ThermoPlastic Olefin 4086059 208141381 2008-04-25T16:53:10Z Chowbok 54304 clean up, Replaced: ® → using [[Project:AutoWikiBrowser|AWB]] '''[[ThermoPlastic]] Olefin''' (TPO) is a trade name that refers to [[polymer]]/filler blends usually consisting of some fraction of PP ([[polypropylene]]), PE ([[polyethylene]]), BCPP (block copolymer [[polypropylene]]), rubber, and a reinforcing filler. Common fillers include, though are not restricted to talc, fiberglass, carbon fiber, [[wollastonite]], and MOS(Metal Oxy Sulfate). Common rubbers include EPR ([[ethylene-propylene rubber]]), [[EPDM]] (EP-diene rubber), EO (ethylene-octene), EB (ethylene-butadiene), SEBS (Styrene-ethylene-butadiene-styrene). Currently there is a great variety of commercially available rubbers and BCPP's. They are produced using [[regioselective]] and [[stereoselective]] catalysts known as [[metallocene]]s. The metallocene catalyst becomes embedded in the polymer and cannot be recovered. The geometry of the metallocene catalyst will determine the sequence of [[chirality (chemistry)|chirality]] in the chain, as in, [[atactic]], [[syndiotactic]], [[isotactic]], as well as average block length, molecular weight and distribution. These characteristics will in turn govern the microstructure of the blend. The components are blended together at 210 - 270 °C under high shear. A twin screw extruder or a continuous mixer may be employed to achieve a continuous stream, or a Banbury compounder may be employed for batch production. A higher degree of mixing and dispersion is achieved in the batch process, but the superheat batch must immediately be processed through an extruder to be pelletized into a transportable intermediate. Thus batch production essentially adds an additional cost step. 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 a vaguely crystalline structure known as a [[spherulite]]. Unlike metals, a spherulite cannot be described in terms of a [[crystal structure|lattice]] or unit cell, but rather as a set of polymer chains that pack down closely next to one another and form a dense core. The PP and PE components of a blend constitute the "crystalline phase", and the rubber 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, we can achieve a higher flexural modulus. TPO blends have densities 0.92 - 1.1 TPO is frequently found in outdoor applications such as roofing because it does not degrade under solar UV radiation, a common problem with nylons. TPO is used extensively in the automotive industry. TPO is easily processed by injection molding, profile extrusion, and thermoforming. TPO cannot be blown, or sustain a film thickness less than 1/4 mil (about 6 micrometres), where 1 mil is equal to 0.001 inch. [[Category:Plastics]] [[Category:Plastics industry]]