Mixed percolating network and mechanical properties of polypropylene/talc composites

Abstract

Injected polypropylene/talc composites were studied to evaluate the conditions leading to the formation of a mixed talc/polymer crystalline lamella percolating network and the influence of such a network on the nanocomposite mechanical properties. The talc was either conventional micrometer-sized (conventional talc) or submicrometer-sized particles (l-talc). In the case of l-talc, several talc fractions were studied, ranging from 3 to 30 wt %. The nanocomposite crystallinity was characterized with differential scanning calorimetry and wide-angle Xray scattering. Talc was found to act as a nucleating agent, and only the a phase was detected. Through quantification on a Wilchinsky diagram, the talc particles were found to lie in the sample plane, the polypropylene crystalline lamellae being orthotropically distributed perpendicularly to the talc particles. The mechanical properties of the composites were tested in different directions by tensile and compression tests. The mechanical behavior of the composites confirmed the microstructural model. For low talc loadings, the composite moduli could not be well fitted by a law of mixtures. The large difference between the observed and predicted moduli was attributed to the formation of a mixed percolating network, including talc particles and polypropylene crystalline lamellae. At high talc loadings, when the mixed percolating network was completely formed, the reinforcement could well be described by parallel coupling, which indicated a classical reinforcement mechanism. Finally, the value of the critical talc fraction, at which the mixed percolating network was formed, was examined as a function of talc.

Optimization of the crystallinity of polypropylene/submicronic-talc composites: The role of filler ratio and cooling rate

“…The composites were finally injection-molded into 2 mm thick sheets. The actual filler ratio of the various composites was precisely determined after compounding by means of thermogravimetry [37]. The actual ratio was very close to the nominal value adjusted at the stage of compounding, the standard deviation not exceeding 1%, so that the nominal values were taken into account in this study.…”

“…Using such filler particles with sub-micronic size enables to increase the specific area of the filler with respect to the former kind of fillers and to overcome the quite common problem of exfoliation and dispersion of the second kind of fillers. Besides, unlike CaCO 3 and kaolin, µ-talc has been developed as a lamellar-like filler thanks to a specific delamination technique from the producer that provides better reinforcing capacities at equivalent volume fraction [17,37], owing to a very good dispersion that prevents the detrimental formation of aggregates [38]. It was shown in a previous study that the combination of the nucleating effect and the lamellar-like shape of µ-talc particles generates a rigid percolating network of polymer crystallites and filler particles that contributes to the enhancement of the composite stiffness [36].…”

Non-Isothermal Crystallization Kinetics and Activation Energy for Crystal Growth of Polyamide 66/Short Glass Fiber/Carbon Black Composites

“…Industrial polymer-based composites use mineral fillers and fibers as reinforcing agents [4][5][6]. These agents enhance the polymer's mechanical properties while also decreasing production expenses [3].…”

“…In recent years, most researchers have focused on studying the non-isothermal crystallization kinetics of polymers and the way in which they can be affected by reinforcing fillers [1][2][3][4][5][6]28,29]. For example, Layachi et al [1] studied the non-isothermal crystallization kinetics of 15 wt.% glass fiber or 0.4 wt.% carbon black reinforced PA66 at different cooling rates.…”