Effect of multiple extrusions on the impact properties of polypropylene/clay nanocomposites

Abstract

Polypropylene (PP)-based polymer nanocomposites containing organically modified montmorillonite (OMMT) with and without maleic anhydride grafted PP, were compounded by twin-screw extrusion. The extrusion process was repeated various numbers of times to increase the extruder residence time (T R ) and, through that, the particle dispersion. Rheological measurements fitted to a modified Carreau-Yasuda model defining a melt yield stress were used to indicate changes in the particle dispersion with regard to T R . This analysis showed a monotonically increased dispersion of clay particles in the PP matrix with increasing extruder T R . The small-strain tensile properties were tested at both ambient (20 C) and elevated (90 C) tem-peratures, and no significant changes were observed in the tensile strength or modulus as a function of T R . Instrumented Izod impact tests showed that the nanocomposite impact strength (r i ) increased monotonically with increased T R by 70% from least dispersed to best dispersed, which was still 20% below the level for neat PP. Both the fracture initiation energy and propagation energy increased with T R , but the primary effect on r i came from the fracture propagation energy, which delivered 80% of the improvement. V C 2012Wiley Periodicals, Inc. J Appl Polym Sci 126: 620-630, 2012

Comparison of the performance of masterbatch and liquid color concentrates for mass coloration of polypropylene

“…The absence of a melt yield stress might be due to the low concentration of pigment particles in PP compared to other studies . The values for the zero shear viscosity with different extruder retention times can be seen in Table , where the viscosity is seen to decrease with increasing extruder retention time, which were also found in the study done by Klitkou et al . This decrease implies a possible degradation of the polymer due to the mechanical and thermal treatment which is consistent with the correlation between molecular weight of the polymer and the polymer viscosity …”

“…and W. Lertwimolnun and B. Vergnes . The absence of a melt yield stress might be due to the low concentration of pigment particles in PP compared to other studies . The values for the zero shear viscosity with different extruder retention times can be seen in Table , where the viscosity is seen to decrease with increasing extruder retention time, which were also found in the study done by Klitkou et al .…”

“…When pigments and fillers are added to PP fibers, the structure changes resulting in changed strength and processing conditions . The additives can work as nucleating agents and initiate certain crystal phases influencing the strength of PP as highly crystalline polymers are stiffer than amorphous polymers and the different crystal phases result in different strength .…”

“…The pigments used are pigment white 6, pigment green 7, and pigment blue15:3. To obtain different degrees of mixing for the same material, multiple extrusion cycles are applied, thereby increasing the residence time, T R . With different degrees of mixing, it is possible to investigate the difference in dispersion between the two color concentrates and to see if the same degree of dispersion can be obtained for the two types.…”

The effect of matrix morphology on dynamic-mechanical properties of polypropylene/layered silicate nanocomposites

“…Water-assisted extrusion of PP/clay nanocomposites at different conditions, including high shear rates, was investigated [44,45], and the best mechanical and thermal properties were achieved when the clay was mixed in the slurry state, due to the highest level of dispersion reached by the synergistic effect of water, and high shear rates [45]. The effect of multiple extrusions on the impact properties of PP/clay nanocomposites was investigated by Klitkou et al [46]. Different conditions and equipment for extrusion and injection molding were proposed in the literature to alter the tensile strength and modulus, fatigue properties, and fracture and thermal behavior of PP/clay nanocomposites [47][48][49][50][51][52][53].…”