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Polymer nanocomposites present remarkably enhanced mechanical and tribological properties with respect to their matrices even at a low loading of nanofillers. Here, cupric oxide (CuO) nanoparticles (nano-CuO) were in situ filled into ultra-high-molecularweight polyethylene (UHMWPE) to inhibit a possible agglomeration encountered in the preparation by mechanical mixing. The filled CuO nanoparticles were highly dispersed in UHMWPE with a reliable interface combination. The CuO nanoparticles in the matrix play a role for heterogeneous nucleation, resulting in an enhancement in degree of crystallinity of UHMWPE. The elastic modulus and the elongation at break of the nanocomposites also presented an improvement, indicating a good compatibility between the nano-CuO and the matrix. The average sliding friction coefficient of UHMWPE against 45 # steel was reduced by up to 34% after the in situ filling of CuO nanoparticles, and the wear mechanism was found to transform from adhesive to fatigue wear after the introduction of nano-CuO. It is concluded that the in situ filling can improve the dispersion of CuO nanoparticles in UHMWPE, and markedly promote the mechanical properties and tribological performance of UHMWPE.

In situ filling of nanomaterials into polymers facilitates the dispersion of the nanofillers and their interface combination with the matrices, and reduces the agglomeration encountered in the nanocomposites prepared by a mechanical mixing method. Polytetrafluoroethylene (PTFE) nanocomposites filled with SiO2 nanospheres (SNS) were fabricated by an in situ sol–gel method in this paper. The SNS in situ filled was highly dispersed in PTFE and showed an excellent combination with the matrix, and the fabricated SNS/PTFE nanocomposites were found a pronounced improvement in stiffness, hardness, glass transition temperature, and hydrophobicity in comparison with the pristine PTFE and the ones prepared by mechanical mixing with the same content. Furthermore, significantly reduced coefficients of friction and volume wear rates were observed on the SNS/PTFE nanocomposites prepared by in situ sol–gel. An operating temperature high up to 200°C and very low volume wear rate were accessible on the optimized SNS/PTFE nanocomposite by in situ filling. The methodology, in situ filling of nanofillers into matrices, might pave a way to prepare nanocomposites with excellent mechanical, thermal, and tribological properties.

In situ filling raises a possibility to restrain the agglomeration of nanomaterials in macromolecule matrices, which usually is encountered in the nanocomposites prepared by a mechanical mixing method. In this work, the nanocomposites of ultra‐high molecular weight polyethylene (UHMWPE) filled with nanosized hydroxyapatite (HAP) were fabricated by an in situ hydrothermal method. The fabricated HAP/UHMWPE nanocomposites exhibited a high dispersion degree of HAP nanoparticles (NPs) and a marked improvement in stiffness, strength, toughness, glass‐transition temperature, and hydrophilicity compared with the matrix and the reference composites prepared by mechanical mixing. Furthermore, pronouncedly decreased coefficients of friction and volume wear rates were observed on the in situ fabricated HAP/UHMWPE nanocomposites under dry friction, the lubrications of water, or cell culture fluid against a steel ring. The in situ fabricating strategy suggests a way to prepare highly dispersed nanocomposites, and the resulting HAP/UHMWPE nanocomposites might indicate a significant clinical prospect.

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