Adhesive Beads Research Articles

Open time studies of cold curing polyurethane adhesives using a standardized spatula test setup suitable for near-production conditions

The presented studies introduce a new set-up and method to analyse the maximum open time of cold curing adhesives in a production environment. By using this new set-up, a manual spatula test, Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR) and a rheological method, the curing reaction of two cold curing two component polyurethane adhesives, were investigated. Furthermore, the effect of different joining times on the bonding behaviour were investigated using single lap shear samples.The lap shear tests showed that the prior problem for industrial applications is the dimensional accuracy rather than the adhesion to the substrates as all samples showed cohesive or substrate near cohesive failure even when joined after the maximum open time. All used methods showed a coherent curing behaviour for both adhesives. However, the derived times as well as their accuracies vary depending on the used method. Using the easy manual spatula test, the open time is determined by the sensory feelings of the testing person while pressing a wooden spatula into the adhesive bead and is often used in industrial applications. However, the accuracy lies only within 10–20 s especially for slow curing adhesives. In comparison, the ATR-FTIR method, which is based on the decrease of the isocyanate group during the reaction, showed shorter times, whereas longer times were determined by observing the complex viscosity increase of the rheological measurements. Even though the ATR-FTIR and rheological measurements showed reproducible times due to the required laboratory environment and testing procedure, they are therefore not suitable for production conditions. As the introduced new method is based on the manual spatula test, it is suitable for the production environment with the advantage of a good reproducibility. Furthermore, with this method decreasing maximum open times were observed for increasing bead cross sections.

Formulation and Evaluation of Mucoadhesive Beads of Dexamethasone

The goal of the current study was to formulate and evaluate mucoadhesive Dexamethasone beads to significantly lengthen the duration of the drug's stay in the GI system to treat Crohn’s disease. Dexamethasone is a corticosteroid that acts as an anti-rheumatic and anti-inflammatory. To decrease the dosage frequency Dexamethasone adhesive beads were formulated for Intimate contact with the underlying absorption surface is made possible by a prolonged stay at the location, which enhances the drug's therapeutic effectiveness. In the current study, calcium chloride and aluminium chloride were utilised as cross-linking agents to create Dexamethasone mucoadhesive beads employing adhesive polymers like sodium alginate, HPMC, and Eudragit L-100. The prepared beads' entrapment efficiencies ranged from 57.15 to 99.16%. Regarding entrapment effectiveness, particle size, surface properties, and in-vitro drug release experiments, the impact of bioadhesive polymers and cross-linking ions was assessed. The MPS-7 delayed the drug's release for 12 hours, which may be related to the cross-linking agent aluminium chloride. According to drug release kinetics, all of the formulations were more linear concerning zero order (r2=0.99) than concerning first order (r2=0.751 to 0.828). Super Case 2 Transport was discovered to be the precise release mechanism.

Generative Adversarial Networks for Data Augmentation in Structural Adhesive Inspection

The technological advances brought forth by the Industry 4.0 paradigm have renewed the disruptive potential of artificial intelligence in the manufacturing sector, building the data-driven era on top of concepts such as Cyber–Physical Systems and the Internet of Things. However, data availability remains a major challenge for the success of these solutions, particularly concerning those based on deep learning approaches. Specifically in the quality inspection of structural adhesive applications, found commonly in the automotive domain, defect data with sufficient variety, volume and quality is generally costly, time-consuming and inefficient to obtain, jeopardizing the viability of such approaches due to data scarcity. To mitigate this, we propose a novel approach to generate synthetic training data for this application, leveraging recent breakthroughs in training generative adversarial networks with limited data to improve the performance of automated inspection methods based on deep learning, especially for imbalanced datasets. Preliminary results in a real automotive pilot cell show promise in this direction, with the approach being able to generate realistic adhesive bead images and consequently object detection models showing improved mean average precision at different thresholds when trained on the augmented dataset. For reproducibility purposes, the model weights, configurations and data encompassed in this study are made publicly available.

The formation of residual stresses in the bonding of automotive glass

This article discusses the formation of residual stresses during the assembly of automotive glass. The influence of various parameters of the adhesive bead on the spatial deviations of glasses during their installation is shown. Currently, the glass assembly technology involves filling the gap between the automotive glass and the car body with a glue roller. It has been established that the formation of residual stresses is influenced by the width and thickness of the glue roll, with a minimum width of the glue roll during drying, a discontinuity of the glue joint along the contour is possible, and with a maximum width, unacceptable residual deformations occur in the glass, which lead to cracks.

Improved glass bonding with plasma treatment

Bonding of automotive glass is generally performed with 1C PUR adhesive on a primed ceramic frit or naked glass surface. The aim of this research was to replace the chemistry of the primer with an atmospheric pressure plasma treatment (APPT) with compressed air for cleaning and activation directly before bonding. Characterization of the glass surface was performed with surface energy through contact angle, XPS, TOF-SIMS and adhesive peel bead test. The results show that APPT treatment can clean the surface, improve the wetting, improve the bonding but reduce the number of non bridging oxygen for the adhesive to bond to. The highest measured spot temperature of the glass during APPT was measured up to 270 °C, but the temperature was depending on process parameters. A reduction in non bridging oxygen was also seen during heating of the reference glass at 100 °C. A further reaction was seen when measured after a 550 °C heating. A modified APPT treatment with deionized water as precursor was used. The results show that the APPT with water does not lower the level of non bridging oxygen and the bonding was further improved.

Studies on Rebamipide Loaded Gastroretentive Alginate Based Mucoadhesive Beads: Formulation & In-vitro, In-vivo Evaluation

Introduction: Oral route is the most common and convenient route to deliver the drug. Many oral drug delivery systems were developed to improve drug bio availability; gastro retentive drug delivery system is one of them. Gastroretentive drug delivery system is the system in which a drug can remain in the gastric region for several hours in order to prolong its gastric residence time. The purpose of this work was to develop and evaluate rebamipide loaded gastro retentive alginate based muco adhesive beads. Materials and Methods: Rebamipide loaded alginate beads were prepared by ionotropic gelation and polyelectrolyte complexation method. Prepared beads were characterized for IR, DSC, SEM and evaluated for dissolution and stability studies. Results: The FTIR spectra revealed that there were no interaction between drug and excipients. The particle size analysis showed that beads with 3% of sodium alginate were spherical in shape. The mucoadhesion study reveals that as concentration of alginate and carbopol 934 increases percentage of mucoadhesion also increases. Conclusion: From in-vivo study it was concluded that the prepared formulation showed better control on ulcer than that of pure rebamipide. Rebamipide was successfully formulated as gastroretentive floating and mucoadhesive alginate beads by using ionotropic gelation and polyelectrolyte complexation method. Key words: Rebamipide, Gastroretentive, Alginate beads, Mucoadhesion and Carbopol 934.

Process Simulation and Automatic Path Planning of Adhesive Joining

Adhesive joining is frequently used in the automotive industry. In the pursuit of reducing weight, adhesive joining is important due to the possibility of joining different types of materials. The process is often automatised in order to reduce cycle time. In this paper we aim to present a novel framework that includes detailed process simulation and automatic generation of collision free robot paths and in this way improve the quality of the joint and reduce both cycle time and processing time. To verify the simulations, the properties of the adhesive bead have been compared to experiments with good agreement.

Adhesives under pressure: How compressible are they?

The properties of a bonded structure largely depend on the quality of the industrial bonding process. The latter comprises the conveying the adhesive from the drum, the pipe system, the dispensing, and the application of the adhesive bead. Whilst detailed knowledge about the mechanical properties of cured adhesives is readily available, relatively little is known about the non-cured adhesives whilst they are being processed.

Degenerate peptide recognition by Candida albicans adhesins Als5p and Als1p.

Candida albicans and Saccharomyces cerevisiae expressing the adhesins Als5p or Als1p adhere to immobilized peptides and proteins that possess appropriate sequences of amino acids in addition to a sterically accessible peptide backbone. In an attempt to further define the nature of these targets, we surveyed the ability of yeast cells to adhere to 90- micro m-diameter polyethylene glycol beads coated with a 7-mer peptide from a library of 19(7) unique peptide-beads. C. albicans bound to ca. 10% of beads from the library, whereas S. cerevisiae expressing Als5p or Als1p bound to ca. 0.1 to 1% of randomly selected peptide-beads. S. cerevisiae expressing Als1p had a distinctly different adherence phenotype than did cells expressing Als5p. The former adhered in groups or clumps of cells, whereas the latter adhered initially as single cells, an event which was followed by the build up of cell-cell aggregates. Beads with adherent cells were removed, and the peptide attached to the bead was determined by amino acid sequencing. All adhesive beads carried a three-amino-acid sequence motif (tau phi+) that possessed a vast combinatorial potential. Adherence was sequence specific and was inhibited when soluble peptide identical to the immobilized peptide was added. The Als5p adhesin recognized some peptides that went unrecognized by Als1p. The sequence motif of adhesive peptides identified by this method is common in proteins and offers so many possible sequence combinations that target recognition by the Als proteins is clearly degenerate. A degenerate recognition system provides the fungi with the potential of adhering to a multitude of proteins and peptides, an advantage for any microorganism attempting to establish a commensal or pathogenic relationship with a host.

Multiparticle adhesive dynamics: hydrodynamic recruitment of rolling leukocytes.

The slow rolling motion of leukocytes along the walls of blood vessels mediated by specific receptor-ligand adhesion is important in inflammation and occurs in postcapillary venules over a wide range of wall shear stresses and vessel diameters. The ability of hydrodynamic collisions between cells to induce capture of free-stream leukocytes to a selectin-bearing surface under shear flow was studied experimentally by using a cell-free assay. It was found that carbohydrate-coated spherical beads, representing model leukocytes, tend to attach to the adhesive wall 4-5 cell diameters up- or downstream of a slowly rolling or stationary adhesive bead. A key feature of such "hydrodynamic recruitment" is that only glancing, indirect collisions occurring close to the plane will result in downstream attachment. A direct numerical simulation of cell capture and rolling that includes multiparticle hydrodynamic interactions is shown to reproduce the observed behavior accurately. The theory predicts that hydrodynamic recruitment will occur in the absence of buoyancy effects and over a range of shear rates, suggesting that the mechanism may be important in vivo. This theory is supported by measurements of leukocyte capture in vivo using the hamster cheek pouch model.

Analytical modelling of the automated dispensing of adhesive materials

The integrity of joints is a critical issue in structural bonding and the shape of adhesive beads needs to be consistent. The right amount of adhesive must be dispensed and to ensure this, the disp...

Use of vision in dispensing control and inspection of adhesives

SUMMARYA prototype system utilizing a vision technique to monitor the parameters of adhesive beads or sealants is presented. The system uses a structured light technique to investigate adhesive beads and extract information about the shape of the bead from binary images. The geometrical model of the bead, the relationship between this model and the shape of a line of light on the image are investigated. The models for calculating the parameters of the bead and the height of the camera are analyzed. Control strategies are suggested.

Adhesives as an aid to the assembly of aerospace components

It is proposed to use thick adhesive films to assist in the assembly of sheet metal components into sub-assemblies for the aerospace industry. In this application the adhesive is not used to bond the components together structurally but is used to accommodate misfit between components due to their flatness tolerance, and thereby subdue the burns that are formed when the components are drilled in preparation for riveting. This short paper discusses initial results showing how the adhesive film prevents the formation of burrs. It also reports the behaviour of dispensed adhesive beads when filling the tapered gaps generated in the varying geometry associated with the out-of-flatness of the components. The experimentation shows that surface tension effects result in non-linear variations in the filling of such tapered gaps.

A vision system for the on-line quality control of adhesive beads

Abstract A new application for a structured-light technique — to monitor adhesive beads — is presented. This sensing system, which is based mostly on software, is used to investigate adhesive or sealant beads, on line, while they are dispensed and achieves a very short cycle time. The programming concept, which provides a powerful tool for many process-control applications, is described here in the process of automatically dispensing adhesives and sealants. The performance of the system is analysed and suggestions for future development are offered. The image processing methodology will enable a variety of quality assurance problems to be addressed in the automatic extrusion of adhesives and sealants.

A vision system for the on-line quality control of adhesive beads

A vision system for the on-line quality control of adhesive beads

Permissive effect of substratum contact on DNA synthesis in concanavalin A-treated lymphocytes.

The effects of contact with a solid surface (in the form of adhesive microcarrier beads (Cytodex)) on the induction of proliferation of human blood lymphocytes after exposure to concanavalin A (Con A) were investigated. The duration of the lag phase preceding DNA synthesis was identical in the presence and absence of beads. The kinetic course of initiation of DNA synthesis was exponential but with different rate constants both in the presence and in the absence of beads during the first 4 days of the culture period. Cytodex exerted its effect by increasing the proportion of cells initiating DNA synthesis in response to Con A. To elucidate whether lymphocytes responded to Con A exposure in a dose-dependent manner, cells were seeded at different concentrations and exposed to Con A for different times. At 36 and 48 h after start of stimulation the proportion of cells synthesizing DNA increased with increasing cell number in the cultures. In contrast, the portion of cells synthesizing DNA was markedly decreased at high cell densities 60, 72 and 96 h after start of stimulation. In the presence of microcarrier beads, however, the proportion of cells synthesizing DNA was proportional to the cell number in the cultures also after 60, 72 and 96 h.