This article explores the application of antioxidants as additives in polymers to enhance their durability and performance. Polymers are widely used in various industries due to their versatile properties, but they are susceptible to degradation when exposed to environmental factors such as heat, light, and oxygen. The incorporation of antioxidants into polymer formulations can effectively inhibit oxidation reactions and prevent the chain scission process, thereby extending the material’s lifespan.
Keywords: Antioxidant, Additives, Polymers.
Polymers are widely used in various industries due to their versatile properties. However, exposure to environmental factors such as heat, light, and oxygen can cause oxidative degradation of polymers, leading to reduced performance and shorter lifespans (Figure 1). Antioxidants are effective additives used to inhibit or delay such degradation processes. This report provides an overview of antioxidants used in polymers, including their definition, properties, applications, and a conclusion summarizing their significance.
Antioxidants are substances that prevent or delay oxidation reactions by interrupting the chain reactions initiated by free radicals. In polymers, antioxidants inhibit the oxidative degradation caused by the presence of free radicals, which can lead to polymer chain scission, discoloration, loss of mechanical properties, and other detrimental effects. It is shown in Figure 2.
Antioxidants used in polymers possess certain key properties that contribute to their effectiveness. These properties include.
a) High thermal stability: Antioxidants must remain stable at elevated processing and operating temperatures to provide long-term protection to polymers.
b) Low volatility: Antioxidants should have minimal vapor pressure to avoid evaporation during processing and use.
c) Compatibility: They should be compatible with the polymer matrix to ensure uniform distribution and efficient protection.
d) Synergistic effects: Some antioxidants exhibit enhanced performance when used in combination with other additives, such as stabilizers or UV absorbers.
Different types of antioxidants are used in various polymer applications, including:
These antioxidants act as radical absorbers by transferring hydrogen atoms to free radicals and thus terminate the oxidation chain reaction. For example, we can refer to some phenolic structures with functional groups with high steric hindrance (for example, Irganox 1010 whose molecular structure is shown in Figure 3) and Hindered Amine Light Stabilizers (HALS). Of course, it is necessary to mention that the use of amino antioxidants has an effect on the color of the final product and their use in many applications is limited.
These antioxidants cause the decomposition of peroxides formed during the oxidation process. Common secondary antioxidants that have phosphite or phosphonite groups or compounds containing organic sulfur and dithiophosphonates are widely used in this field. Some other common secondary antioxidants are thioesters such as dilauryl thiodipropionate (DLTDP), distearyl thiodipropionate (DSTDP) and some phosphites (for example Irgafos 168 whose molecular structure is shown in Figure 4). It should be noted that phosphites together with primary phenolic antioxidants exhibit synergistic properties. Phenolic antioxidants and phenol phosphite compounds provide excellent protection against thermo-oxidative degradation and discoloration of polymers.
The choice of antioxidants depends on various factors, including:
1) type of base polymer,
2) extrusion temperature,
3) and functional goals for the application of the final product, depends.
For example, it is better to use secondary antioxidants such as antioxidant 168 for packaging products. Because their oxidation mainly occurs during the production process. Meanwhile, for plastic products used in open space, the combination of antioxidant 1010 and antioxidant 168 should be used, because oxidation can occur for such products both in the production process and during the consumption cycle.
Also, antioxidants added in agricultural films are used to improve thermal stability, prevent color change and maintain transparency. In another application, since most pipes are used outdoors, they are exposed to external environmental factors for a long time, which leads to the oxidation of these products. Therefore, the use of appropriate antioxidants in these products is very important.
Antioxidants find extensive applications in various polymer systems, Some of these applications are shown in Figure 5:
a) Polyolefins: Antioxidants are used in polyethylene (PE) and polypropylene (PP) to prevent degradation caused by heat, light, and processing.
b) Polystyrene (PS) and ABS: Antioxidants protect these polymers from discoloration, embrittlement, and loss of mechanical properties during processing and long-term use.
c) Polyvinyl chloride (PVC): Antioxidants ensure the stability and integrity of PVC products exposed to heat, UV radiation, and oxidative environments.
d) Rubber: Antioxidants are utilized in rubber applications, such as tires and seals, to prevent aging, cracking, and degradation.
Also, in the textile industry, antioxidant masterbatches are used to protect fibers and fabrics from oxidative damage. This issue helps to prevent color change, decrease in strength and deterioration due to exposure to light, heat and environmental factors. Antioxidant masterbatches are usually widely used in the production of synthetic fibers, yarn and textiles.
In addition, antioxidant masterbatches are used in cosmetics and personal care products to prevent oxidative damage and maintain product stability. This issue helps to protect the formulas containing oils, fats and other vulnerable substances against oxidation and will lead to a longer shelf life and greater efficiency of the products.
Antioxidants play a vital role in preserving the integrity and performance of polymers by mitigating oxidative degradation. By interrupting the oxidation chain reactions and scavenging free radicals, antioxidants enhance the lifespan and maintain the properties of polymers. Their high thermal stability, low volatility, and compatibility with polymer matrices make them essential additives in numerous applications. To ensure optimal performance, it is crucial to select the appropriate antioxidant type and concentration for each polymer system, considering the specific processing and usage conditions.
By: Zahra Davatgari
Edition by : Dr. Mehrnaz Bahadori
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