Emulsion polymerization of acrylic monomers to improve the properties of pressure sensitive adhesives

Chemistry

Dissertation for Master's Degree

Abstract

Acrylic-based pressure-sensitive adhesives are more expensive than rubber-based adhesives, but have longer life and resistance to high temperature, chemicals, UV, solvents, light, soft doers and the environment. Modification of acrylic pressure-sensitive adhesives is useful for improving adhesion properties. In this research, emulsion polymerization of acrylic monomers has been investigated to improve the properties of pressure-sensitive adhesives. Emulsion polymerization of acrylic monomers was investigated in terms of the effect of the amount of acrylic acid and butyl acrylate copolymer, initiator, surface active agent, temperature, and in terms of the effect of silicate nanoparticles on the detachment adhesion strength and viscosity of acrylic resin. In high amounts (10 grams) of copolymer of acrylic acid and butyl acrylate, the detachment adhesion strength increased and the viscosity decreased. In high amounts (20 grams) of acrylic acid and butyl acrylate copolymer, the detachment adhesion strength decreased and the viscosity increased, which indicates that it is better not to use acrylic acid and butyl acrylate copolymer in amounts above this range for making pressure-sensitive adhesive. The maximum detachment adhesion strength was obtained in the amount of initiator (1.25 g, 0.005 mol). With the increase in the amount of the initiator, the detachment adhesion strength decreased and the viscosity increased strongly. In the amount of surfactant (70 g, 1.61 mol), a strong increase in viscosity was observed, and with a further increase in the amount of surfactant, the viscosity decreased. In the amount of surface active substance (105 g, 2.41 mol), the highest detachment adhesion strength was obtained. At temperatures above 60°C, the adhesion strength of detachment increased, while at temperatures above 65°C, the adhesion strength of detachment decreased. The best temperature for having high peel adhesion strength in such formulation was 65 C?. As the temperature increased, the viscosity first had a small value, then it increased sharply at 68 ?C. The detachment adhesion strength of powdered silicate nanoparticles was zero. Detachment adhesion strength and viscosity increased in the sample of silicate nanoparticles mixed by ultrasonic method (2%). Viscosity was also reduced in powdered silicate nanoparticles and mixed silicate nanoparticles without ultrasonication (2%) (using a conventional stirrer).

Key words: emulsion polymerization, pressure-sensitive adhesives, emulsifier, initiator, surfactant, copolymerization of vinyl acetate and butyl acrylate.

1-1 Introduction

Most synthetic polymers are produced in petrochemical complexes and chemical factories. It is then sent to manufacturing companies that perform conversion processes such as formulation, mixing, extrusion and molding. The processes required to produce final goods are mainly physical. This means that the product is obtained without any chemical reaction. Some polymers, which are called resins, are given to manufacturers as precursors by chemical industries. In these cases, manufacturers turn them into final products by performing chemical reactions. There is also an intermediate stage in resins. that smaller polymers or pre-polymers reach their final properties by performing chemical reactions and creating new chemical bonds. Therefore, it is much more possible to modify them. Different types of resins, such as polyester resins, polyurethane, alkyd epoxy, phenol-formaldehyde, urea-formaldehyde, melamine-formaldehyde, furan, acrylics, etc. in various fields of industry such as paint, glue, coating, textile, textiles, etc. are used (Bard[1], 2005).

Modification of resins is very useful. Because by changing their chemical nature and physical properties, certain application properties can be achieved. Since many different types of reactive materials can be combined with the final resin, the variety of final properties and the power of modification in the case of resins are much more prominent compared to other polymers (Bard, 2005).

The use of nano silicate [2] in the emulsion polymerization of acrylic resin is also useful.The effect of ultrasonicated [3] and non-ultrasonic nano silicate on the detachment adhesion strength and viscosity [4] of acrylic resin can be investigated. By applying suitable conditions in various devices [5], ultrasound waves increase the speed and ability of absorption through internal and external mass transfer. Disturbances caused by ultrasound waves due to the application of mechanical pressures cause the particles to become finer (Noskaya [6] et al., 1999).

1-1-1 Acrylic resins

Acrylics have a high resistance to ultraviolet rays and oxygen, but they are very expensive (Zhouri, 2011, p. 100). Acrylic resins are obtained from the polymerization of methyl, ethyl and butyl esters of acrylic acid and methacrylic acid alone or together under the effect of heat and suitable initiators. Polymerization of acrylic resins can be done by mass method for casting or by emulsion and solution methods. Acrylic resins are widely used in the industry due to their transparency, brightness, ease of manufacture, and low mass. These resins have excellent optical properties. They are even used for camera lenses and devices. Due to their dielectric strength, acrylic plastics and resins are often used for sealing high voltage lines and cable ties (Bard, 2005). They are widely used in textile, paint, cellulose, leather and also in adhesive industries. In fact, paints and other coatings alone are the most used for acrylic resins [7] (about 33%). Other main uses of acrylic resins in order of importance are: woven and non-woven fabrics [8], adhesives, polishes and waxes, graphics and printing industry, sealants and cement and concrete additives. There are thousands of special types of acrylic drains that are engineered for specific applications. Their consumption reaches millions of tons annually (Van Herk[9], 2005).

1-1-3 Adhesives

Any mineral or organic material, whether natural or synthetic, that can connect other materials through their surface is called an adhesive. Casein glues, starch, rubber saps, blood and bitumen are examples of organic glues. The two groups of synthetic adhesives, soft heat and hard heat, are classified into plastic and rubber classes: 1-1-3-1 Soft heat adhesives, hot melt adhesives[10] seem to be a good example of soft heat adhesives. which include polyethylene, isobutylene, polyamides and polyvinyl acetate in this group of adhesives. Polyvinyl chloride glue, which works very well for connecting parts of polyvinyl chloride, is also in the group of soft heat glues. Polyvinyl acetate glue, which has the best adhesion in cellulosic materials, is used in large quantities as wood and paper glue (Namati, 2011, p. 12).

Polyvinyl butyral film is placed between the layers of glass in the windshield of cars. It plays an important role in front passenger safety. It has great adhesion to glass. This film prevents pieces of glass from being thrown towards the passengers when the windshield is broken. In addition, since the reflection coefficient of this polymer is equal to that of glass, it cannot be distinguished from glass by the eye and cannot be seen. It also has a very high resistance to the ultraviolet rays of the sun and does not get destroyed (Namati, 2011, p. 12). Among the most famous thermosetting plastic adhesives, we can refer to double or twin adhesives, which often have an epoxy base. which have very strong adhesion and use this combination as an excellent adhesive for iron, glass and ceramic parts. Another good feature of this adhesive is its optimal performance at temperatures above 80°C. Also, they have very little sensitivity to moisture (Namati, 2013, p. 12).