Processing, thermoplastics barrel temperatures

The injection molding process for glass filament reinforced pellets is identical to that for un-reinforced or filled thermoplastics. The main differences will be in the treatment of the screw to limit its wear, and a 10-30°C higher barrel temperature compared to un-reinforced thermoplastic compounds because of higher melt viscosity. 

Europrenes have thermoplastic polymer melt processing properties and characteristics of TPEs. At melt processing temperatures, they behave as thermoplastics, and below the PS Tg of 203 to 212°F (95 to 100°C) the copolymers act as cross-linked elastomers, as noted earlier. Injection-molding barrel temperature settings are from 284 to 374°F (140 to 190°C). Extrusion temperature at the head of the extruder is maintained between 212 and 356°F(100and 180°C). 

Injection moulding has been briefly described in Chapter 8. The use of filled materials does not significantly effect the moulding process although higher barrel temperatures and greater injection pressures may be required. Table 7 compares the properties of some reinforced and unreinforced thermoplastics and illustrates how the presence of reinforcing fibre improves most of the mechanical and physical characteristics of polymers. 

Paul Troester started manufacturing single-screw extruders (SSE) in 1892, but only in 1935 the first SSE for thermoplastics was introduced. Four years later, Paul Leistritz built electrically heated, air cooled SSE, having L/D = 10, automatic temperature control, variable screw speed, and nitrided barrel. The machine is considered prototype of the modem extmders. The SSE offered continuous processing capability, but it was notoriously poor as a mixer. Furthermore, under the standard processing conditions, a significant non uniformity in the shear history had resulted in large temperature differences of the melt, AT = 60°C. To alleviate the... 

Tianjin P(3HB-4HB) and Tianan PHBV can be molded via injection molding. The temperature profile in the injection molding barrel is different than conventional thermoplastics with the hottest temperature at the first zone and the coolest temperature at the nozzle. PHAs can be exposed to a temperature range between 160°C and 190°C. PHAs viscosity is too large for injection molding at temperatures below 160°C. PHAs can thermally decompose at temperatures above 190 C. PHAs also require a heated mold to enhance crystallinity. The injection molding parameters for P(3HB-4HB) are displayed in Table 4.4. Injection molding process conditions are similar for PHBV. 

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