Anita Vaxman

Innovative ESD thermoplastic composites structured through melt flow processing

The amount of carbon black required to impart electrical conductivity to an insulating polymer can be dramatically reduced by its selective localization in a multi-component system which includes the insulating polymer The present report describes property-structure relationships of polypropylene/nylon/glass fiber (PP/PA/GF) composites with consistent resistivity levels within the 10/sup 6/-10/sup 9/ ohms/sq range achieved at very low carbon black loadings (less than 2%). The quaternary composites studied structure spontaneously during the hot compounding/processing steps and have unique triple-percolation structures. The results were compared with typical carbon black filled materials, which usually contain 15 to 20 wt% carbon black and are too conductive to meet the 10/sup 6/-10/sup 9/ ohms/sq range.

Novel Electrically Conductive Injection Moldable Thermoplastic Composites For ESD Applications

Publisher Summary This chapter describes new thermoplastic composites for injection molding, containing carbon blacks (CB) or CB/carbon fibers (CF) in relation to their electrical and mechanical behavior, as compared to the existing CB-filled thermoplastic compounds. The influence of CB content on the volume resistivity of an injection-molded polypropylene (PP) composite, compared with the resistivity of reference unreinforced PP compounds containing different CB grades, is also presented. The characteristic insulating to conducting transition was observed for all the systems studied. The percolation concentration for the CarmelStat composite occurs at about 1 wt% CB, which is significantly lower compared with the reference CB-filled PP compounds. It has been confirmed that in CB-filled polymers, at low CB concentrations the CB particles are isolated and the electrical resistance is high, while beyond a critical loading (greater than 10 wt%), particles form structures that provide an electrical network through the insulative polymer matrix. Small changes in filler concentration correspond to multiple order of magnitude changes in the electrical resistivity. The mechanical properties of CB-filled thermoplastics can be tailored by reinforcing the polymer with glass fibers and by modifying the polymer with rubber.

New injection moldable ESD compounds based on very low carbon black loadings

The electrical resistivity, mechanical properties, outgassing, ion contamination and particle-shedding characteristics of new electrostatic dissipative (ESD) injection moldable thermoplastic composites containing carbon black and glass fibers were studied. The results for polypropylene, polybutylene terephthalate and polycarbonate based compounds were compared to typical carbon black and carbon fiber filled materials. Injection moldable composites with desired resistivities in the static dissipative range (10/sup 6/-10/sup 9/ /spl Omega//sq) for conveying in production lines, storage, shipment and for cleanroom applications, having good and balanced mechanical properties can be prepared by combining a number of polymeric materials with glass fibers and less than 2 wt% carbon black.

Quantitative Measurement of Fiber Orientation and Fracture, Void and Weld-Lines in Short Fiber Reinforced Thermoplastic Composites

Mechanical properties of short fiber reinforced thermoplastics depend on fiber length and fiber orientation distribution produced during melt flow processing. The incorporation of short fibers into thermoplastic polymer melts increases their viscosity and the presence of fibers, increasing in length, results also in an increasing viscosity. Breakage of glass fibers during flow through a rheometer, also a serious problem in melt processing of short fiber reinforced thermoplastics, is demonstrated and analyzed. Short fibers greatly improve the mechanical properties of polymers, but may severely weaken molded parts at their weld-line. A quantitative determination of the glass fiber ori entation distribution in the weld-line region was done by analyzing photomicrographs of polished sections. Fiber orientation parallel to the weld-line, normal to the flow direction, causes a dramatic loss of tensile strength. Another factor playing an important role in fiber-filled thermoplastics is the associated void content. Unexpectedly high void volume fractions were estimated from density results. Reflected light micrographs of polished extrudates confirmed the existence of voids and their increasing content with increasing shear rate, fiber loading, fiber length and temperature.