High-density polyethylene Subject

Although some polymers may be satisfactory when used under the stress of static loads, they may fail when subjected to impact. The impact resistance, or resistance to brittle fracture, is a function of the molecular weight of a polymer. Thus uhmwpe is much more resistant to impact failure than general purpose high-density polyethylene (hdpe). The impact resistance of brittle polymers is also increased by the addition of plasticizers. Thus polyvinyl chloride (PVC), plasticized by relatively large amounts of dioctyl phthalate, is much less brittle than unplasticized rigid PVC. 

Industry estimates indicate that up to 5% of the total resin production finds its way into prototype or mill shape plastic products. By mill shapes is meant those primary uniform configuration subject to established cross-sectional and length tolerances. While this estimate is necessarily conjectural, the best available information indicates that this range is accurate. Modem Plastics magazine estimated mill shape production for 1968 in acrylics, cellulose, nylon, acetal, polycarbonate, high density polyethylene, polypropylene, poly(vinyl chloride), and copolymers to approach 336.4 million pounds. Total United States resin production for 1968 slightly exceeded 16 billion pounds. 

Since fully cured thermoset sheets cannot be resoftened, forming is not appKcable to them. Common materials subjected to thermoforming are thermoplastics such as polystyrene, cellulose acetate, cellulose acetate butyrate, PVC, ABS, poly(methyl methacrylate), low- and high-density polyethylene, and polypropylene. The bulk of the forming is done with extruded sheets, although cast, calendered, or laminated sheets can also be formed. 

Plastics are subject to attack by some aggressive fluids and chemicals. However, not all plastics are attacked by the same materials. It is generally possible, therefore, to select a plastic matrix to meet a particular condition. Some plastics, such as high-density polyethylene (HDPE), are immune to almost any commonly found solvents. A few such as polytetrafluoroethylene (PTFE) are immune to almost any corrosive conditions. 

We may think that corrosion problems are exclusive to metallic materials, or at least to materials characterized by electronic conductivity, and this is probably true as regards electrochemical corrosion. However, for example, rubber is subject to SCC in environments containing ozone, polystyrene is subject to SCC in environments containing aliphatic hydrocarbons, high-density polyethylene may be subject to SCC (e.g., in benzene), and ice is subject to cracking in environments containing alcohol. 

In Section 24.1.3 we have discussed among others the time-temperature correspondence principle. An example of application of that principle is shown in Fig. 24.10. The results pertain to high density polyethylene (HOPE) subjected to different levels of predrawing [58]. The draw ratio is defined as... 

Panthapulakkal and Sain [10] reported that the water absorption of wheat straw-filled high-density polyethylene (HDPE) composite to be lower than corncob-filled HDPE and greater than corn straw-filled composite. The greater amount of water absorption recorded by corncob-filled composites was attributed to the greater amount of hemicellulose present in corncob. When used in composites, incorporation of com-patibilizer may decrease water uptake this may consequently enhance the mechanical properties of the composites upon being subjected to water. 

Determination of the crystalline polymer fraction at different temperatures allows the construction of melting curves. Their form mirrors the morphology of the polymer determined by the thermal treatment it was subjected to. In the case of high density polyethylene the melting curves differ for rapid and slow cooling of the melt (Fig. 5.7, curves 1,2). Curve 3... 

High-density polyethylene, Sholex 6050, may serve as an example. The materials were subjected both to thermal degradation and y-irradiation together with 2,4,6-tri-tert-butyl nitrosobenzene. As in the case of mechanical degradation of polymers in the presence of nitrosobenzene, ESR spectra from nitroxide radicals were observed... 

Polymers have been extensively studied by 2D IR correlation spectroscopy. A number of temperature-, pressure-, time-, and composition-dependent IR spectral variations of polymers have been subjected to the 2D correlation analysis. We showcase here the study of a seemingly simple premelting of a high-density polyethylene (HDPE) film as an illustrative example of the application of 2D correlation spectroscopy in polymer science. 

---