In the sandwich injection molding process (co-injection),two different polymer melts are sequentially injected into a mold to form a part with a skin/core structure.Sandwich molding can be used for recycling,improving barrier and electrical properties,or producing parts with tailored mechanical properties.In this study the evaluation of flexural modulus and impact strength of co-injected plaques have been investigated.Virgin and short glass fiber reinforced (10 and 40%) polypropylene were used in six different combinations of sandwiched layers.The skin and core thicknesses were measured by optical microscopy and used to calculate the theoretical flexural modulus,which was compared to the experimentally measured modulus.Fiber orientation states were also observed by scanning electronic microscopy (SEM) at some specific locations and their effect on mechanical properties discussed.The experimental results indicate that an important improvement in transverse modulus,near the gate,is obtained when the virgin polypropylene (PP) is used as a skin and 40% short glass fiber polypropylene (PP40) as core.When both skin and core are made of PP40,the flexural moduli are slightly higher than conventionally injected PP40.
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