Melt processing factors

Certain melt processing factors have to be considered in order to eliminate problems. Some of these factors can be compensated by the available plasticator and die/mold adjustments. An unsteady balance of shear forces causes the interfacial instability. Examples of the factors include ... 

The principles of thermoplastic melt processing can perhaps best be illustrated by reference to Figure 8.1 illustrating extrusion, injection moulding, bottle blowing and calendering operations. In order to realise the full potential of the process it is necessary to consider the following factors ... 

The type of manufacturing process, reaction conditions, and catalyst are the controlling factors for the molecular structure of the polymers [4-8]. The molecular features govern the melt processability and microstructure of the solids. The formation of the microstructure is also affected by the melt-processing conditions set for shaping the polymeric resin [9]. The ultimate properties are, thus, directly related to the microstructural features of the polymeric solid. 

As discussed in Chapter 5, the solids-conveying rate for a specific screw is directly proportional to screw speed. That is, if the screw speed is increased by a factor of two the solids-conveying rate will nearly double. The melting flux of the screw as measured in kg/(h-m2) at the barrel wall, however, will not increase at the same rate. Typically, the melting flux will increase by 40% for a doubling of the screw speed [1]. In order to complete the melting process, additional area at the... 

Whilst the physical and chemical nature of the filler will determine its effectiveness in a functional role, the presence of sohd additives in thermoplastics melts inevitably influence their processability. The extent to which this occurs depends on many factors including the amount of filler present, possible interactive effects between the filler and polymer, or between the filler particles themselves, together with the conditions experienced during melt processing, in particular the shear and/or elongational flow fields developed. 

Note that the self-complementary and nonself-complementary processes of the same molecularity (n) give identical expressions for the van t Hoff enthalpy of the melting process, but not for the equilibrium constant. The factors in the expressions for K arise from the indistinguishability of 2A monomers in a process like A2 = 2A, while the A and B monomers in an AB = A + B process are distinguishable. 

B. D. Favis, Factors Influencing the Morphology of Immiscible Polymer Blends in melt Processing, in Polymer Blends, Vol. I, D. R. Paul and C. B. Bucknall, Eds., Wiley-Interscience, New York, 1999. 

This review article deals with aromatic polyimides that are processable from the melt or soluble in organic solvents. Conventional aromatic polyimides represent the most important family of heat resistant polymers, but they cannot be processed in the melt, and their application in the state of soluble intermediates always involves a hazardous step of cyclodehydration and elimination of a non-volatile polar solvent. A major effort has therefore been devoted to the development of novel soluble and/or melt-processable aromatic polyimides that can be applied in the state of full imidation. The structural factors conducive to better solubility and tractability are discussed, and representative examples of monomers showing favourable structural elements have been gathered and listed with the chemical criteria. Experimental and commercial aromatic polyimides are studied and evaluated by their solubility, transition temperatures and thermal resistance. An example is also given of the methods of computational chemistry applied to the study and design of polyimides with improved processability. 

The major processing methods that process well over 80wt% of all plastics are extrusion, injection molding, and blow molding. These processes as well as a few others use a plasticator to melt plastics. It is a very important component in a melting process with its usual barrel and screw. If factors such as the proper screw design and/or barrel heat profile are not used correctly fabricated products may not meet or maximize their performance and very important not provide for low cost process. 

In materials that are often used in construction-wood, concrete and steel—there is still an enormous variation in modulus, by a factor of 15 or so. You can also see that most polymer materials, at least in their usual melt processed form, are not very stiff at all, polyethylene having a modulus of about 150 MPa, while even a glassy polymer like atactic polystyrene has a modulus of only about 3000 MPa (about l/20th that of window glass). 

PVDF exhibits a complex crystalline polymorphism, which cannot be found in other known synthetic polymers. There are a total of four distinct crystalline forms alpha, beta, gamma, and delta. These are present in different proportions in the material, depending on a variety of factors that affect the development of the crystalline structure, such as pressure, intensity of the electric field, controlled melt crystallization, precipitation from different solvents, or seeding crystallization (e.g., surfactants). The alpha and beta forms are most common in practical situations. Generally, the alpha form is generated in normal melt processing the beta form develops under mechanical deformation of melt-fabricated specimens. The gamma form arises under special circumstances, and the delta form is obtained by distortion of... 

The properties of block copolymers that are most affected by molecular architecture are elastomeric behavior, melt processability, and toughness in the solid state. The effects of such copolymers in polymer blends can obviously also be strongly influenced by the same factors. 

We have approached the subject in such a way that the book will meet the requirements of the beginner in the study of viscoelastic properties of polymers as well as those of the experienced worker in other type of materials. With this in mind. Chapters 1 and 2 are introductory and discuss aspects related to chemical diversity, topology, molecular heterodispersity, and states of aggregation of polymers (glassy, crystalline, and rubbery states) to familiarize those who are not acquainted with polymers with molecular parameters that condition the marked viscoelastic behavior of these materials. Chapters 1 and 2 also discuss melting processes and glass transition, and factors affecting them. 

Melt Processes for Oral Solid Dosage Forms, p. 2251. Physiological Factors Affecting Oral Drug Delivery, p. 2866. 

Melting takes place at a constant temperature. The molar heat of fusion tells us that every mole of Na, 23 grams, absorbs 2.6 kj of heat at 97.5°C during the melting process. We want to know the amount of heat that 5.0 grams would absorb. We use the appropriate unit factors, constructed from the atomic weight and to find the amount of heat absorbed. 

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