Polymers, widely used in various industries, often require modifications to meet specific performance requirements. Polymer additives play a crucial role in enhancing the properties and functionality of polymers. These additives are incorporated into polymer matrices to improve their processing, mechanical, thermal, electrical, and aesthetic characteristics. This article provides a comprehensive overview of polymer additives, their types, functions, and examples. Furthermore, it highlights the importance of additives in polymer applications, shedding light on the significant advancements made in this field. The information presented here is supported by relevant references to provide an in-depth understanding of polymer additives.
Polymers, macromolecules composed of repeating units, have become indispensable materials in modern industries. However, to achieve specific performance criteria, polymers often require modifications. Polymer additives serve as effective tools to tailor and enhance the properties of polymers, ensuring they meet the desired requirements. By adding additives to polymer matrices, manufacturers can optimize processability, improve mechanical strength, increase durability, enhance flame resistance, provide UV protection, and achieve various other desirable attributes. This article aims to elucidate the significance of polymer additives and provide an extensive overview of the different types of additives and their functionalities.
Definition of Polymer Additives: Polymer additives are substances incorporated into polymer matrices to modify their properties or improve their processability. These substances are typically added in small quantities and can profoundly impact the characteristics and performance of the polymers. Additives can be classified into various categories based on their intended purpose, chemical composition, and mechanism of action.
Antioxidants are additives that inhibit the oxidation and degradation of polymers. They protect against thermal and oxidative degradation caused by heat, light, or environmental factors, preventing loss of mechanical properties and prolonging the service life of polymers (figure 1) Common antioxidants include hindered phenols, phosphites, and thioesters.
In polymers, antioxidants are classified into two categories: primary antioxidants (also known as primary stabilizers) and secondary antioxidants (also known as secondary stabilizers). Let’s explore each category:
1. Primary Antioxidants (Primary Stabilizers): Primary antioxidants are compounds that are added to polymers during processing or polymerization to provide initial protection against oxidation. They function by reacting with and neutralizing free radicals formed during the initiation of oxidation. Primary antioxidants scavenge and stabilize these free radicals before they can propagate and cause further degradation of the polymer. Common primary antioxidants include:
Hindered Phenols: Examples include Irganox®1010 , Irganox®1076 , and Irganox®1098.
2. Secondary Antioxidants (Secondary Stabilizers): Secondary antioxidants are typically used in combination with primary antioxidants to provide extended protection against oxidation over the lifetime of the polymer. They function by decomposing hydroperoxides, which are intermediates formed during the oxidation process, thereby preventing further oxidation reactions. Secondary antioxidants scavenge and neutralize hydroperoxides to prevent the chain reaction of oxidation. Common secondary antioxidants include:
• Phosphites: Examples include Irgafos® 168 and Ultranox® 626.
• Thioesters: Examples include DLTDP (Dilauryl thiodipropionate) and DSTDP (Distearyl thiodipropionate).
• Hindered Amines: Examples include Tinuvin® 622, Tinuvin® 770, and Chimassorb® 944.
The combination of primary and secondary antioxidants provides comprehensive antioxidant protection throughout the processing, use, and aging of the polymer. The selection of specific primary and secondary antioxidants depends on factors such as the type of polymer, processing conditions, intended application, and desired performance requirements (figure 2).
UV radiation is produced by the sun and can also be emitted by artificial sources such as tanning beds and some types of lamps. When sunlight reaches the Earth’s surface, it contains UV-A, UV-B, and a small amount of UV-C rays. However, the Earth’s atmosphere, particularly the ozone layer, absorbs a significant portion of UV-B and UV-C rays, providing protection against their harmful effects (Figure 3).
UV stabilizers protect polymers from the harmful effects of UV radiation. These additives absorb or reflect UV light, reducing the degradation and discoloration caused by UV exposure. UV stabilizers can be categorized into UV absorbers and hindered amine light stabilizers (HALS). HALS (Hindered amine light stabilizers) is a common category of UV stabilizers that act as absorbers of free radicals resulting from the impact of ultraviolet rays on the polymer chain. They trap the resulting free radicals and neutralize their destructive function. By preventing the formation of free radicals, HALS can significantly reduce the degradation of polymers. They are especially effective in polyolefins and other materials sensitive to oxidation.
Filler masterbatches, also known as filler compounds, are additives that are used in the plastic industry to combine fillers in polymer matrices (Figure6). Fillers are solid particles such as calcium carbonate, talc or glass fibers that are added to polymers to improve properties and reduce costs. The filler masterbatches act as carriers of these materials and facilitate their dispersion and uniform distribution in the polymer. In the following, some common features of filling masterbatches are mentioned:
• Reducing costs
• Creating advanced mechanical properties
• Improvement of dimensional stability
• Increased heat resistance
• Surface finish and appearance
• Electrical and thermal conductivity
Color additives add color to polymers and double their attractiveness and beauty. This additive is perhaps one of the most widely used additives in the manufacture of various polymer products. These additives can be organic or inorganic pigments, dyes or color concentrates. Colors are widely used in product packaging, consumer goods and various other industries (Figure 8).
Impact modifiers are additives used in polymers to improve toughness and resistance to impact forces. Polymers inherently possess properties such as high strength and stiffness, but may be prone to brittleness upon impact or sudden pressure (Figure 9). Impact modifiers increase the energy absorption capacity of polymers by providing flexibility and toughness, allowing them to withstand impact without breaking. Incorporating impact modifiers in polymers brings several advantages. Among them, it improves the material’s resistance to cracking, cut sensitivity and impact strength, making it suitable for applications where durability and impact resistance are critical. Impact modifiers can also increase the processability of materials because they can improve the flow of the polymer melt, reduce melt viscosity, and facilitate easier processing during molding or extrusion.
Various types of impact modifiers are used in polymers, each of which offers specific advantages and compatibility with different polymer systems. Some commonly used impact modifiers include:
• Elastomers
• Core-shell polymers
• Thermoplastic polyurethanes (TPU)
• Grafted copolymers
The selection of an appropriate impact modifier depends on factors such as the base polymer, processing conditions, intended application, and desired mechanical properties. The impact modifier concentration in the polymer matrix can be adjusted to achieve the desired level of toughness and impact resistance. Impact modifiers are used in a wide range of industries, including automotive, construction, consumer goods, and packaging. They are also used in the production of various products such as car parts, pipes, films, sheets and impact-resistant containers.
Various additives in the polymer industry play a very important role in increasing the properties and performance of polymers. Various types of additives are discussed in this article, including antioxidants, UV stabilizers, flame retardants, lubricants, antistatic agents, slip agents, fillers, nucleating agents, colors, impact modifiers, anti-fog additives, slip additives. And plasticizers offer a wide range of functions to meet specific application needs. Understanding the capabilities and benefits of these additives allows manufacturers to optimize polymer formulations and develop high-performance materials for various industries.
By: Zahra Davatgari
Edition by: Dr. Mehrnaz Bahadri
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