Study On Preparation And Property Of Polypropylene/montmorillonite Nanocomposites

Polypropylene(PP),as a kind of universal plastic,has some shortcomings,such as the brittleness in low temperature,the low tenacity,aging,and so on.PP is not perfect in property and must be modified in order to be used widlely.The occurrence of nanocomposites brings the modification of PP the new methods.The montmorillonite(MMT) with structure of a layer of forms are the ideal natural mineral wich was prepared into nanocomposites.PP/MMT nanocomposites were applied for industrialization with good prospect at present.In this thesis,PP grafted MAH was used as compatilizer,PP/MMT nanocomposites were prepared through two-steps by melt intercalation,realized the complex on a nanometer of yardstick of PP and MMT.The main results were as follow: Organic montmorillonites were prepared by treating Na-montmorillonites with different long-chain alkyl quaternary ammonium ions.The org-MMT were characterizered by FT-IR,XRD and TGA.The results indicated that alkyl ammonium ions had been intercalated into the layered silicate of org-MMT.The layer spacing of hexadecyl trimethyl ammonium(HTAB) modified MMT increased from 1.523nm to 3.740nm. As far as PP/MMT nanocomposites prepared from HTAB modified MMT at 200℃　 were concerned,when the MMT content was 2% and compatilizer content was 11.3%,the obtained nanocomposites showed the best mechanical properties with tensile strength 38.01 MPa and flexural strength 70.10MPa.The tensile strength and flexural strength increased by 24.6% and 102.4 % compared with those of PP. XRD spectrum showed that the layer spacing of MMT in nanocomposites increased further compared with that of org-MMT.The morphology of impact fracture surfaces were investigated by SEM : There are absence of clear organic and inorganic phases in PP/MMT nanocomposites,MMT dispersion in the matrix of PP had reached a nanometer yardstick. The mechanism of impact fracture of nanocomposites was toughness fractures while PP was frangibility fractures. The crystallization property were investigated by means of differential scanning calorimetry(DSC).The results showed that the addition of MMT has nucleation effect in crystallization of PP and the crystallization velocity of PP was quickened , the crystallinity was enhanced. Studying on kinetics of isothermal crystallization showed that the constant K(t) of crystallization rate and half period of crystallization t1/2 of PP/MMT nanocomposites relied on the crystallization temperature slightly. The Avrami index(n) of PP value was between from 3.46 to 4.12 ,which is in phase nucleating mechanism ,while The Avrami index(n) of PP/MMT nanocomposites was about 3, which is out of phase nucleating mechanism typically. Through studying on kinetics of non-isothermal crystallization,it was shown that at the same cooling rate, the t1/2 of PP/ MMT nanocomposites was decreased and tp was increased compared with that of PP.As indicated that MMT has functioned as a kind of nucleating centers during the non-isothermal crystallization process of PP. The activation energies(? E)of PP/ MMT nanocomposites were increased than that of PP.