A Rheological Study on the Kinetics of Hybrid Formation in Polypropylene Nanocomposites

Abstract

We present an experimental investigation on the creep behavior of molten polypropylene organically modified clay nanocomposites. The nanocomposite hybrids were prepared by melt intercalation in an extruder in the presence or absence of a compatibilizer. They were subsequently annealed and simultaneously characterized using high-temperature wide-angle X-ray diffraction and controlled stress rheometry. The creep resistance of compatibilized hybrids was significantly higher than that of uncompatibilized hybrids and also increased with annealing time. The microstructure of the nanocomposites as investigated by TEM and high-temperature WAXD showed the presence of clay crystallites dispersed within the polymer matrix. The creep data together with the microstructural investigation are probably indicative of a small amount of exfoliation from the edges of the clay crystallites during extrusion and annealing. The zero shear viscosity of the compatibilized nanocomposites containing greater than 3 wt % clay was at least 3 orders of magnitude higher than that of matrix resin and the uncompatibilized hybrids. Importantly, the large increase in zero shear viscosity was not accompanied by any increase in the flow activation energy compared to the matrix polymer. The compatibilized hybrids also showed an apparent “yield” behavior. We conclude that the solidlike rheological response of the molten nanocomposite originates from large frictional interactions of the clay crystallites. Compatibilizer has a significant influence in modifying the rheological behavior.

Dynamic melt flow of nanocomposites based on poly-ε-caprolactam

“…The authors concluded that an anisometric structure is responsible for the non-linear¯ow behavior. Galgali et al (2001) investigated creep behavior of melt intercalated NC of PP with organoclay and MA-PP. The latter was added at a ratio of either 0:1 or 1:1 in respect to organoclay.…”

“…The tests under a blanket of dry nitrogen were accompanied by the time-dependent increase of PA-6 molecular weight that had to be taken into account. The PNCs belong to the category of end-tethered nanocomposites, reported to show a complex rheological behavior (Krishnamoorti and Giannelis 1997;Ho mann et al 2000aHo mann et al , 2000bRen et al 2000;Solomon et al 2001;Galgali et al 2001). The rheological properties of polyamides are known to depend on the measurement time.…”

Melt compounding of different grades of polystyrene with organoclay. Part 2: Rheological properties

“…Furthermore, because the clay platelets align during flow, the power-law index for PNC is smaller after shearing than before (24). When the clay content increases, the transition from the Newtonian to the power-law flow region shifts toward lower frequency (17,20,28). Especially, at high clay loadings (e.g., w Ն 10 wt%), the Newtonian plateau disappears for frequencies w Ն 0.1 rad/s.…”

“…PCL (16), polypropylene (PP) (17,18), PA-12 (19), PEG (20), poly(styrene-b-isoprene) PS-PI block copolymer (21,22), PS (23Ϫ25), etc. The values of the initial slope, gЈ or g Љ, depend on the degree of dispersion and concentration of organoclay platelets.…”

Rheology of Polymers with Nanofillers

“…It is noteworthy that exfoliation is not the only mechanism leading to slope reduction (e.g., formation of clay aggregates, phase separation, or presence of compatibilizer micelles leads to similar effects) [Lepoittevin et al, 2002]. Similarly, melt blending PP: PP-MA = 0: 1 or 1: 1 with C6A resulted in intercalated CPNC with d 001 = 3.3 nm [Galgali et al, 2001]. The low-frequency (ω = 0.06 to 1 rad/s) "terminal" slope was analyzed using the dependence where w represents wt% of compatibilizer and clay.…”