RGO-Coated Polyurethane Foam/Segmented Polyurethane Composites as Solid-Solid Phase Change Thermal Interface Material

Thermal Conductivity and Phase-Change Properties of Boron Nitride-Lead Oxide Nanoparticle-Doped Polymer Nanocomposites

Thermally conductive phase-change materials (PCMs) were produced using the crosslinked Poly (Styrene-block-Ethylene Glycol Di Methyl Methacrylate) (PS-PEG DM) copolymer by employing boron nitride (BN)/lead oxide (PbO) nanoparticles. Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA) methods were used to research the phase transition temperatures, the phase-change enthalpies (melting enthalpy (ΔH_m), and crystallization enthalpies (ΔH_c)). The thermal conductivities (λ) of the PS-PEG/BN/PbO PCM nanocomposites were investigated. The λ value of PS-PEG/BN/PbO PCM nanocomposite containing BN 13 wt%, PbO 60.90 wt%, and PS-PEG 26.10 wt% was determined to be 18.874 W/(mK). The crystallization fraction (F_c) values of PS-PEG (1000), PS-PEG (1500), and PS-PEG (10,000) copolymers were 0.032, 0.034, and 0.063, respectively. XRD results of the PCM nanocomposites showed that the sharp diffraction peaks at 17.00 and 25.28 °C of the PS-PEG copolymer belonged to the PEG part. Since the PS-PEG/PbO and the PS-PEG/PbO/BN nanocomposites show remarkable thermal conductivity performance, they can be used as conductive polymer nanocomposites for effective heat dissipation in heat exchangers, power electronics, electric motors, generators, communication, and lighting equipment. At the same time, according to our results, PCM nanocomposites can be considered as heat storage materials in energy storage systems.

Effect of GO on the Structure and Properties of PEG/Biochar Phase Change Composites

In recent years, phase change materials (PCMs) have been widely used in waste heat utilization, buildings, and solar and wind energy, but with a huge limitation from the low thermal conductivity, photothermal conversion efficiency, and low latent heat. Organic PCMs are eyecatching because of its high latent heat storage capability and reliability, but they still suffer from a lack of photothermal conversion and sharp stability. Here, we prepared sharp-stable PCMs by establishing a carbon material frame system consisting of graphene oxide (GO) and biochar. In particular, surfactants (CTAB, KH-560 and KH-570) were employed to improve the dispersity of GO in PEG. The differential scanning calorimetry results shows that the latent heat of PEG modified by CTAB grafted GO (PGO-CTAB) was the highest (191.36 J/g) and increased by 18.31% compared to that of pure PEG (161.74 J/g). After encapsulation of PGO-CTAB in biochar, the obtained composite PCM with the amount of biochar and PGO-CTAB in weight ratio 4:6 (PGO-CTAB/CS6(6)) possesses relatively high latent heat 106.51 J/g with good leak resistance and thermal stability, and with obviously enhanced thermal conductivity (0.337 W/(m·K)) and photothermal conversion efficiency (77.43%), which were higher than that of PEG6000 (0.325 W/(m·K), 44.63%). The enhancement mechanism of heat transfer and photothermal conversion on the composite PCM is discussed.

Performance of Thermal Interface Materials

The thermal interface materials (TIMs) used for improving thermal contacts are considered in terms of the performance, performance consideration criteria, performance evaluation methods, and material development approaches. The performance is described mainly by the thermal contact conductance, which refers to the conductance across the thermal contact surfaces that sandwiches the TIM. This conductance depends on the conformability, thermal conductivity, and small-thickness feasibility. However, the vast majority of published work does not consider this conductance, but only the thermal conductivity within the TIM. The highest TIM performance is exhibited by the thermal pastes and low-melting alloys.

Design of Intrinsically Flame-Retardant Vanillin-Based Epoxy Resin for Thermal-Conductive Epoxy/Graphene Aerogel Composites

Vanillin, as a lignin-derived mono-aromatic compound, has attracted increasing attention due to its special role as an intermediate for the synthesis of different biobased polymers. Herein, intrinsically flame-retardant and thermal-conductive vanillin-based epoxy/graphene aerogel (GA) composites were designed. First, a bifunctional phenol intermediate (DN-bp) was synthesized by coupling vanillin with 4, 4'-diaminodiphenylmethane and DOPO, and the epoxy monomer (MEP) was obtained by the epoxidation reaction with DN-bp and epichlorohydrin. Then, various amounts of MEP and diglycidyl ether of bisphenol A (DER) were mixed and cured. Interestingly, the flexural strength and modulus were greatly enhanced from 72.8 MPa and 1.3 GPa to 90.3 MPa and 2.8 GPa, respectively, at 30 wt % MEP, due to the rigidity of MEP and strong intermolecular N-H hydrogen bonding interactions. Meanwhile, the cured epoxy achieved a UL-94 V0 rating with a low P content of 1.06%. The flame-retardant vanillin-based epoxy was then impregnated into the thermal conductive 3D GA networks. The obtained epoxy/graphene composite showed excellent flame retardancy and thermal conductivity [λ = 0.592 W/(m·K)] with only 0.5 wt % graphene in the system. Based on these results, we believe that this work would represent a novel solution for the preparation of high-performance biobased flame-retardant multipurpose epoxies.

Thermal, Mechanical and Electrical Properties of Carbon Fiber Fabric and Graphene Reinforced Segmented Polyurethane Composites

Thermal conductive materials with reliable and high performances such as thermal interface materials are crucial for rapid heat transferring in thermal management. In this work, carbon fiber fabric and graphene reinforced segmented polyurethane composites (CFF-G/SPU) were proposed and prepared to obtain superior thermal, mechanical and electrical properties using the hot-pressing method. The composites exhibit excellent tensile strength and can withstand a tensile force of at least 350 N without breaking. The results show that, comparing with the SPU material, the thermal conductivity is increased by 28% for the CFF-G/SPU composite, while the in-plane electrical conductivity is increased by 8 orders of magnitude to 175 S·m^-1. The application of CFF-G/SPU composite as a winding thermal interface material with electric-driven self-heating effect presents good performances of fluidity and interface wettability. The composite has great advantages in phase transition and filling the interfacial gap in the short time of few seconds under the condition of electrical field, with the interface temperature difference between two layers significantly reduced.

Flexible Polyurethane Foams from Epoxidized Vegetable Oils and a Bio-Based Diisocyanate

Bio-polyols from epoxidized soybean and linseed oils and caprylic acid or 3-phenyl butyric acid were prepared using an environmentally friendly, solvent-free method evaluating the presence of triethylamine as catalyst. Side reactions, leading to a cross-linking structure with high density, were reduced, introducing the catalyst and properly tuning the reaction conditions. A medium functionality value of around 3 along with a hydroxyl number up to around 90 mg KOH/g, narrow polydispersity index, and relatively low molecular mass up to 2400 g/mol were the experimental targets. From selected bio-polyols and an aliphatic partially bio-based isocyanate, a series of water blown polyurethane (PU) foams was produced, estimating the effect of the chemical nature of substituents in the polyol backbone on the PU properties. The apparent density of the foams was in the range of 79–113 kg/m³, with higher values for foams from the aromatic acid. Flexible polyurethane foams with open cell structure from bio-based polyols were obtained, with higher cavity size and lower pore sizes for foams from caprylic acid. The bio-based flexible PU foams showed comparable Young’s moduli (14–18 kPa) and compression deflection values (4.6–5.5 kPa) and exhibited an almost complete recovery of their initial size.

Thermal Properties of Surface-Modified and Cross-Linked Boron Nitride/Polyethylene Glycol Composite as Phase Change Material

A thermally conductive phase change material (PCM) was fabricated using polyethylene glycol (PEG) and boron nitride (BN). However, the interfacial adhesion between the BN and the PEG was poor, hindering efficient heat conduction. Grafting polyvinyl alcohol (PVA) onto the surface of BN and cross-linking due to hydrogen bonding between the hydroxyl groups in PVA and oxygen atoms in PEG improved the wettability of fillers. By employing this strategy, we achieved a thermal conductivity value of 0.89 W/mK, a 286% improvement compared to the thermal conductivity of the pristine PEG (0.23 W/mK). Although the latent heat of composites decreased due to the mobility of the polymer chain, the value was still reasonable for PCM applications.