The alignment of cellulose microcrystals in a 6.9% (w/w) colloidal aqueous suspension under shear was
characterized using small angle synchrotron radiation scattering. Prior to shearing, the microcrystals
appeared randomly oriented and went through a two-step alignment process with increasing shear rate.
At shear rates lower than 5 s-1, the X-ray scattering patterns indicated little or no preferential alignment
in the shear direction; however, in the plane perpendicular to the shear direction, the microcrystals were
preferentially oriented in the vertical direction. At shear rates of 5 s-1 and higher, the microcrystals were
aligned horizontally along the shear direction. These orientation phenomena were found to be dependent
on shear rate and completely reversible. They are likely due to the presence of planar domains of randomly
oriented microcrystals which align at low shear rates and are broken up at higher shear rates enabling
alignment of the individual microcyrstals.
Numerous examples in the literature illustrate how the coextrusion of film with three or more polymeric layers is economically used to achieve a desirable mix of end‐use characteristics. More recently, layer‐multiplying devices permit two polymers of widely dissimilar solid‐state properties to be combined into unique microlayer and nanolayer structures with hundreds or thousands of alternating layers. If the layers are thin enough, the key properties of the constituents can combine synergistically. The microlayer structure is also an effective research tool. Because the microlayer and nanolayer structures contain large specific interfacial areas, they are ideal for fundamental studies of phenomena such as interdiffusion and adhesion. Three examples of microlayered materials with up to 1024 layers illustrate the versatility of this coextrusion process: talc‐filled PP, PC/SAN, and HDPE/LLDPE.
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