Tensile properties of fumed silica filled polydimethylsiloxane networks

Tensile properties of fumed silica filled hydroxylated polydimethylsiloxane (PDMS) networks were investigated in the current work. Similar to unfilled bimodal networks, unimodal networks filled with concentrated fumed silica exhibit non-Gaussian effect and improved ultimate tensile properties. The concept of “hierarchical network” was proposed to depict the networks exhibiting non-Gaussian effect at sufficiently high strains. It was found that the reinforcing effect originates from both the effective volume effect from filler volume and polymer–filler interaction and the synergistic effect between network chains within the “hierarchical network”. Experimental results showed that filler’s dispersion, concentration, specific surface area and surface chemistry have a great influence on the tensile properties, which could be interpreted by analyzing the variation of both effective volume effect and synergistic effect.     

Engineering the coefficient of thermal expansion and thermal conductivity of polymers filled with high aspect ratio silica nanofibers

The thermomechanical properties of epoxy filled with two different types of silica nanofillers: spherical nanoparticles and nanofibers were investigated as a function of silica nanofiller aspect ratio and concentration. Results indicated that at room temperature and at 8.74% silica nanofiber concentration (by volume) the thermal conductivity of epoxy increased twofold and coefficient of thermal expansion (CET) decreased by ∼40%. Silica nanofiber filled epoxy showed 1.4 times greater CET and 1.5 times greater thermal conductivity compared to spherical nanoparticle filled epoxy. The significant changes observed in thermomechanical properties of silica nanofiber filled epoxy were attributed to its high aspect ratio by constraining the polymer matrix as well as reducing the phonon scattering due to the formation of a continuous fiber network within the matrix. In addition to being electrically insulating, the improved properties of silica nanofiber filled epoxy make it an extremely attractive material as underfill and encapsulant in advanced electronic packaging industry.     

Dynamic mechanical analysis and thermal properties of LLDPE/EVA/modified silica nanocomposites

The effect of hexamethylene disilazane modified nanosilica on the dynamic mechanical analysis (DMA), crystallization, melting and thermal degradation behavior of linear low density polyethylene/ethylene vinyl acetate copolymer (LLDPE/EVA) blends are explored.Detailed DMA analysis is carried out in order to investigate the reinforcing behavior of nanosilica adopting Kerner–Nielson model. Oxidative degradation and thermal stabilities of samples are also studied by the thermogravimetery analysis. The high content of nanosilica particles results in significant shift of degradation temperature to higher temperatures in the oxygen atmosphere. This behavior might be attributed to the barrier properties of nanoparticles against oxygen and gaseous degradation products. However, incorporation of modified nanosilica into LLDPE/EVA blend is decreased the onset of degradation temperature of the unfilled system. In nitrogen atmosphere, no changes are observed in the thermal degradation range and only a reduction is documented in the onset of degradation temperature. Considering important role of onset of degradation temperature, activation energy of starting of degradation temperature is calculated utilizing Kissinger-Ozawa model in both oxygen and nitrogen atmospheres. Results showed that activation energy of degradation reaction is decreased by ∼ 20 kJ/mol. This decrease is owing to the release of modifiers from the nanoparticles.     

Dynamic mechanical analysis of fumed silica/cyanate ester nanocomposites

Fumed silica particles with average primary particle diameters of 12 and 40 nm were combined with a low viscosity bisphenol E cyanate ester resin to form composite materials with enhanced storage modulus and reduced damping behavior, as evidenced by dynamic mechanical analysis (DMA). The storage modulus increased with volume fraction of fumed silica in both the glassy and rubbery regions, but the increase was more pronounced in the rubbery region. The maximum increase in storage modulus in the glassy region was 75% for 20.7 vol% of 40 nm fumed silica, while the same composition showed a 231% increase in the rubbery storage modulus. Furthermore, decreases in damping behavior were used to estimate the effective polymer-particle interphase thickness. The glass transition temperature of the nanocomposites was not changed significantly with increasing volume fraction.     

Effect of crab shell particles on the thermomechanical and thermal properties of polybenzoxazine matrix

For various molecular ratios ranging between 0% and 30%, the effect of Crab Shell Particles (CSP) on the thermal and thermomechanical properties of polybenzoxazine has been studied. The high contents of CaCO₃ particles in CSP clearly improve both the thermomechanical and thermal properties of the polybenzoxazine corresponding to a gain in storage modulus and glass transition temperature of 137% and 25%, respectively, at 30% CSP loading. Thermal analysis reveals that the polybenzoxazine matrix filled with CSP also increases the initial decomposition temperatures and the char yield of composites which reaches 49% at maximum CSP content.     

Thermal conductivity and dynamic mechanical analysis of NiZn ferrite nanoparticles filled thermoplastic natural rubber nanocomposite

The effect of NiZn ferrite nanoparticles on the thermal behaviour of thermoplastic natural rubber (TPNR) composite is investigated. Melt blending technique was employed to prepare TPNR matrix, which comprised of natural rubber (NR), liquid natural rubber (LNR) and high-density polyethylene (HDPE) in a ratio of 20:10:70. Dynamic mechanical analysis results show that the thermal stability of the nanocomposites enhanced with increasing filler loading. Moreover, thermal conductivity of the nanocomposites increased with filler content until 8 wt%, which is believed to be the optimum loading that formed the suitable percolated network for phonon conduction facilitation.     

Rheological behaviors of fumed silica filled polydimethylsiloxane suspensions

Rheological behaviors of fumed silica filled hydroxylated polydimethylsiloxane suspensions were investigated in both static and dynamic shear modes. Both viscosity and modulus increase with filler’s concentration and specific surface area, however, they decrease with the improved dispersion and proper surface modification. In addition to the effective volume effect of filler’s excluded volume and polymer–filler interaction, the polymer-mediated filler–filler interaction contributes significantly. Such an interaction was classified according to the particle distance, and the concept of “inter-particle excess energy” was proposed. A combination of effective volume effect and inter-particle excess energy can be used to interpret the rheological behaviors of the nanocomposites.     

Facile preparation of graphene nanoribbon filled silicone rubber nanocomposite with improved thermal and mechanical properties

In the present study, graphene nanoribbon was prepared through unzipping the multi walled carbon nanotubes, and its reinforcing effect as a filler to the silicone rubber was further investigated. The results showed that carbon nanotubes could be unzipped to graphene nanoribbon using strong oxidants like potassium permanganate and sulfuric acid. The prepared graphene nanoribbon could homogeneously disperse within silicone rubber matrix using a simple solution mixing approach. It was also found from the thermogravimetric analysis curves that the thermal stability of the graphene nanoribbon filled silicone rubber nanocomposites improved compared to the pristine silicone rubber. Besides, with the incorporation of the nanofiller, the mechanical properties of the resulting nanocomposites were significantly enhanced, in which both the tensile stress and Young’s modulus increased by 67% and 93% respectively when the mass content of the graphene nanoribbon was 2.0 wt%. Thus it could be expected that graphene nanoribbon had large potentials to be applied as the reinforcing filler to fabricate polymers with increased the thermal and mechanical properties.     

Study on thermal properties of graphene foam/graphene sheets filled polymer composites

The polymer composites composed of graphene foam (GF), graphene sheets (GSs) and pliable polydimethylsiloxane (PDMS) were fabricated and their thermal properties were investigated. Due to the unique interconnected structure of GF, the thermal conductivity of GF/PDMS composite reaches 0.56 W m⁻¹ K⁻¹, which is about 300% that of pure PDMS, and 20% higher than that of GS/PDMS composite with the same graphene loading of 0.7 wt%. Its coefficient of thermal expansion is (80–137) × 10⁻⁶/K within 25–150 °C, much lower than those of GS/PDMS composite and pure PDMS. In addition, it also shows superior thermal and dimensional stability. All above results demonstrate that the GF/PDMS composite is a good candidate for thermal interface materials, which could be applied in the thermal management of electronic devices, etc.     

Thermo-mechanical properties of polysulfone based nanocomposites with well dispersed silica nanoparticles

The effect of the filler on the thermo-mechanical properties of polysulfone filled nanocomposites was studied considering different loads of silica nanoparticles (0, 1, 2, 5 and 10 wt%). Thermal characterization showed that: (i) the degradation temperature slightly increases with the content of particles; (ii) glass transition temperature is not affected by the presence of the particles, suggesting a weak interaction between the matrix and the particles. Although thermogravimetric analysis indicate there may be certain favorable interactions between the polymer and the filler, they must not be so important as to reduce chain mobility nearby the surface of the particles. Mechanical properties (modulus of rupture, hardness, indentation modulus, etc.) remain almost constant up to relatively high contents of nanoparticles (5 wt%). A significant increase was only observed for the sample with 10% of nanoparticles suggesting that, in this system, interconnection between particles must exist to efficiently modify the polysulfone properties.     

Micromechanically-based effective thermal conductivity estimates for polymer nanocomposites

The Effective Continuum Micromechanics Analysis Code was modified to predict the effective thermal conductivities of composites containing multiple distinct nanoheterogeneities (fibers, spheres, platelets, voids, etc.) each with an arbitrary number of coating layers based upon either the modified Mori–Tanaka or modified self-consistent methods for steady state heat conduction. A parametric study was performed to investigate the effect of nanoreinforcement morphology, volume fraction, orientation, and nanoreinforcement–resin interphase properties on calculated effective thermal conductivities. Predicted thermal conductivities matched experimentally measured values for vapor-grown carbon nanofiber/polypropylene, exfoliated graphite flake/epoxy, glass microsphere/polystyrene, cupric oxide sphere/epoxy, and aluminum sphere/epoxy composites.     

High performance polyurethane/functionalized graphene nanocomposites with improved mechanical and thermal properties

This communication reported the substantial improvement in the mechanical and thermal properties of a polyurethane (PU) resulting from the incorporation of well-dispersed graphene oxide (GO). The stress transfer benefited from the covalent interface formed between the PU and GO. The Young’s modulus of the PU was improved by ∼7 times with the incorporation of 4 wt% GO, and the improvement of ∼50% in toughness was achieved at 1 wt% loading of GO without losing elasticity. Significant improvements were also demonstrated in the hardness and scratch resistance measured by nano-indentation. Thermogravimetric analysis revealed that the decomposition temperature was increased by ∼50 °C with the addition of 4 wt% GO.     

Synthesis and characterization of novel waterborne polyurethane nanocomposites with magnetic and electrical properties

The novel nanocomposites derived from waterborne polyurethane and nano-Fe₃O₄ (WPU/Fe₃O₄) have been successfully synthesized by in situ polymerization progress. The nano-Fe₃O₄ particles prepared by co-precipitation method were modified by using oleic acid (OA) to improve their compatibility with monomers. The chemical structures, morphology, thermal behavior, mechanical properties, magnetic properties and electrical properties of the WPU/Fe₃O₄ nanocomposites were investigated by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), X-ray diffraction (XRD), atomic force microscope (AFM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMA), vibrating sample magnetometer (VSM) and high resistance meter respectively. The results indicated that the Fe₃O₄ nanoparticles modified by oleic acid could be homogeneously dispersed in the WPU and the introduction of ones was obviously improving the thermal properties, magnetic properties and electrical properties of WPU/Fe₃O₄ nanocomposites. The resulting WPU/Fe₃O₄ nanocomposites would be having the potential applications in microwave absorption.     

Growing polystyrene chains from the surface of graphene layers via RAFT polymerization and the influence on their thermal properties

The polystyrene (PS) macromolecular chains were grafted on the surface of graphene layers by reversible addition-fragmentation chain transfer (RAFT) polymerization. In this procedure, a RAFT agent, 4-Cyano-4-[(dodecylsulfanylthiocarbonyl) sulfanyl] pentanoic acid, was used to functionalize the thermal reduced graphene oxide (TRGO) to obtain the precursor (TRGO-RAFT). It can be calculated that the grafting density of PS/graphene (PRG) composites was about 0.18 chains per 100 carbons. Successful in-plain attachment of RAFT agent to TRGO and PS chain to TRGO-RAFT was shown an influence on the thermal property of the PRG composites. The thermal conductivity (λ) improved from 0.150 W m⁻¹ K⁻¹ of neat PS to 0.250 W m⁻¹ K⁻¹ of PRG composites with 10 wt% graphene sheets loading. The thermal property of PRG composites increased due to the homogeneous dispersion and ordered arrangement of graphene sheets in PS matrix and the formation of PRG composites.     

Evaluation of thermal,mechanical, and electrical properties of PVDF/GNP binary and PVDF/PMMA/GNP ternary nanocomposites

Graphene nanoplatelet (GNP) was incorporated into poly(vinylidene fluoride) (PVDF) and PVDF/poly(methyl methacrylate) (PMMA) blend to achieve binary and ternary nanocomposites. GNP was more randomly dispersed in binary composites compared with ternary composites. GNP exhibited higher nucleation efficiency for PVDF crystallization in ternary composites than in binary composites. GNP addition induced PVDF crystals with higher stability; however, PMMA imparted opposite effect. The binary composite exhibited lower thermal expansion value than PVDF; the value further declined (up to 28.5% drop) in the ternary composites. The storage modulus of binary and ternary composites increased to 23.1% and 53.9% (at 25 °C), respectively, compared with PVDF. Electrical percolation threshold between 1 phr and 2 phr GNP loading was identified for the two composite systems; the ternary composites exhibited lower electrical resistivity at identical GNP loadings. Rheological data confirmed that the formation of GNP (pseudo)network structure was assisted in the ternary system.     

Effects of aluminium nitride inclusions on thermal and electrical properties of epoxy and polypropylene: An experimental investigation

Thermal and dielectric properties of polymers reinforced with micro-sized aluminium nitride (AlN) particles have been studied. A set of epoxy–AlN composites, with filler content ranging from 0 to 25 vol% is prepared by hand lay-up technique. With similar filler loading, polypropylene -AlN composites are fabricated by compression molding technique. Density (ρ_c), effective thermal conductivity (k_eff), glass transition temperature (T_g), coefficient of thermal expansion (CTE) and dielectric constant (ε_c) of these composites are measured experimentally. The various experimental data were interpreted using appropriate theoretical models. Incorporation of AlN in both the resin increases the k_eff and T_g whereas CTE of composite decreases favourably. The dielectric constant of the composite also found to get modified with filler content. With improved thermal and modified dielectric characteristics, these AlN filled polymer composites can possibly be used for microelectronics applications.     

Synthesis and characterization of novel hyperbranched polyimides/attapulgite nanocomposites

Novel hyperbranched polyimides/attapulgite (HBPI/AT) nanocomposites were successfully synthesized by in situ polymerization. HBPI derived from novel 2,4,6-tri[3-(4-aminophenoxy)phenyl]pyridine (TAPP) and 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA). 4,4′-diphenylmethane diisocyanate (MDI) modified AT copolymerized with HBPI and the nanocomposites formed multilinked network. Chemical structure, morphology, thermal behavior, and mechanical properties of nanocomposites were investigated by Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), thermal gravimetric analysis (TGA), dynamic mechanical analysis (DMA), and tensile testing et.al. Results indicated that modified AT was homogeneously dispersed in matrix and resulted in an improvement of thermal stability, mechanical properties and water resistance of HBPI/AT nanocomposites.     

Synthesis and characterizations of modified expanded graphite/emulsion styrene butadiene rubber nanocomposites: Mechanical,dynamic mechanical and morphological properties

The present research work demonstrated the reinforcing effect of expanded graphite (EG) and modified EG (MEG) with and without carbon black (CB) on the physical, mechanical and thermo-mechanical properties of emulsion polymerized styrene butadiene rubber (SBR) vulcanizates. In separate batches, EG and MEG flakes with and without CB were incorporated into the SBR by melt blending. The microstructures of the nanocomposites were precisely characterized by wide angle X-ray diffraction (WAXD) analysis and high resolution transmission electron microscope (HR-TEM). EG and MEG filled SBR compounds showed improvement in the curing features, mechanical, thermal and dynamic mechanical properties than their respective controls.     

Graphite-like carbon nitride and functionalized layered double hydroxide filled polypropylene-grafted maleic anhydride nanocomposites: Comparison in flame retardancy,and thermal,mechanical and UV-shielding properties

Graphite-like carbon nitride (g-C₃N₄) and borate modified layered double hydroxides (LDH-B) were successfully fabricated by thermal pyrolysis and modified aqueous miscible organic solvent treatment methods, respectively. Then these nano-additives were introduced to prepare polypropylene-grafted maleic anhydride (PP-g-MA)/g-C₃N₄ and PP-g-MA/LDH-B nanocomposites using a modified solvent mixing strategy. Several important parameters of the nanocomposites including thermal, mechanical and UV-blocking properties were investigated. Results indicated that pure g-C₃N₄ exhibited 347.6 and 427.2 °C increase in onset decomposition temperature under air and nitrogen conditions, respectively, compared with LDH-B. In case of PP-g-MA nanocomposites, both T_-10 and T_-50 (the temperature at 10% and 50% weight loss, respectively) were improved by 14.6 and 27.7 °C, respectively, by the addition of g-C₃N₄ while those only increased by 2.3 and 17.8 °C upon introducing LDH-B. Furthermore, PP-g-MA/g-C₃N₄ system showed a remarkable increment (9.8 °C) in crystallization temperature while an increase of 4.2 °C for PP-g-MA/LDH-B nanocomposite. Introducing g-C₃N₄ and LDH-B into PP-g-MA led to a reduction of 28% and 19% in pHRR, respectively. It was noted that the incorporation of g-C₃N₄ caused significant improvement in storage modulus from 2445.0 MPa for neat PP-g-MA to 2783.5 MPa for PP-g-MA/g-C₃N₄ while that of PP-g-MA/LDH-B was dramatically decreased by 27.3%. Optical results indicated that PP-g-MA/g-C₃N₄ was rendered fascinating UV adsorption ability relative to PP-g-MA/LDH-B. It is expected that the novel two-dimensional nanomaterial could bring new creativity into polymer composites.     

Effect of surface treatment on thermal stability of the hemp-PLA composites: Correlation of activation energy with thermal degradation

The thermal behavior of hemp-poly lactic acid composites with both untreated and chemically surface modified hemp fiber was characterized by means of activation energy of thermal degradation. Three chemical surface modification employed were; alkali, silane and acetic anhydride. Model-free isoconversion Flynn–Wall–Ozawa method was chosen to evaluate the activation energy of composites. The results indicated that composites prepared with acetic anhydride modified hemp had 10–13% higher activation energy compared to other composites. Further, among the three surface modifications, acetic anhydride resulted in higher activation energy (159–163 kJ/mol). Fourier transform infrared spectroscopy supported the findings of thermogravimetric analysis results, wherein surface functionalization changes were observed as a result of surface modification of hemp fiber. It was concluded that, higher bond energy results in higher activation energy, which improves thermal stability. The activation energy data can aid in better understanding of the thermal degradation behavior of composites as a function of composite processing.