Polypropylene specific gravity

Density. Aciyhcs have a low specific giavity (1.12—1.19) compaied to all of the piimaiy natuial fibeis and most synthetic fibeis. Nylon has a similar specific gravity (1.14) and the polyolefins have lower specific gravities, eg, 0.90 for polypropylene. Again the modacryhcs and some aciyhcs with high levels of comonomer of low molar volume are exceptions. Verel and Dynel, for example, have specific gravities of 1.37 and 1.31, respectively. 

This is used most often in process plants. It is a tough, low-cost material with probably the widest range of chemical resistance of any of the low-cost plastics. On a volume basis, PVC is more favorable than polypropylene because the modulus of PVC is considerably higher than that of polypropylene, so it will form more rigid structures when used at the same thickness. On a weight basis it is not as favorable as PVC because it has a specific gravity of 1.4 compared with 0.92 for polypropylene. 

Monofilament polypropylene fibres were prepared by direct extrusion having a rectangular cross section of 0.5 x 1.3 mm, a length of 40 mm, a specific gravity of 0.91, a tensile strength of 120 MPa, and an elongation at break of 14%. The fibers were placed under 18% humidity at ambient temperature air and then treated with 20% F2 and 80% N2 at apressure of 45 kPa at 38°C for 2.5 hours. Thereafter the reaction vessel was evacuated, and the product was isolated. 

High-Density Polyethylene Foams These foams are defined by the specific gravity (ca. 0.96 g/cc) and melt index of the basic resin. They have been used extensively in the U.S. and Europe, particularly for materials-handling applications, such as boxes, crates, and pallets because, imtil recently, they were much cheaper than polypropylene (13). 

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-... 

For 85% wood-flour-filled polypropylene calculations of density (specific gravity) would be as follows ... 

The specific gravity of PVC at room temperature is close to 1.4 g/cm. Compared with other commodity polymers (PE, PP) it is a very high density. For the same volume of product one has to use about 60% more PVC as compared with polyethylene or polypropylene. The very high density of PVC is most likely the biggest disadvantage of PVC which contributes to increased weight of Ihe product and the cost of raw materials required to produce it. 

The specific gravities of fully crystalline and fully amorphous polypropylene are 0.9363 and 0.8576, respectively [86], and those of the partially crystalline resin and fiber are usually about 0.905. The bulk density of pellets is approximately 34 Ib/ft. ... 

Micro-synthetic fibres are defined as those having diameters less than 0.3 mm and macrosynthetic fibres are those with diameters greater than 0.3 mm. Their specific gravity is 0.91 (polypropylene fibres) or 1.14 (nylon fibres). 

The wet and washed chips are le-slumed in rinse water in an agitated tank, and pumped through a set of hydrocyclones to separate the "light" components (polyethylene base cups and polypropylene labels) from the "heavy" components (PET and aluminum bottle tops). The specific gravities are as follows ... 

The specific heat of dry wood does not have a strong dependence on specific gravity and is roughly 0.324 cal/(g K) or 1360 J/(kg K) [17]. This is about half the specific heat of common polyolefins such as polypropylene and polyethylene, for which values are approjdmately 2-3000 J/(kg K.)... 

The addition of talc to polypropylene does not seem to have a significant effect on melt flow rate. Because of its higher specific gravity (2.78 versus 0.91-0.94 for unfilled polypropylene), talc causes a slight increase in measured melt flow... 

Because talc has a specific gravity of 2.78, the addition of talc to polypropylene will increase the specific gravity of the compound. The lower cost of most talc ( 0.20-0.30 per pound), relative to the polymer cost ( 0.53-0.58 per pound, combined with 0.20 per pound compounding costs) will give a lower cost per pound for the compounded material. The higher specific gravity of the compound, however, can result in the cost per volume actually increasing, as shown in Fig. 8.24. 

Even though vulcanized EPDM has some oil resistance, in contrast to unvulcanized EPDM which has virtually none, a rubber with inherent oil resistance should be even better. For this reason, more polar rubbers have replaced EPDM in applications where oil resistance is critical. Dynamic vulcanizates of nitrile rubber with polypropylene are the most important example. Commercial grades are somewhat harder than EPDM equivalents (between 70 on the Shore A scale to 40 on the Shore D scale) and are also more dense (about 1.0-1.1 specific gravity) (26,49). 

In the United States, plastic pellets were identified in the Atlantic Ocean along the southern coast of New England and in the eastern seaboard (Colton 1974 Hays and Cormons 1974 Ryan 1988). In the Pacific Ocean, pellets have been reported since 1974 (Wong et al. 1974 Day et al. 1990). Most of the plastic pellets found in marine oceans have been identified as polyethylene (PE), polypropylene (PP), or polystyrene (PS) (CEE Plastics in the Ocean 1987). Those three plastics will float since they have specific gravities less than 1 (PE and PP) or near 1 (PS). All other plastics have specific gravities greater than water and can sink to the ocean floor unless they are made into a buoyant container or bottle. 

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