Fiber association and network formation in PLA/lignocellulosic fiber composites.

PLA composites were prepared in an internal mixer with a lignocellulosic fiber having relatively large aspect ratio. Fiber content changed between 0 and 60 vol% and the homogenized material was compression molded to 1 mm thick plates. The composites showed anomalous behavior above certain fiber content. Their modulus and especially their strength decreased drastically and modeling also proved the loss of reinforcement at large fiber contents. Micromechanical testing showed that the mechanism of deformation and failure changes at a critical fiber content. Microscopic analysis indi-cated the formation of a network purely from geometrical reasons. The inherent strength of the network is very small because of the weak forces acting among the fibers. This weak inherent strength makes the structure of the composites very sensitive to pro-cessing conditions, and decreases strength, reproducibility as well as reliability

Condensed Mode Cooling for Ethylene Polymerization: Part III. The Impact of Induced Condensing Agents on Particle Morphology and Polymer Properties

The presence of different commonly used induced condensing agents (icas) in the gas phase polymerization of ethylene on the supported catalyst has a significant impact on the crystallinity and the molecular weight distribution of the resulting high density polyethylene. The crystallinity of the polymer is found to be higher in the presence of vaporized n-pentane or n-hexane, than in “dry mode” (i.e., with no ica). This is primarily attributed to the mechanism of crystallization of polymer chains in presence of the solubilized ica which might act to promote solvent vapor annealing. In addition, vaporized ica also provokes a significant increase in the weight average molecular weight, with values being estimated at over one million