Polyethylene analytical techniques

Most commercial polymers are substantially linear. They have a single chain of mers that forms the backbone of the molecule. Side-chains can occur and can have a major affect on physical properties. An elemental analysis of any polyolefin, (e.g., polyethylene, polypropylene, poly(l-butene), etc.) gives the same empirical formula, CH2, and it is only the nature of the side-chains that distinguishes between the polyolefins. Polypropylene has methyl side-chains on every other carbon atom along the backbone. Side-chains at random locations are called branches. Branching and other polymer structures can be deduced using analytical techniques such as NMR. 

Some particular processes can require very high pressures for special applications (i.e. in explosive welding and plating), but pressures between 100 and 1000 bar can be found easily in different industrial processes. Typical examples are the synthesis of ammonia, the synthesis of methanol and the production of low-density polyethylene, but also analytical techniques as high-pressure liquid chromatography. Other important implications are for the storage and transportation of fluids and enhanced oil recovery. 

It was of Interest In this study to develop a simple analytical technique which would allow one to easily examine the complex effects of peroxide-polyethylene Interactions In the presence of a phenolic antioxidant stabilizer additive. 

These materials often have the same, or close to the same, chemistry as the base polymer. Therefore, they are often difficult to detect with ESCA or other analytical techniques. Typically the contaminants can be present in layers Inm to lOnm thick, even after solvent cleaning. They just continue to diffuse to the surface after solvent cleaning. Polyethylene is a particularly bad polymer for this problem. 

Tappi Method T 698 cm-91. Determination of Wetting Tension of Polyethylene and Polypropylene Films and Coatings (Modified Visking Analytical Technique), The Pulp and Paper Institute Atlanta, Georgia, 1983. 

Physical Solution. In this type of process the component being absorbed is more soluble in the liquid absorbent than other components of the gas stream, but does not react chemically with the absorbent. The equilibrium concentration of the absorbate in the liquid phase is strongly dependent on the partial pressure in the gas phase. An example is the absorption of hydrogen sulfide and carbon dioxide in the dimethyl ether of polyethylene glycol (Selexol Process). Relatively simple analytical techniques have been developed for designing systems of this type. 

There are many properties to consider when developing a new UHMWPE material for implant applications. The characteristics of the UHMWPE powder may be measured to verify that there are not variations in different manufacturing lots. After consolidation, when the polyethylene powder is compressed into a solid slab of material via ram extrusion, compression molding, or other techniques including isostatic pressing, manufacturers will test the solid polyethylene slab to determine the quality of the consolidation and to determine if any deleterious effects have occurred. Highly crosslinked UHMWPE is commonly used now, whereby the polyethylene slab is exposed to radiation, which forms chemical bonds between polymer chains. Several analytical techniques have been developed to assess if the material has been exposed to enough radiation to improve the desirable properties of the UHMWPE,... 

---