Solid-State Shear Pulverization

From the Preface This book is the first extended look at a new and multifaceted polymer processing technology that has already been discussed in numerous articles. Called Solid-State Shear Pulverization (S3P), this innovative process produces polymeric powders with unique physical properties not found in the output of conventional size-reduction methods.... This technology, which utilizes a pulverizer based on a modified co-rotating twin-screw extruder..., has profound implications for both the creation of new polymer blends and recycling of plastic and rubber waste. Unlike [earlier processes] where polymers are melted prior to pulverization,...pulverizing mixtures of polymers with the S3P process...does not involve melting. By contrast, S3P maintains polymers in the solid state and avoids the additional heat history that occurs during [other processes], which can be detrimental to the physical properties of pulverized materials. The research and development of the S3P technology...has grown significantly since 1990 from the development of a new plastics recycling process to a much broader polymer processing method that allows intimate mixing of polymers with very different viscosities, sold-state dispersion of additives, including pigments, and continuous production of powder with unique shapes and larger surface areas. Polymeric powders are of growing importance to plastics processors due to the increase use of plastics in various applications, such as rotational molding, powder coatings, and compounding, which require powder as the feedstock. ...[I]t has become clear that this process allows for in-situ compatibilization of dissimilar polymers by applying mechanical energy to cause chemical reactions. This aspect of S3P technology that we describe in this book should [be useful in] developing new polymer blends with the use of pre-made compatibilizing agents. In addition, it has been discovered that S3P efficiently mixes polymer blends with different component viscosities, resulting in the elimination of phase inversion. The S3P process directly produces blends with matrix and dispersed phase morphology like those obtained after phase inversion during a long melt-mixing process. This phenomenon is of practical importance because a long processing time is required by conventional melt-mixing to produce a stable blend morphology. S3P is also advantageous for producing thermoplastic or thermoset powder-coating compounds in a one-step process as opposed to a conventional multi-step operation that involves melt extrusion followed by batch grinding. The major capabilities of this new process can be summarized as follows: o Continuous powder production from plastics or rubber feedstocks o Blending of immiscible polymers o Efficient mixing of polymers with unmatched viscosities o Environmentally friendly recycling of multicolored, commingled plastics waste o Sold-state dispersion of heat-sensitive additives o Engineered plastic/rubber blends Materials and processes well illustrated The text is well illustrated with 60 photographs, micrographs, diagrams and others figures. Here is a small sampling of the captions of these figures. o Particle-size distribution for virgin LDPE powder made with PT-25 pulverizer o Optical photograph of virgin LDPE powder made with PT-25 pulverizer o Layout for a three-stage rubber pulverizer o Flow chart for powder coating production by conventional process and with new S3P technology o SEM image of pulverized virgin PP at 40X (first in series of SEM images of polymer powders) o Optical micrograph of melt-crystallized thin films of unpulverized virgin PP under polarized light o Log of viscosity vs. log shear rate for virgin HDPE after S3P processing o Gel permeation chromatograms (GPC) of polystyrene subjected to S3P processing Color-photo section One of the several functions of Solid-State Shear Pulverization technology is recycling mixed plastic wastStephen H. Carr is the author of 'Solid-State Shear Pulverization', published 2001 under ISBN 9781566768030 and ISBN 1566768039.