Solving the Problems of Plastics Adhesion
Do you know that plastic is a material that is used in practically all products that we use daily? This is due to various factors, including simple processing and low density. Additionally, they are less costly and frequently use less energy during production and processing than other materials. However, a product often consists of many parts made of various materials rather than simply one (plastic) element.
The ideal method for combining various materials is modern bonding technology. However, any joining technique must meet the essential technical requirements while guaranteeing high productivity levels, quality, and dependability.
What is meant by adhesion?
The attraction between two separate phases is known as adhesion. A single theory cannot explain adhesion; however, it is often split into two categories: mechanical interlocking and physical and chemical bonding.
How to solve the problem of adhesion to plastic
Adhesion often results from a mixture of the several processes described below.
When two different phases only adhere to one another mechanically, mechanical interlocking occurs. This often calls for a surface that is a little bit rough so that the other substance may cut the adhesion barrier. For instance, low viscosity glue easily enters surface pores and fissures. After the glue has dried, this causes mechanical anchoring between the two components.
Van der Waals forces make physical bonding and are constantly present. Due to their poor strength, Van der Waals forces often contribute little to the overall bonding strength.
Covalent, ionic, and metallic bonds are common examples of chemical bonds that are significantly stronger than physical ones. Cohesive forces inside the material can be quite powerful due to chemical bondings. There are often just a few available bonding sites, and chemical bonding between two different materials is quite difficult. Plasma therapy is one of the great methods to improve the number of bonding sites.
What is the general principle of adhesion bonding?
For strong adhesion, a low contact angle is required. It is clear from the bonding processes that the coating must expand throughout the substrate to obtain strong adhesion. A smooth spread will make it easier to begin additional binding sites and allow the coating to enter surface structures. Thus, evaluating the substrate’s wettability is common. The contact angle is used to assess bonding problems since it measures wettability.
What is the adhesion process?
An adhesive is used during the manufacturing process of adhesive bonding to connect two or more surfaces. For interaction to occur, the surface of the plastic portion and the adhesive must be in close interaction.
- The surface tension of the part must be greater than that of the adhesive in a liquid condition for the adhesive to wet the surface properly.
Before abrading, the substrate surfaces must be cleared of all dirt and oils. Strong adherence results from properly wetting the glue on clean, rough surfaces.
The substrate material, service temperature, and environment are all important requirements for bonding strength, flexibility, and durability. They all play an important role in selecting the right adhesive.
Assembly and joint design
Effective design reduces peel and cleavage pressures. There might be an increase in tension, compression, and shear stresses.
Applying and spreading
It is important to use the appropriate quantity of the chosen adhesive to cover the substrate surface. The process can performed manually or with dispensing equipment.
A proper assembly of the pieces that will be linked.
What are the advantages and disadvantages of adhesion plastic bonding?
Here are important advantages and sub-advantages:
- Adhesive bonding is a reliable, cost-effective way to gather plastics with metals, wood, ceramics, or other materials.
- The capacity to bind different materials.
- A quick and affordable joining method.
- Offers flexibility and convenience in design.
- Characteristics for sealing (adhesive fills spaces and gaps)
- It offers a thin, undetectable joint
- Joints may be insulating or electrically/thermally conducting.
- Long mixing times are needed.
- Careful substrate (adherent) surface preparation is required
- The problem in separating linked pieces.
- The need to fix (keep together) the linked pieces while they cure.
- Service environment and temperature restrictions;
- Weak creep resistance;
- Modification of characteristics while in use.
Frequently Asked Questions
Here are some important questions.
How to increase adhesion to plastic?
Chemical bonding is difficult when an adhesive does not moisten a surface because it will not fill in surface deficiencies. Since most adhesives have a surface energy of 34 to 36 dynes/cm2, the substrate’s surface energy should ideally be at least 7 to 10 dynes greater than the adhesive’s.
A substrate can be activated to increase adhesion, or the surface can be modified using various techniques.
- Grit Blasting
These procedures will uncover crystalline microstructures with various wetting properties, which will abrade the plastic’s surface and facilitate bonding. These abrasion techniques really take the substrate’s top layer off.
Are all plastics bondable?
Due to their partial dissolvability, some plastics, such as various amorphous polymers, such as PC, PSU, PPSU, PES, PEI, PMMA, PS, and some PI, are simpler to bind. Certain plastics, including ABS and acrylic, are simple to adhere to one another using adhesives and solvent cement. However, some materials, including HDPE and PP, are more challenging to bind.