Layered double hydroxide as nanofiller in the development of polyurethane nanocomposites

Polyurethane (PU)/Dodecyl sulphate intercalated layered double hydroxide (DS-LDH) nanocomposites were successfully synthesized from PU prepolymer and polyol TG (mixtures of glycerol and trimethylolpropane) for the first time. Formation of partially exfoliated structures of PU/DS-LDH nanocomposites was confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Analysis of tensile properties showed significant improvements in tensile strength (TS) and elongation at break (EB) of about 407% and 83% for PU/DS-LDH (3 wt%) nanocomposite. The observed excellent concurrent improvement in TS and EB is attributed to the relatively better reinforcing effect of partially exfoliated DS-LDH layers in PU making the present investigation most noteworthy. In addition, gradual improvement in thermal stability and limiting oxygen index (LOI) with increasing DS-LDH loading makes these nanocomposites versatile and hence suitable for many critical applications.     

Non-covalently modified reduced graphene oxide/polyurethane nanocomposites with good mechanical and thermal properties

Non-covalently modified graphene nanosheets were prepared by reduction graphene oxide with hydrazine hydrate and simultaneous non-covalent functionalization via 1-allyl-methylimidazolium chloride (AmimCl) ionic liquid. Atomic force microscopy revealed that AmimCl ionic liquid modified graphene (IL-G) was well-dispersed in a single exfoliation with a thickness of around 0.96 nm in DMF. Subsequently, the prepared IL-G nanosheets were incorporated into polyurethane (PU) to fabricate IL-G/PU nanocomposites by solution blending. X-ray diffraction disclosed an exfoliated morphology of IL-G nanosheets dispersed in the PU matrix, while the fractured morphology of the IL-G/PU nanocomposites showed that IL-G nanosheets presented a wrinkled morphology when dispersed in the matrix. Both techniques revealed homogeneous dispersion and good compatibility of IL-G nanosheets with PU matrix, indicating the existence of interfacial interactions. At 0.608 wt% loadings of IL-G nanosheets, the tensile strength and storage modulus of the composites were increased by 68.5 and 81.1 %, respectively. High thermal properties were also achieved at a low loading of IL-G nanosheets. An approximately 40 °C improvement in temperature of 5 % weight loss and 34 % increase in thermal conductivity were obtained at just 0.608 wt% loading of IL-G nanosheets.     

Synthesis and characterization of thermoplastic polyurethane/montmorillonite nanocomposites produced by reactive extrusion

The novel polyurethane/montmorillonite (PU/MMT) nanocomposites based on poly (propylene oxide) glycol (POP), 4,4′-diphenymethylate diisocyanate (MDI), 1,4-butanediol (1,4-BD) and MMT has been synthesized using a one-step direct polymerization-intercalation technique by twin-screw extruder. Its structure and thermal properties are characterized by X-ray diffraction (XRD), Transmission electron microscopy (TEM) and High-resolution electron microscopy (HREM), Fourier-transform infrared spectroscopy (FTIR) and Thermogravimetry analysis (TGA), respectively. The results of XRD and HREM analyses show that the silicate layer is well dispersed in PU matrix and this mesostructure can be considered as a delaminated nanocomposites. The TGA analysis indicates that the thermal stability properties of the PU/MMT nanocomposites are increased slightly compared with the pristine PU, due to the increase of the char residue. The mechanical and flammability performances are examined by electronic Universal Tester and Cone calorimetry, respectively. The layered silicate, which acts as a high aspect ratio reinforcement, enhances tensile strength of the PU. Specifically, there is a 25% increase in the tensile strength of PU nanocomposites containing 4 wt.% MMT compared with that of pristine PU. However, the elongation at break of PU/MMT nanocomposites is lower than that of pristine PU. The loading of MMT leads to the remarkably decrease of heat release rate (HRR), contributing to the improvement of flammability performance.     

Morphologies and properties of polyurethane/epoxy resin interpenetrating network nanocomposites modified with organoclay

Polyurethane/epoxy resin interpenetrating network nanocomposites containing various contents of organophilic montmorillonite (oM-PU/EP nanocomposites) were prepared by a sequential polymeric technique and an in situ intercalation method. Transmission electronic microscopy and scanning electronic microscopy analysis showed that the interpenetrating process of PU and EP increases the exfoliation degree of organophilic montmorillonite (oMMT), and that oMMT improves the compatibility and phase structure of polyurethane/epoxy resin interpenetrating polymer networks (PU/EP IPNs). Tensile test, differential scanning calorimetry and thermal gravity analysis proved that the mechanical and thermal properties of the oM-PU/EP nanocomposites are superior to those of the pure PU and PU/EP IPNs.     

Synthesis and properties of waterborne polyurethane/attapulgite nanocomposites

The novel nanocomposites derived from waterborne polyurethane (WPU)/Attapulgite (AT) nanocomposites have been successfully synthesized by in situ polymerization progress. AT functionalized by chemical modification were incorporated as a crosslinker in prepolymer. The chemical structures, morphology, thermal behavior, and mechanical properties of the WPU/AT nanocomposites were investigated by Fourier transform infrared spectroscopy (FTIR), thermo gravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), X-ray diffraction (XRD) and tensile testing respectively. The experimental results indicated that the organically modified attapulgites were homogeneously dispersed in the WPU and resulted in an improvement of thermal stability, tensile strength and elongation at break of WPU/AT nanocomposites.     

Effects of organic chain length of layered zirconium phosphonate on the structure and properties of castor oil-based polyurethane nanocomposites

Three novel organic–inorganic hybrid molecules, layered zirconium phosphates or phosphonates, were synthesized. To study the effects of organic chain length of them on the structure and properties of polymer nanocomposites, the polyurethane/α-zirconium phosphate (PU/ZrP), polyurethane/zirconium 2-aminoethylphosphonate (PU/ZrAEP) and polyurethane/zirconium 2-(2-(2-(2-aminoethylamino)ethylamino)ethylamino) ethylphosphonate (PU/Zr(AE)₄P) nanocomposites were prepared, and characterized by Fourier Transform Infrared (FT-IR) spectroscopy, wide-angle X-ray diffraction (XRD), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC) and tensile testing. It was revealed that morphological, mechanical, and thermal properties of these nanocomposites were strongly dependent on the organic chain length of the layered zirconium phosphonates. The results showed that the fillers with longer chain length exhibited better dispersion in the PU matrix. As expected, the mechanical properties and water resistance were improved with the increasing of organic chain length of fillers, which attributed to better interfacial adhesion between fillers and PU matrix.     

Influence of metal nanoparticle decorated CNTs on polyurethane based electro active shape memory nanocomposite actuators

Polymer nanocomposites based on thermoplastic polyurethane (PU) elastomer and metal nanoparticle (Ag and Cu) decorated multiwall carbon nanotubes (M-CNTs) were prepared through melt mixing process and investigated for its mechanical, dynamic mechanical and electro active shape memory properties. Structural characterization and morphological characterization of the PU nanocomposites were done using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Morphological characterization revealed better dispersion of M-CNTs in the polyurethane, which is attributed to the improved interaction between the M-CNTs and polyurethane. Loading of the metal nanoparticle coated carbon nanotubes resulted in the significant improvement on the mechanical properties such as tensile strength of the PU composites in comparison to the pristine carbon nanotubes (P-CNTs). Dynamic mechanical analysis showed that the glass transition temperature (Tg) of the polyurethane increases slightly with increasing loading of both pristine and metal nanoparticle functionalized carbon nanotubes. The metal nanoparticles decorated carbon nanotubes also showed significant improvement in the thermal and electrical conductivity of the PU/M-CNTs nanocomposites. Shape memory studies of the PU/M-CNTs nanocomposites exhibit remarkable recoverability of its shape at lower applied dc voltages.     

Development of Cellulose Eco‐nanocomposites with Antimicrobial Properties Oriented for Food Packaging

Nanocomposites based on cellulose acetate, a commercial organoclay (Cloisite30B), triethyl citrate and variable content of antimicrobial agents (thymol and cinnamaldehyde), were obtained using a solution casting technique. The properties of the nanocomposites were evaluated using X‐ray diffraction, differential scanning calorimetry, thermogravimetric analysis, mechanical (modulus of elasticity, tensile strength and elongation at break), scanning electronic microscopy, global migration and microbiological testing. A reduction of glass transition (T_g), melting temperature (T_m) and melting enthalpy (?H_m) was also observed when the content of thymol and cinnamaldehyde was increased in the cellulose acetate nanocomposites. In contrast, thermal stability, mechanical performance and morphology of material did not show important differences when the content was modified. Results of global migration were dependent of the kind of simulant used. Finally, the antimicrobial activity was dependent of the essential oil used and its content inside the nanocomposite. An important effect of organoclay on the antimicrobial activity was also observed. Copyright © 2012 John Wiley & Sons, Ltd.     

Preparation and characterization of in situ polymerized cyclic butylene terephthalate/graphene nanocomposites

Graphene-reinforced cyclic butylene terephthalate (CBT) matrix nanocomposites were prepared and characterized by mechanical and thermal methods. These nanocomposites containing different amounts of graphene (up to 5 wt%) were prepared by melt mixing with CBT that was polymerized in situ during a subsequent hot pressing. The nanocomposites and the neat polymerized CBT (pCBT) as reference material were subjected to differential scanning calorimetry, dynamical mechanical analysis, thermogravimetrical analysis, and heat conductivity measurements. The dispersion of the grapheme nanoplatelets was characterized by transmission electron microscopy. It was established that the partly exfoliated graphene worked as nucleating agent for crystallization, acted as very efficient reinforcing agent (the storage modulus at room temperature was increased by 39 and 89 % by incorporating 1- and 5-wt% graphene, respectively). Graphene incorporation markedly enhanced the heat conductivity but did not influence the TGA behavior, except the ash content, due to the not proper exfoliation except the ash content.     

Effects of functional groups on the graphene sheet for improving the thermomechanical properties of polyurethane nanocomposites

Dispersibility of graphene sheets in polymer matrices and interfacial interaction are challenging for producing graphene-based high performance polymer nanocomposites. In this study, three kinds nanofillers; pristine graphene nanoplatelets (GNPs), graphene oxide (GO), and functionalized graphene sheet (FGS) were used to prepare polyurethane (PU) composite by in-situ polymerization. To evaluate the efficacy of functional groups on the graphene sheets, PU reinforced with GNPs, GO, and FGS were compared through tensile testing and dynamic mechanical thermal analysis. The Young's moduli of 2 wt% GO and FGS based PU nanocomposites were found significantly higher than that of same amount of GNPs loading as an evidence of the effect of functional groups on graphene sheets for the mechanical reinforcement. The strong interaction of FGS with PU was responsible to exhibit notably high modulus (25.8 MPa) of 2 wt% FGS/PU composite than the same amount of GNPs and GO loading even at elevated temperature (100 °C).     

Thermal and thermomechanical properties of poly(butylene succinate) nanocomposites

This article describes the thermal and thermomechanical properties of poly(butylene succinate) (PBS) and its nanocomposites. PBS nanocomposites with three different weight ratios of organically modified synthetic fluorine mica (OMSFM) have been prepared by melt-mixing in a batch mixer at 140 degrees C. The structure and morphology of the nanocomposites were characterized by X-ray diffraction (XRD) analyses and transmission electron microscopy (TEM) observations that reveal the homogeneous dispersion of the intercalated silicate layers into the PBS matrix. The thermal properties of pure PBS and the nanocomposite samples were studied by both conventional and temperature modulated differential scanning calorimetry (DSC) analyses, which show multiple melting behavior of the PBS matrix. The investigation of the thermomechanical properties was performed by dynamic mechanical analysis. Results reveal significant improvement in the storage modulus of neat PBS upon addition of OMSFM. The tensile modulus of neat PBS is also increased substantially with the addition of OMSFM, however, the strength at yield and elongation at break of neat PBS systematically decreases with the loading of OMSFM. The thermal stability of the nanocomposites compared to that of the pure polymer sample was examined under both pyrolytic and thermo-oxidative environments. It is shown that the thermal stability of PBS is increased moderately in the presence of 3 wt% of OMSFM, but there is no significant effect on further silicate loading in the oxidative environment. In the nitrogen environment, however, the thermal stability systematically decreases with increasing clay loading.     

Study on mechanical and ablative properties of EPDM/OMMT thermal insulating nanocomposites

In order to enhance the elongation at break, the ablation resistant properties as well as the tensile strength of the thermal insulating materials, organo-montmorillonite (OMMT) was introduced into the short aramid fibers reinforced Ethylene-Propylene-Diene Monomer (EPDM) based nanocomposites. The effects of OMMT content on the mechanical and ablative properties of the nanocomposites were investigated systematically. X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirm that EPDM-matrix has been intercalated into OMMT interlayers after a mixing process on a two-roll mill. The brittle fracture of nanocomposites also indicates that OMMT can lubricate aramid fiber to weaken the interfacial adhesive strength between the fibers and the matrix. As a result, the tensile strength and elongation at break are both improved sharply with OMMT content increasing from 1 phr to 7 phr. However, thanks to the inevitable agglomeration of OMMT with high loading inside the nanocomposites, the tensile strength and elongation at break reduce gently once OMMT is over 7 phr. Furthermore, the ablation resistant properties are improved greatly by increasing OMMT from 1 phr to 11 phr. Therefore, the optimal content of OMMT is 7-11 phr for the thermal insulating nanocomposites with big elongation and excellent ablation resistant properties.     

Microstructure and properties of polyurethane nanocomposites reinforced with methylene-bis-ortho-chloroanilline-grafted multi-walled carbon nanotubes

Methylene-bis-ortho-chloroanilline (MOCA), an excellent cross-linker widely used to prepare cured polyurethane (PU) elastomers with high performance, was used to modify a multi-walled carbon nanotube. PU/carbon nanotube (CNT) nanocomposites were prepared by incorporation of the MOCA-grafted CNT into PU matrix. Fourier transform infrared spectra have shown that the modified CNTs have been linked with PU matrix. The microstructure of composites was investigated by Field-Emission Scanning Electron Microscopy. The results of Dynamic Mechanical Thermal Analysis and Differential Scanning Calorimetry have investigated the grafted CNTs as cross-linker in the cured composites. The studies on the thermal and mechanical properties of the composites have indicated that the storage modulus and tensile strength, as well as glass transition temperature and thermal stability are significantly increased with increasing CNT content.     

Fabrication and high visible light photocatalytic properties of Cu/Cu2O nanocomposites by the one-pot solution-phase hydrothermal method

Cu/Cu2O nanocomposites were synthesized by the one-pot solution-phase hydrothermal method. The resulting products were characterized by X-ray diffraction, field emission scanning electron microscope and X-ray photoelectron spectroscopy. Experimental results indicate that the content of Cu in the Cu/Cu2O CNs increasing with prolonged reaction time. The content of Cu in the Cu/Cu2O CNs plays an important role in the photocatalytic activity. The coexistence of Cu2O and Cu nanoparticles was propitious to the high photocatalytic activity owing to their hetero-junction effect. Compared with the Cu/Cu2O CNs with high Cu content (68-96 wt%) and pure Cu2O, the Cu/Cu2O CNs with low Cu content (2.1-9.2 wt%) exhibited improved photocatalytic activity on the degradation of MO solution under visible light irradiation, at the first 20 min of irradiation, the photodegradation efficiency of MO solution reach up to 99%, it is still as high as 95% even at the end of the fourth cycle. Little change is found in their phase compositions during the photocatalytic reaction process, except partial oxidation of particles surface. The HmechanismH for visible light driven photocatalytic activity enhancement over Cu/Cu2O CNs is discussed.     

Polylactic acid/cellulose whisker nanocomposites modified by polyvinyl alcohol

The aim of this study was to produce biodegradable polylactic acid/cellulose whisker nanocomposites by compounding extrusion and investigate the possibility to use polyvinyl alcohol to improve the dispersion of whiskers in the matrix. Two feeding methods of polyvinyl alcohol and cellulose nanowhiskers were used and evaluated, dry-mixing with polylactic acid prior extrusion or pumping as suspension directly into the extruder. Various microscopic techniques, tensile testing, and dynamic mechanical thermal analysis were used to study the structure and properties of the nanocomposites. Due to immiscibility of the polymers, phase separation occurred with a continuous polylactic acid phase and a discontinuous polyvinyl alcohol phase. The whiskers were primarily located in the polyvinyl alcohol phase and only a negligible amount was located in the polylactic acid phase. This inadequate dispersion of whiskers in the polylactic acid phase was probably the reason why no improvements in thermal properties were seen for the nanocomposites. The relative small improvements in tensile modulus, tensile strength, and elongation to break for the nanocomposites also indicated that it was principally the polyvinyl alcohol phase that was reinforced with whiskers but not the polylactic acid phase.     

Cryogenic properties of SiO2/epoxy nanocomposites

SiO₂/epoxy nanocomposites were prepared using diglycidyl ether of bisphenol-F (DGEBF) type epoxy and tetraethylorthosilicate (TEOS) via the sol-gel process. Silica nanoparticles were collected after burning off the matrix resin and the silica nanoparticles were observed using TEM. The cryogenic tensile properties at 77 K and thermal expansion coefficient of the nanocomposites were studied. The tensile properties at room temperature were also given to compare with the cryogenic tensile properties. The fracture surfaces were examined with scanning electron microscopy (SEM). The effects of silica nanoparticle content have been studied on the cryogenic tensile and thermal properties of the nanocomposites. In addition, the dependence of the glass transition temperature on the silica nanoparticle content has also been examined.     

Mechanical,thermal, and flame-retardant performance of polyamide 11–halloysite nanotube nanocomposites

This study focused on the influence of different filler loadings on the elongation at break and flammability properties of the PA11/FR/HNTs nanocomposites. Polyamide 11 (PA11)/flame-retardant (FR) additives/halloysite nanotubes (HNTs) nanocomposites were melt compounded via twin-screw extrusion for all the compositions. Three FR additive loadings (15, 20, and 25 wt%) and three HNTs loadings (2.5, 5, and 10 wt%) were selected. The formula with 25 % FR and 2.5 % HNT had the lowest additives content and the highest elongation at break of 10.22 % among all UL-94 V-0 rated formulas. A homogeneous dispersion of HNTs in PA11 matrix was observed by transmission electron microscopy. Differential scanning calorimeter measurements indicated that HNTs behaved as nucleating agents by accelerating the rate of crystallization, thus increasing crystallization temperature. The young’s modulus of the PA11 nanocomposites was enhanced with the addition of HNTs. Micro-scale combustion calorimeter results demonstrated that the addition of HNTs also decreased the peak heat release rate of the nanocomposites. These results indicate the effectiveness of HNTs on the mechanical, thermal, and flame-retardant performance of PA11/FR/HNTs nanocomposites.     

Preparation and properties of polystyrene nanocomposites with graphite oxide and graphene as flame retardants

In this study, graphite oxides (GOs) with different oxidation degrees and graphene nanosheets were prepared by a modified Hummers method and thermal exfoliation of the prepared GO, respectively. Polystyrene (PS)/GO and PS/graphene nanocomposites were prepared via melt blending. X-ray diffraction results showed that GOs and graphene were exfoliated in the PS composites. It could be observed from the scanning electron microscope images that GOs and graphene were well dispersed throughout the matrix without obvious aggregates. Dynamic mechanical thermal analysis suggested that the storage modulus for the PS/GO1 and PS/graphene nanocomposites was efficiently improved due to the low oxygen content of GO1 and the elimination of the oxygen groups from GO. The flammability of nanocomposites was evaluated by thermal gravimetric analysis and cone calorimetry. The results suggested that both the thermal stability and the reduction in peak heat release rate (PHRR) decreased with the increasing of the oxygen groups in GOs or graphene. The optimal flammability was obtained with the graphene (5 wt%), in which case the reduction in the PHRR is almost 50 % as compared to PS.     

Isothermal crystallization behavior and mechanical properties of polylactide/carbon nanotube nanocomposites

Carbon nanotube (CNT)–reinforced polylactide (PLA) nanocomposites were prepared using a melt compounding process employing a twin-screw extruder. The isothermal crystallization kinetics of PLA/CNT nanocomposites according to Avrami’s theory were analyzed using differential scanning calorimetry in the temperature range 90–120 °C. There was a significant dependence of CNT on the crystallization behavior of the PLA matrix. The incorporation of CNT improved effectively the crystallization rate of PLA/CNT nanocomposites through heterogeneous nucleation. The nucleating effect of CNTs which increased the number of nucleation sites and decreased the average spherulite size was confirmed using polarized optical microscopy. The rheological properties of the PLA/CNT nanocomposites were also investigated. Changes in the microstructure of the PLA/CNT nanocomposites occurred by incorporating CNT. Furthermore, the tensile strength/modulus and thermal stability of PLA/CNT nanocomposites were enhanced when a very small quantity of CNT was added. This research accounts for the effect of CNTs, which significantly influenced the isothermal behavior, thermal stability, mechanical, and rheological properties of the PLA/CNT nanocomposites, providing a design guide for PLA/CNT nanocomposites in industrial fields.     

纳米HA/PU复合材料的力学性能和热性能

以4 , 4′-亚甲基二环己基二异氰酸酯( H₁₂MDI) 、聚乙二醇、蓖麻油、1 , 4-丁二醇和具有生物活性的纳米羟基磷灰石(n-HA) 为原料, 采用预聚法制备了纳米羟基磷灰石/ 聚氨酯( HA/PU) 复合材料, 并对其力学性能和热性能进行了研究。结果表明: 复合材料的拉伸强度和断裂伸长率随n-HA 含量的增加而提高。当n-HA 的质量百分数为30 %时, 复合材料的综合力学性能达到最佳, 与纯PU 相比, 拉伸强度和断裂伸长率分别提高了186 %和107 %。动态力学分析得出复合材料的储能模量随n-HA 质量百分含量的增加而显著上升。TGA 试验表明HA/PU 纳米复合材料的热稳定性能随n2 HA 的添加得到改善, 而DSC 分析显示n-HA 的加入在一定程度上降低了PU 软段的结晶度。这些结果均表明该n-HA/PU 是一种有应用前景的组织工程材料。