Multiple Scratching Research Articles

Acquired perforating dermatosis in renal dialysis and diabetic patient: a case report

Acquired perforating dermatosis (APD) is an uncommon disease characterized by lesions exhibiting transepidermal elimination of collagen or elastic fibers. APD affects adults and is associated with systemic diseases, mainly diabetes mellitus and renal failure. We report a new Moroccan case of this rare entity. It’s about a 62-year-old patient, followed for diabetes mellitus and renal failure under dialysis and who presented an extremely itchy rash, made of nodules with a keratotic center and associated with multiple scratching lesions. The skin biopsy showed a perforated epidermis with the removal of material containing keratin and collagen. the outcome was favorable with oral corticosteroids with a follow-up of one year. APD is a rare dermatosis that affect considerably the quality of life of patients. its treatment remains suspensive pending the treatment of the cause.

Self-Healing of Abrasion Damage in Epoxy Resin–Ionic Liquid Nanocomposites

The present work describes the self-healing, under ambient conditions, of abrasion surface damage in epoxy resin (ER) modified by a dispersed ionic liquid (IL) phase. The abrasion resistance of ER containing a 9 wt.% of the IL 1-octyl, 3-methylimidazolium tetrafluoroborate (ER + 9IL) was determined by multiple scratching under constant load and by single scratching under progressively increasing load, and compared with that of neat ER. ER + 9IL shows higher instantaneous penetration depth and residual depth values than neat ER. In the case of ER, the viscoelastic recovery process ends after 30 min. For ER + 9IL, the recovery process continues with time to reach a total healing of multiple scratch abrasion grooves after 22–25 h at room temperature. For single scratches under the maximum load of 20 N, ER + 9IL shows an 88 % reduction in surface damage with respect to ER, after 24 h at room temperature. The addition of IL reduces hardness and tensile strength, while increases elongation at break by a 42 %. Hardness test scars on ER + 9IL show an area reduction of approximately 55 % after 5 h. Results are discussed upon the basis of optical and electron (SEM) microscopy and 3D profilometry.

Tribology of novel antibiocorrosion coatings

We have developed inorganic–organic hybrid bioactive composites and antibiocorrosion coatings based on epoxy or polyurethane matrices modified with varying amounts of a silicon organic oligomer. We have incorporated bioactive compound containing bis(η5-cyclopentadienyl) iron and spatial alicyclic fragment or its coordination compounds of Co and Ni. Glass transition regions located with differential scanning calorimetry (DSC) are above +50°C, so that our hybrids can be used for instance as coatings for museum exhibits. DSC shows also beta transitions in the glassy state around −50°C. Thermogravimetric analysis shows high thermal stability. We have also performed scratch resistance testing with linearly increasing load and sliding wear determination by multiple scratching along the same groove. Also here the hybrid formation enhances the scratch resistance. We observe the strain hardening in sliding wear that is the tendency towards a horizontal groove depth asymptote with increasing number of scratches. Water absorption in 720 h does not exceed 0·03 wt-% in all cases. Samples subjected to three months aging under normal temperature and pressure conditions were observed. The initial colours and optical transparency were preserved; no phase separation took place.

Scratch Resistance of New Polystyrene Nanocomposites with Ionic Liquid-Modified Multi-walled Carbon Nanotubes

Multi-walled carbon nanotubes, both neat (MWCNT) and modified (MWCNTm) by the room-temperature ionic liquid (IL) 1-octyl-3-methylimidazolium tetrafluoroborate ([OMIM]BF4), were added in a 1 wt% to polystyrene (PS) to obtain the new nanocomposites (PS + MWCNT and PS + MWCNTm). Friction coefficients and abrasive wear from instantaneous penetration depth, residual depth and viscoelastic recovery were determined for compression-moulded materials as a function of applied normal load and of the number of successive scratches. The new nanocomposites improve the abrasion resistance of neat PS and of the analogous PS nanocomposites containing neat and IL-modified single-walled carbon nanotubes. The lowest friction coefficient and residual depth values, after 15 scratches, under the whole range of applied loads are obtained for PS + MWCNTm, with maximum reduction under the most severe conditions. The influence of sliding direction with respect to flow was studied for injection-moulded PS + MWCNTm under multiple scratching. The most severe surface damage is observed in the transverse direction to injection flow, while the lowest friction coefficient and the highest abrasion resistance and viscoelastic recovery values are obtained in the direction parallel to injection flow, due to the higher mobility of the polymer chains and the additives. Thermal analysis (DSC and TGA), Raman spectroscopy, transmission electron microscopy, X-ray diffraction and XPS surface analysis have been used as characterization techniques. XPS shows that the IL molecules are present on the nanotube surface. According to TGA, the IL content in MWCNTm can be estimated to be of a 12 wt%. Mechanisms of surface damage are discussed upon scanning electron microscopy, 3-D surface topography, surface roughness and profilometry observations.

Abrasive wear under multiscratching of polystyrene + single-walled carbon nanotube nanocomposites. Effect of sliding direction and modification by ionic liquid

Single-walled carbon nanotubes (NTs) and single-walled carbon nanotubes modified (NTms) by the room-temperature ionic liquid (IL) 1-octyl, 3-methylimidazolium tetrafluoroborate ([OMIM]BF 4) were added in a 1 wt.% to polystyrene (PS) and processed by compression or injection moulding to obtain PS + NT and PS + NTm, respectively. Friction coefficients and abrasive wear from penetration depth, residual depth and viscoelastic recovery were determined under multiple scratching. The effect of the moulding process, the additives and the sliding direction was studied. Compression moulded PS shows a transition to more severe damage after a critical number of successive passes. Addition of NTs or NTms to compression moulded PS induces a strain hardening effect and reduces friction, residual depth and viscoelastic recovery. Strain hardening is also observed in injection moulded PS with sliding in the longitudinal and random directions, but not in the transverse direction. The scratch resistance of PS + NTm depends on sliding direction. The lowest friction coefficient and residual depth values, and the highest viscoelastic recovery were found for injection moulded PS + NTm, in the sliding direction parallel to injection flow. Mechanisms of surface damage are discussed upon scanning electron microscopy (SEM), focused ion beam-field emission scanning electron microscopy (FIB-FESEM), 3D surface topography, surface roughness and profilometry observations.

Characterization of orientation in polyethylene by scratch testing

AbstractMicroscratch experiments were performed to evaluate effects of uniaxial stretching by 200 % in low density polyethylene (LDPE) along parallel and perpendicular directions with respect to stretching. Penetration depth, healing depth and viscoelastic recovery have been determined. Clear orientation effects are seen. The direction parallel to the extension axis shows strong resistance to scratching and also the highest recovery (a memory effect). Unoriented material exhibits behavior intermediate between that of oriented samples in parallel and perpendicular directions. The sliding wear was determined by multiple scratching along the same groove and here also was found orientation dependence. Polarized micro-Raman experiments on the oriented LDPE samples were carried out. Since scratching and sliding wear results are strongly affected by polymer orientation, one can use both kinds of tests as a measure of orientation - and also to vary orientation to control tribological properties.

Tribological properties of LDPE + Boehmite composites

AbstractTribological properties of composites of low density polyethylene (LDPE) reinforced with 1, 5, 10, 20 wt% micrometric Boehmite (B) and/or preheated Boehmite (HB) powders were studied in combination with two silane coupling agents (SCAs): vinyltri(2‐methoxyethoxy)‐silane (VTMES)‐SCA 972 and 3‐(trimethoxysilyl)‐propylmethacrylate (3MPS)‐SCA 989. When coupling agents are used, the samples not subjected to preheating provide higher yields of grafting and more bonds introduced on surfaces of Boehmite particles than heated ones. We have determined sliding wear by multiple scratching along the same groove using a micro scratch tester. Instantaneous penetration depth is lowered by the filler addition to LDPE. However, there is less viscoelastic recovery and the residual (healing) depths increase with increasing Boehmite concentration. Friction was determined using a pin‐on‐disk tribometer and also a moving sled friction device. Addition of 20 wt% untreated B and/or HB particles to LDPE matrix reduces friction. However, a more significant improvement of tribological properties results from incorporation of grafted particles; this occurs because of an increase of the filler/matrix interfacial adhesion. Surface morphology seen in scanning electron microscopy confirms this explanation. Friction values for all samples decrease along with the filler concentration increase. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers

Scratch resistance of a polycarbonate + organoclay nanohybrid

A polycarbonate-based nanohybrid has been created containing 1 wt% of Bentone 2010, an organically modified montmorillonite. A micro-section on the nanohybrid obtained using focused ion beam (FIB) and field emission scanning electron microscopy (FESEM) was employed to observe the orientation of the nanoclay inside a polycarbonate (PC) matrix in the cross-section FIB-milled face. A micro-scratch tester was used to measure the scratch resistance in terms of residual (healing) depth Rh under progressive load and in sliding wear. Effects of the number of scratches, normal load and scratch velocity have been evaluated as a function of nanoclay orientation. In sliding wear (multiple scratching along the same groove), our nanohybrid reaches residual depth values that remain constant after a certain number of scratches, a manifes- tation of strain hardening. The number of scratches to induce strain hardening decreases as the normal applied load increases. SEM was used to characterize deformation and wear mechanisms that operate on contacts and the results related to the wear data.

Tribological properties of blends of melamine‐formaldehyde resin with low density polyethylene

AbstractTribological properties of blends of melamine‐formaldehyde resin (MFR) with low density polyethylene (LDPE) containing 1, 5, 10, 20, 25 wt% MFR were investigated. We have determined sliding wear by multiple scratching along the same groove using a micro scratch tester. Instantaneous penetration depth is lowered by the MFR addition to LDPE. However, there is less viscoelastic recovery and the residual (healing) depths increase with increasing MFR concentration. Microindentation hardness increases along with the MFR content. Since MFR is only partially miscible with LDPE, MFR‐rich islands in the PE matrix offer more interfaces and so increase hardness. Friction determined with a pin‐on‐disk tribometer using silicon nitride balls as a function of MFR concentration shows a minimum. The result is explained in terms of surface morphology seen in scanning electron microscopy. At the same time, all blend friction values are lower than for neat LDPE. Wear determined in the pin‐on‐disk tribometer decreases along with the MFR concentration increase. Thus, pin‐on‐disk wear and friction show different faces of blends tribology. Blending can be used to improve tribological properties of LDPE. POLYM. ENG. SCI., 2008. © 2007 Society of Plastics Engineers

Study on effects of the feed on AFM-based nano-scratching process using MD simulation

AFM is a powerful and versatile tool which has the ability to fabricate nanoelectronics and other nanoparts using nano-scratching method. To achieve a deeper understanding on AFM-based nano-scratching process, molecular dynamic (MD) simulation approach is employed. Interactive forces between a rigid pyramidal tool simulating an AFM diamond tip and a copper sample are modeled by the Morse function. Two adjacent scratching tests are carried out at different feeds simulating the multiple scratching tests. Effects of the feed on the scratching process are discussed. Results show that the feed has a significant effect on the deformation of the machined surface, the scratching depth, scratching forces and potential energy. The important effect of the relax process in the MD simulation of AFM-based multiple nano-scratching processes is exhibited, which cannot be ignored when analyzing the variation of the potential energy.

Connection between dynamic mechanical properties and sliding wear resistance of polymers

The viscoelasticity of several polymers has been determined using dynamic mechanical analysis (DMA). For the same materials the sliding wear in multiple scratching along the same groove has also been determined. The materials studied were polycarbonate (PC), polystyrene (PS), styrene/acrylonitrile (SAN), Surlyn, polyethersulfone (PES), acrylonitrile/butadiene/styrene (ABS), polypropylene (PP), polytetrafluoroethylene (PTFE), low density polypropylene (LDPE) and Santoprene (an elastomer). Sliding wear was determined for several constant loads between 5 and 15 N. The penetration depth Rp and the residual depth Rh obtained from wear tests were confronted with DMA parameters: E′, E″ and tan δ. An evident correlation between tan δ and Rp is seen. Both penetration depth and residual depth increase along with tan δ. Surface roughness obtained from atomic force microscopy (AFM) provides another kind of useful tribological information, with the highest value obtained for PS.

Wear of thermoplastics determined by multiple scratching

AbstractWe studied wear resistance in sliding by multiple scratching along the same groove for a variety of thermoplastics: polystyrene, styrene-acrylonitrile, polyamide 6 and polysulfone. Constant-load experiments were carried out with a micro scratch tester for several loads between 2.5 and 15 N; each time 15 scratches were performed. Except for polystyrene, all materials show an asymptotic residual depth as a function of the number of scratch tests performed. In contrast to other materials, polystyrene exhibits brittleness and debris formation. Scanning electron microscopy and scanning probe microscopy were used to characterize the deformation and wear mechanisms and were connected to the wear data obtained by multiple scratching. At 15 N we found a viscoelastic recovery for polystyrene of 27.8% while for polyamide 6 the corresponding value is 80.2%.

Scratch velocity and wear resistance

AbstractUsing a micro-scratch tester we have determined the influence of scratch velocity on the sliding wear resistance of several thermoplastics: polystyrene (PS), styrene-acrylonitrile, polyamide 6, polyethersulfone and polysulfone. Variable velocities (from 1 to 15 mm/min) were applied under two different load configurations: progressively increasing loads from 0.03 to 30 N and multiple scratching under constant loads from 2.5 to 10 N. Penetration and residual depth were measured along a 5 mm length. In the case of PS the scanning electron microscopy images of the progressive load scratch reveal a transition from shear yielding to crazing at low velocity. In multiple scratching tests the residual depths obtained at 1 mm/min are substantially higher than those at 15 mm/min for all thermoplastics tested. This result is explained by contact heating at higher speeds resulting in increased chain relaxation capability and thus more viscoelastic recovery. Scanning probe microscopy was used in order to observe surface damages. Except for PS, all other materials at all velocities exhibit asymptotic behaviour of the residual depth as a function of the number of tests.

Effects of carbon black on tribology of blends of poly(vinylidene fluoride) with irradiated and non-irradiated ultrahigh molecular weight polyethylene

Friction and wear resistance are two vital tribological properties of polymer-based materials but optimization of both is rarely attempted. We have investigated blends of 70 wt% poly(vinylidene fluoride) (PVDF)+30% ultra high molecular weight polyethylene, the latter either un-irradiated or else γ-irradiated. Each sample contained varying amounts of carbon black (CB) and also had a varied degree of crosslinking and irradiation dose. We have determined static and dynamic friction, scratch resistance, and sliding wear in multiple scratching tests. Effects of the irradiation dose and CB concentration have been quantified. The electric conductivity threshold is reflected in a drop of static friction; formation of a continuous phase of the lubricant affects tribology as well as electrical properties—both for irradiated and for un-irradiated samples. The scratch resistance as represented by the residual (healing) depth is affected by crosslinking, by the stage at which irradiation is applied (before or after blending) and by CB addition. Crosslinking by moderate amounts of irradiation provides shallower residual depths while higher doses cause adverse results. Similarly, the CB lubricant can either improve or worsen the scratch resistance. A combination of both approaches produces either better or else worse results than crosslinking alone. Lower friction seems accompanied by higher scratch resistance. A combination of a specific irradiation dose and an optimized CB concentration lowers the sliding wear significantly. Strain hardening in sliding wear determination takes place for all materials studied, irrespective of the extent or radiation-induced crosslinking and of the presence and concentration of carbon black.

Friction and multiple scratch behavior of polymer+monomer liquid crystal systems

We have studied in turn: polystyrene (PS), styrene/acrylonitrile (SAN) and Polyamide 6 (PA6), adding each time to the polymer 1, 3, 5, 7 or 10 wt% of 4,4′-dibutylazobenzene (LC1) which is a monomer liquid crystal (MLC). LC1 reduces both static and dynamic friction of PS and SAN against stainless steels or polytetrafluoroethylene (PTFE). By contrast, friction values are lower for pure PA6 than for PA6 modified with various MLCs or with MoS 2. Multiple scratching tests were carried out with a micro scratch tester on every system between 2.5 and 15 N. The presence of LC1 in PS reduces penetration depth and residual depth and increases the viscoelastic recovery. So far PS was the only polymer, which does not show strain hardening in multiple scratching. The present results confirms this, but it also shows that only 1 wt% of LC reduces the brittleness of PS so that strain hardening appears. This effect is maintained at all higher concentrations of LC1 investigated as well. For SAN or PA6, additions of LC1 reduce penetration depth values with respect to pure polymers, but do not have a significant effect on viscoelastic recovery. Scanning electron microscopy (SEM) was used to study the deformation and wear mechanisms, and to relate the data obtained in multiple scratch sliding wear tests. For PS we see in SEM that increasing the LC1 concentration causes a more ductile behavior, with less crack nucleation. For SAN the debris accumulation in sliding wear is mitigated by the presence of the liquid crystalline lubricant. No debris formation is observed in PA6, with or without a lubricant.

Evaluation of the scratch resistance with nano‐ and multiple scratching methods

The scratch resistance of automotive clear coats was investigated by a single and multi scratch test procedure. New data characteristic for the reflow capability, the scratch hardness and the lateral scratch resistance were generated and evaluated. A correlation between single and multi scratch data was established.

Wear mechanisms in reciprocal scratching of polycarbonate, studied by atomic force microscopy

An atomic force microscopic (AFM) was used to study the microwear process of polycarbonate (PC). Testing included multiple scratching (scan-scratching) and line-scratching using a microfabricated Si 3N 4 AFM tip of 10–20 nm radius. Interfacial adhesion, friction, the effect of number of cycles, scratching speed and the interaction of scratches were studied. Unlike previous reports, projections as a result of polycarbonate volume increase were observed after reciprocal scratching on the same track (without AFM tip lateral feed). In spite of analytically predicted elastic/plastic contact, no plastic deformation was found during the tests. A model, based on the cracks formation and growth process was suggested to explain these phenomena. The importance of lateral feed in the process of wear particles formation was shown. No scratching speed effect on friction or microwear was found.