TPO based nanocomposites. Part 2. Thermal expansion behavior

The linear thermal expansion behavior of thermoplastic polyolefin, or TPO, nanocomposites based on a polypropylene/elastomer/masterbatch mixture was examined using a thermomechanical analyzer (TMA). For these experiments the masterbatch consisted of a mixture of organoclay and maleated polypropylene. The nanocomposites were prepared in a twin-screw extruder. The effects of both the elastomer domains and the filler particles on the thermal expansion behavior of the nanocomposites were investigated by means of transmission electron microscopy (TEM) and atomic force microscopy (AFM). The addition of elastomer tends to increase the linear coefficient of thermal expansion, CTE. On the other hand, the addition of clay significantly reduces the thermal expansion in both the flow (FD) and transverse directions (TD) of injection molded specimens; however, the extent of reduction of CTE in the FD is much greater than in the TD. The CTE in the normal direction (ND) increases when either the clay or elastomer content is increased. The trends in thermal expansion for the nanocomposites are discussed in terms of the morphology of both dispersed clay and elastomer phases based on TEM and AFM observations and subsequent particle analyses.