The Preparation Of Polyol Based Metal Alkoxide Zinc-mannitol And Its Property Research On Thermal Stability Of Rigid Poly(Vinyl Chloride)

It is generally believed that poly（vinyl chloride）（PVC） has the attributes of low cost, good corrosion and abrasion resistance, and excellent electrical insulating property. It is one of the most extensively produced and utilized thermoplastics all around the world. Unfortunately, PVC undergoes autocatalytic degradation through hydrogen chloride（HCl） elimination during its thermal processing due to the defects of its molecular structure, resulting in the deterioration of physical and chemical properties. In order to maximize the practical value of PVC, the addition of thermal stabilizers prior to processing is the most efficient and convenient solution to restrain this thermal degradation. With respect to the commonly used stabilizers, more and more restrictions have been imposed on lead compounds due to the high toxicity, the requirement of co-stabilizers for the long-term thermal stability inprovement is the drawback for metal soaps, organic tin compounds are of high price on account of the complex production process and have peculiar smell, liquid mixed metal stabilizers are faced with the challenge of curbing the volatilization of organic chemicals, rare earth stabilizers are also limited for their quite poor effects and high cost for research and development; consequently, developing novel PVC thermal stabilizers with excellent performance has been the research subject for many researchers.In this paper, polyol based metal alkoxide Zinc-Mannitol（Zn-Man） was synthesized through an alcohol exchange reaction, using zinc acetate, ethanol and mannitol. FTIR, elemental analysis and XPS was utilized to characterize the product, which was then used as a main thermal stabilizer for PVC, and the effect was evaluated through Congo red testing, conductivity measurements, thermal aging testing, TGA and ultraviolet-visible spectroscopy test, and the thermal degradation kinetics of activation energy was also calculated. With the purpose of improving the shortages of Zn-Man shown in the testing, Zn-Man was compounded with commonly used additives with specific functions, calcium stearate（Ca St₂）, zinc stearate（Zn St₂） and stearoyl benzoyl methane（β-diketone）, to further improve the comprehensive IV performance. Besides, the possible thermal stabilizing mechanism was discussed. Specific contents are as follows:1. Zn-Man was prepared through the alcohol exchange reaction. Precursor zinc acetate and mannitol with the mole ratio of 1:2 was taken, the zinc acetate and 60 m L of ethanol firstly reacted at 120 oC for 3 h, the excess ethanol was evaporated. Subsequently, the obtained solid resultant reacted with mannitol at 165 oC for another 2 h, and proper cyclohexane serving as the water-carrying agent was added in this process, and the target product Zn-Man was obtained after distilling off the cyclohexane. Experiments showed that excessive dosage of zinc acetate which remained in the product did harm to the thermal stability of PVC; excessive addition of ethanol benefited to the preparation in the first stage, and the applicable dosage was about 4 times, the presence of ethanol not only involved in the reaction directly, but also supplied the liquid environment; and too high reaction temperature led to the decomposition of product.2. The target product Zn-Man was characterized: FTIR indicated new Zn-O bond was generated in Zn-Man compound, a strong absorption peak was observed near 695.8 cm-1; XPS demonstrated, after the reaction, both the binding energy and full width at half maximum of 2p3/2 peak of zinc in Zn-Man were changed, 0.7 e V shift in binding energy was occurred, and the full width at half maximum changed from 3.76 e V to 3.12 e V. The obtained formula of Zn-Man was（C6H13.1O6.6）2Zn1.2 from elemental analysis, which approximately agreed with the theoretically calculated（C6H13O6）2Zn.3. The efficiency of Zn-Man was tested. A series of thermal stability performance testing showed Zn-Man possessed decent long-term stability for rigid PVC, compared with commercially used stabilizer Ca/Zn soaps, Zn-Man could prolong the thermal stability time to 101.5 min, raise the initial degradation temperature to 270.5 oC and postpone the occurrence of degradation reaction, and the "zinc buring" phenomenon did not occur within 180 min during testing. The thermal stabitity machanism was explored through back titration method, Zn Cl2 compounding method and quantum chemical calculations, results showed that Zn-Man could substitute for the labile chlorine atoms of PVC chains through nucleophilic attack and absorb the released HCl, and chelate Zn Cl2 during the thermal stabilizing process thus to inhibit "zinc buring".4. Synergistic effects of Zn-Man with Ca St₂/Zn St₂ mixture, Ca St₂, Zn St₂ and β-diketone were explored, respectively. Thermal stability testing showed Zn-Man possessed improved initial coloring when compounded with Ca St₂/Zn St₂, Zn St₂ and β-diketone; and the thermal stability was further prolonged when mixed with Ca St₂/Zn St₂ and β-diketone, to 165.2 and 164.7 min, respectivrly; but excess dosage of them deteriorated the long-term thermal stability instead. The optimal addition ratio was 3/1. However, the synergistic effect between Zn-Man and Ca St₂ was small. The synergistic effects of Zn-Man on improved thermal stability could mainly be attributed to: a, the hydroxyl groups in Zn-Man on chelating Zn Cl2 for Zn-Man/Ca St₂/Zn St₂ and Zn-Man/Zn St₂ systems containing Zn St₂; b, the nucleophilic reaction between enol-tautomer form of β-diketone and labile chloride atoms in PVC chains, and Zn-Man served as HCl acceptor for Zn-Man/β-diketone system.