Clarifying Agent Di-(3,4-dimethylbenzylidene) Sorbitol And Transparent Polypropylene

Polypropylene has been one of the fastest growing general plastics for decades. The developments and application of PP were recently limited due to its transparency and glossiness. Clarifying agents are efficient to improve the transparency of PP. In order to elucidate the mechanism of PP crystallization and the improving efficiency of transparency of PP with DMDBS, the synthesis of DMDBS and its application as PP clarifying agent were studied in this paper.Chapter 1 reviewed the literatures of transparent polypropylene, and introduced the different types and characteristics of clarifying agents used in polypropylene. Crystallization behavior and its related kinetics of clarifying agents were discussed, and all kinds of features of DMDBS on PP were studied.Chapter2 discussed synthesis and characterization of di-(3,4-dimethylbenzylidene) sorbitol(DMDBS) by means of condensation reaction between sorbitol and 3,4-dimethyl benzaldehyde using toluene-p-sulfonic as acid catalyst. The effects of reaction solvent system, feeding mode, S/B ratio, catalyst content and reaction time were examined. The optimum reaction condition was obtained so that DMDBS with the purity of 99.6% and the melting point of 265.7℃ (Peak temperature was 273.1℃) was successfully produced in which the high yield of 99.5% was reached. The experimental results also showed that appropriate treatment whose procedure should be neutralization, water wash, solvent wash, refine, purification and vacuum drying was very necessary.Chapter3 discussed the effects of DMDBS on the crystallization behavior, mechanical properties, melting property, thermal stability and transparency of PP added DMDBS. The experimental results indicated that T_c⁰, T_c^p, T_c^f and T_c^on were increased, specially T_c^p increased by 15-20℃;and that the spherocrystal size, crystallization peak width, â–³T_c^L, D and â–³T_c² were decreased. Those results showed that the speed of crystallization was increased so that the spherocrystal with small uniform was formed. The small uniform spherocrystal decreased the influences of the refraction and reflection on PP, so that the transparency, glossiness, and mechanical properties of PP were improved. The glossiness of PP with 0.3% DMDBS wasenhanced by 44%, in addition to tensile-strength, flexural-strength, notch impact strength and Rockwell hardness by above 15% 9% 11% and 3 %, respectively. The kinetics of nonisothermal crystallization was studied by means of Mandelkern's theory. Comparing to those of PP without clarifying agent, in the case of nonisothermal crystallization of PP with the addition of DMDBS, t_1/2 decreased by 27 %-48%, n was close to 3 and Z_t was dramatically increased by 51%-387%, respectively. The experimental results showed that the crystallization of PP with the addition of DMDBS should belong to homogeneous three-dimensional nucleation crystallization. The temperature and speed of crystallization, the crystallinity and degree of spherocrystal uniformity were improved due to the addition of the present clarifying agent. It was known that air atmosphere would accelerate the decomposition of clarifying agent, pure PP and PP with DMDBS, and the DMDBS in PP would have the adverse effect on stability of PP when its temperature succeeded the limitation. The degradation of the PP with and without DMDBS could be considered as a first-order reaction. The apparent activation energy of PP with DMDBS was either 203kJmol^-1 in air atmosphere or 224 kJmol^-1 in N₂ atmosphere, which were substantially higher than that for pure PP (120 kJmor^-1 in air and 128 inN2), respectively.Chapter4 summarized the main conclusions of this research work.