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

Abstract

Polystyrene‐based nanocomposites (PNC) were prepared using three grades of polystyrene (different molecular weights). The resin was melt‐compounded with 0 to 10 wt% of commercial organoclay in a co‐rotating twin‐screw extruder. Owing to thermo‐oxidative degradation the degree of dispersion was poor. The rheological properties of PNC were determined under dynamic and steady state shear as well as under extensional flow conditions. At the higher clay content, dynamic strain sweep demonstrated that the storage and loss moduli decrease continuously with an increase of strain. To characterize this nonlinear viscoelastic behavior, the Fourier‐transform rheology was applied. The low strain frequency sweep showed that the storage and loss moduli increase with organoclay content. The extracted zero‐shear viscosity data were used to calculate the intrinsic viscosity and then the aspect ratio of dispersions. In spite of nonlinear viscoelastic behavior, the time‐temperature superposition was observed in the full range of concentration. The horizontal and vertical shift factors were found to be almost independent of organoclay content and molecular weight of PS. For comparison, PNC was also prepared by the solution method. A high degree of dispersion was obtained, reflected in the aspect ratio: p = 269, to be compared with p = 16 calculated for the melt‐compounded PNC. Polym. Eng. Sci. 44:1061–1076, 2004. © 2004 Society of Plastics Engineers.

Melt compounding of different grades polystyrene with organoclay. Part 3: Mechanical properties

“…Good results were also obtained using polycarbonate [18,19] or epoxy [20]. Generally, it is quite difficult to exfoliate clay in low-polarity polymers, such as polystyrene [21,22] or polyolefins [23].…”

“…These are coded as LMW, MMW, and HMW, for low (M w ϭ 230 kg/mol), medium (M w ϭ 270 kg/mol), and high (M w ϭ 310 kg/mol) weight average molecular weight respectively [21,22]. The organoclay (Cloisite 10A) is a MMT (cation exchange capacity [CEC] ϭ 0.926 meq/g, d 001 ϭ 1.17 nm) intercalated with 1.25 meq/g of di-methyl benzyl hydrogenated tallow ammonium chloride (2MBHTA), which increased the interlayer spacing to d 001 ϭ 1.92 nm.…”

“…Thus, deterioration of the PS matrix seems to be the main culprit for the reduced performance at longer residence times. The thermooxidative degradation of PS seems to be responsible for the loss of performance [21,22].…”

Numerical simulation of polymer nanocomposites using self-consistent mean-field model

“…The motivation for the inclusion of the solid platelet interactions was provided by the well-known thermal instability of organoclays under normal polymer processing conditions, which leads to the progressive removal of the intercalant from the clay surface, often resulting in the reaggregation of the platelets. 1,52 Using the one-dimensional model ͑without the solid surface present͒, the simulation successfully identified the optimum range of the operational parameters such as the grafting density and the statistical chain length of a compatibilizer macromolecule for the three values of the binary interaction parameters between the host and compatibilizer polymer chains, hg . Results of the application of the methodology to real system, viz., fully preintercalated organoclay with polypropylene ͑PP͒ and end-functionalized PP as compatibilizer ͑i.e., hg ϭ0), suggest that for the best performance, about 4% of the clay sites should be reacted with a compatibilizer of similar molecular weight ͑MW͒ as that of PP.…”

PVT of amorphous and crystalline polymers and their nanocomposites

“…The experimental details and discussions may be found in [11,12,14,[32][33][34][35]. Fitting the PVT data Eqs.…”