Guohua Li

Traditional approaches to constructing thermally conductive networks typically necessitate costly equipment and intricate processes, rendering them unsuitable for mass production and commercialization. Here, we propose a facile strategy to construct highly oriented boron nitride/polyacrylate pressure-sensitive adhesive frameworks by a calendering process. A UV light-based bulk polymerization method is adopted to prepare the pressure-sensitive adhesives (PSAs), which makes the preparation process solvent-free and volatile organic compound (VOC)-free, and environmentally friendly compared to emulsion and solvent-based pressure-sensitive adhesives. This simple, economical and scalable method provides new ideas and ways for the preparation of advanced thermal conductive networks. The highly oriented and flexible m-BNNSs/polyacrylate pressure-sensitive adhesive composites (m-BNNSs/PSAs-Ori) exhibited a significantly high thermal conductivity (TC) of 0.9552 W/(m·K) at 25 wt% filler content. Significantly, m-BNNSs/PSAs-Ori composites showed a better thermal response than the single-layer thermally conductive pressure-sensitive adhesive. Moreover, the composites also possess excellent electrical insulation and mechanical properties. This exploration not only provides a reasonable design scheme for thermal interface materials, but also promotes the practical application of polyacrylate pressure-sensitive adhesive composites in thermal management.

Three different acrylate monomers containing butyl acrylate, 2‐hydroxyethyl acrylate, and acrylic acid were designed to synthesize polyacrylate pressure‐sensitive adhesives (PSAs) by bulk polymerization process initiated via radical photo‐initiators under UV irradiation and UV‐thermal dual curing. Thermal crosslinker, KL‐1202, with trifunctional isocyanate groups was introduced into the prepolymer to form an intermolecular crosslinking network structure. An emphasis was placed on the effect of the KL‐1202 content on the microstructure and adhesive properties of PSAs. The viscosity and composition of prepolymer synthesized by UV initiation were tested by a rotational viscometer and Fourier transform infrared spectroscopy, respectively. The degree of crosslinking of the final PSA was evaluated by the gel content value obtained via Soxhlet extraction, while the molecular weights of the soluble parts of PSA polymers were measured by gel permeation chromatography. Dynamic mechanical analysis was used to characterize the viscoelastic performance of PSAs. Moreover, the adhesive properties of PSAs were determined through a series of tests including loop tack force, peel force, and shear resistance. It was found that the C=C double bond and the isocyanate group disappeared after UV radiation and thermal curing process. Dual‐cure acrylate PSAs compensate for limitations in UV‐induced cure of thick coatings. The T_g value, storage modulus (G′), and shear resistance of PSAs were improved while the loop tack force and peel force of PSAs decreased as the KL‐1202 content increased.

Polyacrylic pressure-sensitive adhesives (PSAs) based on butyl acrylate (BA), 2-hydroxyethyl acrylate (HEA), and acrylic acid (AA) were prepared by a bulk polymerization process triggered by a radical photoinitiator under UV irradiation and UV-crosslinking. 1,6-Hexanediol diacrylate (HDDA) with difunctional groups was introduced into the PSAs to modify semi-interpenetrating network structures. The effect of HDDA content on the pressure-sensitive performance was comprehensively tested. The viscosity of the prepolymer was measured by a rotational viscometer. Prepolymers obtained by a photoinduced process and UV crosslinking process were confirmed via Fourier transform infrared spectroscopy (FTIR). All double bonds participated in the copolymerization without any remaining monomers, which reflected the concept of green environmental protection. Gel content in the crosslinked portion was examined by Soxhlet extraction, whilst the soluble molecular weight of PSAs was characterized by gel permeation chromatography (GPC). The viscoelastic properties of polymer films were determined by dynamic mechanical analysis (DMA). The T_g value and storage modulus (G′) of the PSAs were enhanced with the addition of HDDA. Moreover, three fundamental adhesive properties, i.e. loop tack force, peel force and shear strength of PSAs, were measured. The results showed that UV crosslinking technology achieved a good balance of the three forces with excellent pressure-sensitive properties.

Polyethylene/exfoliated graphite platelet (PE/EGP) composites with enhanced thermal conductivities were developed. EGP was obtained by zirconium dioxide-based ball-milling technique using urea as a modifying agent. The PE/EGP composites were prepared using a HAAKE rotational rheometer followed by a hot press operation. The structure and morphology of the EGP were characterized by X-ray diffraction, Raman spectroscopy, and Scanning electron microscopy. The thermal conductivities, mechanical properties, and crystallinities of PE and PE/EGP composites were systematically investigated. The thermal conductivities of PE/EGP composites increased with increasing amount of EGP. When the amount of EGP added was 10 wt%, the thermal conductivity of the composite reached 0.87 W/(m∙K), which was twice higher than that of PE. The tensile strength of the composite was more than doubled compared with that of PE matrix, while the elongation at break decreased. EGP could be uniformly dispersed in PE matrix as confirmed by SEM observation. DSC analysis showed that the addition of EGP to PE matrix increased the crystallization peak temperature and the crystallinity of the composite.