Plastics polymer viscosity

Of the models Hsted in Table 1, the Newtonian is the simplest. It fits water, solvents, and many polymer solutions over a wide strain rate range. The plastic or Bingham body model predicts constant plastic viscosity above a yield stress. This model works for a number of dispersions, including some pigment pastes. Yield stress, Tq, and plastic (Bingham) viscosity, = (t — Tq )/7, may be determined from the intercept and the slope beyond the intercept, respectively, of a shear stress vs shear rate plot. 

The situation becomes most complicated in multicomponent systems, for example, if we speak about filling of plasticized polymers and solutions. The viscosity of a dispersion medium may vary here due to different reasons, namely a change in the nature of the solvent, concentration of the solution, molecular weight of the polymer. Naturally, here the interaction between the liquid and the filler changes, for one, a distinct adsorption layer, which modifies the surface and hence the activity (net-formation ability) of the filler, arises. Therefore in such multicomponent systems in the general case we can hardly expect universal values of yield stress, depending only on the concentration of the filler. Experimental data also confirm this conclusion [13],... 

Density, a topic that is taught in the early weeks of a chemistry course, is introduced in Chapter 6, Polymer Solutions and Dispersions. Why not use some plastic samples for density experiments Have the students identify the plastic from its density. This will enforce the concept that density is an intensive property of matter. The discussion of viscosity can also fit into a presentation on H-bonding. The explanation of polymer viscosity is ver useful for a teacher using the Chemistry in the Community curriculum. It is an excellent reference for the experiment that has the students determining viscosity by tuning the rate of fall of a plastic bead in various organic liquids. 

In plastics, relative viscosity can be defined as the ratio of the viscosity of a concentrate to that of the neat carrier polymer at the same temperature. In this use, relative viscosity predicts relative jetness—defined in the same manner—more accurately than the carbon black loading in a concentrate. A mismatch between masterbatch and letdown viscosities causes incomplete mixing and is the reason that relative jetness can decrease with an increase in relative viscosity [5]. 

The dilution effect, causing the viscosity of the concentrated solution to be lowered even further, and to fall between the viscositis of the plasticized polymer and the pure solvent. 

If r pCI denotes the viscosity of a plasticized but undiluted polymer at the critical molecular weight (calculated by using the lowered values of Tg and Epoo for the plasticized polymer), then the solution viscosity (rjss) can be calculated by using Equation 13.4 or Equation 13.5, as appropriate, with Mcr calculated from Equation 13.34 (or a refined version of it with a slightly smaller power of p in the denominator) being used instead of the Mcr of the polymer melt. 

Estimate the viscosity of the plasticized but undiluted polymer with Mw=Mcr at the temperature of interest (T pcr ) by utilizing equations 13.9, 13.10 and 13.11 with the Tg and the Epoo of the plasticized polymer rather than the Tg and the Epoo of the pure polymer. 

As an added difficulty, the plasticizer s solvation effect In PVB appears to enhance the polymer viscosity drop with temperature. Unfortunately, this raises the leakage current of a... 

ISO 3219, Plastics Polymers in the liquid, emulsified or dispersed state Determination of viscosity with a rotational viscometer working at defined shear rate, 1993. 

The diene hydrocarbon rubbers are often blended with hydrocarbon oils. The oils decrease polymer viscosity and reduce hardness and low temperatures brittle point of the cured product. They are thus closely analogous to the plasticizers used with thermoplastics but are generally known as softners. Three main types of softners are distinguished aliphatic, aromatic, and naphthenic. The naphthenics are preferred for general all-round properties. 

ISO 1043 provides for each plastic (polymer) to be identified by a sequence of symbols (an abbreviation) which indicates its chemical structure. Additional letters (codes) identify its use, fillers, and basic properties, such as density or viscosity. An example is given in Figure 1-3. 

The free volume theory originated some years later than the lubricity and the gel theories, when the evolution of different properties of polymers as a function of temperature, specific volume, thermal expansion coefficients, or viscosity was attempted to be explained.The relationships between these properties and some variables corresponding to polymer stracture, such as molecular weight or terminal groups content, the presence of another monomer and, of course, the presence of plasticizers, was also explained. For plasticized polymers the theory attempted to explain the diminution of the glass transition temperature with the plasticizer content. This theory is a contribution of different authors, but it was postulated by Fox and Floiy. The theory is still being used to explain some properties of plasticized polymers, i.e., viscoelastic properties. ... 

Material scientists can predict an approximate amormt of plasticizer reqirired for composition irsing experience, because marty plasticizers reduce viscosity of a polymer nearly to the same extent (this statement has, certainly, a lot of exceptions). In some applications 75% polymer in a composition with 25% plasticizer gives ttseftrl properties over a temperatirre range of material rrse (e.g., lowering low temperature properties of butadiene-nitrile rabbets by 10-15 C with preservation of remaining technical properties). In other... 

As mentioned above, the macromolecules develop into more extended conformations in a good solvent or plasticizer. This increases the viscosity of dilute solutions of polymer. Viscosity changes are used for comparative evaluation of polymer-plasticizer interaction. The plasticizer may also decrease the interaction between polymeric chains and this reduces the viscosity of concentrated polymeric solutions. Incompatible plasticizers, on the other hand, may considerably reduce the viscosity of polymer compositions even in small quantities (less than 1%) by acting as internal lubricants. 

Classical rubber processing is time and effort consuming because of the high polymer viscosities working in of vulcanization accelerators, fillers, plasticizers, activators, etc., must be carried out on roll mills, the vulcanization must take place in heated presses. In contrast, liquid rubbers have low viscosities, and so, can be more easily processed. These have already been known for a long time in the case of silicones, polyurethanes, polyesters, and polyethers, but have only been very recently developed in the case of diene rubbers. 

Plasticization can be explained by several theories which are initially based on physical observations such as the decrease of elastic moduli, viscosity or glass transition temperature. Since the beginning of the 1940s, scientists have elaborated different theories which all tried to clarify critical phenomena observed in plasticized polymer materials. 

Plasticizers are considered nonvolatile solvents. They act to soften a material by separating the polymer chains allowing them to be more flexible. As a result, the plasticized polymer is softer with greater extensibility. Plasticizers reduce the melt viscosity and glass transition temperature of the polymer. In order for the plasticizer to be a solvent for the polymer, it is necessary for the solubility parameter of... 

The reasons for the popularity of calcium carbonate in plastics are its ready availability and low cost, together with its favourable particle shape which does not increase the polymer viscosity excessively, nor lower the strength and impact resistance by too much. 

Introduction of WF in LDPE results in a slight increase in the viscosity of the melt. The addition of 10% NR is not conducive to change the value of the indicator, while 20% NR plasticizes polymer composite during the heating process, which improves its workability. When adding EPDM observed the opposite result, as in the processing of cross-linked EPDM [11], which leads to a sharp increase in the viscosity of the melt, as a consequence of the material does not flow. 

It is now important to calculate the stress exerted by the particles. This stress is equal to aApgfZ. For polystyrene latex particles with radius 1.55 pm and density 1.05 g cm , this stress is equal to 1.6 x 10 Pa. Such stress is lower than the critical stress for most EH EC solutions. In this case, one would expect a correlation between the settling velocity and the zero shear viscosity. This is illustrated in Chapter 7, whereby v/a is plotted versus 7(0). A linear relationship between log( /a ) and log 7(0) is obtained, with a slope of —1, over three decades of viscosity. This indicated that the settling rate is proportional to [7(0)] . Thus, the settling rate of isolated spheres in non-Newtonian (pseudo-plastic) polymer solutions is determined by the zero shear viscosity in which the particles are suspended. As discussed in Chapter 7, on rheological measurements, determination of the zero shear viscosity is not straightforward and requires the use of constant stress rheometers. 

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