THERMAL AND MECHANICAL PROPERTIES OF POLY(PROPYLENE CARBONATE)NANOCOMPOSITES WITH VARIOUS ORGANO-MODIFIED MONTMORILLONITES

Hexadecyl trimethylamine bromide (HTAB) modified montmorillonite (OMMT) was prepared by cationic exchange between Na~+ and quaternary amine ion,and the layer distance increased by 0.74 nm from 1.26 nm of Na-MMT to 2.00 nm of OMMT,which was very important for late polymer intercalation.Moreover,the existence of long alkyl tail in OMMT enhanced its hydrophobicity,which was beneficial for melt intercalation.The poly(propylene carbonate)(PPC)/OMMT nanocomposites were prepared by melt intercalation of PPC into OMMT,where the as polymerized PPC with number average molecular weight of 8.5×10~4 was end-capped by maleic acid anhydride before use,and the layer distance increased from 2.00 nm of OMMT to 3.91 nm of PPC/OMMT nanocomposites when the OMMT content increased from 0 to 7 wt%.X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed that the PPC/OMMT nanocomposites displayed an intercalated-and-flocculated structure,which was attributed to the strong interaction among the hydroxyl groups at the edges of the layered OMMT.Thermogravimetric analyses (TGA),differential scanning calorimetry (DSC) and mechanical performance testing (Zwick/Z010,Germany) were used for investigation of the thermal and mechanical properties of the nanocomposites.The Young's modulus increased with increasing OMMT content when the OMMT content was below 5 wt%. When 1 wt% of OMMT was added in the composite,the Young's modulus of the composite increased by 46.4% from 691.4 MPa to 1012 MPa,once the OMMT content in the composite reached 5 wt%,the Young's modulus increased by 61.8% from 691.4 MPa of pure PPC to 1119 MPa of the nanocomposite.In addition to the layered structure of OMMT in the composite,the existence of hydrogen bonding interaction between the hydroxyl groups at the edge of layered OMMT and carbonyl groups in PPC may be another important factor for the above sharp increase.When the OMMT content was over 5 wt%,the dispersion efficiency of OMMT in PPC decreased and inhomogeneous aggregates of OMMT appeared,leading to drop of Young's modulus,in another respect,the long alkyl tails in OMMT may act as plasticizer to PPC,also leading to decrease of Young's modulus.It should be noted that,unlike the significant change of Young's modulus,the tensile strength of the nanocomposite only showed a slight increase of 8.9% from 43.6 MPa to 47.5 MPa.The thermal decomposition temperature of nanocomposite increased with increasing OMMT load,compared with pure PPC,the thermal decomposition temperature increased by 32.3℃ from 258.6℃ to 290.9℃,which was attributed to the retarding effect of the layered OMMT structure against thermal decomposition.Accordingly,the T_g of the nanocomposites also showed a slight increase of 2.4℃ from 30.9℃ to 33.3℃.Therefore,incorporation of OMMT in PPC/OMMT composites may be a potential way to raise the thermal and mechanical performance of PPC.