LLDPE density

Table 1 Diffusion data for low molecular weight organic substances in Polyethylenes (PE s) Low Density Polyethylene (LDPE) and Linear Low Density Polyethylene (LLDPE) [Densities up to 0.930 g/cnr (at room temperature)].

ASTM D 5815 Standard Test Method for Determination of Phenolic Antioxidants and Erucamide Slip Additives in Linear Low-Density Polyethylene Using Liquid Chromatography This ASTM is very similar to ASTM D 1996, except that LLDPE samples are analyzed, and extraction is performed with either isobutanol or isopropanol prior to liquid-chromatographic separation. Isopropanol is recommended as the extraction solvent for lower crystallinity LLDPE (density 0.925 g/ cm and below), and isobutanol is recommended as the extraction solvent for higher crystallinity LLDPE. As the standard notes, besides Irganox 1010, Irganox 1076, and Isonox 129, the test method should be applicable for the determination of other antioxidants such as Ultranox 626, Ethanox 330, Santanox R, and Topanol CA, but the applicability of this test method has not been investigated for these antioxidants. Precision of the procedure is somewhat poorer compared to that of ASTM D 1996 ... 

VLDPE/LLDPE Density = 0.90-0.93 g/cm Melt point = 100-130X... 

Linear low-density polyethylene (LLDPE) is a variation of HDPE. It is synthesized similarly, but LLDPE has a much higher content of comonomer, such as hexene or octene. Incorporation of comonomer in the chain yields short chain branches of a specified length (Fig. 1.5). By controlling the amount of branch points through comonomer content, degree of crystallinity - hence density - can be controlled. Variants of LLDPE are known as very low-density polyethylene (VLDPE) and ultra low-density polyethylene (ULDPE). LLDPE density is generally in the range of 0.88 to 0.93 g/cm. ... 

LLDPE made uses 1-hexene as comonomer, approximately 35% uses 1-butene, and approximately 25% uses 1-octene. Only a small fraction is made using 4-methyl-1-pentene. Hexene and butene copolymers are more prevalent because they are less expensive than octene and because they are commonly used in the gas-phase process, which accoimts for most of the global LLDPE production. For LLDPE, density is strongly controlled by comonomer content. Conventional LLDPE basically covers the density range of0.915-0.940. Within that density range, and also lower density ranges, there are common product family subsets. Table 1 shows comonomer content and subsequent density ranges for commercial LLDPE. 

OLEFIN POLYTffiRS - POLYETHYLENE - LINEAR LOW DENSITY POLYETHYLENE] (Vol 17) LLDPE. See Linear low density polyethylene. 

Linear Low Density Polyethylene. Films from linear low density polyethylene (LLDPE) resias have 75% higher tensile strength, 50% higher elongation-to-break strength, and a slightly higher but broader heat-seal initiation temperature than do films from LDPE. Impact and puncture resistance are also improved over LDPE. Water-vapor and gas-permeation properties are similar to those of LDPE films. 

The majority of spunbonded fabrics are based on isotactic polypropylene and polyester (Table 1). Small quantities are made from nylon-6,6 and a growing percentage from high density polyethylene. Table 3 illustrates the basic characteristics of fibers made from different base polymers. Although some interest has been seen in the use of linear low density polyethylene (LLDPE) as a base polymer, largely because of potential increases in the softness of the final fabric (9), economic factors continue to favor polypropylene (see OlefinPOLYMERS, POLYPROPYLENE). 

Commercial production of PE resias with densities of 0.925 and 0.935 g/cm was started ia 1968 ia the United States by Phillips Petroleum Co. Over time, these resias, particularly LLDPE, became large volume commodity products. Their combiaed worldwide productioa ia 1994 reached 13 X 10 metric t/yr, accouatiag for some 30% market share of all PE resias ia the year 2000, LLDPE productioa is expected to iacrease by 50%. A aew type of LLDPE, compositioaaHy uniform ethylene—a-olefin copolymers produced with metallocene catalysts, was first introduced by Exxon Chemical Company in 1990. The initial production volume was 13,500 t/yr but its growth has been rapid indeed, in 1995 its combiaed production by several companies exceeded 800,000 tons. 

Crystallinity and Density. These two parameters, which are closely related, depend mosdy on the amount of a-olefin in the copolymer. Both density and crystallinity of ethylene copolymers are also influenced by their compositional uniformity. Eor example, for LLDPE resias with different a-olefin (1-hexene) content, the density (g/cm ) is as follows ... 

The second type of solution polymerization concept uses mixtures of supercritical ethylene and molten PE as the medium for ethylene polymerization. Some reactors previously used for free-radical ethylene polymerization in supercritical ethylene at high pressure (see Olefin POLYMERS,LOW DENSITY polyethylene) were converted for the catalytic synthesis of LLDPE. Both stirred and tubular autoclaves operating at 30—200 MPa (4,500—30,000 psig) and 170—350°C can also be used for this purpose. Residence times in these reactors are short, from 1 to 5 minutes. Three types of catalysts are used in these processes. The first type includes pseudo-homogeneous Ziegler catalysts. In this case, all catalyst components are introduced into a reactor as hquids or solutions but form soHd catalysts when combined in the reactor. Examples of such catalysts include titanium tetrachloride as well as its mixtures with vanadium oxytrichloride and a trialkyl aluminum compound (53,54). The second type of catalysts are soHd Ziegler catalysts (55). Both of these catalysts produce compositionaHy nonuniform LLDPE resins. Exxon Chemical Company uses a third type of catalysts, metallocene catalysts, in a similar solution process to produce uniformly branched ethylene copolymers with 1-butene and 1-hexene called Exact resins (56). 

Countries produciug commodity LLDPE and their capacities, as well as production volumes of some U.S. companies, are Hsted iu Table 5. Iu most cases, an accurate estimate of the total LLDPE production capacity is compHcated by the fact that a large number of plants are used, iu turn, for the manufacture of either HDPE or LLDPE iu the same reactors. VLDPE and LLDPE resius with a uniform branching distribution were initially produced in the United States by Exxon Chemical Company and Dow Chemical Company. However, since several other companies around the world have also aimounced their entry into this market, the worldwide capacity of uniformly branched LLDPE resins in 1995 is expected to reach a million tons. Special grades of LLDPE resins with broad MWD are produced by Phillips Petroleum Co. under the trade name Low Density Linear Polyethylenes or LDLPE. 

Density. Density of LLDPE is measured by flotation in density gradient columns according to ASTM D1505-85. The most often used Hquid system is 2-propanol—water, which provides a density range of 0.79—1.00 g/cm. This technique is simple but requires over 50 hours for a precise measurement. The correlation between density (d) and crystallinity (CR) is given hy Ijd = CRj + (1 — Ci ) / d, where the density of the crystalline phase, ify, is 1.00 g/cm and the density of the amorphous phase, is 0.852—0.862 g/cm. Ultrasonic methods (Tecrad Company) and soHd-state nmr methods (Auburn International, Rheometrics) have been developed for crystallinity and density measurements of LLDPE resins both in pelletized and granular forms. 

Polyolefins are manufactured and used in much greater quantity than any other class of plastics. The principal polyolefins are polyethylenes of various densities (LDPE, LLDPE, HDPE) and polypropylene (PP) (see Olefin polymers). 

---