Extruding compounds, commercially

Commercial impact modified PP were developed during the early 1970 s by melt blending about 5 to 25 wt% ethylene-propylene rubbers (EP or EPDM) with the polypropylene homopolymer via extruder compounding [Holzar, 1966]. Some LDPE or HOPE is often used to assist the dispersabUity of the EP rubber and enhance the impact/modulus balance of the product [D Orazio,... 

However, one of our customers (27) found it to be an effective additive to polyethylene terephthalate in order to increase the strength and reduce the striation when the polymer was extruded into polyester film. This certainly was an unexpected commercial success. I would regard this commercial success as pure luck on our part. After all. Dr. Walsh s group designed the compound to be a flame retardant. 

The scale-up starts with optimization of the compounding conditions in a laboratory-scale TSE, having the screw diameter D < 35 mm. Owing to the difference in thickness of the molten polymer between this and commercial size extruders (D > 100 mm), it is advisable that the scale-up involves an intermediate stage, a mid-size TSE with D > 50 mm. The experience also showed that it is more difficult to scale up from 30 to 50 mm than from 50 to 200 mm TSE. Thus, the intermediary step may save a large amount of time, material, and the plant production capability. 

Although commercial twin-screw extruders can be as large as 300 mm size, capable of compounding up to 40 ton/hr, the acmal type and size of the equipment used depends on the type of the polymer blend and the production volume. Normally, for engineering polymer blends, twin-screw extmders of about D = 90 mm size (L/D = 30 to 40) and capable of compounding at 700 to 1000 kg/hr, are used. For blending PVC or elastomer blends other types of compounding equipment are used, e.g. Farrell continuous mixer (FCM), Buss co-kneader, or a batch mixer, such as Banbury. 

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