Thermoplastic olefin
This article needs additional citations for verification. (November 2015) |
Thermoplastic olefin, thermoplastic polyolefin (TPO), or olefinic thermoplastic elastomers refer to polymer/filler blends usually consisting of some fraction of a thermoplastic, an elastomer or rubber, and usually a filler.[1]
Outdoor applications such as roofing frequently contain TPO because it does not degrade under solar UV radiation, a common problem with nylons.[2] TPO is used extensively in the automotive industry.
Materials
Thermoplastics
Thermoplastics may include polypropylene (PP), polyethylene (PE), block copolymer polypropylene (BCPP), and others.
Fillers
Common fillers include, though are not restricted to
Elastomers
Common elastomers include
Creation
Components for TPO are blended together at 210 - 270 °C under high
Structure
The geometry of the metallocene catalyst will determine the sequence of
As in metal alloys the properties of a TPO product depend greatly upon controlling the size and distribution of the microstructure. PP and PE form lamellar crystallites separated by amorphous regions that can grow into a variety of microstructures ranging from single crystals from dilute solution crystallization to fiberous crystals and shish-kabob structures. Thin films from quiescent melts can form spherulitic impinging structures that display cylindrically symmetric birefringence. The PP and PE components of a blend constitute the "crystalline phase", and the rubber and branched PE chains and PE/PP end groups gives the "amorphous phase".
If PP and PE are the dominant component of a TPO blend then the rubber fraction will be dispersed into a continuous matrix of "crystalline" polypropylene. If the fraction of rubber is greater than 40% phase inversion may be possible when the blend cools, resulting in an amorphous continuous phase, and a crystalline dispersed phase. This type of material is non-rigid, and is sometimes called TPR for ThermoPlastic Rubber.
To increase the rigidity of a TPO blend, fillers exploit a surface tension phenomena. By selecting a filler with a higher surface area per weight, a higher flexural modulus can be achieved. Specific density of TPO blends range from 0.92 to 1.1.
Application
TPO is easily processed by injection molding, profile extrusion, and thermoforming. However, TPO cannot be blown, or sustain a film thickness less than 1/4
References
- ISBN 9781859570449.
- ^ "What is TPO Roofing". Retrieved 2017-07-06.