Structure and properties of hybrid PLA nanocomposites with inorganic nanofillers and cellulose fibers

Polylactide reinforced with 3 wt% of organo-modified montmorillonite, 5 wt% of stearic acid-modified calcium carbonate nanoparticles, 15 wt% of cellulose fibers (PLA/MMT, PLA/NCC, PLA/CF) and hybrid composites containing 15 wt% of fibers in addition to montmorillonite (PLA/MMT/CF) or calcium carbonate (PLA/NCC/CF) were prepared and examined. The nanoparticles were dispersed in polylactide almost homogeneously; montmorillonite was exfoliated during processing. T_g of polylactide remained unaffected but its cold crystallization was enhanced; the cold-crystallization behavior of the hybrid composites was dominated by nanofillers nucleating ability. The fibers and calcium carbonate decreased whereas exfoliated montmorillonite improved the thermal stability of the materials. Polylactide, PLA/NCC and PLA/MMT exhibited ability to plastic deformation, although the latter the weakest. Tensile behavior of the hybrid composites was strongly influenced by the fibers and similar to that of PLA/CF. All the fillers increased the storage modulus below T_g; that of PLA/MMT/CF and PLA/NCC/CF was improved with respect to polylactide by 50% and 45%, respectively.     

聚乳酸/石墨/多壁碳纳米管复合材料的制备及性能

通过共溶剂法制备了由石墨(GN)和多壁碳纳米管(MWCNTs)掺杂的聚乳酸(PLA)纳米复合材料,借助扫描电镜等手段,研究了MWCNTs用量对复合材料微观结构、热稳定性、导热和导热性能及介电性能的影响。结果显示,MWC-NTs和GN在PLA基体中形成了稳定的导电和导热网络结构,从而导致复合材料具有较低的导电和导热逾渗阈值,其值约为MWCNTs/GN=0.5/1。MWCNTs和GN均匀分散和协同增强效应促使复合材料热稳定性、导热和导电性能明显提高。与纯PLA相比,填料在逾渗阈值附近的复合材料的初始分解温度提高了近16℃,导热系数提高了1倍,体积电阻降低了109数量级。     

Synergistic effects in network formation and electrical properties of hybrid epoxy nanocomposites containing multi-wall carbon nanotubes and carbon black

Epoxy nanocomposites including multi-wall carbon nanotubes (MWCNT) and carbon black (CB) were produced and investigated by means of electrical conductivity measurements and microscopical analysis. Varying the weight fraction of the nanoparticles, electrical percolation behaviour was studied. Due to synergistic effects in network formation and in charge transport the inclusion of both MWCNT and CB in the epoxy matrix leads to an identical electrical behaviour of this ternary nanocomposite system compared to the binary MWCNT-epoxy system. For both types of nanocomposites an electrical percolation threshold of around 0.025 wt% and 0.03 wt% was observed. Conversely, the binary CB nanocomposites exhibit a three-times higher percolation threshold of about 0.085 wt%. The difference between the binary MWCNT-epoxy and the ternary CB/MWCNT-epoxy in electrical conductivity at high filler concentrations (e.g. 0.5 wt%) turns out to be less than expected. Thus, a considerable amount of MWCNTs can be replaced by CB without changing the electrical properties.     

石墨烯多壁碳纳米管/超高分子量聚乙烯导电复合材料的制备及性能

为了比较超高分子量聚乙烯(UHMWPE)在单一填充和混合填充时, 复合材料导电性的差别。在超声和肼的作用下, 通过对氧化石墨烯(GO)、 多壁碳纳米管(MWCNTs)和超高分子量聚乙烯水/乙醇分散液减压蒸馏及热压制备了隔离型MWCNTs/UHMWPE、 石墨烯(GNS)/UHMWPE和MWCNTs-GNS/UHMWPE导电复合材料。经SEM、 TEM测试发现, 导电填料分散于UHMWPE颗粒表面, 热压后形成隔离结构。隔离型的MWCNTs/UHMWPE和GNS/UHMWPE复合材料均表现出较低的导电逾渗(0.148%和0.059%, 体积分数,下同), 但MWCNTs/UHMWPE复合材料的电导率(2.0×10^-2 S/m, 1.0%, 质量分数, 下同)明显高于相同填料含量下的GNS/UHMWPE复合材料。 MWCNTs-GNS/UHMWPE复合材料表现出了更低的逾渗(0.039%) 和较高导电性能(1.0×10^-2 S/m, 1.0%), 其拉伸强度和断裂伸长率随填充剂含量的增加呈现出先上升后下降的趋势。     

Comparison of rheological and electrical percolation phenomena in carbon black and carbon nanotube filled epoxy polymers

Epoxy nanocomposite suspensions including multi-wall carbon nanotubes (MWCNTs) and carbon black (CB) were produced and investigated by means of combined rheological and electrical analysis. The rheological percolation behaviour was compared to the electrical percolation behaviour. Due to similar dynamic agglomeration mechanisms the difference between the rheological and the electrical percolation threshold in the cured state is identical for MWCNT and CB filled systems. Non-covalent matrix–nanoparticle interactions in uncured epoxy suspensions are negligible since the onset of electrical and rheological percolation in the uncured state coincidence. Furthermore, the electrical percolation threshold in the cured state is always lower than in the uncured state because of the high tendency of CB and MWCNTs to form conductive networks during curing. The difference between rheological and electrical percolation threshold is dependent on the curing conditions. Thus, the rheological percolation threshold can be considered as an upper limit for the electrical percolation threshold in the cured state. Due to the formation of co-supporting networks multi-filler (MWCNTs and CB) suspensions exhibit a similar rheological behaviour as the binary MWCNT suspensions. For both types of suspensions a rheological percolation threshold of around 0.2 and 0.25 wt% was determined. Conversely, the binary CB nanocomposites exhibit a four-times higher percolation threshold of about 0.8 wt%. The difference between the binary MWCNT suspension and the ternary CB/MWCNT suspension in storage shear modulus at high filler concentrations (~0.8 wt%) turns out to be less than expected. Thus, synergistic effects in network formation are already present in the epoxy suspension and get more pronounced during curing.     

Effects of poly(oxyethylene)-block structure in polyetheramines on the modified carbon nanotube/poly(lactic acid) composites

The hybrids of multi-walled carbon nanotube and poly(lactic acid) (MWCNT/PLA) were prepared by a melt-blending method. In order to enhance the compatibility between the PLA and MWCNTs, the surface of the MWCNTs was covalently modified by Jeffamine® polyetheramines by functionalizing MWCNTs with carboxylic groups. Different molecular weights and hydrophilicity of the polyethermaines were grafted onto MWCNTs with the assistance of a dehydrating agent. The results showed that low-molecular-weight Jeffamine® polyetheramine modified MWCNTs can effectively improve the thermal properties of PLA composites. On the other hand, high-molecular-weight and poly(oxyethylene)-segmented polyetheramine could render the modified MWCNTs of well dispersion in PLA, and consequently affecting the improvements of mechanical properties and conductivity of composite materials. With the addition of 3.0 wt% MWCNTs, the increment of E′ of the composite at 40 °C was 79%. For conductivity, the surface resistivity decreased from 1.27 × 10¹² Ω/sq for neat PLA to 8.30 × 10⁻³ Ω/sq for the composites.     

Positive Temperature Coefficient Effect of Polypropylene/Carbon Nanotube/Montmorillonite Hybrid Nanocomposites

Ternary polypropylene/multiwalled carbon nanotube/montmorillonite (PP/MWNT/MMT) nanocomposites were prepared by melt compounding of a ball-milled MWNT and MMT mixture in a Haake mixer at a screw rotation rate of 200 r/$hbox{min}$. The electrical conducting behavior of such hybrid composites was examined. The results showed that the conducting behaviors of PP/MWNT/MMT nanocomposites were strongly dependent on the MWNT and MMT contents. The percolation concentration of such hybrid nanocomposites was 1.0 wt% MWNT. Furthermore, percolating PP/1.0 wt% MWNT/MMT nanocomposites exhibited a positive temperature coefficient (PTC) effect. The PTC transition temperature can be regulated over a broader temperature range by varying the MMT contents. Hybridization of nanofillers provides a facile methodology to fabricate conducting polymer nanocomposites with tunable PTC transition temperatures.      

In situ probe nanophase transition in nanocomposite using thermal AFM

Nanocomposites made from inorganic nanoparticles and polymers have many applications in optics, electronics and biomaterials. However, the glass transition temperature (T_g) of a nanocomposite is very difficult to measure accurately by conventional thermal analysis such as DSC or TMA when the concentration of the nanoparticle reaches a threshold of the percolation network. At this threshold stage, the phase transition in the nano domains of the matrix is too small to be detected by macroscale thermal analysis. We have developed a methodology basis on thermal atomic force microscope (AFM) to monitor the nanophase transition of the nanocomposite in situ upon heating. This method has demonstrated the capability in determining the T_g of a nanocomposite made by spherical SiO₂ nanoparticles dispersed in polyacrylate. The threshold of the percolation network of this nanocomposite is at 40 wt% of SiO₂ nanoparticles according to the results of refractive index, AFM, nanoindentation, DSC, TMA and TGA.     

Percolation behaviour of polypropylene glycol filled with multiwalled carbon nanotubes and Laponite

The percolation behaviour of the hybrid composites of polypropylene glycol (PPG) filled with multiwalled carbon nanotubes (MWCNTs) and Laponite RD (Lap), or with MWCNTs and organo-modified Laponite (LapO) was studied by wide angle X-ray diffraction (XRD), microscopic image analysis, and electrical conductivity measurements. Cetyltrimethylammoniumbromide (CTAB) was used as an organo-modifier of Laponite. The Lap and LapO were found to have rather different affinity to PPG. XRD data have evidenced finite PPG integration inside Lap and complete exfoliation of LapO stacks in a PPG matrix. In PPG + MWCNT composites containing no Lap or LapO, increase of MWCNT concentration above the critical value C_p ∼ 0.4 wt% resulted in percolation. The value of the percolation threshold, C_p, was practically the same for hybrid PPG + MWCNT + Lap composites. However, it noticeably decreased (C_p ∼ 0.2 wt%) in PPG + MWCNT + LapO materials. The observed behaviour of the percolation threshold may be attributed to the effects exerted by LapO on the size of MWCNT aggregates, state of their dispersion and homogeneity of their spatial distribution.     

The effect of silane treated- and untreated-talc on the mechanical and physico-mechanical properties of poly(lactic acid)/newspaper fibers/talc hybrid composites

This paper evaluates the effect of the addition of silane treated- and untreated- talc as the fillers on the mechanical and physico-mechanical properties of poly(lactic acid) (PLA)/recycled newspaper cellulose fibers (RNCF)/talc hybrid composites. For this purpose, 10 wt% of a talc with and without silane treatment were incorporated into PLA/RNCF (60 wt%/30 wt%) composites that were processed by a micro-compounding and molding system. PLA is utilized is a bio-based polymer that made from dextrose, a derivative of corn. Talc is also a natural product. The RNCF and talc hybrid reinforcements of PLA polymer matrix were targeted to design and engineer bio-based composites of balanced properties with added advantages of cost benefits besides the eco-friendliness of all the components in the composites. In this work, the flexural and impact properties of PLA/RNCF composites improved significantly with the addition of 10 wt% talc. The flexural and impact strength of these hybrid composites were found to be significantly higher than that made from either PLA/RNCF. The hybrid composites showed improved properties such as flexural strength of 132 MPa and flexural modulus of 15.3 GPa, while the unhybridized PLA/RNCF based composites exhibited flexural strength and modulus values of 77 MPa and 6.7 GPa, respectively. The DMA storage modulus and the loss modulus of the PLA/RNCF hybrid composites were found to increase, whereas the mechanical loss factor (tan delta) was found to decrease. The storage modulus increased with the addition of talc, because the talc generated a stiffer interface in the polymer matrix. Differential scanning calorimetry (DSC) thermograms of neat PLA and of the hybrid composites showed nearly the similar glass transition temperatures and melting temperatures. Scanning electron microscopy (SEM) micrographs of the fracture surface of Notched Izod impact specimen of 10 wt% talc filled PLA/RNCF composite showed well filler particle dispersion in the matrix and no large aggregates are present. The comparison data of mechanical properties among samples filled with silane-treated- and untreated- talc fillers showed that the hybrid composites filled with silane treated talc displayed the better mechanical prosperities relative to the other hybrid composites. Talc-filled RNCF-reinforced polypropylene (PP) hybrid composites were also made in the same way that of PLA hybrid composites for a comparison. The PLA hybrid bio-based composites showed much improvement in mechanical properties as compared to PP-based hybrid counterparts. This suggests that these PLA hybrid bio-based composites have a potential to replace glass fibers in many applications that do not require very high load bearing capabilities and these recycled newspaper cellulose fibers could be a good candidate reinforcement fiber of high performance hybrid biocomposites.     

Electrical and rheological properties of double percolated poly(methyl methacrylate)/multiwalled carbon nanotube nanocomposites

Electrical and rheological properties of nanocomposites based on poly(methyl methacrylate) (PMMA) and multiwalled carbon nanotube (MWCNT) were studied from view points of double percolation by adding crosslinked methyl methacrylate-butadiene-styrene (MBS) copolymer particles to lower percolation threshold concentration of MWCNTs. It was found that the critical concentrations of MWCNTs for the percolation in the nanocomposites decrease and then increase with increasing the MBS contents of the nanocomposites. It is postulated that the addition of MBS at low concentrations results in double percolation of MWCNT and the significant decrease of critical concentration for the percolations. However, adding MBS particles in large amounts results in limited space for the distribution of MWCNTs and less efficient dispersion of the MWCNTs and the increase of the critical concentrations of MWCNTs for the percolations. Rheological properties and change of T(g)s reflect large interfacial areas in the well dispersed nanocomposite and were also interpreted to support the speculations for the effects of MBS contents and MWCNT concentrations of PMMA/MWCNT nanocomposites.     

Carbon black/graphite nanoplatelet/rubbery epoxy hybrid composites for thermal interface applications

Hybrid composites were developed by dispersing carbon black (CB) nanoparticles and graphite nanoplatelets (GNPs) at 4–6 and 12–14 wt%, respectively, into rubbery epoxy resin. SEM analysis showed that CB particles improved the dispersion of GNPs in the hybrid composite. The thermal conductivity of 4 wt% CB/14 wt% GNP-15/rubbery epoxy hybrid composite, 0.81 W/m K, is ca. four times higher than that of rubbery epoxy. When silane-functionalised, the fillers reduced the viscosity of the hybrid dispersion and made the hybrid composite highly electrically insulating. Nevertheless, filler functionalisation decreased the composite’s thermal conductivity by only 16.6%. Compression testing showed that the hybrid fillers increased the compressive modulus and strength of rubbery epoxy by nearly two and three times, respectively. Overall, the hybrid composites with their thermal paste-type morphology, low viscosity, high compliance, improved thermal conductivity and, when fillers are functionalised, low electrical conductivity makes them promising materials as thermal interface adhesives.     

Thermal and mechanical properties of phenolic-based composites reinforced by carbon fibres and multiwall carbon nanotubes

The thermal, mechanical and ablation properties of carbon fibre/phenolic composites filled with multiwall carbon nanotubes (MWCNTs) were investigated. Carbon fibre/phenolic/MWCNTs were prepared using different weight percentage of MWCNTs by compression moulding. The samples were characterized by scanning electron microscopy (SEM), flexural tests, thermal gravimetric analysis and oxyacetylene torch tests. The thermal stability and flexural properties of the nanocomposites increased by increasing MWCNTs content (wt% ⩽1), but they decreased when the content of MWCNTs was 2 wt%. The linear and mass ablation rates of the nanocomposites after modified with 1 wt% MWCNTs decreased by about 80% and 52%, respectively. To investigate the material post-test microstructure, a morphological characterization was carried out using SEM. It was shown that the presence of MWCNTs in the composite led to the formation of a strong network char layer without any cracks or opening.     

Preparation and characterization of sulfonated poly(1,3,4-oxadiazole)/multi-walled carbon nanotube composite films with high performance in electric heating and thermal stability

For manufacturing thermally stable electric heating composite films, a sulfonated poly(1,3,4-oxadiazole) (sPOD) was synthesized and it was composited with pristine MWCNT of 0.1–10.0 wt% by an ultrasonicated solution mixing and casting. SEM images revealed that the pristine MWCNTs were dispersed well in the composite matrix via π–π interaction between the MWCNTs and the aromatic rings of sPOD backbone. The electrical resistivity of the composite films decreased considerably from ∼10⁹ Ω cm to ∼10⁰ Ω cm with the increment of the MWCNT content by forming a percolation threshold at ∼0.026 wt%. The composite films with 5.0–10.0 wt% MWCNT contents, which had sufficiently low electrical resistivity of ∼10³–10⁰ Ω cm, exhibited excellent electric heating performance by attaining high maximum temperatures as well as electric energy efficiency. Since the dominant thermal decomposition of the composite films took place at ∼500 °C, sPOD/MWCNT composite films with low electrical resistivity could be used for high performance electric heating materials for advanced applications.     

Electrical and optical properties of reduced graphene oxide and multi-walled carbon nanotubes based nanocomposites: A comparative study

Graphene and multi-walled carbon nanotubes have attracted interest for a number of potential applications. One of the most actively pursued applications uses graphene and carbon nanotubes as a transparent conducting electrode in solar cells, displays or touch screens. In this work, in situ reduced graphene oxide/Poly (vinyl alcohol) and multi-walled carbon nanotubes/Sodium Dodecyl Sulfate/Poly (vinyl alcohol) composites were prepared by water dispersion and different reduction treatments. Comparative studies were conducted to explore the electrical and optical properties of nanocomposites based on graphene and multi-walled carbon nanotubes. A thermal reduction of graphene oxide was more effective, producing films with sheet resistances as low as 10²–10³ Ω/square with 80% transmittance for 550 nm light. The percolation threshold of the thermally reduced graphene oxide composites (0.35 vol%) was much lower than that of the chemically reduced graphene oxide composites (0.57 vol%), and than that of the carbon nanotubes composites (0.47 vol%). The Seebeck coefficient of graphene oxide films changes from about 40 μV/K to −30 μV/K after an annealing of three hours at 200 °C. The optical absorption of the nanocomposites showed a high absorbance in near UV regions and the photoluminescence enhancement was achieved at 1 wt% graphene loading, while the carbon nanotubes based composite presents a significant emission at 0.7 wt% followed with a photoluminescence quenching at higher fraction of the nanofillers 1.6 wt% TRGO and 1 wt% MWCNTs.     

High-performance conductive materials based on the selective location of carbon black in poly(ether ether ketone)/polyimide matrix

A novel high performance conductive material with excellent comprehensive properties was prepared by melt-blending, and its performances were adjusted by controlling the selective location of carbon black (CB) in poly(ether ether ketone) (PEEK)/thermoplastic polyimide (TPI) matrix. With increasing the CB loadings, the morphology of PEEK/TPI blends changed from sea-island to co-continuous structure, which was owing to the selective location of CB in TPI phase. Notably, with the selective location of CB in the induced co-continuous PEEK/TPI matrix, the electrical percolation threshold was reduced to 5 wt%, which was significantly lower than that of binary PEEK/CB (9 wt%) and TPI/CB (10 wt%) composites. And the electrical conductivity of ternary PEEK/TPI/CB composites was 10⁴ to 10⁶ times higher than that of binary composites at identical 7.5 wt% CB loading, which was attributed to the double percolation effect. Moreover, the incorporation of CB could improve the thermal and mechanical properties effectively.     

Preparation,processing and analysis of physical properties of calcium ferrite-CNTs/PET nano-composite

The present work is focused on the preparation of composites based on Poly(ethylene terephthalate) (PET) and novel nano-hybrid filler composed of Calcium Ferrite (CF)-Carbon Nanotubes (CNTs), obtained by direct growth of CNTs on CF based iron catalysts. The carbon content in the hybrid filler was 76 wt%. Composites loaded with 1.0, 1.5, 2.0, 3.0 wt% of filler were obtained by melt compounding and processed by thin-wall injection molding. Unfilled Poly(ethylene terephthalate) was processed using the same techniques. Structural characterization and physical properties (thermal, mechanical and electrical) were analyzed and correlated to the hybrid filler loading, and to the percentage of carbon nanotubes.     

Electrical, thermal, and mechanical properties of polyarylene ether nitriles/graphite nanosheets nanocomposites prepared by masterbatch route

Graphite nanosheets (GN) reinforced polyarylene ether nitriles (PEN) nanocomposites were successfully fabricated through masterbatch route and investigated for morphological, thermal electrical, mechanical, and rheological properties. The SEM images showed that GN were well coated by phthalonitrile prepolymer (PNP) and dispersed in the PEN matrix. Thermal degradation and heat distortion temperature of PEN/GN nanocomposites increased substantially with the increment of GN content up to 10 wt%. Electrical conductivity of the polymer was dramatically enhanced at low loading level of GN; the electrical percolation of was around 5 wt% of GN. The mechanical properties of the nanocomposites were also investigated and showed significant increase with GN loading. For 10 wt% of GN-reinforced PEN composite, the tensile strength increased by about 18%, the tensile modulus increased by about 30%, the flexural strength increased by about 25%, and the flexural modulus increased by 90%. Rheological properties of the PEN/GN nanocomposites also showed a sudden change with the GN loading content; the percolation threshold was in the range of 3–4 wt% of GN.     

Investigation of physical and chemical properties of polypropylene hybrid nanocomposites

Hybrid nanocomposites fabricated based on an optimized physical and chemical properties modified polypropylene (PP)/polypropylene grafted maleic anhydride (PP-g-MA) with varied concentrations (1–7 wt% at a step of 2 wt%) of organoclay, montmorillonite (MMT). The morphology of the nanocomposites was studied by scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). It was found that partly intercalated and partly exfoliated structure (intercalated–exfoliated structures) existed in the system. The degree of exfoliation is a key factor to determine the reinforcement efficiency. The ratio of exfoliation to intercalation plays an important role in determining the properties of PP nanocomposites and only completely exfoliated silicate layers can significantly improve the properties. PP hybrid nanocomposites showed good thermal stability in the thermogravimetric analysis (TGA). Introduction of ∼3% MMT in the nanocomposites increased the onset temperature of degradation by 27.5 °C compared to that of pure PP, while the 5 wt% MMT resulted the maximum hardness in these nanocomposites. The solvent resistance of PP hybrid nanocomposites slightly increased with increasing the clay content.     

Low temperature charge transport and microwave absorption of carbon coated iron nanoparticles–polymer composite films

In this paper, the low temperature electrical conductivity and microwave absorption properties of carbon coated iron nanoparticles–polyvinyl chloride composite films are investigated for different filler fractions. The filler particles are prepared by the pyrolysis of ferrocene at 980 °C and embedded in polyvinyl chloride matrix. The high resolution transmission electron micrographs of the filler material have shown a 5 nm thin layer graphitic carbon covering over iron particles. The room temperature electrical conductivity of the composite film changes by 10 orders of magnitude with the increase of filler concentration. A percolation threshold of 2.2 and an electromagnetic interference shielding efficiency (EMI SE) of ～18.6 dB in 26.5–40 GHz range are observed for 50 wt% loading. The charge transport follows three dimensional variable range hopping conduction.