Preparation Of Sorbitol Nucleating Agents And Effect On Properties Of Polypropylene

Due to low-temperature brittlethe, notch sensitivity and toughness of polypropylene (PP) limits its applications. To solve this problem, the fundamental way is which adding nucleating agent into PP matrix improves the crystallization properties of PP, thus improves thermal properties and mechanical properties of PP.In this study, 1,3-2,4-dibenzylidene sorbitol (DBS), 1,3-2,4-di (p-hydroxyl) benzylidene sorbitol (DHDBS) or 1,3-2,4-di (p-nitro) benzylidene sorbitol (DNDBS), acted as nucleating agent, were synthesized by acetal reaction from benzaldehyde, p-hydroxyl benzaldehyde, p-nitro benzaldehyde and D-sorbitol, with p-toluenesulfonic acid as catalyst, cyclohexane as solvent and methanol as accelerating agent. Fourier transform infrared (FT-IR) spectroscopy showed that nucleating agents were synthesized. Melting point tests showed that melting point of three kinds of PP nucleating agent was higher than that of PP.The factors, which effect acetal reaction to improve the yield of the nucleating agent, were discussed in this paper. The results showed that preparation of three kinds of polypropylene nucleating agent had same optimum reaction conditions, that the optimum mole ratio of aldehyde to alcohol is 2.1:1, the reaction time is 6h, amount of TSA is 4wt%,amount of cyclohexane is 600wt%, amount of methanol is 20wt%, and the suitable temperature is 65℃.Blends of PP and nucleating agent at mass percents (0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt% and 0.5 wt%) were prepared using solution precipitation method, respectively. The size of the spherulite, which was studied by scanning electron microscope (SEM) and polarizing microscope (PLM), was decreased. Crystallization Morphology and crystallinity was studied by PLM and X-ray diffraction (XRD). The result showed that three kinds of nucleating agent can induceαcrystal generated and increase the degree of crystallization of PP. The molten peak of PP analysed by differential scanning calorimetry (DSC) were rised. It explains that the crystallinity and crystalline perfect degree of modified PP were increased. Thermo-gravimetric (TG) analysis showed that adding nucleating agent can improve the stability and the decomposition temperature of PP. And optimal amount of three kinds of nucleating agent all were 0.3wt %.Blends of PP and different nucleating agent having different mass percents (0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt% and 0.5 wt%) were prepared using a twin screw extruder and were compression molded by injection molding machine. Mechanical properties of PP were measured using impact test enginery and micro-computer control universal test machine. The result showed that three kinds of nucleating agent can improve mechanics properties of PP in different degree. Impact strength, elongation at break, tensile strength, Young's modulus and bending strength of PP were increased 9.86~33.10%, 13.33~71.11%, 51.21~69.59%, 42.46~ 64.45% and 56.99~85.34%, respectively .Optimal amount of three kinds of nucleating agent all were 0.3wt %, and properties of PP modified with 1,3-2,4-di (p-hydroxyl) benzylidene sorbitol (DHDBS) are excellent.