Studies On Environmentally Friendly Thermoplastic Starch/Montmorillonite Nanocomposites

Polymer-matrix nanocomposites, as an important part in nanotechnology field, aredeveloping rapidly and have potential applications. In this thesis, from the view of thesustainable development of the ecology, resources and environment, the naturalcornstarch is plasticized by different plasticizer system, environmentally friendlythermoplastic starch / montmorillonite (TPS/MMT) nanocomposites are prepared bythe melt extrusion technology, and their structures and properties are studiedsystemically.Montmorillonite-reinforced and glycerol-plasticized thermoplastic starchcomposites (MGTPS) were prepared with the method of melt mixture and two timesextrusion, in which sodium montmorillonite was as a kind of reinforced additive andthe glycerol-plasticized thermoplastic starch (GTPS) were used. Fourier Transforminfrared (FT-IR) patterns indicated that in the MGTPS the hydrogen bonds wereformed between the reactive hydroxyl groups of MMT and the hydroxyl groups ofstarch molecules, which weakened the hydrogen bonds between the starch moleculesin GTPS. Scanning electron microscope (SEM) revealed that MMTs being in thesubmicron filling transition state were uniformly dispersed in GTPS, and formedstabile multiphase structure. Comparing with the pure glycerol-plasticizedthermoplastic starch (GTPS), nanocomposites better tensile strength and Youngsmodules, 27.34 MPa and 206.74 MPa respectively. And the thermal stability andwater-resistance improved greatly.The MMTs were activated by the ethanolamine and the citric acid, and the layerdistance was expanded from 1.01 nm to 1.25 nm of EMMT and 1.55 nm of CMMT.The improvement of the layer microenvironment made the MMT easy to react withTPS and form nanocomposites. The formamide / ethanolamine-plasticizedthermoplastic starch/ ethanolamine activated montmorillonite (FETPS/EMMT)nanocomposites,the urea / formamide plasticized thermoplastic corn starch / citricacid-activated montmorillonite (UFTPC/CMMT) nanocomposites and the urea /ethanolamine-plasticized thermoplastic starch / ethanolamine--activatedmontmorillonite (UETPC/EMMT) were prepared with the method of meltintercalation, in which FETPS/EMMT belonged to intercalated nanocomposites, andboth UFTPS/CMMT and UETPS/EMMT belonged to exfoliated nanocomposites.The preparation of these nanocomposites used the hydrogen bonds that formedamong the mall molecule plasticizer, starch and MMT activators, and the differencebetween the melt viscosities.Mechanical properties of the three nanocomposites, FETPS/EMMT ,UFTPS/CMMT and UETPS/EMMT, were obviously better than that of the purethermoplastic starch, and the maximum tensile stress were 7.5 MPa,24.86 MPa and29.81 MPa, the tensile strain were 85.2%,134.5% and 152.1%, and the Youngsmodulus were 145.1 MPa,625.3 MPa and 734.6 MPa respectively. X-ray diffractionindicated that the three nanocomposites all resolved the problem of therecrystallization behavior caused by the long time storing that existed in theconventional GTPS. Moreover, The thermal stability and water-resistant properties ofall the three nanocomposites improved obviously.In the preparation of the nanocomposites, the stronger the hydrogen bond formedamong the MMT activators, plasticizers and starch molecules was, the smaller wasthe shear viscosity. And so the TPS molecular chains were easier to intercalated intothe layers of MMT, which was benefit to form nanocomposites. By contraries, thatwent against to form nanocomposites. It was interesting to note that when thenanocomposites were cooled by the liquid nitrogen, they formed a kind of reticulatefibre structure, which was the main reason that the nanocomposites had bettermechanical properties.