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Semi-crystalline polymers such as polyethylene show brittle fracture under stress if exposed to stress cracking agents. In such polymers, the crystallites are connected by the tie molecules through the amorphous phase. The tie molecules play an important role in the mechanical properties of the polymer through the transferring of load.
It may be noted that, for polymers, the strain is commonly expressed as a “draw ratio”, rather than a strain: in this case, extrapolation of the tangent is carried out to a draw ratio of zero, rather than a strain of -1. Graphical construction indicating criteria for neck formation and neck stabilization.
Poly(p-phenylene vinylene) (PPV, or polyphenylene vinylene) is a conducting polymer of the rigid-rod polymer family. PPV is the only polymer of this type that can be processed into a highly ordered crystalline thin film. PPV and its derivatives are electrically conducting upon doping.
This software works with components designed in CAD to simulate how a polymer behaves when it enters a injection mould cavity. It can predict how the molten material flows and freezes, any part geometry that is too thin or too thick and if there are any weaknesses created in the plastic from defects such as weld lines.
The synthesis and processing of polyacetylene films affects the properties. Increasing the catalyst ratio creates thicker films with a greater draw ratio, allowing them to be stretched further. [8] Lower catalyst loadings leads to the formation of dark red gels, which can be converted to films by cutting and pressing between glass plates. [20]
Draw resonance has not been found to be a function of the flow rate, however. A polymer melt approaching a Newtonian fluid such as PET can have a drawdown ratio of around 20, whereas highly shear thinning and viscoelastic polymer melts such as polyethylene, polystyrene, and polypropylene may have critical drawdown ratios as low as 3.
The higher the drawing ratio, the more extreme the amount of deep drawing. Due to the geometry, forces, metal flow and material properties of the work, there is a limit to the amount of deep drawing that can be performed on a sheet metal blank in a single operation. The drawing ratio is roughly calculated as, DR = Db/Dp.
A printer cartridge made of PPE and polystyrene; it is an example of a product which requires good dimensional stability and accuracy to fit.. PPE blends are used for structural parts, electronics, household and automotive items that depend on high heat resistance, dimensional stability and accuracy.