Polyethylene flexure

The performance properties of PEN present opportunities for replacement of rayon or polyamide in carcass construction. The use of PEN cord in these applications is currently being evaluated in both Asia and Europe. PEN has demonstrated acceptable flexural fatigue equivalent to polyethylene terephthalate (PET) and rayon. It has equivalent toughness to rayon, which is important for sidewall impact resistance. PEN s superior mechanical properties also afford opportunities to use less fiber in carcass construction enabling production of lighter-weight, more fuel-efficient tires. 

Describe the seven different classes of polyethylene and explain how the structural differences affect the tensile strength, crystallinity and flexural modulus of each of the materials. 

Composite formulations were prepared as follows The straw samples as received from INEEL were ground to 0.69 mm in a hammer mill and oven dried to 1.1% moisture. The dried straw samples were then blended with various amounts of high-density polyethylene (HDPE), lubricants, and maleated polyethylene blends (MAPE) (see Table 2). The mixed formulations were then extruded with a 35-mm Cincinnati Milacron Model CMT 35 counterrotating conical twin screw extruder (Cincinnati Milacron, Batavia, OH), which produced a 9.525 x 38.1 mm2 solid cross-section. Flexural strength, density, and water sorption were measured for the extruded samples according to ASTM Standard Methods (13,14). 

Figure 5. The flexural rigidity of degraded cotton print cloth (50-Mrad dose) after application of various acrylic resins (A1-A4) and grafted monomers (M1-M4) PE = polyethylene, AD = air dried. See text for identification of resins and monomers.

From the table It appears that the Izod Impact strength Improves as the Interfacial adhesion increases. This Is also concluded In a recent publication about nylon 6.6 compounded with polyethylene-g-maleic anhydride polymer (15). Addition of more rubber In system 3 (30 %) affords hardly any addltonal Improvement In toughness, but the flexural modulus, which In ABA block copolymers Is already lower than In a dispersed rubber system, Is more than halved. 

The compression-molded bars were placed in polyethylene bags that were filled with distilled water or a 5% saline solution. At periodic intervals several test bars were removed and tested in flexure to determine the apparent loss of strength. These results are summarized in... 

There are many grades of polyethylene available (see Chapter 7 for flexural modulus values for LDPE, LLDPE, and HDPE, supplied by Chevron Phillips Chemical Company). Elexural modulus values vary from 30,000 to 50,000 psi for LDPE, equal to 60,000 psi for one particular LLDPE material (in fact, they can vary from about... 

Polypropylenes are subdivided to homopolymers and copolymers. Homopolymers are more crystalline, have a rather well-defined melting temperature at 161-165°C (322-329°F), softens at about 155°C (311°F), and have a rather narrow molecular weight distribution. Copolymers typically contain some amount of ethylene comonomer and in turn are subdivided to random and block copolymers. Their melting points are in the range of 140-155°C (284-311°F). Polypropylenes have a specific gravity (density) of 0.90-0.91 g/cm which is approximately equal to that of very low-density polyethylene and lower than that of majority of polyethylenes, particularly HDPE (0.941-0.965 g/cm ). PP homopolymers are stiffer than copolymers, with their flexural modulus of 165,000-290,000 psi and 130,000-175,000 psi, respectively. PP homopolymers, in turn, are generally stiffer compared to HDPE, which has flex modulus in the range of 125,000-... 

Flexural strength for polypropylene (6000-7000 psi) is much higher than that for polyethylene (around 1400 psi, if can be measured because of its high flexibility). Compressive strength for PP is also higher than that for HDPE, and for some specific examples they equal to 6720 and 4570 psi, respectively. 

Generally, there is a certain correlation between density, on the one hand, and flexural strength and modulus, on the other, for many other materials, and that correlation is not related to porosity. For example, there is a strong correlation (R = 0.984) between density of all 38 polyethylene materials, listed in Table 7.49 of Chapter 7, including LDPE, LLDPE, HDPE, and their flexural modulus (Figure 6.1). Besides, mineral fillers in WPC materials increase density of the final product and also increase its flexural modulus. However, this chapter is mainly concerned about relationships between density and properties of WPC having the same formulation but produced at different regimes. 

Figure 6.1 A correlation between polyethylene density and its flexural modulus. All materials are products of Chevron Phillips Chemical Company (see text). LDPE, LLDPE, and HDPE are shown with densities of 0.917-0.925, 0.918, and 0.943-0.964, respectively.

As it was mentioned above, flexural strength data for neat polyethylene are typically not reported in the hterature, because the respective samples normally do not break at conditions of ASTM D 790. They just bend. Therefore, data on flexural modulus of neat polyethylene are plentiful in the literature. They are often listed in spedflcations of plastics. 

There is a strong correlation (R = 0.984) between density of all 38 polyethylene materials from Table 7.49, including LDPE, LLDPE, HDPE, and their flexural modulus (Fig. 7.10). 

TABLE 7.49 Flexural modulus data for polyethylene materials (Marlex ) supplied by Chevron Phillips Chemical Company... 

Polyethylene, type (density, g/cm ) Marlex Index Flexural modulus (psi)... 

Fig. 5 shows the yield flexural stresses against 0. Notwithstanding the difficulties of analyzing, the findings made possible by this new compressive and tensile test, our results confirm that SIC and ITS bead treatment is efficient in polyethylene reinforcement. 

Ahmed, S.F.U., Maalej, M. and Paramasivam, P. (2006). Flexural responses of hybrid steel-polyethylene fibre reinforced cement composites containing high volume fly ash. Journal of Construction and Building Materials, 21 1088-1097. 

These may be carried out in extension, torsion or flexure, and are concerned with alternating strains, normally over a range of frequencies and temperatures. Such methods are particularly suited to the study of molecular relaxation processes and have not been applied very extensively to oriented materials, where the studies to date have been more concerned with the static arrangement of structural elements in the materials. However, Takayanagi, and Stachurski and Ward have used dynamic tensile and torsion modulus to study the anisotropy of relaxations in oriented polyethylene. 

Fig. 4.120 Fatigue strength in flexural alternating range of two poly(vinyl chloride)/polyethylene-blends [98Dom].

Polyethylenes because of their carbon - carbon backbones are relatively flexible. Inert fillers are often added to increase flexural modulus. However, inert fillers often increase stiffness af fhe expense of abrasion and impact resistance and, therefore, filler concentrations are kept low. Particulate fillers are most often used since fibrous fillers tend to cause extensive warping and highly anisotropic properties (29). Resultant additive properties such as density or flexural modulus can be approximated for a two component blend by the rule of mixtures (30). Equation 9 demonstrates how the density of a blend can be determined from the concentration and density of its components ... 

Banerjee AN, Saha N, Mitra BC, Flexural behavior of unidirectional polyethylene carbon fibres PMMA hybrid composite laminates, J Appl Polym Sci, 60(1), 139-142, 1996. 

Li Y, Xian XJ, Choy Cl, Guo MI, Zhang ZG, Compressive and flexural behavior of ultra-high-modulus polyethylene fibre and carbon fibre hybrid composites, Composites Sci Technol, 59(1), 13-18, 1999. 

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