金属羧酸盐类成核添加剂对PET结晶成核和分子量的影响

THE EFFECTS OF METAL CARBOXYLATE NUCLEATING ADDITIVES ON THE CRYSTALLIZATION, NUCLEATION AND MOLECULAR WEIGHT OF POLY (ETHYLENE TEREPHTHALATE)

用差示扫描量热仪(DSC)、高效凝胶色谱仪(HPGPC)和粘度法研究了三种不同类型的金属羧酸盐类成核添加剂对聚对苯二甲酸乙二酯(PET)的结晶、成核和分子量的影响。结果表明,由于成核添加剂与PET之间在熔融态下存在化学反应,导致PET有不同程度的分子量下降,同时PET结晶速率发生变化。对不同金属离子的醋酸盐,在金属离子半径相近的条件下,随金属离子电负性下降,PET结晶速率加快;对不同烷基长度的脂肪族羧酸钠盐,烷基分子链越长,PET结晶速率越快;对不同取代基的苯甲酸钠盐,其相应的酸解离常数和溶度参数与PET的结晶速率有一定的内在联系。并从等温结晶的Avrami指数均为3左右,说明金属羧酸盐类成核添加剂所引起的化学成核是三维异相成核。

The effects of three kinds of metal carboxylate nucleating additives on the crystallization, nucleation and molecular weight of poly(ethylene terephthalate)(PET) were studied by differential scanning calorimetry (DSC) , viscosity measurement and high performance gel permeation chromatograpgy (HPGPC) . It is found that there are chemical reactions between nucleating additives and PET in the melt state, resulting in the change of molecular weight and crystallization rate of PET in some degree. In the case of acetates with different metal ions, the lower the electronegativity of the metal ion, the faster is the crystallization rate of PET when the metal ions are of approximate same radius. In the case of sodium alkyl acetates with different alkyl chain length, the longer the alkyl chain, the faster is the crystallization rate of PET. In the case of the sodium benzoates with different substituted groups, the crystallization rate of PET is related to the dissociation constant and solubility parameter of the substituted benzoates. It is also found that the Avrami exponent of the isothermal crystallization of PET is around 3 for both the unnucleated or nucleated PET. Therefore it is suggested that the chemical nucleation caused by metal carboxylate nucleating additives is heterogenous in nature.