Ultraviolet Exposure Time Research Articles

Application of In Situ Microfibrillization to Recycling Ultraviolet‐Aged Poly(Ethylene Terephthalate) (PET) and High Density Polyethylene (HDPE)

The potential of in situ microfibrillization for recycling ultraviolet‐aged high density polyethylene (HDPE) and poly(ethylene terephthalate) (PET) mixtures was investigated. The photodegradation of HDPE and PET was conducted through accelerated irradiation in an ultraviolet (UV) chamber. The ultraviolet‐aged HDPE and PET was melt blended (in 80/20 wt. ratio) and rectangular slit die extruded, followed by hot stretch and quenching; thus the in situ microfibrillar PET/HDPE blends were fabricated. Gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FT‐IR), and contact angle measurements indicate that HDPE and PET suffered photodegradation. There is an increase in yield strength and tensile modulus as well as Vicat softening temperature (VST) tests for in situ microfibrillar blends with increasing UV exposure time, while there is a decrease in these properties for conventional blends, indicating that the in situ microfibrillar blend process has promising potential for recycling plastic mixtures.

UV-generated free radicals (FR) in skin: Their prevention by sunscreens and their induction by self-tanning agents

In the past few years, the cellular effects of ultraviolet (UV) irradiation induced in skin have become increasingly recognized. Indeed, it is now well known that UV irradiation induces structural and cellular changes in all the compartments of skin tissue. The generation of reactive oxygen species (ROS) is the first and immediate consequence of UV exposure and therefore the quantitative determination of free radical reactions in the skin during UV radiation is of primary importance for the understanding of dermatological photodamage. The RSF method (radical sun protection factor) herein presented, based on electron spin resonance spectroscopy (ESR), enables the measurement of free radical reactions in skin biopsies directly during UV radiation. The amount of free radicals varies with UV doses and can be standardized by varying UV irradiance or exposure time. The RSF method allows the determination of the protective effect of UV filters and sunscreens as well as the radical induction capacity of self-tanning agents as dihydroxyacetone (DHA). The reaction of the reducing sugars used in self-tanning products and amino acids in the skin layer (Maillard reaction) leads to the formation of Amadori products that generate free radicals during UV irradiation. Using the RSF method three different self-tanning agents were analyzed and it was found, that in DHA-treated skin more than 180% additional radicals were generated during sun exposure with respect to untreated skin. For this reason the exposure duration in the sun must be shortened when self-tanners are used and photoaging processes are accelerated.

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

AbstractReactive 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

Carbon and hydrogen isotope fractionation of acetic acid during degradation by ultraviolet light

Low molecular-weight carboxylic acids, such as acetic and propionic acids, are abundant organic compounds in carbonaceous chondrites, and are generally enriched in heavy stable isotopes (i.e., 13C and D) relative to terrestrial organic compounds. In this study, we have determined carbon and hydrogen isotopic fractionation of acetic acid, and site-specific carbon isotopic fractionation of acetic acid, during degradation by ultraviolet (UV) light. Acetic acid became enriched in 13C and D with increased UV exposure times. The isotopic fractionation factors (α) of total, methyl and carboxyl carbon of acetic acid were 0.9922, 1.0022 and 0.9823 respectively, and the α value for hydrogen was 0.9875. These results suggest that UV degradation could be a process for yielding 13C- and D-enrichment of acetic acid in natural environments.

A new approach of studying correlation between outdoor exposure and indoor accelerated corrosion test for high polymer materials

The correlation between outdoor exposure and indoor accelerated corrosion test for high polymer materials was investigated according to the variation of the functional group of exposure models aged. Environment aging intesities at different zones (Wuhan and Lasa with the same latitude) and the influences of indoor accelerating factors including water and ultraviolet on weathering performance of high polymer materials were also studied by comparing different indoor accelerated corrosion testing results. The experimental results show that: by testing variations of carbonyl exponent of polythene (which represented the degradation behavior of high polymer materials due to ultraviolet oxidation of double bond) and ultraviolet absorbance of polycarbonate (which represented the degradation behavior of high polymer materials due to abevacuation of branched chain), the degradation behavior of high polymer materials could be studied. Carbonyl exponent of polythene exposed in Wuhan and Lasa for 1 year was equal to that exposed in indoor cycle ultraviolet for 128 h and 170 h, respectively, the ultraviolet absorbance of polycarbonate exposed in Wuhan for 1 year was equal to that exposed in indoor cycle ultraviolet for 240 h. The ratio of environment aging intensity of Lasa to Wuhan was around 1.2. With the prolongation of cycle accelerated ultraviolet exposure time, the variations of carbonyl exponent of polythene and the ultraviolet absorbance of polycarbonate were in the same shape of first order exponential decay curve. Accompanied with ultraviolet, the effect of water condensated on the sample on weathering performance of polythene was more significant than that of polycarbonate.

Surface functionalization of polyolefin films via the ultraviolet‐induced photografting of acrylic acid: Topographical characterization and ability for binding antifungal agents

AbstractThe photoinduced graft copolymerization of acrylic acid with ultraviolet radiation onto films of poly(vinyl chloride), polypropylene, and polyethylene was studied. Benzophenone was used as the initiator for most of the experiments performed. The percentage of grafting was determined by gravimetric measurements, and the characterization of the grafted films was carried out by chemical analysis (Fourier transform infrared spectroscopy, volumetric titration, and dye adsorption). In all samples, the grafted yield increased with the ultraviolet exposure time. High levels of grafting were obtained at room temperature. In addition, optical and atomic force microscopy allowed the topography of the modified films to be studied as a function of the reaction time. The pendant functional groups that were grafted were then used to bind antifungal agents, such as natamycin and crystal violet, and the antifungal properties of the films were demonstrated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:2254–2263, 2006

Influence of ultraviolet irradiation on the optical properties of amorphous Sb10Se90 thin films

Amorphous Sb10Se90 thin films were prepared by thermal evaporation of the bulk glass. The changes in the optical properties (transmittance, optical gap, absorption coefficient, refractive index and extinction coefficient) have been measured in the wavelength range 500–900 nm of virgin and ultraviolet (UV) illuminated films. Analysis of the optical absorption data shows that the rule of non-direct transitions predominates. It is found that the optical energy gap decreases (photo-darkening) and the refractive index increases with the increase of UV exposure time. The dispersion of the refractive index (n) has been discussed in terms of Wemple–Didomenico single oscillator model. The oscillator energy E0 and the dispersion energy Ed have been determined and discussed in terms of UV exposure time. The photo-darkening was discussed in terms of some of the current literature models.

A photolithographic method to create cellular micropatterns

Here we describe a simple and rapid system for creation of patterned cell culture substrates. This technique is based on (1) printing a mask on a standard overhead transparency, (2) coating a thin layer of a photocrosslinkable chitosan on a slide, (3) exposing the slide and mask to ultraviolet (UV) light, and (4) rinsing the uncrosslinked polymer to expose the underlying cell-repellent patterns. Photocross-linkable chitosan does not require photoinitiators, it is non-toxic and forms flexible, biocompatible hydrogel upon short ( approximately min) UV exposure. Patterns of various shapes (lanes, squares, triangles, circles) were created on two surfaces commonly used for cell culture: glass and tissue culture polystyrene. The pattern size could be varied with a mum resolution using a single mask and varying UV exposure time. Cardiac fibroblasts formed stable patterns for up to 18 days in culture. Cardiomyocytes, patterned in lanes 68-99 microm wide, exhibited expression of cardiac Troponin I, well developed contractile apparatus and they contracted synchronously in response to electrical field stimulation. Osteoblasts (SAOS-2) localized in the exposed glass regions (squares, triangles, or circles; 0.063-0.5mm(2)). They proliferated to confluence in 5 days, expressed alkaline phosphatase and produced a mineralized matrix.

UV Activation Treatment for Hydrophobic Wafer Bonding

Enhanced hydrophobic bond strength can be achieved by exposing prime grade silicon wafers to ultraviolet (UV) light and heat prior to bonding. The following independent variables were explored: platen temperature, UV exposure time, oxygen-containing vs non-oxygen-containing (nitrogen only) bonding atmosphere, and annealing temperature. The results suggest exposure to UV can be used as an activation process which removes the passivation of the silicon surface rendering the silicon highly reactive. Exposure of silicon wafers to UV appears to be a promising low-temperature surface activation method.

Mass patterning of polysiloxane layers using spin coating and photolithography techniques

Polysiloxane (PSX) containing 2,2-dimethoxy-2-phenylacetophenone (DMPA) photoinitiator has been used as a photosensitive polymer. Thus, thin PSX films have been deposited by spin coating and patterned thanks to standard ultraviolet (UV) photolithography. The influences of the different technological parameters (PSX dilution, spin speed, UV exposure time) have been studied in so as to understand the polysiloxane deposition and cross-linking phenomena. Finally, the whole process has been optimised. Results evidence the realisation of high quality PSX patterns for the development of mass-fabricated ion sensitive layers in the field of chemical microsensors.

Ultraviolet irradiation-induced K+ channel activity involving p53 activation in corneal epithelial cells

Recent studies from our lab found that ultraviolet (UV) irradiation induces a voltage-gated potassium (Kv) channel activation and subsequently activates JNK signaling pathway resulting in apoptosis. The present study in rabbit corneal epithelial (RCE) cells is to investigate mechanisms of UV irradiation-induced Kv channel activity involving p53 activation in parallel to DNA damage-induced signaling pathway. UV irradiation-induced signaling events were characterized by measurements of JNK activation and further downstream p53 phosphorylation. UV irradiation elicited an early response in the cell membrane through activation of Kv channels to activate the JNK signaling pathway and p53 phosphorylation. Exposure of RCE cells to UV irradiation within a few min resulted in JNK and p53 activations that were markedly inhibited by suppression of Kv channel activity. However, suppression of Kv channel activity failed to prevent p53 activation induced by extended DNA damages through prolonging UV exposure time (more than 15 min). In addition, caffeine inhibited UV-induced activation of SEK, an upstream MAPK kinase of JNK, resulting in suppression of both Kv channel-involved and DNA damage-induced p53 activation. Our results indicate in these cells that UV irradiation induces earlier and later intracellular events that link to activation of JNK and p53. The early event in response to UV irradiation is initiated by activating Kv channels in the cell membrane, and the later event is predominated by UV irradiation-caused DNA damage.

Standardized Collimated Beam Testing Protocol for Water/Wastewater Ultraviolet Disinfection

Ultraviolet (UV) irradiation has emerged as a viable alternative for water/wastewater disinfection. Laboratory dose-response data from collimated-beam tests are commonly used as a basis for determining the necessary delivered UV dose for full-scale UV systems as measured by UV intensity and exposure time. While researchers often think that germicidal dose can be estimated confidently in a collimated beam system, the reported dose-response relationships vary considerably. Numerous factors may affect the test results to some extent. They include apparatus setup, column dimensions, UV lamp type and output, intensity measurement, shutter type and operation, petri dish specifications, sample volume and depth of the liquid, mixing condition, laboratory settings, microbial organism preparation and testing, and water quality. The methodology used to calculate the UV dose for collimated beam tests is also a critical factor. To ensure reproducibility or to have a meaningful comparison of results from different collimated beam tests, a standardized protocol for collimated beam testing and its dose calculation is necessary. The standardized collimated beam test can then serve as a tool to calibrate the dose calculation models for field-scale UV reactors and, consequently, to meaningfully compare the dose values derived from these models. A comprehensive standardized collimated beam testing protocol is warranted to advance applications of UV disinfection for water/wastewater. However, development of such a protocol is a significant research effort that will require input from researchers of various technical and disciplinary backgrounds. In addition, some technical issues still need to be clarified by further research. This paper presents important issues associated with collimated beam testing in the context of developing a standard protocol as well as future research needs. The main objective is to serve as a starting point for development of a standardized collimated beam testing protocol that is universally acceptable by researchers, industries, and regulatory agencies.

Preparation of chlorinated poly(vinyl chloride)‐g‐poly(N‐vinyl‐2‐pyrrolidinone) membranes and their water permeation properties

AbstractChlorinated poly(vinyl chloride) (CPVC) membranes for microfiltration processes were prepared with the combined process of a solvent evaporation technique and the water‐vapor induced‐phase‐inversion method. CPVC membranes with a mean pore size of 0.7 μm were very hydrophobic. These membranes were subjected to surface modification by ultraviolet (UV)‐assisted graft polymerization with N‐vinyl‐2‐pyrrolidinone (NVP) to increase their surface wettability and decrease their adsorptive fouling. The grafting yields of the modified membranes were controlled by alteration of UV irradiation time and NVP monomer concentration. The changes in chemical structure between the CPVC membrane and the CPVC‐g‐poly(N‐vinyl‐2‐pyrrolidinone) membrane and the variation of the topologies of the modified PVC membranes were characterized by Fourier transform infrared spectroscopy, gel permeation chromatography, and field emission scanning electron microscopy. According to the results, the graft yield of the modified CPVC membrane reached a maximum at 5 min of UV exposure time and 20 vol % NVP concentration. The filtration behavior of these membranes was investigated with deionized water by a crossflow filtration measurement. The surface hydrophilicity and roughness were easily changed by the grafting of NVP on the surface of the CPVC membrane through a simultaneous irradiation grafting method by UV irradiation. To confirm the effect of grafting for filtration, we compared the unmodified and modified CPVC membranes with respect to their deionized water permeation by using crossflow filtration methods. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3188–3195, 2003

Single-step fabrication of diffraction gratings on hybrid sol–gel glass using holographic interference lithography

Single-step fabrication of diffractive surface relief gratings on an ultraviolet (UV) sensitive hybrid sol–gel glass is presented. The gratings are imprinted on the negative-tone sol–gel glass based on a holographic interference lithographic system. Characteristics of the sol–gel glass including refractive index and film thickness have been discussed and experimental results are presented as a function of baking temperature and UV exposure time respectively. The grating relief profiles are measured by an atomic force microscope and the measured groove depths are found in good agreement with the theoretical results determined by the Gerchberg–Saxton phase retrieval algorithm. It is promising to utilise the new material for various diffractive optical elements fabrication.

Synthesis of nanoparticles in Langmuir monolayer

A novel approach to create ultrathin planar nanoparticulate structures based on the controllable synthesis of nanoparticles directly in Langmuir monolayer at the gas/liquid interface and subsequent deposition of monolayer is introduced. In this approach, all initial reagents are present only in monolayer and reactions of nanoparticles synthesis are initiated by decomposition of organometallic compounds under electromagnetic radiation. The changes in the shape of compression isotherm of stearic acid (SA)/iron pentacarbonyl mixed monolayer under the varying of the time of exposure to the ultraviolet light have been studied. STM images of mixed monolayers deposited onto the graphite substrate revealed synthesized iron isotropic and anisotropic magnetic nanoparticles with the characteristic size varied from 20 to 150 Å in dependence on the ultraviolet exposure time and monolayer compression.

A novel technique for the fabrication of laboratory scale model functionally graded materials

In this work, the authors describe the design, fabrication and testing of model functionally graded materials (FGMs). The inhomogeneous property variations were generated by altering material properties through selective ultraviolet (UV) irradiation. Poly(ethylene co-carbon monoxide) (ECO) was chosen to make the FGMs because of its rapid degradation under UV light. Irradiated ECO becomes stiffer, stronger and more brittle with increasing irradiation time. Through a series of tension tests, the authors characterized the mechanical behavior of the specific ECO used as a function of UV exposure time. Furthermore, by controlling exposure time, specimens with continuously and discretely varying mechanical properties were produced. The resulting graded materials exhibited a Young's modulus that varied from about 160 MPa to 250 MPa and a strain to failure that varied from about 900 percent to 10 percent over the width in a 150 mm wide specimen. Microhardness measurements were used to determine the differences between discretely and continuously varying mechanical properties.

Positron annihilation and diffraction studies of the photopolymers based on the acrylate oligomers

Abstract Positron annihilation lifetime and X-ray diffraction measurements were made on photopolymers based on acrylate oligomers. Polymerization was caused by exposure to ultra violet light. The measurements were made on photopolymer specimens with different ultra violet light exposure times. The longest positron lifetime, τ 3 , was associated with the pick-off annihilation of orthopositronium (o-Ps) trapped in voids. Interatomic distances and coordination numbers for the investigated samples have been determined from X-ray data. Ultra violet light exposure time affects mainly the sizes of the voids. The nearest neighbour distances and coordination numbers are independent of the ultra violet exposure time.

Studying the Curing Kinetics of a Diacrylate by Using Infrared Spectroscopy

Fourier transform infrared (FT-IR) spectroscopy was used to study the photopolymerization of 4,4'-bis(acryloyl)biphenyl (BAB), dispersed in the liquid crystal (E7). The infrared absorbance of the carbon–carbon double bond of the acrylate group was monitored to follow the course of the polymerization and to determine the extent of cure. It was also observed that a major change in the character of the infrared absorbance band shape and position of the acrylate carbonyl group accompanied the reduction of the carbon–carbon double-bond absorbance. Curing was found to be rapid, on the order of minutes. It was found that the reaction did not proceed appreciably after a brief initial exposure to ultraviolet (UV) radiation. This result implies that this type of system may be time-stable with programmable degrees of cure. It was also discovered that single continuous doses of UV exposure produced a higher degree of cure than equivalent UV exposure times administered in multiple shorter doses. This observation indicates the existence of a relatively long induction period in this system. The long induction period may be caused by a UV screening effect due to the other components of this system.

Thermally stimulated current measurements on a UV irradiated organic photoreceptor layer

Thermally stimulated current (TSC) measurements have been performed on a xerographic photoreceptor which has been treated with ultraviolet (UV) radiation. The charge transport layer of the photoreceptor consists of a polyester molecularly doped with an arylamine substituted hydrazone which was observed to undergo UV induced rearrangement to an indazole derivative. The indazole derivative is transparent to the wavelength component inducing the photo-reaction so that the depth of converted material gradually extends farther into the CTL with UV exposure time. The xerographic residual potential variation with irradiation time is attributed to the formation of a potential barrier to transfer of charge from hydrazone hopping states to indazole hopping states. The mobility activation energy obtained from TSC measurements is 0.22 eV for unirradiated material, which decreases to 0.12 eV after 1200 s of irradiation. The latter energy is identified as a signature of the potential barrier. This identification is corroborated by the correlation between the decrease of the residual potential and the increase of the TSC activation energy after 3600 s of irradiation.

EFFECTIVENESS OF ULTRAVIOLET IRRADIATION IN REDUCING THE NUMBERS OF SALMONELLA ON EGGS AND EGG BELT CONVEYOR MATERIALS

The effectiveness of ultraviolet (UV) irradiation in potentially reducing Salmonella on eggs and in egghandling facilities was evaluated using four primary parameters: test materials, UV intensity, time of UV exposure, andinitial Salmonella contamination levels. Decontamination of fiber and plastic egg transfer belts, egg shells, and metal wasattempted. The results showed that each of these elements varied in its capacity for sterilization by UV whencontaminated with Salmonella. Regression models for system design were developed to define the relationship among UVintensity, Salmonella contamination level and time of UV exposure for each material.