What Is Adhesive Glue?
Adhesive glue is a type of substance that can be applied to the surfaces of two or more objects to hold them together. These substances may be natural or synthetic.
The bond formed by adhesives depends primarily on their adhesion and cohesion properties. Understanding these properties can help you choose the right adhesive for a given application.
Chemical Composition
Adhesive glue is a liquid that can be used to wet and bond two different surfaces. It is made of a combination of polymers and additives to modify its properties, such as tack, gap filling, and durability.
The most common adhesive is a cyanoacrylate adhesive, which contains a small number of large molecules that polymerize when they come in contact with a substrate’s surface. The rate at which these adhesives polymerize depends on the type of substrate and its chemical environment. For example, if the surface of the substrate is acidic, cyanoacrylate will take longer to cure than it would on a basic surface.
A cyanoacrylate adhesive may also contain other additives, such as a plasticizer and stabilizer. These can increase its flexibility, as well as its tack and adhesion strength.
In addition, some adhesives are formulated to reduce their environmental impact. These include products made with organic solvents, which are less likely to contribute to ozone depletion and to air pollution, and those that can be diluted in water without losing their properties.
Synthetic adhesives consist of prepolymers, oligomers, or polymers that are synthesized from petrochemically derived raw materials. They can be applied as liquids or emulsions, and are typically cured in water by further reaction of the oligomers and the addition of a cross-linking agent or catalyst.
Some animal glues are based on proteins extracted from milk (casein). These are widely used in wood joining and sandpaper manufacture, but have been modified or entirely replaced by synthetic adhesives.
These are often considered to be “self-healing” because the hydrogen adhesive glue bonds that hold these glues together are not broken when they are pulled apart, and if they are displaced by moisture or heat, new bonds will form. This self-healing behavior is not exclusive to animal glue; it is seen in many filler-filled cross-linked polymers.
Cohesive Strength
Cohesive strength is an adhesive’s internal ability to hold itself together under stress. It is determined by the chemical composition of an adhesive and the curing/setting conditions.
Adhesive strength is a critical factor when selecting the appropriate adhesive for a specific application. However, there are many other factors that may also be important, such as speed of cure, environmental resistance, thermal resistance, suitability for automation and price.
The cohesive strength of an adhesive depends on its chemical composition, surface energy, and a number of other factors that affect the bonding interface between two substrates. These include intermolecular forces, mechanical bonding and micromechanical adhesion.
It is also affected by how well the glue wets the substrate, which can be influenced by both adhesion and cohesive forces. For example, if the cohesive forces in an adhesive are high enough, the glue might spread over the surface of the substrate and create better adhesion.
This is why adhesives are designed to be able to wet the surface of their substrates. This helps the adhesive to penetrate into the surface structures, resulting in better mechanical interaction at the bonding interface.
There are a few types of adhesives, including solvent and water-based. These are known as hot or cool melt adhesives because they’melt’ and’set’ when heated.
The cohesive strength of an adhesive is usually measured by the simple single lap shear test. This is a good screening and process control test but does not account for adherend bending and peel loads, which are more significant. Moreover, the test specimen is not very uniform over the bond area, which can result in uneven stress distribution.
Surface Energy
Adhesive glue is a pressure-sensitive adhesive that can bond two dissimilar substrates together. When two materials are bonded together, there are several factors that need to be considered including surface tension and texture of the substrates, bond strength, product application, design and environmental conditions.
When it comes to adhesion, the most important factor to consider is the surface energy of a substrate. This is the excess energy that flows on the surface of a material, measured in dynes/cm.
High surface energy (HSE) materials have a very strong molecular attraction, which makes them easy to bond. Low surface energy (LSE) materials have a weak molecular attraction, making them harder to bond with adhesives.
A high surface energy substrate will aid the wetting of the adhesive, allowing it to spread across the surface and increase the contact area. While a low surface energy substrate will avert wetting, leaving liquid droplets to bunch up at an awkward angle to the substrate, which is known as wet out.
Many plastics and composites have a relatively low surface energy, requiring special pressure-sensitive adhesives that are designed to work well on them. The surface energy of these types of materials is usually between 36 and 100 dynes/cm.
The surface energy of these substrates can be altered with treatments such as flame treatment or plasma treatment. These methods often add cost and complexity to the process, but can be effective in modifying surfaces with little loss of performance.
Resistant to Stress
A strong adhesive glue is a critical factor in ensuring that joints are made to last. It also helps to reduce the risk of damage when a joint is subjected to high-intensity stress.
The strength of an adhesive depends on a number of factors. Some of these include the chemical composition, surface energy, and temperature.
Temperature effects on an adhesive’s strength are particularly important because they change the elasticity of the adhesive. At a certain temperature, called the glass transition temperature (Tg), an adhesive’s structure changes to a more rubbery/soft state.
Additionally, temperature increases the stresses in a bond. This can lead to a degradation of the bond, a breakdown in the adhesion of the substrate and an increase in the failure rate.
In addition, the strength of an adhesive is affected by the surface of the substrate and how it is prepared. This can affect its initial adhesion and the amount of time it takes to fully set.
For some types of adhesives, the strength can be increased by using different types of gluing materials or by making improvements to the bonding process. This includes using the adhesive glue right glue for a particular application and preparing the surfaces correctly for adhesive bonding.
An increase in the thickness of an adhesive can also help to improve the strength of a joint. This is particularly true for adhesives that are resistant to shearing.
Resistant to Moisture
The resistance to moisture of adhesive glues is a crucial issue for wood products. This is because moisture can significantly affect the strength of bonded joints in a wood product. It can also be detrimental to the quality of the glued joint by causing damage to wood.
The time required for typical bonded geometries (such as single lap joints or double cantilever beams) to reach moisture equilibrium can be quite long. This can be an obstacle to the development of adhesives with improved moisture resistance and bonding performance.
To overcome this barrier, we have developed a long-chain biomaterial with hyper-branched structure. The long-chain biomaterial HD was synthesized through graft copolymerization of HBPA with DAS, and subsequently, a novel SM/TGIC-based adhesive was prepared by blending the SM with HD and incorporating crosslinking agent-triglycidyl isocyanurate (TGIC) to enhance the adhesive’s water-resistance properties.
We have found that by reducing the TGIC dosage and incorporating HD, the adhesives have a better toughness as well as a higher residual rate and less moisture uptake. Additionally, the SM/TGIC/HD-5 had a greater wet shear strength than that of the SM and SM/TGIC/DAS-5 adhesives.
The results of the morphological analysis indicated that the fracture surfaces of the SM and SM/TGIC adhesives were cluttered and disorganized. In the case of the SM/TGIC, this is likely due to poorly bonded SM molecules being crosslinked with the TGIC group. The SM/TGIC adhesive, on the other hand, had a compact fracture surface due to its improved crosslinking density. Moreover, the SM/TGIC/HD-5 adhesive had a high residual rate that exceeded the SM and SM/TGIC/DAS-5 residual rates by 18.5% and 12.3%, respectively. Furthermore, the resulting plywood had higher wet shear strength that met the shear strength requirements for indoor use.