PS exhibited a normal shear thinning behavior. However, PMMA presented a shear thickening behavior at moderate-to-high shear rates, indicating the possible formation of entanglements. Overall, the findings of this work confirm that the materials' rheology has an appreciable correlation with the energy consumption in polymer extrusion and also most of the findings are in agreement with the previously reported investigations. Therefore, further research should be useful for identifying possible correlations between key process parameters and hence to further understand the processing behavior for wide range of machines, polymers, and operating conditions.

<p>This thesis describes the experimental results of liquid polymer droplets levelling on thin films of identical polymer liquid. Through varying the thickness of the underlying polymer film relative to the size of the droplet height, we have observed a crossover in the dynamics between droplets spreading on very thin films to droplets levelling on films thicker than the droplet itself. In the thin film regime, the underlying film behaves as a pre-existing precursor film and the droplet spreads according to the well-known Tanner's law where the droplet height, d₀, decreases in time as d₀ ~ t^-1/5. In the opposite regime, when the film thickness is much greater than the initial droplet height, the droplet levels with a much stronger time dependence compared to Tanner's law spreading, d₀ ~ t^-1/2. Not only have we observed the two extreme cases, we have also experimentally observed levelling behaviour of intermediate systems, where the droplet height and film height are on the same order. We have captured experimentally the crossover behaviour of droplets spreading on thin films to droplets levelling on thick films. In addition, we have developed a theoretical model that accurately captures the physics of this crossover using the lubrication approximation for thin film flows. The relevant background information will be presented as well as a detailed description of the sample preparation techniques required to fabricate spherical caps atop thin films of identical material.</p> / Master of Science (MSc)

Putting on or taking off clothes helps the body to stay within the comfortable temperature range (toavoid shivering or sweating) at different activity levels and ambient conditions. Clothes with built-inthermo-regulating properties would mean maintained comfort without putting on or taking off clothesthat frequently. Integration of phase change materials (PCMs) in clothes is one way of achievingthermo-regulating properties. When the body temperature goes up, the PCM melts and absorbs theheat from the body in the form of latent heat (cooling effect). When the temperature drops, the PCMcrystallizes and the stored heat is released again (warming effect).Research on thermo regulating fibres of the bi-component type containing PCM in the core has beenconducted at Swerea IVF in Mölndal, Sweden, for some time. It has been found that high molecularweight HDPE is a suitable viscosity modifier for hydrocarbon waxes used as PCM. The preparation ofcore materials has so far been done in a batch wise fashion in the way that molten wax has beensoaked into pelletized HDPE at around 180°C during prolonged times followed by melt compoundingin a Brabender batch kneader (0.3 kg per batch). Besides being very impractical for larger productionvolumes the method involves long residence times at high temperatures which may induce thermaldegradation reactions. The objective of the present diploma (master’s thesis) work was to develop acontinuous mixing method to produce PCM/HDPE blends and to test the resulting material in bicomponentfibers with a Nylon (PA6) sheath and to characterize the resulting fiber properties in termsof strength and latent heat.It was proven possible to compound HDPE with large amounts (70%) of octadecane (PCM) on aBrabender twin screw extruder. HDPE was metered to the extruder hoper by means of a screw feederand wax was continuously fed to the hoper in the liquid state by means of a heated membrane pump.To facilitate mixing HDPE in form of powder instead of pellets was used. The extruded threads weresolidified in a water bath followed by granulation. Bi-component fibers were successfully producedfrom such materials. Fibers containing 15 to 42% Octadecane were produced showing heat of fusionsin the range 26 to 86 J/g and tenacities in the range 33 to 16 cN/tex. The heat of fusion of the fiberscompares favorable with existing commercial products showing values in the range 5-15 J/g (acrylicand cellulosic fibres containing microencapsulated hydrocarbon waxes). The peak melting point ofoctadecane measured by DSC was found to be depressed some 4-5°C in the fibers compared to pureoctadecane (28°C). Such a melting point depression is important to consider when choosing type ofhydrocarbon wax. / Program: Magisterutbildning i textilteknologi

The research described in this thesis originated from an idea to develop new body protection for the sport of fencing. The ultimate goal is to develop body armour which would be flexible, wearable, washable, light and breathable, offer protection from injuries and cover the entire body of a sportsman. A new material which exhibits shear thickening behaviour has been specially developed for this purpose in the process of this investigation. The material was designed and synthesised as a soft polymeric system which is flexible, chemically stable and able to increase the value of its modulus of elasticity upon impact at a high strain rate, while remaining in its soft gel-like elastomeric state when low strain rate deformation is applied. The polymeric system that has been developed is based on interpenetrating polymeric networks (IPN) of immiscible polyurethane/urea-ester/ether and poly(boron)n(dimethylsiloxane)m (where on average m ≈ 16 n). In addition, as the polydimethylsilane (PDMS) based polymeric system strongly tends to phase separation, the siloxane polymeric network was chemically cross-linked to the polyurethane polymeric network through polyurethane chemical cross-link-bridges. In order to introduce polyurethane cross-links to a siloxane-based polymeric network, some of the attached methyl groups in the PDMS polymeric backbone were substituted by ε-pentanol groups. The resulting polymeric system combines properties of an alternating copolymer with IPN. The actual substitution of the methyl groups of PDMS into alternating ε-pentanol groups was performed by Grignard reaction of trifunctional chlorosilane monomers, magnesium and 1,5-dibromopentane. Chemical analytical techniques like FT-IR, 13C NMR and 1H NMR spectroscopy were used to reveal the chemical structure of the synthesised polymeric network. The mechanical and dynamical properties of the obtained polymeric system were analysed by dynamic mechanical analysis (DMA). This part of the investigation indicated that the novel polymeric system exhibited shear thickening behaviour, but only at a narrow diapason of deformations (i.e., deformations between 2 to 3 % of the length of the sample). At this limited diapason of deformation an effective increase of the modulus of elasticity from 6 MPa (at lower frequencies, i.e., up to ≤6 Hz of the applied oscillating stress) to 65 MPa (at frequencies between 12.5 to 25 Hz) was obtained. However, no increase in the modulus of elasticity was recorded at deformations below 1.5 % or above 3.5 % of length of the sample at the same frequencies (0 to 25Hz) of the applied oscillating stress.

A determinação do espectro de relaxação de polímeros utilizando dados de tensão oscilatória de baixa amplitude pode ser calculada assumindo-se que existe uma única função contínua H(&#955;) capaz de descrever o comportamento viscoelástico linear. O objetivo deste trabalho é determinar esta função ou uma aproximação da mesma utilizando um algoritmo estocástico denominado Simulated Annealing. A estratégia proposta é similar a proposta por Jensen (2002), entretanto, a lista de resfriamento do algoritmo foi modificada, objetivando-se uma maior robustez do referido algoritmo. A ferramenta computacional foi calibrada de forma a estimar com acurácia o espectro de relaxação discreto de outros polímeros. Os métodos de interpolação lagrangeana e de regressão não-linear foram aplicados para obter a função contínua do espectro de relaxação, a partir de um conjunto discreto de dados. Os resultados obtidos para o polietileno linear de baixa densidade (PELBD) comprovaram a eficiência da ferramenta computacional de otimização, sendo extremamente próximos aos fornecidos pelo reômetro AR 2000 (CENPES/PETROBRAS). / The determination of the relaxation spectrum using data from small amplitude oscillatory shear rate was accomplished by assuming that exists a unique continuous function H(&#955;) which describes linear viscoelasticity. The aim of this work is to determine this function or a close approximation using a computer stochastic algorithm called Simulated Annealing (SA). The strategy is the same proposed by Jensen, but the cooling schedule of SA algorithm was modified, in order to enhance the robustness of the referred algorithm. Besides, a calibration procedure was conducted for estimate accurate relaxation spectrum for other polymers. Lagrangean interpolation and nonlinear regression techniques were applied in order to obtain the continuous function that represent relaxation spectrum, using discrete data. The results generated for low linear density polyethylene (LLDPE) indicate the efficiency of the optimization computational tool, being extremely close to that produced by AR 2000 rheometer (CENPES/PETROBRAS).

A determinação do espectro de relaxação de polímeros utilizando dados de tensão oscilatória de baixa amplitude pode ser calculada assumindo-se que existe uma única função contínua H(&#955;) capaz de descrever o comportamento viscoelástico linear. O objetivo deste trabalho é determinar esta função ou uma aproximação da mesma utilizando um algoritmo estocástico denominado Simulated Annealing. A estratégia proposta é similar a proposta por Jensen (2002), entretanto, a lista de resfriamento do algoritmo foi modificada, objetivando-se uma maior robustez do referido algoritmo. A ferramenta computacional foi calibrada de forma a estimar com acurácia o espectro de relaxação discreto de outros polímeros. Os métodos de interpolação lagrangeana e de regressão não-linear foram aplicados para obter a função contínua do espectro de relaxação, a partir de um conjunto discreto de dados. Os resultados obtidos para o polietileno linear de baixa densidade (PELBD) comprovaram a eficiência da ferramenta computacional de otimização, sendo extremamente próximos aos fornecidos pelo reômetro AR 2000 (CENPES/PETROBRAS). / The determination of the relaxation spectrum using data from small amplitude oscillatory shear rate was accomplished by assuming that exists a unique continuous function H(&#955;) which describes linear viscoelasticity. The aim of this work is to determine this function or a close approximation using a computer stochastic algorithm called Simulated Annealing (SA). The strategy is the same proposed by Jensen, but the cooling schedule of SA algorithm was modified, in order to enhance the robustness of the referred algorithm. Besides, a calibration procedure was conducted for estimate accurate relaxation spectrum for other polymers. Lagrangean interpolation and nonlinear regression techniques were applied in order to obtain the continuous function that represent relaxation spectrum, using discrete data. The results generated for low linear density polyethylene (LLDPE) indicate the efficiency of the optimization computational tool, being extremely close to that produced by AR 2000 rheometer (CENPES/PETROBRAS).