Plastic, viscosity characteristics

Rheology is the study of flow and deformation of materials under the influence of external forces. It involves the viscosity characteristics of powders, liquids, and semisolids. Rheological studies are also important in the industrial manufacture and applications of plastic materials, lubricating materials, coatings, inks, adhesives, and food products. Flow properties of pharmaceutical disperse systems can be of particular importance, especially for topical products. Such systems often exhibit rather complex rheological properties, and pharmaceutical scientists have conducted fundamental investigations in this area [58-64],... 

Yield stress and plastic viscosity. The most important rheological characteristic determining the foam behavior ( solid-shaped or fluid-shaped ) is the yield stress To. This variable was calculated in [379] for a two-dimensional foam model ... 

The primary reason for utilizing a dispersion resin system is to obtain the benefit of fluid properties. With viscosity characteristics in mind, we must consider this qualification for the plasticizers used in plastlsols. 

Diisooctyl phthalate (DIOP) n. C6H4 (COOC8Hi7)2. a primary plasticizer for PVC, ethyl cellulose, cellulose nitrate, and polystyrene. In vinyls, its performance is similar to that of dioctyl phthalate except that it is slightly less volatile than DOP and produces better viscosity characteristics in plastisols. DIOP is FDA-approved for foodpackaging materials and medical applications involving contact with water, but not with fats. 

As simplified characteristics of extruded catalyst pastes, we have chosen the plastic strength Pj , plastic viscosity Tij and the dynamic limit of catalyst paste fluidity P. ... 

Historically, most discussions on polymer flow focus only on viscosity. However, with many of the newer resins that are highly impact modified or have high elasticity, viscosity tells only part of the story for flow behavior. Two plastics can have identical viscosity characteristics and yet mold differently. Elastic response and the polymer s ability to transmit pressure become increasingly important as part designs increase in complexity. Both viscous and elastic response are required to properly characterize flow through complex cavities (22). 

The plastic viscosity and the theoretical yield value decreased gradually. In the case of Eucarol AGE/EC and SS the yield value did not change characteristically above a water content of 65%. 

In addition to its behavior in viscoelastic behavior in plastic products, viscosity of plastics during processing provides another important relationship to product performances (Chapter 1). Different terms are used to identify viscosity characteristics that include methods to determine... 

The dimensioning of plastics components for defined operating times and corresponding service life has to fulfill strict requirements. Components made from unreinforced plastics exhibit viscoelasticity, physical and geometric non-linearity. In reinforced plastics, viscosity is less critical, but inhomogeneity, layer sequence and anisotropy become relevant. The exact determination of these characteristics is always a very complicated mathematical task. 

The resistance to plastic flow can be schematically illustrated by dashpots with characteristic viscosities. The resistance to deformations within the elastic regions can be characterized by elastic springs and spring force constants. In real fibers, in contrast to ideal fibers, the mechanical behavior is best characterized by simultaneous elastic and plastic deformations. Materials that undergo simultaneous elastic and plastic effects are said to be viscoelastic. Several models describing viscoelasticity in terms of springs and dashpots in various series and parallel combinations have been proposed. The concepts of elasticity, plasticity, and viscoelasticity have been the subjects of several excellent reviews (21,22). 

ASTM D883 defines a filler as "...a relatively inert material added to a plastic to modify its strength, permanence, working properties, or other quaHties or to lower costs." EiHers (qv) that modify the properties and characteristics of epoxies are employed in epoxy resins for a variety of reasons. Then principal functions are to control viscosity, reduce shrinkage and the coefficient of thermal expansion, effect a cost reduction, and color the epoxy resins. 

The thickness of the tape is controUed by the sHp characteristics, the height of the doctor blade, the casting rate, and the pressure head of the sHp reservoir behind the doctor blade. SHp viscosities in the range of 1 5 Pa-s (10—50 P) are used to cast tapes at 5—100 cm/s. To achieve the desired strength and flexibUity in the green tape, tape casting slurries contain more binder than those used in sHp casting, as weU as a plasticizer to ensure flexibUity. 

Plasticizers (qv) are usually present at lower concentrations compared to general-purpose mbber-based compounds, because of their volatility at typical ACM service temperatures and/or their partial extractabiflty by the aggressive fluids where acryflc elastomers are employed. Other additives are therefore required to improve processibiflty. These processiag aids act as lubricating agents and enhance the release characteristics of the acryflc compound and/or reduce compound viscosity. 

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