Polymer‐metal hybrid (PMH) structures, also known as metal‐polymer hybrid (MPH) structures, have received considerable attention from industry and academia due to the societal need for developing strong, lightweight, and durable structures for several applications in strategic areas, such as transportation, household appliances, energy, and biomedical devices. Injection overmolding is an advantageous technique for manufacturing PMH structures as it combines automation, a fast process, cost efficiency, and dimensional accuracy. This review presents a comprehensive discussion of recent advances reported in the literature concerning PMH structures fabricated by direct‐adhesion injection overmolding. Following a general introduction, the fundamentals of the injection overmolding technique are presented. Next, the potential of some metal surface preparation methods to ensure good adhesion, and thus outstanding mechanical performance in injection overmolded PMH structures is discussed. Correlations are then made between metal surface features, processing parameters, and the mechanical strength of injection overmolded polymer‐metal joints. Some applications of injection overmolded PMH structures are explored, and, lastly, the main conclusions and prospects on the use of injection overmolding are presented.

Polypropylene (PP) composites with cellulose nanofibril (CNF), lignocellulose nanofibril (LCNF) or bleached kraft wood pulp (BWKP) cellulose microfibril compatibilized by maleic anhydride grafted polypropylene were produced by different approaches. Samples containing 10-30 wt% filler were prepared by mixing cellulose aqueous suspensions and PP through solid-state shear pulverization. The flakes obtained were compounded by twin-screw melt extrusion (MSE) followed by injection molding (IM) into standard specimens. Reference samples with 30 wt% CNF or LCNF were prepared through a standard procedure, which involved freeze-drying of nanofibrils aqueous suspensions before MSE and IM, whereas a sample with 30 wt% BWKP was prepared directly by MSE and IM. Injection-molded specimens were characterized by scanning electron microscopy, differential scanning calorimetry, thermogravimetry, and tensile and notched impact tests. The thermal behavior of the PP matrix in the composites was not significantly affected by the filler type and content and processing route as well. CNF and LCNF reinforced PP composites showed inferior mechanical properties, due to the formation of nanofibrils agglomerates in the PP matrix, regardless of the processing route adopted. Highly filled (30 wt%) BWKP composites presented superior mechanical properties with significant increase in the modulus, tensile strength, and impact strength due to the formation of well-dispersed microfibrils bundles in the PP matrix. A comparative analysis showed that the composites developed in this study present similar or even superior mechanical performance for given filler content to other natural fiber reinforced PP composites reported in the literature.

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