Superficial Cracks Research Articles

Optical microscopic study of the stress induced corrosion of brass and aluminium in dilute electrolyte, and the inhibition effect of Cedrus Atantica and Ocimum Basilicum

Optical microscopic analysis of the stress induced (85% calculated stress) corrosion of brass in 1M ammonium sulfate [(NH4)2SO4] + 1M copper (II) sulfate (CuSO4) solution, and aluminium in 0.5M, 1M and 2M sulfuric (H2SO4) solution at 10% and 20% addition of Cedrus Atlantica and Ocimum basilicum Linn. essential oil extracts were documented. The optical images obtained showed the effect of both extracts on the alloys. Optical images of aluminium in the presence of Cedrus Atlantica showed increased susceptibility of the alloy to localized and general corrosion compared to Ocimum basilicum Linn which enhanced the corrosion resistance of aluminium. Cedrus Atlantica increased the susceptibility of alpha brass to corrosion compared to the solution without it. In the absence of Cedrus Atlantica, general surface deterioration was observed without any localized corrosion. However, at 10% Cedrus Atlantica concentration superficial crack was observed. The crack further increased to visible intergranular crack (fracture) at 20% Cedrus Atlantica concentration. Ocimum basilicum Linn performed effectively at 10% concentration, sustaining the corrosion resistance of brass in 1M (NH4)2SO4 + 1M CuSO4 solution. At 20% Ocimum basilicum Linn concentration superficial cracking appeared.

Effect of Exposure Environment and Calcium Source on the Biologically Induced Self-Healing Phenomenon in a Cement-Based Material

Microbially induced calcium carbonate precipitation (MICP) presents a sustainable, environmentally friendly solution for repairing cracks in cement-based materials, such as mortar and concrete. This self-healing approach mechanism enables the matrix to autonomously close its own cracks over time. In this study, specimens (50 mm in diameter and 25 mm in height) were exposed to submersion and a wet–dry cycle environment. The solution considered a nutrient-rich suspension with calcium lactate, urea, calcium nitrate, and Bacillus subtilis or Sporosarcina pasteurii in a biomineralization approach. The self-healing efficiency was assessed through optical microscopy combined with image processing, focusing on the analysis of the superficial crack closure area. S. and B. subtilis exhibited notable capabilities in effectively healing cracks, respectively, 8 mm2 and 5 mm2 at 35 days. Healing was particularly effective in samples placed in a submerged environment, especially with a 69 mM concentration of calcium lactate in bacterial suspensions containing B. subtilis, where 87.5% of a 4 mm2 crack was closed within 21 days. In contrast, free calcium ions in the solution, resulting from anhydrous cement hydration, proved ineffective for S. pasteurii biomineralization in urea-rich environments. However, the addition of an external calcium source (calcium nitrate) significantly enhanced crack closure, emphasizing the critical role of calcium availability in optimizing MICP for bio-agents in cement-based materials. These findings highlight the potential of MICP to advance sustainable self-healing concrete technologies.

Quality and microstructure of tilapia fillets (Oreochromis niloticus) subjected to different freezing methods

The Nile tilapia (Oreochromis niloticus) fillets were frozen with static air (SA) at -20 °C, air blast freezing (AF) at -25 °C, combined method (CM - immersion in liquid nitrogen followed by AF) and cryogenic freezing (CF - immersion in liquid nitrogen). The effects of different freezing methods and of storage time at -18 °C (0, 30, 60 and 90 days) on fillet quality were evaluated. The temperature records were obtained, and the freezing times were determined by monitoring the temperatures of the geometric centers of the fillets. For CF, CM, AF and SA, the freezing times were 5.32, 127, 146 and 268 min, respectively. The quality of the frozen fillets was evaluated by measuring pH, volatile nitrogenous bases (TBV-N), thiobarbituric acid reactive substances (TBARS), and fatty acids and by obtaining a texture profile and performing scanning electron microscopy (SEM). The samples frozen by CF, after storage, had the highest levels of TBV-N because the high freezing rate produced superficial cracks that negatively affected the quality of the fillets. Freezing the samples with SA produced the worst quality indices and the microstructure was visibly damaged, with greater spaces between the fibers left by ice crystals. For all parameters evaluated, freezing with AF and CM resulted in fast freezing rates and better-quality tilapia fillets for 90 days of storage.

Analytical computation of stress intensity factor for multi-physics problems

This work presents a methodology for the analytical calculation of the stress intensity factor when the stress distribution on the crack surfaces is non-homogeneous. At first, a polynomial function is used to express the non-homogenous stress distribution. Subsequently, the principle of superposition of effects is applied, and the stress intensity factor is computed by multiplying each polynomial term by its respective geometric factor. Finite element fracture model is used to compute the geometric factor of the single polynomial grade. To explain the method, a spherical body is considered, with central and superficial cracks. Each geometric factor depends on a normalized geometrical parameter (the ratio between the crack length and sphere radius). The proposed methodology is applied to determine the stress intensity factor in the case of a crack driving force caused by diffusive fields, such as the concentration gradient in particles of electrodes active material in lithium-ion batteries. The methodology allows to speed up the fracture computation, then it is used to give electrode design guidelines to limit the fracture likeliness and mechanical degradation in lithium-ion batteries, as well as it is the basis for the development of algorithms assessing the capacity loss and the remaining useful life of lithium-ion batteries in real-time.

In situ preparation of nano cone-like structures on 3D printed titanium alloy implants via one-step femtosecond laser manufacturing for better osseointegration, anti-corrosion, and anti-fatigue

The poor surface conditions and osseointegration capacity of 3D printed Ti6Al4V implants (3DPT) significantly influence their performance as orthopedic and dental implants. In this work, we creatively introduce a one-step femtosecond laser treatment to improve the surface conditions and osteointegration. The surface characterization, mechanical properties, corrosion resistance, and biological responses were investigated. These results found that femtosecond laser eliminated defects like embedded powders and superficial cracks while forming the nano cones-like structures surface on 3DPT, leading to enhanced osseointegration, anti-corrosion, and anti-fatigue performance. Molecular dynamics simulations revealed the ablation removal mechanism and the formation of nano cone-like structures. These findings were further supported by the in vivo studies, showing that the FS-treated implants had superior bone-implant contact and osseointegration. Hence, the one-step femtosecond laser method is regarded as a promising surface modification method for improving the functional performance of Ti-based orthopedic implants.

Antimicrobial Hydrophobic SiO2-TiO2-PDMS Films: Effect of Indirect Ultrasonic Irradiation on the Synthesis Process

Film applications’ recent advances in the alimentary industry mainly focus on extending product shelf life. Researchers have investigated the use of nanomaterials as active packaging to shield food product contents from the outside elements and prevent bacterial development. In this context, the use of sonochemistry energy offers a friendly and efficient opportunity to obtain this kind of film. However, access to an ultrasonic homogenizer is limited because of the cost and accessories. In this work, a self-cleaning coating based on the SiO2-TiO2-PDMS composite was obtained by the sol–gel method coupled with indirect sonochemical energy. Two sonication reaction times were used to investigate its impact on the final composite’s chemical, morphological, and antibacterial properties. TEM and SEM techniques indicate an amorphous morphology and superficial cracks in SiO2-TiO2-PDMS films over aluminum foil. At the same time, AFM reveals a rise in rugosity with a value of Ra = 18.7 ± 2.47 nm, increasing the sonochemical reaction time. Non-significative changes by FTIR-ATR analysis were observed. The antibacterial evaluation was conducted, and the results indicate that both composites exhibited superior effectiveness. Specifically, the S40 film demonstrated a significant reduction in the growth of Gram-negative cells (E. coli, P. putida, and P. aeruginosa), with reductions ranging from 50% to 95%. In contrast, the reduction in Gram-positive cells (S. aureus) was less than 10%. These findings underscore the potential application of the SiO2-TiO2-PDMS film as active packaging.

Manufacturing evaluation of seven medical device companies during the production of a 3D-printed titanium pelvic implant

Powder bed fusion (PBF) technology has become a popular manufacturing method to fabricate custom metallic implants. This trend has generated some regulatory concerns because traditional developing guidelines are not suitable for three-dimensional (3D)-printed implants. This is due to the layered microstructure of additive manufactured parts that produces mechanical properties different than those of traditionally manufactured parts. The inappropriate choice of the process parameters and postprocessing methods can lead to fabrication errors that could negatively affect mechanical properties and dimensional accuracy. The objective of the study was to perform a preliminary evaluation of the quality of manufacturing provided by the medical device industry and identify the best 3D printing practices. We designed a pelvic bone reconstructing implant and asked seven companies to manufacture it in Ti6Al4V with PBF technology. We inspected some important aspects of the manufacturing quality of the prototypes received by evaluating geometrical precision and microstructural integrity in the surface and in the matrix, including a qualitative assessment of voids and grain morphology. Results demonstrated a great difference among the implant prototypes. Two companies proved to be superior and provided defect-free implants. The other five produced evidence of some defects including: geometrical deviations (maximum values of up to 5 mm); heterogeneous acicular grain morphologies; broken sections of lattice structures; and internal and superficial voids and cracks that could potentially compromise functional and clinical performance. To our knowledge, this is the first study analyzing the production of several custom implant additive manufacturers based on a geometrical and microstructural evaluation of the same pelvic implant fabrication. The imperfections found in some prototypes produced by companies certified to commercialize personalized implants highlight the urgent need for technical standards that regulate the safe development of 3D-printed implants. Further analyses are required to determine the actual clinical and mechanical consequences of such imperfections. The results also show that when additive manufacturing is adequately managed, it can be a valid manufacturing method to fabricate defect-free implants.

DETECTION OF STRUCTURAL PROBLEMS AND DAMAGES BY OBSERVATIONAL INSPECTIONS IN "CUMBA" AND "KABALTI" IN DIYARBAKIR

Suriçi Region in Diyarbakır is the part of the city surrounded by historical walls and home to many historical and traditional buildings. Keeping the architectural elements that make up the traditional texture of the region alive is important in terms of preserving the historical texture. Aim: This study was conducted to identify and evaluate the structural problems and damages in the current state of the ‘‘cumba’’ and ‘‘kabaltı’’, which are traditional architectural elements that have survived to the present day in the Suriçi Region. Method: In the study, some extant ‘‘cumba’’ and "kabaltı" were examined on site and field work was carried out. Structural problems and damages in the buildings were detected observationally. Detected damages are grouped under the following headings: damages caused by natural conditions such as temperature change or humidity, damages caused by material losses, and damages caused by user error. Problems and damages in the buildings examined during the field study were documented with photographs. Results: It was observed that the existing damages were concentrated in the stone and wooden materials used. Color change, surface distortion and deflection damage caused by climatic effects were detected. Loss of surface and binding mortar in stone material; in the wooden material, crusting, rotting and superficial crack damage occurred. Non-specific interventions in carrier systems have caused user-related damage. Conclusion: The ‘‘cumba’’ and ‘‘kabaltı’’, which are aesthetic parts of traditional city architecture, are architectural elements that should be protected. In this study, the structural problems and damages detected are included in the table created to contribute to the precautions to be taken, restoration applications or zoning regulations in the context of urban texture of these buildings, whose current condition and damages were determined by observational detection method.

Efficacy of Contrast Medium-assisted Imaging in Diagnosing Cracked Tooth

Introduction: This experimental study aimed to evaluate the efficacy of contrast medium-aided intraoral periapical radiographic imaging in the detection of cracked teeth and to determine optimal in-vitro compression force for crack detection. Methods: 27 extracted human lower premolar teeth were randomly divided into two groups: the control group, which was imaged using the conventional radiography and the experimental group which was imaged using a contrast medium (Iopamidol®). Both group were examined by transillumination to confirm the presence of a crack prior to imaging. A compression test using a Universal Testing Machine was used to induce the crack. Two dental clinicians blinded to the imaging technique evaluated the images and determined the presence or absence of cracks. Results: The force needed to produce a superficial crack ranges from 200N to 500N with a median compression force of 400N. The range of force to produce partial crack was 200N to 550N with the median force slightly higher than superficial crack which is 435N. The force to produce dentinal fracture ranges from 300N to 1100N with the highest median of 525N. The results showed that there were no visible cracks were detected in IOPA with/without contrast medium. Conclusions: The study did not find contrast-enhance IOPA to be effective in detecting cracks, but the study did establish the optimal median compression force values for inducing cracks which is between 400N to 525N. IOPA with contrast medium is not an effective diagnostic tool for cracked teeth compared to transillumination.

High Energy Density Welding of IN792 Ds Superalloy

Ni base superalloys are commonly employed in the industrial fields of aerospace, automotive and energy production due to their excellent mechanical properties and corrosion resistance at high temperature. Superficial defects and cracks may occur during both manufacturing process of components and their service life. High energy density welding techniques, electron beam (EBW) and laser beam (LBW) welding, can be used to create efficient repairs. Joints, obtained by EBW and LBW of IN792 directionally solidified (DS) superalloy, have been investigated to determine the presence of defects, and evaluate the mechanical properties related to specific microstructural features. The results showed that a pre-heating temperature (PHT) higher than 200 °C is always necessary to prevent the formation of hot cracks in the molten zone (MZ) and heat affected zone (HAZ). The process parameters have been optimized to get a good quality of the seams (lack of macro-defects, a good penetration depth and width). Some preliminary test of post-welding heat treatments (PWHTs) have been investigated to homogenize as far as possible the microstructure and the mechanical properties across the seams. The results obtained by the two techniques, EBW and LBW, have been compared and discussed.

Effect of phase transformation on the ductile to brittle transition behavior of Ti–V–Nb–Zrx body-centered cubic high-entropy alloys at elevated temperatures

Single-phase body-centered cubic (BCC) lightweight Ti–V–Nb–Zrx solid-solution alloys were fabricated by reducing the Zr concentration within the range of 0–5 at% to improve the mechanical properties of equimolar TiVNbZr alloy at elevated temperatures. The fabricated Zrx alloys indeed exhibited greater strength above 800 °C than TiVNbZr, but some special mechanical responses occurred at 800 °C: (ⅰ) superficial cracks with different lengths and amounts along the high-angle grain boundaries (HAGBs) on the compressed sample surface, and (ⅱ) near-brittle fracture of the tensile stress-strain curves. Based on the analysis of the deformed and undeformed surface, local stress concentration and phase transformation were responsible for the cracks and difference in compression behavior, and atmospheric oxygen, deformation localization and phase transformation were mainly responsible for the tensile fracture difference at 800 °C. Phase transformation promote stress dispersion, combined with better oxidation resistance, which make the Zr-containing alloys fractured via the transgranular mode in tensile test. In particular, the Zr3 alloy exhibited work hardening and tensile ductility. Based on the tensile and compression properties of the Zrx alloys, it was found that at RT and 600 °C, atomic size difference (δ) governed alloy strength; from 800 to 1000 °C, δ and melting temperature (Tm) co-operatively governed alloy strength; at 1200 °C, alloy strength was independent of δ, but dependent on Tm. The fabricated Ti–V–Nb–Zrx alloys have medium mechanical properties but a small strength loss at high temperatures, and are suitable for various RT deformation processing methods.

Analytical computation of stress intensity factor for active material particles of lithium ion batteries

The stress intensity factor is a widely used parameter in linear elastic fracture mechanics to assess the stress field near the crack tip, and it is usually defined as the product between the remote stress, the square root of the crack length, and a geometric factor depending on the geometry of the test specimen, the size and location of the crack. However, this well-established expression cannot be used in case of non-constant stress distribution on crack surfaces, typically resulting from diffusive field. This work presents an analytical procedure to compute the stress intensity factor due to any kind of stress distribution that can be expressed as a polynomial. Firstly, the non-constant stress distribution is expressed as a polynomial. Then, the stress intensity factor is computed according to the principle of superposition of effects, as the sum of the stress components of each single polynomial grade and the corresponding geometric factors. The geometric factors for sphere with central and superficial cracks are determined using a finite element model, and closed-form expressions for these geometric factors are provided as functions of a normalized geometric parameter. These functions can be used in case of any stress loading and spherical geometry. The analytical procedure is specifically applied to assess the stress intensity factor caused by stress resulting from lithium diffusion in active material particles of lithium ions batteries electrodes. The results are compared with those obtained using a multiphysics finite element fracture model, showing good agreement and demonstrating the accuracy of the proposed analytical procedure. Then, the procedure presented in this work enables avoiding expensive multiphysics simulations and can be used to develop fast, accurate, and computationally efficient lithium ion batteries degradation models for the online estimation of the capacity decay with charge/discharge cycles.

On the use of non-destructive testing for the measurement of self-healing in lime-based mortars

The study of self-healing construction materials has increased in popularity over the last couple of decades. Nevertheless, most research has predominantly focused on cement-based materials and work on other type of binders such as lime-based mortars remains rather limited. Despite the multiple testing methods available to assess the efficacy of self-healing, these techniques are not always suitable for materials of different mechanical strengths and behavior. In order to further expand the knowledge on self-healing beyond the high-strength cement-based materials, self-healing has been studied on low-strength binders. Here it is shown how the use of non-destructive testing with ultrasonic pulse velocity (UPV) can help determine the self-healing capacity of low-strength mortars. A hydrated-lime:metakaolin mortar mix and cement mix were cast and damaged after 7 days of curing. The samples were damaged under compression using 70 % of the average compressive strength. Before and after damaging, the samples were tested by UPV and superficial cracks were studied by microscopy. The samples were then placed under wet-dry cycles of 1 h wet/23 h dry or submersion for 28 days and tested again. As healing proceeded, an increase in the UPV was observed. Microscopy measurements confirmed visually the self-healing of cracks in all samples. The mechanical strength of both formulations was similar after healing when compared to a non-damaged and non-healed sample. These results show the necessity for techniques that are tailored to the mechanical nature of the different studied materials and opens up the possibility of further investigating self-healing in a wider variety of construction materials.

Effects of Iron Salts on Demineralization and Discoloration of Primary Incisor Enamel Subjected to Artificial Cariogenic Challenge versus Saline Immersion

This study aimed to assess the effects of iron salts on the demineralization and discoloration of primary incisor enamel subjected to artificial cariogenic challenge (ACC) versus saline immersion. In this in vitro experimental study, 90 primary incisors were evaluated in 10 groups (n = 9). Five groups were subjected to ACC, and the other five were immersed in saline. Ferrous sulfate, ferrous fumarate, ferrous ammonium citrate, and ferrous gluconate were added to both saline and cariogenic solutions. The solutions were refreshed every 48 h. After 14 days, the teeth were removed from the media and their demineralization was inspected via scanning electron microscopy (SEM). Energy-dispersive X-ray spectroscopy (EDX) was also performed. The color of the specimens was measured at baseline and after the intervention using the Vita Shade Guide. Data were analyzed by the Kruskal-Wallis test, one-way ANOVA, and Tukey's test. The color change of specimens subjected to ACC was greater than the color change of those in saline (p = 0.083). The teeth subjected to ACC showed greater iron uptake than did those in saline (p = 0.023). SEM assessment revealed a regular pattern of enamel prisms, with some broken prisms and superficial cracks in the teeth immersed in saline. The teeth subjected to ACC showed numerous fractures and cracks, which were greater in the ferrous sulfate group. Immersion in ACC increased the structural porosities and led to greater iron uptake and, consequently, higher discoloration. The maximum structural changes and subsequent staining were noted in the ferrous sulfate group, followed by ferrous ammonium citrate, ferrous fumarate, and ferrous gluconate.

Parametric study of the correlation between location and size of superficial cracks in the deflection of traditional tiles based on finite element analysis

Superficial cracks are one of the common defects in the manufacturing of traditional ceramic tiles. Such defects do not only damage the appearance of the product, but also affect their mechanical behavior. Understanding the correlation between superficial cracks and deflection is key for the traditional ceramic tile industry. However, the related bibliography is very rare, and its importance is systematically ignored during design and manufacturing. In this work, we investigate the impact of the location and size of superficial cracks over the deflection of traditional ceramic tiles. A technique based on FEA (finite element analysis) is validated through experimental data and used to undertake a statistical, parametric research. The study shows that location and depth of the defect have an exponential cross-correlation over deflection and could be characterized together through a single surface. On the contrary, the width and sharpening of the defect barely interfere.

Behaviour of mass timber members subjected to consecutive blast loads

This paper presents the results of an experimental and analytical investigation into the behaviour of full-scale glued-laminated timber (glulam) beams and cross-laminated timber (CLT) panels subjected to consecutive shock-tube-simulated blast loads. Superficial crack development was observed in the glulam specimens even when loaded within their elastic range. However, these cracks did not appear to affect the overall stiffness and strength of the specimens, as proven through subsequent loading and verification of the experimental resistance curves. Extensive propagation of rolling shear damage was prevalent within the transverse layers of the CLT specimens once flexural failure initiation occurred. Following significant rolling shear damage, the composite nature of the CLT panels were observed to degrade, corresponding to a loss of stiffness and strength. An equivalent single-degree-of-freedom (eSDOF) modelling methodology, capable of taking into consideration the dynamic behaviour of both specimen types and damage accumulation due to subsequent loading, is presented and validated using the experimental test data.

Shockwave and spallation in silver and other materials by sub‐ns laser pulse at 1016 W/cm2 intensity

AbstractThe laser spallation effect due to intense shockwaves caused by a brief and intense laser pulse irradiating a target surface, 2 mm thick, has been investigated for silver and other materials. For 300 ps IR laser pulse, at intensities of the order of 1016 W/cm2, the shockwave may produce deformations of the back‐face in ductile materials, such as Ag, Cu and Al. In heavy materials with high tensile strength, such as Ta, the shockwave produces cracks in the bottom of the laser crater but not deformation in the back‐face, while in brittle materials, such as monocrystalline Ge, it produces only superficial cracks and flaking, but not deformation and spallation of the back‐face. In thick polymeric materials, such as high‐density polyethylene, the ablated crater shape is well defined and the shockwave is strongly damped, and no deformation has been observed in the back‐face. The laser ablation yield and the ion acceleration in the backward direction have been measured by mass lost and time‐of‐flight measurements. SEM microscopy of the different irradiated targets, showing details of the crater size, edges, flaking and deformation in the back‐face, useful for a discussion on the shockwave propagation and shock pressure calculation, is presented.

Determination of Cyclic Load Limits for Plasma‐Sprayed Copper Tracks on Material Extrusion‐Based Printed Surfaces

Herein, copper particles are deposited on additively manufactured surfaces and investigations are performed to determine the mechanical properties and the impact of copper tracks on the surfaces. The basic investigation covers quasistatic tests, namely, tensile and three point bending, for three different printing orientations and two infill variations (+45°/−45° and 0°/90°), which shows no remarkable differences. In addition, a copper track is sprayed via atmospheric pressure plasma spraying (APPS) onto the polymeric samples and characterized regarding hardness and electric conductivity. Furthermore, a specific application for the copper track on the polymer substrate is recreated by a cyclic three point bending with a novel sample geometry (T‐shaped). The sprayed copper track has 60% of the hardness and 40% of the indentation modulus of bulk copper. Depending on the substrates’ topography, the electric conductivity varies from 7% to 18% of bulk copper. The lifetime of the copper track (i.e., conductivity) is strongly dependent on the deformation and the fracture of the polymer underneath. The underlying failure mechanism is triggered either by the topography of the polymer substrate or as a consequence of the damage in the copper track, leading to superficial cracks in the polymer surface.

TOWARD QUALITY IMPROVEMENT OF ELECTRODEPOSITED HARD METAL Mo/Cu COATINGS: SUITABILITY FOR CIGS SOLAR CELL APPLICATIONS

Bright and thick molybdenum (Mo) coatings with good purity and adhesion were electrodeposited on Copper (Cu)-supported Mo/Cu, which is based on aqueous bath containing molybdate ions. All the electrodeposition process was carried out at a fixed duration of 1200[Formula: see text]s, according to five different current densities 400, 450, 500, 550, and 600[Formula: see text]mA/cm2 at room temperature [Formula: see text]C. Metallic Mo deposits structure may correspond to that of body-centered cubic (bcc) structure. The lattice parameter, residual stress, crystallites size, micro-strain, and dislocation densities were inferred from Mo (110) texture. Synthetized Mo coatings have relatively same rough surface morphology (50–60[Formula: see text]nm) characterized by some superficial cracks, small uniform grain size having change less than 14%, low residual stress and a good adhesion, a good conductivity, and an appropriate purity that has reached 94 (Mo %wt.). We have deduced that structural and electrical properties of Mo deposits did not obey the existing cracks at surfaces. One important result was that the most cracked and unstressed coating obtained at 450[Formula: see text]mA/cm2 was the same coating having the best purity (Mo %wt.), the best conductivity, and highest free electrons mobility. We suggest that appearance of cracks is closely related to electrochemical facts such as the deposition rate and hydrogen evolution reaction process since cracks decrease beyond 450[Formula: see text]mA/cm2. A good correlation between each investigated property was, also, established and discussed.

Synthesis and Characterizations of Eco-Friendly Organosolv Lignin-Based Polyurethane Coating Films for the Coating Industry.

Three different formulations of bio-based polyurethane (PU), varying the weight ratio between Organosolv lignin and a commercial isocyanate, were synthesized. The coating formulations were characterized by SEM, pyrolysis-GC/MS, FTIR spectroscopy and FTIR mapping, which confirmed the successful formation of urethane bonds between commercial isocyanate and hydroxyl groups deriving from lignin. The coatings were applied on beech wood samples to measure color and contact angles, and eventually FTIR mapping of the coated wood samples was performed. FTIR mapping is an interesting tool to monitor the distribution of PU chemical bonds on the coating surface and to evaluate the homogeneity of the applied coating films. Increasing the lignin content of the PU coatings results in more red-yellow and darker tones, while the commercial PU coating is transparent. For a higher lignin concentration, the solid content as well as the weight gain of the applied coatings increase. A higher percentage of lignin in the prepared PU formulations leads to superficial cracks and therefore higher coating permeability compared to the commercial PU, but the prepared lignin-based PU coating still makes a raw wood surface significantly more hydrophobic. Apparently, additives such as film-formers with low surface tension to counteract cracks’ formation are necessary to improve the performance of lignin-based PU coatings.