With bone injuries such as bone fractures, it is often necessary to fix individual parts of the bone. Thus, the bones grow together and can be strained more quickly. By default, screws and other implants are used so far. The partners of the research project "bone adhesive" now follow an innovative and mild approach. They pursue the development of a biopolymer, which can be applied to the bone parts and bonds these together. The porous polymer is replaced over time by regenerating bone material and the resulting degradation products can be disposed by the body. The procedure should be possible even with complicated fractures in the low-load range. The aim is further to reduce the risk of post-operative complications using a minor intervention and to avoid a second intervention for implant removal.
The use in the human body poses high demands on the biopolymer. The material must be biocompatible without toxic components or toxic degradation products. It also needs to adhere very well in the presence of body fluids such as blood and synovial liquid. In order to ensure all this, the project is divided into three phases: After the development of appropriate product candidates, compatibility assessments are carried out in cell cultures. In the last phase, investigations will take place in the animal model.
Besides the Institute of Orthopaedic Research and Biomechanics at the University of Ulm and the German University of Cairo, four small and medium-sized companies from Germany are involved in the project - FABES Forschungs-GmbH (Munich), InnoTERE GmbH (Radebeul), provenion GmbH (Kirchseeon) and Unavera ChemLab GmbH (Mittenwald). The project is funded by the German Federal Ministry for Economic Affairs and Energy as part of the Central Innovation Program for SME. The project was initiated by the IBB Netzwerk GmbH within its cooperation network "BioPlastik".
Silicone adhesives have now received a wide acceptance for use in healthcare applications
Soft skin adhesive gels are particularly used for wound care applications, especially for wound dressings.
The gel technology:
As a result, dressings using soft silicone favorably impact the time required for dressing change,decrease
changing frequency, alleviate pain management, and result in overall reduction in cost.
Reduced pain upon removal from skin is a desirable adhesive property for wound care applications, but it can only be achieved if adhesion to skin is decreased, which could be detrimental if the adhesiveis used to hold a medical device in place.
In order to hold a medical device in place on a long period of time, PSA are preferred to silicone gels. Viscoelastic properties of such adhesives explain the strong adhesion to the skin of the medical device, without lifting or falling off for long periods of time. However, such adhesives have high adhesion to skin values making them difficult and painful to remove.
During the present lecture, we would like to draw attention to the design of the silicone adhesives to enhance patients’ benefits and devices’ performances. For this purpose, we focused on a viscoelastic approach. We will present characterizations of different silicones relating to these characteristics. Based on the viscoelastic window concept, our approach aimed at defining innovative solutions to adapt to who requires a strong adhesion to hold a medical device in place, while being able to remove it gently a with minimal patient trauma.
Presently, silicone adhesives are far from having developed all their potential at the service of patients and innovation is under way for the design of new constructions
Silicone adhesives are widely known in many industrial applications. Predominantly as sealants in the construction industry, but also in many other areas, e.g. oil pan sealants in automotive applications or oven door adhesives in home appliances.
A set of distinct properties, such as high thermal-, UV- and weathering resistance or chemical neutrality, make them indispensable as high performance materials.
Not as widely recognized they also play a vital role as sensitive, skin friendly adhesives in modern, advanced wound care.
This talk will present a general overview on advanced wound care applications, focusing on the specific properties and use of silicone elastomer adhesives and their advantages over traditional adhesives.
Without doubt adhesive bonding is considered the preferred joining technology in modern light weight design. Although state of the art industrial adhesives are considered as high-tech products which if used correctly allow zero fault production some bonded joints fail generally due to adhesive application errors. According to ISO 9001 adhesive bonding is considered a "special process" because there is no non-destructive test for adhesive application processes that can test with 100% certainty for any errors. Therefore all possible errors throughout the manufacture of the finished product must be ruled out by "managing" the whole production process. But ISO 9001 has its limitations as it merely stipulates the minimum requirements of a quality management system not of the bonding process. The new DIN 2304 is filling this gap by defining the structures of an "organization" - namely a company using adhesives - required for correct application of the technology. At the end its implementation minimizes faults, saves money, generates trust, promotes the wider use of adhesives, and sustainably improves the image of adhesive bonding.
The thorough investigation of adhesive bonding has led to a wide industrial application. Especially for structural bonding the knowledge of the mechanical behaviour is decisive for the design of reliable joints. A new application is often validated by a set of experimental tests considering e.g. processing parameters, material and surface of the adherends as well as in-service loads and influences like ageing. The huge number is cost- and time-consuming. The authors wanted to find a new method to investigate adhesive bonding which bridges the gap between investigations on a molecular scale and macroscopic destructive testing.
The analysis of the micro-mechanical behaviour of adhesives under load is particularly challenging as the adhesive is geometrically and optically hidden by the adherends. Surface based methods for the determination of strains are therefore limited to the rather small fraction of the visible adhesive surface. In this work the application of in-situ computed tomography and particle tracking is investigated as a method to analyse the micro-mechanical behaviour of adhesive bonds. The method is described and its application is discussed. The volumetric displacement field of lap shear specimen is investigated in depth by in-situ computed tomography and particle tracking (see Figure). The influence of ageing on the internal displacement field is shown.
In civil engineering bonded glass facades are called “structural-glazing” (SG) or “structural-sealant-glazing” (SSG) facades. Due to architectural requirements the surfaces of these facades should not be optically destroyed by fixings such as metal fasteners. Hence there is a need for thin jointings. Typically structural silicone sealants are used for this purpose. In the following only silicone adhesives are considered while the presented mechanical treatment can be applied to other adhesives as well.
Due to governmental building regulations conservative design methods in terms of simple hand formulas (“mickey-mouse” formulas from ETAG002) with a high global safety factor have to be used. Ongoing research up to now showed the silicones to have constitutive equations which include hyperelasticity (nonlinear stress-strain behavior), temperature and strain-rate dependence. When undergoing cyclic loadings, first tests showed the silicone-adhesives underlie the “Mullins-Effect”.
Up to now, research in civil engineering focused on determining the material law for a nonlinear spring element of the Neo-Hooke or Mooney-Rivlin type based on structural silicone test data. Temperature or strain-rate dependence as well as damaging effects cannot be modelled in this fashion. In aero-engineering however more sophisticated models, based on the generalized Maxwell element, have been used successfully for the description of the rheology of poly-urethanes or other elastomers.
In this talk a generalized Maxwell-element for the description of the rheology of structural silicone adhesives will be introduced. It is given a short discussion on the process of determining the model and its parameters. In a concluding remark on the properties of the model future enhancements of this description of structural silicone adhesives will be shown.
Since the invention of the carboxyl terminated butadiene acrylonitrile (CTBN) by BF Goodrich and its introduction under the trade name Hycar (today Hypro by CVC) CTBN and their adducts are one of the most commonly used toughening agents for structural 1C epoxy systems.
Although of the success story of CTBN there are limitations of the use of CTBN looking on epoxy systems of the new generation for structural bonding system, electronical application and light weight applications, including composites and prepregs. Limitations among others are handling issues (high viscous materials), minor suitability for 2C epoxide systems and limited service temperatures in final applications.
This makes us thinking to design our own elastomers to make a more precise modification possible. The first results are the latest resins from our Polycavit® range like Polycavit® 3511 and Polycavit® 3550. The difference is the specific design of the elastomer while persuading two tracks. Both tracks enable the formulator with a higher degree of freedom to formulate, means he gets the same performance as with CTBN adducts but with less. Since the Polycavit® 3511stands for the latest generation of elastomer adducts the Polycavit®3550 describes a new family of a functionalized elastomer being compatible to an epoxy resin matrix.
We will give an overview of the materials in use for toughening of (1C-) epoxy systems and will show that in regard of the nature of the base resin, the structure of the elastomer and functionality distribution of the elastomer the final properties of a (1C-) epoxy system can be highly improved. Finally we will give a small outlook of ideas while cross thinking to what is already done in other applications and “simply” needed to be adopted.
Cardolite has developed new epoxy curing agents, called phenalkamine and phenalkamide, based on Cashew Nutshell Liquid (CNSL) technology for 2K-epoxy adhesives applications. These products are designed to meet the challenging industry requirements including zero VOC, solvent free, labeling friendly, fast processing, increased durability, and contribute to sustainability.
Phenalkamine and phenalkamide curing agents have a high bio-content and are best suited for structural and construction epoxy adhesives that require fast strength development at low temperature, excellent mechanical strength, durability, surface tolerance, and label friendly products while free of phenols and solvents. Phenalkamide is a chemically modified hybrid material that can provide longer pot-life and excellent bond strength over various substrates.
In this paper we will presents their adhesive performances in clear and formulated systems along with excellent durability under various conditions.
To a certain extent, adhesive bonding of measurement equipment is very common in science and technology, e. g. adhesive bonding of small scale strain gauges. Comparing to that, the adhesive bonding of the entire equipment for a fully autonomously pile driving monitoring of an impact driven large scale foundation structure of about 60 m length and 6 m in diameter for an offshore wind farm is a completely new dimension of application.
Several offshore wind farms are currently under construction or in the finishing state in the North- and
Baltic Sea. To protect the marine environment from extreme load noise caused by impact pile driving of the
large-scale foundations, different noise reduction techniques are in use. Geotechnical engineers of the TU
Braunschweig were investigating combined methods for reducing that noise , and in 2014 they had the
opportunity to install full measurement equipment for the investigation of dynamic pile deflections during
pile driving alongside the current construction of an offshore wind farm in the German North Sea.
Due to certification issues conventional methods of fastening like screwing or welding were not permitted at this stage. Instead, adhesive bonding of the full equipment (sensors, cables, shielding, recorder/computer) was successfully applied and withstood impact driving with several thousand blows of up to 1,200 g (1,200 times earth acceleration). The author would like to present the concept and preceded testing of the adhesive bonding applied within the research project “triad” (funded by German BMWi, FKZ 0325681).
Electrically and thermally conductive adhesives are epoxy or acrylate resins filled with metallic fillers. Electrically conductive adhesives are often used as a more effective alternative to conventional soldering. They are particularly suitable for making electrical contacts on temperature-sensitive substrates, as their curing temperature lies clearly below soldering temperature. In addition the adhesives are much more flexible than solder and are therefore better able to withstand vibrations. A further advantage over soldering is that conductive adhesives are lead- and solvent-free.
Electrically conductive adhesives have typically been formulated using silver spheres, or beads, for the conductive filler. As a general rule, the higher the concentration of filler, the better the conductivity. Unfortunately this also contributes to higher costs due to the high price of silver. Conventional silver bead fillers frequently led to problems during the dispensing process. The adhesives were too viscous, and frequently trapped air bubbles. During production, it was not uncommon for dispensing equipment to clog and require maintenance.
New generation electrically conductive adhesives contain improved selections of metallic filling materials, notably silver flakes. Newly developed conductive adhesives incorporating silver flake fillers are now very well suited for jetting and screen printing. Dispensing nozzles and valves operate without clogging, which eliminates down-time and increases manufacturing productivity.
Pivotal for the electrical conductivity is the filling grade, as the conductivity of the electrical current occurs through direct contact of the metal particles.
The second most important contributor to conductivity of an adhesive is the geometry and grain size distribution of the filling materials.
The particle size distribution of the silver fillers directly influence the electrical conductivity and thus the electrical resistance of the entire system.
Apart from the particle size distribution, the geometry of the particles also influence the condutivity. Decisive is the average number of contacts between the particles. Therefore, particles with corn flake shape and surface irregularities are preferred.
The total conductivity of an electrically conductive adhesive matrix results from the individual contact resistance between the metallic filler particles. Uncured residues within the matrix and impurities of the metallic filler can lead to oxide layers on the metal particles, resulting in higher resistance and lower conductivity values. To minimize filler impurities, precious metals such as silver (or gold) are used as filler materials.
Another aspect which has a large impact on the conductivity of any adhesive is the curing process. An evenly cured epoxy adhesive reduces the strain in the matrix and also lowers dissimilar resistance in the adhesive layer. Thermal curing of the adhesive produces crosslinking of the base polymer in which the metal particles are embedded. If the curing process is insufficient (i.e. too low curing temperature or too short curing time) the crosslinking of the base polymer is insufficient. The base polymer remains too soft, which can result in shifting of the metal fillers when influenced by external mechanical forces.
The conductivity of the adhesives can also be influenced by climatic influences. Especially humidity and exposure to higher temperatures can influence the conductivity.
Functional adhesives are advanced materials that offer more than just bonding things together. Responding to the specific needs of an application, they feature additional physical properties that help to either enable or inhibit the transition of heat, light, electrical current, mechanical force or vibration across the bond line. In automotive component and vehicle assembly, electrically conductive adhesives are increasingly used for mounting and connecting power chips, sensors, electrical heating elements, cameras, mirrors, and the like. Correspondingly, there are many assemblies that need a good thermal management, like power circuits, LED lamps, heat exchangers, motors or batteries. In this case, heat transfer between components can often be accomplished by using thermally conductive adhesives. In order to provide for high mechanical, thermal and chemical stability, functional adhesives are frequently based on epoxy resins. The resulting composites enable both force-fitted and conductive joints as an alternative to traditional soldering, welding and mechanical fixing, but avoiding high thermal loads or problems with difficult material combinations. The talk will give a short survey on current and prospective applications of functional, electrically and thermally conductive adhesives in automotive assembly, as well as a short insight into the challenge of developing such materials.
Bonding is a well-accepted joining technology in airplane production. These applications are not full-automatic with robots but handmade. insight into the challenge of developing such materials.
However rising sales figures of airplanes combined with the demand of lower production cost push the automation in aerospace industry.
Most of the used adhesives are designed in the late 1970’s, when nobody was aiming to design them towards automatic use.
So users are facing extreme problems to automatize these processes. This presentation will show the problems, a possible technology and some proven solutions.
The polyurethane chemistry is relatively old but is continuously further developing since Otto Bayer made
his first experiment in 1937. Today a lot of trends are under discussion like bio-based, light weight,
recyclability, flame retardancy, low emission, non-hazardous.
The presentation gives a short overview about the state of the art and new development paths. It gives answers to technical properties, applications and commercial possibilities of polyurethane adhesives. Henkel is the world’s largest supplier of polyurethane adhesives and sealants.
Polyurethane adhesives are highly versatile materials used in high-performance applications. Polyurethanes allow a wide range of raw materials to modify properties, and can be made moisture-curing, two component reactive or non-reactive hot melt. Two of the key trends driving market growth are a growing emphasis on sustainability plus a continuing need to enhance performance and longevity. Croda has now extended its range of bio-based polyols with an innovative technology, to meet this industry need for adhesives of the future. This paper will demonstrate the higher performance and durability with these new polyols in reactive polyurethane adhesives and PU dispersions.
The advanced polyols bring polyurethane adhesives with excellent strength while offering high flexibility. The polyols are based on natural oil chemistry, offering (low temperature) flexibility to the bond to allow shock absorption or adhesion of flexible substrates. Low adhesive viscosity provides ease of application, while enhanced wetting brings good adhesion to a variety of substrates. Innovation has brought a step-change in strength in addition to the high adhesive flexibility. The strong mechanical performance is combined with excellent durability. This is highly relevant for demanding applications like automotive and electronics adhesives. The technology is suitable for multi-material design, offering versatile adhesion and coping with variations in thermal expansion. This allows use in laminate structures and lightweight construction, combining metal with composites and plastics.
Since the introduction of CO2-based polyols onto the adhesive market, the formulators have quickly seen the significant benefits contributed by these new materials in terms of adhesive performance. Specifically, we have seen a significant impact on reactive hot melt adhesives, packaging adhesives, panel adhesives and water-based PU dispersions. The enhancements are based on a wide range of property improvements contributed by these new materials i.e. higher strength, lower extractables, lower calorific value, non-yellowing, improved hydrolysis resistance, etc. The other important aspect of these polyols concerns their influence on the carbon footprint of adhesives and we will discuss how the manufacturing is set up to minimize impact on resources and on the environment. Lastly, since this technology, although now fully commercial, is still in its infancy, we will discuss future direction and some of the exciting developments in the pipeline.
Cleaning and pre-treatment of the surface is an important prerequisite for a high-quality adhesive bond area. In the laser process only dirt particles, oxide layers and other contaminations are vaporized by bundled light only.
Laser pre-treatment leaves the metallic surface free of contamination and well prepared for bonding. The substrate is not damaged by the laser light. Metallic materials can be "modified" within the upper boundary layer using appropriately intensified laser parameters. This means the surface of the substrate can be enlarged respectively, modified to match the bonding mechanisms. By targeted modification of the surface, the corrosion behavior of light alloys can be improved significantly. The substrate is resistant to age and environmental damage. The laser light removes oxide layers including superficial contamination, e.g. from light alloy surfaces. The near-surface zone in the area of typically ~ 1 μm is remelted within a few nanoseconds, the melt quickly being cooled simultaneously. By dissolving the grain boundaries and due to the heat capacity of the part a "quenching” occurs. This results in a new micro-crystalline amorphous and rough boundary layer (adaptive layer) with significantly decreased element corrosion behavior. The modification processes is automatic when exposed to air without any protective gas. The new, passivation oxide layer on top of the melt forms a very stable bond with the adhesive. Combined with the decreasing electro-chemical potential of current aluminum and magnesium alloys this leads to long-term, age-resistant bonds. Short-term remelting leads to additional microcraters" that cause a significant surface enlargement and thus an increased load transmission particularly under shear load.
Light weight constructions are not only relevant in the airplane industry but are also becoming more and
more relevant in automotive designs. Besides steel and aluminum alloys, CFR’s are coming into focus. Due to
their high strength, thin structures and small weight constructions are possible.
Even more so than for metal plates, the joining technologies for fibre resins are challenging. Welding as
well as screwing and riveting reach their limits with these materials. Welding is limited because of the
difficulties to join different materials and screwing as well as riveting due to the fact that CFR materials
are getting damaged by screw or rivet holes.
With adhesive bonding CFR materials can be joined with other materials without damaging fibre directions or the material itself. But how about joining removable connections? Böllhoff und DELO designed a method to achieve removable connections without the shown limits. For this a so called ONSERT which is a plastic part containing a screw is bonded to the CFR. Due to the transparent plastic food of the ONSERT it can be bonded with light curing adhesives in seconds.
ONSERTs can be used for a lot of applications especially where parts have to be fixed but do not need to carry structural loads. In airplanes, for instance, hundreds of thousands of aircraft pins are installed annually. Cover plates or insulation material can be attached as well as floor panels for fixing fire protection components. In the future, ONSERT can be used for the attachment of these real components. The vehicle construction increasingly relies on CFRP, in particular for the b- and c-pillars. With ONSERT, for example, the cable harness can be attached to studs which are bonded to these pillars. Further possible applications are clips, brackets for sensors or attachment parts.
Multi-material lightweight car body construction requires suitable joining technologies. Various innovative bonding solutions have been developed and optimized for the specific application cases. Vehicle construction, joining substrates, defined performance and the production process are determinating approach which has to be evaluated and implemented. For applications in the body shop a new hot curing one component adhesive technology was developed allowing the absorption of tensions caused by different thermal expansion of the combined substrates. This enables high structural multi-material boding integrated in the existing body shop process. For a "cold body shop" or applications in the assembly line one and two component polyurethane based adhesives for structural multi-material bonding are available.
Novel Fields of Application for Adhesives and Sealants Based on Silane Terminated Polymers Adhesives and sealants based on silane terminated polymers have attracted much attention in the past and there are currently many well established products on the market (e.g. parquet adhesives). Their benefits include an excellent adhesion to many substrates (metals, minerals, etc.), no labeling obligation, no bubbling, paintability, UV and weathering resistance. However, this technology is limited for many industrial applications due to some weaknesses (e.g. slow curing, weak tear resistance). This presentation will feature further fields of application based on new formulations, including the field of wind and solar energy.
Today silane-modified polymers are used as binder materials in many different adhesive applications. Typical applications are assembly adhesives or construction sealants but also flooring and roofing applications. More and more silane-modified polymers are used to replace PU-based systems in specific applications, because of increasing labelling & safety discussions. Adhesive formulations based on silane-modified polymers are moisture curing systems.
Silane-modified polymers with lateral crosslinking functions (NEW-SPs) represent a new technology which differs significantly in production process to silane-terminated polymers in the market. NEW-SPs offer alternative ways & possibilities for adhesive developments in a growing market which has to adapt to changing market requirements: NEW-SPs with lateral silane functions accounts for improved cure-through properties, higher elastic recovery and a better stability of the polymers.
In this paper two recent developments from Jowat aqueous dispersions R&D are presented.
1. New emission-reduced foil adhesive:
Consumers are becoming more aware of healthy living conditions and environmental aspects like potential emissions from building products play an important role in this. “Green products”, “green homes” and several eco-labels for the classification of emissions are daily topics in the media. However, products with reduced emissions are not just a market trend- they represent a real shift in the daily use of these materials. Legislation is working hard to come up with corresponding regulations, especially for building and furnishing products. Among several national rating systems the German “AgBB” (Committee for Health-Related Evaluation of Building Products) and especially the French initiative “Émissions dans l'air intérieur” is presently considered to be the strictest system. A new vinyl acetate copolymer dispersion has been developed for the lamination of wooden composite boards with thermoplastic foils and decor paper foils, that shows significantly lower emission values compared to standard EVA-based foil adhesives. Due to this emissions reduction by a factor of 25 that adhesive was rated with “A+”- the best classification level. The adhesive is free of plasticizers and solvents and main product advantages include very low formaldehyde emission, high initial strength, good heat resistance and neutral pH value.
2. Aqueous dispersion for bonding of Wood-Plastic-Composites:
Together with the Department of Polymer Engineering, KTP (Kunststofftechnik Paderborn), at the University of Paderborn a fundamental research project about the challenge of bonding Wood Plastic Composites (WPC) with dispersion adhesives has been completed a few months ago. As the hardening mechanism is characterized by the evaporation of the dispersion medium (water), the challenge is to remove the moisture of the liquid adhesion film from the joining zone. In conventional applications, dispersion adhesives are used to bond wood pieces, paper, or other porous materials. Wood Plastic Composite, however, which is a compound material with wood as fiber and typically a thermoplastic polymer as the matrix material, is not per se permeable to water. The task was therefore to modify the WPC device so that the water can exit the joining plane and to optimize the adhesive formulation for these substrates. In this paper the results are presented, showing that for some WPC applications dispersion adhesives can be a suitable solution. This project was financed by the European Regional Development Fund (ERDF) of the European Union in conjunction with the German State of North-Rhine-Westphalia under the auspices of the motto “Investment in Our Future”.
A major share of pressure sensitive adhesives for tapes, labels and films are based on acrylic
However, when it comes to applications where water resistance is key - e.g. outdoor applications - some reluctance in the market to use water-borne systems can be found. There is an often-heard statement: “What comes out of water will go into water”. Does this statement hold water?
Within this presentation a general understanding about the phenomena, which occur in adhesive films under wet conditions, is outlined. Based on these findings, dispersions were designed and compared to state-of-the-art solvent-borne or UV-hotmelt acrylics.
Cyan acrylic adhesives (known as Superglue) will be introduced as a new adhesive generation for pressure
sensitive tapes as roll goods and die cuts.
How does the system works, why does it works, achievable performance level and application examples where to use this new products.