Tribophysical Interpretation of Scaling Effects in Friction and Wear for Polymers

Polymers are used in dry sliding applications due to self-lubricating ability. Most work from literature focuses on mechanical effects causing transfer and results from small-scale testing. Friction and wear of polymers are influenced by visco-elastic deformation and sliding temperature and depend on the test configuration. In present work, tribophysical or tribochemical effects on worn surfaces and debris are investigated on micro-scale explaining transitions in tribological performance. Extrapolations of friction and wear data from small-scale testing towards large-scale testing are discussed in relation to polymer structures and wear debris mobility depending. Sliding applications at either high-temperature (100 to 260°C) or high-load (8 to 150 MPa) conditions are covered in this work, using high-performance polymers such as sintered or thermoplastic polyimide, or engineering polymers such as polyamide, polyoxymethylene, polyethylene terephthalate and polyethylene. The effect of internal lubricants such as graphite, PTFE and silicon oil is investigated. Experimental techniques are presented in a first part of this work. Small-scale sliding tests are done on a cylinder-on-plate configuration and large-scale sliding is done on flat-on-flat configurations. An analytical model to calculate the maximum polymer surface temperature T* during sliding is introduced and verified. A change from integrated flash temperature concept to bulk temperature concept should be considered at high loads, agreeing to a transition in visco-elastic polymer deformation. Raman spectroscopy and thermo-analytical polymer analysis are used to characterise wear products. The importance of wear debris interactions forming transfer is demonstrated like this. Micro-scale to small-scale relations in friction and wear for polyimides are investigated in the second part of this work. The relation between tribological behaviour and brittleness, hydrolysis and imidisation is investigated on molecular scale. Small-scale to large-scale testing correlations for engineering polymers are discussed in the third part of this work. Four experimental models comparing small-scale and large-scale tribological data are evaluated with a single or two mechanical parameters. The most extensive is a macroscopic geometry model considering the influence of thermal effects, sample geometry and contact conditions. Large-scale to full-scale extrapolation is illustrated in the fourth part by a case study on the redesign of a ball-joint with polymer bearing elements

Morphologies and thermal variability of patterned polymer films with poly(styrene-co-maleic anhydride)

Patterned films of poly(styrene-co-maleic anhydride) copolymers were deposited by dip-coating from acetone solutions. A qualitative study of the film morphologies shows the formation of polymer spheres with smaller diameters at higher amounts of maleic anhydride (MA), and long-fibrous features at higher molecular weights. Upon heating, the films progressively re-assemble with short- and long-fibrous structures as a function of heating time and temperature. In parallel, the film morphologies are quantified by image processing and filtering techniques. The differential scanning calorimetry confirms the higher glass transition temperatures with increasing amount of MA. The analysis with Raman spectroscopy shows interactions between the molecules in solution and effects of ring-opening (hydrolysis) and ring-closure (formation of MA) during drying of the films. The water contact angles on the patterned films are within the hydrophilic range. They mainly correlate with the amount of MA moieties calculated from spectroscopy, while the roughness parameters have a minor effect. The variations in film patterns illustrate the self-assemble ability of the copolymers and confirm a heterogeneous molecular structure, as previously assumed

The role of game rules in architectural design environments

'Experimenting' and 'observing' are crucial actions in architectural design thinking. They rely heavily on the representation environment used (e.g. sketching, scale models, sketch tools, CAD tools, etc.) and the 'game rules' at play in these environments. In this brief paper, we study the role of this representation environment in the overall architectural design thinking process. From this brief study, we indicate two design and implementation approaches to implement and design with such game rules in virtual design environments

Nanostructured polymer coatings for controlling the wettability of fibrous surfaces

In this research we present a new approach for modifying and functionalizing the surface properties of fibrous substrates, especially cellulose-based products, by the deposition of organic nanoparticle coatings. The partial imidisation of high-molecular weight poly(styrene-maleic anhydride) in presence of ammonium hydroxide results in a stable water-borne dispersion of nanoparticles with sizes of 50 to 100 nm. The hydrophobic properties of coated paper surfaces are governed by a unique combination of chemical (degree of imidisation) and topographic (porosity and roughness) effects: it has been found that the contact angle increases at a higher degree of imidisation and higher surface roughness. As such, maximum advancing contact angles in the range of 140 to 150° and receding contact angles of 50° can be obtained on paper surfaces

Effects of atmospheric plasma treatment on adhesion and tribology of aromatic thermoplastic polymers

After cold plasma treatment of poly(ethylene terephthalate) and poly(ether-ether ketone) surfaces by dielectric barrier discharge (DBD) under atmospheric (air) conditions, variations in surface chemistry and morphology were investigated in relation with adhesion and tribological properties. According to XPS measurements, surface oxidation caused the formation of low molecular weight moieties of carboxylic acids. The latter resulted in more hydrophilic surfaces according to water contact angle measurements, with mainly a higher polar surface energy component. In parallel, the surface roughness of originally polished surfaces reduced due to flattening of local surface asperities after DBD. The DBD significantly improved the adhesive shear strength for different glue types in polymer/polymer and polymer/steel joints, while the best adhesion was observed for a two-component epoxy type adhesive. Under dry sliding conditions, the coefficients of friction were lower after DBD compared to pristine samples only under mild sliding conditions (v = 0.05 m/s; p < 1 MPa.m/s), while the higher normal loads caused an increase in coefficients of friction likely due to the higher contributions of surface deformation. Most interestingly, the lower coefficients of friction after DBD were observed under oil lubrication and after cleaning the sliding track (‘run-out’ condition), due to the better retention of oil at the sliding surface for plasma-treated polymers

Charge-discharge characteristics of textile energy storage devices having different PEDOT:PSS ratios and conductive Yarns configuration

Conductive polymer PEDOT:PSS, sandwiched between two conductive yarns, has been proven to have capacitive behavior in our textile energy storage devices. Full understanding of its underlying mechanism is still intriguing. The effect of the PEDOT to PSS ratio and the configuration of the electrode yarns are the focus of this study. Three commercial PEDOT:PSS yarns, Clevios P-VP-AI-4083, Ossila AI 4083, and Orgacon ICP 1050, as well as stainless steel and silver-coated polybenzoxazole (Ag/PBO) yarns, in various combinations, were used as solid electrolytes and electrodes, respectively. Analyses with NMR, ICP-OES, TGA, and resistivity measurement were employed to characterize the PEDOT:PSS. The device charge-discharge performance was measured by the Arduino microcontroller. Clevios and Ossila were found to have identical characteristics with a similar ratio, that is, 1:5.26, hence a higher resistivity of 1000 Ω.cm, while Orgacon had a lower PEDOT to PSS ratio, that is, 1:4.65, with a lower resistivity of 0.25&#8315;1 Ω.cm. The thermal stability of PEDOT:PSS up to 250 &#176;C was proven. Devices with PEDOT:PSS having lower conductivity, such as Clevios P-VP-AI-4083 or Ossila AI 4083, showed capacitive behavior. For a better charge-discharge profile, it is also suggested that the PEDOT to electrode resistance should be low. These results led to a conclusion that a larger ratio of PEDOT to PSS, having higher resistivity, is more desirable, but further research is needed

Biochar characterization of raw versus spent common ivy: Inorganic nutrient behavior

Hedera sp., common Ivy, a lignocellulosic evergreen vine, is commonly seen in gardens and yards all over the globe. It is an excellent candidate to be applied in vertical green walls to improve ecosystems in future green cities (e.g. fine particulate matter adsorption). These green walls need to be trimmed regularly, thus leaving a major residue stream which could be promising as biomass feedstock for biochar fertilizer production. However, common Ivy contains valuable compounds (e.g. etheric oils and triterpene saponins) increasing the process’ added value. These should preferably be extracted prior to thermal conversion. The aim of this study is therefore to investigate the influence of extraction methods on the final properties of common ivy’s biochar using conventional pyrolysis. Investigated extraction methods include a Soxhlet ethanol extraction and a steam distillation, to obtain respectively a triterpene saponin and volatile oil extract. The influence of these extractions on the biochar properties was studied by comparing the thermal conversion and biochar properties of spent, extracted, biomass with raw biomass. Studied properties include biochar yield, elemental composition (CHNO), amount of inorganic nutrients, specific surface area, and presence of harmful heavy metals. The guidelines of the European Biochar Certificate are used to evaluate said properties. Furthermore, the pyrolysis process parameters, temperature and heating rate, were optimized to improve said biochar properties for application as fertilizer. Tested pyrolysis temperatures were 400, 550 and 700 °C. Results show that biochar yield from raw ivy was inversely proportional with pyrolysis temperature ranging from 29.6 ± 0.6% at 400 °C, 25.4% ± 0.03 at 550 °C and 23.0 ± 0.06 % at 700 °C. It was found that steam distillation lowers the amount of heavy metals in the material, whilst the inorganic nutrients are retained, thus enhancing the biochar’s potential as fertilizer. Furthermore, nitrogen content remained constant, around 2%, before and after pyrolysis both for raw and spent ivy, these results indicate that high-quality biochars were produced. To further understand biochar’s chemical behavior in soils, structural properties and morphology are being investigated further, specific surface area via BET, general pore structure using SEM, surface functional groups with FT-IR and, aromaticity with CP/MAS 13C NMR results will be presented accordingly