Search

Structural composites with high fracture toughness have wide applications in various fields. However, achieving high toughening efficiency at low fabricating cost is still challenging. Here, one-dimensional carbon nanofibers (CNFs) were incorporated into the ethylene-octene copolymer (POE)-toughened polypropylene (PP) blends. The fracture behaviors of the samples were systematically researched under different load conditions, such as impact load condition, three-point bending test and single-edge notched tensile (SENT) measurement, and then the toughening mechanisms were proposed. The results indicated that CNFs dramatically enhanced the fracture toughness of the PP/POE blends due to that CNFs prevented the initiation and propagation of crazes. Furthermore, through incorporating an additional annealing treatment, the fracture mechanism of composites changed from crazing fracture to shear yielding-crazing fracture, which endowed CNFs with more apparent toughening effect. For example, at POE and CNF contents of 25 wt% and 1 wt%, the annealed composite sample showed the impact strength of 69.4 kJ/m2 and elongation at break of 395.3%, which were increased by 208.4% and 92.0% compared with the unannealed binary blend, respectively. This work gives a novel insight to understand the toughening effect of one-dimensional nanofillers in the plastics/elastomer blends, and the methods may be used to toughen the other blend composites. • Super-toughened PP/POE/CNF composite samples were fabricated. • Fracture behaviors of samples under different load conditions were investigated. • The microscale damage mechanism of PP was tailored via different ways. • The dependence of CNF toughening effect on damage mechanism of PP was clarified. [ABSTRACT FROM AUTHOR]

Synchronously achieving high thermal conductivity, electrical insulation and excellent mechanical properties in one flexible thermal management material is still a great challenge. In this work, a stereocomplex (SC) crystallites cross-linking method was developed to prepare the graphene nanoplatelets (GNPs) filled cellulose nanofibers (CNFs) composite films. The SC crystallites formed between adjacent GNPs exhibit the physical crosslinking effect, which not only prevents the transmission of electron while maintaining the heat diffusion ability in plane but also intensifies the interaction between GNPs to form the integrated GNP network in the whole composite films, endowing the composite films with excellent strength and toughness. As a consequence, the composite films with nacre-like structure exhibit high in-plane thermal conductivity (9.36 W m−1K−1) and high electrical insulation (3.1 × 109 Ω m) with extremely high stability during the repeated bending and heating/cooling measurements. Furthermore, the composite film containing 5 wt% filler exhibits an excellent tensile strength of 111.8 ± 6.1 MPa and high toughness of 24.5 ± 2.0 MJ m−3, which are 51.1% and 75.0% higher than those of the pure CNFs film, respectively. This work provides a valuable strategy for the fabrication of the CNFs-based composite films with promising properties that have great potential as the next-generation thermal management materials. [Display omitted] • The graphene nanoplatelets filled cellulose nanofibers composite films were prepared. • The stereocomplex crystallites between adjacent graphene nanoplatelets were formed. • The films have excellent thermal conductivity, electrical insulation and toughness. [ABSTRACT FROM AUTHOR]

With the rapid development of electrical equipment and integrated circuits, packaging materials with high heat dissipation capability are in great demand. Reducing the interfacial thermal resistance is still a great challenge in polymeric composites. Herein, surface-induced polyamide acid (PAA) polymerization on boron nitride nanosheets (BNNSs) was firstly achieved, and then the BNNS@PAA was introduced into the polymerization system of polyimide (PI). The dependence of microstructures and performances of the composites on imidization degree of BNNS@PAA was systematically investigated. The results show that there is an appropriate imidization temperature (120 °C), at which the composite with only 10 wt% BNNS@PAA exhibits high thermal conductivity (2.11 W/m·K), excellent mechanical properties (with tensile strength of 97.2 MPa and elongation at break of 19.8%), and good dielectric properties (with a discharged energy density of 3.67 J/cm3 and a charge-discharge efficiency of 87.4% at the field of 300 MV/m). [Display omitted] [ABSTRACT FROM AUTHOR]

Based on the rapid development of electronic device performance, heat dissipation has become an urgent problem in packaging materials relating to polymeric composites. Meantime, the severe environmental pollution and energy crisis have also become great problems. Therefore, the development of renewable polymers with high thermal conductivity is a considerable way to reduce the dependence on petroleum-based polymers. Here, we report a convenient method for the preparation of renewable high thermal conductivity composites. Firstly, the stereocomplex crystallites (SCs) granules are prepared through the melt blending of poly(l -lactic acid) (PLLA) and poly(d -lactic acid) (PDLA) at a mass ratio of 1:1. Then, the PLLA/graphene nanoplatelets (PLLA/GNP) composite is coated on the surface of the SC granules by solution blending. Finally, the segregated and double-percolated structures with multiscale SCs form in the PLLA/GNP@SC composites through the compression molding method. The results show that the thermal conductivity of the PLLA/GNP@SC composites are much better than that of the PLLA/GNP composite under the same load of GNPs. The thermal conductivity of the PLLA/GNP@SC composite containing only 2 wt % GNPs reaches 0.96 W m−1K−1, which is 336.4% and 71.4% higher than those of the pure PLLA (0.22 W m−1K−1) and the PLLA/GNP (0.56 W m−1K−1) composite, respectively. The PLLA/GNP@SC composites also exhibit good mechanical properties at high temperatures due to the formed SC microcrystals at the interface between segregated SC granules and continuous PLLA/GNP phase. Moreover, the PLLA/GNP@SC composites also exhibit ultrahigh thermal resistance, flame retardance, and electrical conductivity. This work provides a new way for manufacturing the green multifunctional high thermal conductivity composite. [Display omitted] Poly(l -lactic acid) composites with segregated structure were fabricated. Multiscale stereocomplex crystallites were constructed in the composites. The interfacial adhesion between granules and continuous phase was enhanced. The composites showed high thermal conductivity and thermo-mechanical properties. [ABSTRACT FROM AUTHOR]

Shape memory polymers (SMPs) are a type of smart materials that can recover to the original shape from a set temporary shape under external stimulus, but SMPs are prone to be damaged during repeated deformation and recovery. Therefore, it is of great significance to improve the self-healing ability of SMPs. In this work, ethylene-vinyl acetate copolymer (EVA)/polycaprolactone (PCL)/polypyrrole (PPy) blend composites were prepared via simple melt blending. In this system, PPy nanoparticles, as photothermal fillers, selectively distributed in the PCL component, enable the EVA/PCL blend with a co-continuous structure to exhibit excellent photo-induced shape memory performance with a shape recovery ratio of 100%. Thanks to the excellent photothermal effect of PPy nanoparticles and the melting and recrystallization behaviors of linear EVA and PCL chains, the blend composites also exhibit outstanding photo-induced self-healing performance for different forms of damage, and the considerable healing efficiencies for the bent, scratched and cut samples reach 85.68%, 94.63% and 86.49%, respectively. Compared with the traditional thermal-induced self-healing shape memory composites, near infrared (NIR) irradiation can not only remotely manipulate the shape memory behavior of these composites, but also can accurately and selectively heal the damaged areas without distinct impact on the performance of intact areas. The above dual functions, along with the comprehensive performances and simple preparation process of these materials, enable the EVA/PCL/PPy blend composites to be the ideal candidates for many potential applications, including soft robots, smart packaging, biomedical devices, etc. [Display omitted] • Photo-induced shape memory composites with self-healing ability were prepared. • PPy nanoparticles were selectively distributed in switching domains. • The blend composites exhibited excellent photo-induced shape memory performance. • Photo-induced self-healing performance for different forms of damage was achieved. [ABSTRACT FROM AUTHOR]

Efficiently designing the interfacial interaction between nanoparticles and components of the blends to achieve the controllable microstructure evolution and resultant performances is still greatly challenging. This work reports the modification of the carbon nanofibers (CNFs) through different strategies. The CNFs before and after being modified were introduced into poly(L -lactic acid)/thermoplastic polyurethane (PLLA/TPU) blend. It is found that the pristine CNFs exhibit little toughening effect on the blend due to the poor interfacial interaction between pristine CNFs and the components of the blends. Hydrogen bonding interaction is formed between the hydroxylated CNFs and the components of the blends, which induces the morphological transition from the sea-island structure to the co-continuous structure, resulting in the improvement of the fracture toughness of the blend to a certain extent. While the epoxidized CNFs simultaneously exhibit the covalent bonding interactions with the two components of the blend and consequently, the epoxidized CNFs play a role in compatibilization, resulting in the blend with high fracture toughness. In addition, compared with the pristine CNFs, modified CNFs endow the blend with more outstanding light-induced mechanical-damage-healing behaviors and shape memory performances. This work not only reveals the influence mechanisms of the interfacial interaction between CNFs and the components of the blend on the microstructure and macroscopic properties of the PLLA/TPU blend, but also provides an effective way for the preparation of the PLLA-based blend composites with structural-functional integration [Display omitted] • The PLLA-based blend composites containing differently modified CNFs are prepared. • Hydroxylated CNFs induce morphological transition of blend via hydrogen bonding. • Epoxidized CNFs play a role in compatibilization for blend via covalent bonding. • The samples show high toughness, great self-healing and shape memory performances. [ABSTRACT FROM AUTHOR]

Enhancing the synergistic efficiency of different fillers in the composites is very significant from viewpoints of reducing fabricating cost and acquiring promising comprehensive properties. Inspired by the stem parasitic plant cuscuta austrails (dodder), the highly efficient conductive network in the composites was constructed through the 'rigid' submicron vapor grown carbon fibers (s-VGCFs) and 'reelable' carbon nanotubes (CNTs), in which the homogeneously dispersed s-VGCFs acted as the framework while CNTs bridged adjacent s-VGCFs and also partly entangled on s-VGCFs. Compared with the binary composites containing only s-VGCFs (or CNTs), the presence of very small quantity of CNTs (or s-VGCFs) led to the significant reduction of percolation thresholds from 3.082 wt% to 0.876 wt% (or from 0.258 wt% to 0.024 wt%), and the extremely high synergistic efficiency of 1.5 × 107 was achieved. Specifically, the impact of different compounding sequences on the hybrid network structure of fillers was also discussed. This work provides a new strategy to construct the hybrid network structure of fillers with extremely high synergistic effect and it might be applied in fabrication of the conductive composites with excellent mechanical properties. [ABSTRACT FROM AUTHOR]