A novel method for high-resolution imaging of coating distribution within a rough-textured plywood surface

A new method was developed which enabled us to obtain high-resolution images of the distribution of an oil-borne stain in a saw-textured plywood surface. The method involved treating 90 μm thick plywood sections, which had been cut transversely through the wood-coating interface using a sliding microtome, with osmium tetroxide (OsO₄) prior to examination with a field-emission scanning electron microscope (FE-SEM) operating in backscattered electron imaging (BEI) mode. The combination of OsO₄ staining and use of FE-SEM-BEI afforded excellent contrast differentiation between the coating and wood cell walls, revealing coating penetration into even nano-size cell wall cracks and delaminations formed during band-sawing of the plywood. The novel technique described adds a new dimension to probing wood–coating interface.     

Reactivity,chemical structure,and molecular mobility of urea–formaldehyde adhesives synthesized under different conditions using FTIR and solid‐state 13C CP/MAS NMR spectroscopy

This study was conducted to investigate the effects of reaction pH condition and hardener type on the reactivity, chemical structure, and molecular mobility of urea–formaldehyde (UF) resins. Three different reaction pH conditions, such as alkaline (7.5), weak acid (4.5), and strong acid (1.0), were used to synthesize UF resins, which were cured by adding four different hardeners (ammonium chloride, ammonium sulfate, ammonium citrate, and zinc nitrate) to measure gel time as the reactivity. FTIR and ¹³C‐NMR spectroscopies were used to study the chemical structure of the resin prepared under three different reaction pH conditions. The gel time of UF resins decreased with an increase in the amount of ammonium chloride, ammonium sulfate, and ammonium citrate added in the resins, whereas the gel time increased when zinc nitrate was added. Both FTIR and ¹³C‐NMR spectroscopies showed that the strong reaction pH condition produced uronic structures in UF resin, whereas both alkaline and weak‐acid conditions produced quite similar chemical species in the resins. The proton rotating‐frame spin–lattice relaxation time (T_1ρH) decreased with a decrease in the reaction pH of UF resin. This result indicates that the molecular mobility of UF resin increases with a decrease in the reaction pH used during its synthesis. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2677–2687, 2003     

Effect of stitching and weave architecture on the high strain rate compression response of affordable woven carbon/epoxy composites

In this study, experimental investigations on stitched and unstitched woven carbon/epoxy laminates under high strain rate compression loading are discussed. Stitched/unstitched laminates are fabricated with aerospace grade plain and satin weave fabrics with room temperature curing SC-15 epoxy resin using affordable vacuum assisted resin infusion molding process. The samples are subjected to high strain rate loading using modified compression split Hopkinson’s pressure bar at three different strain rates ranging from 320 to 1149 s⁻¹. Results are discussed in terms of unstitched/stitched configuration, fabric type and loading directions. Dynamic compression properties are compared with those of static loading. Failure mechanisms are characterized through optical and scanning microscopy.     

MRT Letter: High resolution SEM imaging of nano‐architecture of cured urea‐formaldehyde resin using plasma coating of osmium

Nanoarchitecture of cured urea‐formaldehyde (UF) resins was examined with a field‐emission scanning electron microscope (FE‐SEM) after coating samples with osmium, which is considered to produce particles of considerably smaller size compared to other metal coatings used in SEM studies. This method enabled comparison of the nanoarchitecture of UF resins of low (1.0) and high (1.6) formaldehyde/urea (F/U) mole ratios to be made, based on imaging of extremely small size particles as part of UF resin architecture, not described before. Imaging revealed presence of relatively large globular particles (148.084–703.983 nm size range) as well as smaller substructures (28.004–39.604 nm size range) as part of the architecture of 1.0‐mole UF resin. Globular particles were also present in 1.6 mole UF resin, but of considerably smaller size (14.760–50.269 nm). The work presented demonstrates usefulness of osmium coating in unraveling the intricacies of the nanostructural organization of cured UF resins, prompting wider application of this immensely useful but grossly underutilized metal coating type in high resolution SEM examination of biological and materials samples. Microsc. Res. Tech. 76:1108–1111, 2013. © 2013 Wiley Periodicals, Inc.     

Enhancing exterior performance of clear coatings through photostabilization of wood. Part 2: coating and weathering performance

Clear-coated boards have not been recommended for use in exterior conditions since irradiation with visible and UV radiation darkens them and photodegrades the lignin in the wooden surface beneath the coating, leading to delamination and subsequent catastrophic coating failure due to the continued action of sun, rain, and biological factors. Many approaches to rectify this problem have been explored. Chemical modification of the surface with hexavalent chromium, reaction with various anhydrides, grafting of UV absorbers, and esterification are among the methods attempted. A second approach has been via the clear coating itself where UV absorbers, antioxidants, and ultrafine titanium and iron oxides have been added. However, these have had limited or no success in stopping photodegradation processes. Since the main cause of photodegradation is photooxidation of lignin in the wooden surface as a consequence of free radical reactions initiated by UV irradiation, the approach taken in the present study, in an attempt to enhance the weathering performance of clear-coated boards outdoors, was to delignify the surfaces of wooden boards and then apply clear coatings to try and retard possible photodegradation. Two different pretreatments were used. Firstly, chemical surface delignification with a peracetic acid treatment created a partial delignification to a depth of 2–3 mm while still retaining the structural integrity of the surface. Secondly, a preweathering treatment, which resulted in a 100-μm-deep delignification zone, was compared. The coatings applied to the exposure surface of the pretreated boards were either polyurethane or an acrylic varnish. The clear-coated boards were exposed to exterior and accelerated weathering regimes for 3 years or 3000 h, respectively. Pretreated coated boards did not darken and yellow on exposure but untreated coated boards did. However, despite apparently arresting photodegradative processes on board surfaces, there were no significant gains in the performance ratings of coated pretreated boards over those of coated untreated control boards. Explanations for this involve the effectiveness of design factors incorporated into boards for exposure trials. These factors were the fungicidal dipping of boards before coating, precoating the exposure surface with a reactive primer, and applying a full polyurethane system to the back side and edges of boards. Both pretreatments resulted in clear-coated board surfaces that performed very similarly on exposure outperforming systems reported previously. It was surprising to observe that the preweathering treatment, which resulted in a 100-μm-deep delignification zone, performed as effectively as the chemically pretreated boards with 2- to 3-mm treatment zone. However, preweathered surfaces had lost all lignin in the middle lamella and there was cell separation, whereas in peracetic acid-treated boards, there was more or less complete lignin removal from the cell corner middle lamella only and partial lignin removal from other cell wall regions. Furthermore, it is anticipated that refinements in treatment methods and coating formulations will bring desired benefits and future work should focus in this area.     

Micro-Morphological Features of Cured Urea-Formaldehyde Adhesives Detected by Transmission Electron Microscopy

This work examined micro-morphological features responsible for the crystallinity of cured urea-formaldehyde (UF) adhesives, using transmission electron microscopy (TEM) to identify and characterize distinctive crystalline structures in resins obtained with different formaldehyde to urea (F/U) mole ratios and hardener levels. The TEM examination of cured UF resin adhesives impregnated into wood cell lumen revealed the presence of spherical particles with variable diameter and number per unit area. The diameter and number/area of the spherical particles increase for decreasing F/U mole ratio and decrease with an increase in the hardener levels, an effect which is closely related to their crystallinity. Therefore, the present findings suggest that the spherical particles are responsible for the crystallinity of cured UF resin adhesives. The results also indicate that crystalline structures represent an inherent feature of cured UF resin adhesives, particularly for low F/U mole ratios, even though these resins are usually classified as amorphous and cross-linked thermosetting polymers.     

XAFS study of europium chloride at high temperatures

Local structural changes in europium dichloride around europium ion at high temperature are evaluated by using X-ray absorption fine structure technique. A distinct phase shift in EXAFS oscillation observed between 700 and 950K arises from Eu²⁺ to Eu³⁺ oxidation. Referring to the difference in EXAFS oscillation between oxide and oxychloride of lanthanum, the chemical state of europium on oxidation is identified mainly as Eu₂O₃.     

Micro-Osteoperforations Induce TNF-α Expression and Accelerate Orthodontic Tooth Movement via TNF-α-Responsive Stromal Cells

Micro-osteoperforations (MOPs) have been reported to accelerate orthodontic tooth movement (OTM), and tumor necrosis factor (TNF)-α has been reported to play a crucial role in OTM. In this report, the influence of MOPs during OTM was analyzed. We evaluated the expression of TNF-α with and without MOPs by RT-PCR analysis. A Ni-Ti closed coil spring was fixed between the maxillary left first molar and the incisors as an OTM mouse model to move the first molar in the mesial direction. MOPs were prepared on the lingual side and mesial side of the upper first molars. Furthermore, to investigate the target cell of TNF-α for osteoclast formation during OTM with MOPs in vivo, we created four types of chimeric mice in which bone marrow of wild-type (WT) or TNF receptor 1- and 2-deficient mice (KO) was transplanted into lethally irradiated WT or KO mice. The results showed that MOPs increased TNF-α expression, the distance of tooth movement and osteoclast formation significantly. Furthermore, mice with TNF-α-responsive stromal cells showed a significant increase in tooth movement and number of osteoclasts by MOPs. We conclude that MOPs increase TNF-α expression, and tooth movement is dependent on TNF-α-responsive stromal cells.     

Electrochemical Corrosion Behavior of Dental/Implant Alloys in Artificial Saliva

The corrosion behavior and passive film characteristics of various dental alloys such as Co-Cr, Ni-Cr, Cu-Ni-Al, and commercially pure Ti (c.p. Ti) were evaluated in artificial saliva medium by utilizing electrochemical impedance spectroscopy (EIS), Tafel polarization, and cyclic polarization studies. EIS studies were carried out for various durations viz. 1 h, 1 day, and 7 days to evaluate the stability of passive film and change in corrosion characteristics with respect to time. Electrochemical parameters such as E_corr, i_corr, corrosion rate, passive film characteristics with respect to time were obtained from various studies mentioned above. The corrosion resistance decreased in the order Cu-Ni-Al > cp Ti > Co-Cr (Commercial) > Ni-Cr > Co-Cr (DRDO developed) in artificial saliva solution.