Mixing of Fillers with Plastics

Deriving the maximum benefit from the incorporation of fillers into polymers depends upon achieving a uniform distribution of well wet-out individual particles and/or fibers. 

For most applications of filler incorporation into plastics, most processors now use extmders, either single-screw or twin-screw, to achieve the desired compounds. The primary task to be accomplished in extrusion compounding generally include the following steps  

There may be significant differences between single- and twin-screw extruders in how they achieve the above functions. 

Frequently, either the polymer or the filler(s) may contain too much moisture such that predrying is required, otherwise unremoved moisture may 

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A comparatively new group of materials— thermoplastic elastomers or thermoplastic rubbers —combines the ease of processing of thermoplastics with qualities of traditional vulcanized rubbers, especially elasticity. Because of convenience in processing there is much interest too in blends of plastics with elastomers, which may be modified by the inclusion of filler or glass fibre. As an example, a rubber-like material that can be processed as a thermoplastic can be made by blending and melt-mixing an ethylene-propylene rubber with polypropylene. The use of such blends may be helpful when there are needs to reclaim and re-process material, and in order to obtain products with qualities intermediate between those of the main components of the blends. 

No noticeable segregation of the mix was found to be produced by the fillers. In fact, the cohesiveness of the mix was greatly improved with vent dust. During the mixing of the many batches none of the plastic fillers was observed to flow to the top. An analysis of the concrete samples showed that the mixing procedure had evenly distributed the plastic chips. 

From the same figure it is possible to analyze the size effect of HDPEflake and HDPEfine. For mix No. 1 with the two plastic levels, it is observed that the fine graded filler caused a bigger reduction in the strength than the strength decrease produced by the FIDPEflake. 

Figure 12.11. Tensile strength of post-consumer plastic containers reprocessed with different fillers. [Adapted, by permission, from La Mantia F P. Recycling of PVC Mixed Plastic Waste, ChemTec Publishing, Toronto, 1996.]...

The same approach can be applied to plastics, filled with ATH (or any other filler). A compounded mix of 60% ATH and 40% HDPE was prepared and a sample of the filled plastic was ashed. Theoretically, the amount of ash should be 39.23% by weight. This figure can be obtained by taking 65.38% ash content in ATH and taking 60% of it (because the ATH was diluted by 40% of HDPE). If to introduce the correction that there were only 2.86 water molecules per ATH (see above), the amount of ash should be 40.0%. 

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