This disclosure relates to thermoplastic compositions, in particular thermoplastic compositions containing an inorganic filler, methods for the manufacture of such compositions, and articles formed from the compositions.
Polycarbonates are useful in the manufacture of articles and components for a wide range of applications, from automotive parts to electronic appliances. Because of their broad use, particularly in metal replacement applications, such as in automotive applications, there is a need for increased stiffness and reduced coefficient of thermal expansion, while at the same time maintaining excellent ductility and flow properties.
One known method of increasing stiffness in polycarbonates is by the addition of inorganic particulate fillers such as clay, talc, and mica. Such compositions, specifically talc- and/or mica-filled polycarbonates and polycarbonate blends, can degrade upon processing. As used herein, “degrade” and “degradation” of polycarbonates or polycarbonate blends are known to one skilled in the art and generally refer to a reduction in molecular weight and/or an adverse change in mechanical or physical properties.
The addition of inorganic particulate fillers can also adversely affect the ductility and/or flow of polycarbonates and polycarbonate blends. Use of talc can also give rise to poor stress transfer at the polymer-talc interface, leading to a reduction in tensile and flexural properties.
Various filler treatments intended to address the above drawbacks have been developed, including acid treatment (see, e.g., US Publication No. 2006/0287422) and silane treatment. However, neither acid nor silane treatment has been found to counter the adverse impact of talc on ductility or flow properties when added to polycarbonate blends with acrylonitrile-butadiene-styrene. To improve the ductility of polymer-filler compositions, there are reports of rubber particle encapsulation in the polymer matrix. This too comes at a cost of reduced tensile and flexural properties. Thus, there remains a need in the art for methods to reduce or eliminate filler-induced polymer degradation, while at the same time improving the ductility and flow properties of filled polycarbonate blends.