Parameters melt flow

Ionomer resins are produced in multiple grades to meet market needs, and prospective customers are provided with information on key processing parameters such as melt-flow index. Nominal values for many other properties are Hsted in product brochures. The ASTM test methods developed for general-purpose thermoplastic resins are appHcable to ionomers. No special methods have been introduced specifically for the ionomers. 

Free phenol is a major concern in the manufacture of novolac resins. This is true for several reasons. The strongest drivers are probably EPA classification of phenol as a Hazardous Air Pollutant and worker safety concerns. However, free phenol also has significant technical effects on such parameters as melt flow characteristics. In this role, free phenol may undermine the desired effects of a molecular weight design by increasing flow beyond the desired point. Since free phenol is often variable, the effects on flow may also cause variation in product performance from batch to batch. Fig. 18 shows the effects of free phenol on the flow across a series of molecular weights. Free phenol contents between 1 and 10% are commonly seen. In recent years, much work has been aimed at reducing the free phenol. 

The molecular weight of the continuous phase is an important parameter that affects the mechanics and the melt flow of the end product. It can be controlled by the use of a suitable chain transfer agent (e.g., /er/-dodecyl mercaptan Ct = 4.0) or their combinations (e.g., primary mercaptans Or = 26.0 and dimeric a-methyl styrene Ct = 0.1) [132]. 

The value Pcr, critical pressure, is a fundamental parameter of the nature of gas-containing melt flows below this critical point, the flow becomes two-phase. This point was established by C. D. Han and C. A. Villamizer [8] by direct observations of the flow in a transparent channel. Data presented by these authors pertain to the case of incomplete decomposition of the blowing agent prior to its entrance into the channel. Obviously, Pcr depends on the amount of gas. 

Thus, both the mean droplet size and the size distribution may be predicted using these correlations [Eqs. (26), (27), (28), or (29) and Eqs. (30), (31)] for given process parameters and material properties. For a given atomizer design, the standard deviation of droplet size distribution has been found to increase with the melt flow rate, but appears to be less sensitive to the gas flow rated5 Moreover, the variation of the standard deviation is very atomizer- and melt-specific. An empirical correlation which fits with a wide range of atomization data has the following form ... 

Figure 4.26 displays examples of Vicat softening temperatures (VST) versus VA content. The other important parameter for VST is the melt flow index. 

Plasticized PVC has the same structures as rigid PVC, except that plasticizer enters the amorphous phase of PVC and makes the he molecules elastomeric. The grains break down to l- rnr primary particles winch become the melt flow units. The crystallites are not destroyed by plasticizer. Table 2 provides a list of the PVC physical parameters. 

The lumped-parameter model approach becomes particularly useful when dealing with the plasticating extrusion process discussed in the next subsection, where, in addition to melt flow, we are faced with the elementary steps of solids handling and melting. 

In practice, the complete viscosity functions are often not specified for polymer melts. Instead, the melt flow rate (MFR) and/or the melt volumetric rate (MVR) is used. These parameters specify how much polymer mass and/or volume will flow out of a normalized flow channel within a specific period (e. g [cm3/10 min]) when subjected to stress (see DIN EN ISO 113, ASTM D1238). Low-viscosity, easily flowing polymers have high MFR or MVI values, while high viscosity/slow flowing polymers have low MFR or MVI values. These values are listed e.g. in plastics databases such as CAMPUS [3],... 

Melt flow rate or melt flow index may be obtained by applying a specified weight to force a sample of the plastic, heated to a specified temperature, through a hole of stated diameter the amount extruded in this way in ten minutes is the parameter required. The actual conditions of test may be varied according to the material and the requirements of processing but in general the rate of shear is far lower than is experienced in reality in most melt processes (in other words, this is a low shear rate test). 

Copolymerization. Vinyl chloride can be copolymerized with a variety of monomers. Vinyl acetate [9003-22-9], the most important commercial comonomer, is used to reduce crystallinity, which aids fusion and allows lower processing temperatures. Copolymers are used in flooring and coatings. This copolymer sometimes contains maleic acid or vinyl alcohol (hydrolyzed from the poly(vinyl acetate)) to improve the coating s adhesion to other materials, including metals. Copolymers with vinylidene chloride are used as barrier films and coatings. Copolymers of vinyl chloride with maleates or fumerates are used to raise heat deflection temperature. Copolymers of vinyl chloride with acrylic esters in latex form are used as film formers in paint, nonwoven fabric binders, adhesives, and coatings. Copolymers with olefins improve thermal stability and melt flow, but at some loss of heat-deflection temperature (100). Copolymerization parameters are listed in Table 5. 

Nevertheless, due to its relative simplicity, the melt flow index is one of the most popular parameters is the plastics industry, especially for polyethylenes. Here the melt index is a good indicator of the most suitable (end) use. Table 24.2 gives some data. A melt flow index of 1.0 corresponds to a melt viscosity of about 1.5 x 104 N s/m2 (= 1.5 x 105 poises)... 

Like all thermoplastics, HIPS is a non-Newtonian fluid. This means that the viscosity depends not only on the temperature, but also on the shear rate. As a result, the melt flow rate increases proportionally with increasing pressure. In Figures 12.5-12.7, the temperature is also shown as a parameter. 

Molecular weights are not often measured directly for control of production of polymers because other product properties are more convenient experimentally or are thought to be more directly related to various end uses. Solution and melt viscosities are examples of the latter properties. Poly(vinyl chloride) (PVC) production is controlled aceording to the viscosity of a solution of arbitrary concentration relative to that of the pure solvent. Polyolefin polymers are made to specific values of a melt flow parameter called melt index, whereas rubber is characterized by its Mooney viscosity, which is a different measure related more or less to melt viscosity. These parameters are obviously of some practical utility, or they would not be used so extensively. They are unfortunately specific to particular polymers and are of little or no use in bringing experience with one polymer to bear on problems associated with another. 

Figure 24 Chondrite-normalized abundances of REEs in a wall-rock harzburgite from Lherz (dotted lines— whole-rock analyses), compared with numerical experiments of ID porous melt flow, after Bodinier et al. (1990). The harzburgite samples were collected at 25-65 cm from an amphibole-pyroxenite dike. In contrast with the 0-25 cm wall-rock adjacent to the dike, they are devoid of amphibole but contain minute amounts of apatite (Woodland et al., 1996). The strong REE fractionation observed in these samples is explained by chromatographic fractionation due to diffusional exchange of the elements between peridotite minerals and advective interstitial melt (Navon and Stolper, 1987 Vasseur et al, 1991). The results are shown in (a) for variable t t ratio, where t is the duration of the infiltration process and t the time it takes for the melt to percolate throughout the percolation column (Navon and Stolper, 1987). This parameter is proportional to the average melt/rock ratio in the percolation column. In (b), the results are shown for constant f/fc but variable proportion of clinopyroxene at the scale of the studied peridotite slices (<5 cm). All model parameters may be found in Bodinier et al. (1990). As discussed in the text, this model was criticized by Nielson and Wilshire (1993). An improved version taking into account the gradual solidiflcation of melt down the wall-rock thermal gradient and the isotopic variations was recently proposed by Bodinier et al. (2003).

The EWF tests were named with a eode indicating material, erosshead rate and orientation, in that order. In this way, PC20-10T (or P) results correspond to tests carried out on PC20 blends tested at 10 mm/min in 90° (or 0°) crack propagation with respect to the melt flow direction. It is important to mention that even the fact that tensile parameters were determined on thicker (4 mm) dumbbell specimens could invalidate their use in EWF validations due to some morphological and crystallinity differences, some SEM observations and DSC measurements on plaques and dumbbell test specimens verified that these microstructural features are quite similar on both specimen geometries (Table 1). 

Indeed, as obvious from both exemples given in Fig. 2, the transition could thus be determined accurately within 0.1-0.2 decades of test speeds with few samples in a relative short time frame. Moreover, as the apparent values (Kimax) are always lower than the effective parameters (Keff), none of the material descriptor would be overestimated. In addition, since Kjmax-values have been shown to provide a semi-quantitative evaluation (in terms of test speed or temperature) of fracture resistance parameters, a coherent material comparison would be possible over the whole investigated range. This remark remains true as long as the grades have similar rp. For iPP grades, it should be checked (and considered with more caution) when materials exhibit different particle and matrix melt flow rates, or different crystalline structures. It should also be investigated in detail when different polymer families (ABS versus HIPS or rubber modified iPP) are compared. 

A major goal in the physics of polymer melts and concentrated solutions is to relate measurable viscoelastic constants, such as the zero shear viscosity, to molecular parameters, such as the dimensions of the polymer coil and the intermolecular friction constant. The results of investigations to this end on the viscosity were reviewed in 1955 (5). This review wiU be principaUy concerned with advances made since in both empirical correlation (Section 2) and theory of melt flow (Section 3). We shall avoid data confined to shear rates so high that the zero shear viscosity cannot be reliably obtained. The shear dq endent behavior would require an extensive review in itself. 

In the past, equivalency between grades has usually been identified by comparing certain basic properties such as density and melt flow index (the amount of plastic which flows under given conditions of temperature, pressure and time). Although these are quite acceptable for many non-critical usages, further parameters must be considered particularly when the plastic is... 

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