Density, resin

Density. Density is the mass of unit volume at a given temperature. For solid resins, density is evaluated according to DIN 51 757 at 20°C, whereas for liquid resins DIN 1995 U2 at 20°C is more appropriate. Densities of resins usually are in the range 0.88 to 1.15 g/cm. ... 

The level of short-chain (SCB) and long-chain (LCB) branches control the solid resin density of a PE resin. For example, the level of SCB is controlled by the amount of alpha olefin comonomer incorporated into LLDPE resin as a pendant group. The random positioning of the pendant groups disrupts the crystailization process when the polymer is cooled from the molten state, causing the level of crystallinity to decrease with increasing amounts of alpha olefin comonomer. 

Thermoplastic structural foams with bulk densities not less than 50% of the solid resin densities are considered. Cellular morphology, uniform-density cell behaviour, the I-beam concept in designing, core-density profile and the role of the skin, mechanical properties, and ductile-brittle transitions are discussed. 63 refs. 

Resin Density. A resin density, pR, of 1.22 g/ml was used in this study. 

The classification of PE resins has developed in conjunction with the discovery of new catalysts for ethylene polymerization as well as new polymerization processes and applications. The classification (given in Table 1) is based on two parameters the resin density and its melt index. This classification provides a simple means for a basic differentiation of PE resins, even though it cannot easily describe some important distinctions between the structures and properties of various resin brands. 

Microsphere volnme fraction is 0.60 b> Values calculated using microsphere particle density of 237 kg/m3 and resin density of 1400 kg/m3... 

It should be noted that the dependence observed on particular variations of resin-solution system characteristics (swelling, solution, and resin densities) when transferring from one ionic form to another may prove unreliable. The effectiveness of countercurrent columns of different types may differ from the effectiveness of columns with a fixed bed that respond differently. 

Industrial polyethylenes are commonly classified and named using acronyms that incorporate resin density or molecular weight. lUPAC names are not typically used. In a few cases, copolymers are named using abbreviations for the comonomer employed. Nomenclature typically used for industrial polyethylenes will be discussed in this section. (Molecular weight will be discussed in section 1.4.)... 

BOX 4.8 Measurement of Swollen Resin Density Apparent Resin Density... 

A further useful resin density measurement is provided by the apparent density (Box 4.8) when defined as dry kilogram per litre... 

The typical resin densities may range from 0.6 g/cc to 1.3 g/cc for organic polymers. Silicate materials may be more dense up to 6 g/cc. Since the fermentation broth or other biochemical fluid may be more dense than water, the slow flow rates that are usually involved may require resins that have a greater density than water. A minimum flow rate may be necessary to maintain a packed bed when a fluid denser than water is being processed by a medium density resin. If this is not possible, an up-flow operation or batch process may be necessary. This is discussed in more detail in Sec. 6. 

Enhanced (3-hydride transfer from a tertiary carbon does not fully explain all of the observations of increased MI when comonomer is added to the reactor. In some cases, the addition of comonomer has a powerful effect on the MW, although little or no density suppression is observed. In these cases, activity is sometimes (but not always) inhibited as well. For example, isobutylene does not incorporate well, tends to mildly inhibit the polymerization, has little or no effect on resin density, and once incorporated does not even have a (3-hydride group that can eliminate. Yet isobutylene also leads to a major increase in MI when it is added to the reactor. As another contrary example, some catalysts, such as Cr/AIPO4, do not incorporate 1-hexene very effectively, but they do display an exaggerated MI response to 1-hexene. 

The increase in HLMI exceeds that usually expected from the elimination of (3-hydride from the tertiary carbon atom of an inserted branch, as is evident by the fact that the polymer density barely changed with addition of 1-hexene. As expected, vinylidene appeared in the polymer upon addition of 1-hexene to the reactor with any of these three catalysts, because of (3-hydride elimination from the tertiary carbon atom. However, Cr/AlP04 produced nearly three times more vinylidene than Cr/silica, although it incorporated only a fourth as much 1-hexene branching. This comparison indicates that Cr/A1P04 has a strong tendency to terminate immediately after 1-hexene incorporation (Scheme 34A). This tendency, which may result from the phosphate acidity, can drive up the MI without affecting the resin density, because a terminal branch has little influence on the polymer crystallinity. 

In addition to incorporated oligomers, which produce even-numbered branches, methyl branching is also detected in small amounts in the polymers made with many organochromium (but not chromium oxide) catalysts. Chromocene is especially known for this behavior [303,654,679,680]. It is usually thought to result from (3-hydride elimination to the chromium, followed by reinsertion of the same chain or (perhaps a comonomer) in the backwards 2,1 position. The number of methyl branches formed is usually not large enough to have a significant effect on the resin density. 

In this way the subtleties of the normal commercial polyethylene grades are reproduced faithfully, but without the expense of purchasing, purifying, and storing a-olefin comonomer. Continuous addition of the organochromium compound directly into the reactor, or with the chromium oxide catalyst to a pre-contacting vessel which flows to the reactor, provides precise and instantaneous control of the resin density (i.e. level of branching). 

To predict the resin density at any time in the reactor, the following relationship has been found The specific volume of the polymer (the inverse of the density) varies linearly with the square root of the 1-hexene to ethylene reactant concentration ratio in the reactor [726]. This rule holds approximately true, because it is based on the concept of "excluded volume." That is, each branch on a polymer chain causes it to occupy more space. Comonomer incorporation usually becomes more efficient with increasing reaction temperature for Cr/silica catalysts. 

With an air-quench, the density of the fully-crosslinked epoxy drops from 1.230 to 1.215 gm/cm. With sub-Tg annealing, an Increase of 0.82% in the resin density was observed during the 140°C aging. This fits the "free volume collapse" model in which the resin densifies. Figure 16 simimarlzes these observations. 

R = weight % of resin in the composite r = weight % of reinforcement in the composite D = resin density d = reinforcement density... 

Whereas the projected area determines the clamping force, the weight or volume of a shot determines the capacity of the IM machine required. For the hot runners of TPs, the shot size includes the gate and runners. Capacities of machines are generally rated in ounces of general purpose PS with other resins, convert to the correct capacity by relating the resin densities to that of PE. If the shot size is based on volume, densities are not involved. 

Most importantly the development of gas-phase processes allowed the energy-intensive high-pressure polymerization process to be replaced by the far more energy-efficient low-pressure process. The gas-phase processes offer the greatest versatility of products in terms of resin density and melt index of polyethylenes. From an environmental standpoint the gas-phase reaction is of particular interest and offers several advantages over the conventional technology as recently summarized by Joyce [9]. 

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