Comparative Characterization of PP Nano- and Microcomposites by In-Mold Shrinkage Measurements and Structural Characteristics Rodolfo Revilla-Dı ´az, Sau ´l Sa ´nchez-Valde ´s, * Fernando Lo ´pez-Campos, Francisco Javier Medellı ´n-Rodrı ´guez, Maria Luisa Lo ´pez-Quintanilla Introduction During the last few years, polymer nanocomposites have attracted significant interest, both in industry and acade- mia. They represent a new class of composite materials containing dispersion of nanometric size (1–100 nm) particles in a polymer matrix. Among the different nano- particles used in polymer nanocomposites, clay is pre- ferred because it provides two distinct opportunities to process polymer clay nanocomposites, namely intercala- tion and exfoliation. Experimental investigations have indicated that they exhibit a considerable enhancement of strength, modulus, flame-retardant and heat distortion temperature that are not displayed by the individual phases or by conventional composite counterparts. [1–6] Poly(propylene) (PP) exhibits an attractive combination of low cost, low weight, and extraordinary versatility in terms of properties, applications and recyclability. [7] How- ever, due to the low polarity of this resin, it is difficult to get an exfoliated and homogenous dispersion of the clay layer at the nanometer level in the polymer matrix. This is Full Paper Poly(propylene)-clay nanocomposites and poly(propylene) containing conventional inorganic fillers such as calcium carbonate (CaCO 3 ) and glass fiber were used in a comparative study focusing on dimensional stability, structure, mechanical and thermal properties. Micro- and nanocomposites were prepared by melt blending in a twin-screw extruder. The relative influence of each filler was observed from dimensional stability measurements and structural analysis by WAXD, TEM, and thermal and mechanical properties. At equal filler loadings, PP/clay nanocomposites exhibit an improvement in dimensional stability and were the only com- posites capable of reduced shrinkage in both in-flow and cross- flow directions. The flexural modulus of PP increased nearly 20% by compounding with 4% organoclay, as compared to a similar performance obtained by compounding with 10 wt.-% of CaCO 3 or approximately 6 wt.-% of glass fiber. The HDT and thermal stability of PP were enhanced by using nanoclay as filler. R. Revilla-Dı ´az, F. Lo ´pez-Campos Universidad Tecnolo ´gica de Coahuila, Av. Industrial Metalu ´rgica 2001, Ramos Arizpe, Coahuila, 25900, Me ´xico S. Sa ´nchez-Valde ´s, M. L. Lo ´pez-Quintanilla Centro de Investigacio ´n en Quı ´mica Aplicada (CIQA), P.O. Box 379, Saltillo, Coahuila, 25100, Me ´xico Fax (52)(844) 4 38 98 39; E-mail: saul@ciqa.mx F. J. Medellı ´n-Rodrı ´guez Centro de Investigacio ´n y Estudios de Posgrado/FCQ/UASLP, Av. Dr. Manuel Nava 6 Zona Universitaria, 78210, Me ´xico 762 Macromol. Mater. Eng. 2007, 292, 762–768 ß 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/mame.200700019