Aging resistance of modern polypropylene in Wuhan
DATE：2021/3/23 8:52:22 / READ： / SOURCE：This station
Aging resistance of modern polypropylene in Wuhan
PVDF solar backplane membrane equipmentPP is an easily aging resin. Because of the use of old products, there is a great demand for anti-aging modification of PP. PP has good stability in the absence of oxygen. However, due to the existence of tertiary carbon atoms in the structure of PP, it is easy to age and degrade under the action of heat, oxygen and light in the process of granulation, storage and use, and even lose its excellent comprehensive physical and mechanical properties and keep the relative molecular weight of PP unchanged. PVDF solar backplane membrane equipment www.handern.com
The oxidation aging process of PP was carried out according to the mechanism of free radical bonding reaction. In order to protect polymer from oxidation or delayed oxidation effect. It is necessary to break down the automatic oxidation cycle of polymer. There are two kinds of harmful Chinese products in the oxidation seeding ring, which are free radicals (P., poo., Po.. ho +), The other is hydroperoxides (roohd). Accordingly, the compounds that interact with two kinds of Chinese products are also divided into two categories: free radical capture agents (also known as health terminated host oxygen) and double peroxides decomposition agents (also known as auxiliary antioxidants). The other function of the main antioxidant is to obtain free radicals and make them no longer participate in the oxidation cycle. The function of the auxiliary antioxidant is to decompose the double peroxides and make them harmless products. PVDF solar backplane membrane equipment www.handern.com
Traditional chain terminated antioxidants mainly include hindered phenyl ester and aromatic secondary gum. This kind of radical capture mainly acts on oxygen centered radicals, such as burning radical, peroxide radical (R0.), alkoxy radical (RO.) and Xing radical (HO.), but the former is the main one. Because of their short life and high activity, they quickly extract hydrogen atoms from the polymer chain to form alkyl radical. Under the condition of oxygen enrichment, the alkyl radical is transformed into the radical of alkyl peroxide. PVDF solar backplane membrane equipment www.handern.com
Under the condition of dilute oxygen (such as in a large extruder), it is very important to burn radicals, but the traditional chain terminated antioxidants are not competent for capturing alkyl radicals. In recent years, a new type of antioxidant has been developed, whose mechanism is based on the so-called "pull push effect". The characteristic of these compounds is that they can capture two macromolecular free radicals. The first step is to act as chlorine donor, and the second step is to combine with macromolecular free radicals. Obviously, the free radical formed after the second step must be more stable than the macromolecular free radical in order to complete the second step. Theoretically, the following three factors determine the stability of the free radical: steric hindrance, electron resonance structure and electron withdrawing and electron donating substituents. Benzofuranone can meet the above conditions. As a new type of antioxidant, it can make up for the shortcomings of traditional antioxidants, especially capture alkyl radicals in dilute oxygen. Combined with other antioxidants, it has excellent synergistic effect and can greatly improve the cost performance.
Auxiliary antioxidants are also called preventive antioxidants, because they can decompose hydroperoxides without generating free radicals, so they can prevent chain branching. Sometimes it is necessary to distinguish between equivalent and catalytic hydroperoxides. As the most typical representative of the equivalent type of ammonia peroxide decomposition agent, hypodermic acid ester reduces the double peroxides to corresponding alcohols and transforms itself into hypodermic acid. In addition, hypodermic acid ester can also react with peroxide free radical and alkoxy free radical in principle. Hindered aromatic sulfite can also be used as main antioxidant.
Organic sulfides are the most important transport aid antioxidants, which can be converted from two moleculars of double peroxides. Alkali containing organic acids are decomposing agents of double peroxides. It is worth noting that dicarbamate and triacetate are also very effective decomposing agents of convenient ammonia peroxides, but they are rarely used for the stabilization of thermoplastics.
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