Elastomers show improved properties when reinforced with nanoclay at low filler loadings, but dispersion of the clay is difficult in non‐polar polymers, such as ethylene propylene diene monomer (EPDM). In this work several compatibilization approaches were studied, including the addition of EPDM modified with maleic anhydride (EPDM‐g‐MA) and the use of organoclay modified with maleic anhydride‐grafted liquid vinyl polybutadiene (LVPB‐g‐MA). The use of LVPB‐g‐MA‐modified organoclay increased the degree of dispersion as measured by X‐ray diffraction, giving increased thermal stability and modulus, and decreased swelling. Flame resistance was poorer for the EPDM/LVPB‐g‐MA‐modified organoclay system compared to the unmodified EPDM/organoclay compound. The resistivity of the nanoclay‐filled composites was lower than the reference EPDM compound, but dielectric properties for the LVPB‐g‐MA modified organoclay were similar to the reference.magnified image
Thermoplastic polyurethane (TPU) and silicon tooling with microscale features on its surface was employed to investigate the impact of three factors on the quality of injection molded microscale features: (1) optimized process parameters, (2) use of a more flexible thermoplastic material, and (3) used as an antistiction coating. The molded parts and tooling surface were characterized by atomic force, confocal, and scanning electron microscopy. Although both improved filling of the tooling trenches, higher mold temperatures significantly enhanced replication, but faster injection velocities contributed moderately to replication quality. With medium aspect ratio (2.3:1) trenches, the antistiction coating doubled depth ratios, enhanced the edge definition and flatness of the features, and significantly reduced tearing of the features during ejection. The flexibility of the TPU permitted easier part ejection and left less polymer residue on the tooling surface in comparison to polycarbonate and other thermoplastic polymers. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers
While the effect of vacuum venting has been reported for injection molding of micro and nanoscale features, the limited research has produced conflicting results. To clarify the positive effect of vacuum venting on replication of microscale features, this work focused on the interactions between vacuum venting and (1) feature size, (2) material type in terms of melt viscosity and wettability, and (3) injection velocity and mold temperature. A metal-polymer hybrid tooling with a range of positive microscale features was employed to mold polystyrene and polymethylmethacrylate parts. Overall, vacuum venting always effective in feature definition (sharpness of edges) enhancement, but provided increases in depth ratio that depended on material (melt viscosity and wettability) and processing conditions (i. e., injection velocity, and mold temperature).
Although high aspect ratio micro and nanoscale polymer features have been replicated in a range of polymers using injection molding, researchers have also used tooling inserts with a range of sizes, aspect ratios, and tooling materials. In this work, microscale features with molded in polymethylmethacrylates using three types of tooling with similar features. The tooling materials included silicon wafers with an antistiction coating, gold-coated nickel inserts, and a metal-polymer hybrid tooling. Tooling was evaluated based on the ease of melt filling and part ejection; the replication quality as characterized using optical profilometry, confocal microscopy, and scanning electron microscopy; and the damage to the tooling after repeated use. With lower aspect ratio features, the tooling type did not significantly affect replication, but for higher aspect ratio features the hybrid tooling provided far better replication than the silicon tooling. This difference was attributed to retardation of heat transfer in the features of the hybrid tooling. All three tooling materials exhibited polymer-free surfaces after injection molding.
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