Processing Modified PPE

Drying. Although modified PPE resin has the lowest moisture absorption of any engineering plastic and may be molded as received in many applications, it is a good practice, particularly where surface appearance is critical, to dry modified PPE resin before molding. Modified PPE resins should not be dried longer than 8 h. Excessive drying may result in loss of physical properties, color shift, loss of processability, or a combination of the three. 

Melt temperature. Since modified PPE resins cover a wide range of compositions and melt viscosities, the manufacturers recommended melt temperatures should be consulted. The majority of thermoplastic molding materials are sensitive to prolonged exposure to heat. Long residence times and excessive melt temperatures should be avoided to minimize material degradation. It is suggested that melt temperatures be measured using handheld pyrometers. These measures should be taken on the thermoplastic melts after the machine is on cycle. 

Mold temperature. The usual range for processing unreinforced modified PPE grades is from 150 to 200°F (66 to 93°C). Operating molds in this temperature range can also be used to improve flow, knit-line strength, and surface finish. 

Shot size. The shot size should at least in part dictate the size of machine used. It is generally suggested that the optimum shot be 40 to 

60% of the barrel capacity of the machine. However, shots that are 20 to 75% of machine capacity have been successfully molded when temperatures were precisely maintained and all processing conditions were very closely controlled. 

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