Polyethylene history

Polyethylene History Major Product and Process Innovations... 

R.A.V. Raff, J.B. Allison, Polyethylene (Interscience Publication, New York, 1956) Germ. Pat. Appl., B25064 (1955). http //en.wildpedia.org/ wild/Polyethylene History... 

Some materials are able to withstand quite lengthy thermal histories , a term loosely used to describe both the intensity (temperature) and the duration of heating. Polyethylene and polystyrene may often be reprocessed a number of times with little more than a slight discoloration and in the case of polyethylene some deterioration in electrical insulation properties. 

Andrew Keller (1925-1999) who in 1957 found that the polymer polyethylene, in unbranched form, could be crystallised from solution, and at once recognised that the length of the average polymer molecule was much greater than the observed crystal thickness. He concluded that the polymer chains must fold back upon themselves, and because others refused to accept this plain necessity, Keller unwittingly launched one of the most bitter battles in the history of materials science. This is further treated in Chapter 8, Section 8.4.2. 

An important subdivision within the thermoplastic group of materials is related to whether they have a crystalline (ordered) or an amorphous (random) structure. In practice, of course, it is not possible for a moulded plastic to have a completely crystalline structure due to the complex physical nature of the molecular chains (see Appendix A). Some plastics, such as polyethylene and nylon, can achieve a high degree of crystallinity but they are probably more accurately described as partially crystalline or semi-crystalline. Other plastics such as acrylic and polystyrene are always amorphous. The presence of crystallinity in those plastics capable of crystallising is very dependent on their thermal history and hence on the processing conditions used to produce the moulded article. In turn, the mechanical properties of the moulding are very sensitive to whether or not the plastic possesses crystallinity. 

PET, see Polyethylene terephthalate Petit, Rowland, 524 Petroleum, catalytic cracking of, 100 composition of, 99-100 gasoline from. 99-100 history of, 99 refining of, 99-100 Pharmaceuticals, approval procedure for, 165 origin of, 164 Phenol(s), 599... 

Polyethylene terephthalate also has the tendency, because it is produced by a condensation polymerization process, to depolymerize under high pressure and temperatures in the presence of water. Although this is usually a negative attribute, it can be utilized to regenerate pure monomers which can be repolymerized to make fresh polymer. This avoids the issues experienced by reprocessing resins, as the new resin has not experienced a previous heat history. A major drawback to this process is the requirement that the monomers used in polymerization processes must be highly pure, Unfortunately, this process is extremely costly and not performed on a commercial scale. 

Polyethylene polymers history of, 17 701-702 simulations of, 16 747 Polyethylene products, Ziegler-Natta catalysts for, 26 540-543 Polyethylene resins, 17 700-703 applications for, 17 703 Polyethylenes, classification of, 17 701t. 

Rokudai, M., Mihara, S., and Fujiki, T., Influence of Shearing History on the Rheo-iogical Properties and Processability of Branched Polymers. II. Optical Properties of Low-Density Polyethylene Blown Films, /. Appl. Polym. Set, 23, 3289 (1979)... 

The 1 hour treatment at 160°C will be more severe than necessary for some samples and Inadquate for others. We have observed that storage at 160°C for as much as a day may be required to remove detectable aggregates in solutions of very high molecular weight linear polyethylene samples. In any event, the appropriate duration of such treatments can be assessed by the method discrlbed here. That is to say, the solution history should be adjusted so that direct measurements of by LALLS (without the SEC columns) yields clean recorder traces (as in Figure 1) and second vlrlal coefficients which are in accord with Kok-Rudin predictions of such values for the measured... 

A second approach to biodegradable packaging is to blend polyethylene with a second synthetic polymer with polar repeating units that are capable of degradation, such as ester linkages (chapter 12). Poly(caprolactone) represents such a class of polymer, which has a long history of compatibility ( with a variety of polymers and degradability (5) recently, improved miscibility and Glm properties have been reported when poly(caprolactone) is blended with commodity plastics... 

Schreiber and co-workers have noted very persistent history effects in linear polyethylenes (69). Fractions which have been crystallized from dilute solution required times of the order of hours in the melt state at 190° C in order to attain a constant die swell behavior upon subsequent extrusion. The viscosity on the other hand reached its ultimate value almost immediately. The authors concluded from this result that different types of molecular interactions were responsible for elastic and viscous response. However, other less specific explanations might also suffice, since apparent viscosity might be relatively intensitive to the presence of incompletely healed domain surfaces, while die swell, requiring a coordinated motion of the entire extrudate, might be affected by planes of weakness. It would... 

In this article we have reviewed our recent work with NMR analysis on various kinds of linear polyethylene samples. It has become evident that the refined NMR analysis gives us much important information on the phase structure of samples in terms of molecular mobility, and establishes that there is no unified phase structure for polymer samples. The phase structure of samples varies over a very wide range, depending strongly on the sort of samples involved as well as on the mode of crystallization or the history of those samples. We should emphasize that there are significant differences in phase structure among the bulk-crystals, the solution-crystals, and the fiber samples, particularly in the conformation of molecular chains in the noncrystalline content. We should not confuse these phase structures with each other. The phase structures are evidently different, sample by sample, as their macroscopic properties also differ one from another. 

The detailed analyses of polyethylene samples with various histories, show appreciable variation of the setting angle, the a axis dimension, and lattice distortion. These changes are small but appreciable, and some of them are in a linear relation, but some are not. Similar phenomena will be found in other polymers, and the reason may be interesting. 

Polyethylene glycol also has a long history of use as an agent for protein precipitation (4). It shares some of the positive attributes of ammonium sulphate in having a low heat of solution and not promoting denaturation of proteins. It appears that after the addition of polyethylene glycol, proteins are excluded from the space occupied by the hydrated polymer, and their effective concentration is increased to a level incompatible with solubility. It is less effective in the purification of IgG but is useful for the isolation of the larger IgM. 

Chapters 9 through 12 demonstrate thermodynamic, or exergy analysis of industrial processes. First, Chapter 9 deals with the most common energy conversion processes. Then, Chapter 10 presents this analysis for an important industrial separation process, that of propane and propylene. Finally, Chapter 11 analyzes two industrial chemical processes the production of polyethylene. Chapter 12 is included to discuss life cycle analysis in particular its extension into exergetic life cycle analysis, which includes the "fate" or history of the quality of energy. 

Polyethylene oxide) (PEO) is a semicrystalline water-soluble polymer [64, 65], with a crystallinity that is very sensitive to the thermal history of the sample, making this property interesting as an indicator of degradation. Because it is biodegradable and biocompatible, PEO is a good candidate for environmental and medical applications [66-68]. The mechanisms of thermo- and photo-oxidation of PEO have already been investigated [69, 70] on the basis of IR identification of the oxidation products and are summarized in Scheme 10.1. 

---