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A new theoretical concept is given which provides an efficient and consistent method for predicting flow and heat transfer characteristics of the melting zone for a large singlescrew extruder. In contradistinction to previous theories, significant melt accumulation in the molten films as observed experimentally is considered, instead of postulating the melt accumulation in the "melt pool". The mathematical model has been obtained by the simultaneous solution of the momentum and energy equation of the melt flow and solid bed, allowing for the existence of the pressure gradient. The theory is supplemented by a numerical example which shows good agreement with experimental data obtained on a 90 mm extruder with polypropylene, where the down-channel pressure profile and the profile of the solid bed were taken as yardsticks for the melting process. For exact determination ofthe area for applicability of this theory, more experimental information is required.

This paper deals with the early stages of blend morphology development as occurs in a screw extruder. Using combinations of similar polymers (polystyrene and styrene-butadiene copolymer) and dissimilar polymers (PS and EVA) as model systems, it has been concluded that during melting the scale of segregation between the blend components is reduced by orders of magnitude within fraction of a second residence time. During the early stages of morphology development, the melting pellets produce fine lamellar structures (thickness of the order of pm) that extend over much of the melting zone before being broken up by capillary forces. The origin and the deformation history of the lamellar structures have been successfully interpreted by a new theory. Y I B WFg. 3. The "three-layer" B model for two components and the coordinate system.

A kinetic investigation on the monoesterification reaction of the maleic anhydride residue (MA) in styrene‐maleic anhydride copolymers with aliphatic alcohols was carried out in ethyl benzene solution. By comparison to classic catalysts such as tributylamine (TBA) and pyridine, 4‐dimethylaminopyridine (4DMAP) is by far the most effective catalyst for this reaction. While both general base and nucleophilic mechanisms contribute to the reaction catalyzed by TBA or pyridine, a nucleophilic mechanism prevails with 4DMAP. This reaction is reversible, and its chemical equilibrium constant decreases significantly with increasing temperature. Both kinetic and thermodynamic results showed that in the presence of 4DMAP, the forward and reverse reactions are second and first order, respectively. The existence of side reactions, reactivity of two styrene‐maleic anhydride copolymers of different MA contents as well as two aliphatic alcohols of different lengths are also addressed. © 1993 John Wiley & Sons, Inc.

This paper addresses the apparent controversy surrounding the role of the solid bed mechanics in the Maddock melting mechanism. It is demonstrated that the inability of the melting models based on the freely deformable solid bed concept to predict accurately the pressure gradients in the melting zone is not exclusively due to the highly simplified isothermal Newtonian treatment of the melt pool as presumed previously. This study has shown that when using a non isothermal non‐Newtonian flow model for the melt pool, the freely deformable solid bed concept still results in unrealistically low pressure gradients while it may give good predictions of the melting rates. To the contrary, when a rigid solid bed is assumed, the pressure predictions tend to represent the experimental data more closely, whereas the theoretical melting rates seems to become less realistic. In view of the fact that both the freely deformable and the rigid solid bed concepts show such inconsistencies, it has been concluded that the mechanics governing the solids and melt transport in the melting zone require some additional examination, most notably, the influence of the constitutive behavior of the solid bed and of the cross‐channel melt circulation around the solid bed, and possibly of the melting kinetics for semicrystalline polymers.