Preparation Of PET/Montmorillonite Nanocomposites And Study On The Crystallization

Poly(ethylene terephthalate)(PET) is a semicrystalline thermoplastic plastics，which have many advantages, but the disadvantages, for example, low crystallizationrate and poor impact performance, limit its application in some fields.Montmorillonite (MMT) is natural nano filler. The properties of polymer, such ascrystallization rate, mechanical properties, barrier properties and flame retardancy,will be changed by adding a small amount of MMT. Therefore, researchers havefocused on the preparation of PET/MMT nanocomposites by adding modified MMT.In this article, two kinds of organic modifier, CTAB and KH-560, were used toprepare C-MMT and C-S-MMT. Several kinds of nanocomposites (PET/MMT,PET/C-MMT, PET/C-S-MMT, PET/DK2and PET/DK5) were prepared by meltintercalation subsequently. At last, we investigated the relationship among PET,organic modifier and MMT, and the relationship between structure and performancein PET/Montmorillonite nanocomposites. The main works are as follows:(1) Na-MMT was modified by CTAB (named C-MMT). Na-MMT was modifiedby CTAB and KH-560(named C-S-MMT). Na-MMT, C-MMT and C-S-MMT werestudied by WAXD, FTIR and TG. The results of WAXD and FTIR showed thatintercalators intercalated into MMT and the interlayer spacing of MMT increased.The surface of montmorillonite was covered by KH-560, which was also investigatedby TG. There are three stages of decomposition in C-MMT and C-S-MMT. The initialdecomposition temperature of C-MMT and C-S-MMT is about230℃.(2) Na-MMT, C-MMT, C-S-MMT, DK2and DK5were separately compositedwith PET by melt intercalation in different proportions. So several kinds ofcomposites were prepared, which named PET/MMT, PET/C-MMT, PET/C-S-MMT,PET/DK2and PET/DK5. The analysis of structure was made by WAXD. It was foundthat the dispersion of MMT in PET was affected by its type and content.PET/C-MMT, PET/C-S-MMT, PET/DK2-3%and PET/DK2-5%were intercalatednanocomposites. PET/MMT and PET/DK2-1%were exfoliated nanocomposites. However, PET/DK5was microcompiste. The thermostability of nanocomposites wasinvestigated by thermogravimetry (TG). The results showed that the thermal stabilityof PET, which was related with dispersion of MMT, increased by adding MMT toPET. Two methods, KAS and FWO, were employed to calculate the activation energyduring thermal degradation. It also showed that MMT can increase thermal stabilityof PET.(3) Crystallization property of PET, PET/MMT, PET/C-MMT, PET/C-S-MMTand PET/DK2was studied by Differential Scanning Calorimetry (DSC). After addingMMT to PET matrix, the degree of superheat and supercooling of nanocomposites(PET/MMT, PET/C-MMT, PET/C-S-MMT and PET/DK2) was lower than that ofPET, and the crystallization peak temperature of nanocomposites was higher than thatof PET, indicating that MMT can act as nucleating agent, which was affected by itsdispersion. Non-isothermal crystallization of PET, PET/MMT, PET/C-MMT,PET/C-S-MMT and PET/DK2were also studied. Non-isothermal crystallizationkinetics of PET/MMT nanocomposites were analyzed by Jeziorny approach. Thecrystallization activation energy was calculated by three methods and nucleatingactivity of MMT, C-MMT, C-S-MMT and DK2was calculated. It was found thatmontmorillonite can act as a nucleating agent and increase crystallization rate of PET.