Blends compounding and processing

White, J.L and Bumm, S.H. (2011) Polymer blend compounding and processing, in Encyclopedia of Polymer Blends (eds A.I. Isayev and S. Palsule), Wiley-VCH, Weinheim, pp. 1-26. 

The twin-screw injection molding extruder is an injection molding machine that is capable of both blending/compounding and extrusion in one step. Because it is a one step process, the fibers never go through the entire extrusion process as well as the pelletization that limits the fiber size, but are blended into the molten plastic before injection. The screw part of this machine is based on a non-intermeshing, counterrotating twin-screw extruder (Chapter 5). One of the screws in this machine is capable of axial movement and has a non-return valve on the end. This action enables the screw to inject and mold parts. 

The oldest and most common method of POM toughening is by incorporation of TPU. Delrin POM/TPU blends were commercialized in 1960. The others followed, e.g., Celcon , Duraloy , Formaldafil , Fulton KL, Hostaform , RTP 800, TC, or Ultraform . These alloys have high impact strength and elastic recovery that depend on composition, morphology, as well as on the compounding and processing methods. Examples of these blends are listed in Table 1.66. 

To support these new tendencies the research community has been asked to provide better predictive methods for the multicomponent blends as well as improved sensors for the closed-loop process control. In particular, the evolution of morphology during the compounding and processing steps is of paramount importance. Microrheology and coalescence are the keys to describing the structure evolution of polymer blends. 

The properties of the finished articles made from immiscible blends are governed by the morphology created as a result of the interplay of processing conditions and inherent polymer characteristics, including crystallizability. Therefore, a scientific understanding of the crystallization behavior in immiscible polymer blends is necessary for the effective manipulation and control of properties by compounding and processing of these blends. 

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