Sheets of low-density polyethylene

The general compliance equation for transverse isotropy (see Appendix 1, Section A1.7)is 

The experimental result implies that (2si3 + X44) is much greater than either 5n or S33, because when 6 = 45° the terms will be equally weighted. 

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Figure 7.7 The variation of Eq, 45 and 90 with draw ratio in cold-drawn sheets of low-density polyethylene. Modulus measurements taken at room temperature (Reproduced with permission from Raumann and Saunders, Proc. Phys. Soc., 11, 1028 (1961))...

Figure 7.8 The variation of E, and E with draw ratio in cold-drawn sheets of low-density polyethylene. Modulus measurements taken at —125 °C.

Figure 8.11 Model of morphology of oriented and aimealed sheets of low-density polyethylene. This photograph shows the structure of the be sheet a, b and c axes indicate the crystallographic directions in the crystalline regions. (Reproduced with permission from Stachurski and Ward, J. Polym. Set A2, 6, 1817 (1968))...

Rg. 16-19. Pscudoequilibrium Young s modulus parallel ( o) and perpendicular ( 90) to draw direction for cold-drawn sheets of low-density polyethylene, at — 125 C. (Gupta and Ward. ) Reproduced by permission, from Reference 105, p. 382, by courtesy of Marcel Dekker, Inc. 

These deficiencies became very apparent when Ward and co-workers [53] studied the mechanical behaviour of well-defined lamellar textures. Rolling and annealing processes established by Hay and Keller [54] enable sheets of low-density polyethylene to be produced with well-defined crystallographic and lamellar orientations (Figure 9.13), and it was possible to study the behaviour of three types of special structure sheet illusttated in Figure 9.14 be sheet , in which the c axes of the crystallites lie along the initial draw direction, the b axes lie in the plane of the sheet and the a axes are normal to the plane of... 

Hot-melt spray adhesives will bond successfully carpets, fabrics, laminating panels, metals (both painted and unpainted), and both polyethylene and polypropylene film and sheet. Two important commercial uses at the time of writing are bonding sleeves of low-density polyethylene to ductile iron pipes and bonding sound-deadening materials and carpets to the floors of motor cars. 

Gupta and Ward found modulus crossover points in drawn and annealed sheets of low density po yethylene and also in the b-c and it-b sheets similar to that observed by Takayanagi in drawn and annealed high density polyethylene. The crossover points were attributed to inter-lamellar shear. When the tensile stress is applied along the draw direction ( measurements in a drawn and annealed sheet) or along either the c or a direction in the special structure sheets ( , and Ea measure-... 

There has been considerable interest in recent years in calendered sheets which are to be used in the uncured state (see Section 8.5). In this case, the use of EPMs and EPDMs with a very high green strength is imperative. The addition of low density polyethylene further improves the calendering properties of the compound and the tenacity of the finished sheet. 

Table 6 shows the sales estimates for principal film and sheet products for the year 1990 (14). Low density polyethylene films dominate the market in volume, followed by polystyrene and the vinyls. High density polyethylene, poly(ethylene terephthalate), and polypropylene are close in market share and complete the primary products. A number of specialty resins are used to produce 25,000—100,000 t of film or sheet, and then there are a large number of high priced, high performance materials that serve niche markets. The original clear film product, ceUophane, has faUen to about 25,000 t in the United States, with only one domestic producer. Table 7 Hsts some of the principal film and sheet material manufacturers in the United States.

The state of the art is a combination of linear low-density polyethylene (PE-LLD) with hmestone for diaper back sheets. By biaxial orientation, the balance of mechanical permeability requirements can be obtained. Because of its PE-like characteristics Ecoflex is a good choice for a biodegradable back sheet. Ecoflex provides a good regulatory basis for these applications because of the positive results of the primary skin irritation test according to OECD 404, as well as the guinea pig test according to OECD 406. 

You have been asked to comment on the likely effectiveness of a proposed 1-mm-thick linear low-density polyethylene (LLDPE) plastic sheet for retaining benzene present at ppm levels in a wastewater. To be considered effective, the plastic sheet must retain the benzene for at least 20 years. 

Cross-linked polyethylene foams are produced by eilher radiation or chemical cross-linking of an extruded expandable sheet containing a chemical blowing agent. These products have finer texture and a softer, more resilient feel than extruded low density polyethylene foams and are used in comfort cushioning and cushion packaging applicutinns. 

Cross-linked low-density polyethylene foam can be produced by batch and continuous processes. The cross-linking is accomplished by chemical or irradiation methods. Chemical cross-linking of PE foam is produced in a batch process, and because of production economics is limited to "plank products." The radiation cross-link process permits the continuous production of cross-linked PE foam. This process is limited, however, to production of relatively thin cross sections (up to 3/8 inch) or sheet products (6). 

Polyolefins. Low density polyethylene and polypropylene have been developed as sheet and hollow fiber mlcroporous membranes, respectively, for use In plasmapheresis. Polyethylene Is made porous by stretching the annealed film ( ), while polypropylene la made porous by coextruding hollow fibers with a leachable plasticizer. Neither membrane has been prepared with small pore dimensions suitable for protein rejection. These polyolefin membranes are characterized by good chemical stability, but require special surfactant treatments to make them wettable. Their low deformation temperature precludes the use of steam sterilization. Because they are extruded without the usual antl-oxldants and stabilizers, their stability la lower than Injection molding formulations of the same polymer. 

During the 1970s Jersey Standard s chemical product portfolio had been reduced to resemble that in 1960. Its primary chemical business remained the production of ethylene, basic polymers (including LDPE, linear low-density polyethylene (LLDPE) using the Unipol process, licensed from Union Carbide, PP, and polyvinyl chloride (PVC), plasticizers (particularly for vinyl production), elastomers, and synthetic rubbers. Profits returned. The 1974 balance sheet listed earnings of 456 million on revenue of 3.3 billion, making Exxon Chemical one of the five most profitable chemical companies worldwide. 

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