POLYOLEFIN-CLAY NANOCOMPOSITES PREPARED WITH AID OF POWER ULTRASOUND
A continuous ultrasound assisted process using a single screw extruder with an ultrasonic attachment was developed to prepare polyolefin/clay nanocomposites of varying clay concentrations. Isotactic polypropylene (PP) and high density polyethylene (HDPE) were chosen as a polymeric matrix. A partial intercalation of polymer molecules into clay galleries, which occurs at short residence times (on the order of seconds), was observed, as evident from the measurements by X-ray diffraction and transmission electron microscopy. The obtained results indicated the rapid intercalation of polyolefin/clay nanocomposite without the matrix being chemically modified. Two methods for fabrication of PP/clay nanocomposites using a continuous ultrasound assisted process were compared. In the first approach, where a two stage process was implemented, the nanocomposites were prepared using a co-rotating twin screw extruder followed by a single screw extruder equipped with ultrasonic die attachment. In the second method, where a single stage process was used, the nanocomposites were compounded by a single screw extruder with two mixing sections and ultrasonic die attachment. Single stage process led to less polymer degradation at the fixed gap size. Variations of flood and starved feeding, and gap size during single stage process were studied. Results indicate that intercalation and matrix degradation under ultrasound were higher for flood feeding and for smaller gap. Both single and two stage processes produced PP based nanocomposites exhibiting higher elongation at break and toughness. The melt intercalation of HDPE/clay nanocomposites was also observed under ultrasonic treatment at various amplitudes leading to increase of the elongation at break and toughness. The Young’s modulus of untreated and treated nanocomposites increased significantly with the increase of clay loading. But the modulus of treated samples showed lower values than that of untreated ones. Oxygen permeability of treated HDPE/clay nanocomposites was reduced up to 20% as compared to untreated samples. The effect of ultrasound on the structure and properties of nanocomposites prepared from PP/maleated PP/clay blends was evaluated. No synergetic effect between polypropylene modified with maleic anhydride and treatment by high power ultrasound in preparation of nanocomposites has been detected. The modified Halpin-Tsai theory of composite materials has been employed in order to predict the effect of incomplete exfoliation of clay platelets on the Young’s modulus of the nanocomposites. A good agreement between experimental and theoretical data has been observed when reduction of the reinforcement efficiency of clay had been incorporated through reduced aspect ratio of elementary clay platelets.
School:The University of Akron
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:polyolefin nanocomposites ultrasound
Date of Publication:01/01/2006