Effects of ultraviolet aging on the surface properties and tribological performance of polyformaldehyde

Ultraviolet aging restricts the outdoor application of polyformaldehyde as the friction material. In this work, ultraviolet aging processes were applied to polyformaldehyde specimens and effects of the processes on their surface properties and tribological performance were evaluated. Surface morphology results show that a thin layer of white powder and micro‐cracks with further ramifications in other directions were observed on the surfaces after 400 h of ultraviolet exposure, while it is not detectable for the unaged specimens. Analysis of aging surface indicates that ultraviolet leads to the increase of micro‐cracks and the degree of crystallinity. All the tribological test results demonstrate that with the extension of ultraviolet aging time, (i) the process of damage on polyformaldehyde surface induced by ultraviolet aging is first slowly and faster afterward; (ii) the fluctuation of the friction coefficients of polyformaldehyde/GCr15 rubbing pairs increases; and (iii) the wear rate of polyformaldehyde markedly increase after aging test 400 h. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44684.     

Surface Modification of Polycarbonate by Ultraviolet Radiation and Ozone

The effect of ultraviolet (UV) radiation in the presence of ozone as a surface treatment for polycarbonate is examined in regards to changes in the wettability, adhesion, and surface mechanical properties. Standalone, 175-µm-thick films of a commercially available polycarbonate were exposed to UV radiation from sources of different power with various treatment times in the presence of supplemental ozone. Significant decreases in the water contact angle were observed after exposure to UV radiation in the presence of ozone. After several variations in the experimental setup, it was determined that the change in water contact angle is a function of the UV irradiance and the work of adhesion follows a master curve versus UV irradiance. Nanoindentation experiments revealed that the modulus of the top 500 nm of the surface is increased following UV exposure, attributable to surface cross-linking. Adhesion tests to the surface (conducted by a pneumatic adhesion tensile test instrument) showed little change as a function of UV exposure. Analysis of adhesion test failure surfaces with X-ray Photoelectron Spectroscopy (XPS) showed the locus of bond failure lay within the bulk polycarbonate and the measured bond strength is limited by the bulk properties of the polycarbonate and/or the creation of a weak boundary layer within the polymer.     

Tailoring the properties of deposited thin coating and print features in flexography by application of UV-ozone treatment

Printed functional materials are a rapidly growing area of interest for low-cost high-speed device manufacture with flexographic printing seen as a route to achieving this. The relationship between surface tension of the ink and surface free energy (SFE) of the photopolymer plate is a key for optimum performance. However, traditional methods of surface tension modification of the ink/coating often cannot be employed for functional inks. In this research, rapid, permanent modification of flexographic printing plate’s SFE is achieved through controlled UV-ozone treatment, and the effects of the treatment on the polar and dispersive component of SFE are analyzed by Fourier transform infrared attenuated total reflectance spectroscopy, swelling experiments, and roughness measurements. Printing trials using the modified printing plates reveal improved print uniformity and control of deposited ink layer thickness, as well as improved print features—particularly track and pad junctions which can be problematic for printed electronic applications. The ability to rapidly tailor printing plate SFE is of benefit to all volume printing applications. Furthermore, it is of critical importance for functional printing and printed electronics where surface tension of the ink is determined by the functional material and chemical modification is not possible or desirable.     

Synthesis of butadiene-acroleine block polymers

Summary From GPC and ¹H NMR results, we have shown that block polymers built with acroleine and butadiene units can be synthesized. Moreover, the cross-linkage ability of the acroleine blocks in these products under UV irradiation has been checked. This is very interesting for an industrial application. Indeed, homopolyacroleines can be used as a photopolymer layer to prepare negative or positive printing plates.     

Synergistic effect of hyperthermal atomic oxygen beam and vacuum ultraviolet radiation exposures on the mechanical degradation of high-modulus aramid fibers

The synergistic effect of atomic oxygen and vacuum ultraviolet (VUV) radiation exposures was investigated on the mechanical properties of high-modulus aramid fibers. Tensile tests were performed on single fibers. It was found that both tensile strength and Young's modulus decreased significantly due to the simultaneous exposures of atomic oxygen and vacuum ultraviolet radiation. In contrast, the surface of aramid fiber exposed to ultraviolet alone showed no change in tensile strength and Young's modulus. X-ray photoelectron spectroscopy showed that atomic oxygen exposure leads to oxidization and decomposition of amid groups, that only VUV exposure does not change the fiber surface, and that VUV exposure decreased oxidized components on the oxidized fiber surface exposed to atomic oxygen and ultraviolet simultaneously. Scanning electron microscopy revealed that the diameter of the fiber was not influenced so much by atomic oxygen and ultraviolet exposures, but the fiber surface became substantially rougher than the aramid fiber surface exposed to atomic oxygen alone.     

Degradation assessment of LDPE multilayer films used as a greenhouse cover: Natural and artificial aging impacts

This article focuses on the assessment and understanding of the mechanism of natural and artificial aging processes of a triple‐layer film made of low‐density polyethylene (LDPE) used as greenhouse cover. The film material contains color dye and ultraviolet–A (UV–A) and infrared (IR) stabilizers and antioxidant. The combined effect of temperature variations and UV–A radiations, of the natural and artificial aging, on the physical properties (free surface energy and yellow color measurements), mechanical behavior (tensile tests), thermal stability (TGA and DSC analysis), and structural stability (FTIR analysis) was investigated. The natural aging was conducted on a greenhouse, located in northern Algeria, over a period of 7 months. However, the artificial aging was performed at four different agricultural greenhouse simulating conditions of temperature and UV–A radiation (namely, at 40°C, 40°C with UV–A, 50°C, and 50°C with UV–A) for periods of aging up to 5486 h (7.6 months). The results revealed that, the maximum loss of the yellow color additives occurs at 2981 h under the natural aging process and at 2440, 1096, 1340, and 121 h under the four artificial aging conditions, respectively. There was an observed increase in the films free surface energy and a significant degradation in the mechanical properties with aging time. This can be correlated with the film material structural changes. The natural aging of the film in North Africa is almost equivalent to artificial aging at 40°C. The concurrent effect of temperature and UV–A radiations induced polymer chains scission leading to faster degradation in the film material and consequently a reduction in its durability and service lifetime. The results show also that the measured parameters are directly related to the limit of use criterion for evaluating the lifespan of agricultural greenhouse LDPE covers. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Ultraviolet radiation aging impact on physicochemical properties of crosslinked polyethylene cable insulation

This article deals within the study of the effect of artificial radiations on physical and chemical properties of the crosslinked polyethylene (XLPE) material, widely used for manufacturing high-voltage cables. Within this framework, several experimental tests, using essential characterization techniques, were performed to study XLPE behavior under ultraviolet (UV) aging. Attenuated total reflection Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, X-ray diffraction, and scanning electron microscopy were thus carried out to identify the main structure changes of the material before and after exposure to UV. In addition, appearance changes and DC (Direct Current) volume resistivity were evaluated. The obtained results showed that UV radiation has a great effect on the physicochemical properties of XLPE cable insulation. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48575.     

A macroscopically nondestructive method for characterizing surface mechanical properties of polymeric coatings under accelerated weathering

The surface of coatings and plastics is the first target in any degradation process initiated by ultraviolet (UV) radiation or mechanical stress (via scratch and abrasion). Surface damage can lead to changes in optical, morphological, and mechanical properties and can result in pathways for ingress of moisture and corrosive agents. Current test methods for monitoring performance of protective coatings focus on chemical properties and optical properties, such as color and gloss measurements, or invasive tests such as abrasion and cross-cut adhesion. In this study, a macroscopically nondestructive performance protocol using nanoindentation metrology via a well-controlled scratch test was applied to evaluate the scratch resistance and monitor the surface mechanical property changes in a protective coating under accelerated weathering. Polyurethane (PU) coatings with different polyol compositions were chosen for this study. Coating specimens were exposed to high-intensity UV radiation at 55°C and 75% RH conditions. Exposed specimens were removed at specified UV exposure times for surface modulus/hardness and scratch resistance characterization via nanoindentation and scratch test. The effect of polyol type and UV radiation dose on the scratch damage (scratch morphology) was investigated and correlated with the surface hardness and modulus of the materials.     

Surface characterization of hydrophilic coating obtained by low‐pressure CH4?O2 plasma treatment on a polypropylene film

The use of surface treatments at industrial level is generalized as they allow obtaining a wide variety of properties such as soft in the touch, hydrophilic behavior, and biocompatibility. The use of low‐pressure plasma techniques with organic gases or organic mixtures is an easy way to obtain surface coatings very small in depth through plasma‐polymerization processes that can be assimilated to a plasma‐enhanced chemical vapor deposition (PECVD) process. In this work, we have carried out a plasma‐polymerization process on a polypropylene (PP) film to obtain a hydrophilic coating. To obtain this, the film surface has been treated on a low‐pressure plasma reactor with a methane–oxygen mixture gas with a volume ratio of 80 : 20, respectively. The chemistry changes in the outermost layers of the deposited coating have been investigated with X‐ray photoelectron spectroscopy (XPS). The different processes that take part as a consequence of the interaction between the plasma gas species and the PP film surface mainly drive to the deposition of an organic layer, which is functionalized with oxygen‐based species as XPS study reveals. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Studies on Polybenzoxazine/Capron PK4/octakis(dimethylsiloxypropylglycidylether) Silsesquioxane Nanocomposites for Radiation Resistant Applications

Polymeric materials can erode when exposed to the radiation environment that includes atomic oxygen (AO), ultraviolet (UV) ionizing radiation, and ultrahigh vacuum (UHV). Many studies have been devoted to develop polymeric materials that can withstand decades of exposure on radiation. In this connection an attempt has been made to develop polyhedral oligomeric silsesquioxane (POSS) reinforced capron PK₄ (CPL) modified polybenzoxazine nanocomposites in the present work and to assess their ability to resist radiation for a prolonged period. Varying weight percentages of (0, 1, 3, and 5 wt%) POSS were reinforced in to 1:1 (w/w) PBZ/CPL copolymerization through chemical ring opening polymerization. The POSS reinforced PBZ/CPL nanocomposites have been studied their tensile strength and morphological behavior before and after exposure of UV irradiation. Data resulted from the studies indicated that the neat PBZ-CPL has significantly eroded after UV exposure, whereas POSS reinforced PBZ/CPL composites have eroded only an insignificant extent and the value of tensile properties are reduced to a small extent. The POSS reinforced nanocomposites during exposure under UV radiation undergo changes on the surface and lead to the formation of silica (Si-O-Si) passivation layer. The formation of silica layer protects (act as inert layer) from further erosion of the composites and was ascertained from SEM images. Data obtained from thermal and dielectric studies indicate that thermal stability and dielectric behavior of composites were appreciably improved when compared with those of neat PBZ/CPL matrix.     

Decrease in fluorescence and phosphorescence intensity of nylon 66 impurities by exposure to ultraviolet radiation

The effects of exposure to ultraviolet radiation on the fluorescence and phosphorescence intensity of impurities in nylon 66, sometimes called gel, were measured using color image processing. The fluorescence intensity of the gel particles and of the polymer showed an approximately exponential decay with the time of exposure to ultraviolet radiation, with decay constants in the range 0.5 to 1.0 h^?1. Analysis of images that were acquired over several hours also indicated a decrease in the phosphorescence intensity of the gel particles. Image processing provides a simpler and less expensive method of luminescence analysis than the spectroscopic techniques used previously to examine the effects of exposure to ultraviolet radiation on the phosphorescence properties of nylon 66 impurities. © 1995 John Wiley & Sons, Inc.     

UVA and UVC modification of photo polymeric surface and application for flexographic deposition of thin coatings

The object of this research was to perform, characterize, and apply the functional modification of flexographic photo polymeric printing plate surface by UVA and UVC post‐treatments. Photo polymeric printing plates have an important application in functional printing, where new printing inks/coatings and substrate formulations are used and the specific qualitative requirements must be met. The limitations of materials and processes often require expensive reformulations of the functional inks to achieve printability. Results of this research showed that the modification of the photo polymeric printing plate surface at the end of its production process can be used to precisely adjust the printing ink transfer to the printing substrate and thus eliminate the need for changing the ink/coating composition. By applying specific UV post‐treatment, one can create a flexographic coating deposition system of tailored properties adjustable to variable reproduction systems with high quality requirements. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43526.     

Comparison of the effects of gamma and ultraviolet radiation on wool keratin

The effects of γ-radiation (⁶⁰Co) on some chemical and physical properties of wool keratin are compared and contrasted with the effects of ultraviolet radiation in the UVC (200–280 nm) region. The effect of UVC doses up to 25 J/cm² (equivalent to 20 min exposure to a bank of high intensity lowpressure mercury arcs) on fabric strength is small (≤5%), whereas γ-irradiated wool experiences strength reductions of ≥15% at doses over 100 kGy. Colour changes following UVC and γ-irradiation are quite different: UVC wool is initially green changing to yellow under ambient conditions, γ-treated wool becomes pink-red at doses 25–250 kGy, and yellow at higher doses. The chromophores produced by UVC are easily removed by oxidative bleaching with hydrogen peroxide, whereas γ-treated wool remains yellow even at relatively low doses (25–50 kGy). This has implications for the use of γ-radiation as a means of sterilising wool for compliance with quarantine regulations. The effects of the two forms of radiation on the natural fluorescence of wool, permanent setting, printing properties and the epicuticle layer are also described.     

Polymere in der drucktechnik

Three main processes are used in the printing industry: Letterpress, Lithography and Gravure printing. In the early fifties polymer coatings have been introduced in lithographic printing plates formulations. Later, similar systems have proved to be suitable for letterpress, and very recently for gravure printing layers, too. Most polymer formulations used in printing techniques generally have the following features in common: ? They are light sensitive ? They are coated on to a flat substrate ? After imagewise exposure the more soluble areas of the coatings are removed in a development step. The requirements for the polymers used in printing layers are as different as the characteristics of each individual printing process. ? The importance of the specific optical properties of the polymers is demonstrated discussing some negative acting light sensitive systems, amongst them the photopolymerisation of monomers.     

Adhesion Between Rubber Compounds and Copper-film-coated Steel Plates

Three copper-film-coated steel plates (abbreviated hereafter as copper-coated plate) with different thicknesses of copper film 30 to 90 nm were prepared and their adhesion properties to rubber compounds were examined. The high adhesion of copper-coated plates to the rubber compound containing resinous bonding additives was obtained at normal and over-cure conditions The copper-coated plate containing an amount of copper coating sufficient to plate the surface with a uniform copper layer showed better adhesion than that having a small amount of copper coating on its surface. The stability against green humidity aging and the cause for the high adhesion of the copper-coated plate were discussed compared with those of the brass plate.     

Adhesion Between Rubber Compounds and Copper-film-coated Steel Plates

Three copper-film-coated steel plates (abbreviated hereafter as copper-coated plate) with different thicknesses of copper film 30 to 90 nm were prepared and their adhesion properties to rubber compounds were examined. The high adhesion of copper-coated plates to the rubber compound containing resinous bonding additives was obtained at normal and over-cure conditions The copper-coated plate containing an amount of copper coating sufficient to plate the surface with a uniform copper layer showed better adhesion than that having a small amount of copper coating on its surface. The stability against green humidity aging and the cause for the high adhesion of the copper-coated plate were discussed compared with those of the brass plate.     

Gloss and degradation of hydroxyl polyacrylic resin/hexamethylene‐1,6‐diisocyanate coatings under ultraviolet and natural‐exposure aging

Reactive coatings of hydroxyl polyacrylic resin (HPAR) with hexamethylene‐1,6‐diisocyanate were carried out under accelerated 313‐nm ultraviolet (UV) aging for 2000 h and under natural exposure in Lhasa, Tibet, for 24 months. With UV irradiation and exposure time, the gloss changes in coatings with HPAR containing 3.0% or less hydroxyl groups decreased exponentially, whereas the gloss decay of coatings with HPAR containing over 4.5% hydroxyl groups decreased linearly. During 254‐nm UV aging, the gloss changes in coatings with HPAR containing 1.4% or less hydroxyl groups decreased as a Gaussian function. The weather resistance of a coating was correlated to the HPAR, UV irradiation, temperature, and humidity. Scanning electron microscopy indicated that there were degradation reactions and that some substance was lost in the matrix polymer during accelerated UV aging; then, uneven surfaces appeared and caused decreased gloss. Accelerated UV aging was faster than natural‐exposure aging, and the aging velocity of 254‐nm UV was 3–5 times faster than that of 313‐nm UV. Through the changes in the gloss, the aging tolerance of a coating could be monitored, and its aging resistance could also be predicted. The dynamic mechanical thermal analysis results showed that the coatings had good properties. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1271–1278, 2007     

Textiles screen‐printed with photochromic ethyl cellulose–spirooxazine composite nanoparticles

Photochromic compounds change colour on exposure to light, while the reversion may be attributable either to radiation or may be thermal. The use of photochromism on fabrics can provide new opportunities to develop smart textiles; for example, sensors and active protective clothes. Ethyl cellulose‐1,3‐dihydro‐1,3,3,4,5 (and 1,3,3,5,6) ‐pentamethyl‐spiro‐[2H‐indole‐2,3′‐(3H)naphtha(2,1‐b)(1,4)oxazine] composites were prepared by an oil‐in‐water emulsion, solvent evaporation method in order to form easily suspendable and fatigue‐resistant photochromic nanoparticles in screen‐printing paste. Their size was well below 1 μm and did not change substantially over a wide range of dye concentrations. After screen‐printing, a homogenous photochromic layer was built on a cotton substrate surface, which represented substantial blue colour development in CIELab colour space measurements because of ultraviolet light, even at a dye concentration of 0.045% w/w. The addition of a photodegradation inhibitor, Tinuvin 144, further increased the coloration of the printed fabric.     

Effect of ultraviolet-A radiation on surface structure,thermal, and mechanical and electrical properties of liquid silicone rubber

Liquid silicone rubber (LSR) products outdoors are often subjected to high intensity of ultraviolet (UV)-A radiation. However, the influence of UV-A radiation on LSR is rarely studied. To study the influence of UV-A radiation on LSR, the surface of LSR with UV-A aging time was characterized by tests at different detection depths [X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDS), and Fourier transform infrared spectroscopy (FTIR)]. The operation properties (thermal stability and mechanical and electrical properties) for outdoor insulators were also analyzed. It was found that the porous surface and the loose layer of LSR increased, but the growth rate of them decreased as UV-A aging time increased. SiO₂ fillers were lost in the surface. C H bonds in  CH₃ and  CH₃ in Si CH₃ increased with aging time. The increased crosslinking density increased the thermal stability, hardness, dielectric loss tangent, relative dielectric constant, and volume resistivity and decreased elongation-at-break. The mechanical strength initially increased and then decreased. Based on the proposed aging mechanism, the UV-A resistance of LSR can be improved by reducing the amount of hydrogen-containing silicone oil and by increasing the molecular weight of raw rubber. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47652.     

Preparation,properties, and laser processing of poly(ɛ-caprolactone)/poly(lactic acid) blends with addition of natural fibers as a potential for printing plates application

In this research, biodegradable blend of poly(ɛ-caprolactone) (PCL) and poly(lactic acid) (PLA) is proposed as a new material for the production of a printing plate for embossing process. Printing plates for embossing consist of raised printing elements and recessed nonimage elements. In production of printing plates, laser technology was used in order to form a relief printing plate. The embossing process is based on the principle of the pressure of the relief printing plate into the printing substrate, which causes the controlled deformation of the substrate and three-dimensional (3D) effect. Coir fibers (CFs) were added as a natural filler to PCL/PLA blends to improve and adjust the properties of produced blends. Scanning electron microscopy micrographs, dynamic mechanical analysis analysis, roughness, and hardness were measured on prepared materials, and 2D and 3D microscopy was conducted on laser engraved printing plates. Results have shown that the addition of CFs improved the mechanical properties of produced materials. DMA results indicate the semicrystalline structure of all prepared blends, and that the addition of CFs raises the elasticity of the composites. Laser engraving showed that it is possible to engrave the produced biodegradable materials and to use it as a material for production of printing plates.