Achieving a Collapsible, Strong, and Highly Thermally Conductive Film Based on Oriented Functionalized Boron Nitride Nanosheets and Cellulose Nanofiber

Boron nitride nanosheet (BNNS) films receive wide attention in both academia and industry because of their high thermal conductivity (TC) and good electrical insulation capability. However, the brittleness and low strength of the BNNS film largely limit its application. Herein, functionalized BNNSs (f-BNNSs) with a well-maintained in-plane crystalline structure were first prepared utilizing urea in the aqueous solution via ball-milling for the purpose of improving their stability in water and enhancing the interaction with the polymer matrix. Then, a biodegradable and highly thermally conductive film with an orderly oriented structure based on cellulose nanofibers (CNFs) and f-BNNSs was prepared just by simple vacuum-assisted filtration. The modification of the BNNS and the introduction of the CNF result in a better orientation of the f-BNNS, sufficient connection between f-BNNS themselves, and strong interaction between f-BNNS and CNF, which not only make the prepared composite film strong and tough but also possess higher in-plane TC. An increase of 70% in-plane TC, 63.2% tensile strength, and 77.8% elongation could be achieved for CNF/f-BNNS films, compared with that for CNF/BNNS films at the filler content of 70%. Although at such a high f-BNNS content, this composite film can be bended and folded. It is even more interesting to find that the in-plane TC could be greatly enhanced with the decrease of the thickness of the film, and a value of 30.25 W/m K can be achieved at the thickness of ∼30 μm for the film containing 70 wt % f-BNNS. We believe that this highly thermally conductive film with good strength and toughness could have potential applications in next-generation highly powerful and collapsible electronic devices

Completely Green Approach for the Preparation of Strong and Highly Conductive Graphene Composite Film by Using Nanocellulose as Dispersing Agent and Mechanical Compression

Graphene films receive tremendous attention due to their ultrahigh electrical and thermal conductivities, which show great application prospects in modern electronic devices. However, the brittleness and low strength of graphene films largely limit their use in advanced applications. And the preparation processes of graphene films reported so far are also not completely green. In this work, a novel strong and green graphene composite film with outstanding electromagnetic interference shielding effectiveness (EMI SE), electrical and thermal conductivities was successfully fabricated by using nanofibrillated cellulose (NFC) as dispersing agent and mechanical compression. In this way, graphene nanosheets (GNs) were not only efficiently dispersed in the aqueous solution but also linked together by NFC to enhance mechanical strength of the prepared films. Simultaneously, mechanical compression could powerfully induce strong alignment and increase the contact area of the GNs. As a result, the optimum electrical and thermal conductivities of the obtained films reached up to 988.2 S cm^–1 and 240.5 W m^–1 K^–1, respectively, along with a high tensile strength of 61 MPa and a superior EMI SE of 43 dB with only ≈13 μm in thickness. Even more, the resultant films revealed excellent flame resistance. And the NFC can be removed by burning the films, resulting in complete graphene films with much higher electrical and thermal conductivities. The manufacturing route in our study is facile, cost-effective and completely green for the preparation of strong and highly conductive graphene-based thin films

Design and Preparation of a Unique Segregated Double Network with Excellent Thermal Conductive Property

It is still a challenge to fabricate polymer-based composites with excellent thermal conductive property because of the well-known difficulties such as insufficient conductive pathways and inefficient filler–filler contact. To address this issue, a synergistic segregated double network by using two fillers with different dimensions has been designed and prepared by taking graphene nanoplates (GNPs) and multiwalled carbon nanotubes (MWCNT) in polystyrene for example. In this structure, GNPs form the segregated network to largely increase the filler–filler contact areas while MWCNT are embedded within the network to improve the network-density. The segregated network and the randomly dispersed hybrid network by using GNPs and MWCNT together were also prepared for comparison. It was found that the thermal conductivity of segregated double network can achieve almost 1.8-fold as high as that of the randomly dispersed hybrid network, and 2.2-fold as that of the segregated network. Meanwhile, much higher synergistic efficiency (<i>f</i>) of 2 can be obtained, even greater than that of other synergistic systems reported previously. The excellent thermal conductive property and higher <i>f</i> are ascribed to the unique effect of segregated double network: (1) extensive GNPs–GNPs contact areas via overlapped interconnections within segregated GNPs network; (2) efficient synergistic effect between MWCNT network and GNPs network based on bridge effect as well as increasing the network-density