Enhanced mechanical and thermal properties of rigid polyurethane foam composites containing graphene nanosheets and carbon nanotubes

The comparative study of rigid polyurethane foam (RPUF) nanocomposites based on graphene nanosheets (GNSs) and carbon nanotubes (CNTs) has been reported. A GNS content of 0.3 wt% in polyol turns to be optimal for its foamability with the isocyanate component, as verified by rheology measurements. Scanning electron microscopy and transmission electron microscopy observations reveal a homogeneous dispersion of GNSs and CNTs in the RPUF nanocomposites. Only 0.3 wt% loading of GNSs and CNTs led to 36% and 25% improvement respectively in the compressive modulus of the RPUF nanocomposites. Meanwhile, 16 °C and 14 °C improvements in the glass transition temperature confirm the important role of both the nanofillers in the heat resistance of RPUF nanocomposites. These results additionally indicate that GNSs work more effectively than CNTs in mechanical property and heat resistance enhancement of the RPUF nanocomposites. The superiority of GNSs over CNTs can be attributed to their wrinkled surface structure, unique two‐dimensional geometrical morphology and higher specific surface area, which results in stronger interaction and restriction of segmental motion at the interface between the GNSs and the RPUF matrix. In addition, changes in the thermal conductivity of the nanocomposites are negligible, indicating that incorporation of GNSs and CNTs will not hinder the application of RPUF nanocomposites as thermal insulators. On the contrary, the enhancement in mechanical properties and heat resistance will undoubtedly expand the application range of polyurethane foam materials. Copyright © 2012 Society of Chemical Industry     

硬质聚氨酯泡沫塑料研究进展

介绍了合成硬质聚氨酯泡沫塑料的主要原料,包括主体成分和发泡剂、泡沫稳定剂等;对硬质聚氨酯泡沫塑料的物理性能,如力学性能、阻燃性能、老化性能等及其在工程上的应用情况进行了综述。     

Influence of nanoclays on electrical and morphological properties of thermoplastic polyurethane/multiwalled carbon nanotube/clay nanocomposites

Nanocomposites of thermoplastic polyurethanes (TPUs), multiwalled carbon nanotubes (MWCNTs) and clays were prepared via melt processing using polyether‐ and polyester‐based TPUs, MWCNTs, and organically modified nanoclays (Cloisite C30B and C25A). Coaddition of clays and MWCNTs to TPU nanocomposites increased their electrical conductivities above those without any clay. Nanoclay alone is shown to produce no effect on electrical conductivity. TEM results show that the coaddition of nanoclay affects the nanocomposite morphology by changing the MWCNT distribution. Clay C25A and MWCNTs were observed to form network structures in the nanocomposites, resulting in improved electrical conduction. Interaction between MWCNTs and clays as well as an increase in nanocomposite viscosity caused by the coaddition of clays may influence the morphology change. Most of the nanocomposites containing both MWCNTs and clay exhibited higher dielectric constants, indicating higher electrical conductivities. Tensile properties investigations confirmed the reinforcing effects of the MWCNTs and clays. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Thermal,mechanical and acoustic damping properties of flexible open‐cell polyurethane/multi‐walled carbon nanotube foams: effect of surface functionality of nanotubes

This article demonstrates the properties of open‐cell flexible polyurethane foams incorporating multi‐walled carbon nanotubes. Three different types of highly functionalized nanotubes having carboxyl, hydroxyl and amide functional groups were synthesized. Neat polyurethane foam and three nanocomposite foams filled with 0.1 wt% of treated nanotubes were prepared. It was found that thermal stability, mechanical properties and acoustic damping were improved significantly by incorporation of small amounts of nanotubes. The nanotubes modified with carboxyl groups were found to have much more influence compared to the other two functional groups, possibly due to better interfacial interaction and improved dispersion. Scanning electron microscopy revealed micro‐cells with average diameters less than 5 µm in the skeleton of foams filled with nanotubes modified with hydroxyl and carboxyl, the formation of which was attributed to the generation of gaseous materials through the reaction with isocyanate. Such micro‐cells were found to be influential in improving mechanical and acoustic damping. Copyright © 2010 Society of Chemical Industry     

Preparation and properties of a novel elastomeric polyurethane/organic montmorillonite nanocomposite

A novel elastomeric polyurethane (EPU)/organic montmorillonite (OMMT) nanocomposite has been synthesized. 18 Alkane‐3 methyl‐amine chloride and dihydroxethyl‐12 alkane‐3 methyl‐amine chloride were used as intercalation agents to treat Na⁺‐montmorillonite and for forming two kinds of OMMTs. The better OMMT was chosen according to fourier transform infrared spectroscopy (FTIR) and wide angle X‐ray diffraction (WAXD). Three types of EPU/OMMT nanocomposites were synthesized by in situ polymerization of EPU, with different amounts of OMMT. A combination of FTIR, WAXD, and transmission electronic microscopy (TEM) studies showed that EPU/OMMT composites were on the nanometer scale and the segmented structure of EPU was hindered by the presence of the OMMT, due to the reaction between toluene diisocyanate (TDI) and the intercalation agents. Properties such as tensile property, differential scanning calorimeter (DSC), and thermogravimetric analysis (TGA) were researched and compared. Results showed that the EPU/3% OMMT had the best physical and mechanical properties because of its uniform dispersion of the organic silicate layers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3578–3585, 2006     

The influence of carbon nanotube aspect ratio on the foam morphology of MWNT/PMMA nanocomposite foams

Polymer nanocomposite foams, products from the foaming of polymer nanocomposites, have received increasing attention in both the scientific and industrial communities. Nanocomposite foams filled with carbon nanofibers or carbon nanotubes with high electrical conductivity, enhanced mechanical properties, and low density are potential effective electromagnetic interference (EMI) shielding materials. The EMI shielding efficiency depends on the electrical conductivity and bubble density, which in turn, depend on the properties of the filler. In the current study, multi walled carbon nanotubes (MWNT) with controlled aspect ratio were used to alter the bubble density in MWNT/poly(methyl methacrylate) (PMMA) nanocomposites. It was found that the nanocomposite foams filled with shorter MWNT had higher bubble density under the same foaming conditions and MWNT concentration. Both the ends and sidewalls of carbon nanotubes can act as heterogeneous bubble nucleation sites, but the ends are more effective compared to the sidewalls. Shorter nanotubes provide more ends at constant MWNT concentration compared to long nanotubes. As a result, the difference in the foam morphology, particularly the bubble density, is due to the difference in the number of effective bubble nucleation sites.     

催化剂DABCO8154对硬质聚氨酯泡沫塑料性能的影响

采用一步法合成聚氨酯硬质泡沫塑料,考察了催化剂DABCO8154对聚氨酯塑料发泡体系的发泡时间、表观密度、热稳定性能、力学性能等的影响。随着DABCO8154用量的增加,发泡时间缩短,表观密度先下降后提高。压缩性能、弯曲性能随着DABCO8154含量增加逐渐降低。随着DABCO8154的加入,制品热稳定性提高。     

Effect of annealing treatment on the structure and properties of polyurethane/multiwalled carbon nanotube nanocomposites

The thermoplastic polyurethane/multiwalled carbon nanotube (TPU/CNT) nanocomposites with high conductivity and low percolation threshold value were prepared by melting blending and annealing treatment. The effect of annealing process on the microphase structure and the properties of TPU/CNT nanocomposites was studied. It has been shown that CNT flocculation can occur in TPU/CNT nanocomposites during the annealing process. At a critical CNT content, which defined the percolation threshold, CNTs could form conductivity network. The conductive percolation threshold value of TPU/CNT nanocomposites was decreased from 10 to 4% after annealing process, and the conductivity of TPU/CNT nanocomposites with 10 vol % of CNT could reach 1.1 S/m after an annealing time of 1 h. The significant enhancement of electrical conductivity was influenced by the annealing time and the content of CNTs. The formation of CNT networks was also verified by dynamic viscoelastic characterization. The results of X‐ray diffraction and differential scanning calorimetry indicated that annealing process reinforced the microphase separation of the nanocomposites. Mechanical properties test showed that the annealing treatment was in favor of improving the mechanical properties; however, further increase in the annealing time has negative effect on the mechanical properties. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Modeling and statistical understanding: The effect of carbon nanotube on mechanical properties of recycled polycaprolactone/epoxy composites

Recycling of polymer composites has been explored in an attempt to reutilize materials. Several efforts have opted to address this subject from many perspectives including mechanical, chemical, and thermal recycling. Others have also delved into the self-healing materials to remedy this dilemma. However, few studies have delved into understanding the role of carbon nanotube (CNT) in self-healing based recycled polymer composites. Therefore, in this study, experimental and simulation tools were utilized to understand the recycling process when CNTs were incorporated within recycled polycaprolactone/epoxy composites. A polynomial regression model, as a facile approach, was established to simulate the process-property relationship, which is essential for the successful implementation of the future of manufacturing. It found that, by adding CNTs, a reduction in the determined degree of crystallization was induced which correlated with the obtained reduction in the modulus and toughness. Strategies for enhancing mechanical properties have been pointed out for future endeavors.     

Effect of foam density on the properties of water blown rigid polyurethane foam

Density is an important parameter that influences the properties and performances of rigid polyurethane foam (PUF). Rigid PUF with different densities were prepared by varying the amount of distilled water as blowing agent. This investigation reports the mechanical, morphological, water absorption, thermal conductivity, and thermal behavior of rigid PUF varying with the density, which controls the foam architecture. The density of the PUF decreased from 116 to 42 kg/m³ with an increase in the amount of water from 0.1 to 3.0 parts per hundred polyol by weight (phr), respectively. It was found that the mechanical properties of the PUFs changed with the foam density. The results of water absorption of the PUFs showed that water absorption increased with decrease in density, due to increase in the cell size and decrease in the cell‐wall thickness. The thermal conductivity measurements showed that the thermal conductivity decreased with increase in density. It was due to the decrease in cell size. The thermal analysis of the PUFs shows that the glass transition temperature increases with the decrease in foam density, but the thermal stability decreases with the decrease in foam density. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

纳米二氧化硅改性硬质聚氨酯泡沫塑料的研究

采用浇注成型法合成密度为250 mg/cm3的纳米SiO2改性硬质聚氨酯泡沫塑料(PUR-R),研究了纳米SiO2含量及偶联剂处理对纳米SiO2改性PUR-R的各种力学性能的影响。结果表明:直接使用纳米SiO2,可使PUR-R的某些力学性能得到提高,而偶联剂处理可进一步改善纳米SiO2对PUR-R的增强作用,用偶联剂改性过的纳米SiO2增强PUR-R与纯PUR-R相比,除断裂伸长率降低外,其他力学性能如拉伸强度、压缩强度、弯曲强度、冲击强度及弯曲模量等均有所提高。     

碳纳米管/聚氨酯复合材料的粘接性能

利用超声分散、酸处理以及表面活性剂分散的方法将碳纳米管分散到蓖麻油中,制备了蓖麻油型聚氨酯/碳纳米管(PUR/CNTs)复合材料,观察了该复合材料的微观结构,探讨了CNTs用量、酸处理时间以及表面活性剂的用量对复合材料粘接性能的影响。结果表明,随着蓖麻油中CNTs用量的增加,该复合材料的粘接强度不断提高,当增加到2%时,粘接强度提高84.4%;硝酸处理3 h的聚氨酯/碳纳米管复合材料的粘接强度最大,比未酸处理的复合材料增加15%;表面活性剂分散的聚氨酯/碳纳米管复合材料的粘接强度能得到进一步的提高。     

Physical properties of water‐blown rigid polyurethane foams containing epoxidized soybean oil in different isocyanate indices

To explore the potential of isocyanate usage reduction, water‐blown rigid polyurethane foams were made by replacing 0, 20, and 50% of Voranoll® 490 in the B‐side of the foam formulation by epoxidized soybean oil (ESBO) with an isocyanate index ranging from 50 to 110. The compressive strength, density, and thermal conductivity of foams were measured. The foam surface temperature was monitored before and throughout the foaming reaction as an indirect indication of the foaming temperature. Increasing ESBO replacement and/or decreasing isocyanate index decreased the foam's compressive strength. The density of the foam decreased while decreasing the isocyanate index to 60. Further decrease in isocyanate index resulted in foam shrinkage causing a sharp increase in the foam density. The thermal conductivity of foams increased while decreasing the isocyanate index and increasing the ESBO replacement. Mathematical models for predicting rigid polyurethane foam density, compressive strength, and thermal conductivity were established and validated. Similar to compressive strength, the foaming temperature decreased while decreasing the isocyanate index and increasing the ESBO replacement. Because of the lower reactivity of ESBO with isocyanate, the rate of foaming temperature decrease with decreasing isocyanate index was in the order of 0% > 20% > 50% ESBO replacement. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Mechanical and thermal properties of phenolic/glass fiber foam modified with phosphorus‐containing polyurethane prepolymer

Phenolic foam exhibits outstanding flame, smoke and toxicity properties, good insulation properties and low production costs. However, the brittleness and pulverization of phenolic foam have severely limited its application in many fields. In this study, a novel phosphorus‐containing polyurethane prepolymer (DOPU) modifier was firstly synthesized, and then the foaming formula and processing of toughening phenolic foam modified with DOPU and glass fiber were explored. The structure and reactive behavior of prepolymer and phenolic resin were investigated using Fourier transform infrared spectroscopy. The effects of DOPU and glass fiber on the apparent density, compressive strength, bending strength and water absorption were investigated. The results suggested that the apparent density, compressive strength and bending strength of modified phenolic foam tended to increase irregularly with increasing content of DOPU. The addition of DOPU led to lower water absorption of glass fiber‐filled foam. Thermal stability and flame retardancy were examined using thermogravimetric analysis and limiting oxygen index (LOI) tests. It was found that foam with 3% DOPU and 0.5% glass fiber added exhibited good thermal stability and high char yields. The LOI value of modified phenolic foams decreased with increasing DOPU content, but it still remained at 41.0% even if the amount of modifier loaded was 10 wt%. © 2012 Society of Chemical Industry     

The effect of carbon nanotube hydrophobicity on the mechanical properties of carbon nanotube‐reinforced thermoplastic polyurethane nanocomposites

Double walled carbon nanotubes (DWNT) were functionalized by reacting methanol, dodecylamine, or octadecylamine with a toluene 2,4‐diisocyanate linker through a two‐stage reaction procedure. TGA coupled with FTIR analysis of both the decomposition products and the DWNT samples demonstrated that the functionalization procedure was successful and proceeded as expected for all samples. A preliminary investigation of the reinforcing capabilities of the functionalized DWNT in a thermoplastic polyurethane host polymer was then conducted. Tensile testing of the resultant nanocomposites demonstrated that the octadecylamine functionality provided the greatest enhancement in tensile strength and toughness. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Physical properties of water‐blown rigid polyurethane foams from vegetable oil‐based polyols

Fifty vegetable oil‐based polyols were characterized in terms of their hydroxyl number and their potential of replacing up to 50% of the petroleum‐based polyol in waterborne rigid polyurethane foam applications was evaluated. Polyurethane foams were prepared by reacting isocyanates with polyols containing 50% of vegetable oil‐based polyols and 50% of petroleum‐based polyol and their thermal conductivity, density, and compressive strength were determined. The vegetable oil‐based polyols included epoxidized soybean oil reacted with acetol, commercial soybean oil polyols (soyoils), polyols derived from epoxidized soybean oil and diglycerides, etc. Most of the foams made with polyols containing 50% of vegetable oil‐based polyols were inferior to foams made from 100% petroleum‐based polyol. However, foams made with polyols containing 50% hydroxy soybean oil, epoxidized soybean oil reacted with acetol, and oxidized epoxidized diglyceride of soybean oil not only had superior thermal conductivity, but also better density and compressive strength properties than had foams made from 100% petroleum polyol. Although the epoxidized soybean oil did not have any hydroxyl functional group to react with isocyanate, when used in 50 : 50 blend with the petroleum‐based polyol the resulting polyurethane foams had density versus compressive properties similar to polyurethane foams made from 100% petroleum‐based polyol. The density and compressive strength of foams were affected by the hydroxyl number of polyols, but the thermal conductivity of foams was not. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Physical properties of garnet‐filled polyurethane foam composite

Garnet‐filled polyurethane foam composite was prepared by solvent‐free reaction. Density, hardness, and compression strength were measured to study its basic physical properties. Percent volume loss and arithmetical mean surface roughness were investigated as an abrasion property to determine its potentiality as an abrasive and establish a relationship between basic properties and abrasion properties. These properties were measured as functions of blowing agent content, and garnet was used as filler. The particle size of the garnet and the polyol mixing ratio were also changed to investigate the dependence of properties on formulation. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1336–1343, 2001     

Electrical conductivity and major mechanical and thermal properties of carbon nanotube‐filled polyurethane foams

The carbon nanotubes (CNTs)/rigid polyurethane (PU) foam composites with a low percolation threshold of ～ 1.2 wt % were prepared by constructing effective conductive paths with homogeneous dispersion of the CNTs in both the cell walls and struts of the PU foam. The conductive foam presented excellent electrical stability under various temperature fields, highlighting the potential applications for a long‐term use over a wide temperature range from 20 to 180°C. Compression measurements and dynamical mechanical analysis indicated 31% improvement in compression properties and 50% increase in storage modulus at room temperature in the presence of CNTs (2.0 wt %). Additionally, the incorporation of only 0.5 wt % CNTs induced remarkable thermal stabilization of the matrix, with the degradation temperature increasing from 450 to 499°C at the 50% weight loss. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Comparative study of physical properties of water‐blown rigid polyurethane foams extended with commercial soy flours

The use of renewable resources (mainly carbohydrates) in rigid polyurethane foam has been known to offer several advantages, such as increased strength, improved flame resistance, and enhanced biodegradability. Less attention has been directed to inexpensive protein‐based materials, such as defatted soy flour. The objectives of this study were to develop water‐blown rigid polyurethane foams, containing defatted soy flour, that have acceptable or improved physical properties which also lower the cost of the foam formulation and to compare the properties of developed foams extended with three kinds of commercial soy flour. Water‐blown low‐density rigid polyurethane foams were prepared with poly(ether polyol)s, polymeric isocyanates, defatted soy flour, water, a catalyst mixture, and a surfactant. Soy flour and the initial water content were varied from 0 to 40% and from 4.5 to 5.5% of the poly(ether polyol) content, respectively. A standard laboratory mixing procedure was followed for making foams using a high‐speed industrial mixer. After mixing, the mixture was poured into boxes and allowed to rise at ambient conditions. Foams were removed from boxes after 1 h and cured at room temperature for 24 h before measurement of the thermal conductivity and for 1 week before other property tests. Foam properties were determined according to ASTM procedures. Measurement of the physical properties (compressive strength, modulus, thermal conductivity, and dimensional stability under thermal and humid aging) of these foams showed that the addition of 10–20% of three kinds of soy flour imparted water‐blown rigid polyurethane foams with similar or improved strength, modulus, insulation, and dimensional stability. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 10–19, 2001     

Effect of ingredient ratios of rigid polyurethane foam on foam core panels properties

One‐step manufacturing process (in‐situ foaming) provide great potential for the production of foam core panels. Polyurethane (PU) foam showed good applicability for use for in‐situ foaming. Here, the effect of ingredient ratios of rigid PU foam on foam performance and panel properties is investigated. It was observed that the isocyanate (ISO) content and polyols (PO) type and content significantly change the foam and panel properties. Foam cell density, as the most important factor influencing the foam characteristics, was higher in foams with higher ISO and polyether content. Bending strength, internal bond and screw withdrawal resistance of the foam core panels were significantly enhanced when the ISO and polyether content was increased in the foam formulation. Varying the ISO content had no influence on panel properties with higher content of polyester (60%) in the PO blend. Varying the foam ingredient ratios did not change the thickness swelling, while the water absorption was dependent on the foam components ratios. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44722.