Filled grades

When designing mouldings in reinforced and filled PP, the general guidelines for design of the product and the mould are the same as those for unreinforced PP. However, filled and reinforced grades require some extra consideration  

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Polyethylene is the lowest-cost plastic commercially available. Mechanical properties are generally poor, particularly above 50°C (120°F), ana pipe must be hilly supported. Carbon-filled grades are resistant to sunlight and weathering. 

Whereas Tefzel is said to be an internally stablised copolymer of TFE and ethylene, other copolymers that are compounds of similar copolymers with stabilisers of antioxidants are now also available (Hostaflon ET by Hoechst and Aflon by Asahi Glass Co.). Glass-fibre-filled grades are also available. 

Glass-fibre-filled grades of these toughened polymers are also available but these do not show the same improvement in toughness over normal glass-fibre-filled nylons. 

The manufacturers stress ease of processing as a particular feature of the material. Recommended melt temperatures are in the range 320-340°C and mould temperatures are 135-165°C. Mould shrinkage of glass-filled grades is usually of the order of 0.2-0.4% in the flow direction and up to twice this value in the transverse direction. The materials are notable for their ability to withstand vapour phase and infrared soldering processes. 

Applications of the elastomeric polyamides include keyboard pads, sports footwear, loudspeaker gaskets and, in the case of filled grades, watch straps. 

Units Test method Unfilled grades Glass-filled grades ... 

A low moulding shrinkage (0.005-0.007 cm/cm) in unfilled grades down to about 0.002 cm/cm in 30% glass-fibre-filled grades. 

To reduce strains in mouldings, fairly high mould temperatures are recommended (65-95°C in unfilled and up to 120°C in glass-filled grades). 

The unfilled grades are of little importance, with the following filled grades being of commercial interest ... 

The bulk factor (i.e. ratio of the density of the moulding to the apparent powder density) of powder is usually about 2-3 but the high-shock grades may have bulk factors of 10-14 when loo.se, and still as high as 4-6 when packed in the mould. Powder grades are quite easy to pellet, but this is difficult with the fabric-filled grades. 

As with poly(ethylene terephthalate) there is particular interest in glass-fibre-filled grades. As seen from Table 25.8, the glass has a profound effect on such properties as flexural modulus and impact strength whilst creep resistance is also markedly improved. 

High softening temperatures (glass-fibre-filled grades are better than polycarbonates and modified PPOs). 

Carbon-fibre-filled grades exhibit interesting tribological properties and useful antistatic behaviour. 

As is common for crystalline thermoplastics the deflection temperature of unfilled grades is similar to Tg (quoted as being in the range 45-70°C) while for glass-filled grades it is much closer to the T of 225°C. 

Poor abrasion resistance of unfilled grades, although special filled grades are available with very good abrasion resistance. 

A number of these materials offer service temperatures in excess of 200°C and fibre-filled grades can be used above 300 C. 

Nylon (Polyamide) PA is a crystalline plastic and the first and largest consumption of the engineering thermoplastic. This family of TPs are tough, slippery, with good electrical properties, but hygroscopic and with dimensional stability lower than most other engineering types. Also offered in reinforced and filled grades as a moderately priced metal replacement. 

The mineral, talc and, especially, fibreglass-filled grades are more rigid and have better behaviour and lower creep when the temperature rises. 

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