Thermoplastic olefin (TPO) is a multiphase composition in which one phase includes a material that is hard and stiff at room temperature and fluid when heated and another phase that includes an elastomeric material that is soft and rubberlike at room temperature. Various blends of materials can be included in the TPO, where typically there are portions of a thermoplastic polymer, an elastomer, and a filler to provide rigidity. TPOs can be designed to be tough and durable and can be tailored to meet specific application requirements such as being weather-resistant, paintable, scratch-resistant, and presenting low odor and low temperature ductility, among other options. Other notable aspects of TPOs include chemical resistance and the ability to be recycled. TPO is used in various applications, including automotive, building and construction, and other industrial applications. Particular examples of TPO articles include automotive components including bumpers, interior and exterior trim, floor mats, grips, and seals.
Respective portions of thermoplastic polymer, elastomer, and filler can be tailored to provide certain properties depending on the application. Examples of thermoplastic polymers include polypropylene (PP), polyethylene (PE), and/or block copolymer polypropylene (BCPP), among others. Examples of elastomers include ethylene propylene rubber (EPR), EPDM (EP-diene rubber), ethylene-octene (EO), ethylbenzene (EB), and/or styrene ethylene butadiene styrene (SEBS), among others. Examples of fillers include talc, calcium carbonate, fiberglass, carbon fiber, wollastonite, and/or MOS (Metal Oxy Sulfate), among others. Depending upon the type of filler used, characteristics of the resulting TPO can be modified to enhance strength, scratch resistance, impact resistance, and weight, among other characteristics. TPO can be processed by injection molding, profile and sheet extrusion, and thermoforming.
Certain TPO articles can exhibit undesirable weathering and changes in appearance such as loss of color fastness and gloss changes following extended exposure to the ambient environment. It has been discovered that such appearance changes are typically due to ultraviolet (UV) radiation exposure, and hence, such TPO articles may be produced to include a sufficient amount of UV stabilizers. However, in other circumstances, it has been found that certain TPO articles, and especially TPO articles produced using a thermoforming process, exhibit an appearance of premature wear or fade that results in the appearance of whitening on an exposed surface of the TPO articles. Such whitening effects occur even when the TPO articles include sufficient UV stabilizers.
Accordingly, it would be advantageous to provide a TPO article that maintains a surface finish, including particular gloss and color retention characteristics, where the TPO article is resistant to weathering and premature whitening, even when the article is the product of thermoforming.