Study On Heat Stabilizing Performance Regularity And Mechanism Of (Organic) Metal Of Organic Acid On PVC

Polyvinyl chloride (PVC) is used in a variety of fields because of exenllent performence. However, it is prone to degradation and loss of use value in the thermal process, so the heat stabilizers become the indispensable additives. Traditional efficient heat stabilizers are either incompatible with environmental regulations or expensive. The research trend of heat stabilizers for PVC must be environmental friendly, efficient, cost-effective and low toxic.Through the study of (organic) metal of organic acid on the thermal stability of PVC, this thesis elaborate thermal stability of the change law and the exact mechanism, provide the direction for the excellent performance, environmental heat stabilizer. The main contents and results of this dissertation are as follows:1. Heat stabilization of several para-substituted benzoic acid metal salts on PVC were studied by oven discoloration method. The experimental results as following:(1) It showed that the heat stabilizing performance of para-substituted benzoates improves with increase of the electron-withdrawing character of groups in the molecule linked to carbonyl C atom of the carboxylate radical and the polarization force of the metal ion.(2) According to this progressive change law of heat stabilizing performance and the characteristics of molecular structure, it can be speculated that para-substituted benzoates stabilize PVC by electrophilic reaction with PVC using their carbonyl C atom of the carboxylate radical and/or metal ion as the electrophilic atoms, but not by the traditional Frye and Horst’s mechanism. Therefore, the exact mechanism of heat stabilization of heat stabilizers for PVC need to be clarified by further research. 2. The heat stabilization of several dialkyltin substituted benzoates on PVC were studied. The experimental results as following:(1) It was shown that the heat stabilizing performance of dialkyltin substituted benzoates improves with increase of the electron-withdrawing character of groups linked to carbonyl C atom in the carboxylate radical and the polarization force of the metal ion.(2) The electronic effect of Butyl is similar as octyl,their dialkyltin salts have similar thermal stability. Since the electron-withdrawing ability of dialkyltin laurate is less than dialkyltin substituted benzoates, its thermal stability is not better than dialkyltin substituted benzoates.(3) According to this progressive change law of heat stabilizing performance and the characteristics of molecular structure, it can be speculated that dialkyltin substituted benzoates stabilize PVC by electrophilic reaction with PVC using their carbonyl C atom in the carboxylate radical as the electrophilic atoms. This means that the traditional Frye and Horst’s theory on mechanism of heat stabilization of heat stabilizers does not apply to dialkyltin substituted benzoates, and therefore, the exact mechanism of heat stabilization of heat stabilizers need to be clarified by further research.3. The heat stabilization of several dicarboxylic dibutylltin on PVC were studied. The experimental results as following:(1) It showed that the heat stabilizing performance of dicarboxylic dibutyltin improves with increase of the Ionization constant of acid groups. Dibutyltin maleate and dibutyltin o-phthalic acid undermin conjugated structure amd inhibite its discoloration because of Diels-Alder cycloaddition reaction.(2) According to this progressive change law of heat stabilizing performance and the characteristics of molecular structure, it can be speculated that dicarboxylic dibutyltin stabilize PVC by electrophilic reaction with PVC using their carbonyl C atom of the carboxylate radical and/or dialkyltin ion as the electrophilic atoms, but not by the traditional Frye and Horst’s mechanism. Therefore, the exact mechanism of heat stabilization of heat stabilizers for PVC need to be clarified by further research.4. The heat stabilization of several dibutylltin substituted thiophenol on PVC were studied. The experimental results as following:(1) It showed that the heat stabilizing performance of dialkyltin p-substituted thiophenol improves with increase of the electron-withdrawing character of groups in the molecule of substituent group. The change law of p-substituted thiophenol are the same as p-substituted thiophenol dibutyltin. Because Sn2+is (18+2) electronic configuration with strong polarization force.When p-substituted thiophenol become p-substituted thiophenol dibutyltin, which bring Sn2+ion with a strong electron-withdrawing, electron withdrawing ability of p-substituted thiophenol dibutyltin enhanced and its thermal stability is improved.(2) According to this progressive change law of heat stabilizing performance and the characteristics of molecular structure, it can be speculated that dialkyltin p-substituted thiophenol stabilize PVC by electrophilic reaction with PVC using their carbonyl C atom of the carboxylate radical and/or dialkyltin ion as the electrophilic atoms, but not by the traditional Frye and Horst’s mechanism. Therefore, the exact mechanism of heat stabilization of heat stabilizers for PVC need to be clarified by further research.