Hot Glue as a Non-Metallic Adhesive
Adhesive is defined as a non-metallic substance capable of bonding two substrates using adhesion mechanisms (created between the adhesive and substrate) and cohesive mechanisms (occurring within the adhesive mass itself). As understood from this definition, adhesives are non-metallic materials, and most adhesives are composed of organic polymers that are in liquid form when applied and become solid after curing and hardening.
Given this explanation, have you ever wondered how this simple and practical adhesive, always available at home, workplaces, and factories, is created? The development of adhesives has seen significant advancements from ancient times to the present, playing a crucial role in advancing technology and industry.
If you are interested in producing adhesives, understanding how they are made and the differences among various types will help you decide on the best materials for adhesive manufacturing and use the right formulation and equipment based on your needs. Join us at “Ana Chemistry Araz” for more insights.
What is Adhesive?
Adhesive generally refers to any sticky substance that is applied in a liquid form and hardens to hold objects together. Essentially, it is a material used to create a connection between two objects, possessing the ability to bond with other surfaces. The interaction and process of forming a bond between the adhesive and the object is also referred to as adhesion. Other terms like glue, paste, cement, and glaze are also used interchangeably with adhesive.
Compared to other methods of joining materials, such as stitching, mechanical fastening, thermal bonding, etc., adhesives have broader applications and can be used with more materials. Adhesives distribute stress more effectively over the entire bonding surface, reducing the likelihood of bond failure. They also create a more aesthetically pleasing and flexible design, making them more cost-effective than other bonding methods. The bonding process also takes less time.
Types of Adhesives
Adhesives come in various types and can be classified into two main categories: natural and synthetic, based on their source of production. Natural adhesives are made from organic sources like plant starch, natural resins, or animal components and are also known as bio-adhesives. Synthetic adhesives are made from artificial materials, such as polymers, and generally include emulsion adhesives, thermoplastics, and thermosets. Adhesives can also be grouped based on their bonding methods. In “reactive adhesives,” a chemical reaction is required to create a bond, while “non-reactive adhesives” do not need a chemical change to bond. However, physical changes may occur during the bonding process.
History of Adhesive Production
The history of the first use of adhesives dates back to 400 BC. The earliest evidence of adhesives is found in cave paintings, where researchers believe ancient artists used a type of adhesive to bond pigments to the cave walls and protect the artwork from moisture. Archaeologists have discovered pottery whose pieces were joined using tree sap.
Between 150-100 BC, paintings depicted the process of application of adhesive. Further explorations in Egypt reveal that a type of animal glue was used for joining and adhering coffins. In ancient times, the Greeks and Romans used a kind of adhesive for bonding thin surfaces like wood.
During this period, animal glues were discovered and were often combined with other materials such as egg whites, milk, cheese, grains, and animal hides to enhance durability and strength. The production process of animal glues involved boiling animal hides to obtain a viscous, gelatinous mixture, which was then dried and stored as powder.
When using the glue, the powder would be mixed with water and heated until the desired viscosity was reached. At this time, the Romans utilized beeswax and pitch to repair the hulls of their boats and ships, while egg whites were used for attaching gold leaf. They also used animal glues as a hair gel.
From the 15th century onward, with the widespread use of wooden tools, the necessity of using adhesives became more pronounced. In 175, the first patent for a fish-based adhesive was granted. This was followed by patents for adhesives derived from animal bones, natural rubber, fish, and casein. The first adhesive factory was established in the Netherlands and produced glue from animal hides, which was made available only to wooden tool manufacturers. By 190, several adhesive factories had been established in the United States.
In the 192s, adhesive production became a key aspect of the industrial revolution. As this revolution continued, significant technical advancements in adhesive manufacturing occurred, and producers began using new raw materials in their formulations. During this time, the first plastic polymer, primarily used in billiard balls, was synthesized.
Before this, billiard balls were made from elephant ivory. World War II spurred rapid growth in the synthetic adhesive industry, driven by the need for the production of elastomers and plastics.
Components of Adhesives in the Modern World
Today, various materials are used in the production and formulation of adhesives. Adhesives consist of different chemical components, each performing specific functions. A significant turning point in adhesive history was the invention of synthetic adhesives in the 20th century. These adhesives are made from polymer materials that possess greater bonding properties and suitability for various applications.
Today, polymers are typically used in adhesive manufacturing. Polymers liquefy at high temperatures and dissolve in suitable solvents. They play a crucial role in enhancing adhesive strength. In fact, polymers form very strong covalent bonds with each other, which is why these adhesives exhibit high adhesion. Other essential materials present in adhesive formulations include solvents, which account for their viscosity. Industrial adhesives may also contain stabilizers, fillers, thickeners, plasticizers, and anti-foam agents. Nowadays, adhesive production often involves complex formulations, each with specific functionalities.
Components of Adhesives Include:
- Primary Resins
- Solvents
- Fillers
- Plasticizers
- Reinforcers
- Thickeners
- Thixotropic Agents
- Antioxidants
- Antifungal Agents
- Emulsifiers
- Wetting Agents
Of course, in addition to the above components, other products are also utilized in the production of various types of adhesives.
Conclusion
In general, modern adhesives are classified as polymer mixtures or polymeric materials that can be utilized in liquid or semi-liquid forms. In the production of these products, various chemical materials are used, depending on the application and quality. Ana Chemistry Araz, using the highest quality chemicals and the best adhesive formulations, is one of the leading adhesive manufacturers in Iran.