Fuente: Journal of applied polymer Lugar: RESEARCH ARTICLE This study used selective microwave sintering technology, through which discrete short fibers in the thermoplastic matrix were sintered into a continuous fiber network. By introducing UHMWPE short fibers containing graphite and Fe3O4 into the PA11 matrix, a continuous fiber network was formed in situ after microwave treatment, which significantly improved the mechanical properties of the composite material and provided a new path for the preparation of high-performance thermoplastic composite materials.

ABSTRACT
High-performance thermoplastic polymer-matrix composites (PMCs) were critical materials in high-end manufacturing. However, short fiber-reinforced composites exhibited limited mechanical properties, while the processing of continuous fiber-reinforced composites was rather complex. Herein, we proposed a selective microwave sintering strategy that enabled the in situ formation of a continuous UHMWPE fibers network modified with graphite and Fe3O4 within polyamide 11 (PA11) composites. During microwave sintering, the modified short fibers absorbed microwaves and generated heat, resulting in interfacial sintering and bonding of the fibers to form a continuous network within the PA11 matrix. The bonding point density of fibers in the composite material reached 330 units/cm3. A notable notched impact strength of 45.8 kJ/m2 was achieved in the UHMWPE fiber-reinforced composite containing only 3 wt% graphite and 3 wt% Fe3O4 after microwave treatment, representing a 154% enhancement compared to the PA11 matrix. Furthermore, when compared to untreated short-fiber composites: the tensile strength of microwave-treated PA11/UHMWPE@3Fe3O43G composite was 51 MPa, a 79% increase over the untreated short fiber composite (28.5 MPa), while the flexural strength showed a 22.7% improvement, reaching 93.5 MPa. This was a new paradigm for designing high-performance thermoplastic composites with promising potential for lightweight structural applications.