The physical properties of polyurethane/graphite nanosheets/carbon black foaming conducting nanocomposites

Using polyester polyol and diphenylmethane diisocyanate (MDI) as basic component, and using graphite nanosheets (GN) and carbon black (CB) as conductive filler, polyurethane/graphite nanosheets/carbon black foaming conducting nanocomposites have been prepared by filling mold curing reaction. The morphology, electrical properties and mechanical properties of the prepared PU/GN foams have been investigated. It showed that the percolation threshold effect of PU/GN composite occurred at the content around 12 wt.% of the GN, which was lower than that of carbon black (CB) composite. Besides, PU/GN foams showed much better conductive properties and mechanical properties than that of CB system.     

Green polyurethane nanocomposites from soy polyol and bacterial cellulose

With increased environmental concerns, fluctuations in oil prices, and dependency on oil, there has been an emergence in the use of biobased polyurethanes prepared with polyols derived from plant oils, such as soybean oil. In this study, novel polyurethane materials were synthesized using polyols obtained from soybean oils. The polyurethanes were produced by reacting the polyols with polymeric isocyanate with an isocyanate index of 100 at 150 °C for 2 h for complete curing. The mechanical properties of this biobased polyurethane were improved by incorporating novel nanosized cellulose produced from bacteria. The source of the bacterial cellulose nanofibrils was a commercially available food product nata-de-coco. A fine dispersion of the nanocellulose fibrils in biobased polyurethane matrix was achieved by using a high speed homogenizer at 30,000 rpm, which was observed by field emission transmission electron microscopy and scanning probe microscopy. The average diameter size of the cellulose fibers were determined to be 22 ± 5 nm by scanning probe microscopy. The flexural strength and modulus were improved even at 0.125 wt% bacterial cellulose concentration and the optimum nanocomposite was obtained with 0.250 wt% concentration due to good interaction of isocyanates and the cellulose. Dynamic mechanical analysis supported the flexural testing data for modulus values. Transparent thick nanocomposite samples show one additional advantage of the nanocomposite technology.     

Reinforcement of polyurethane composites with an organically modified montmorillonite

A clay with reactive activity prepared by treatment of natural montmorillonite with Methylene-bis-ortho-chloroaniline (MOCA) was incorporated into polyurethane matrix and a series of PU/clay nanocomposites were obtained by in situ polymerization. The microstructure of the nanocomposites with different content of the clay was examined by atomic force microscopy (AFM). The thermal and mechanical properties of the nanocomposites with different organic clay content were characterized by dynamic mechanical thermal analysis (DMTA) and thermogravimetric analysis (TGA). It was found that the moduli and thermal stability of the nanocomposites were improved with augment of clay, especially, for the PU/9 wt% MO-MMT nanocomposite, compared to pure PU, the storage modulus and the loss modulus were increased by about 300% and 667% at −45 °C, respectively.     

Structure–property relationships in polyurethanes derived from soybean oil

Two types of soy polyols have been prepared, one with secondary OH groups resulted from epoxidation of soybean oil followed by methanolysis (polyol type I) and the other with primary OH groups created from hydroformylation of soybean oil followed by hydrogenation (polyol type II). Cast polyurethane resins were prepared from these two types of polyols with Isonate 2143L, and rigid polyurethane foams were prepared from a blend of soy polyol and glycerol with PAPI 2901. Polyol II is much more reactive than polyol I towards polyurethane formation. This is evidenced from studies on polyurethane gel-times, glass transitions and rigid foam mechanical strengths. The reaction for the polyurethane formation is more complete for polyol II resulted from its higher reactivity than polyol I, although a less rigid polyurethane material is resulted from polyol II than from polyol I. Polyol type II also requires lower amounts of catalysts for rigid foam formulation. Both rigid foam systems produce foams having the required mechanical strength. The polyol II foam system behaves much like conventional rigid foam systems where the strength are proportional to system OH content, while the less reactive polyol I system does not.     

Processing and characterization of polyurethane nanocomposite foam reinforced with montmorillonite–carbon nanotube hybrids

This study investigates the effect of montmorillonite carbon nanotube hybrids on the final properties of polyurethane (PU) nanocomposite foams. The hybrids were fabricated by chemical vapour deposition and dispersed in rigid polyurethane foam by an in situ polymerization process. The resulting morphology and dispersion were evaluated by scanning electron microscopy, optical microscopy and transmission electron microscopy. PU nanocomposite foams have revealed the presence of cells of smaller size and an increase of cell density when compared to neat polymer foams. Thermogravimetric studies revealed that addition of the hybrids nanoparticles improve the thermal properties of the resulting nanocomposites. Addition of small amounts of montmorillonite carbon nanotube hybrids has enhanced the compressive properties of the resulting PU nanocomposite foams making it suitable for several applications.     

Effect of nanoclays on physico-mechanical properties and adhesion of polyester-based polyurethane nanocomposites: structure–property correlations

Polyester–polyurethane nanocomposites based on unmodified and modified montmorillonite clays were compared in terms of their morphology, mechanical, thermal, and adhesive properties. Excellent dispersion of the modified nanoclay in polymer with 3 wt% loading was confirmed from X-ray diffraction, and low-, and high-magnification transmission electron micrographs. The properties of the clay-reinforced polyurethane nanocomposites were a function of nature and the content of clay in the matrix. The nanocomposite containing 3 wt% modified clay exhibits excellent improvement in tensile strength (by ~100%), thermal stability (20 °C higher), storage modulus at 25 °C (by ~135%), and adhesive properties (by ~300%) over the pristine polyurethane.     

Novel nanocellulosic xylan composite film

Nanocellulosic-xylan films were prepared employing oat spelt xylan, cellulose whiskers and a plasticizer. The mechanical properties of the films were evaluated using tensile testing under controlled temperature and humidity conditions. The tensile data showed that the addition of sulfonated cellulose whiskers lead to a substantial improvement in strength properties. Addition of 7 wt% of sulfonated whiskers increased the tensile energy absorption of xylan films by 445% and the tensile strength of the film by 141%. Furthermore, films to which 7% cellulose whiskers were added showed that nanocellulose whiskers produced with sulfuric acid (sulfonated whiskers) were significantly better at increasing film strength than cellulose whiskers produced by hydrochloric acid hydrolysis of cellulosic fibers.     

Carbon black–clay hybrid nanocomposites based upon EPDM elastomer

The present study explored the effect of nanoclay on the properties of the ethylene–propylene–diene rubber (EPDM)/carbon black (CB) composites. The nanocomposites were prepared with 40 wt% loading of fillers, where the nanoclay percentage was kept constant at 3 wt%. As the modified nanoclay contains the polar groups and the EPDM matrix is nonpolar, a polar rubber oil extended carboxylated styrene butadiene rubber (XSBR), was used during the preparation of nanocomposites to improve the compatibility. Primarily the nanoclay was dispersed in XSBR by solution mixing followed by ultrasonication. After that EPDM-based, CB–clay hybrid nanocomposites, were prepared in a laboratory scale two roll mill. The dispersion of the different nanoclay in the EPDM matrix was observed by wide-angle X-ray diffraction (WAXD) and high resolution transmission electron microscopy. It was found that the mechanical properties of the hybrid nanocomposites were highly influenced by the dispersion and exfoliation of the nanoclays in the EPDM matrix. Thermo gravimetric analysis, scanning electron microscopy and dynamic mechanical thermal analysis was carried out for each nanocomposite. Among all the nanocomposites studied, the thermal and mechanical properties of Cloisite 30B filled EPDM/CB nanocomposite were found to be highest.     

Acoustic properties of polyurethane compositions enhanced with multi‐walled carbon nanotubes and silica nanoparticles

In this study, in order to enhance acoustic properties of polyurethane (PU) foams multi‐walled carbon nanotubes (MWCNT) and/or silica nanoparticles were added to polyol‐isocyanate composition up to 2 wt%, and acoustic properties of polyurethane foam samples with small amount of carbon nanotubes and silica nanoparticles (spherical and/or amorphous types) were determined in the frequency range from 50 Hz up to 6400 Hz. Acoustic properties, especially absorption coefficient of the produced samples were measured for all the prepared samples and results were investigated to come up with the best polyurethane samples that can be applied for sound absorption application at the desired frequency range. It was found that double combination of carbon nanotubes and silica nanoparticles, especially 0.7 wt% carbon nanotubes and 0.2 wt% spherical silica nanoparticle added polyurethane composition has better sound absorption ratio overall all frequencies levels compared to the other samples. Thus, it is possible to obtain polyurethane nanocomposite with a higher amount of carbon nanotube by weight at the same time enhancing sound absorption properties. Moreover, there is a synergic effect between carbon nanotubes and silica nanoparticles when mixed and added into polyurethane matrix at predetermined levels to get enhanced acoustic response with a higher level of carbon nanotube in polyurethane foam.     

Physico-chemical and mechanical properties of nanocomposites prepared using cellulose nanowhiskers and poly(lactic acid)

A range of nanocomposites were prepared using cellulose nanowhiskers (CNWs) and poly(lactic acid) (PLA) via a solvent casting process. Acid hydrolysis process was used to produce CNWs from bleached cotton. Structural morphology and surface topography of the CNWs and nanocomposites were examined using transmission (TEM) and scanning electron microscopy. TEM images revealed rod-like whiskers in the nano-scale region which were dispersed within the PLA matrix. The presence of the functional groups of CNWs and PLA were confirmed via FTIR analysis. Tensile tests were conducted on thin films and the nanocomposites containing 1 wt% CNWs showed a 34 and 31% increase in tensile strength and modulus, respectively, compared to pure PLA. The dynamic mechanical analysis showed that the tensile storage modulus also increased in the visco-elastic temperature region with increasing CNWs content in the nanocomposites. Thermogravimetric analysis showed that all the materials investigated were thermally stable from room temperature to 210 °C. A positive effect of CNWs on the crystal nucleation of PLA polymer in the nanocomposites was observed using differential scanning calorimetry and X-ray diffraction analysis. The degradation profiles of the nanocomposites in deionised water over 1 week revealed a mass loss of 1.5–5.6% at alternate temperatures (25, 37 and 50 °C) and at the same conditions the swelling ratio and water uptake were seen to increase with CNWs content in the nanocomposites, which was strongly influenced by the presence of crystalline CNWs.     

Structure and thermal properties of poly(lactic acid)/cellulose whiskers nanocomposite materials

The goal of this work was to produce nanocomposites based on poly(lactic acid) (PLA) and cellulose nanowhiskers (CNW). The CNW were treated with either tert-butanol or a surfactant in order to find a system that would show flow birefringence in chloroform. The nanocomposites were prepared by incorporating 5 wt% of the different CNW into a PLA matrix using solution casting. Field emission scanning electron microscopy showed that untreated whiskers formed flakes, while tert-butanol treated whiskers formed loose networks during freeze drying. The surfactant treated whiskers showed flow birefringence in chloroform and transmission electron microscopy showed that these whiskers produced a well dispersed nanocomposite. Thermogravimetric analysis indicated that both whiskers and composite materials were thermally stable in the region between 25 °C and 220 °C. The dynamic mechanical thermal analysis showed that both the untreated and the tert-butanol treated whiskers were able to improve the storage modulus of PLA at higher temperatures and a 20 °C shift in the tan δ peak was recorded for the tert-butanol treated whiskers.     

Semi-rigid biopolyurethane foams based on palm-oil polyol and reinforced with cellulose nanocrystals

In this study, water-blown biopolyurethane (BPU) foams based on palm oil were developed and cellulose nanocrystals (CNC) were incorporated to improve the mechanical properties of the foams. In addition, the foams were compared with petroleum polyurethane (PPU) foam. The foam properties and cellular morphology were characterized. The obtained results revealed that a low-density, semi-rigid BPU foam was prepared using a new formulation. CNC as an additive significantly improved the compressive strength from 54 to 117 kPa. Additionally, cyclic compression tests indicated that the addition of CNC increased the rigidity, leading to decreased deformation resilience. The dimensional stability of BPU foams was increased with increasing CNC concentration for both heating and freezing conditions.Therefore, the developed BPU nanocomposite foams are expected to have great potential as core material in composite sandwich panels as well as in other construction materials.     

Effect of surface modifications of carbon black (CB) on the properties of CB/polyurethane foams

The effect of surface modifications of carbon black (CB) on its dispersion in polyether polyol and CB/polyurethane (PU) foams and the properties of the CB/PU composite foams was investigated. Pristine CB (p-CB) was oxidized in nitric acid to obtain oxidized CB (o-CB), and then by the esterification reaction between the carboxyl groups of o-CB and the hydroxyl groups of polyether polyol, polyol grafted CB (g-CB) was obtained. Optical microscopy, scanning and transmission electron microscopy observations showed that surface modifications effectively improved the dispersion of CB in polyether polyol and in the final composite foams. Compared with the p-CB/PU foams, the o-CB/PU and g-CB/PU composite foams exhibited improved conductivities, storage moduli, and increased glass transition temperatures. The compressive strengths of the p-CB/PU and o-CB/PU composite foams decreased with the increase of filler contents, but g-CB has no negative effect on the compressive strength even at a filler content as high as 8 phr. Furthermore, the cell sizes for the o-CB/PU and g-CB/PU composite foams were more uniform than those of p-CB/PU foams.     

Isocyanate-rich cellulose nanocrystals and their selective insertion in elastomeric polyurethane

Cellulose nanocrystals (CNC) were successfully obtained and modified with 1,6-hexamethylene diisocyanate (HDI) by means of in situ polymerization varying the CNC/HDI molar ratio to evaluate the number of anchored chains to the CNC. The modification was examined by elemental analysis, nuclear magnetic resonance (¹³C NMR) and attenuated total reflection Fourier transform infrared spectroscopy (IR-ATR). Nanocomposites containing 1.5 wt% CNC, modified and unmodified, were prepared by solvent casting. Thermal and mechanical properties of the resulting films were evaluated from the viewpoint of polyurethane microphase separated structure, soft and hard domains. CNC were effectively dispersed in the polyurethane matrix and depending on surface chemistry, the nanoreinforcement interacts selectively with matrix nanodomains. This interpretation is supported by differences in thermal and mechanical properties of the nanocomposites and also confirmed by AFM images. Isocyanate rich cellulose nanocrystals interacted with matrix hard phase, promoting physical association with hard segments, enhancing stiffness and dimensional stability versus temperature of the nanocomposite.     

How hybridization with zinc oxide whiskers and carbon fibers affects the thermal diffusivity and mechanical properties of poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactic acid) nanocomposites

The enhanced thermal diffusivity and mechanical properties of poly(l-lactic acid) (PLLA) nanocomposites reported here are based on the percolation network formed when PLLA is hybridized with short carbon fibers (CFs) and functionalized zinc oxide whiskers. The PLLA nanocomposite containing 30 wt% (≈9.5 vol%) ZnO whiskers and 10 wt% (≈8.1 vol%) CFs had a thermal diffusivity almost as high as that of stainless steel and an insulator-level electrical resistivity (>10¹⁰ Ωm). Modifying the surface of the ZnO whiskers by esterifying them using specific alcohols with long linear alkyl chains improved the elastic strength and toughness of the nanocomposites significantly. These results suggest that hybridizing PLLA with short CFs and functionalized ZnO whiskers yields nanocomposites with high thermal diffusivity as well as high electrical resistivity and excellent mechanical properties.     

Polyethylene/palygorskite nanocomposites with macromolecular comb structure via in situ polymerization

Polyethylene/palygorskite nanocomposites with “macromolecular comb” structure were prepared via in situ polymerization. The TiCl₄ catalyst was first loaded on the surface of the nanoscale whiskers of palygorskite. Subsequently the ethylene was introduced into the reaction system, and the polyethylene molecular chain was generated directly at the surface of the palygorskite whiskers. As a result, a polyethylene molecular chain with “macromolecular comb” structure was generated. The product thus obtained was blended with regular polyethylene to make a polymer blend, which was characterized by transmission electron microscope (TEM). Finely dispersed palygorskite whiskers in polyethylene matrix were found, which resulted in the improvement of mechanical strength of the polymer blends. Compared with regular polyethylene, the impact strength and tensile strength of the polymer blend were improved by 63.5% and 21.3% respectively at 25°C, when the palygorskite content of the nanocomposite was 20 wt%.     

From cellulosic waste to nanocomposites. Part 2: synthesis and characterization of polyurethane/cellulose nanocomposites

New polyurethane (PU)-based nanocomposites were synthesized through two-step in situ polymerization by incorporating low loading levels of spherical cellulose nanoparticles (CNs). Structural, mechanical, thermal, and morphological characterization of the nanocomposites was done with infrared spectroscopy, X-ray diffraction, tensile test, dynamic mechanical thermal analysis, thermogravimetry, differential scanning calorimetry, and field emission scanning electron microscopy. The results showed with incorporation of CNs there was no significant change in the structure of PU. However, the addition of 1 % CNs into PU increased the modulus nearly 42 % and tensile strength by 112 %. On the contrary, elongation at break decreased with increasing nanoparticles contents, but the nanocomposites maintained an elongation of greater than 800 %, which was still a large elongation. The thermal stability of PU enhanced with increasing the small amounts of nanoparticles. Also, incorporating of the CNs improved the phase separation between the soft and hard domains which led to an upward shift in melting temperatures and enthalpy of crystalline phase melting. These results were very encouraging in terms of using CNs as an inexpensive nanofiller and improving the mechanical and thermal properties of PU without using solvents in nanocomposite preparation.     

A facile approach to prepare regenerated cellulose/graphene nanoplatelets nanocomposite using room-temperature ionic liquid

This study presents the preparation of regenerated cellulose (RC)/graphene nanoplatelets (GNPs) nanocomposites via room temperature ionic liquid, 1-ethyl-3-methylimidazolium acetate (EMIMAc) using solution casting method. The thermal stability, gas permeability, water absorption and mechanical properties of the films were studied. The synthesized nanocomposite films were characterized by Fourier transform infrared (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The T20 decomposition temperature of regenerated cellulose improved with the addition of graphene nanoplatelets up to 5 wt%. The tensile strength and Young's modulus of RC films improved by 34 and 56%, respectively with the addition of 3 wt% GNPs. The nanocomposite films exhibited improved oxygen and carbon dioxide gas barrier properties and water absorption resistance compared to RC. XRD and SEM results showed good interaction between RC and GNPs and well dispersion of graphene nanoplatelets in regenerated cellulose. The FTIR spectra showed that the addition of GNPs in RC did not result in any noticeable change in its chemical structure.     

Mechanical,tribological and heat resistant properties of fluorinated multi-walled carbon nanotube/bismaleimide/cyanate resin nanocomposites

Bismaleimide containing cyanate resin(BMI/CE) pre-ploymer was used as resin matrix. Fluorinated multiwalled carbon nanotubes(F-MWCNTs) were used as fillers to prepare F-MWCNT/BMI/CE nanocomposites via a solution intercalation method. The influence of F-MWCNT content on the mechanical, tribological and heat resistant properties of the nanocomposites was investigated. The morphology of the fracture surface and the wear surface of nanocomposites were characterized by scanning electron microscopy.Results show that the addition of F-MWCNTs is beneficial to improving the mechanical and tribological properties of the nanocomposites. It's worth noting that when the content of F-MWNTs was 0.6 wt%, the performances of nanocomposite are optimized(i.e., highest impact strength, lowest frictional coefficient and wear rate). In addition, the nanocomposites exhibit good thermal stability in comparison with BMI/CE.     

具有负温度系数效应的导电硬质聚氨酯泡沫

采用高能球磨分散方法制备了稳定的聚合物多元醇/碳纳米管分散液,并通过原位聚合制备了导电聚氨酯（PU）/碳纳米管（CNTs）硬质泡沫复合材料。采用扫描电镜（SEM）表征了泡沫复合材料的结构,研究了CNTs含量对泡沫材料导电性的影响以及泡沫材料的负温度系数（NTC）效应,通过压缩测试考察了泡沫材料的力学性能。结果表明,CN...